persistence and transformation of carbosulfan in laterite and coastal alluvium soils of kerala

PERSISTENCE AND TRANSFORMATION OF CARBOSULFAN

IN LATERITE AND COASTAL ALLUVIUM SOILS OF KERALA AND

ITS EFFECT ON SOIL ORGANISMS

DHANYA. M . S

(2014 – 11 - 152)

DEPARTMENT OF SOIL SCIENCE AND AGRICULTURAL CHEMISTRY

COLLEGE OF AGRICULTURE

VELLAYANI, THIRUVANANTHAPURAM-695 522

KERALA, INDIA

2016


IN LATERITE AND COASTAL ALLUVIUM SOILS OF KERALA

AND ITS EFFECT ON SOIL ORGANISMS

by DHANYA. M. S

(2014-11-152)

THESIS

Submitted in partial fulfilment of the

requirements for the degree of

MASTER OF SCIENCE IN AGRICULTURE

Faculty of Agriculture

Kerala Agricultural University




KERALA, INDIA

2016

DECLARATION

I, hereby declare that this thesis entitled “PERSISTENCE AND TRANSFORMATION OF

CARBOSULFAN IN LATERITE AND COASTAL ALLUVIUM SOILS OF KERALA

AND ITS EFFECT ON SOIL ORGANISMS” is a bonafide record of research work done by

me during the course of research and the thesis has not previously formed the basis for the award

to me of any degree, diploma, associateship, fellowship or other similar title, of any other

University or Society.

Vellayani, Dhanya. M. S

06-09-2016 (2014 - 11-152)

ii

CERTIFICATE

Certified that this thesis entitled “PERSISTENCE AND TRANSFORMATION OF


AND ITS EFFECT ON SOIL ORGANISMS” is a record of research work done

independently by Ms. Dhanya M. S under my guidance and supervision and that it has not

previously formed the basis for the award of any degree, diploma, fellowship or associateship to

her.

Vellayani, Dr. Thomas George

-09-2016 (Major Advisor, Advisory Committee)

Professor (Soil Science & Agrl. Chemistry)

All India Network Project (AINP) on Pesticide Residues

College of Agriculture, Vellayani

iii

CERTIFICATE

We, the undersigned members of the advisory committee of Ms. Dhanya. M. S, a candidate for

the degree of Master of Science in Agriculture with major in Soil Science and Agricultural

Chemistry, agree that this thesis entitled “PERSISTENCE AND TRANSFORMATION OF


AND ITS EFFECT ON SOIL ORGANISMS” may be submitted by Ms. Dhanya. M. S., in

partial fulfillment of the requirement for the degree.

Dr. Thomas George Dr. Sumam George

(Chairman, Advisory Committee) (Member, Advisory Committee) Professor

(SS&AC) Professor and Head Dept. of Soil Science & Agrl. Chemistry Dept. of Soil Science & Agrl. Chemistry AINP on Pesticide Residues College of Agriculture, Vellayani

College of Agriculture, Vellayani

Dr. K. C. Manorama Thampatti Dr. Thomas Biju Mathew (Member, Advisory Committee) (Member, Advisory Committee)

Professor Professor Dept. of Soil Science & Agrl. Chemistry (Department of Agricultural Entomology)

College of Agriculture, Vellayani Pesticide Residue Research and Analytical Laboratory, (PRRAL) College of Agriculture, Vellayani

EXTERNAL EXAMINER

(Name and Address)

iv

ACKNOWLEDGEMENT

With utmost reverence and deep sense of admiration, I express my heartfelt gratitude and

indebtedness to God almighty for the help rendered during my M.Sc. programme and giving me

the courage and strength to pursue this endeavor to completion.

I express my exuberant pleasure to express my deep sense of gratitude to

Dr. Thomas George, Professor, Department of Soil Science and Agricultural Chemistry, AINP

on Pesticide Residues and chairman of my Advisory committee for his valuable guidance,

constant encouragement, timely advice, overwhelming support and care rendered during the

research period without which this piece of work would not have been materialized. I proudly

acknowledge that this manuscript has gained its completeness under the kind supervision and

inspiration of my guide and he has been a valuable support for both academic and personal

level, for which I am extremely grateful.

I am very much grateful to the timely support, sincere efforts, valuable suggestions

motherly affection and constant encouragement from the beginning till the end offered by Dr.

Sumam George, Professor and Head, Department of Soil Science and Agricultural Chemistry

which played a major role for the successful completion of this work.

I am deeply indebted to Dr. K. C. Manorama Thampatti, Professor Department of Soil

Science and Agricultural Chemistry for her invaluable guidance, inspiring support,

encouragement during the course of my investigation.

I feel immense pleasure to avail the opportunity to convey my heartfelt thanks to Dr.

Thomas Biju Mathew, Professor, Department of Agricultural Entomology, Pesticide Residue

Research and Analytical Laboratory for providing necessary facility, selfless help and

encouragement during my M. Sc. programme.

I owe my immense gratitude with pleasure to Dr. N. Saifudeen, Professor and Head

(Retired), Department of Soil Science and Agricultural Chemistry, Dr. Sumam Susan

Vargheese, Professor and Head (Retired), Department of Soil Science and Agricultural

v

Chemistry ex- members of my advisory committee for the encouragement and constructive

criticisms rendered during the course of my work.

I wish to record my special thanks to the generous and selfless help of Dr. S. Naseema

Beevi, Professor (Retired), Department of Agricultural Entomology rendered to me during the

course of my work.

Words are inadequate to express my special and sincere thanks to Dr. Ushakumari

Professor, Department of Soil Science and Agricultural Chemistry, Dr. Ambily Paul, Assistant

Professor, Department of Agriculture Entomology and Dr. K. S Premila, Professor, Department

of Agricultural Entomology for their moral support, love, care, motivation, suggestion and

affection rendered throughout the study.

My study will not be a complete one if I forget to show my gratitude to my teachers in

Department of Soil Science and Agricultural Chemistry Dr. P. B Usha, Dr. Usha Mathew, Dr.

Sudharmai Devi, Dr. B. Aparna, Dr. Gladis, Dr. Biju Joseph, Dr. B. Rani and Dr. Sam T

Kurumthottical, for their friendly approach, well wishes and constant encouragement during

the study.

I am equally grateful to Dr. Vijayaraghava Kumar, Professor and Head, Department of

Agricultural Statistics, for his valuable guidance in statistical analysis and interpretation.

I wish to express my sincere gratitude to Dr. Komala Amma, Professor (Retired)

Department of Soil Science and Agricultural Chemistry and Dr. S. Shehana, Professor

(Retired), Department of Soil Science and Agricultural Chemistry for their valuable support and

wishes during my study.

I wish to express my sincere and special thanks to Visal chettan and Pratheesh chettan

for their help, support, encouragement and brotherly affection which helped me a lot for

completing this thesis work

This thesis would not have been completed without the support of Preetha Chechi,

Emile Chechi, Sreekkutty Chechi, Shyju Chettan, Sreelal chettan, Vishnu, Neethu Chechi,

vi

Mithra Chechi, Salmon Chettan, George Chettan, Pradeep chettan, Rejith Chettan, , Sabari,

Binoy Chettan, Anil Chettan, Prathibha Chechi, Priya Chechi, Surya Chechi, Reshmi Chechi,

Deepa Chechi, Dhanya Chechi, Shyja Chechi and Swapna Chechi. I gratefully venerate the

un-sizable help from each of them.

I wish to express my special thanks to Shoney Chechi, Dathan Sir and Visweswaran Sir

for their timely advice, encouragement and wishes during my research work .

I would like to express my thanks to my seniors, Sreya Chechi, Anila chechi, Sreeja

Chechi, Sai Chettan, Sangeetha Chechi, Emile Chechi, Meera Chechi, Naveen Sir, Priya

Chechi and Faseela Chechi for their support and motivation during my course.

I owe my gratitude to the non teaching staff of Department of Soil Science and

Agricultural Chemistry, Shiny Chechi, Biju Chettan, Geethu Chechi, Soumya Chechi, Priya

Chechi, Vijayakumar Chettan, Aneesh Chettan, Anil Chettan and Rajesh Chettan for their

timely support during my M. Sc. Programme.

I wish to express my whole hearted thanks to my juniors, Dhanesh, Dhanya, Ragi,

Anjana, Aswathi and Usha for their help, support and care.

Words fail to express my sincere thanks to my dear friends Reshma, Arya, Jaya, Nikitha,

Amala, Anusree, Anju K K, Aaruni, Thamil, Shewtha, Jaffin, Molu, Leena, Libi, Dhanya P,

Nimisha, Rami, Reshma S, Shani, Suvarna, Faseela, Jobin, Thasni, Janish and Amju for

their affection and emotional support during these days without which my work wouldn’t have

been completed.

I sincerely acknowledge the Kerala Agricultural University for providing the necessary

facilities and support during my course.

Diction is not at all enough to express my feelings towards my family, especially my

beloved Achan, Amma, Ammomma, Jayan annan , Rakesh annan, Lekshmi Chechi, and my

Appoos, who supported, guided and encouraged me always, without their prayers and blessings

this work would not have been completed.

Again I wish to thank all who helped me directly or indirectly for the completion of this work

vii

CONTENTS

Sl. No. Particulars Page No.

1. INTRODUCTION 1-3

2. REVIEW OF LITERATURE 4-20

3. MATERIALS AND METHODS 21-35

4. RESULTS 36-85

5. DISCUSSION 86-100

6. SUMMARY 101-106

7. REFERENCES 107-121

ABSTRACT 122-125

APPENDIX I-V

viii

LIST OF TABLES

Table No

Title Page No

1. Environmental factors influencing the pesticide persistence 1

2. Analytical methods followed to test the physico - chemical

parameters in soil 9

3. The glass wares, equipments, and reagents used for residue

analysis

22

4. Details of Certified Reference Materials (CRMs) used for

the preparation of pesticide mixture 24

5. Multiple- reaction monitoring (MRM) and Liquid

Chromatograph (LC) parameters for carbosulfan and its

metabolites.

25

6. Physico-chemical properties of laterite soil 28

7. Physico-chemical properties of coastal alluvial soil 37

8. Mean recovery of carbosulfan and its metabolites when

spiked at 0.05 mg kg-1 level in laterite soil 38





11 Mean recovery of carbosulfan and its metabolites when

spiked at 0.05 mg kg-1 level in coastal alluvial soil 40



13 Mean recovery of carbosulfan and its metabolites when


14 Migration of carbosulfan in laterite soil column when

loaded at100 µg level 41

ix

15

Migration of carbofuran formed in laterite soil column

when loaded with 100 µg carbosulfan 44


loaded at 150 µg level 45

17 Migration of carbofuran formed in laterite soil column



loaded at 200 µg level 46

19 Migration of carbofuran formed in laterite soil column


20 Migration of carbosulfan in the coastal alluvial soil column

when loaded at 100 µg level 49

21 Migration of carbofuran formed in coastal alluvial soil column when loaded with 100 µg carbosulfan

49

22 Migration of carbosulfan in the coastal alluvial soil column when loaded at 150 µg level

50

23 Migration of carbofuran formed in coastal alluvial soil

column when loaded with 150 µg carbosulfan 50

24 Migration of carbosulfan in the coastal alluvial soil column

when loaded at 200 µg level 51

25 Migration of carbofuran formed in coastal alluvial soil

column when loaded with 200 µg carbosulfan 51

26 Dissipation of carbosulfan 25 EC in laterite soil under laboratory and cropped conditions

54

27 Dissipation of carbosulfan 25 EC in coastal alluvial soil

under laboratory and cropped conditions 56

28 Dissipation of carbosulfan granules in laterite soil under

laboratory and cropped conditions 58

29 Dissipation of carbosulfan granules in coastal alluvial soil under laboratory and cropped conditions

59

30 Overall dissipation of carbosulfan as influenced by soil,

formulation, crop and treatment levels 61

31 Dissipation of carbosulfan as influenced by treatment levels

63

x

32 Dissipation of carbosulfan as influenced by interaction of soil, formulations and conditions

64

33 Dissipation of carbosulfan as influenced by soil,

formulations and treatment levels 66

34 Dissipation of carbosulfan as influenced by interaction of crop and treatment levels

67

35 Metabolites of carbosulfan 25 EC in the laterite soils under

laboratory condition 69

36 Metabolites of carbosulfan 25 EC in the coastal alluvial soil under laboratory condition

70

37 Metabolites of carbosulfan granules in laterite soil under

laboratory condition 72

38 Metabolites of carbosulfan granules in the coastal alluvial soil under laboratory condition

73

39 Metabolites formed in the laterite soil by application of

carbosulfan 25 EC in the cropped condition 75

40 Metabolites formed in the coastal alluvial soil by application of carbosulfan 25 EC in the cropped condition

77

41 Metabolites formed in the laterite soil by application of

carbosulfan granules in the cropped condition 78

42 Metabolites formed in the coastal alluvial soil by the application of carbosulfan granules in the cropped condition

80

43 Effect of carbosulfan treatments on the population of soil organisms in laterite soil

81

44 Effect of carbosulfan treatments on the population of soil organisms in coastal alluvial soil

84

xi

LIST OF FIGURES

Figure

No.

Title Between

Pages

1 Degradation pathway of carbosulfan in oranges 20-21

2 Mobility of carbosulfan 25 EC at 100 µg in laterite soil

88-89

3

Mobility of carbosulfan 25 EC at 150 µg in laterite

soil

88-89

4 Mobility of carbosulfan 25 EC at 200 µg in laterite

soil 88-89

5 Mobility of carbosulfan 25 EC at 100 µg in coastal alluvial soil

88-89

6

Mobility of carbosulfan 25 EC at 150 µg in coastal

alluvial soil

90-91

7 Mobility of carbosulfan 25 EC at 200 µg in coastal alluvial soil

90-91

8 Mobility of carbofuran formed from carbosulfan 25 EC at 100 µg in laterite soil

91-92

9 Mobility of carbofuran formed from carbosulfan 25 EC at 150 µg in laterite soil

91-92

10 Mobility of carbofuran formed from carbosulfan 25

EC at 200 µg in laterite soil 91-92

11 Mobility of carbofuran formed from carbosulfan 25 EC at 100 µg in coastal alluvial soil

91-92

12 Mobility of carbofuran formed from carbosulfan 25

EC at 150 µg in coastal alluvial soil 91-92

13 Mobility of carbofuran formed from carbosulfan 25 EC at 200 µg in coastal alluvial soil

91-92

14

Half life of carbosulfan 25 EC in laterite soil under

laboratory and cropped conditions 93-94

xii

15 Half life of carbosulfan 25 EC in coastal alluvial soil

under laboratory and cropped conditions 93-94

16 Half life of carbosulfan granules in laterite soil under

laboratory and cropped conditions 94-95

17 Half life of carbosulfan granules in coastal alluvial

soil under laboratory and cropped conditions 94-95

18 Degradation of carbosulfan 25 EC in laterite soil at 1 mg kg-1 level under laboratory condition

96-97

19 Degradation of carbosulfan 25 EC in laterite soil at 2.5 mg kg-1 96-97

20 Degradation of carbosulfan 25 EC in laterite soil at 5 mg kg-1 96-97

21 Degradation of carbosulfan 25 EC in laterite soil at 1

mg kg-1 level under cropped condition 96-97

22 Degradation of carbosulfan 25 EC in laterite soil at 2.5 mg kg-1 level under cropped condition

96-97

23 Degradation of carbosulfan 25 EC in laterite soil at 5

mg kg-1 level under cropped condition 96-97

24 Degradation of carbosulfan 25 EC in coastal alluvial soil at 1 mg kg-1 level under laboratory condition

97-98

25 Degradation of carbosulfan 25 EC in coastal alluvial

soil at 2.5 mg kg-1 level under laboratory condition 97-98

26 Degradation of carbosulfan 25 EC in coastal alluvial soil at 5 mg kg-1 level under laboratory condition

97-98


soil at 1 mg kg-1 level under cropped condition 97-98

28 Degradation of carbosulfan 25 EC in coastal alluvial soil at 2.5 mg kg-1 level under cropped condition

97-98


soil at 5 mg kg-1 level under cropped condition 97-98

30 Degradation of carbosulfan granules in laterite soil at 1 mg kg-1 level under laboratory condition

97-98

31 Degradation of carbosulfan granules in laterite soil at 2.5 mg kg-1 level under laboratory condition

97-98

xiii

32 Degradation of carbosulfan granules in laterite soil at 5 mg kg-1 level under laboratory condition

97-98

33 Degradation of carbosulfan granules in laterite soil

at 1 mg kg-1 level under cropped condition 97-98

34 Degradation of carbosulfan granules in laterite soil at 2.5 mg kg-1 level under cropped condition

97-98

35 Degradation of carbosulfan granules in laterite soil at 5 mg kg-1 level under cropped condition

97-98

36

Degradation of carbosulfan granules in coastal alluvial soil at 1 mg kg-1 level under laboratory

condition

98-99

37

Degradation of carbosulfan granules in coastal

alluvial soil at 2.5 mg kg-1 level under laboratory condition

98-99

38


alluvial soil at 5 mg kg-1 level under laboratory condition

98-99

39 Degradation of carbosulfan granules in coastal alluvial soil at 1 mg kg-1 level under cropped condition

98-99

40 Degradation of carbosulfan granules in coastal alluvial soil at 1 mg kg-1 level under cropped condition

98-99

41


alluvial soil at 1 mg kg-1 level under cropped condition

98-99

42 Effect of carbosulfan on the microbial population of laterite soil

98-99

43 Effect of carbosulfan on the microbial population of coastal alluvial soil

99-100

xiv

LIST OF PLATES

Plate

No.

TITLE Between

Pages

1 Saturation of the soil column for mobility study 30-31

2 Eluting the soil column after treatment 30-31

3 Cut pieces of soil column for residue analysis 30-31

4 Persistence study under cropped condition 32-33

5 Persistence study under laboratory condition 32-33

6 Enumeration of soil bacteria 34-35

7 Enumeration of soil fungi 34-35

8 Enumeration of soil actinomycetes 34-35

9 Enumeration of soil arthropods 34-35

xv

LIST OF APPENDICES

Plate

No.

TITLE Between

Pages

1 Calibration curve of standard carbosulfan and its metabolites

I

2 Chromatogram of standard of carbosulfan and its

metabolites at 0.005 mg kg-1

II

3 Chromatogram of recovery of carbosulfan and its metabolites from laterite soil

III

4 Chromatogram of recovery of carbosulfan and its

metabolite from coastal alluvial soil

IV

5 Mass spectra of carbosulfan and its metabolite at 0.01 mg kg-1

V

xvi

LIST OF ABBREVIATIONS

@ - At the rate ai - Active ingredient

AINP - All India Network Project % - Per cent

µg - Microgram

BDL - Below Detectable Level

CAS - Chemical Abstract Service

Ca - Calcium

CEC - Cation Exchange Capacity

C D - Critical Difference

CFU - Colony Forming Unit

CIB & RC - Central Insecticide Bureau & Registration

Committee

CIPAC - Collaborative International Pesticides

Analytical Council

CIRCOT - Central Institute for Research on Cotton

Technology

cm - Centimeter

CRD - Completely Randomized Design

CRM - Certified Reference Material

dS - Deci Siemen

DS - Soluble Dust

EC - Emulsifiable Concentrate

EC - Electrical Conductivity

EFSA - European Food Safety Authority

et al - And others

xvii

Ex. Ca - Exchangeable calcium

Ex. Mg - Exchangeable magnesium

FMC - Food Machinery Corporation

Fig. - Figure

g - Gram

G - Granules

h - Hour

ha - Hectare

i.e - That is

IPCS - International Programme on Chemical Safety

K - Potassium

KAU - Kerala Agricultural University

kg - Kilogram

LC - Liquid Chromatography

LOD - Limit of Detection

LOQ - Limit of Quantity

Mg kg-1 - Megagram per kilo gram

Mg m-3 - Megagram per meter cube

Mg - Magnesium

mg - Milligram

Ml - Milli Litre

mm - Millimeter

mM - Millimolar

N - Nitrogen

O.M - Organic matter

P - Phosphorus

ppm - Parts per million

PRRAL - Pesticide Residue Research and Analytical laboratory

xviii

PSA - Primary Secondary Amine

QuEChERS - Quick, Easy, Cheap, Effective, Rugged and Safe

S - Sulphur

S. E - Standard Error

SS & AC - Soil Science and Agricultural Chemistry

USEPA - United States Environment Protection Agency

Var. - Variety

WHC - Water Holding Capacity

xix

Introduction

1. INTRODUCTION

The objective of farming is to provide sufficient and affordable food, fuel

and fibre to human and animals. The conventional system of agriculture is not

sufficient to feed the growing population. At present India is the second largest

populous nation after china in the universe with a population of around 1.25

billion which may reach first position by 2022. Use of high yielding varieties

with good management practices and mechanization resulted in the enormous

increase in the agriculture production and hence became intensive. Along with

this, the loss of agriculture produce by weeds, insects, disease, rats etc were

significantly increased. It was reported that, 30 per cent crop yield potential in

India is being lost due to disease, insects and weeds, and in terms of quantity, it is

about 30 Mt of food grain. In order to minimize these losses, use of pesticides

were popularized and became an inevitable input in the modern agriculture sector.

India is using very less amount of pesticide when compared to other developed

countries, India has a per hectare consumption of 0.6 kg pesticide (Mannocsa,

2009).

Among the various pesticides used, furadan, a 3 per cent granular

formulation of carbofuran manufactured by Food Machinery Corporation (FMC)

has been the largest selling granular insecticide in India since 1970s. In

India, carbofuran was registered for more than 25 crops and has a special place in

Indian agriculture. Even after four decades of its introduction in India, it

continued to be one of the most preferred insecticides for rice, banana and

sugarcane. In terms of toxicity, carbofuran was categorized under extremely toxic

insecticide with red label. Due to its high mammalian toxicity (LD50 8-18 mg kg-1

for rat) its use was discontinued in Kerala in 2011 and fourteen chemicals, with

less mammalian toxicity including carbosulfan were suggested as the alternative

for carbofuran to prevent the attack of nematodes in rice, banana, brinjal and

cardamom. Carbosulfan was also suggested as a replacement for phorate, which

was used for controlling pest attack in paddy

1

(Anon., 2011). Carbosulfan is coming under the category of highly toxic with

blue label, used against sucking and lepidopteran pest with an LD50 value of 101-

250 mg kg-1 for rats and hence was considered to be relatively safe for handling.

It acts on the insect by inhibiting the activity of acetylcholine esterase.

Carbosulfan get metabolized to carbofuran, 3 keto carbofuran, 3- hydroxy

carbofuran and to certain phenol derivatives. So, the toxicity of carbosulfan is not

only due to carbosulfan itself, but with these primary metabolite compounds also.

It is also manufactured by FMC and was available as Emulsifiable Concentrate

(25 EC), Granules (6 G) and as Soluble Dust (25 DS). It was recommended for

use in rice, chilli and cotton by Central Insecticide Bureau & Registration

Committee (CIB & RC) at 250 g ai ha-1 and in rice, cardamom and banana by

KAU @ 16.7 kg ha-1 of carbosulfan 6 G. But irrespective of the recommendation,

the farmers are using carbosulfan in higher dose in the field and even in the poly

houses. It was reported that, carbosulfan creates certain chromosomal aberrations

in rat and has inhibitory effect on soil microbes. Even though its parent

compound is less toxic, the metabolites have the same toxic effect as that of

carbofuran. With careless application of carbosulfan, there may be a chance of

more lethal effect than carbofuran due to the toxicity from the parent compound

as well as from metabolites and sometimes the higher concentration of application

may even lead to contamination of the surface water bodies or even the

underground water. So, there was an urgent need to study the transport and

transformation process of carbosulfan in soil. Since it is a widely used soil

pesticide against nematodes in Kerala, it was studied in two prominent soil types

of Kerala, viz., laterite (Sandy Loam) and coastal alluvial soil (Loamy Sand). The

study on persistence and degradation was done using the widely used two

formulations on carbosulfan such as EC and granules in the laboratory and in the

cropped conditions, with chilli (Ujwala variety) as the test crop in order to

compare the variation in persistence of carbosulfan in soil with and without the

crop.

2

The main objectives of the experiment were,

To study the persistence of carbosulfan in laterite and coastal alluvial soils

of Kerala under laboratory and cropped condition with EC and granule

formulation

To study the metabolism of carbosulfan in soil by monitoring the

formation of metabolite in the soil from 0 th day to 30th day (upto Below

Detectable Level) after Emulsifiable Concentration (EC) and granule (G)

treatment.

To study the mobility of carbosulfan 25 EC in laterite and coastal alluvial

soil columns

To study the effect of carbosulfan on soil organisms (bacteria, fungi

actinomycetes and arthropods) by application of carbosulfan 25 EC and

granule in normal and double doses.

3

Review of Literature

2. REVIEW OF LITERATURE

The term pesticide includes compounds like fungicides, herbicides,

insecticides, nematicides, plant growth regulators, rodenticides, molluscicides and

others. A pesticide should be lethal to the target organism, but it should not produce

any harmful effect on the non-target species such as man and other mammals and

should disappear after performing its pesticidal action.

Carbosulfan is a carbamate pesticide belongs to highly toxic category. The

mechanism of toxicity of carbosulfan is based on reversible inhibition of acetyl

cholinesterase (for carbamates generally). It is recommended for use in rice, banana,

cotton and chilli and considered to have moderate persistence in soil. It is used

widely as a substitute for carbofuran, irrespective of its recommendation by CIB &

RC. In this context, a study was conducted to understand its persistence, degradation,

mobility and also its effect on soil organisms in two soil types of Kerala viz., laterite

and coastal alluvial soils in cropped as well as non cropped condition. The previous

works that related to above topic is reviewed under the below heads.

2.1 PESTICIDE USE SCENARIO

Mathur (1999) reported that, in India the 76 per cent of the pesticide used are

insecticides, as against 44 per cent globally. Reports shows that, among the various

states using pesticides, Uttar Pradesh is the largest consumer followed by Punjab,

Haryana and Maharashtra. Regarding the pesticide share across agricultural crops,

cotton account for 45 per cent followed by rice (25%), chillies/ vegetables/ fruits (13-

24%), plantations (7-8%), cereals/ millets/ oil seeds (6-7%), sugarcane (2-3%) and

others (1-2%), (Abhilash and Singh, 2009). The pattern of pesticide usage in the

world indicates that, in developed countries among the various pesticides, herbicides

are mostly used (Zhang et al., 2011).

4

https://en.wikipedia.org/wiki/Toxicity

https://en.wikipedia.org/wiki/Acetylcholinesterase_inhibitor

https://en.wikipedia.org/wiki/Acetylcholinesterase

https://en.wikipedia.org/wiki/Acetylcholinesterase

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2984095/#CIT0098

2.1.1 Benefits of Pesticides

Large number of benefits has been derived from pesticide use in forestry,

domestic use and in public health and definitely in agriculture sector, upon which the

Indian economy is largely dependent. It played a major role in the increase of food

grain production from 50 million tons in 1948–49, to almost 5 folds to 240 million

tons by the end of 2010 from 169 million hectares of permanently cropped land.

Pesticides have been a vital input contributing to the production and productivity of

crops reducing the losses due to insect pests, weeds which inturn can considerably

reduce the quality and quantity of produce.

Warren (1998) reported that, in the 20th century tremendous increase in the

crop yield is noted in United States by the use of pesticides. Similarly Webster et al.

(1999) reported that, considerable economic loss is monitored in the crop yield

without pesticides and when pesticides were applied it showed significant yield

increase.

Kole et al. (1999) identified that, in the environment the pesticides are

subjected to photochemical / biochemical transformation to produce metabolites

which are comparatively less-toxic than the parent compound to both human beings

and the environment but sometimes it may leads to more toxic compound also.

2.1.2 Disadvantages of Pesticides

Pesticides can contaminate soil, water or other natural bodies. In addition to

controlling insect pests or weeds, pesticides can be lethal to natural enemies including

birds, fishes, aquatic organisms and non-target plants. Insecticides are generally

categorized under acutely toxic class of pesticides, but herbicides can also pose risks

to non-target organisms. In a study it has been estimated that, less than 0.1

percentage of the pesticide applied to crops actually reaches the target pests while 99

percentage of the pesticide enters the environment directly or indirectly,

5




contaminating soil, water and air, where it can adversely affect non-target organisms

(Carriger et al., 2006). Pesticides can even reach the water bodies through runoff

from treated plants and soil. Contamination of groundwater by pesticides is also

widespread. Abhilash and Singh (2009); Vijgen et al. (2011) reported that, pesticides

that exhibit high persistency especially like DDT, organochlorine, endosulfan, endrin,

heptachlor, lindane and their transformation products (TPs). Even though most of

them are now banned still their residues are found in the soil.

2.2 MOBILITY OF PESTICIDES

Mobility may result in redistribution of pesticide within the application site or

movement of some amount of pesticide off site. Pesticides that leach through soil

column may reach ground water.

At least 143 pesticides and 21 of their transformation products have been

found in ground water, from every major chemical class (Anon., 2009). Pesticides

frequently detected in ground water are triazine and acetanilide herbicides that were

used extensively on corn and soybeans. Carbamate insecticides such as aldicarb

cause ground water contamination problems (Toth and Buhler, 2009).

Pesticide contamination of ground water is a natural issue because ground

water is used for drinking by 50 percentage of the population. Concern about

pesticides in ground water is especially acute in rural agricultural areas where over 95

percent of the population relies upon ground water for drinking (Begum et al., 2008).

Mobility is affected by many factors, such as soil and pesticides properties,

topography, canopy, ground cover, soil organic matter, texture, structure and crop

management practices which inturn govern the potential for groundwater or surface

water contamination by pesticides (Kerle et al., 2007). Ferencz and Balog (2010)

reported that, polar pesticides are important and they mainly includes carbonates,

fungicides and some organophosphorus insecticides and their Transformation

6

Products (TPs), which can be moved from soil either by runoff or leaching, thereby

contributing to contamination of water sources.

Field soils show considerable variations in properties such as clay content,

organic matter, bulk density and moisture that can affect the mobility and thus the

fate of pesticides in the soil environment (Di and Aylmore, 1997). Soil properties

(organic matter, soil texture and soil acidity), pesticide properties (solubility,

adsorption and persistence), pesticide application (rate of application and application

method) and weather conditions are the factors affecting leaching (Osman and

Cemile, 2010).

Study by Rice and Cherniak (1997); Gabarino et al. (2002) showed that,

pesticides including new generation pesticides like chlorothalonil, chlorpyrifos,

metalachlor, terbufos and trifluralin have been detected in Arctic environmental

sample.

Mc Connell et al. (1997); Lenoir et al. (1999); Thurman and Cromwell

(2000); Harman et al. (2003) identified the presence of new generation pesticides in

the Sierra Nevada mountains. Studies by Muir et al. (2004) have identified the ability

of some of these new generation compounds to undergo short-range atmospheric

transport to ecologically sensitive regions such as the Chesapeake Bay. High levels

of pesticides chlordecone were detected in coastline, rivers, sediments and

groundwater in the Caribbean island of Martinique due to its massive application on

banana plantations (Bocquene and Franco, 2005).

2.3 PERSISTENCE OF PESTICIDES

The term persistence was introduced into the pesticide scientific literature

to describe the continuing existence of certain insecticides in the environment and is

now applied to any organic chemical that has biological activity. However, from an

environmental point of view, molecules that persist in nature are undesirable for

7







many reasons. Some are intrinsically toxic and deleteriously affect humans, animals,

agricultural crops, wildlife, fish and other aquatic organisms, or microorganisms.

According to Navarro et al. (2007), persistence may be defined as the

tendency of the pesticide to conserve its molecular integrity, physical, chemical and

biological characteristics in a medium through which it is distributed and transported.

According to Beevi et al. (2014), residues of pesticides like DDT and

endosulfan residues were found in cardamom soils of Idukki district even though they

were not applied in these soils for the past 10 years which reveals the high

persistence nature of these pesticides.

Alexander (2000) reported that, the longer the molecule remains in the

environment, the greater is the exposure of susceptible individuals or populations and

greater is the risk or harmful effects. In a similar study Ryang et al. (1988) reported

that, the half-lives of alpha endosulfan and ethoprophos were 6 and 12 days longer

under poly ethelene mulching than under non-mulching conditions under red pepper

cultivation. In a study Gevao et al. (2000) reveals that, when the adsorption of a

pesticide is high its availability in the soil solution decreases, as a result the material

available to biota also decreases and the adsorption process will increase with

increase in the surface area of the clay or with increasing the organic matter content

of the soil.

Usually the persistence is expressed in terms of half life of the pesticide.

Half-life is the time it takes for a certain amount of a pesticide to be reduced by half.

This occurs as it dissipates or breaks down in the environment. According to Hanson

et al. (2015), a pesticide will break down to 50 percentage of the original amount

after a single half-life, 25 percent will remain after two half-lives and 12 percent will

remain after three half-lives. This continues until the amount remaining is nearly

8

zero. In general, the longer the half-life, the greater the potential for pesticide

movement.

Kerle et al. (2007) reported that, pesticides can be divided into three

categories based on half-lives: non persistent pesticides with a typical soil half-life of

less than 30 days, moderately persistent pesticides with a typical soil half-life of 30 to

100 days, or persistent pesticides with a typical soil half-life of more than 100 days.

Table 1. Environmental factors influencing the pesticide persistence (Hanson et al.,

2015).

In tropical soil, due to acidic nature, the H+ ion concentration is high and it has

a positive charge and can adsorb anionic molecules while in alkaline soil it can

adsorb positively charged pesticides (Calvet, 1989). According to Liu et al. (2000)

Environmental Factors Role in Persistence

Sunlight Radiation breaks chemical bonds and create secondary

products

Microbes Bacteria and fungi can break down chemicals, creating

biodegradation products

Plant / animal metabolism Plants and animals can change chemicals into forms

that dissolve better in water (metabolites)

Water Water breaks chemicals thus dissolve better in water

Dissociation Chemicals can break apart into new products

Sorption Chemicals that stick tightly to particles thus restricted

from moving away

Bioaccumulation Some chemicals can be absorbed by plants/animals

from the soil, water, food, and air

9

ionisation determines the charge of the pesticide and hence its adsorption to the clay

particle. Volume and branching as well as the electronic structure influences the

adsorption process by the nature and arrangement of the functional group in it

(Barriuso et al., 2008). The adsorption of glyphosate is high even it is highly soluble

and this is because it forms anionic group on dissociation and that will bind with the

Fe and Al present in the soil. Here the process of adsorption is very high than the

solubilization and thereby it is highly adsorbed to the soil particle (Mamy and

Barriuso, 2005).

For nonpolar pesticides, the increase in water content decreases the adsorption

process. Since water is highly polar than the pesticides it will compete for the

adsorption site, thereby reduce the adsorption process (Roy et al., 2000). With

increasing depth, adsorption decreases because of low organic matter (Coquet and

Barriuso, 2002). According to Andreu and Pico (2004), the acidic situation enhances

the adsorption for ionizable pesticides like 2,4-D,2,4,5-T, picloram, and atrazine.

Organic matter increases the surface area as well as the proliferation of

microbes leading to chelation of the pesticides in soil and hence ultimately lead to

increase in adsorption (Benoit et al., 2008). In kaolinite soil, the adsorption is less

because of less surface area while in montmorillonite the adsorption is high since it is

an expanding clay mineral. In sandy loam soil, the adsorption of endosulfan is

comparatively less (George et al., 2009).

According to Edwards et al. (2009), with increasing soil moisture by increase

in rainfall, the hydrophilic nature of OM increases, hence the area for adsorption also

increases. In non tilled soil, the adsorption is high, because in less disturbed soil, the

organic matter is very high (Larsbo et al., 2009).

For physical adsorption where the force of attraction is weak. Temperature

decreases the process of adsorption and if the adsorption is chemical in nature

(electrostatic forces), it will increase with increase in temperature, ie, temperature

10


helps better ionization of the pesticide and that will leads to the better adsorption

(Hulscher and Cornelissen, 1996). But according to Osman and Cemile (2010), with

high rainfall, sometimes highly soluble pesticide may leach away and thus became

very less to be adsorbed to the soil. Time has also an influence on the adsorption,

with change in time, the rate of adsorption changes. In certain cases, the rate may

increase or decrease due to the process of degradation (Mamy and Barrisuo, 2007).

2.4 DEGRADATION OF PESTICIDES IN SOIL

A pesticide applied for pest control purpose will get converted to metabolites

generally called as transformation products. A large number of transformation

products (TPs) were recorded from various pesticides (Barcelo and Hennion, 1997;

Roberts, 1998; Roberts and Hutson, 1999). The degradation can be biotic or abiotic.

Abiotic degradation takes place mainly through photochemical or thermochemical

ways, while biotic degradation is through biochemical reactions mediated by

microbes (Graebing et al., 2003).

2.4.1 Degradation of Pesticides by Light (Photo Degradation)

The direct photolysis of pesticides on the soil surface is restricted to a depth of

0.2- 0.3 mm while mean indirect photolysis is restricted to 0.7 mm for the out door

experiments (Herbert and Miller, 1990). Photochemical transformations occur

commonly in the soil and they may totally destroy or appreciably modify a number of

different types of pesticides (Konstantinou et al., 2001). However, such processes

rarely convert pesticides to inorganic compounds in soils, and many of these

reactions only bring about a slight modification of the molecule so that the

metabolites are frequently similar in structure, and often in toxicity to their parent

precursors.

11




2.4.2 Degradation of Pesticides by Microbes (Biochemical Degradation)

Biochemical degradation depends on the behaviour of the pesticides, organic

carbon content, pH of the soil, biological activity and distribution of the microbes,

temperature and moisture content (Rodriguez et al., 2001).

The soil organic carbon content generally had a positive influence on

degradation (Guo et al., 2000). A small content of the organic matter in the soil can

increase the pesticide volume in a particular area by binding with that pesticide and

that also helps in the degradation of the pesticide (Lotter et al., 2003). In some cases,

the photochemical pre-treatment integrated with microbial degradation will lead to

complete degradation and detoxication of some pesticides as occurs with atrazine

(Chan et al., 2004).

Some microorganisms are capable of using certain pesticides as their only

source of carbon and nitrogen, like Pseudomonas (with 2,4-D and paraquat),

Nocardia (with dalapon and propanyl) or Aspergillus (with trifluralin and picloram).

Also the increase in microbial activity with atrazine pollution was noticeable after

lengthy incubation (Moreno et al., 2007). There is almost no biodegradation of

chlordecone (organochlorine insecticide) because of its highly chlorinated cage-like

structure that makes chlordecone a poor carbon source for bacteria (Cabidoche et al.,

2009).

2.5 EFFECT OF PESTICIDES ON SOIL ORGANISMS

Pesticides interact with soil organisms and their metabolic activities may be

altered (Singh et al., 2002). The residues of pesticides can harm non target organisms

including animals ranging from beneficial soil microorganisms soil insects, non-

target plants, fish, birds, and other wildlife. A study on the effect of pesticide effects

on earthworms showed severe negative effects on growth and reproduction (Shahla

and Dsouza, 2010).

12

http://www.sciencedirect.com/science/article/pii/S0167880907001934#bib38

An integrated study on a Round-up resistant soya field in Argentina showed

that, deleterious effect of these pesticides on earthworm population (Casabe et al.,

2007). Similarly microbes related study conducted in orchards in the South Africa

indicated adverse effects of spraying with pesticides (chlorpyrifos and azinphos

methyl) on earthworm’s biomass and cholinesterase activity and concluded that,

earthworms were detrimentally affected by the pesticides due to chronic and

intermittent exposure (Reinecke and Reinecke, 2007). Studies revealed that,

glyphosate affect the predatory arthropods and cause behavioural changes in them

(Evans et al., 2010)

Decrease in the number of spiders and richness of collembolan were noticed

after application of chlorpyrifos (Fountain et al., 2007). Studies revealed that,

glyphosate affect the predatory arthropods and cause behavioural changes in them.

U.S. Geological Survey (1999); US EPA (2000) found that chlorpyrifos, a common

contaminant of urban streams, is highly toxic to fish, and causing fish death in

waterways near treated fields or buildings.

2.6 CARBAMATE PESTICIDES – INTRODUCTION

The carbamates pesticides were mainly used in agriculture as insecticides,

fungicides, herbicides, and nematicides. In addition, they are used as biocides for

industrial or other applications and in household products and in public health vector

control. Thus, these chemicals are a part of the large group of synthetic pesticides

that have been developed, produced, and used on a large scale in the last 40 years.

The general formula of the carbamates is:

O

|| H

R1- C –N

R2

13



where R1 and R2 are alkyl or aryl groups.

The light absorption characteristics of carbamates contribute to their rapid

decomposition (by photodegradation or photodecomposition) under aqueous

conditions. Thus, the hazards of long-term contamination with carbamates were

comparatively less. Carbamate insecticides are mainly applied on the plants, and can

reach the soil while carbamate nematicides and herbicides are applied directly to the

soil.

Carbamates are toxic for worms and other organisms living in the soil.

Although a great reduction in the earthworm population may occur when applying

carbamates to the soil, numbers will return to normal, because of the rather rapid

breakdown of these compounds (IPCS, 1982).

Matthew et al. (2007) observed that enzyme mediated degradation takes

place in the case of carbamate pesticides. The largest proportion of bound residues

was found for carbamates, and in particular, for dithiocarbamates. In this study,

authors further summarized and discussed factors that affect formation of bound

residues, viz., chemical properties as well as soil and environmental conditions

(Barriuso et al., 2008). In a lab study for understanding the persistence of 6

carbamate pesticides oxamyl, carbaryl, phorate, phosphamidon, carbofuran, and

methomyl on ten soils of Aligarh district under different temperatures, concentration,

FYM, nitrogen concentration, pesticide concentration, and pH range revealed that,

degradation of the pesticide increased with high temperature, FYM, nitrogen and

moisture while it was slow with increased pesticide concentration. The degradation

was rapid in alkaline soil than neutral or acidic soil (Bansal, 2009). Barra et al.

(2010) noted that, the microbial concentration in the soil increased with decrease in

the concentration of aldicarb and carbofuran.

14

Several factors influence the biodegradation of carbamates in soil, such as

volatility, soil type, soil moisture, adsorption, pH, temperature and

photodecomposition (Osman and Eldib, 1972). Environmental conditions that favour

the growth and activity of microorganisms also favour the degradation of carbamates.

The first step in the metabolic degradation of carbamates in soil is hydrolysis. The

hydrolysis products will be further metabolized in the soil-plant system.

Certain carbamates may reach groundwater and as a result it may

contaminate drinking-water. In certain cases, the use of toxic carbamates may cause

a significant reduction in non-target organisms. Contamination of groundwater and

drinking water sources by aldicarb, a carbamate was also reported (Soren and Stelz,

1991).

2.7 CARBOSULFAN

Carbosulfan is a systematic insecticide belonging to the carbamate class and is

the pro-insecticide of carbofuran. It is not very stable, it decomposes slowly at room

temperature. Carbosulfan is used as an insecticide, nematicide and acaricide. When it

gets degraded, it forms carbofuran which is a banned pesticide in Kerala due to its

toxicity. The European Union banned the use of carbosulfan in 2007. Its

oral LD50 for rats is between 90 to 250 mg kg-1, and is only slightly absorbed

through skin (LD50 > 2000 mg kg-1 for rabbits).

2.7.1 Salient Features of Carbosulfan

Common name: Carbosulfan

Chemical name: 2, 3-di hydro-2, 2-di methyl benzo furan-7-

yl (di butyl amino thio) methyl carbamate

CAS Registry No.: 55285-14-8

CIPAC No: 417

Synonyms: FMC 35001, Marshal, Sheriff

15

https://en.wikipedia.org/wiki/Carbamate

https://en.wikipedia.org/wiki/Decomposition_reaction

https://en.wikipedia.org/wiki/Room_temperature

https://en.wikipedia.org/wiki/Room_temperature

https://en.wikipedia.org/wiki/Insecticide

https://en.wikipedia.org/wiki/European_Union

https://en.wikipedia.org/wiki/LD50

https://en.wikipedia.org/wiki/Rat

https://en.wikipedia.org/wiki/Skin

https://en.wikipedia.org/wiki/Rabbit

Molecular Structure

Odour No specific odour

Molecular formula: C20H32N2O3S

Molecular weight: 380

Vapour pressure: 2.69 x 10-7 mm Hg at 25°C

Melting point: Carbosulfan is a liquid. It decomposes at elevated

temperature

Boiling point 219.3°C

Hydrolysis Hydrolyzes at pH < 9

Photolysis Mainly to carbofuran and dibutyl amine in aqueous

solutions

Half-life 1.4 days at pH 7

4-8 days in distilled water

Solubility in water 0.3 mg L-1 at pH 9 and 25°C

Solubility at 23°C Miscible in all proportions in hexane, toluene, acetone

and acetonitrile

Solubility at 20°C >250 g L-1 in dichloro methane, methanol and ethyl

acetate

2.7.2 Carbosulfan as a Crop Protectant

Carbofuran is generally applied as granules to flooded rice paddies or as a

spray to the basal portion of leaf sheath. Carbosulfan is an analog of carbofuran

developed and recommended for use as an effective substitute for carbofuran. It has

been reported to be very effective against the insect pests, which can not be

controlled by organo-chlorine or organophosphorous insecticides (Sahoo et al.,

1990). It has been proposed for the control of pyrethroid resistant mosquitoes

16

(Guillet et al., 2001). Cabosulfan is used as an alternative of endosulfan 35 per cent

EC and 4 per cent DP in paddy against gall midge and stem borer, in cotton against

aphids, jassids and thrips and in chilli against thrips. Carbosulfan is widely used in

agriculture as a broad spectrum insecticide against caterpillars, green leaf hoppers,

white - backed plant hoppers, brown plant hoppers, gall midges, stem borers, leaf

folder of paddy and white aphids of chilies (Giri et al., 2002).

Hot water treatment at 50°C for 30 minutes followed by foliar spraying of

carbosulfan 0.1per cent at 40 days after transplanting reduced white tip nematode by

34 per cent, thereby increasing rice yield by 87 per cent over un treated control

(ICAR, 2010). Carbosulfan 6 per cent G and carbosulfan 25 per cent EC were

recommended in chilli while carbosulfan 25 per cent DS was recommended in cotton.

Treatment of cotton seed with carbosulfan at 20g kg-1 of seed or imidacloprid at 7.5g

kg-1 seed was introduced as a new protection technique against aphids and jassids

(CIRCOT, 2002).

In rice, Carbosulfan 6 per cent G at1000 g ai ha-1 is recommended against

stem borer, gall midge, leaf hopper and leaf folder, while a dosage of 200-250 g ai

ha-1 of carbosulfan 25 EC against Brown Plant Hopper (BPH), Green Plant Hopper

(GPH), white aphid and leaf folder in chilli. In cotton, 15 g carbosulfan 25 per cent

DS per kg seed is recommended against jassids, aphids and thrips (CIBRC, 2012).

Carbosulfan 6 G is recommended @ 6.7 kg ha-1 as a substitute for carbofuran

3 G in rice against stem borer, gall midge, BPH, GLH, hispa and against nematodes

in rice, banana and cardamom (KAU, 2011).

2.7.3 Movement of Carbosulfan in Plant and Soil

The insecticide compounds concentrations in the foliage of brussels sprouts,

cauliflower and sugar beet crops were higher when they were higher in the soil. At

harvest, no residue of either carbosulfan, furathiocarb, carbofuran, or any of its

17

metabolites were observed in the flower of cauliflower, or in the brussels sprouts

themselves (Rouchard et al., 1990).

During plant growth, each of the insecticides (and their soil metabolites) was

transported from soil into the plant foliage, where it could give a secondary plant

protection against the foliage insects by transporting to plant from soil. For systemic

insecticides such as carbofuran, carbosulfan and furathiocarb, the weights per plant of

insecticide compounds transported from soil into the foliage were greater than they

were with the non systemic chlorpyrifos and chlorfenvinphos (Rouchard et al., 1991).

Continuous use of carbosulfan and carbofuran in soils leads to contamination

of surface water bodies (Thapinta and Hudak, 2000). Lysimetric studies on the

movement of carbosulfan and monocrotophos showed the presence of residues at the

bottom of lysimeter at 1.52 > 2.1 > 2.74 m, that means the concentration of residues

were decreasing at higher water table depth (Ilyas et al., 2010).

2.7.4 Persistence of Carbosulfan

Studies on the dislodgeable residues of carbosulfan and three of its major

metabolites in leaves, fruits and soil in an orange grove in Florida showed that,

carbosulfan and carbofuran dissipation were rapid in fruits during fall season (3- 4

folds in 3 days) and slower during winter seasons (1.5 time in 3 days). In both

periods the persistence has higher in soil than in fruit and leaves (2-3 folds in 8 days).

Most important metabolite of carbosulfan is carbofuran which persisted more than the

parent material in orange leaves in both seasons ( Nigg et al., 1985). Reports reveals

that, carbosulfan and its major metabolite carbofuran have low persistence in water

and have medium persistence in soil solution of tropical low land rice fields and

irrigated rice fields (Pedro et al., 2005).

18

When carbosulfan was added to sand and a medium of sand and organic

matter, the bioavailability is more in pure sand medium indicating that the organic

matter fixes the pesticide and thus reduces its toxic effect( Hautier et al., 2007).

The studies on the persistence of carbosulfan in red loam, alluvial and black

soil revealed that, the carbosulfan residues reached below detectable level within 75

days in red loam and alluvial soils while 90 days in black soil. The half life of

carbosulfan were 15, 12, and 14 days in black, red and alluvial soils respectively at 5

mg kg-1 level of fortification, while the half life were 12,10 and 11 days at 10 mg kg-1

level of fortification (Kamala and Chandrasekaran, 2015).

2.7.5 Degradation of Carbosulfan

Carbosulfan is chemically stable under alkaline conditions, but undergoes

rapid chemical hydrolysis (Ramanand et al., 1989) to carbofuran and dibutyl amine at

pH below 6 (Sahoo et al., 1990). In the environment, carbosulfan is first metabolized

to carbofuran, then to 3-hydroxy-carbofuran and thereafter to 3-keto carbofuran. This

is a special case in which a less toxic pesticide (carbosulfan, LD50, 101- 250 mg kg-1

for rats) is transformed to a more toxic one (carbofuran, LD50 8 mg kg-1 for the same

species). Under field conditions, the toxic effect of carbosulfan is mainly due to the

transformation to its carbofuran metabolite (Tomlin,1995).

The pesticide dissipation in rice - fish production system revealed that,

carbosulfan is rapidly converted to carbofuran in all rice eco-system components,

except for the rice leaves where its occurrence as the original compound lasted 7

days. Carbofuran was the main metabolites which persisted for 30 days in soil

(Varca et al., 1998). Carbosulfan on one hand and the sum of carbofuran, 3-hydroxy

carbofuran and 3- keto carbofuran and their conjugates on the other hand were

considered as the relevant residues to assess the consumer exposure and risk (EFSA,

2009).

19

2.7.6 Effect of Carbosulfan on Organisms

Effect of carbosulfan on soil microflora on arable soil receiving single

application produced significant biomass reduction while repeated application of

carbosulfan did not show any detectable deleterious effect on soil microbial biomass,

thereby suggesting substantially different effect on soil biomass produced by single

or repeated application of pesticide (Duah and Johnson, 1996). Carbosulfan has been

reported to induce chromosome aberrations in rat (Topaktas et al., 1996).

Carbosulfan @ 1, 2 and 10 per cent of recommended field rate when applied

to the soil showed the increase in mortality rate of beneficial insects Bemidion

lambros by 50, 57 and 100 per cent respectively (Hautier et al., 2007). Carbosulfan

treated soil had less evolution of CO2 indicating initial inhibitory effect on microbial

activity and that gained positive stimulation with time. (Latif et al., 2008). It is noted

that, the seed treatment of chickpea with aqueous solution of carbosulfan declined

Melodogyne. incognita population in the soil by 38-70 percent, while R. reniformis

by 32-66 percent (Meher et al., 2010). Carbosulfan is extremely toxic to mammals

and its toxicity is mediated through inhibition of acetyl choline esterase enzyme.

(Karami-Mohajeri and Abdollahi, 2010).

20

Fig. 1. Degradation pathway of carbosulfan in oranges (Carla et al., 2005)

Materials and Methods

3. MATERIALS AND METHODS The present study entitled “Persistence and transformation of carbosulfan in

laterite and coastal alluvium soils of Kerala and its effect on soil organisms” has been

carried out to assess the dynamics of carbosulfan in laterite and coastal alluvial soils

under laboratory as well as cropped conditions using Emulsifiable Concentrate (EC)

as well as Granule (G) formulations of the pesticide, to study its migration tendency

in the packed soil columns and also to study the effect on soil organisms.

3.1 PHYSICO- CHEMICAL ANALYSIS OF SOILS

The study was conducted in two types of soils viz., sandy loam and loamy

sand soils of Kerala. The laterite soil was collected from the identified locations of

College of Agriculture, Vellayani, Thiruvananthapuram, Kerala, while coastal

alluvial soil was collected from various locations near Kazhakkoottam,

Thiruvananthapuram, Kerala at a depth of 0-15 cm using a spade. Along with this,

core samples were also taken for the physical analysis. The collections were done

during September 2015. The collected soil samples were spread, mixed and shade

dried for one week and the physicochemical analysis of the two soils were carried

out as per standard procedures given in Table 2.

3.2 VALIDATION OF MULTI RESIDUE METHODS FOR PESTICIDE RESIDUE

ANALYSIS IN SOIL

A mixture of the analytical standards of carbosulfan and its metabolites viz.,

carbofuran, 3- hydroxy carbofuran and 3- keto carbofuran were fortified in soil at

three different levels ( 0.05, 0.25 and 0.5 mg kg-1). Extraction and clean up methods

were performed by adopting QuEChERS multi residue estimation method.

3.2.1 Technical programme

Design: CRD

21

Table 2. Analytical methods followed to test the physico chemical parameters in soil

Sl.

No Parameter Method Reference

1 Texture International pipette method Piper ( 1966)

2 Bulk density Core method

Gupta and Dakshnamoorthy

(1980)

3 Particle density Pycnometer method


(1980)

4

Water Holding

Capacity (WHC) Core method


(1980)

5 Field capacity Pressure plate apparatus


(1980)

6 pH pH meter with glass electrode Jackson(1973)

7

Electrical

Conductivity (EC) Conductivity meter Jackson(1973)

8

Cation Exchange

Capacity (CEC)

Neutral N ammonium acetate

method Jackson(1973)

9 Organic carbon Walkley and Black method Jackson(1973)

10 Available Nitrogen Alkaline permanganate method Jackson(1973)

11

Available

Phosphorus

Bray No 1 extraction and

Spectrophotometry Jackson(1973)

12 Available Potassium

Neutral N ammonium acetate

extraction & Flame Photometry Jackson(1973)

13 Exchangeable Ca Versanate method Jackson(1973)

14 Exchangeable Mg Versanate method Jackson(1973)

15 Available Sulphur Turbidimery method Jackson(1973)

22

Treatments:3

Replication: 6

Treatments

T1- 0.05 mg kg-1 analytical standard mixture

T2- 0.25 mg kg-1 analytical standard mixture

T3- 0.50 mg kg-1 analytical standard mixture.

3.2.2 Laboratory Glass Ware, Chemical Reagents and Equipments

The glass wares, chemical reagents and equipments used for the study were

given in Table 3. The reference analytical standards of the pesticides were purchased

from Sigma Aldrich, USA and stored in deep freezer at a temperature below -20 °C,

without exposure to light and moisture.

Initially, the glass wares were washed with tap water and then they were

immersed overnight in 1 per cent laboline and then again washed with tap water.

After that, they were dipped in boiling water for 2 hrs and rinsed with acetone and

were kept in the oven at 50 0C for 3 hrs for drying. The plastic tubes were similarly

washed and kept at room temperature for drying. The syringes were thoroughly pre-

rinsed with acetone and then with methanol before use.

3.2.3 Preparation of Mixture of Standard Insecticides

The steps involved in the preparation of standard mixture of carbosulfan and

its metabolites were as follows

3.2.3.1 Procurement of Certified Reference Material (CRM)

The CRMs of carbosulfan, carbofuran, 3-OH carbofuran and 3-keto

carbofuran were procured from M/S. Sigma Aldrich, USA. Required quantities of

23

Table 3. The glass wares, equipments, and reagents used for residue analysis

Laboratory Glass wares Chemical Reagents Equipments

Beakers 100, 250, and 500

mL

Acetone AR grade Analytical Balance

Centrifuge tubes 15 mL

and 50 mL

Acetonitrile HPLC grade Laboratory centrifuge

Class A pipettes 0.5 mL, 1

mL, 2 mL, 10 and 20 mL

Magnesium sulphate

(hydrated) AR grade

Mechanical shaker

Conical flasks and

standard flasks 250 mL,

500 mL and 1 L

Methanol HPLC grade Vortex shaker

Graduated test tubes 5mL

and 10mL

Primary Secondary Amine TurboVap Evaporator

Micro pipettes 100 µl, 1

mL and 5mL

Sodium chloride (AR

grade)

Rotory vacuum flash

evaporator

Separating funnels 750

mL and 1 L

Ammonia solution Liquid Chromatograph -

Mass Spectrometer

TurboVap tubes 20 mL

and 30 mL

Dichloromethane

PVC pipes (50 x 2.5cm) Sodium Sulphate

Hypodermic syringe 10

mL and Randisc

24

each of the standards were weighed to prepare the analytical standard solutions of

known concentrations.

Table 4. Details of CRMs used for the preparation of pesticide mixture

Sl.

No

Compound Formula CAS Number Purity

1 Carbosulfan C20H32N2O3S 55285-14-8 99.4%

2 Carbofuran C12H15NO3 1563-66-2 99.9%

3 3-OH Carbofuran C12H15NO4 16655-82-6 99.1%

4 3-Keto Carbofuran C12H13NO4 16709-30-1 98.5%

3.2.3.2 Preparation of Standard Solution

Standard stock solutions of carbosulfan and its metabolites (1000 mg L−1)

were prepared in methanol and stored at -20°C in deep freezer.

3.2.3.3 Intermediate Stock Solution and Working Standards

Intermediate standards of 100 mg kg-1 of carbosulfan and its metabolites were

prepared by diluting the required quantity of stock solution with methanol.

Aliquots of intermediate standards were taken in separate standard flasks in

order to prepare working standards of 10 mg kg-1 of each compound. From this

working standard (10 mg kg-1) a mixture of all these four compound were prepared in

methanol solvent and stored in refrigerator for further use. From this, working

standard serial dilution was done to obtain 1, 0.5, 0.25, 0.1, 0.05, 0.025 and 0.01 mg

kg-1 concentrations. The individual standards of different insecticides were injected

in Liquid Chromatography – Mass Spectrometer and a calibration curve was prepared

by plotting concentration vs. peak area.

25

3.2.4 Fortification of Soil with Standard Insecticide Mixture

A fixed quantity of 10 g each of air dried (2 mm sieved) soil samples were

taken in 18 50 mL centrifuge tubes and were spiked separately with 0.05 mL, 0.25

mL and 0.5 mL each of 10 mg kg-1 working standard mixture to get 0.05, 0.25 and

0.5 mg kg-1 levels respectively.

3.2.5 Recovery Experiment

A recovery experiment was conducted to standardize the procedure for

extraction and clean up processes. The experiment was conducted by adding a known

quantity of insecticide mixture to soil and trying the extraction process using different

solvent systems. All the chemicals and solvents used in the research were either of

analytical grade or HPLC grade.

3.2.5.1 Extraction

The soil samples were extracted using acetonitrile and also extraction using

acetonitrile after addition of ammonia were done and the efficiency of the extractions

were assessed. QuEChERS method was adopted for acetonitile extraction of spiked

pesticides from soil. For this purpose, 10 g of air dried, sieved (2 mm) soil was

weighed in a 50 mL centrifuge tube and spiked with the standard insecticide mixture

and evaporated to release the solvent vapours. The soil samples were spiked with

0.05, 0.25 and 0.5 mL each of 10 mg kg-1 solution to get 0.05, 0.25 and 0.5 mg kg-1

levels of each of the spiked compounds. To this, 4 g magnesium sulphate, followed

by 1g sodium chloride and 20 mL acetonitrile were added, shaken for 2 minutes in a

vortex shaker and was centrifuged for 4 minutes at 3300 rpm. A 10 mL supernatant

was transferred to a 15 mL centrifuge tube using a micro pippette and 0.25 g primary

secondary amine and 1.5 g magnesium sulphate were added and was shaken for

30 seconds in vortex followed by centrifugation at 4400 rpm for 10 minutes. After

the centrifugation, 4 mL of the cleaned supernatant extract was transferred to a turbo

26

tube and evaporated to dryness at 40 °C using turboVap. The dry residue was

redissolved in methanol and the volume was made upto 1mL, filtered through 0.22

μm poly vinylidene fluoride (PVDF) syringe filter and passed to a vial which was

wrapped with parafilm to avoid evaporation. In the second method, a slight

modification was tried in the QuEChERS method with addition of 0.5 mL of 10 per

cent ammonia solution after spiking of the pesticide in the soil while all other steps

were same as that of QuEChERS method.

3.2.5.2 Estimation

The cleaned extracts were analyzed on a Liquid Chromatograph equipped

with Triple Quadrupole Mass Spectrometer (Sciex – API 3200). The samples as well

as the standards were injected to the equipment.

3.2.5.2.1 LC- MS System

The ACQUITY ultra performance LC system was used for chromatographic

separation with a column size of 5 µm particle size placed in a column oven at 40 °C.

Elution was done using two elutents (solvent mixtures), viz.,

A: 10 per cent methanol in water + 0.1 per cent formic acid + 50 mM ammonium

acetate

B: 10 per cent water in methanol + 0.1 per cent formic acid + 50 mM Ammonium

acetate.

The flow rate remained constant at 0.8 mL min-1 and the injection volume was 10

µL.

Then the effluent from LC was introduced into triple quadrupole API 3200

MS/MS system. It contains ion source gas 1 (at 50 psi), ion source gas 2 (at 40 psi)

and curtain gas (at 30 psi) with ion source temperature, 550 °C and ion spray voltage

source of 5000 V. The residues were quantified in MS/MS system. For each analyte,

27

two Multiple Reaction Monitoring (MRM) transitions were taken. The other

compound dependent parameters used were shown in Table 5.

Table 5. Multiple- reaction monitoring (MRM) and Liquid Chromatography (LC)

parameters for carbosulfan and its metabolites.

* DP- Declustering Potential, EP- Entrance Potential, CEP- Collision Cell Entrance

Potential, CE -Collision energy, CXP- Collision cell Exit Potential.

3.2.5.3 Residue Quantification and Recovery Experiment

Pesticide residues in the sample (mg kg-1) =

Peak area of sample x Concentration of standard injected x Dilution factor

Peak area of standard

Dilution Factor (DF) = Volume of solvent added x Final volume of the extract

Weight of sample (g) x volume of extract taken for concentration

Sl

No

Compound Retention

time (min)

Precursor

ion Q1 mass

(Da)

Precursor

ion Q2

mass (Da)

DP CEP CE CXP

1 Carbosulfan 5.52

5.52

381.2

381.2

118.1

160.1

42

42

31

31

33

22

1

1

2 Carbofuran 2.21

2.20

222.1

222.1

165.2

123.0

30

30

16.04

26.36

17

29

2

2

3 3-OH

Carbofuran

1.28

1.28

238.1

238.1

181.1

163.1

28

28

24

24

16

21

1

1

4 3-Keto

Carbofuran

1.78

1.79

236.1

236.1

179.1

151.1

33

33

22

23

18

18

1

1

28

Percentage recovery (%) = Concentration of pesticide residue obtained x100

Concentration of pesticide residue added.

Relative standard Deviation (RSD) = Standard deviation x 100

Mean Recovery

A method with Recovery percentage in a range of 80-120 and the Relative Standard

Deviation (RSD) value < 20 will be selected for the study. Limit of quantification

(LOQ) was 0.01 mg kg-1. Limit of Detection (LOD) was 0.005 mg kg-1. The

concentration of carbosulfan and its metabolites in the samples were derived from the

calibration curve and chromatogram of the standards of these compounds. These

calibration curve and chromatograms are appended from I- V.

3.3 MOBILITY OF CARBOSULFAN IN SOILS

The mobility of carbosulfan in the two soil columns were assessed by

analyzing the residues at different depths after loading 3 levels of carbosulfan and

subsequent elution with different levels of water as detailed below.

3.3.1 Technical Programme

Design- CRD

Treatment -12 (3 levels of pesticide and 4 levels of water)

Replication-3

Treatments-

T1-100 µg level of carbosulfan EC + 20 mL water



29










Studies on the mobility of carbosulfan was done by using packed soil column

method by loading the given formulation so as to give 100, 150 and 200 µg of

carbosulfan on top of the preloaded column, followed by leaching with measured

amount of water. A laterite soil sample of 191 g and 183 g of coastal alluvial soil

were packed in the PVC columns of height 50 cm and 2.5 cm inner diameter to a

height of 25 cm maintaining the bulk density, simulating field compaction level and

were fixed firmly to burette stands. The lower end of the columns were firmly

fastened by using muslin cloth so as to retain the soil as per the desired bulk density.

The lower end of the soil column was immersed to a conical flask containing water

for 12 h for saturation. On the next day, the saturated soil column was top loaded

with 5 g soil to which required quantity of carbosulfan was added to get 100, 150 and

200 µg level and kept immersed in dry conical flask for collecting the leachate. The

columns were eluted by controlled addition of water at 20 mL, 40 mL, 80 mL and

160 mL, respectively, using drip system at a steady flow in accordance with the

hydraulic conductivity of the soils viz., 0.4 mL min-1 for laterite and 0.6 mL min-1 for

30

Plate 1. Saturation of the soil column for mobility study

Plate 2. Eluting the soil column after treatment

Plate 3. Cut pieces of soil column for residue analysis

coastal alluvial soil obtained from the analysis. The water used for elution

correspond to 50, 100,200 and 400 mm rainfall in field condition and can be used for

prediction of relative mobility along with water under field situation. The leachates

obtained were collected in the conical flasks kept under the soil column. After the

leaching was completed, the leachate as well as the soil were analyzed for residues.

For the soil sample analysis, the pipes / soil columns were cut into 5 portions of 5 cm

each viz., 0-5 cm, 5-10 cm, 10-15 cm, 15-20 cm and 20-25 cm and the residues

present in each of the vertical soil fractions were extracted and quantified.

3.3.2 Monitoring of Pesticide Residues in Leachate

The leachates were separately collected and from each sample a 20 mL

subsample was transferred to a separatory funnel to which 50 mL distilled water was

added. Then 5 g sodium chloride and 20 mL dichloro methane were added followed

by mechanical shaking to cause layer separation and the lower layer was collected in

the round bottom flask after passing it through a funnel containing anhydrous sodium

sulphate. The extraction was repeated two more times using 20 and 10 mL of

dichloromethane each time. The collected extracts were concentrated using a flash

evaporator and were made upto 2 mL using methanol and the residues were estimated

with LC-MS/ MS.

3.4 STUDIES ON THE PERSISTENCE OF CARBOSULFAN IN SOIL

Studies on the persistence of carbosulfan in the two soils viz., laterite and

coastal alluvial were done using EC and granule formulation at three levels (1, 2.5

and 5 mg kg-1) in the laboratory as well as in the field in cropped situation using chilli

(Uujwala) as the test crop. The commercial formulation of carbosulfan (Marshal

25EC and Sheriff 6G) manufactured by FMC was purchased from local market. The

experiment was planned as per the following statistical design.

31

3.4.1 Technical Programme

Design- CRD

Treatments -3

Replication-5

Treatments

T1-Fortification with 1 mg kg-1 carbosulfan formulation

T2- Fortification with 2.5 mg kg-1 carbosulfan formulation

T3- Fortification with 5 mg kg-1 carbosulfan formulation

For conducting the laboratory study, one kg soils each were brought to field

capacity level by adding measured quantity of distilled water (90 mL kg-1 of laterite

and 70 mL kg-1 for coastal alluvial) in the conical flask and spiked separately at 1,2.5

and 5 mg kg-1 levels of carbosulfan using the two formulations, homogenized and

kept aside for 2 hours (0th day). A 10 g soil was taken from the conical flask in

triplicate and analyzed for the residue estimation. Likewise samples were drawn on

1st, 3rd , 5th,7th,10th, 15th , 20th and 30th day for analysis of residues and to identify the

metabolites formed .

In the field condition, chilli crop (variety Ujwala) was raised in the grow bag

as per package of practices recommendation. When the plants were in the flowering

stage, the soils were spiked using the two formulations of carbosulfan at 1, 2.5 and 5

mg kg-1 levels maintaining the moisture at field capacity. The sample analysis were

done on 0, 1, 3, 5, 7, 10, 15, 20, and 30th day as in the case of laboratory study. The

levels of carbosulfan persisting at different time intervals were recorded from which

half life value was calculated.

32

Plate 4. Persistence study under cropped condition

Plate 5. Persistence study under laboratory condition

3.4.2 Calculation of Half Life Period

Theoretically, the pesticide residue should decrease logarithmically with time

since amount lost per unit time should be proportional to the total present at anytime

because all were exposed equally to weathering and degradation (Hoskins, 1981). A

graph should be plotted with time (t) against log of residue parameters (log D), ‘D’

indicates residue in ppm. The graph shows a linear trend which indicates that log D

can be represented as a linear function of ‘ t’ (in days or weeks). The model is,

D =k1E+logk2, that means D = k2 where k2 represent initial deposits. The time

required to reduce D to D/2 is defined as half life so it is calculated as t1/2= log2 / k1

3.5 STUDIES ON THE DEGRADATION OF CARBOSULFAN IN SOIL

Studies on the degradation of carbosulfan were done by analyzing the level of

carbosulfan at different time intervals along with the formation of metabolites such as

carbofuran, 3- hydroxy carbofuran and 3-keto carbofuran in the soil from the parent

compound. The disappearance and corresponding appearance of different metabolites

formed is helpful in studying the chemo-dynamics of carbosulfan in the soils and

thereby arriving at the relative persistence/ stability of carbosulfan in the respective

soils under study.

3.6 EFFECT OF CARBOSULFAN ON MICROBIAL POPULATION

3.6.1 Soil Sampling

A representative area of each of the soil under study was selected from which

an area of 1 m2 was earmarked for treatment application. The required number of

plots to suit the statistical design for collection of the soil from each of the treatment

at two levels were selected. Sufficient space was provided between plots to avoid

cross contamination. Control plots were applied with water and the other plots were

33

applied with granular and EC formulations of carbosulfan at two levels, each in three

replicates.

Soil samples (1 kg) were taken from each of the treatments, combined,

homogenized and sub sample was taken for enumeration of macro and

microorganisms prior to treatment application with the granule and EC formulations

of carbosulfan. Soil samples of 1 kg each were treated with the two formulations of

carbosulfan each at two concentrations 2 hours before treatment and post treatment

samples were taken after 24 hrs of treatment with carbosulfan at 250 g ai ha-1 and

500 g ai ha-1 of formulation at 0-15 cm depth, from which sub samples were taken for

enumeration of soil organisms in treated samples.

3.6.2 Enumeration of Bacteria, Fungi and Actinomycetes

Enumeration of bacteria, fungi and actinomycetes were done by serial dilution

technique (Johnson and Curl, 1972) and then inoculation of the diluted solutions to

respected media under asceptic condition in the laminar airflow chamber and the

plates were incubated at 20°C for the multiplication of the organisms and the colony

formed were counted using a colony counter.

3.6.2.1 Preparation of Media

The media used for enumeration of bacteria, fungi and actinomycetes are

different. Specific media like Potato Dextrose Agar is used for enumeration of fungi

while tryptone soya agar is used for bacteria and casein agar is used for

enumeration of actinomycetes.

3.6.3 Enumeration of Soil Arthropods

The population of macro arthropods in the two soils were assessed by

counting their number in one kg soil by spreading it into a thin layer.

34

Plate 6. Enumeration of soil bacteria

Plate 7. Enumeration of soil fungi

Plate 8. Enumeration of actinomycetes

Plate 9. Enumeration of soil arthropods

For counting the micro arthropods like collembolan and mites, Berlese -

Tullgren funnel method (Macfadyen, 1961) was adopted. For this, 250 g soil

alongwith litter was taken, and with minimum disturbance it was placed on a wire

gauge over a steep slanting funnel. At the lower end of the funnel, a beaker

containing 100 mL of a mixture of ethanol : water in the proportion 75 : 25 was

placed. The upper portion of the funnel was heated gently using a 40W electric bulb

for a period of 24 hrs. Then the arthropods in the soil migrate gently from the heated

upper portion of the soil to lower layers from where it will be collected in the beaker

placed at the tip of the funnel. After 24 hrs, 5 mL of the solution mixture was

transferred to a petri -plate and the number of arthropods were counted under a

binocular microscope. The number of arthropods thus obtained can be used to get the

number of arthropods in 1 kg soil .

3.7 STATISTICAL ANALYSIS

The data generated was statistically analyzed using analysis of variance

(Gomez and Gomez, 1984) and from the dissipation data half life of carbosulfan was

worked out using Hoskins formula (Hoskins, 1981).

35

Results

4. RESULTS

The results of the study entitled ‘Persistence and transformation of

carbosulfan in laterite and coastal alluvium soils of Kerala and its effect on soil

organisms’ are presented under the following headings.

4.1 PHYSICO- CHEMICAL ANALYSIS OF SOILS

Physical and chemical characters of the two soils used for the study were

analyzed as per standard procedures and the results obtained are presented in Tables 6

and 7.

4.1.1 Physico - Chemical Properties of Laterite and Coastal Alluvial Soils

The results of physicochemical analysis of the two soils were presented in

Tables 6-7. Among the two soils selected, one was sandy loam and the other was

loamy sand in texture. The porosity of coastal alluvial soil is comparatively lesser

than the laterite soil. Water holding capacity and field moisture level of laterite soil is

higher compared to coastal alluvial soil. The particle density and bulk density of the

laterite soils were 2.63 and 1.6 Mg m-3 respecively and for coastal alluvial soil it was

2.56 and 1.58 Mg m-3. The pH of the soils were 5.3 and 5.08 and hence both are

strongly acidic in nature. The EC of the soils were also 0.63 and 0.77 dS m-1. The

cation exchange capacity was more for coastal alluvial amounting to 5.18 c mol kg-1

soil while it was 3.08 cmol kg-1 for laterite soil. The organic matter content and

nutrient contents of coastal alluvial soil was higher than that of the laterite soil. The

organic matter contents of coastal alluvial soil and laterite soils was 0.41 and 0.84

per cent respectively. The status of primary and secondary nutrients were relatively

low for coastal alluvial soil.

36

Table 6. Physico-chemical properties of laterite soil

Sl No. Parameters Results

1 Texture Sandy Loam

2 Sand 61.24 %

3 Silt 27.20 %

4 Clay 11.56 %

5 Bulk density 1.60 Mg m-3

6 Particle density 2.63 Mg m-3

7 Porosity 40.68 %

8 Field Moisture 10.75 %

9 Water Holding Capacity (WHC) 14.09 %

10 pH 5.08

11 Electrical Conductivity (EC) 0.63 dSm-1

12 Cation Exchange Capacity (CEC) 3.08 cmol 100g-1

13 Organic Matter (OM) 0.41 %

14 Available Nitrogen 175.6 kg ha-1

15 Available Phosphorus 22.4 kg ha-1

16 Available Potassium 156.8 kg ha-1

17 Exchangeable Calcium 0.02 meq 100g-1

18 Exchangeable Magnesium 0.03 meq 100g-1

19 Exchangeable Sulphur 4 mg kg-1

37

Table 7. Physico-chemical characters of coastal alluvial soil

Sl No. Parameters Results

1 Texture Loamy Sand

2 Sand 80.68 %

3 Silt 8.48 %

4 Clay 10.84 %

5 Bulk density 1.58 Mg m-3

6 Particle density 2.56 Mg m-3

7 Porosity 38.28 %

8 Field Moisture 7.03 %

9 pH 5.18

10 Electrical Conductivity (EC) 0.77 dSm-1

11 Water Holding Capacity (WHC) 13.18 %

12 Cation Exchange Capacity (CEC) 5.18 cmol kg-1

13 Organic Matter (OM) 0.84 %

14 Available Nitrogen 263.42 kg ha-1

15 Available Phosphorus 28 kg ha-1

16 Available Potassium 264.40 kg ha-1

17 Exchangeable Calcium 0.03 meq 100g-1

18 Exchangeable Magnesium 0.04 meq100g-1

19 Exchangeable Sulphur 6 mg kg-1

38

4.2 MULTI RESIDUE METHODVALIDATION IN SOIL

The method validation for extraction of carbosulfan and its metabolites from

soil were done by spiking with the respective standards so as to obtain a

concentration of 0.05, 0.25 and 0.5 mg kg-1 followed by extraction using acetonitrile

and the residue estimated at different concentrations in the soil are given in the

following Tables 8-13.

4.2.1 Mean Recovery of Carbosulfan and its Metabolites in Laterite Soil

The mean recovery percentage at 0.05 mg kg-1 level of fortification for

carbosulfan and its metabolites in laterite soil ranged from 87-95 per cent (Table 8).

For 3-hydroxy carbofuran, the highest recovery is obtained (95%). The Relative

Standard Deviation (RSD) values obtained ranged from 7.5 to 12.2, and the standard

deviation was from 6.6-11.5 per cent. So for all these compounds, the recovery

percentage obtained were within the satisfactory range (80-120%) and the RSD

values obtained were also in the satisfactory range (< 20) for all the spiked

compounds, and the method is found suitable at 0.05 mg kg-1.

The mean recovery percentage at 0.25 mg kg-1 level of fortification of the

compounds in laterite soil ranged from 90.9 - 98.3 per cent (Table 9). The highest

recovery per centage is obtained for carbofuran which is 98.3 per cent. The RSD

calculated ranged from 7.9-10.5 per cent. The standard deviation ranged from 7.2 -

10.3 per cent. Since all the parameters obtained for this level of fortification is within

the satisfactory range, the method is suitable for adoption in the studies.

The mean recovery per centage of various compounds spiked at 0.5 mg kg-1 in

laterite soil ranged from 94.8-99.2 per cent (Table 10). The highest recovery per

centage was obtained for 3-hydroxy carbofuran. Lowest recovery per centage was

obtained for 3-keto carbofuran. For carbosulfan, the recovery per centage was 97.2

39

Table 8. Mean recovery of carbosulfan and its metabolites when spiked at 0.05 mg

kg-1 level in laterite soil

Mean of six replications







Compound Recovery Percentage Standard Deviation Relative Standard

Deviation (RSD)

Carbosulfan 94.00 9.31 9.91

Carbofuran 92.80 8.61 9.20

3-hydroxy carbofuran 95.00 11.50 12.20

3-keto carbofuran 87.00 6.60 7.50


Deviation (RSD)


Carbofuran 98.30 10.30 10.50




Deviation (RSD)


Carbofuran 95.20 8.60 9.00



40


kg-1 level in coastal alluvial soil



kg-1 level in Coastal Alluvial soil



kg-1 level in coastal alluvial soil



Deviation (RSD)


Carbofuran 88.40 4.10 4.60




Deviation (RSD)


Carbofuran 94.30 7.60 8.10




Deviation (RSD)

carbosulfan 96.40 7.30 7.40

Carbofuran 90.80 4.10 4.50

3-hydroxy

carbofuran 90.40 4.10 4.60


41

per cent. The RSD values ranged from 6.9-11.6 per cent and the standard deviation

ranged from 6.6-11.5 per cent.

4.2.2 Mean Recovery of Carbosulfan and its Metabolites in Coastal Alluvial Soil

The mean recovery percentage of carbosulfan and its metabolites spiked at

0.05 mg kg-1 in coastal alluvial ranged from 88.4-92 per cent (Table 11). The RSD

value ranged from 4.6-8.9 and standard deviation ranged from 4.1-8.2 per cent. The

highest recovery was obtained for 3-keto carbofuran. For carbofuran and 3-hydroxy

carbofuran, same RSD values were obtained.

From Table 12, the recovery percentage for the compounds spiked at 0.25 mg

kg-1 in coastal alluvial soil ranged from 92.00 - 100.60 per cent. The highest recovery

percentage at this concentration was for 3-hydroxy carbofuran and the lowest was for

carbosulfan. The RSD values ranged from 6.1-9. Per cent and the standard deviation

ranged from 5.70 - 9.10 per cent.

From Table 13, the recovery percentage of carbosulfan and its metabolites at

0.5mg kg-1 level of fortification in coastal alluvial soil ranged from 90.40 - 97.60.

Here carbofuran and 3-hydroxy carbofuran had almost similar recovery percentage, ie

values 90.80 and 90.40 per cent respectively. The RSD value obtained were in the

range of 4.50-8.40 and the standard deviation ranged from 4.10 - 8.40. The

chromatogram, calibration curve and mass spectra of the standards and recovery

experiments are appended in appendix 1 to V.

4.3 MOBILITY OF CARBOSULFAN IN SOIL

The mobility of carbosulfan was determined by analyzing the residue found at

different depths of the two soil columns through which definite concentration of the

pesticides (100, 150 and 200 µg) was allowed to elute by application of definite

42

volume of water (20, 40, 80 and 160 mL) to the column. The results obtained were

given in the following tables.

4.3.1 Mobility of Carbosulfan and Carbofuran in Laterite Soil

Data on the downward migration of carbosulfan 25 EC by application at 100

µg in laterite soil when eluted with 20, 40, 80 and 160 mL of water are presented in

Table 14. The data revealed that, when 20 mL water was added, carbosulfan moved

upto 10 cm depth and majority of carbosulfan residues (1.503 mg kg-1) were confined

to the top 0-5 cm layer of soil. When the water used for elution increased to 40 mL,

the migration was detected upto 15 cm and the quantity of carbosulfan in the top

layer was reduced (0.011 mg kg-1). When the water for elution was 160 mL, more

migration was noticed and a further decrease in the concentration of carbosulfan was

noticed at top 0- 5 cm, indicating a more migration of carbosulfan with increase in

volume of water for elution.

Data regarding the downward movement of carbofuran detected in soil by

addition of carbosulfan 25 EC at 100 µg in laterite soil was presented in Table. 15.

The data revealed that, when 20 mL water was used for elution, the residue obtained

at 0-5 cm was 0.353 mg kg-1. With increase in the volume of water to 160 mL, there

is lower retention of carbofuran at 0-5 cm layer and the migration was noticed upto

15 cm.

Data on the downward migration of carbosulfan 25 EC with application at 150 µg in

laterite soil when eluted with 20, 40, 80 and 160 mL of water is presented in Table

16. The data revealed that, when 20 mL water was added, carbosulfan moved upto

10 cm depth and majority of carbosulfan residues (2.293 mg kg-1) were confined to

the top 0-5 cm layer of soil. When the water used for elution increased to 40 mL, the

migration was detected upto 15 cm and the quantity of carbosulfan in the top layer

was reduced (1.810 mg kg-1). When the water for elution was 160 mL,

43

Table 14. Migration of carbosulfan in laterite soil column when loaded at100 µg level

Mean of three replications

Table 15. Migration of carbofuran formed in laterite soil column when loaded with

100 µg carbosulfan

Mean of three replications *BDL- Below Detectable Level (0.01 mg kg-1)

Depth of soil column/

Leachate

Residues ( mg kg-1) at different depths

20 mL 40 mL 80 mL 160 mL

0-5cm 1.503 1.043 0.364 0.044

5-10cm 0.016 0.045 0.032 0.283

10-15cm BDL 0.011 0.015 0.026

15-20cm BDL BDL BDL BDL


Leachate BDL BDL BDL BDL


Leachate


20 mL 40 mL 80 mL 160 mL

0-5cm 0.353 0.241 0.117 0.015

5-10cm BDL BDL 0.013 0.053

10-15cm BDL BDL BDL 0.012




44

Table 16. Migration of carbosulfan in laterite soil column when loaded at 150 µg level

Mean of three replications Table 17. Migration of carbofuran formed in laterite soil column when loaded with 150 µg carbosulfan


Depth of

soil column/ Leachate


20 mL 40 mL 80 mL 160 mL

0-5cm 2.293 1.810 0.762 0.267

5-10cm 0.029 0.067 0.166 0.573

10-15cm BDL 0.014 0.036 0.041

15-20cm BDL BDL 0.012 0.020



Depth of



20 mL 40 mL 80 mL 160 mL

0-5cm 0.572 0.432 0.153 0.082

5-10cm 0.011 0.020 0.032 0.104

10-15cm BDL BDL 0.020 0.079




45

Table 18. Migration of carbosulfan in the laterite soil column when loaded at 200 µg level


Table 19. Migration of carbofuran formed in laterite soil column when loaded with 200 µg carbosulfan

Mean of three replications *BDL- Below Detectable Level (0.01 mg kg-1

Depth of



20 mL 40 mL 80 mL 160 mL

0-5cm 3.553 2.437 1.303 0.049

5-10cm 0.065 0.193 0.364 0.383

10-15cm 0.011 0.015 0.130 0.026

15-20cm BDL BDL 0.012 0.020


Leachate BDL BDL BDL 0.013

Depth of soil

column/ Leachate


20 mL 40 mL 80 mL 160 mL

0-5cm 0.724 0.511 0.294 0.002

5-10cm BDL 0.031 0.081 0.102

10-15cm BDL BDL 0.014 0.035




46

more migration was noticed upto 20 cm and a further decrease in the concentration of

carbosulfan was noticed at top 0- 5 cm, indicates more migration of carbosulfan with

increased volume of water for elution.

Data regarding the downward movement of carbofuran by adding carbosulfan

25 EC at 150 µg in laterite soil was presented in Table 17. The data revealed that

when 20 mL water was used for elution, the residue obtained at 0-5 cm was 0.572 mg

kg-1. With increase in the volume of water to 160 mL there is lower retention of

carbofuran at 0- 5 cm layer and the migration was noticed upto 15 cm.


µg in laterite soil when eluted with 20, 40, 80 and 160 mL of water are presented in

Table 18. The data revealed that, when 20 mL water added, carbosulfan was moved

upto 15 cm depth and majority of carbosulfan residues (3.553 mg kg-1) confined to

the top 0-5cm layer of soil. When the water used for elution increased to 80 mL, the

migration was detected upto 20 cm and the quantity of carbosulfan in the top layer

was reduced (1.303 mg kg-1). When the water for elution was 160 mL, more

migration was noticed upto 25 cm and a further decrease in the concentration of

carbosulfan was noticed at top 0-5 cm. The leachate also had the residues of

carbofuran (0.013 mg kg-1) indicating more migration of carbosulfan with increased

volume of water for elution.


25 EC at 200 µg in laterite soil was presented in Table 19. The data revealed that,

when 20 mL water was used for elution, the residue obtained at 0-5 cm was 0.724 mg

kg-1, and with increasing the volume of water to 160 mL there was lower retention of

carbofuran at 0- 5 cm layer and the migration was noticed upto 20 cm. The leachate

did not show any detectable residues of carbofuran.

47

4.3.2 Mobility of Carbosulfan and Carbofuran in Coastal Alluvial Soil


µg in coastal alluvial soil when eluted with 20, 40, 80 and 160 mL of water is

presented in Table 20. The data revealed that, when 20 mL water was added

carbosulfan was moved upto 15 cm depth and majority of carbosulfan residues (1.783

mg kg-1) were confined to the top 0-5cm layer of soil. When the water used for

elution increased to 80 mL, the migration was detected upto 20 cm and the quantity

of carbosulfan in the top layer was reduced (0.616 mg kg-1). When the water for

elution was 160 mL more migration was noticed upto 25 cm and a further decrease

in the concentration of carbosulfan was noticed at top 0-5 cm ( 0.319 mg kg-1). The

leachate showed no residues of carbofuran, even with an increased volume of water

used for elution.


25 EC at 100 µg in coastal alluvial soil was presented in Table 21. The data revealed

that, when 20 mL water used for elution the residue obtained at 0-5 cm was 0.212 mg

kg-1. With increase in the volume of water to 160 mL, there was a lower retention of

carbofuran at 0-5 cm layer (0.042 mg kg-1) and the migration was noticed upto 15 cm.

The leachate did not show any carbofuran residues.



presented in Table 22. The data revealed that, when 20 mL water added, carbosulfan

was moved upto 15 cm depth and majority of carbosulfan residues (2.201 mg kg-1)

confined to the top 0-5cm layer of soil. When the water used for elution increased to

80 mL, the migration was detected upto 20 cm and the quantity of carbosulfan in the

top layer was reduced (0.928 mg kg-1). When the water for elution was 160 mL,

more migration was noticed upto 25 cm and a further decrease in the concentration of

carbosulfan was noticed at top 0- 5 cm and that was 0.509 mg kg-1.

48

Table 20. Migration of carbosulfan in the coastal alluvial soil column when loaded at

100 µg level


Table 21. Migration of carbofuran formed in coastal alluvial soil column when loaded with 100 µg carbosulfan



Leachate

Residues ( mg kg-1 ) at different depths

20 mL 40 mL 80 mL 160 mL

0-5cm 1.783 1.038 0.616 0.319

5-10cm 0.243 0.418 0.506 0.484

10-15cm 0.012 0.037 0.085 0.118

15-20cm BDL BDL 0.021 0.033



Depth of soil

column/ Leachate

Residues ( mg kg-1 ) at different depths

20 mL 40 mL 80 mL 160 mL

0-5cm 0.212 0.152 0.093 0.042

5-10cm 0.091 0.047 0.076 0.056

10-15cm BDL BDL 0.014 0.025




49

Table 22. Migration of carbosulfan in the coastal alluvial soil column when loaded at

150 µg level


Table 23. Migration of carbofuran formed in laterite soil column when loaded with 150 µg carbosulfan


Depth of soil column/ Leachate


20 mL 40 mL 80 mL 160 mL

0-5cm 2.201 1.806 0.928 0.509

5-10cm 0.320 0.521 0.770 0.416

10-15cm 0.014 0.047 0.103 0.201

15-20cm BDL BDL 0.048 0.016




Leachate


20 mL 40 mL 80 mL 160 mL

0-5cm 0.322 0.211 0.108 0.083

5-10cm 0.039 0.044 0.059 0.091

10-15cm 0.011 0.003 0.024 0.035

15-20cm BDL BDL 0.014 0.021



50

Table 24. Migration of carbosulfan in the coastal alluvial soil column when loaded at 200 µg level

Mean of three replications Table 25. Migration of carbofuran formed in coastal alluvial soil column when loaded with

200 µg carbosulfan



Leachate


20 mL 40 mL 80 mL 160 mL

0-5cm 3.073 2.563 1.583 0.718

5-10cm 0.420 0.712 0.495 0.684

10-15cm 0.106 0.079 0.260 0.414

15-20cm BDL 0.029 0.166 0.139

20-25cm BDL 0.014 0.050 0.094

Leachate BDL BDL 0.016 0.030


Leachate


20 mL 40 mL 80 mL 160 mL

0-5cm 0.523 0.359 0.141 0.091

5-10cm 0.057 0.116 0.086 0.077

10-15cm BDL 0.01 0.044 0.048

15-20cm BDL BDL 0.014 0.020



51



that when 20 mL water was used for elution the residue obtained at 0-5 cm was 0.322

mg kg-1. With increase in the volume of water to 160 mL, there was a lower retention

of carbofuran at 0- 20 cm layer and the migration was noticed upto 20 cm. The

leachate did not show the carbofuran residues.



presented in Table 24. The data revealed that, when 20 mL water was added,

carbosulfan moved upto 15 cm depth and majority of carbosulfan residues (3.073 mg

kg-1) confined to the top 0-5cm layer of soil. When the water used for elution

increased to 40 mL, the migration was detected upto 25 cm, and the quantity of

carbosulfan in the top layer was reduced (2.563 mg kg-1). When the water for elution

was 160 mL, more migration was noticed upto 25 cm and a further decrease in the

concentration of carbosulfan was noticed at top 0- 5 cm and that was 0.718 mg kg-1.

The leachate had a residue content of 0.030 mg kg-1 .



that when 20 mL water was used for elution, the residue obtained at 0-5 cm was

0.523 mg kg-1. With increase in the volume of water to 160 mL, there was a lower

retention of carbofuran at 0- 20 cm layer and the migration was noticed upto 20 cm.

The leachate did not show the carbofuran residues.

4.4 PERSISTENCE OF CARBOSULFAN IN SOIL

The persistence of carbosulfan in the laterite as well as in the coastal alluvial

soil were studied at three levels of carbosulfan viz., 1, 2.5 and 5 mg kg-1 using EC as

well as granular (G) formulation under laboratory condition as well as in the cropped

52

condition. The half life of the compounds at different treatment levels and

formulation under the above two situations were also found out after quantifying the

residue level in the soil on the 0th, 1st, 3rd, 5th, 7th, 10th, 15th, 20th and 30th day. The

results obtained are given in the following Tables 26- 29.

4.4.1 Dissipation of Carbosulfan 25EC in Laterite Soil under Laboratory and

Cropped Conditions

The data on the persistence or dissipation of carbosulfan 25EC in laterite soil

under laboratory and cropped conditions are presented in Table 26. The data revealed

that by the application of EC formulations, the concentration of carbosulfan in soil

decreased with time. When the pesticide is applied in the bare soil, the pesticide

remained for upto 30 days, even though its quantity is very less. But in the cropped

condition, it remained only upto 15 days. The half life period of carbosulfan is high

under laboratory study while it was less under cropped condition at all treatment

levels. With higher the treatment concentration, higher the half life. In laboratory

condition at 1 mg kg-1 level, the residues were obtained upto 30th day, on the 0th day,

the residue obtained was 0.834 mg kg-1 while on 30th day it was 0.011 with a

corresponding half life of 5.08 days. For 2.5 and 5 mg kg-1 also, the residues were

obtained upto 30th day. For 2.5 and 5 mg kg-1 treatments, the residues obtained on the

0th day were 2.08 and 4.18 mg kg-1, respectively, and on 30th day that were 0.021 and

0.232 mg kg-1 with corresponding half life of 7.69 and 10.53 days, respectively.

In the cropped condition at 1 mg kg-1 level, the residues were obtained upto 10th day.

On the 0th day, the residue was 0.645 mg kg-1 and that on 10th day was 0.130 with a

corresponding half life of 2.17 days. For 2.5 and 5 mg kg-1 the residues were

obtained upto 15th day. On the 0th day, the residues obtained were 1.792 and 3.71 mg

kg-1 respectively and on 15th day that were 0.176 and 0.435 mg kg-1 with

corresponding half life of 4.60 and 5.24 days respectively. The half life period was

nearly halved in cropped condition than the laboratory condition. So a faster

53

Table 26. Dissipation of carbosulfan 25 EC in laterite soil under laboratory and cropped condition

Treatment

Mean residues of carbosulfan (mg kg-1)

Days after treatment

0 1 3 5 7 10 15 20 30 t1/2

(Days)

T1(1mgkg-1 in

laboratory

condition)

0.834 0.821 0.761 0.651 0.523 0.340 0.232 0.041 0.011 5.080

T2(2.5mg kg-1 in

laboratory

condition)

2.081 1.870 1.392 1.112 0.933 0.872 0.720 0.263 0.021 7.690

T3(5mg kg-1 in

laboratory

condition)

4.182 3.991 3.501 3.081 2.841 2.110 1.793 1.072 0.232 10.530

T4(1mg

kg-1 in cropped

condition)

0.645 0.622 0.598 0.436 0.224 0.130 BDL BDL BDL 2.170

T5(2.5mg kg-1

in cropped

condition)

1.792 1.620 1.320 1.040 0.748 0.542 0.176 BDL BDL 4.600

T6(5mg kg-1 in

cropped

condition)

3.710 3.090 2.961 2.731 2.161 1.470 0.435 BDL BDL 5.240

Mean of five replications

*BDL- Below Detectable Level (0.01 mg kg-1

54

dissipation was observed in the cropped condition compared to the laboratory

condition.

4.4.2 Dissipation of Carbosulfan 25 EC in Coastal Alluvial Soil under

Laboratory and Cropped Conditions

The data regarding dissipation of carbosulfan in coastal alluvial soil by

treating the soil with carbosulfan 25 EC under laboratory and cropped conditions

were presented in Table 27. It is seen that, the residues were decreased from 0th day

to 15th day in laboratory and cropped condition at 1 mg kg-1 while it was 0th to 20th

day for higher level of treatment under cropped condition. The initial recovery of

carbosulfan was higher under laboratory study but at 20th day, the recovery was

higher for cropped condition at 5mg kg-1 level of fortification. In laboratory

condition at 1 mg kg-1 level the residues were obtained upto 15th day, on the 0th day

the residue obtained was 0.727 mg kg-1 while on 15th day, it was 0.012 with a

corresponding half life of 2.35 days. For 2.5 and 5 mg kg-1, the residues were

obtained upto15th and 20th day respectively. On the 0th day, the residues obtained

were 1.59 and 2.43 mg kg-1 respectively and on 15th day that were 0.088 and 0.135

mg kg-1with corresponding half life of 2.91 and 4.96 days respectively.

In the cropped condition at 1 mg kg-1 level, the residues were obtained upto

15th day, on the 0th day, the residue was 0.418 mg kg-1 and that on 10th day was 0.011

with a corresponding half life of 2.95 days. For 2.5 and 5 mg kg-1, the residues were

obtained upto 20th day. On the 0th day the residues obtained were 0.717 and 0.959 mg

kg-1 respectively and on 20th day that were 0.045 and 0.078 mg kg-1 with

corresponding half life of 4.59 and 5.13 days respectively. The half life obtained

were higher for laboratory study than cropped condition. With increasing the

pesticide concentration, the half life was also increased.

55

Table 27. Dissipation of carbosulfan 25 EC in coastal alluvial soil under laboratory and cropped

condition

Treatment



0 1 3 5 7 10 15 20 30 t1/2

(Days)

T1(1 mg kg-1 in

laboratory

condition) 0.727 0.646 0.448 0.248 0.211 0.115 0.012 BDL BDL 2.350

T2(2.5 mg kg-1 in

laboratory


T3(5 mg kg-1in

laboratory

condition) 2.431 1.540 1.172 1.010 0.872 0.521 0.216 0.135 BDL 4.960

T4(1 mg kg-1 in

Cropped

condition) 0.418 0.387 0.348 0.276 0.128 0.094 0.011 BDL BDL

2.950

T5(2.5 mg kg-1

in cropped

condition) 0.717 0.672 0.644 0.567 0.333 0.120 0.095 0.045 BDL

4.590

T6(5 mg kg-1in

cropped

condition) 0.959 0.846 0.748 0.673 0.439 0.253 0.118 0.078 BDL

5.130

Mean of five replications *BDL- Below Detectable Level (0.01 mg kg-1)

56

4.4.3 Dissipation of Carbosulfan Granules in the Laterite Soil under


The data regarding the dissipation of carbosulfan in the laterite soil by treating

with carbosulfan granules in the laboratory and cropped conditions are presented in

Table 28. The result revealed that, the residues were increased from 0th – 7th day and

0th -3rd day in the soil under laboratory and cropped condition respectively. For

granular treatments, the higher residue content was observed for cropped condition

than the laboratory condition. In this, except 5mg kg-1 level of treatment, all other got

the residues only upto 15th day and for 5mg kg-1 level, the residues persisted upto 20th

day. In laboratory condition, at 1 mg kg-1 level, the residues obtained upto 15th day.

On the 0th day, the residues obtained were 0.042 mg kg-1 and on 15th day, it was

0.023 mg kg-1 with a corresponding half life of 9.88 days. For 2.5 and 5 mg kg-1, the

residues were obtained upto 15th day. On the 0th day, the residues obtained were

0.246 and 0.725 mg kg-1 respectively. On 15th day, that were 0.113 and 0.442 mg

kg-1 with corresponding half life of 10.50 and 11.50 days, respectively.

In the cropped condition, at 1 mg kg-1 level, the residues were obtained upto

10th day. On the 0th day, the residue was 0.238 mg kg-1 and that on 10th day, was

0.109 mg kg-1 with a corresponding half life of 3.26 days. For 2.5 and 5 mg kg-1, the

residues were obtained upto 15th and 20th days respectively. On the 0th day, the

residues obtained were 0.700 and 1.05 mg kg-1 and that were 0.176 and 0.435 mg kg-1

on 15th and 20th days respectively with corresponding half life of 4.60 and 5.24 days

respectively. The half life was higher for laboratory study than the cropped condition.

4.4.4 Dissipation of Carbosulfan Granules in Coastal Alluvial Soil under


As regards to the dissipation of carbosulfan in coastal alluvial soil by treating

with carbosulfan granules under laboratoryoratory and field conditions are presented

57

Table 28. Dissipation of carbosulfan granules in laterite soil under laboratory and cropped condition

Mean of five replication *BDL- Below Detectable Level (0.01 mg kg-1)

Treatment



0 1 3 5 7 10 15 20 30 t1/2

(Days)

T1(1 mg kg-1 in

laboratory


T2(2.5 mg kg-1 in

laboratory


T3(5 mg kg-1 in

laboratory

condition) 0.725 0.727 0.813 1.050 1.200 0.721 0.455 0.211 BDL 11.500

T4(1 mg

kg-1 in cropped

condition) 0.238 0.297 0.452 0.426 0.249 0.109 BDL BDL BDL

3.260

T5(2.5 mg kg-1

in cropped


5.160

T6(5 mg kg-1 in

cropped

condition) 1.050 1.191 1.582 1.450 1.011 0.702 0.442 0.160 BDL

7.300

58

Table 29. Dissipation of carbosulfan granules in coastal alluvial soil under laboratory and

cropped condition

Mean of five replications

*BDL- Below Detectable Level (0.01 mg kg-1)

Treatment

Mean residues of carbosulfan ( mg kg-1)


0 1 3 5 7 10 15 20 30 t1/2

(Days)

T1(1 mg kg-1 in

laboratory


T2(2.5 mg kg-1 in

laboratory


T3(5 mg kg-1 in

laboratory


T4(1 mg

kg-1 in cropped


5.700

T5(2.5 mg kg-1

in cropped


6.510

T6(5 mg kg-1 in

cropped

condition) 0.913 0.940 1.09 0.985 0.810 0.622 0.461 0.230 BDL

9.820

59

in Table 29 it is seen that, a higher retention of the residues were obtained in the

cropped condition In laboratory condition at 1 mg kg-1 level, the residues were

obtained upto 15th day. On the 0th day, the residue obtained was 0.094 mg kg-1 while

on 15th day it was 0.011 with a corresponding half life of 8.99 days. For 2.5 and 5 mg

kg-1 the residues were obtained upto15th day. On the 0th day, the residues obtained

were 0.268 and 0.405 mg kg-1 respectively, and on 15th day, that were 0.116 and

0.222 mg kg-1 with corresponding half life of 9.45 and 10.65 days respectively.

In the cropped condition at 1 mg kg-1 level, the residues were obtained upto

15th day. On the 0th day, the residue was 0.033 mg kg-1 and that on 15th day was 0.011

with a corresponding half life of 5.7 days. For 2.5 and 5 mg kg-1, the residues were

obtained upto 15th and 20th days respectively. On the 0th day, the residues obtained

were 0.611 and 0.913 and on 15th and 20th day it was 0.141 and 0.230 mg kg-1 with

corresponding half life of 6.51 and 9.82 days respectively.

4.4.5 Overall Dissipation of Carbosulfan as Influenced by Soil Type,

Formulation, Crop, Treatment Levels and their Combined effects

The data on the overall dissipation of carbosulfan influenced by soil type,

formulation, crop and treatment levels were presented in Table 30. The data revealed

that, in laterite soil, the retention of carbosulfan was comparatively higher than the

coastal alluvial soil. Carbosulfan persisted for more time in laterite soil. The residue

detected on 20th day in laterite soil was 0.13mg kg-1 while that in the coastal alluvial

soil was 0.04 mg kg-1. Thus, a fast degradation of carbosulfan was noticed in coastal

alluvial soil than the laterite soil. The granular formulation shows a residue content

of 0.14 mg kg-1 on 20th day while for EC formulation the residue was 0.03 mg kg-1.

The residue obtained in the laboratory condition was higher than that in the cropped

condition during all the days. On the 20th day, it was 0.13 mg kg-1 under laboratory

condition while it was 0.04 mg kg-1 under cropped condition. The data regarding the

influence of treatment levels on the dissipation of carbosulfan are presented in Table

60

Table 30. Overall dissipation of carbosulfan as influenced by soil, formulation, crop and treatment levels

* S1- Laterite soil, S2- Coastal Alluvial soil, F1- Granules, F2- EC, T1- Laboratory condition, T2- Cropped condition

Treatments* Mean residues of Carbosulfan ( mg kg-1)


0 1 3 5 7 10 15

20th

day

Factor-1 soils

S1 0.87 1.3 1.36 1.12 0.94 0.66 0.42 0.13

S2 0.75 0.63 0.76 0.51 0.47 0.25 0.16 0.04

Factor-2 Formulations

F1 0.92 1.4 1.67 1.01 0.82 0.57 0.34 0.14

F2 0.69 0.49 0.46 0.62 0.59 0.34 0.24 0.03

Factor-3 Crop

T1 1.01 1.02 1.14 0.79 0.74 0.51 0.35 0.13

T2 0.59 0.9 0.99 0.84 0.67 0.41 0.23 0.04

SE 0.009 0.006 0.008 0.013 0.004 0.006 0.003 0.002

CD 0.026 0.016 0.023 0.035 0.011 0.016 0.008 0.005

61

31. The data revealed that with increased concentration / treatment levels, a

corresponding increase in the residue level was seen.

The influence of different combined effects of soil, formulations and

conditions on the dissipation of carbosulfan are presented in Table 32. The effect of

granule formulation under laterite soil showed higher residues than all other

combined effects. The effect of the two formulations viz., EC and granules under

coastal alluvium soil showed same residues on 20th day. The effect of EC formulation

under laterite soil with showed second most residues on 20th day. The combined

effects S1F2- laterite soil with EC formulation and S2F2- coastal alluvium soil with

EC formulation were on par on 0th day. On 20th day, S2F1 (coastal alluvium soil with

granules) and S2F2 (coastal alluvium soil with EC) were on par and all other

combined effects were significantly different.

The combined effect of soil type and condition / crop showed highest residue

content in the combined effect of laterite soil under laboratory condition on the 20th

day (0.20 mg kg-1). The combined effect of coastal alluvial soil with cropped

situation showed second highest residue of 0.06 mg kg-1. The lowest residue content

was for the combined effect of laterite soil under cropped condition (0.02 mg kg-1).

On 10th day S2T1 (coastal alluvium soil under laboratory condition) and S2T2

(coastal alluvium soil under cropped condition) are showing residue content on par

and all others were significantly different.

The combined effect of formulations and conditions presented in Table 32

revealed that, on the 0th day, the combined effect of EC formulation under laboratory

condition showed maximum residues (1.59 mg kg-1) among all other combined

effects. On the 20th day, the highest residue was obtained for combined effect of

granule formulation under laboratory condition (0.36 mg kg-1). The combined effect

of EC with laboratory condition showed residues to the tune of 0.09 mg kg-1 on 20th

day. The lowest residue content was obtained for combined effect of EC formulation

62

Table 31. Dissipation of carbosulfan as influenced by treatment levels

*P1- 1 mg kg-1, P2- 2.5 mg kg-1, P3- 5 mg kg-1

Treatments*

Residues of carbosulfan ( mg kg-1)


0 1 3 5

7

10 15 20

P1 0.33 0.41 0.39 0.32 0.34 0.13 0.06 0.01

P2 0.69 0.89 0.99 0.69 0.54 0.36 0.22 0.04

P3 1.39 1.6 1.81 1.4 1.2 0.88 0.59 0.203

SE 0.0114 0.0071 0.0101 0.0154 0.005 0.007 0.0035 0.0023

CD 0.032 0.0197 0.028 0.043 0.013 0.019 0.009 0.0064

63

Table 32. Dissipation of carbosulfan as influenced by interaction of soil, formulations and conditions

*S1- Laterite soil, S2- Coastal Alluvial soil, F1- Granules, F2- EC, T1- Laboratory condition, T2- Cropped condition

Interactions*

Mean residues of Carbosulfan ( mg kg-1)


0 1 3 5 7 10 15 20

Interaction of soil and formulations

S1F1 1.05 1.19 1.31 0.95 0.73 0.42 0.38 0.24

S1F2 1.69 1.38 0.95 0.65 0.44 0.31 0.24 0.06

S2F1 0.79 0.86 1.14 0.52 0.40 0.22 0.12 0.04

S2F2 1.70 1.41 1.19 0.74 0.38 0.27 0.14 0.04

Interaction of soil and condition

S1T1 1.18 1.30 1.36 1.10 1.07 0.76 0.59 0.20

S1T2 0.96 0.82 0.77 0.69 0.60 0.57 0.26 0.02

S2T1 0.85 0.79 0.72 0.40 0.31 0.25 0.11 0.04

S2T2 0.62 0.55 0.51 0.46 0.44 0.25 0.21 0.06

Interaction of formulation and crop

F1T1 1.44 1.60 1.97 1.06 0.97 0.70 0.53 0.36

F1T2 0.39 1.20 1.37 0.95 0.67 0.44 0.16 0.05

F2T1 1.59 1.16 0.81 0.59 0.45 0.29 0.17 0.09

F2T2 0.81 0.78 0.72 0.69 0.67 0.39 0.21 0.03

SE 0.013 0.008 0.012 0.018 0.006 0.008 0.004 0.003

CD (0.05) 0.037 0.023 0.032 0.049 0.015 0.022 0.011 0.008

64

with cropped condition. In this table on 7th day the combined effects F1T2 (Granule

formulation under cropped condition) and F2T2 (EC formulation under cropped

condition) were on par and on 15th day, the residues detected by the combined effects

of F1T2 (granule formulation under cropped condition) and F2T1 (EC formulation

under laboratory condition) were on par.

The combined effect of soil types and treatments on the dissipation of

carbosulfan are presented in Table 33 and it showed that, the combined effect of

laterite soil with 5 mg kg-1 level of carbosulfan had high retention (0.29 mg kg-1).

The combined effect of coastal alluvial soil with 1 mg kg-1 level of carbosulfan

resulted in residue level below the detectable level. On 0th day, the combined effect of

two soils with 2.5 mg kg-1 level of treatment was found to be on par. From 3rd day to

7th day and on 15th day, the combined effects of laterite soil with 2.5 mg kg-1 and

coastal alluvial soil with 5 mg kg-1 level showed as on par. On the 20th day, the

combined effect of laterite soil with 1 mg kg-1 and coastal alluvial soil combined

effect with 2.5 mg kg-1 were on par in terms of residue content.

The combined effect effect of formulations and treatment levels given in

Table 33 revealed that, a higher retentions of carbosulfan as granules with 5 mg kg-1

level treatment (0.34 mg kg-1). The combined effect of EC formulation with 1 mg

kg-1 level showed BDL residues on 20th day. On 20th day, the combined effects

F1P1 (granules formulation at 1 mg kg-1) and F2P2 (EC formulation at 2.5mg kg-1)

are on par and all others were significantly different. For EC formulation, the highest

residue content was seen with 5 mg kg-1 level on all days.

The combined effect of crop/ condition with treatment levels presented in

Table 34 revealed that on all the days of incubation, the 5 mg kg-1 level under

laboratory condition showed highest residue content (0.23 mg kg-1) than all other

combination. On 5th day, the combined effect of T1P1 (laboratory condition at 1 mg

kg-1) and T2P1 (cropped condition at 1 mg kg-1) were found to be on par. On 20th day

65

Table 33. Dissipation of carbosulfan as influenced by soil, formulations and treatment levels

S1- Laterite soil, S2- Coastal alluvial soil, F1- EC, F2- Granules, P1, P2, P3- 1, 2.5 and 5 mg kg-1 respectively.*BDL-Below

Detectable Level

Interactions*

Residues of carbosulfan ( mg kg-1)


0 1 3 5 7 10 15 20

Interaction of soil and treatment levels

S1P1 0.36 0.46 0.46 0.43 0.32 0.17 0.08 0.02

S1P2 0.71 1.10 1.20 0.84 0.67 0.49 0.29 0.07

S1P3 1.53 2.30 2.44 2.09 1.80 1.32 0.89 0.29

S2P1 0.42 0.36 0.32 0.24 0.19 0.08 0.03 BDL

S2P2 0.69 0.63 0.59 0.53 0.39 0.23 0.16 0.02

S2P3 1.24 0.92 1.17 0.79 0.66 0.43 0.29 0.11

Interaction of formulation and treatment levels

F1P1 0.40 0.61 0.67 0.40 0.27 0.17 0.64 0.02

F1P2 0.74 1.30 1.54 0.81 0.61 0.44 0.28 0.08

F1P3 1.64 2.40 2.82 1.82 1.60 1.10 0.68 0.34

F2P1 0.86 0.49 0.36 0.24 0.11 0.09 0.46 BDL

F2P2 1.05 0.76 0.62 0.47 0.32 0.28 0.17 0.02

F2P3 1.57 1.13 0.99 0.76 0.69 0.66 0.51 0.07

SE 0.016 0.010 0.014 0.022 0.007 0.009 0.005 0.002

CD (0.05) 0.045 0.030 0.039 0.060 0.019 0.027 0.014 0.006

66

Table 34. Dissipation of carbosulfan as influenced by interaction of crop and treatment levels

T1- Laboratory condition, T2- Cropped Condition, P1- 1 mg kg-1, P2- 2.5 mg kg-1, P3- 5 mg kg-1 *BDL-BelowDetectableLevel

Treatments

Residues of carbosulfan (mg kg-1)

Days after treatments

0 1 3 5 7

10 15 20

T1P1 0.39 0.44 0.44 0.32 0.29 0.16 0.08 0.02

T1P2 0.78 0.91 0.74 0.64 0.57 0.42 0.26 0.07

T1P3 1.87 1.70 1.61 1.41 1.4 0.94 0.71 0.23

T2P1 0.37 0.36 0.33 0.29 0.20 0.09 0.03 BDL

T2P2 0.71 0.67 0.59 0.53 0.51 0.31 0.18 0.02

T2P3 1.31 1.25 1.08 0.97 0.92 0.83 0.48 0.10

SE 0.016 0.010 0.014 0.022 0.007 0.009 0.005 0.002

CD (0.05) 0.045 0.030 0.039 0.060 0.019 0.027 0.014 0.006

67

T1P1 and T2P2 (Cropped condition with 2.5 mg kg-1) were found to be on par. T2P1

shows BDL residues on the 20th day. The cropped condition combined effect with 5

mg kg-1 level (T2P3) shows lesser residue content than the laboratory situation

combined effect with 5 mg kg-1 level (T1P3) on all the days.

4.5 DEGRADATION OF CARBOSULFAN IN SOIL

Carbosulfan, primarily a pro-insecticide which when applied to the soil will

get metabolized and the major metabolites viz., carbofuran, 3-hydroxy carbofuran and

3-keto carbofuran will be formed. There exists an inverse relation between the

metabolites formed and concentration of carbosulfan. The formation of metabolite

increased with a consequent lowering of carbosulfan concentration with time. The

data on degradation of carbosulfan in the two soils applied as two formulations in two

situations are presented in the following tables.

4.5.1 Metabolism of Carbosulfan 25 EC in Laterite Soil under Laboratory

Condition

The data on the metabolism of carbosulfan in laterite soil by using EC

formulation under laboratory condition is presented in Table 35. The result revealed

that, the presence of carbofuran formed from carbosulfan was detected from 0th day

which increased upto 15th day and then declined at all levels (1, 2.5 and 5 mg kg-1).

The maximum carbofuran was formed on 15th day and then declined thereafter. On

0th day the residues obtained were 0.239, 0.610 and 0.746 mg kg-1 at 1, 2.5and 5 mg

kg-1 levels respectively, and that were obtained upto 45th day which were 0.357, 0.954

and 1.80 mg kg-1 respectively. Other metabolites formed from carbofuran during its

degradation were 3- hydroxy carbofuran and 3- keto carbofuran. Formation of 3-

hydroxy carbofuran was observed from 3rd day onwards and was maximum on 15th

day and then declined. In the case of 3-keto carbofuran, maximum residue was

obtained on 20th day after treatment.

68

Table 35. Metabolites of carbosulfan 25 EC in the laterite soils under laboratory condition

Mean of five replications, *BDL- Below Detectable Level (0.01 mg kg-1)

Compound Treatment

Level

Residues in mg kg-1


0 1 3 5 7 10 15 20 30 45

Carbofuran 1 mg kg-1 0.239 0.303 0.475 0.496 0.724 0.777 1.951 1.34 0.877 0.357

2.5 mg kg-1 0.610 0.704 0.816 0.951 1.345 1.525 3.082 2.781 1.631 0.954

5 mg kg-1 0.746 0.856 1.050 1.240 1.520 1.861 4.660 4.021 3.170 1.800

3-Hydroxy

carbofuran 1 mg kg-1 BDL BDL BDL BDL 0.011 0.012 0.013 0.011 0.011 BDL

2.5 mg kg-1 BDL BDL 0.011 0.012 0.012 0.014 0.015 0.014 0.012 BDL

5 mg kg-1 BDL 0.011 0.011 0.013 0.014 0.012 0.291 0.132 0.078 0.011

3-Keto

carbofuran 1 mg kg-1 BDL BDL BDL BDL BDL BDL 0.011 0.013 0.014 0.011

2.5 mg kg-1 BDL BDL BDL BDL 0.015 0.017 0.016 0.111 0.017 0.013

5 mg kg-1 BDL BDL 0.014 0.017 0.026 0.038 0.121 0.156 0.036 0.008

69

4.5.2 The Metabolism of Carbosulfan 25 EC in Coastal Alluvial Soil under

Laboratory Condition

The data on the metabolism of carbosulfan in coastal alluvial soil by using EC


that, the presence of carbofuran formed from carbosulfan was detected on 0 th day and

increased upto 10th day and then declined at all the three levels. The maximum

carbofuran was formed on 10th day and then declined thereafter. On 0th day, the

residues obtained were 0.284, 0.533 and 1.181 mg kg-1 at 1, 2.5 and 5 mg kg-1 levels

respectively, and that were obtained upto 45th day which were 0.111, 0.114 and 0.212

mg kg-1 respectively. Formation of 3- hydroxy carbofuran was observed from 3rd

day onwards for 1 mg kg-1 level and for 2.5 and 5 mg kg-1 level, it started from 0th

day itself and was maximum on 15th day and then declined. In the case of 3-keto

carbofuran, maximum residue was obtained on 15th day after treatment.

4.5.3 The Metabolism of Carbosulfan in Laterite Soil by Using Granule

Formulation under Laboratory Condition

The data on the metabolism of carbosulfan in laterite soil by using granule


that, the presence of carbofuran formed from carbosulfan was detected on 0 th day and

increased upto 10th day and then declined at all levels of treatments. The maximum




mg kg-1 respectively. Formation of 3- hydroxy carbofuran was observed from 3rd day

onwards at 1 mg kg-1 level of treatment and for 2.5 and 5 mg kg-1 level it started from

0th day itself and was maximum on 15th day and then declined. In the case of 3-keto


70

Table 36. Metabolites of carbosulfan 25 EC in the coastal alluvial soil under laboratory condition


Compound Treatment

Level Residue in mg kg-1


0 1 3 5 7 10 15 20 30 45

Carbofuran 1 mg kg-1 0.284 0.360 0.415 0.573 0.666 0.360 0.296 0.232 0.136 0.011

2.5 mg kg-1 0.533 0.628 0.735 0.837 0.931 0.751 0.516 0.446 0.279 0.114

5 mg kg-1 1.181 1.727 1.845 1.655 2.155 1.342 1.172 0.981 0.755 0.212

3-Hydr oxy carbofuran

1 mg kg-1 BDL BDL 0.011 0.011 0.013 0.014 0.015 0.014 0.011 BDL

2.5 mg kg-1 0.011 0.012 0.013 0.014 0.014 0.014 0.015 0.014 0.012 0.011

5 mg kg-1 0.013 0.015 0.016 0.015 0.016 0.013 0.014 0.015 0.012 0.012

3-Keto carbofuran

1 mg kg-1 BDL BDL 0.002 0.024 0.025 0.027 0.030 0.020 0.069 0.011

2.5 mg kg-1 BDL 0.015 0.015 0.057 0.065 0.0635 0.077 0.059 0.160 0.012

5 mg kg-1 0.011 0.011 0.051 0.121 0.237 0.391 0.414 0.281 0.106 0.058

71

Table 37. Metabolites of carbosulfan granules in laterite soil under laboratory condition


Compound Treatment

Level

Residue in mg kg-1


0 1 3 5 7 10 15 20 30 45

Carbofuran 1 mg kg-1 0.129 0.193 0.223 0.272 0.314 0.331 0.212 0.129 0.089 BDL

2.5 mg kg-1 0.321 0.373 0.409 0.467 0.517 0.581 0.346 0.234 0.109 BDL

5 mg kg-1 0.515 0.676 0.725 0.810 0.973 1.0975 0.820 0.689 0.522 BDL

3-Hydroxy

carbofuran 1 mg kg-1 BDL BDL 0.011 0.011 0.012 0.016 0.012 0.011 0.011 BDL

2.5 mg kg-1 0.011 0.012 0.013 0.014 0.014 0.014 0.013 0.014 0.012 BDL

5 mg kg-1 0.013 0.015 0.016 0.016 0.016 0.018 0.013 0.011 0.014 BDL

3-Keto carbofuran

1 mg kg-1 BDL BDL 0.002 0.024 0.025 0.027 0.030 0.020 0.069 BDL

2.5 mg kg-1

BDL 0.015 0.015 0.057 0.065 0.064 0.077 0.059 0.106 BDL

5 mg kg-1

0.013 0.011 0.052 0.121 0.237 0.391 0.414 0.281 0.160 BDL

72

4.5.4 The Metabolism of Carbosulfan Granules in Coastal Alluvial Soil under

Laboratory Condition

The data on the metabolism of carbosulfan in coastal alluvial soil by using

granule formulation under laboratory condition is presented in Table 38. The result

revealed that the presence of carbofuran formed from carbosulfan was detected on 0th

day and increased upto 7th day and then declined at all levels of treatments. The

maximum carbofuran was formed on 7th day and then declined thereafter. On 0th

day, the residues obtained were 0.047, 0.297 and 0.787 mg kg-1 at 1, 2.5 and 5 mg

kg-1 levels respectively, and that were obtained upto 30th day which were 0.036, 0.148

and 0.314 mg kg-1 respectively. Formation of 3- hydroxy carbofuran was observed

from 5th day onwards at 1 mg kg-1 level of treatment and for 2.5 and 5 mg kg-1 level,

it started from 1st day itself and was maximum on 15th day and then declined. In the

case of 3-keto carbofuran, maximum residue was obtained on 7th day after treatment.

4.5.5 The Metabolism of Carbosulfan 25 EC in Laterite Soil under Cropped

Condition

The data on the metabolism of carbosulfan in laterite soil by using EC

formulation under cropped condition is presented in Table 39. The result revealed the

presence of carbofuran formed from carbosulfan on 0th day and increased upto 7th day

and then declined at all levels of treatments. The maximum carbofuran was formed

on 7th day and then declined thereafter. On 0th day, the residues obtained were 0.027,

0.083 and 0.126 mg kg-1 at 1, 2.5and 5 mg kg-1 levels respectively, and that were

obtained upto 30th day which were 0.023, 0.095 and 0.129 mg kg-1 respectively.

Formation of 3- hydroxy carbofuran was observed from 1st day onwards at 5 mg kg-1

level of treatment and for 1 and 2.5 mg kg-1 level it started from 7th and 3rd day,

respectively and was maximum on 7th day and then declined. In the case of 3-keto


73

Table 38. Metabolites of carbosulfan granules in the coastal alluvial soil under laboratory condition.


Compound Treatment

Level

Residue in mg kg-1


0 1 3 5 7 10 15 20 30 45


2.5 mg kg-1 0.297 0.415 0.447 0.533 0.564 0.419 0.314 0.299 0.148 BDL

5 mg kg-1 0.787 0.885 0.936 0.982 1.131 1.010 0.807 0.629 0.314 BDL

3-Hydroxy carbofuran

1 mg kg-1 BDL BDL BDL 0.011 0.011 0.012 0.012 0.011 0.011 BDL

2.5 mg kg-1 BDL 0.011 0.013 0.012 0.014 0.016 0.045 0.015 0.012 BDL

5 mg kg-1 BDL 0.013 0.014 0.015 0.016 0.011 0.018 0.015 0.012 BDL

3-Keto carbofuran

1 mg kg-1 BDL BDL BDL 0.011 0.014 0.012 0.012 0.011 BDL BDL

2.5 mg kg-1

BDL BDL 0.014 0.012 0.015 0.014 0.013 0.013 0.012 BDL

5 mg kg-1

0.011 0.012 0.013 0.016 0.019 0.015 0.014 0.013 BDL BDL

74

Table 39. Metabolites formed in the laterite soil by application of carbosulfan 25 EC in the cropped condition


Compound Treatment

Level Residue in mg kg-1 Days after treatment

0 1 3 5 7 10 15 20 30 45


2.5 mg kg-1 0.083 0.113 0.189 0.435 0.529 0.395 0.259 0.195 0.095 BDL

5 mg kg-1 0.126 0.226 0.322 0.591 0.763 0.553 0.309 0.225 0.129 BDL


1 mg kg-1 BDL BDL BDL BDL 0.013 0.011 BDL BDL BDL BDL

2.5 mg kg-1 BDL BDL 0.011 0.013 0.014 0.012 0.011 BDL BDL BDL

5 mg kg-1 0.011 0.013 0.020 0.020 0.012 0.020 0.018 BDL BDL BDL

3-Keto

carbofuran 1 mg kg-1

BDL BDL BDL 0.012 0.014 0.016 0.012 BDL BDL BDL

2.5 mg kg-1

BDL 0.011 0.011 0.016 0.019 0.020 0.011 BDL BDL BDL

5 mg kg-1

0.011 0.020 0.020 0.031 0.045 0.065 0.016 BDL BDL BDL

75


Cropped Condition

The data on the metabolism of carbosulfan in coastal alluvial soil by using EC

formulation under cropped condition is presented in Table 40. The results revealed

the presence of carbofuran formed from carbosulfan as detected on 0th day and

increased upto 10th day and then declined at all levels of treatment. The maximum




mg kg-1 respectively. Formation of 3- hydroxy carbofuran was observed from 1st day

onwards at 5 mg kg-1 level of treatment and for 1 and 2.5 mg kg-1 level, it started

from 7th and 5th day, respectively and was maximum on 10th day and then declined.

In the case of 3-keto carbofuran, maximum residue was obtained on 10th day after

treatment.

4.5.7 The Metabolism of Carbosulfan Granule in Laterite Soil under Cropped

Condition

The data on the metabolism of carbosulfan in laterite soil by using granule

formulation under cropped condition is presented in Table 41. The result revealed

that, carbofuran formed from carbosulfan was detected on 0th day and increased upto

10th day and then declined at all levels of treatments. The maximum carbofuran was

formed on 10th day and then declined thereafter. On 0th day, the residues obtained

were 0.035, 0.095and 0.255 mg kg-1 at 1, 2.5 and 5 mg kg-1 levels respectively, and

that were obtained upto 45th day which were 0.021, 0.234 and 0.417 mg kg-1

respectively. Formation of 3- hydroxy carbofuran was observed from 1st day onwards

at 5 mg kg-1 level of treatment and for 1 and 2.5 mg kg-1 level it started from 10th and

5th day, respectively and was maximum on 10th day and then declined. In the case of

3-keto carbofuran maximum residue was obtained on 15th day after treatment.

76

Table 40. Metabolites formed in the coastal alluvial soil by application of carbosulfan 25 EC in the cropped condition


Compound Treatment


0 1 3 5 7 10 15 20 30 45

Carbofuran 1 mg kg-1 0.254 0.309 0.379 0.453 0.511 0.549 0.368 0.235 BDL BDL

2.5 mg kg-1 0.346 0.402 0.493 0.549 0.613 0.688 0.486 0.317 BDL BDL

5 mg kg-1 0.434 0.483 0.574 0.634 0.702 0.874 0.613 0.444 BDL BDL

3-Hydroxy

carbofuran 1 mg kg-1 BDL BDL BDL BDL 0.012 0.021 0.014 BDL BDL BDL

2.5 mg kg-1 BDL BDL BDL 0.010 0.015 0.023 0.012 BDL BDL BDL

5 mg kg-1 BDL 0.011 0.015 0.018 0.024 0.031 0.015 BDL BDL BDL

3-Keto carbofuran

1 mg kg-1 BDL BDL BDL BDL 0.013 0.028 0.012 BDL BDL BDL

2.5 mg kg-1

BDL BDL BDL 0.013 0.025 0.037 0.013 BDL BDL BDL

5 mg kg-1

BDL 0.014 0.018 0.027 0.045 0.065 0.026 0.014 BDL BDL

77

Table 41. Metabolites formed in the laterite soil by application of carbosulfan granules in the cropped condition


Compound Treatment


0 1 3 5 7 10 15 20 30 45

Carbofuran 1 mg kg-1 0.035 0.056 0.120 0.279 0.311 0.477 0.209 0.021 BDL BDL

2.5 mg kg-1 0.095 0.128 0.310 0.503 0.686 0.845 0.515 0.234 BDL BDL

5 mg kg-1 0.255 0.335 0.482 0.806 0.984 1.250 0.741 0.417 BDL BDL


1 mg kg-1 BDL BDL BDL BDL BDL 0.012 0.011 BDL BDL BDL

2.5 mg kg-1 BDL BDL BDL 0.014 0.018 0.013 0.011 BDL BDL BDL

5 mg kg-1 BDL 0.011 0.011 0.012 0.012 0.011 0.011 BDL BDL BDL

3-Keto carbofuran

1 mg kg-1 BDL BDL BDL BDL 0.011 0.012 0.012 0.010 BDL BDL

2.5 mg kg-1 BDL BDL 0.012 0.012 0.014 0.014 0.021 0.016 BDL BDL

5 mg kg-1 0.011 0.012 0.012 0.014 0.015 0.057 0.109 0.068 BDL BDL

78

4.5.8 The Metabolism of Carbosulfan Granules in Coastal Alluvial Soil under

Cropped Condition

The data on the metabolism of carbosulfan in coastal alluvial soil by using

granule formulation under cropped condition is presented in Table. 42. The result

revealed that, carbofuran formed from carbosulfan was detected on 0th day and

increased upto 7th day and then declined at all levels of treatments. The maximum


residues obtained were 0.239, 0.610 and 0.746 mg kg-1 at 1, 2.5and 5 mg kg-1 levels


mg kg-1 respectively. Formation of 3- hydroxy carbofuran was observed from 0th day

onwards at 5 mg kg-1 level of treatment and for 1 and 2.5 mg kg-1 level, it started

from 5th and 3rd day, respectively and was maximum on 10th day and then declined.

In the case of 3-keto carbofuran, maximum residue was obtained on 10th day after

treatment.

4.6 EFFECT OF CARBOSULFAN ON SOIL ORGANISMS

The effect of carbosulfan on soil microbes in laterite and coastal alluvial soils

were studied after addition of carbosulfan EC and granules at normal (250 g ai ha-1)

and at double doses (500g ai ha-1) to the two soils under field condition. The results

of enumeration of various microbes viz., bacteria, fungi, actinomycete and arthropods

are presented in the following tables.

4.6.1 Effect of Carbosulfan on Microbial Population in Laterite Soil

The effect of carbosulfan on bacterial load when applied in laterite soil is

presented in Table. 43. The data revealed that, the bacterial population was found to

be increased by treating with EC formulation in normal (250 g ai ha-1) and double

(500 g ai ha-1) doses. The application of EC formulation at normal dose has a

bacterial population of 9.45 x 106 cfu g-1 (37.75 % increase) and at double dose, the

79

Table 42. Metabolites formed in the coastal alluvial soil by the application of carbosulfan granules under cropped condition


Compound Treatment


0 1 3 5 7 10 15 20 30 45

Carbofuran 1 mg kg-1 0.034 0.176 0.242 0.299 0.306 0.223 0.088 BDL BDL BDL

2.5 mg kg-1 0.289 0.432 0.538 0.626 0.734 0.544 0.281 0.079 BDL BDL

5 mg kg-1 0.796 0.817 0.843 0.930 1.09 0.834 0.529 0.238 BDL BDL

3-Hydroxy

carbofuran 1 mg kg-1 BDL BDL BDL 0.013 0.022 0.027 0.011 BDL BDL BDL

2.5 mg kg-1 BDL BDL 0.014 0.018 0.024 0.032 0.021 0.031 BDL BDL

5 mg kg-1 0.011 0.014 0.019 0.026 0.035 0.043 0.022 0.011 BDL BDL

3-Keto carbofuran

1 mg kg-1 BDL BDL 0.012 0.015 0.018 0.024 0.013 0.012 BDL BDL

2.5 mg kg-1 BDL 0.013 0.023 0.027 0.035 0.041 0.022 0.017 BDL BDL

5 mg kg-1 0.017 0.019 0.025 0.028 0.041 0.079 0.039 0.019 BDL BDL

80

Table 43. Effect of carbosulfan treatments on the population of soil organisms in laterite soil

Treatments

Bacterial

Population

(106cfu g-1 soil)

Fungal

Population (104

cfu g-1soil)

Actinomycetes

Population

(104cfu g-1soil)

Arthropod

Population (per kg

soil)

Carbosulfan 25 EC at 250g ai ha-1

9.451 (+ 37.75)

4.485 (- 22.27)

4.225 (- 14.56)

10.750 (- 18.87)

Carbosulfan 25 EC at 500 g ai ha-1

7.200 (+ 4.96)

5.330 (- 11.01)

3.355 (-32.15)

5.750 (-56.60)

Carbosulfan G at 250g ai ha-1

4.790 ( _ 30.17)

3.595 (- 40.06)

6.585 (+ 33.16)

6.750 (- 49.06)

Carbosulfan G at 500g ai ha-1

5.550 ( -19.09)

6.100 ( + 1.92)

3.820 (- 22.75)

7.750 (- 41.51)

Control 6.860 5.985 4.945 13.250

CD (0.05) 1.268 0.581 1.21 2.39

Mean of four replications, *cfu- colony forming units

Values in the paranthesis indicate per cent enhancement (+) or per cent inhibition (-) in the population over control.

81

bacterial population was 7.2x106 cfu g-1 (4.96 %) over the control population

(6.86x106 cfu g-1). The data revealed 32.79 per cent inhibition in the bacterial

population at double dose of application of EC compared to normal dose. The

granules treated soils in normal and double doses had population 4.75 and 5.55 x106

cfu g-1 respectively. The highest inhibition (30.17 %) in the bacterial population was

found by using carbosulfan granules in normal dose.

In the case of fungal population, except for granules at double doses all other

treatment inhibited fungal population over the control soil. Statistically, the fungal

population with granule application at double dose was on par with that in the control

soil. All other treatments were significantly different with EC treatment in the normal

dose which inturn resulted in 22.27 per cent reduction over control, while at double

doses, the corresponding inhibition was only 11.01 per cent. The granular treatment

in the normal dose resulted in 4.06 per cent reduction while at double doses, a 1.92

per cent increase in the count of fungi was observed over control.

The soil treated with granules at normal dose showed highest (6.585x 104 cfu

g-1) actinomycetes count which was 33.16 per cent more than the control. All other

treatments inhibited the activity of actinomycetes than the control soil. Application of

EC form at double dose resulted in maximum inhibition (32.15 %), than granule at

double dose (22.75 %), which indicated a high potential for inhibition by EC at

higher concentrations.

The effect of carbosulfan application on the arthropod count revealed a

significant inhibition from all the treatments, with maximum inhibition with EC at

double dose. Granular formulations significantly suppressed the population of

arthropods to the tune of upto 49 per cent. The initial population of 13.25 kg-1 soil got

declined to 10.75 and 5.75 by EC application while it got declined to 6.75 and 7.75

kg-1 soil with granular application, indicating significant negative effect on arthropod

population.

82

4.6.2 Effect of Carbosulfan on the Microbial Population of Coastal Alluvial Soil

The data regarding the effect of carbosulfan on microbial population in

coastal alluvial soil was presented in Table. 44. The soil treated with carbosulfan EC

in normal and double the doses had a bacterial population of 19.5 and 12.27 x 106 cfu

g-1 soil indicating 66.38 and 4.56 per cent increase respectively, over the control

(11.735x106 cfu g-1) soil. The soil treated with carbosulfan granules in normal dose

showed the highest bacterial population of 20.36 x106 cfu g-1 (73.44 % increase)

among all the treatments. In the double dose granule application it was 10.2 x 106 cfu

g-1 soil indicating a further reduction of 60.36 per cent over the normal granule

application. The statistical analysis showed that, the normal dose application of EC

and granules are on par and all other treatments including double dose of EC and

granules were on par with the control soil as regards to bacterial population.

In control soil, the fungal population was 7.66x104 cfu g-1 soil, while when

treated with EC at normal dose, the population increased to 9.715 x104 cfu g-1 and

got declined to 5.215 x104 cfu g-1, at double doses of EC indicating considerable

inhibition (58 %) at higher dose over the normal dose. In the case of granule

treatment, the fungal population was inhibited at both the levels to 6.6 at normal dose

and 4.8 x104 cfu g-1 in double dose, from 7.7 x104 cfu g-1 in control. The double dose

application of granule resulted in an inhibition of upto 36.86 per cent of fungal

population. Statistical analysis of the treatments revealed that, the double dose

application of the EC and granules were on par and all other treatments were found to

be significantly different.

The effect of carbosulfan on the actinomycetes population revealed that, both

the normal dose of EC and granules had a positive effect on the actinomycetes

population, but at double doses, both the formulations had a negative effect. The

control soil had a population of 3.89 x104 cfu g-1, which got enhanced to 4.45 and 4.6

x104 cfu g-1 indicated 14.63 and 18.51 per cent increase respectively, for normal

83

Table 44. Effect of carbosulfan treatments on the population of soil organisms in

coastal alluvial soil

Treatments

Bacterial

Population

(106cfu g-

1soil)

Fungal

Population (104

cfu g-1 soil)

Actinomycetes

Population

(104cfu g-1soil)

Arthropod

Population (per

kg soil)

Carbosulfan 25EC at 250 g ai ha-1

19.525

(+ 66.38)

9.715

(+ 26.74)

4.459

(+ 14.63)

12.500

(- 28.57)

Carbosulfan 25EC at 500 g ai ha-1

12.270

(+ 4.56)

5.215

(– 31.96)

2.215

(- 43.06)

9.750

(- 44.29)

Carbosulfan G at 250 g ai ha-1

20.354

(+ 73.44)

6.565

(- 14.35)

4.610

(+ 18.51)

10.500

(- 40.00)

Carbosulfan G at 500 g ai ha-1

10.200

(- 13.08)

4.840

(- 36.86)

3.227

(- 17.04)

8.750

(- 50.00)

Control 11.735 7.665 3.890 17.500

CD (0.05) 2.400 0.878 0.368 1.485

Mean of four replications, *BDL- Below Detectable Level, cfu- colony forming unit

Values in the paranthesis indicate per cent enhancement (+) or per cent inhibition (-)

in the population over control.

84

doses of EC and granule and were found on par with each other. When the dose was

doubled the population declined to 2.21 and 3.23x104 cfu g-1 soil indicating 43.06 and

17.04 per cent reduction, respectively in EC and granules, which differ significantly.

The effect of carbosulfan application on the arthropod count was checked and

all the treatments in general decreased the arthropod count. In control soil, the total

count was 17.5 kg-1 which got decreased to 10.75 kg-1 soil corresponding to a 28.57

per cent inhibition by EC application at normal dose. The effect of normal dose of

EC and double dose of granule were on par. With increased concentration of the EC

the arthropod count declined upto 44.29 per cent over control. The granule

application at normal dose decreased the population by 40 per cent while that for

double dose was 50 per cent.

85

Discussion

5. DISCUSSION

Carbosulfan is one among the few carbamate insecticides now available for

pest control purposes and is preferred over other insecticides owing to its more safety,

less toxicity, availability in solid and liquid forms and wide application spectrum.

Though carbosulfan is relatively safe, it is reported to get metabolized resulting in the

formation of carbofuran and other derivatives such as 3- hydroxy and 3-keto

carbofuran. So, this metabolism is likely to pose certain risks in the use of

carbosulfan in soil. In this context, a study was conducted on the persistence and

transformation of carbosulfan in laterite and coastal alluvial soils of Kerala and its

effect on soil organisms. The results obtained from the study are discussed under the

following heads.

5.1 PHYSICO - CHEMICAL PROPERTIES OF SOIL

The physico - chemical properties of the two soils were estimated as per

standard procedures and the results are presented in Tables. 6 and 7. The two soils

used for the study were strongly acidic with a pH 5.08 for laterite soil and 5.18 for

coastal alluvial soil. The porosity, bulk density, particle density, WHC and field

moisture percentage were more in laterite soil than coastal alluvial soil. The EC and

CEC were more in coastal alluvial soil compared to laterite soil. Primary and

secondary nutrients were also high in coastal alluvial soil due to high organic matter

(0.84 %) content, high CEC (7.11 cmol kg-1) and low 1:1 clay minerals. In laterite

soil, the low CEC and OM and the high content of 1:1 clay minerals resulted in a

decreased reserve of primary and secondary nutrients. The laterite soil comes under

the sandy loam soil type with > 60 per cent total sand content, 27 per cent silt content

while the coastal alluvial soil comes under the loamy sand soil type with > 80 per

cent total sand and 8.48 per cent silt content. So, the hydraulic conductivity of

coastal alluvial soil is more (0.6 mL min-1) than laterite soil (0.4 mL min-1). The

more silt and clay content in laterite soil resulted in the relatively high WHC and field

86

moisture percentage in laterite soil than coastal alluvial soil. Laterite soil comes

under the taxonomic class of Typic Kandiustult of Vellayani Series while coastal

alluvial belongs to the taxonomic class of Ustic Quartzipsamment.

5.2 STANDARDIZATION OF ANALYTICAL PROCEDURE FOR

MULTIRESIDUE METHOD VALIDATION

The result of recovery experiment for standardizing the analytical procedure

for estimation of carbosulfan and its metabolites (Table 8-13) in the two soils

revealed that, extraction of the residues using acetonitrile followed by MgSO4 and

Primary Secondary Amine (PSA) sorbent clean up and centrifugation to collect

supernatant was found to be satisfactory and suitable at 0.05, 0.25 and 0.50 mg kg-1

levels. The recovery percentage ranged from 80- 99.20 per cent and 88.40 - 100.60

per cent in laterite soil and coastal alluvial soil respectively and relative standard

deviation ranged from 6.90 - 11.60 and 4.50- 8.40 for laterite and coastal alluvial soil

respectively. Since the values of recovery percentage and Relative Standard

Deviation (RSD) fall in the acceptable range of 70-110 per cent and < 20,

respectively and considering the less time, less solvent requirement and the

economics of the operation, the method was adopted for further analysis of

carbosulfan and its metabolite in soil.

5.3 MOBILITY OF CARBOSULFAN IN SOIL UNDER DIFFERENT

TREATMENTS

The mobility of carbosulfan as well as carbofuran in soil columns eluted with

water under different levels of carbosulfan were monitored in the laterite and in the

coastal alluvial soil using carbosulfan 25 EC at 100, 150 and 200 µg level of

carbosulfan loaded on the top and subsequent elution with 20, 40, 80 and 160 mL of

water, as per standard procedure which was considered equivalent to 50, 100, 200 and

400 mm of rainfall in the field condition.

87

5.3.1 Mobility of Carbosulfan in Laterite Soil

The data on the mobility of carbosulfan in soil column containing laterite and

coastal alluvial soil loaded at 100, 150 and 200 µg each of carbosulfan and eluted

with different volumes of water viz., 20, 40, 80 and 160 mL are given in Tables 15-

16 and the depth wise proliferation of residues depicted in Fig. 2-4.

The mobility of carbosulfan when loaded with 100 µg carbosulfan in laterite

soil was depicted on the Fig. 2. When leached with 20 mL water, the residues were

detected upto 10 cm only and 95 per cent of the residues were confined to the surface

layers alone. When the volume of water increased upto 160 mL, the residues moved

further down and were detected upto 15 cm and most of the residues were detected in

the 0-5 cm layer. It can be inferred from the above observations that carbosulfan

possess a high water solubility, (0.3 mg kg-1) due to which it moved down with

percolating water and at the same time possess a high adsorption to soil (Adsorption

Coefficient of 8500 mL g-1) which adsorbed the molecule on the upper layer and

when thoroughly eluted, it moved further, till a balance between the two is achieved.

Thus, the application of 20 mL water (T1) equivalent to 50 mm rainfall confined the

carbosulfan residues at the top layers while the application of 80 and 160 mL

equivalent to 200 and 400 mm rainfall respectively resulted the residues to leach

down to more deeper layers.

At 150 µg level of carbosulfan, downward mobility when eluted with

different volumes of water is depicted in Fig. 3. The data revealed that, at 20 mL

water addition, the residues were detected upto 10 cm and the concentration of

carbosulfan markedly increased in each layer than 100 µg level of application. With

increasing volume of water used for leaching purpose, the residues further moved

down and were detected upto 20 cm depth but in very low concentration.

At 200 µg level of carbosulfan, downward mobility when eluted with different

volume of water is depicted in Fig. 4. The data revealed that, at 20 mL

88

Fig. 2. Mobility of carbosulfan 25 EC at 100 µg in laterite soil

Fig. 3. Mobility of carbosulfan 25 EC at 150 µg in laterite soil

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0-5cm 5-10cm 10-15cm 15-20cm 20-25cm Leachate

Re

sid

ue

s in

mg

kg-1

DepthT1 T2 T3 T4

T1-100 µg carbosulfan EC + 20 mL water T2-100 µg carbosulfan EC + 40 mL waterT3-100 µg carbosulfan EC + 80 mL water T4-100 µg carbosulfan EC + 160 mL water

0

0.5

1

1.5

2

2.5


Re

sid

ue

s in

m

g kg

-1

DepthT1 T2 T3 T4


Fig. 4. Mobility of carbosulfan 25 EC at 200 µg in laterite soil.

Fig. 5. Mobility of carbosulfan 25 EC at 100 µg in coastal alluvial soil

0

0.5

1

1.5

2

2.5

3

3.5

4


Re

sid

ue

s in

m

g kg

-1

Depth T1 T2 T3 T4


0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2


Re

sid

ue

s in

m

g kg

-1

Depth T1 T2 T3 T4


water addition the residues were detected upto 10 cm and a further increase in the concentration

was noticed than 150 µg level application. With increase in the volume of water used for

leaching upto 160 mL for the leaching purpose, the residues further moved down upto 25 cm and

the leachate also showed the presence of carbosulfan residues, even though its concentration was

very low.

This result is in accordance with the findings of Sreekumar and Shah (2014) in which

the residues of atrazine, imidacloprid and certain fertilizers moved to the deep layers from 12

cm to 30 cm by initial application of 100 mL 0.01 M CaCl2 and further addition of 50 mL 0.01 M

CaCl2. According to Ngan et al. (2005), the solubility of pesticide has a major role in its

movement in the soil column and hence with more volume of water added to the soil the

solubility of carbosulfan get increased and thus it moved to deeper layers. This is contrary to the

results of Shabeer and Gupta (2011) in which the movement of capropamid in soil when applied

at 50 µg level was detected with 95 per cent residues in the top 0-5 cm layer and no residues in

the leachate.

5.3.2 Mobility of Carbosulfan in Coastal Alluvial Soil

The data on the mobility of carbosulfan in soil column containing coastal alluvial soil

loaded at 100, 150 and 200 µg and eluted with different volumes of water viz., 20, 40, 80 and

160 mL water are given in the Tables 16-18 and the depth wise proliferation of residues are

depicted in Fig. 5-7.

The mobility of carbosulfan when loaded with 100 µg carbosulfan in coastal alluvial

soil is depicted in Fig. 5. When leached with 20 mL water, the residues were detected upto 15

cm which was higher than that of laterite soil under the same condition where the residues

moved upto 10 cm only. When the volume of water was increased upto 160 mL, the residues

moved further down and were detected upto 20 cm and most of the residues were detected in 0-5

cm layer. This may be due to the effect of solubility of the compound on the movement of

carbosulfan. The migration

89

Fig. 6 Mobility of carbosulfan 25 EC at 150 µg in coastal alluvial soil

Fig. 7. Mobility of carbosulfan 25 EC at 200 µg in coastal alluvial soil

0

0.5

1

1.5

2

2.5


Re

sid

ue

s in

m

g kg

-1

DepthT1 T2 T3 T4


0

0.5

1

1.5

2

2.5

3

3.5

4


Re

sid

ue

s in

m

g kg

-1

DepthT1 T2 T3 T4


of carbosulfan was found to be more in coastal alluvial soil than laterite soil which

can be presumably due to the predominance of macropores in the coastal alluvial soil

than the laterite soil.


different volume of water is depicted in Fig. 6. The data revealed that, at 20 mL

water addition, the residues were detected upto 15 cm and the concentration of

carbosulfan markedly increased in each layer than 100 µg level of application. With

increase in the volume of water used for leaching purpose, the residues moved further

down and were detected upto 20 cm and 25 cm depth at 80 mL and 160 mL water

respectively but in very low concentrations.


different volumes of water is depicted in Fig. 7. The data revealed that, with 20 mL

water addition, the residues could be detected upto 15 cm and a further increase in the

concentration was noticed than 150 µg level application in each layer. With increase

in the volume of water used for leaching upto 160 mL, the residues further moved

down upto 25 cm and the leachate also showed the presence of carbosulfan residues,

even though its concentration was very low but higher than that in the laterite soil.

The study on mobility revealed that, the movement of carbosulfan was more

in the coastal alluvial soil, because at 100 µg level, the movement was upto 10-15 cm

in laterite while that was upto 15-20 cm level in coastal alluvial soil. At 150 µg

level, the residues moved upto 15-20 cm layer in laterite soil while in the coastal

alluvial soil it was 20-25 cm. At 200 µg level, the residues found in the leachate was

comparatively higher than the laterite. So, it shows that, there may be a chance of

ground water pollution in coastal alluvial soil when the higher dose application of

carbosulfan intercept with high rainfall condition. This result is similar to the findings

of Osman and Cemile (2010) increased rainfall can result in ground water pollution

by leaching down of the pesticides. This result was also similar to the reports of

Kumar and Philip (2006) that endosulfan mobility was found to be more in sandy soil

90

than clayey soil. This result opposes the findings of Singh et al. (2013) regarding the

mobility of lindane in soil with high organic matter where high organic matter

content restricted the movement of pesticide to the deep layers and confined only to

the surface layers (0-6 cm).

5.3.3 Mobility of Carbofuran in Laterite Soil

The mobility of carbofuran in the soils were tracked along with carbosulfan

where carbofuran was not directly used or loaded in the soil column. Carbofuran was

detected from time of start of elution which could be formed as metabolite of

carbosulfan formed directly from it. The mobility of carbofuran was also tracked in

soil columns which is discussed hereunder.

The mobility of carbofuran in laterite soil is depicted in Fig. 8-10. The result

showed that, mobility of carbofuran at 100 µg level (Fig. 8.) of carbosulfan

application along with 20 mL water equivalent to 50 mm rainfall confined the

carbofuran residues upto 5 cm only, while application of 160 mL water equivalent to

400 mm rainfall migrated the residues upto 15 cm in the soil column.

At 150 µg level (Fig. 9), the presence of residues was found upto 15 cm at

160 mL water application while at 20 mL water the residues moved only upto 10 cm.

The concentration of residues in these layers were increased than the 100 µg level of

application. At 200 µg level application of carbosulfan, the residues found upto 20

cm layer by 160 mL water (Fig. 10) and for 20 mL water it was confined to 10 cm

only. But there was no carbofuran residues in the leachate .

5.3.4 Mobility of Carbofuran in Coastal Alluvial Soil

The mobility of carbofuran in coastal alluvial soil is depicted in Figures. 11-

13. In coastal alluvial soil at 100 µg level (Fig. 11.) the residues were found upto 15

cm layer for 160 mL, while for 20 mL water, the residues could be obtained upto 10

cm. At 150 µg level (fig 12) also, the residues were found upto 20 cm by application

of 160 mL water and the presence of residues from other treatments were found less

91

Fig. 8. Mobility of carbofuran formed from carbosulfan 25 EC at 100 µg in laterite

soil

Fig. 9. Mobility of carbofuran formed from carbosulfan 25 EC at 150 µg in laterite

soil

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4


Re

sid

ue

s in

p m

g kg

-1

Depth T1 T2 T3 T4

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7


Re

sid

ue

s in

m

g kg

-1

Depth T1 T2 T3 T4

T1-150 µg carbosulfan EC + 20 mL water T2-150 µg carbosulfan EC + 40 mL water T3-150 µg carbosulfan EC + 80 mL water T4-150 µg carbosulfan EC + 160 mL water


Fig. 10. Mobility of carbofuran formed from carbosulfan 25 EC at 200 µg in laterite soil

Fig. 11. Mobility of carbofuran formed from carbosulfan 25 EC at 100 µg in coastal

alluvial soil

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8


Re

sid

ue

s in

m

g kg

-1

DepthT1 T2 T3 T4


0

0.05

0.1

0.15

0.2

0.25


Re

sid

ue

s in

m

g kg

-1

DepthT1 T2 T3 T4


Fig. 12. Mobility of carbofuran formed from carbosulfan 25 EC at 150 µg in coastal alluvial soil

Fig. 13. Mobility of carbofuran formed from carbosulfan 25 EC at 200 µg in coastal

alluvial soil

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35


Re

sid

ue

s in

m

g kg

-1

Depth T1 T2 T3 T4


0

0.1

0.2

0.3

0.4

0.5

0.6


Re

sid

ue

s in

m

g kg

-1

Depth T1 T2 T3 T4


in the deep layers. At 200 µg level (Fig. 13.), the residues were found upto 20 cm

and with increasing concentration of application of carbosulfan, the residue level in

each layer was also increased. In coastal alluvial soil also, the leachate did not show

the presence of carbofuran.

The migration of carbofuran was comparatively slow than that of carbosulfan

in two soils that may be the reason why the leachate showed no residues of

carbofuran. In coastal alluvial soil, the movement of carbofuran was slightly higher

than that in laterite soil. This is similar to the study by Lalah and Wandiga (1996)

where the movement of carbofuran was slightly higher in sandy soils than other soils.

The results of mobility of carbosulfan and carbofuran can be summarized as

follows. With increased concentration and increased volume of water for elution, the

movement of carbosulfan and carbofuran were increased. This indicates that, increase

in rainfall from 50 to 400 mm can have a high influence on the movement of

carbosulfan and carbofuran and there by influence the contamination also. In coastal

alluvial soil, the movement of carbosulfan and carbofuran was found to be higher

than in the laterite soil. The movement of carbofuran was comparatively slow than

carbosulfan. This is contrary to the results of Lalah and Wandiga (1996) rapid

movement of carbofuran could be noticed in soil. The movement of carbosulfan and

carbofuran in soil columns can be considered to be the net effect of adsorption

coefficient and water solubility. Carbosulfan with high adsorption coefficient and

water solubility moved down by virtue of the high water solubility while cabofuran

with low adsorption coefficient and low water solubility moved down due to less

adsorption. In both soils, at 200 µg level application of carbosulfan and 160 mL

water application resulted in residues in the leachate so it indicates that increased

concentration and increased rainfall can result in underground water contamination

especially in the coastal alluvial soil.

92

5.4 PERSISTENCE OF CARBOSULFAN

The effect of different treatments on the persistence of carbosulfan in laterite

and coastal alluvial soils were studied in the laboratory and under cropped condition

using EC and granule formulation .

5.4.1 Dissipation of Carbosulfan 25 EC in Laterite Soil

The dissipation of carbosulfan 25 EC in laterite soil is presented in Fig. 14.

The result showed that, T3 has the highest half life (10.53 days) ie 5 mg kg-1 level of

carbosulfan application in laboratory condition showed the maximum residue content.

The smallest half life (2.17 days) is for T4 in which 1 mg kg-1 carbosulfan 25 EC

was added in the cropped condition. The half life of T4, T5 and T6 (1, 2.5 and 5 mg

kg-1 under cropped condition respectively) were small compared to T1, T2 and T3 (1,

2.5 and 5 mg kg-1 under laboratory condition respectively). Thus, the result showed

that, in the cropped condition, carbosulfan was dissipated at a faster rate than the

laboratory condition. This may be due to the assimilation by crop, degradation by

microbes or by certain rhizospheric effects. This result adheres to the reports of

George et al. (2009) that the half life obtained for endosulfan under the laboratory

condition was comparatively higher than the actual field condition which they

attributed to the lower rate of exposure of the pesticide to environmental conditions

like sunlight, temperature and wind.

5.4.2 Dissipation of Carbosulfan 25 EC in Coastal Alluvial Soil

The dissipation of carbosulfan 25 EC in coastal alluvial soil is depicted in

Fig. 15. The result revealed that, T6 representing 5 mg kg-1 level in the cropped

condition had the highest half life (5.13 days) compared to all other treatments. The

smallest half life (2.35 days) was showed by T1 representing 1 mg kg-1 level in the

laboratory condition. In coastal alluvial soil, the EC formulation showed higher half

life in the cropped condition than the laboratory condition. It is contrary to the result

of laterite soil. This may be due to the higher organic matter content of coastal

93

Fig. 14. Half life of carbosulfan 25 EC in laterite soil under laboratory and cropped conditions

Fig. 15. Half life of carbosulfan 25 EC in coastal alluvial soil under laboratory and cropped

conditions

0

2

4

6

8

10

12

T1 T2 T3 T4 T5 T6

Day

s

Treatments Half Life

T1- 1 mg kg-1 in laboratory condition, T2- 2.5 mg kg-1 in laboratory condition , T3- 5 mg kg-1 in laboratory condition, T4- 1 mg kg-1 in cropped condition, T5- 2.5 mg kg-1 in cropped condition T6- 5 mg kg-1 in cropped condition

0

1

2

3

4

5

6

T1 T2 T3 T4 T5 T6

Day

s


T1- 1 mg kg-1 in laboratory condition, T2- 2.5 mg kg-1 in laboratory condition , T3- 5 mg kg-1

in laboratory condition, T4- 1 mg kg-1 in cropped condition, T5- 2.5 mg kg-1 in cropped condition T6- 5 mg kg-1 in cropped condition

alluvial soil. The coastal alluvial soil had comparatively higher organic matter

(0.84 %) content than laterite soil (0.41 %) in the natural condition itself. In the

cropped condition as organic matter is again added might have again increased and

lead to more adsorption of carbosulfan on its surface and hence more retention and

persistence. This result is in corroboration with the earlier findings obtained in the

study conducted for chlorpyrifos by George et al. (2007) where higher application of

organic manure increased the persistence of chlorpyrifos. Similarly, the high organic

matter and low pH increased the persistence of fipronil in soil (Mandal and Singh,

2013 ). But this is contrary to the result obtained for George et al. (2009) that

laboratory condition resulted in a higher half life for endosulfan than cropped

condition due to lower exposure to environmental conditions such as temperature,

light etc.

5.4.3 Dissipation of Carbosulfan Granules in Laterite Soil

The dissipation of carbosulfan granules in laterite soil is represented in Fig.

16. It showed that, T3 had the highest half life (11.5 days) and T4 had the lowest half

life (3.26 days) period. So, 1 mg kg-1 application in the cropped condition showed

the lowest half life and 5 mg kg-1 application in the laboratory condition showed the

highest half life. This is similar to the case of carbosulfan 25 EC in the present study.

Here, the variation among T1, T2 and T3 were very small compared to the case of EC

formulation. But in cropped condition, the degradation was comparatively faster than

the laboratory condition. The half lives obtained for granules were higher than EC

formulation. This result is similar to the result of Liu et al. (2015) for chlorpyrifos in

which the granule formulation had half lives of 4.1 to 4.36 times more than the EC

formulation and he mentioned that the granules release the pesticides in a controlled

manner so there may be low risk of environmental pollution too.

94

Fig. 16. Half life of carbosulfan granules in laterite soil under laboratory and cropped conditions

Fig. 17. Half life of carbosulfan granules in coastal alluvial soil under laboratory and cropped

conditions

0

2

4

6

8

10

12

14

T1 T2 T3 T4 T5 T6

Day

s



0

2

4

6

8

10

12

T1 T2 T3 T4 T5 T6

Day

s

TreatmentsHalf Life


5.4.4 Dissipation of Carbosulfan Granules in Coastal Alluvial Soil

The dissipation of carbosulfan granules in coastal alluvial soil represented in Fig. 17.

The result revealed that, the highest half life was obtained for T3 and the lowest is for T4

formulation. T3 represents the 5 mg kg-1 level of carbosulfan application in the laboratory

condition and T4 represents the 1 mg kg-1 application of carbosulfan granules in cropped

condition. In this case, the cropped condition showed relatively shorter half life period than the

laboratory condition in coastal alluvial soil. This result is contrary to the result of carbosulfan 25

EC in coastal alluvial soil, in which the cropped condition showed longer half life than

laboratory condition. This may due to the inherent difference between the two formulations.

The persistence of carbosulfan can be summarized as follows : the half lives obtained for

granule formulations were comparatively higher than the EC formulation. This may be due to the

change in the release of carbosulfan from the two formulations. When we are applying the EC

formulation, we are directly applying it to the soil as solution while when we are adding the

granules it may take some times for the granules to disintegrate and to release the pesticide. In

laboratory condition, the half life was found to be more than the cropped condition and this may

be due to the rhizospheric effect and assimilation by plants in the cropped condition. In coastal

alluvial soil, the half life in the cropped condition was comparatively higher than the laterite soil

and this can be due to the higher organic matter in the coastal alluvial soil than the laterite soil

and thus resulted in high adsorption and there by retention of the pesticide for longer period. In

laboratory condition, the laterite soil has relatively higher persistence than coastal alluvial soil. It

can be due to better degradation of carbosulfan in coastal alluvial soil due to better microbial

population than laterite as a result of high organic matter content. Similar result was reported by

Sahoo et al. (1998) in which, the carbosulfan degradation was much faster in non sterilized

media than the sterilized media. With increase in the concentration of the carbosulfan treatment

from 1 to 5 mg kg-1 levels, the persistence was found to be more which can

95

be presumably due to the lethal effect of carbosulfan on microbes and there by the consequent

decreasede rate of microbial degradation .

5.5 DEGRADATION OF CARBOSULFAN IN SOIL

The study of the metabolism of carbosulfan in laterite and coastal alluvial soil under the

laboratory and cropped conditions was done using EC and granule formulation. The metabolites

formed were monitored on the 0, 1, 3, 5, 7, 10, 15, 20, 30 and 45th day.

5.5.1 Metabolism of Carbosulfan 25 EC in Laterite Soil under Laboratory Condition and

Cropped Condition

The metabolism of carbosulfan 25 EC in the laterite soil under laboratory condition is

depicted in Figures. 18-20. It is seen that, from the 0th day itself the degradation of carbosulfan

started and along with that, the formation of carbofuran was noticed. The carbofuran

concentration was maximum on the 15th day, and along with this, the metabolites such as 3- keto

carbofuran and 3- hydroxy carbofuran were also formed but at 1 mg kg-1 level of treatment, the

concentration was too low and from 0- 5 mg kg-1 level, the concentration of these two

metabolites increased. At 1 and 2.5 mg kg-1 levels, the carbosulfan residues were found upto 30th

day and with increasing the treatment level to 5 mg kg-1, the residues were found upto 45th day

while the presence of the other two metabolites were found upto 45th day. The concentration of

3- keto carbofuran was found to be more than the 3- hydroxy carbofuran. Similar results were

reported by Nigg et al. (1985) in which, the carbosulfan application resulted in the formation of

carbofuran and 3 hydroxy carbofuran but the concentration of 3- hydroxyl carbofuran was very

low due to its low rate of formation or fast disappearance. Under cropped condition it is

presented in Figures. 21-23. The maximum carbofuran concentration was on 7th day and the

formation of the other two metabolites were very low in concentration.

96

Fig. 18. Degradation of carbosulfan 25 EC in laterite soil at 1 mg kg-1 level under laboratory condition

Fig. 19. Degradation of carbosulfan 25 EC in laterite soil at 2.5 mg kg-1 level under laboratory condition

*3-OH carbofuran indicates 3- hydroxy carbofuran

0

0.5

1

1.5

2

2.5

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days

carbosulfan carbofuran 3-OH carbofuran 3-Keto carbofuran

0

0.5

1

1.5

2

2.5

3

3.5

0 1 3 5 7 10 15 20 30 45

Re

sid

us

in

mg

kg-1

Days

Carbosulfan Carbofuran 3-OH carbofuran 3-Keto Carbofuran

Fig. 20. Degradation of carbosulfan 25 EC in laterite soil at 5 mg kg-1 level under laboratory condition

Fig. 21. Degradation of carbosulfan 25 EC laterite soil at 1 mg kg-1 level under cropped condition


0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days

carbosulfan carbofuran 3 OH carbofuran 3-Keto carbofuran

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days

carbosulfan carbofuran 3-OH carbofuran 3- Keto carbofuran

Fig. 22. Degradation of carbosulfan 25 EC laterite soil at 2.5 mg kg-1 level under

cropped condition

Fig. 23. Degradation of carbosulfan 25 EC laterite soil at 5 mg kg-1 level under cropped condition


0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days


0

0.5

1

1.5

2

2.5

3

3.5

4

0 1 3 5 7 10 15 20 30 45

resi

du

es

in

mg

kg-1

Days




The metabolism of carbosulfan in coastal alluvial soil under laboratory

condition is depicted in Figures. 24-26. It is seen that a decreasing trend of the

carbosulfan from 0th day and the subsequent carbofuran formation from the 0th day

onwards. The carbofuran was maximum on 7th day . The formation of 3- keto

carbofuran and 3 hydroxy carbofuran were prominent at 1 and 2.5 mg kg-1 levels. The

maximum residues of 3- keto carbofuran was noticed on 30th day at these two levels

of treatment. At 5 mg kg-1 level of treatment, the maximum 3- keto carbofuran was

obtained on 20th day. The metabolites formed in coastal alluvial soil by application

of EC under cropped condition is illustrateded in Figures. 27-29. It is found that,

from the 0th day itself, the carbosulfan was decreasing and the carbofuran was

maximum on the 10th day. In this case also, the concentration of the other two

metabolites were very low.

5.5.3 Metabolism of Carbosulfan Granules in Laterite Soil under Laboratory

and Cropped Conditions

The application of granules in the laterite soil under laboratory study is

presented in Figures. 30-32. The result showed that, the carbosulfan residues

increased from 0th day to 7th day and then decreased. The carbofuran was found from

the 0th day itself and the was maximum on the 10th day. The formation of 3 hydroxy

carbofuran and 3 keto carbofuran were also noticed and the second one formed

comparatively higher in concentration. At 1 and 2.5 mg kg-1, level the maximum

residues of 3 keto carbofuran were noticed on the 30th day and at 5 mg kg-1 level, the

maximum residues were found on the 15th day. Under cropped conditions as

illustrated in Figures. 33-35, the residues were found to increase which may be due to

the controlled release of the carbosulfan from granules and on the 10 th day, the

97

Fig. 24. Degradation of carbosulfan 25 EC in coastal alluvial soil at 1 mg kg-1 level under laboratory condition

Fig. 25. Degradation of carbosulfan 25 EC in coastal alluvial soil at 2.5 mg kg-1 level under laboratory condition


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days


0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days


Fig. 26. Degradation of carbosulfan 25 EC in coastal alluvial soil at 5 mg kg-1 level under laboratory condition

Fig. 27. Degradation of carbosulfan 25 EC in coastal alluvial soil at 1 mg kg-1 level

under cropped condition


0

0.5

1

1.5

2

2.5

3

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

es

in m

g kg

-1

Days


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days


Fig. 28. Degradation of carbosulfan 25 EC in coastal alluvial soil at 2.5 mg kg-1 level under cropped condition

Fig. 29. Degradation of carbosulfan 25 EC in coastal alluvial soil at 5 mg kg-1 level under cropped condition


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 1 3 5 7 10 15 20 30 45 45

Re

sid

ue

s in

m

g kg

-1

Days


0

0.2

0.4

0.6

0.8

1

1.2

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days


Fig. 30. Degradation of carbosulfan granules in laterite soil at 1 mg kg-1 level under laboratory condition

Fig. 31. Degradation of carbosulfan granules in laterite soil at 2.5 mg kg-1 level under laboratory condition


0

0.05

0.1

0.15

0.2

0.25

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days

carbosulfan carbofuran 3 OH carbofuran 3-Keto carbofuran

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days


Fig. 32. Degradation of carbosulfan granules in laterite soil at 5 mg kg-1 level under laboratory condition

Fig. 33. Degradation of carbosulfan granules in laterite soil at 1 mg kg-1 level under cropped condition


0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days


0

0.1

0.2

0.3

0.4

0.5

0.6

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Dayscarbosulfan carbofuran 3-OH carbofuran 3- Keto carbofuran

Fig. 34. Degradation of carbosulfan granules in laterite soil at 2.5 mg kg-1 level under cropped condition

Fig. 35. Degradation of carbosulfan granules in laterite soil at 5 mg kg-1 level under cropped condition


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days


0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 1 3 5 7 10 15 20 30 30 45

Re

sid

ue

s in

m

g kg

-1

Days


carbofuran was maximum. In this case also, the concentrations of 3 keto and 3-

hydroxy carbofuran were very low in concentration.

5.5.4 Metabolism of Carbosulfan Granules in Coastal Alluvial Soil Under


Metabolism of carbosulfan granules applied in coastal alluvial soils under

laboratory conditions is depicted in Figures. 36-38. The result revealed that,

concentration of carbosulfan increased from 0- 3rd day and then declined. Formation

of carbofuran increased and maximum amount was noticed on 7th day. Formation of

the other two metabolites were at very low concentrations. Application under

cropped conditions (Figures. 39-41) also showed an initial increase in carbosulfan

residue upto 3rd day and then a decline along with the formation of carbofuran, 3 keto

and 3 hydroxy carbofuran at comparatively higher concentrations in cropped

condition than under laboratory condtion. These result were similar to the findings of

Pal et al. (2005) on the effect of organic matter and nutrient addition on the faster

degradation of pesticides in soil by enhancing the microbial growth and enzyme

activity.

5.6 EFFECT OF CARBOSULFAN ON SOIL ORGANISMS

The effect of carbosulfan on the microbial population of the two soils were

studied using EC and granule formulation each at normal (250g ai ha-1 ) and at double

(500 g ai ha-1) doses. A control or pre treatment sample was also maintained to

assess the relative inhibition/ enhancement of microbial population by the treatments.

5.6.1 Effect of Carbosulfan on the Microbial Population in Laterite Soil

The result of the effect of carbosulfan treatment on the bacterial population in

laterite soil is presented in Fig. 42. It is seen that, an increase in the population by

application of EC formulation in the normal dose. A slight increase was observed by

double dose application of EC but was statistically on par with control population.

Granular application resulted in a decline in the bacterial population at both the doses.

98

Fig. 36. Degradation of carbosulfan granules in coastal alluvial soil at 1 mg kg-1 level under laboratory condition

Fig. 37. Degradation of carbosulfan granules in coastal alluvial soil at 2.5 mg kg-1 level under

laboratory condition


0

0.1

0.2

0.3

0.4

0.5

0.6

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days


0

0.1

0.2

0.3

0.4

0.5

0.6

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days


Fig. 38. Degradation of carbosulfan granules in coastal alluvial soil at 5 mg kg-1 level under

laboratory condition

Fig. 39. Degradation of carbosulfan granules in coastal alluvial soil at 1 mg kg-1 level under

cropped condition


0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days


0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days


Fig. 40. Degradation of carbosulfan granules in coastal alluvial soil at 2.5 mg kg-1 level under

cropped condition

Fig. 41. Degradation of carbosulfan granules in coastal alluvial soil at 5 mg kg-1 level under cropped condition


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

mg

kg-1

Days


0

0.2

0.4

0.6

0.8

1

1.2

0 1 3 5 7 10 15 20 30 45

Re

sid

ue

s in

m

g kg

-1

Days


Fig. 42 Effect of carbosulfan on the microbial population of laterite soil Bacterial population is in 106 cfu mL-1, fungi and actinomycetes population in 104 cfu mL-1 and arthropod population in per kilo gram

soil

0

2

4

6

8

10

12

14

Carbosulfan 25 EC -

normal dose

Carbosulfan 25 EC

at double dose

Carbosulfan G at

normal dose

Carbosulfan G at

double dose

Control

Po

pu

lati

on

Treatments

Bacterial Population Fungal Population Actinomycetes Population Arthropod Population

Increase in the concentration of EC and granules resulted in a decline in the bacterial

population. This is contrary to the report of by Zhou et al. (2012) on the effect of

butachlor and carbofuran on methanogens. The study showed a slight increase in the

methanogens by application of butachlor and carbofuran in paddy soil. The higher

concentration of the butachlor and carbofuran significantly inhibited the methanogen

population.

A decline in the fungal population was noted by the application of carbosulfan

EC and granules at normal dose and with increasing the concentration, a slight

increase in the population (especially with granules in double dose) was noted than

the normal dose but it was not significant compared to the control soil. In the case of

actinomycetes, the normal dose application of granules had a significant positive

effect on the population and all other treatments decreased the population. The

arthropod population in the soil was decreased by normal dose of carbosulfan

application and it was further decreased by double dose of application.

5.6.2 Effect of Carbosulfan on the Microbial Population in Coastal Alluvial Soil

The effect of carbosulfan on the microbial population in coastal alluvial soil

presented in Fig. 43. Which indicated a marked increase in the bacterial population

by application of EC and granule forms in the normal dose. With increase in the

concentration of both formulations, a decline in the bacterial population was noticed.

The fungal population in the soil was increased by application of EC in normal dose

and all other treatments decreased the population of fungi. In coastal alluvial soil,

normal dose of both formulations of carbosulfan resulted in an increase in the

population dynamics of actinomycetes while that was reduced by the application of

the formulations in double dose. The arthropod population also reduced with all the

carbosulfan treatments. This result is similar to the findings of (Fountain et al., 2008)

that application of chlorpyrifos can result in the reduction of arthropod and predatory

spider populations.

99

Fig. 43 Effect of carbosulfan on the microbial population of coastal alluvial soil Bacterial population is in 106 cfu mL-1, fungi and actinomycetes population in 104 cfu mL-1 and arthropod population in per

kilo gram soil.

0

5

10

15

20

25

Carbosulfan 25 EC -

normal dose

Carbosulfan 25 EC at

double dose

Carbosulfan G at

normal dose

Carbosulfan G at

double dose

Control

Po

pu

lati

on

Treatments

Bacterial Population Fungal Population Actinomycetes Population Arthropod Population

So it can be summarized that, the application of carbosulfan EC and granules

in normal dose created an increase in the bacterial and actinomycetes population. The

fungal population in the coastal alluvial soil was also increased by normal dose of EC

but it created detrimental effect on other organisms. The double dose of application

generally created a significant reduction in the microbial population. The results

revealed that, carbosulfan had an inhibitory effect on arthropod population. It could

be understood from the study that, the different formulations had different effect on

the microbes, which is similar to the result of Holockova et al. (2013) in which the

different formulations of triazole induced different toxic effects on the bovine culture.

Likewise according to Kumar et al. (2002), application of chlorothalonil resulted in

significant reduction in the microbial mass. A slight increase in the pH of the soil

was observed after 24 h of carbosulfan application which then remained stable upto

3rd day and the preferential change in the pH could also have affected the microbial

population in the carbosulfan treated soil.

100

Summary

6. SUMMARY

Pesticides are inevitable in modern intensive agriculture, due to replacement

of traditional varieties with high yielding varieties which are more prone to pest and

disease infestation, which inturn necessitates timely pest control operations for

obtaining optimum expected yield. Among the numerous approaches for managing

the pest, farmers give preference to chemical method, since it provide quick and

efficient result together with its easy availability. An ideal pesticide should disappear

after its pesticidal action and thus it should not produce any harmful effect on

environment or any organism other than the target one either directly or indirectly.

Among the various carbamate pesticides, carbosulfan is used as a substitute

for carbofuran, the use of which was banned in Kerala due to its extreme lethal effect.

Carbofuran comes under extremely toxic category while carbosulfan comes under

highly toxic category. So the handling of carbosulfan is comparatively safer than

carbofuran. But upon degradation of carbosulfan, carbofuran was formed and the

insecticidal toxicity of carbosulfan was mostly due to this carbofuran than the

carbosulfan. The carbofuran degradation resulting in the formation of 3- hydroxy

carbofuran and 3- keto carbofuran which also have toxicological importance. In this

context, a study was conducted to understand the persistence and transformation of

carbosulfan in two major soil types of Kerala viz., Laterite and coastal alluvial soils

by assessing the persistence, transformation and effect on soil organisms as

influenced by the type of formulation and soil factors.

The two soil types, laterite and coastal alluvial were collected from

representative types available Vellayani and Kazhakkoottam, respectively. Their

physico chemical properties were analyzed. A suitable method was validated for the

single step estimation of multiple residues (Carbosulfan + 3 metabolites) in soil by

following modified QuEChERS method.

101

The mobility of carbosulfan was studied by packed soil column method using

100, 150 and 200 µg level of pesticide and elution with 20, 40, 80 and 160 mL of

water equivalent to 50, 100, 200 and 400 mm of rainfall in the field condition. The

persistence study was conducted by application of both carbosulfan 25 EC and

granules at a concentration of 1, 2.5 and 5 mg kg-1 level in laboratory condition and

cropped (growbag) condition with chilli (var, Ujwala) as test crop. The metabolite

formation was studied using the same soil that used for persistence. The residues

were estimated and quantified by using LC-MS/ MS method. The effect on soil

organisms were studied by applying carbosulfan EC and granules at normal (250g ai

ha-1) and double (500 g ai ha-1) doses. The data were statistically analyzed and the

results were summarized below.

1. The physico chemical analysis of the two soils indicated that laterite soil

comes under sandy loam while the coastal alluvial soil comes under loamy

sand. The WHC and porosity of laterite soil was more than coastal alluvial

soil. The two soils were strongly acidic and the EC and CEC of coastal

alluvial soil were found to be higher than that of the laterite soil. The organic

matter content of laterite soil was 0.41 per cent and that of coastal alluvial soil

was 0.84 per cent. The primary and secondary nutrients were comparatively

more for coastal alluvial soil.

2. The efficiency of extraction of carbosulfan and its metabolite from soil was

standardized through recovery experiment. The modified QuEChERS method

with extraction using acetonitrile followed by dispersive solid phase clean up

was found to be suitable. The analytical procedures gave good recovery for

the residues ranging from 80- 99.20 per cent and 88.4- 100.6 per cent in

laterite soil and coastal alluvial soils respectively and relative standard

deviation ranged from 6.9- 11.6 and 4.5- 8.4 for laterite and coastal alluvial

soils respectively.

102

3. The mobility study showed that, with an increase in the volume of water used

for leaching, more migration occurred to the lower layers. Carbofuran was

also detected along with carbosulfan, but was present only at lower

concentration compared to carbosulfan. The extent of migration of

carbosulfan in coastal alluvial soil was found to be more than the laterite soil.

4. The mobility study revealed that, the texture has an important role in the

movement of residues because the coastal alluvial soil having more total sand

which being more inert and more porous showed more migration due to better

infiltration of carbosulfan along with water.

5. The increased concentration of carbosulfan along with more volume of water

used (160 mL equivalent to high rainfall) for elution significantly increased

the migration tendency and there by the residues detected in the leachate also.

6. The half lives (t1/2) of carbosulfan 25 EC in the laterite soil when applied at 1,

2.5 and 5mg kg-1 levels were 5.08, 7.69 and 10.53 days, respectively in the

laboratory condition, while in the cropped condition they were 2.17, 4.60 and

5.24 days, respectively.

7. In coastal alluvial soil, application of carbosulfan 25 EC at 1, 2.5 and 5 mg

kg-1 level resulted in half lives of 2.35, 2.91 and 4.96 days, respectively in the

laboratory condition and 2.95, 4.59 and 5.13 days, respectively, under cropped

condition. So, half lives were more under cropped situation, this may be due

to more retention of carbosulfan in this soil due to increased adsorption under

the influence of more organic matter.

8. The persistence of carbosulfan granule in the laterite soil at the same level of

treatment resulted in half lives of 9.88, 10.50 and 11.50 days in the laboratory

condition and 3.26, 5.16 and 7.30 days, respectively in cropped condition.

9. In coastal alluvial soil, the half lives of carbosulfan granules were 8.99, 9.45

and 10.45 days in the laboratory condition and 5.70, 6.50 and 9.80 days,

103

respectively in the cropped condition at 1, 2.5 and 5 mg kg-1 level of

application.

10. The dissipation study revealed that by applying EC formulation in soil, the

level of residues declined from the 1st day itself due to degradation, while for

granules, an initial increase in the residue level (maximum upto 7th day for

laterite and 3rd day for coastal alluvial soil) was observed and then declined.

The granule formulation had higher persistence than the EC formulation in

both soils.

11. The half life of carbosulfan 25 EC was higher in laboratory condition than

cropped condition in laterite soil, presumably due to assimilation by plants,

degradation by microbes, or photo degradation etc.

12. The half life of carbosulfan 25 EC in coastal alluvial showed a longer half life

in the cropped condition than the laboratory condition which might be due to

the high organic matter content, which can absorb and retain the carbosulfan

for more longer time and thereby increase its persistence.

13. The results showed that organic matter has a significant influence on the

persistence of carbosulfan because organic matter in a certain level

accelerated the process of degradation of carbosulfan that is why in the

laboratory condition coastal alluvial soil showed faster degradation than

laterite soil. But beyond a certain level, there may be a chance of increased

persistence by increased adsorption by organic matter in soil.

14. In granular formulation, the half life obtained with coastal alluvial soil was

more under cropped condition, than for laterite soil, indicating its higher

persistence in coastal alluvial soil, with crop.

15. The study on degradation of carbosulfan revealed the formation of carbofuran

from the 0th day of treatment.

16. The degradation of carbosulfan resulted in formation of carbofuran, which

got further degraded to 3-keto carbofuran and 3- hydroxy carbofuran. The

104

concentration of metabolite formed is in the order of carbofuran> 3-keto

carbofuran> 3-hydroxy carbofuran in the two soils.

17. The normal dose application of carbosulfan 25 EC increased the bacterial

population in the two soils. In coastal alluvial soil, the normal dose of

granules and EC increased the bacterial and actinomycetes population.

18. The fungal population in the soil was increased by normal dose of EC

application in coastal alluvial soil and the arthropod population was decreased

by all carbosulfan treatments in the two soils.

19. The double dose application of carbosulfan has decreased the population of

microbes significantly.

The study concluded that the nutrient content, CEC and OM content of soils were

high for the coastal alluvial soil. In laterite soil the WHC, porosity etc were higher

than coastal alluvial soil. The mobility of carbosulfan EC was found to be higher in

the coastal alluvial soil. A higher dose application of carbosulfan and subsequent

elution with high volume of water resulted in deep migration of carbosulfan beyond

the soil column to the leachate itself. The persistence study revealed that, granule

formulation has a higher half life in both the soils. The half life of carbosulfan 25 EC

in cropped condition was less than that in the laboratory condition in laterite soil

while in coastal alluvial soil cropped condition showed, increased half life than the

laboratory condition due to the influence of organic matter. The metabolite formation

showed the formation of carbofuran on the 0th day itself and the formation of 3

hydroxy carbofuran metabolite was found to be very less than 3 keto carbofuran. The

effect of carbosulfan on soil organism showed that the double dose of application of

both granules and EC resulted in an inhibition in the microbial population, while the

normal dose of the two formulations resulted in a stimulatory effect on certain

microbial population.

105

FUTURE LINE OF WORK

Distribution and fate of applied pesticide in soil, leachate and crop need to be

studied for commonly used soil pesticides.

Impact of soil applied pesticides on soil organisms and the biochemical

mechanisms for the promotion / decline in population need to be assessed at

molecular level.

The possibilities of ground water contamination by commonly used pesticides

in different soils should be studied.

106

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*Original not seen

121


IN LATERITE AND COASTAL ALLUVIUM SOILS OF KERALA

AND ITS EFFECT ON SOIL ORGANISMS

by

DHANYA. M. S

(2014-11-152)

Abstract of the thesis

Submitted in partial fulfilment of the

requirements for the degree of

MASTER OF SCIENCE IN AGRICULTURE

Faculty of Agriculture

Kerala Agricultural University




KERALA, INDIA

2016

ABSTRACT

The study entitled ‘Persistence and transformation of carbosulfan in laterite

and coastal alluvium soils of Kerala and its effect on soil organisms’ was conducted

at Department of Soil Science and Agricultural Chemistry and the laboratory

attached to the All India Network Project (AINP) on Pesticide Residues, College of

Agriculture, Vellayani, Thiruvananthapuram, Kerala during 2015-16. The main

objectives of the experiment were to study the persistence, mobility and

transformation of carbosulfan in laterite and coastal alluvium soils of Kerala (in

cropped and non cropped situation) and to assess its effect on soil organisms. Laterite

and coastal alluvial soils were collected from Vellayani and Kazhakkoottam

respectively. The physico-chemical analysis of the soils were done which revealed

that coastal alluvial soils had an organic matter content of 0.84 per cent while laterite

had only 0.41 per cent. The primary and secondary nutrients were comparatively

higher for coastal alluvial than laterite soil. The method for the estimation of

carbosulfan residues from the soils were validated at 0.05, 0.25 and 0.50 µg g-1 level

of carbosulfan. Modified QuEChERS method with acetonitrile as extracting solvent

and Primary Secondary Amine (PSA) sorbent for clean up was found to be suitable

for the estimation of carbosulfan from the soil.

Mobility of carbosulfan was assessed by loading 3 levels viz., 100, 150 and

200 µg of carbosulfan 25 EC separately on top of soil columns in PVC pipes and

eluting with 20, 40, 80 and 160 mL of water. In the laterite soil, carbosulfan moved

down the soil column and resulted in residue levels ranging from 1.50-0.04, 2.29-0.27

and 3.55-0.05 mg kg-1 at 100, 150 and 200 µg levels, respectively when eluted with

water. In the coastal alluvial soil, the corresponding residues ranged from 1.78-0.32,

2.20-0.51 and 3.07-0.72 mg kg-1 at 100, 150 and 200 µg level after elution with

water. The residues found on the leachate ranged from 0.001-0.01mg kg-1 for laterite

and 0.001-0.03 mg kg-1 for coastal alluvial soil.

The persistence of carbosulfan in the laterite and coastal alluvial soils under

laboratory and cropped (grow bag with chilli Ujwala variety) conditions

122

was studied using two formulations viz., Emulsifiable Concentrate (EC) and granular

formulations each at 1, 2.5 and 5 mg kg-1 levels. The half lives (t1/2) of carbosulfan 25

EC in the laterite soil when applied at 1, 2.5 and 5mg kg-1 levels were 5.08, 7.69 and

10.53 days respectively in the laboratory condition, while in the cropped condition

they were 2.17, 4.60 and 5.24 days, respectively. In coastal alluvial soil, application

of carbosulfan 25 EC at 1, 2.5 and 5 mg kg-1 level resulted in half lives of 2.35, 2.91

and 4.96 days respectively in the laboratory condition and 2.95, 4.59 and 5.13 days

respectively under cropped condition. The persistence of carbosulfan granule in the

laterite soil at the same level resulted in half lives of 9.88, 10.50 and 11.50 days in the

laboratory condition and 3.26, 5.16 and 7.30 days respectively in cropped condition.

In coastal alluvial soil, the half lives of carbosulfan granules were 8.99, 9.45 and

10.45 days in the laboratory condition and 5.70, 6.50 and 9.80 days respectively in

the cropped condition at 1, 2.5 and 5 mg kg-1 level of application.

The three toxicologically important metabolites of carbosulfan viz.,

carbofuran, 3-hydroxy carbofuran and 3-keto carbofuran were monitored and the

metabolite concentration was in the order of carbofuran > 3-keto carbofuran > 3-

hydroxy carbofuran in the two soils.

The effect of EC and granular formulation of carbosulfan on the microbial

load was monitored after normal (250 g ai ha-1) and double (500 g ai ha-1) dose and

found that in laterite soil the bacterial population increased to 9.45 x 106 cfu g-1 soil

from the control population (6.86 x 106 cfu g-1) at normal dose of EC formulation.

Granule application in the normal dose resulted in a higher population of

actinomycetes (6.59 x 104 cfu g-1) than control (4.95 x 104 cfu g-1). In the coastal

alluvial soil, application of EC and granules in the normal dose increased the bacterial

population to 19.53 x 106 cfu g-1 and 20.35 x 106 cfu g-1 soil respectively from the

control population (11.74 x106 cfu g-1). The population of arthropods declined in the

two soils by carbosulfan treatment at both levels.

The study concluded that the mobility of carbosulfan was found to be higher

in the coastal alluvial soil compared to laterite soil. The persistence of

123

carbosulfan was higher in granular formulation than in EC in both soils.

Transformation of carbosulfan gives carbofuran as the major metabolite which on

further degradation gives 3-keto and 3- hydroxy carbofuran in soil. The normal dose

application of carbosulfan had certain positive effect on the soil organisms but the

double dose application resulted in a considerable reduction in the population of

microbes in the two soils.

124

Persistence and transformation of carbosiilfan in laterite and coastal alluvium

soils of Kerala and its effect on soil organisms

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125

Appendix

APPENDIX I

Calibration Curve of Standard Carbosulfan and its Metabolites

Calibration curve of carbosulfan

Calibration curve of carbofuran

Calibration curve of 3- hydroxy carbofuran

Calibration curve of 3- keto carbofuran

APPENDIX II

Chromatogram of Standard of Carbosulfan and its Metabolites at 0.005 mg kg-1

Chromatogram of carbosulfan and its metabolite at 0.005 mg kg-1 in laterite soil

APPENDIX III

Chromatogram of Recovery of Carbosulfan and its Metabolites from Laterite Soil

Recovery of carbosulfan and its metabolites at 0.01 mg kg-1 in laterite soil




APPENDIX IV

Chromatogram of Recovery of Carbosulfan and its Metabolites from Coastal Alluvial Soil

Chromatogram of carbosulfan and its metabolites at 0.01 mg kg-1 in coastal alluvial soil




APPENDIX V

Mass Spectra of Carbosulfan and its Metabolites at 0.01 mg kg-1

Mass spectra of carbosulfan and its metabolites at 0.01 mg kg-1

persistence and transformation of carbosulfan in laterite and coastal alluvium soils of kerala

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