Chapter-4 Remediation of Heavy Metal Infested Coffee ...shodhganga.inflibnet.ac.in/bitstream/10603/86487/11/11_chapter 4.pdf · Remediation of Heavy Metal Infested Coffee Growing

114

Chapter-4

Remediation of Heavy Metal Infested Coffee Growing Soils

4.1. Introduction

Accumulation of heavy metals in surface soils and their subsequent effects on

human health and environment is of greater concern in recent years. Mining related

wastes, such as waste rock and tailings represent potential sources of metals that can be

redistributed to the environment by aerial and fluvial transport. In addition, aerial

deposition of smelter emissions has lead to widespread contamination of surface soils at

various locations through out the world. Other industrial sources, such as foundries,

refineries, pesticides, paints and battery manufacturers are also known to be potential

sources o^ A}^\/y metal contamination in soils. Further, extensive use of fertilizers,

(ameliorate! and sew&ge sludge coupled with effluent irrigations has aggravated the

propensity of heavy metal contamination in agricultural soils. Among the metals, lead and

cadmium are of prime concern when they are present in alarming concentrations. Lead is

of specific concern due to its relative abundance at contaminated sitgs and its known

potential to cause adverse health effects in children (Davies,,aila Wixson, 1988) while

cadmium in soil represents a direct contact risk to both hurpan and ecological receptors

due to its relatively high toxicity and plant uptake (AT^©fC 1999)/^

Owing to the widespread distribution of lead and cadmium in soils resulting from

human activities, and the potential human and ecological risks posed by these metals, it

is desirable to develop cost effective remediation strategies for these metals. Metals in

contaminated soils are often present in chemical forms that exhibit varying degrees of

bioavailability to human and ecological receptors. As a result, there has been great

interest (particularly for lead-contaminated soils) for in situ remedial strategies that render

metals less bio-available, so that the metal-contaminated soil no longer represents an

unacceptable exposure risk. The bioavailability of metals in soils to ecological receptors is

often established by directly measuring uptake of metals into the receptor of interest

(e.g., plants or soil invertebrates). However, indirect methods, such as m^surement of

soil pore-water concentrations or diffusive gradients in thin films {D^yiiou et al., 2000) are

gaining acceptance as viable methods to estimate soil metal concentrations that are

115

available for biological uptake. The technologies available for remediation and rectification

are solidification/stabilization, vitrification, electro-kinetic remediation, soil flushing, phyto-

extraction, phyto-stabilization, and chemical stabilization. Each technology has benefits

and limitations, depending on the remedial objectives targeted and on site specific

factors. For example, at large-area sites with low to moderate levels of shallow

contamination, a plant-based (phyto-extraction or phyto-stabilization) or chemical

amendment strategy will be preferred. However, these technologies are often limited to

surface soils with low to moderate contamination. Further, for sites with contamination at

deeper horizons or high levels of contamination, a more aggressive remedial technology

would be efficient..^

In soils cropped to coffee, hitherto the extent of heavy metal contamination being

meager, of all the methods available for remediation, the chemical stabilization appears to

be more appropriate. In this method, application of various ameliorants such as lime,

phosphates, zeolites, apatites, glauconite, iron oxide material, compost have been tried

for remediation. Liming, presumably the most widely known amelioration in agriculture,

which is an age-old practice in coffee cultivation, decreases the mobility of heavy metals.

By virtue of reduced mobility of heavy metals owing to metal hydrolysis and / or co-

precipitation with applied carbonate in soils, consequently their uptake by the plants

would be drastically reduced/

Zeolites are crystalline, hydrated aluminosilicates of alkali and alkaline earth

cations that possess infinite three dimensional crystal structures. It occurs naturally in the

soils and as well could be synthesized in the laboratory. The use of zeolites for pollution

control depends primarily on its ion-exchange capabilities. Among the natural zeolites,

clinoptilolite, chabazite and phillipsite ha^^^êen evaluated as efficient ameliorants for

environmental cleanup (Tsitsishvilliêtal., 1992). Many studies have revealed that there

would be significant reductjpff in heavy metal accumulation in the plants upon application

of zeolites. Miineyevêt al. (1989) opined that soil application of zeolites would reduce Zn

content in barley tissues, and grain as well as Pb and Cd contents in strawberries and

cherries. Gworek (1^^) found significant reduction in the Pb and Cd contents of several

pot grown crops on amending polluted soils with synthetic zeolites. Similarly, Rebedea

116

and Le/p (1994) reported that synthetic zeolites added to a lead/zinc mine spoil and a soil

polluted with Cu and Cd reduced plant uptake of metal in pot s tud ies^

Phosphate salts are capable of immobilizing Pb in soils due to the low solubility of

lead orthophosphate complexes. Further Zn and Cd were precipitated upon application of

phosphatic compounds. Further, humus in the organic matter with enormous retention

capacity was found to attenuate most of the heavy metals under favourable conditions.

Other soil constituents such as the hydrous oxides of Al, Fe and Mn are known to retain

metals in soils. The enhanced sorption of metals by hydrous oxides may be attributed to

metal binding througjn^specific adsorption. The efficacy of hydrous iron oxide examined by

Mench et ai.'-f1^4) revealed substantial decrement of Cd and Pb contents in rye grass

besides stabilization of these metals in highly polluted %Q\\^^

Phyto-availability of the metals in soils depends on the form in which they are

present. Transformation of the accumulated metals depends mainly on the soil properties

like pH, organic matter content, clay type, CEC, CaCOs, oxides and hydroxides of Fe and

Mn. Based on primary accumulation mechanisms in soils and sediments, heavy metals

can be assorted into six categories: (i) water soluble, (ii) exchangeable, (iii) carbonate

bound, (iv) oxide bound, (v) organically bound and (vi) residual fractions (K^&h^fn et al.,

2007). Some of the forms are easily available for the plant uptake, while some are

available with slight difficulty where as some are unavailable and may become available

in course of^time as a result of natural processes taking place in the soil environment

(Forstp^r, 1985). Considering the mere total content of heavy metal is insufficient to

assess the impact of the contaminant as geochemical forms of heavy metals in soil are

dynamic and their solubility is bound to influence their bioavailability.^

A large number of extractants have been used to assess plant available trace

elements (Gupta and,Afen, 1993; He and^^ngh, 1993). Single extractants like weak

replacement of ion salts (MgCb, CaCl2, and NH4NO3), dilute solutions of either weak

acids (acetic acid) or strong acids (HCI, HNO3) and chelating agents (DTPA, EDTA) have

been tried. These single extractants either are able to release the metals that are

associated with exchange sites on the soil solid phase or form complexes with the free

metal ions in the solution; thereby reducing the activities of the free metal ion in solution^

117

Hence these extractants give only an indication about the total bioavailable metals in the

soil but do not represent the different geochemical forms of the metal. Unfortunately, most

available extractants are less specific than desired. Hence, more than one target site may

be attacked or the release from the target site may be less than the relevant^

Selective sequential extraction procedures have been commonly used for studying

the metal mobility and availability in soils. It involves treatment of soil with a series of

reagents in order to partition the trace element content. Improved phase specificity

is the claimed advantage of this method over the juie of single extractant. Numg r̂ous

extraction schemes have been described (Gupta and Chen, 1975; Stovei>efal., 1976;

Tessier etaf, 1979; Shumap'^87,

Clevengerand Mu\\\nsy^82)/^

With soil quality playing an important role and one of the prime prerequisites in

food production and quality, especially in certain export oriented products like coffee, it is

essential to employ the most efficient and cost effective remediation techniques for

contaminants in soils. To meet this challenge, a laboratory study was conducted to

evaluate the remediation of metals Wby several widely available soil ameliorants such as

lime, zeolites, phosphates fertilizers and compost with the following objectives;

(i) To determine the influence of ameliorants on the chemical form and bioavailability of

heavy metals and

(ii) To compare the efficacy of selected ameliorants as metal stabilizers in metal

induced contaminated soils.

118

4.2. Review of Literature

The concept of chemical remediation involves the use of generally unique and

conventional chemical amendments to induce specific chemical reactions within the soil

matrix that render the metal contaminants inert and/or immobile. These remedies involve

lower rates of amendment addition, which do not substantially alter the vital soil properties

such as bulk density, pore distribution, water holding capacity, permeability, volume,

aggregates and structure. Further, upon application of ameliorant to the soil, the

rhizosphere conditions would be modified to favour the growth of crop plants as well as

microbial biotaj/

A substantial amount of research has been conducted to evaluate the potential

efficacy of chemical stabilization technologies for the remediation of lead and cadmium in

soils. Majority of these studies are laboratory investigations particularly evaluating the

effects of phosphate amendments on lead solubility. Phosphate hasjong been known to

be effective at stabilizing lead, as demonstrated by Nria9wt^74). The concept is to

induce the formation of highly insoluble lead phosphate minerals that have a low

bioavailability, mobility and are stable under a variety of environmental conditions {R\pf

et al., 1994). A large body of research has shown that various forms of phosphate

amendments could be effective at stabilizing lead in soils (Berti and Cunrjjngham, 1997;

Boisson et aU

119

potentially be mitigated by the inclusion of iron (as hydrous ferric oxide) with the

phosphate amendment. Another concern is the effect of continual removal of phosphorus

due to plant growth. Hettiaracjaehf^nd Pierzynski (2002) concluded that plant removal of

phosphorus could reduce the effectiveness of phosphorus amendments on lead

bioavailability, unless sufficient excess was applied or if the phosphorus was added in

combination with manganese ox ide^

Other than phosphorus compounds, several amendments have been evaluated to

stabilize lead and cadmium in acidic soils. Municipal bio-solids are a potentially promising

chemical amendment due to their widespread availability and low cost. Condor et al.

(2001) demonstrated that lime-stabilized bio-solids were capable of immobilizing zinc in

smelter-impacted soils and reduced the eco-toxicity of the soils to earthworms. Lime, a

common soil amendment long used in agriculture, induces a rise in soil pH, causing

metals to precipitate as oxides and carbonates. Lime is anticipated to be effective only for

a relatively short period of time before the pH-buffering capacity is depleted; therefore,

repeated applications are often required (VangronsveLd and Cunningham, 1998). Lime

has been shown to be effective at reducing plant uptake of zinc, but mixed results have

been reported for plant uptake of cadmium (KretDspt-^f., 1998; Pierzynski,9rta Schwab,

1993). Lime was fairly ineffective for treatment of high-zinc-content soils from the

Palmerton Zinc Superfund site, unless the lime was combined withjthe high iron bio-solids

and applied as a phyto-stabilization strategy (Li and Chaney/1998). By virtue of reduced

mobility of heavy metals owing to metal hydrolysis and / or co-precipitation with applied

lime in soils, consequently their uptake by the plants would be drastically reduced

(Shuman, 1985; Kabata-Pendias and Pendias,>1-g§2). /^

Effect of application of manure and compost to contaminated soils on zinc

accumulation by Solanum nigrum inoculated with arbuscular mycorrhiza fungi in naturally

contaminated soils has been studied by Marques el-.at:^008). They found that organic

amendment like manure could induce a reduction in the amount of Zn leached through

the soil by about 70 - 80% by the combination of Solanum nigrum and organic

amendments. Jordaiy(^008) has reported the utilization of spent mushroom compost

(SMC) for the re-vegetation of lead - zinc tailings. Reduction of the contaminant

120

concentrations in the SMC treated soil was observed and growth of Lolium perenne was

facilitated in the amended so i l ^

Amendments that provide sorption sites that have a strong affinity for trace metals

have been shown to effectively stabilize lead and cadmium in soils by limiting the

soluble fraction of the metals in the soil matrix. Addition of iron and/or manganese in a

variety of forms (e.g., hydrous oxides, steel shot, steel sludge, furnace slag, and

zero-valent iron) has been shown to be effective at reducing the teachability,

bioaccessibility, and phytoavailability of lead, cadmium, and zinc (pert!' and

Cunningham, 1997; Chen ei-sfC 2000; Chlopecka ajjet^driano, 1997; Hetti^fat'hchi and

Pierzynsl^^02; Kre>8'et al., 1998; MenchjX^\r,^994; PierzypskTand Schwab, 1993;

Sappin-Didtep^ al., 1997; ShumaDr''t?r97). The ability of oxidesp.f Fe and Mn to

attenuateêjattfc cations has long been demonstrated (Jeripe0968; Shumanĵ J.9S5;

McBrideyf994). The effectiveness of these materials could have been partly due to their

high alkalinity effects in soil and the highest association of metal with iron-manganese

oxide fraction (spêcific adsorption), which is pH dependent (Stanton and BLyigef̂ 1967;

Shuman, 1977)^

Zeolites and aluminosilicates have also been demonstrated to have a high

retention capacity for metalaând can be used as stabilizing agents (Boissdn jt.at:7i999a

Chlopecka and Adjjafio, 1997; Edwards, et al., 1999; Garcia-S^hez et al., 1999

Gwor^1992; Lothenbach &i^t^^997: Miinyev et al., 1990; Rebedda and Lepp, 1994

Vangronsveld and Cunningham, 1998). The stabilization of metals by zeolites can be

explained by its ion exchange capability and by its molecular structure. The molecular

structure strictly controls cage size in zeolites, which results in selective rempval of

cations from the soil solution even when present in trace amounts (Bfek, 1974).

Therefore, zeolites were considered as promising amelioraLntXin soils contaminated

especially with metallic cations because of their tendency to either become fixed in the

cage or adsorb on the zeolites surface (Leppert, 1990)^

Chlopecka and Adriano (1996) mimicked \n-siiu stabilization of metals in cropped

soils using several ameliorants. They concluded that lime; iron oxide, zeolites and apatite

file:///n-siiu

121

could significantly reduce the Zn concentration in tissues of 3-week-old maize, in mature

maize tissues (roots, young leaves, old leaves, stems, grain) and barley. The largest

reduction (over 80%) in Zn uptake by all crops was effected by Fe-rich, which was

consistent with the greatest reduction in soil-exchangeable Zn by this ameliorant. Similar

studies on inactivation of Pb conducted by Bertt-^d Cunningham (1997) revealed

significant changes in soil Pb chemistry, leached Pb from soil and Pb measured by a

physiologically based extraction test (PBET) after incorporation of inexpensive

ameliorants. Adhikari and ^ g h (2008) studied the remediation of cadmium pollution in

soils by different amendments using column method. In this study lime, phosphate, city

compost and gypsum were tried at different concentrations. An effective remediation of

Cd was achieved by lime, phosphate and combination of city compost with lime.

Combined application of lime and city compost reduced the movement of Cd in the soil

profile. It appeared that organic matter controls the sorption of Cd in soils and the amount

of Cd sorbed increased with increasing organic carbon content^

Heavy metal adsorption and their distribution upon coal fly ash and sewage sludge

amendment studied by Tripathy et al. (2005) revealed that amendments provided the

additional sorption sites for metals and consequently higher sorption affinity was

observed. Further, they opined that in acid soils with low metal retention capacity

application of amendments like sewage sludge likely to contain heavy metals

necessitates close monitoring of ground water as well as crops owing to high mobility of

metals. Sewage sludge with lower metal concentration and near neutral pH is more

appropriate for agricultural use on wide variety of soils owing to the favourable soil

reaction activating more organic constituents.

In addressing metal-contaminated soils, it is essential to estimate the bioavailability

of the metals that are hazardous. An approach commonly used for studying the mobility of

metals in soils is to use ,selective sequential extraction procedures such as- those

developed by Kashem'et al. (2007) or Tessier et al. (1979) or Shuman (1985).

The procedures, through the use of extractant of increasing strength, estimate the

distribution of metals among the water soluble, exchangeable, carbonate, oxide, organic

and residual fractions. Undoubtedly, the procedure is essentially operational with

122

adequate precautions initiated for specific reactions. It is erroneous to assume that the

nominal forms extracted from soil samples always represent the real situation. Thus,

metals supposedly associated with the carbonate fraction may be extracted with buffered

acetate solution, although soil pH condition may render it highly unlikely that carbonate

actually exist in soil being extracted. In these circumstances, it must be assumed that the

extracted metals are derived from non-carbonate sources that are impossible to specify.

Nevertheless, despite the errors of uncritical acceptance of results from sequential

extraction analysis, the procedure is still widely used because it is a useful first approach

in assessing the likelihood of mobilization and biological uptake of metals from the soil

Chemical stabilization is a relatively new technology particularly as a strategy to

reduce metal bioavailability in soils and thus seems to have limited application at the field

scale. In general, the field tests indicate that chemical amendments have the potential to

be effective in stabilizing lead, zinc, and cadmium in soils thereby reducing the mobility

and bioavailability of these metals. A major focus of research is the potential for the

amendments to reduce the mobility of metals in contaminated sites/ soilsr'

123

4.3. Materials and Methods

The materials used for remediation of heavy metal contaminated soils and the

methods adopted for the study is made available in this chapter. Coffee soils of RV

Nagar, Andhra Pradesh and Balehonnur, Chikmagalur District in Karnataka with

considerable variation in organic carbon, cation exchange capacity as well as oxides of

iron and manganese were used for remediation of lead and cadmium

4.3.1. Soils f . / i rlu4

124

of 0.5 - 2.0 mm with a CEC of 120 cmol kg"̂ and dominant in oxides of silicon (68.3%),

aluminum (13%) and calcium (4.1%) was obtained from Escott Zeolites, Australia. The

agricultural lime with a neutralizing value or calcium carbonate equivalent of 85 per cent

was opted for remediation. The compost with near neutral pH having C: N ratio of 12 was

utilized in the study. The potassium di-hydrogen orthophosphate an analytical reagent

was used as soluble phosphorus source to attenuate heavy metals^

4.3.3. Metal inoculation and remediation

To simulate the contaminated condition in soils, both Pb and Cd were

simultaneously introduced in the form of their respective nitrates. A critical concentration

of 100 ppm of each metal was maintained in two kg soil samples collected from both the

locations of Balehonnur and RV Nagar. Four ameliorants i.e., zeolites, agricultural lime,

potassium di-hydrogen orthophosphate (KH2PO4 AR grade) and compost were blended

with the soil separately at 1.5, 1.0, 0.5 and 1.0 per cent respectively. One absolute control

with no amendment was also maintained. Each treatment was maintained in three

replications and adequate precaution was taken to maintain the moisture content near to

field capacity so, ^s to facilitate amelioration process. Soils spiked with metals and

mieliorates^were incubated at room temperature (= 25 C) for 60 days. Meanwhile, soil

samples from each treatment were drawn at regular intervals of 15 days constituting a

total of four sets of samples. These were sequentially extracted for various forms of Pb

and Cd to assess their mobility and retention pattern in soils^

4.3.4. Sequential extraction

It is essential to estimate the bioavailability of the metals while addressing metal-

contaminated soils to arrive at valid conclusions as far as metal contamination is

concerned. An approach commonly used for studying the mobility of metals in soils is to

use selective sequential extraction procedures such as those developed by Kasfiem and

Singh (2001) or Tessiir et al. (1979) or Shuman (1985). The procedures, with the use of

extractant of increasing strength, estimate the distribution of metals among the water

soluble, exchangeable, carbonate, oxide, organic and residual fractions. A brief summary

125

of the most recent sequential extraction procedure developed by Kash^m and Singh

(2001) was adopted in the current study is highlighted in the following paragraph/^

Two grams of soil, (2 mm sieved) was placed in a 50 ml polycarbonate centrifuge

tube and the following extractions were performed sequentially.

• F1: Soil sample extracted with 20 mL of distilled water for 1 h at 20°C on a rolling

table. -Water soluble (WS) fraction/^

• F2: The residue from F1 extracted with 20 mL of 1 M NH4OAC, pH 7 for 2 h at 20°C

on a rolling table. -Exchangeable (EXC) fraction^

• F3: Residue from the F2 extracted with 20 mL of 1 M NH4OAC, pH 5 for 2 h at 20°C

on a rolling table. -Carbonate (CARB) bound fraction^

• F4: Residue from the F3 extracted with 20 mL of 0.04 M hydroxylamine hydrochloride

(NH2OH.HCI) in 25 per cent acetic acid (v/v) at pH 3, reaction time 6 h in a water bath

at 80°C with occasional shaking. -Oxide (OX) bound fraction^

• F5: Residue from F4 extracted with 15 mL of 30 per cent H2O2 (adjusted pH 2),

reaction time 5.5 h in water bath at 80°C, with occasional shaking. After cooling, 5 mL

of 3.2 M NH4OAC in 20 per cent (v/v) HNO3 was added; sample was shaken on a

rolling table for 0.5 h at 20°C and finally diluted to 20 mL with water. -Organics (OR)

retained tractiori/

• F6: Residue from F5 fraction, extracted with 20 mL of 7 M HNO3, reaction time was 6

h in a water bath at 80°C with occasional shaking. -Residual (RES) fraction

Sequential extraction and analysis were done in triplicate for each sample. Metals

present in different extracts were determined by atomic absorption spectrophotometer

(GBC 932A). The soil pH (1:1 soil water extract) was determined for each sample./

126

4.4. Results and Discussion

Results of remediation studies on heavy metals like lead and cadmium utilising

various ameliorants are briefly discussed in this section. A close perusal of data revealed

a general decrease in the mobile/ bioavailable fraction of lead and cadmium with time.

Further, the quantum of decrease in the bioavailable fraction in soils was hastened by the

application of ameliorants. Between the two metals, more of cadmium remained in the

labile pool compared to that of lead in both the soils. As far as soil vulnerability to the

metal contamination is concerned, the soils of Balehonnur remained more sensitive to

heavy metals compared to that of RV Nagar.̂

As with any remediation, the overall objective of chemical remediation approach

adopted in the current study is to create a final solution that assures protection of human

health and the environment. With scrupulous and scientific adoption of remediation

techniques, the possibilities of transport of contaminants from the polluted soil to the

agricultural products meant for human consumption could be effectively mitigated/^

Sequential extraction protocol not only gives the phytoavailable metal that need to

be effectively bridled to contain the contamination but also provides valuable implications

while selecting an appropriate ameliorant for remediation. In order to reduce the

phytoavailable fraction of a particular metal, the ameliorant should function in such a way

to enhance the non-labile pool constituting oxide bound, organically retained and residual

fractions at the cost of carbonate bound, exchangeable and water soluble fractions

forming labile pool. The ameliorants selected for the current study were found to work in

this particular mode. The zeolites were likely to enhance the oxide bound fraction while

potassium di-hydrogen orthophosphate would enhance residual fractions and similarly,

the compost would enhance the organic bound fractions in the soil. However, the mode of

action of agricultural lime would likely t o ^ both as a conditioner and as an ameliorant

under favourable soil reactions^

In acid soils, application of lime would trigger the activity of pH dependent charges

and in turn enhance the attenuation capacity of the soils. Soil clays saturated with

127

aluminium and hydrogen would be efficiently replaced for metal retention with the lime

application. Usually, the oxides of iron, aluminium and manganese as well as organic

matter are the major constituents likely to be influenced by the application of lime. In

neutral to alkaline conditions, the persistence of applied lime could be assured and the

possibility of metal retention in sparingly soluble carbonate form is bound to occur. This

would be a testimony for lime as an ameliorant besides an effective conditionej^-'^

4.4.1. Ameliorant attenuation efficacy

Distribution of lead among various forms such as water soluble, exchangeable,

carbonate, oxide, organic and residual fractions along with the pH observed over different

intervals in 1:1 soil-water extract of the soils of Balehonnur is depicted in Table 4.10.

Among these different fractions, invariably the water soluble and exchangeable forms are

considered to be phytoavailable. However, the carbonate bound fractions are also

considered to be phytoavailable depending on the rate of dissolution of carbonates and

the soil reaction. Normally under acidic conditions (pH < 7), existence of calcium

carbonate and retention of metals by it would be a rare phenomenon. Under such

conditions, it must be assumed that the extracted metal (so called carbonate bound

fraction) is derived from non-carbonate sources that are impossible to specify. Further,

this fraction considered to be phytoavailable and cumulated along with water soluble and

exchangeable fractions to arrive at labile or mobile pool of heavy metaL

Sequential extraction of soil samples drawn after 15 days of incubation revealed

the higher efficacy of ameliorants in containing the metal contamination compared to that

of control (Fig 4.10). In this case, cumulated fractions of water soluble, exchangeable and

carbonate bound forms of metal were assigned as phytoavailable and this formed the

very basis for comparison among the ameliorants with respect to their efficacy. Among

the different treatments involving versatile ameliorants, the lowest (12.9%) phytoavailable

lead was observed in the treatment which received KH2PO4 as ameliorant followed by

those of agricultural lime (27.1%), compost (29.3%) and zeolites (30.2%)

128

Table 4.10. Sequential extraction of Pb from lead induced Balehonnur soil at different incubation period after the treatment with different ameliorants

Treatment Lead Fractions (ppm) Total

Pb

Mobile Pool of

Pb, (%)

PH 1:1

Treatment Total

Pb

Mobile Pool of

Pb, (%)

PH 1:1

WS EX CARB OX ORG RES ppm

Mobile Pool of

Pb, (%)

PH 1:1

15 DAYS Control 1.21 5.79 26.25 14.59 7.60 40.96 96.40 34.50 4.4 Zeolite 1.02 5.17 23.55 13.04 9,80 45.78 98.36 30.20 4.5 Lime 1.97 1.73 22.62 14.06 10.40 46.52 97.30 27.10 6.7 KH2PO4 2.17 2.14 8.40 11.47 9.30 65.32 98.80 12.90 5.2 Compost 1.51 5.09 21.99 . 11.85 13.07 43.99 97.50 29.30 4.5 30 DAYS / ( Control 0.59 5.58 25.88 15.91 9.20 38.74 95.90 33.40 4.4 Zeolite 0.92 4.10 16.06 15.14 12.80 48.38 97.40 21.60 4.5 Lime 1.22 1.50 19.78 16.20 14.30 45.30 98.30 22.90 6.7 KH2PO4 1.74 1.86 7.41 13.62 11.40 61.57 97.60 11.30 5.2 Compost 0.84 3.29 19.46, 14.53 17.60 41.18 96.90 24.30 4 .5 . 45 DAYS 7 Control 0.43 2.89 22.30 22.25 12.70 34,98 95.50 26.80 4.5 Zeolite 0.66 3.64 14.10 24.46 13.80 42.04 98.70 18.60 4.4 Lime 0.47 1.43 17,80 18.56 15.20 44.44 97.90 20.10 7.0 KH2PO4 1.00 1.38 6,67 18.82 13.10 57.23 98.20 9.20 5.1 Compost 0.53 2.68 17,20 21.18 18.30 37.01 96.90 21.10 4.5 60 DAYS / Control 0.00 2.65 21,80 23.87 13.40 33.88 95.60 25.60 4.8 Zeolite 0.00 2.57 14,30 26.10 14.70 40.63 98.30 17.20 4.8 Lime 0.40 0.34 18,40 25.53 16.50 36.43 97.60 19.60 7.1 KH2PO4 0.85 0.39 5,55 29.04 14.80 48.17 98.80 6,90 5.4 Compost 0.00 2.24 17,65 26.40 19.80 31.21 97.30 20.40 4.8

WS - water soluble, Ex -Exchangeable, CARB ORG - Organically bound, RES - Residual

Carbonate bound.

However, the treatment not receiving any sort of ameliorant resulted in the highest

(34.5%) phytoavailable lead in the soils. The distribution of Pb into various fractions in

soils receiving no amendments i.e., 'Control' followed the sequence*Residual (42.5%)>'

Carbonate bound (27.2%) > Oxide bound (15.1%) > Organic bound (7.9%) >

Exchangeable (6.0%) > Water Soluble (1.3%) fraction. A similar trend was noticed in all

the treatments but with a lower carbonate bound Pb content in KH2PO4 treatment

compared to others. The range of various fractions in to which Pb speciation was found in

the soils treated with ameliorants was 45.1 - 66.1%, Residual, 8.5 - 23.9% Carbonate

129

bound, 11.6 - 13.3% Oxide bound, 9.4 - 13.4% Organic bound, 1.8 - 5.3% Exchangeable,

and 1.0 - 2.2% Water Soluble. The soil reaction remained acidic in all the treatments and

remained highest (6.7) in case of lime application followed by KH2PO4 (5.2), compost

(4.5) and zeolites (4.5), while the lowest (4.4) was in case of control̂ . '̂-'̂ ^

120

100

80

a 60

f 40 20 ma

Control Zeolite Lime KH2P04 Compost

Amendments

4 I

I Total Pb Available Pb pH

Fig. 4.10. Phytoavailability of lead fraction after 15 days of Incubation

The allocation of lead in to various fractions was quite different in the soils after 30

days of incubation. It was clear from the results that a part of the labile Pb was

transformed into non-labile form over m^time. The Residual fraction of Pb in the soils

receiving ameliorants ranged from 42.5 to 63.1%, Organically bound fraction from 11.7 to

18.2%, Oxide bound fraction from 14.0 to 16.5%, Carbonate bound fraction 7.6 to 20.1%,

Exchangeable fraction from 1.5 to 4.1% and Water Soluble fraction from 0.9 to 1.7% while

the corresponding Pb fractions in 'Control' were 40.4, 9.6, 16.6, 27.0, 5.8 and 0.6%

respectively. The sequence of distribution of lead into various fractions remained very

similar to that on the 15'̂ day after incubation. Fig 4.11 depicts the variation in

phytoavailable Pb with respect to the different amendments after 30 days of Incubation.

Among the various treatments involving competent ameliorants, the lowest (11.3%)

phytoavailable lead was observed in the treatment which received KH2PO4 as ameliorant

followed by those which received zeolites (21.6%), lime (22.9%) and compost (24.3%)^

130

120 _ 100 E 80 o. „ S 60 f 40

20

T 8

Control Zeolite Lime KH2P0^ Compost Amendments iy v

I Total Pb •Available Pb pH

Fig. 4.11. Phytoavailability of lead fraction after 30 days of incubation

However, the treatment not receiving any sort of ameliorant resulted in the highest

(33.4%) phytoavailable lead in the soils. In general, an overall reduction in phytoavailable

Pb over time is evident in all the treatments and also the conspicuous effect of

ameliorants in effectively bridling the contamination is indicated by the results. There was

no appreciable improvement in soil acidity and the measured pH values remained

unchanged in all the treatments over time/^

Control Zeolite Lime KH2P04 Compost Amendments


Fig. 4.12. Pliytoavailability of lead fraction after 45 days of incubation

131

Sequential extraction of soil samples drawn after 45 days of incubation presented

more interesting features indicating gradual decrease in phytoavailable Pb contents with

the lapse of time (Fig 4.12). Among the different treatments involving versatile

ameliorants, the lowest (9.2%) phytoavailable lead was observed in the treatment which

received KH2PO4 as ameliorant followed by those of zeolites (18.6%), lime (20.1%) and

compost (21.1%). It was noticed that, the treatment not receiving any sort of ameliorant

(control) resulted in the highest (26.8%) phytoavailable lead in the soils. Further, there

was no much improvement in soil acidity except in case of lime application where pH

approached neutrality.

After 45 days of incubation, the distribution of applied Pb into different fractions in

the soils receiving amendments was more in non-labile pool compared to that in the

previous two samples drawn at 15 and 30 days after incubation. The Residual fraction of

Pb ranged from 38.2 to 58.3%, Organically bound fraction from 13.3 to 18.9%, Oxide

bound fraction from 19.0 to 24.8%, Carbonate bound fraction 6.8 to 17.8%, Exchangeable

fraction from 1.4 to 3.7% and Water Soluble fraction from 0.5 to 1.0% in soils which

received ameliorants while the corresponding Pb fractions in 'Control' were 36.6, 13.3,

23.3, 23.3, 3.0 and 0.5% respectively. The sequence of distribution of Pb into various

fractions was Residual > Oxide > Carbonate > Organic > Exchangeable > Water Soluble.

The perusal of the results shows that the oxide and organic fractions were enriched with

Pb contents at the cost of other fractions indicating the process of transformation of part

of the labile as well as residual Pb penetrating the structures of oxides and organic

compounds/

The trend of oxide and organic fractions being enriched with Pb at the cost of other

fractions was continued in the soils even after 60 days of incubation (Fig 4.13). Similar

sequence with slightly altered values compared to the previous cases was observed in

these samples. The Residual fraction of Pb ranged from 32.1 to 48.8%, Organically

bound fraction from 15.0 to 20.3%, Oxide bound fraction from 26.2 to 29.4%, Carbonate

bound fraction 5.6 to 18.9%, Exchangeable fraction from 0.3 to 2.6% and Water Soluble

fraction from 0.0 to 0.9% while the corresponding Pb fractions in 'Control' were 35.4, 14.0,

25.0, 22.8, 2.8 and 0.0 % respectively..

132

Control Zeolite Lime KH2P04 Compost Amendments

I Total Pb Available Pb pH

Fig. 4.13. Phytoavailability of lead fraction after 60 days of incubation

So with the lapse of time, the retention by oxides and organics has far

exceeded that of carbonates and the sequence of the distribution of Pb into different

fractions is in the order, Residual > Oxide > Organic > Carbonate > Exchangeable >

Water Soluble. Among the different ameliorants, the lowest (6.9%) phytoavailable lead

was observed in the treatment which received KH2PO4 as ameliorant followed by those of

zeolites (17.2%), lime (19.6%) and compost (20.4%). As usual, the treatment not

receiving any sort of ameliorant (control) resulted in the highest (25.6%) phytoavailable

lead in the soils. Further, there was slight improvement in soil acidity with highest pH (7.1)

being recorded in the treatment receiving lime application followed by that of KH2PO4

(5.4), while pH was 4.8 in all the other treatments which received zeolites, compost as

ameliorants and even in the 'control' receiving no ameliorates.

^AyV^r^^fXA^rtJ^'-

Differential allocation of lead among various fractions along with the pH observed

in 1:1 soil-water extract of the soils of RV Nagar is made available in Table 4.12. Under

neutral to alkaline conditions (pH>7), if not occurrence at least persistence of applied

calcium carbonate and retention of metals by it can not be overlooked. Under such

conditions, it must be assumed that the carbonate bound fraction is sparingly soluble and

relatively unavailable to the plants. After foreseeing the potential hazard likely to occur in

133

near future, it is prudent to incorporate the carbonate bound metal with water soluble and

exchangeable fractions to declare the labile or mobile pool of heavy metal^^

Table 4.12. Sequential extraction of Pb from lead induced R V Nagar soil at different incubation period after the treatment with different ameliorants^

Treatment Lead Fractions (ppm) Total Pb

ppm

Mobile Pool of Pb, (%)

PH 1:1 Treatment

WS EX CARB OX ORG RES

Total Pb

ppm

Mobile Pool of Pb, (%)

PH 1:1

15 DAYS Control 1.60 2.04 9.57 8.34 12.39 61.26 95.20 13.9 7.2 Zeolite 1.18 1.88 8.42 7.16 16.59 64.57 99.80 11.5 7.5 Lime 1.20 1.47 8.76 6.75 12.70 65.50 96.38 11.9 8.0 KH2PO4 1.20 1.91 6.86 5.46 12.73 69.04 97.20 10.3 6.9 Compost 1.52 2.15 7.22 8.27 13.84 62.60 95.60 11.4 7.6

30 DAYS f

Control 1.64 1.65 10.89 21.20 15.83 45.09 96.30 14.7 7.3 Zeolite 1.33 1.58 7.79 21.15 16.20 48.25 96.30 11.1 7.5 Lime 1.01 0.83 8.54 21.77 15.70 48.15 96.00 10.8 7.9 KH2PO4 0.59 1.35 7.88 16.70 14.72 56.06 97.30 10.1 6.8 Compost 0.79 1.4 8.31 19.48 18.20 48.60 96.78 10.8 7.6 45 DAYS f ^ Control 1.73 1.34 8.38 24.71 18.50 42.44 97.10 11.8 7.3 Zeolite 1.31 1.24 6.21 25.06 18.64 44.44 96.90 9.0 7.5 Lime 0.95 0.42 8.22/ 26.00 17.35 42.86 95.80 10.0 7.9 KH2PO4 0.27 1.00 5.25 19.51 16.82 53.55 96.40 6.8 6.9 Compost 0.55 1.30 5.55 24.39 20.22 44.79 96.80 7.6 7.6 60 DAYS ( ^ Control 0.66 1.06 8.91 25.30 18.64 40.63 95.20 11.2 7.5 Zeolite 0.10 0.38 7.50 26.26 19.27 43.79 97.30 8.20 7.7 Lime 0.56 0.37 7.69 30.14 19.62 39.42 97.80 8.80 8.1 KH2PO4 0.00 0.28 5.50 28.22 18.94 43.96 96.90 6.00 7.1 Compost 0.28 0.36 5.89 32.25 23.25 35.37 97.40/ 6.70 7.7

\NS - water soluble, Ex -Exchangeable, CARB - Carbonate bound, ORG - Organically bound, RES - Residual

134

Sequential extraction of soil samples drawn after 15 days of incubation revealed

the higher efficacy of ameliorants in containing the metal contamination compared to that

of control (Fig. 4.14). .

Control Zeolite Lime KH2P04 Compost Amendments v V


Fig.4.14. Phyto-availability of lead fraction after 15 days of incubation

Among the different treatments involving versatile ameliorants, the lowest

(10.3%) phytoavailable lead was observed in the treatment which received KH2PO4 as

ameliorant followed by those of compost (11.4%), zeolites (11.5%) and agricultural lime

(11.9%). However, the treatment not receiving any ^oft (of ameliorant resulted in the

highest (13.9%) phytoavailable lead in the soils. In general, the phytoavailable Pb

remained lower in all the treatments compared to those of Balehonnur soils. The soil

reaction remained near neutral to alkaline in all the treatments and remained highest (8.0)

in soil amended with lime followed by compost (7.6), zeolites (7.5) and control (7.2); while

the lowest (6.9) was in case of treatment, which received KH2P04as amendment. A close

perusal of the data on the distribution of applied Pb in the treatments which received

different ameliorants revealed that the retention of lead in general followed the sequence

of residual fraction (64.7 - 71.0%) > organic (13.1 - 16.6%) > carbonate (7.1 - 9.1%) >

oxide (5.6 - 8.7%) > exchangeable (1.5 - 2.2%) > water soluble (1.2 - 1.6%) fractions

indicating a clear dominance of residual fraction. In the 'Control' which received only

applied Pb without any amendment the distribution of Pb in different forms was 64.3% i n ^ ^

135

Residual fraction, 13.0% in Organically bound fraction, 8.8% in Oxide bound fraction,

10.1% in carbonate bound fraction, 2.1% in Exchangeable form and 1.7% in Water

Soluble fraction, y^

The allocation of lead in to various fractions was quite different in the soils after 30

days of incubation. It was clear from the results that a part of the labile Pb constituting

both water soluble and exchangeable forms as well as non-labile Pb exclusively from

residual fraction were transformed to enrich oxide, organic and carbonate retained

fractions. The general sequence for the ameliorant treated soils was slightly modified

compared to the one observed in previous case with slight changes for residual fraction

(50.1 - 57.6%) > oxide (17.2 - 22.7%) > organic (15.1 - 18.8%) > carbonate (8.1 - 8.9%)

> exchangeable (0.9 - 1.6%) > water soluble (0.6 - 1.3%) fractions while these fractions

for the treatment 'control' were 46.8, 22.0, 16.4, 11.3, 1.7 and 1.7% respectively. The

lowest (10.1%) phytoavailable lead was observed in the treatment that received KH2PO4

as ameliorant (Fig 4.15)^^

120 100

f 80 a 60 f 40

20 ttm Control Zeolite Lime (^ KH2P04,€ompost

Amendments •4/'^

8.5

7.5

6.5

5.5

•Available Pb pH

Fig. 4.15. Phyto-availability of lead fraction after 30 days of incubation

Both agricultural lime and compost treated soils recorded similar (10.8%)

phytoavailable metal followed by that which received zeolites (11.1%); while the treatment

not receiving any sort of ameliorant resulted in the highest (14.7%) phytoavailable lead in

the soils. In general overall reduction in phytoavailable Pb over time was evident in all the

treatments except in 'control' indicating conspicuous effect of ameliorants in effectively

!36

bridling the contamination. There was no appreciable improvement in soil acidity as the

measured pH values remained unchanged in all the treatments over time.


more interesting features indicating gradual decrease in phytoavailable Pb contents with

the lapse of time. The general sequence of distribution of Pb in various fractions for the

soils amended with different ameliorants remained same as that on the 30'̂ day after

incubation though the oxide and organic fractions were enriched with Pb contents at the

cost of other fractions. The residual fraction (44.67 - 55.5%) > oxide (20.2 - 27.1%) >

organic (17.4 - 20.9%)> carbonate (5.4 - 8.6%) > exchangeable (0.4 -1.3%) > water

soluble (0.3 - 1.4%) fraction were noted for the different treatments while the respective

fractions for the 'control' treatment were 43.7, 25.4, 19.1, 8.6, 1.4 and 1.8%. Among the

different treatments involving versatile ameliorants, the lowest (6.8%) phytoavailable lead

was observed in the treatment which received KH2PO4 as ameliorant followed by those of

compost (7.6%), zeolites (9.0%) and lime (10.0%).

However, the treatment not receiving any sort of ameliorant (control) resulted in the

highest (11.5%) phytoavailable lead in the soils (Fig 4.16). Further, there was no

appreciable change in soil reaction in different treatments with the lapse of time./

120 100

? 80 S 60 f 40

20 0 ton

Control Zeolite Lime (KH2P04 Compost Amendments"^^^>i^

8.5

7.5

6.5

5.5


Fig. 4.16. Phyto-availability of lead fraction after 45 days of incubation

137

Similar trend of oxide and organic fractions being enriched with Pb at the cost of

other fractions was continued in the soils even after 60 days of incubation. Sequence

similar to that at 45 days after incubation was obtained with residual fraction

(36.3 - 45.4%) > oxide (27.0 - 33.1%) > organic (19.5 - 23.9%) > carbonate (5.7 -7.9%)

> exchangeable (0.3 - 0.4%) > water soluble (0 - 0.6%) fractions for the ameliorant

treated soils. The soil under the treatment 'Control' recorded 42.7, 26.6, 19.6, 9.4, 1.1 and

0.7% respectively for Residual, Oxide, Organic, Carbonate, Exchangeable and Water

Soluble fractions of Pb. Among the different ameliorants KH2PO4 resulted into the lowest

(6.0%) phytoavailable lead followed by those of compost (6.7%), zeolites (8.2%) and lime

(8.8%) that is depicted in Fig. 4.17. ^

I 80 Q. 60

Control Zeolite Lime i

138

Among the ameliorants, potassium di-hydrogen phosphate (KH2PO4) was found

most efficient in reducing the phytoavailable Pb in both the soils of Balehonnur (Fig 4.18)

and RV Nagar (Fig 4 . 1 9 ) ^

Control

LL Zeolite Lime

Amendments

I Available Pb (15 DAI) ••Available Pb (60 DAI)

Fig.4.18. Temporal variation of phytoavailable Pb wrt ameliorants in Balehonnur soils

16

_ 1 4

XI tt- 10

I 6 10

I' 0. 2 hM

Control Zeolite KH2P04 Lime KH2P0f Compost Amendments

• Available Pb (15 DAI) • Available Pb (60 DAI)

Fig.4.19. Temporal variation of phytoavailable Pb wrt ameliorants in RV Nagar soils

139

In Balehonnur soils, the phytoavallable Pb reduced from 12.9 to 6.9 per cent upon

incubation with KH2PO4 after 15 and 60 days, respectively. Similarly, in RV Nagar soils

the phytoavallable Pb reduced from 10.3 to 6.0 percent after 15 and 60 days,

respectively. Phosphate has long been known to be effective at stabilizing lead, as

demonstrated by Nriagti (1974). The concept is to induce the formation of highly insoluble

lead phosphate minerals that have a low bioavailability and mobility and are stable under

a variety of environmental conditions (Ruby et al., 1994). Current results were

substantiated by the predecessors who have shown that various forms of phosphate

amendments can be effective at stabilizing lead in soils (Berti and Cunningham, 1997

Boisso'n et al., 1999a, b; Chen et al., 1997; Cotter-Howells-fnd Caporn, 1996

Hettiarachchi apd Pierzynski, 2002; Ma^efal., 1993, 1995; Pierzynsl

140

their tendency to either become fixed in the cage or adsorb on the zeolites surface

(Lepp^, 1990y

The conspicuous dual role of agricultural lime as a conditioner as well as

ameliorant was proved in the current studies as evidenced by the impcovement in soil

acidity and retention of metals in the carbonate form. Lime was found a better alternative

next to that of zeolites in reducing the phytoavailable Pb in both the soils of Balehonnur

and RV Nagar. In Balehonnur soils, the phytoavailable Pb reduced from 27.1 to 19.6

percent upon incubation with lime after 15 and 60 days, respectively. Similarly, in RV

Nagar soils the phytoavailable Pb reduced from 11.9 to 8.8 percent after 15 and 60 days,

respectively. These attenuations may be attributed to the fact that by virtue of reduced

mobility of heavy metals owing to metal hydrolysis and / or co-precipitation with applied

lime in soils. Consequ,ently the phytoavailability of heaw^jnetals would be drastically

reduced (Shuman, 1985; Kabata-Pendias and Pendias, 1992). Lime, a common soil

amendment long used in agriculture, induces a rise in soil pH, causing metals to

precipitate as oxides and carbonates. Lime is anticipated to be effective only for a

relatively short period of time before the pH-buffering capacity is depleted; therefore,

repeated applications are often required (Vangronsveld and Strfimngham, 1998).^

'h f ̂ ^ Compost was found a better option in reducing the phytoavailable Pb in both the

soils of Balehonnur and RV Nagar. In Balehonnur soils, the phytoavailable Pb reduced

from 29.3 to 20.4 percent upon incubation with lime after 15 and 60 days, respectively.

Similarly, in RV Nagar soils the phytoavailable Pb reduced from 114 to 6.7»percapt after

15 and 60 days, respectively. Jordan et al. (2008) reports the HreneTicenJ effect of

application of spent mushroom compost (SMC) in reducing the metal contamination from

the lead-zinc contaminated site. Applicafioniof compost and organic manure to soils

naturally contaminated with zinc (^^^^^^3M^ reduce the zinc accumulation by

Solanum nigrum by 40 and 80% respectively as reported by Marques et al. (gD08). The

results of the present study are in agreement with these findings. Condor et al. (2001)

demonstrated that lime-stabilized bio-solids were capable of immobilizing zinc in smelter-

impacted soils and reduced the eco-toxicity of the soils to earthworms. This suggests that

141

the organic amendment in combination witti lime can reduce the phytoavailability of heavy

metals effectively.

In both the soils of Balehonnur and RV Nagar the over all rating of |meliorate§^for

their efficacy in attenuation of lead was in the order of KH2PO4 > Zeolites > Agricultural

lime > Compost^

4.4.2. Cadmium amelioration

Unlike lead, most of the cadmium remained in the labile or phytoavailable pool

despite amelioration in both the soils. The veracity of Cd contamination was higher in the

soils of Balehonnur compared to that of RV Nagai^X

Results pertaining to the assortment of cadmium among various forms such as

water soluble, exchangeable, carbonate, oxide, organic and residual fractions in the soils

of Balehonnur upon incubation for 60 days are made available in Table 4.13. In general,

the phytoavailable Cd fraction reduced with lapse of time. Sequential extraction of soil

samples drawn after 15 days of incubation revealed relatively higher efficacy of

ameliorants with some exceptions in containing the cadmium contamination compared to

that of control (Fig. 4.20). Among the different treatments involving versatile ameliorants,

the lowest (80.8%) phytoavailable cadmium was observed in the treatment which

received agricultural lime as ameliorant followed by that KH2PO4 (81.5%), Zeolite (86.6%)

and compost (86.9%). The maximum phytoavailable Cd (87.2%) was recorded in 'control"

where the soil did not receive any amendment/^

The retention of cadmium in 'Control' followed the sequence of exchangeable

(53.8%) > carbonate (31.1%) > organic (5.8%) > oxide (4.0%) > residual (2.9%) > water

soluble (2.4%) fractions. A similar trend was observed in all the amended soils also

except that for lime. In the agriculture lime amended soil, the sequence was Carbonate

(45.0%) >Exchangeable (35.6%) > Organic (8.6%) >Oxide (6.7%) > Residual (3.9%)>

Water Soluble (0.2%) fraction/'

142

Table 4.13. Sequential extraction of Cd from cadmium induced Balehonnursoil at different incuation period after the treatment with different ameliorants

Treatment Cadmium Fractions (ppm) Total

Cd

Mobile Pool of

Cd, (%)

pH 1:1 Treatment

Total Cd

Mobile Pool of

Cd, (%)

pH 1:1

WS EX CARB OX ORG RES ppm

Mobile Pool of

Cd, (%)

pH 1:1

15 DAYS Control 2.4 53.2 30.7 4.0 5.7 2.9 98.9 87.2 4.4 Zeolite 2.0 52.2 31.0 4.4 5.3 3.5 98.4 86.6 4.5 Lime 0.2 35.0 44.2 6.6 8.5 3.8 98.3 80.8 6.7 KH2PO4 1.7 37.8 38.0 5.7 8.1 3.8 95.1 81.5 5.2 Compost 1.6 45.0 40.1 4.5 5.2 3.3 99.7 86.9 4.5 30 DAYS Control 1.9 45.8 37.6 9.8 2.6 0.5 98.2 86.9 4.4 Zeolite 1.1 37.9 34.8 8.3 3.6 0.4 86.0 85.7 4.5 Lime 0.1 24.9 40.2 10.0 7.0 0.6 82.8 78.7 6.7 KH2PO4 0.5 36.0 31.1 11.0 5.6 0.5 84.8 79.8 5.2 Compost 0.6 39.4 33.5 9.1 2.2 0.5 85.3 86.2 4.5 45 DAYS Control 2.1 45.0 37.3 7.5 1.8 3.9 97.6 86.5 4.5 Zeolite 2.3 37.5 39.4 8.0 1.9 4.0 93.0 85.1 4.4 Lime 1.3 24.9 40.2 9.5 4.3 7.6 87.8 75.6 7.0 KH2PO4 1.8 29.4 34.7 9.0 4.5 5.4 84.8 77.8 5.1 Compost 2.2 40.0 32.5 6.5 2.5 3.3 87.0 85.9 4.5 60 DAYS Control 3.6 40.3 36.5 7.3 1.6 4.0 93.3 86.2 4.8 Zeolite 3.7 32.0 27.3 6.8 1.3 3.2 74.3 84.8 4.8 Lime 0.3 15.3 35.7 11.0 2.4 5.8 70.5 72.8 7.1 KH2PO4 1.9 20.5 30.3 10.7 2.5 4.7 70.6 74.6 5.4 Compost 3.2 38.3 31.1 8.3 2.2 2.2 85.3 85.1 4.8

WS - water soluble, Ex -Exchangeable, CARB - Carbonate bound, ORG - Organically bound, RES - Residual

The sorting of cadmium in to various fractions was quite different In the soils after

30 days of incubation. It is clear from the results that exchangeable and oxide bound

fractions were enriched at the cost of remaining fractions and the general sequence of

distribution of Cd into various fractions was slightly modified compared to the one

observed in previous case with exchangeable (46.6%) > carbonate (38.3%) > oxide

(10.0%) > organic (2.7%) > water soluble (1.9%) > residual (0.5%) fractions for the

treatment 'control'.

143

120

100

E «° S 60 •a O 40

20

0

b Control Zeolite Lime

Amendments

8 7 6 5

- 4 T 3

2 1 0

X a.

I Totaled [Available Cd PH

Fig. 4.20. Phyto-availability of cadmium fraction after 15 days of incubation

The agriculture lime treated soil had the higher carbonate bound fraction (48.6%)

than the exchangeable fraction (30.1%) followed by oxide (12.1%), organic (8.5%),

residual (0.7%) and water-soluble fractions (0.1%) while the soils under other

amendments followed the pattern exhibited by the treatment 'control'. Coming to the

various treatments involving competent ameliorants, the lowest (78.7%) phytoavailable

cadmium was observed in the treatment which received agricultural lime as ameliorant

followed by those of KH2PO4 (79.8%), Zeolites (85.7%), compost (86.2%) and control

(86.9%) as depicted in Fig. 4 . 2 1 ^

Fig. 4.21. Phiyto-availability of cadmium fraction after 30 days of incubation

144


more interesting features indicating gradual decrease in phytoavailable Cd contents with

the lapse of time. It is evident from the results that the oxide, organic and residual

fractions were enriched with Cd contents at the cost of other fractions. The distribution

sequence of the Cd fractions sequence remained very similar to that observed on the 30"̂

day after incubation with exchangeable (46.1%) > carbonate (38.2%) > oxide (7.7%) >

residual (4.0%) > water soluble (2.2%) > organic (1.8%) fractions for 'Control'. Among the

different treatments involving versatile ameliorants, the lowest (75.6%) phytoavailable Cd

was observed in the treatment which received agricultural lime as ameliorant followed by

KH2PO4 (77.7%), zeolites (85.1%) and compost (85.9%) while the highest (86.5 %) was

reported in the 'control' as shown in Fig. 4 . 2 2 ^

120 T 8 100 -

£- 80 ^

a 60 'b-frVb -fa^ 4 ^ 0 40 20 iDXl | > 3 0 ' ^ ' ^ ' ^ ^ J ^ i 0

Control Zeolite Lime (KH2P04 ̂ Compost Amendments ^ • ^ j l / ' ^

^ H Total Cd ^ ^ Available Cd — -pH j


The typical trend of oxide fraction being enriched with Cd was continued in the

soils even after 60 days of incubation. The sequence of distribution of Cd in various

fractions was exchangeable (43.2%) > carbonate (39.1%) > oxide (7.8%) > residual

(4.3%) > water - soluble {3.9%) > organic (1.7%)) for the 'Control'. Except for lime and

KH2PO4 treated soils, the similar trend was observed. The carbonate fraction dominated

the exchangeable fraction in soils treated with lime and KH2PO4. Among the different

145

treatments involving versatile ameliorants, the lowest (72.8%) phytoavailable cadmium

was observed in the treatment which received agricultural lime as ameliorant followed by

KH2PO4 (74.6%), Zeolites (84.8%) and Compost (85.1%). 'Control', which did not receive

any amendment, recorded the highest phytoavailable Cd (86.2%) as shown in Fig. 4.23.

100 J J 8

iitifirl'i' Control Zeolite Lime Q KH2P04 ICompost

Amendments~V"*»^

^ H Total Cd ^ B i Available Cd pH


Differential allocation of cadmium among various fractions observed in the soils of

RV Nagar is made available in Table 4.14. In general, the phytoavailable Cd fractions

were lower in all the treatments compared to those of Balehonnur soils. The data

obtained from sequential extraction of the samples corresponding to the 15 days after

incubation revealed that the retention of cadmium in various fractions followed the

sequence of exchangeable (43.5%) > carbonate (36.5%) > organic (9.0%) > residual

(6.2%) > oxide (4.5%) > water soluble (0.3%) in the soil under the treatment 'Control',

which did not receive any amendment/'

The soils receiving Zeolites and agricultural lime as amendments had higher

carbonate fractions than the exchangeable fraction while the soils treated with KH2PO4

and compost exhibited portioning sequence similar to that of 'Control'. The variation in

phytoavailable Cd in soil samples drawn after 15 days of incubation with respect to the

different ameliorants is presented in Fig. 4.24/

146

Table 4.14: Sequential Extraction of Cd from cadmium induced R V Nagar soil at different incubation period after the treatment with different ameliorants

^

Treatment Lead Fractions (ppm) Total

Cd

Mobile Pool of Cd, (%)

PH 1:1

Treatment Total Cd


PH 1:1 WS EX CARB OX ORG RES ppm


PH 1:1

15 DAYS Control 0.3 38.5 32.3 4.0 8.0 5.5 88.6 80.2 7.2 Zeolite 0.2 27.9 29.5 4.4 10.4 5.6 78.0 73.8 7.5 Lime 0.1 23.5 35.3 6.1 8.3 4.9 78.2 75.3 8.0 KH2PO4 0.2 39.7 30.2 5.8 9.2 5.1 90.2 77.7 6.9 Compost 0.2 31.7 29.6 4.5 10.8 5.9 82.7. 74.4 ,- 7.6 30 DAYS c r r—

Control 0.5 36.8 38.9 14.5 4.9 0.9 96.5 79.0 7.3 Zeolite 0.3 22.7 33.9 19.2 4.8 0.9 81.8 69.6 7.5 Lime 0.2 21.1 42.1 15.8 6.0 1.1 86.3 73.5 7.9 KH2PO4 0.4 30.9 35.3 15.9 4.8 0.8 88.1 75.6 6.8 Compost 0.4 22.0 35.4 16.6 4.8 1.1 80.3 , 72.0 , 7.6 45 DAYS

147

Control Zeolite Lime fKHaPO^ Compost Amendment

I Total Cd I Available Cd pH


The ameliorating efficacy of the different ameliorants used after/1h^30 days of

incubation is depicted In Fig 4.25. The lowest (69.6%) phytoavailable cadmium was

observed in the treatment which received zeolites as amellorant followed by compost

(72.0%), agriculture lime (73.5%), and KH2PO4 (75.6%). Obviously, the treatment not

receiving any sort of amellorant (control) resulted in the highest (79.0%) phytoavailable

cadmium in the soils. In general, overall reduction In phytoavailable Cd over time was

evident in the treatments that received zeolites and compost as amendments

The sorting of cadmium In to various fractions was quite different in the soils after

30 days of Incubation. The results showed that enriching of oxide and carbonate bound

fractions at the cost of remaining fractions had taken place. The sequence of distribution

of Cd in to various forms was slightly modified compared to the one observed for samples

drawn after 15 days of incubation. The distribution of Cd in to various forms for the

'Control' sample was in the order, carbonate bound (40.3%) > exchangeable (38.1%) >

oxide bound (15.0%>) > organic bound (5.1%) > residual (0.9%) > water-soluble (0.5%).

The similar trend was noticed in all the amended soils also.

Sequential extraction of soil samples drawn after 45 days of incubation

indicated gradual decrease In phytoavailable Cd contents with the lapse of time. It was

evident from the results that the oxide, organic and residual fractions were enriched with

Cd contents at the cost of other fractions. Samples drawn from the treatment which did

148

not receive any ameliorant (control) exhibited a sequence of distribution of Cd into various

fractions which was similar to that observed for the samples drawn after 30 days of

incubation i.e., carbonate (40.4%) > exchangeable (36.9%) > oxide (13.4%) > organic

(7.2%) > residual (1.6%) > water soluble (0.6%) fractions. Though the quantities varied,

the distribution pattern of Cd into various fractions was similar in 'control' as well as

amended soils/

ikm 8.5 8 7.5 7 I

^ 6.5 a-- 6 ' 5.5 f 5

Control Zeolite Lime KH^P04 Compost Amendments P L f - ^ * -I 5 Control Zeolite Lime KH2P04 Compost

Amendmenta^V?' sjy ^IHTotal Cd c : i3 Available Cd pH


149

The sequential extraction of the soils from 'Control', sampled after 60 days of

incubation showed an increase in carbonate bound, oxide bound and organically bound

Cd fractions over those in the 45"̂ day sampled soils. The general sequence of

distribution of Cd into different fractions was carbonate (41.6%) > exchangeable (35.3%)

> oxide (14.2%) > organic (7.9%) > residual (0.8%) > water soluble (0.2%) fractions for

'Control' and all other amended soils except that for zeolites amended soils. The zeolites

amended soils showed slightly higher carbonate bound Cd fraction over the

exchangeable form. Lowest (65.1%) phytoavailable cadmium was observed in the

treatment which received zeolites as ameliorant followed by compost (67.8%), agricultural

lime (69.1%) and KH2PO4 (73.4%). Highest (77.1%) phytoavailable cadmium was

recorded in the treatment (control) not receiving any sort of ameliorant (Fig. 4.27)^

100

I 60 Q.

^ 4 0 +

" 20 +

Control Zeolite Lime ^$H2P04 Amendments

I Total Cd I Available Cd pH


In general, chemical amelioration with agriculture lime was efficient for reducing

the phyto-available cadmium concentrations for soils with pH < 7 while Zeolite was

efficient in bringing down the contamination levels of Cd in soils with higher pH (>7). As

far as cadmium attenuation with agricultural lime as an ameliorant is concerned the

phytoavailable Cd reduced from 80.8 to 72.8 percent in Balehonnur soils over a period of

15 to 60 days after incubation (Fig. 4.28)^^^

150

J 85

1 70

Control Zeolite V h l

Lime , KH2P04^ Compost Amendments 'V__JB^ ' -^ '

Fig.4.28. Temporal variation of phytoavailable Cd wrt ameliorants in Balehonnur soils

Cadmium immobilization with lime may be attributed to tlie metal hydrolysis and /

or co-precipitation with applied lime in soils. Consequently the phytoayailability of heavy

metals would be drastically reduced (ShLupaffT 1985; KabatShPendias and Pendias,

1992). Similar results where lime has been found to be effective at reducing plant uptake

of zinc, but mixed results have been reported for plant uptake of cadmium (Krebs et-al-T

1998; Pierzyn^kr^nd Schwab, 1993).^^

KH2PO4 as an ameliorant could reduce the phytoavailability of Cd from 81.5 to

74.6% in these soils. As reported by different workers Cd was precipitated upon

application of phosphate compounds (Brude^pld et al., 1963; lngrajjj.^t al., 1992; Xy-and'

Schwar tz^ 994) and generally, the precipitation reactions were of lower magnitude

entirely dependent on prevailing soil conditions as well as sufficiency of gestation period.

The similar reactions might have resulted in lower attenuation of c a d m i u m ^

In the soils of R V Nagar phytoavailable cadmium content was reduced from 73.8

to 65.0% in Zeolites treated soil followed by Compost which resulted into a reduction of

phytoavailable Cd from 74.4 to 67.8% during the same period of incubation (Fig. 4 .29 ) . ^

151

^ 90 -1

^ 85

^ 80 .

i 75

^ 70 TO

o % 65 ^ 60 ^

L h k ^ Compost

^ 90 -1

^ 85

^ 80 .

i 75

^ 70 TO

o % 65 ^ 60 ^ Control Zeolite Lime /KH2F04

Amendments — v ' ' v ^ ^ Compost

^ 90 -1

^ 85

^ 80 .

i 75

^ 70 TO

o % 65 ^ 60 ^

• Available Cd (15 DAI) • Available Cd (60 DAI)

^ Compost

Fig.4.29. Temporal variation of phytoavailable Cd wrt ameliorants in R V Nagar soils

Present results are well supported by the previous works where zeolites and

aluminosilicates have been demonstrated to have a high retention capacity for metals and

can be used as stabilizing agents (Boisson'et al., 1999a; Chlopecl

152

The efficacy in attenuation of lead by the amelioratives was in the order of

KH2PO4 > Zeolites > Agricultural lime > Comoost fpr.bpth the soils of Balehonnur and RV

Nagar. However, the sequence of(^mellorate^ varied in attenuating cadmium in both the

soils. In Balehonnur soils the sequence with Lime > KH2PO4 > Zeolites > Compost was

effective in amelioration of cadmium while a slightly different sequence was observed for

that in R V Nagar soils with Zeolites > Compost > Lime > KH2P04^

Summary

Soils cropped to coffee receive heavy doses of chemical fertilizers, rock

phosphates and processed municipal sewage wastes and thus likely to be contaminated

with heavy metals like lead and cadmium metals. These metals when present in excess in

soils are bio-available and also can be leached to nearby water sources causing potential

toxicity to(pante)and/or animals. This study evaluated the possibilities of remediation by

means of chemical amendment approach to immobilize these potentially dangerous

elements in soils thereby decreasing their availability to plants. A soil incubation study for

over 60 days was carried out in two different coffee soils (pH 5.6 and 7.2) by amending

them with Potassium di-hydrogen orthophosphate, agricultural lime, zeolite and compost^

It was found that all these chemical amendments were effective in stabilizing lead

and cadmium metals in coffee soils with different efficacies. Potassium di-hydrogen

orthophosphate was the most effective chemical in attenuating lead in coffee growing

soils followed by Zeolite, agricultural lime and compost. In the case of cadmium,

agricultural lirne was superior to other amendments in moderately acidic soils (pH-5.6)

while Zeolite^ was found to be more effective in slightly higher pH (7.2) soils in

attenuating cadmium. All the amendments reduced the bioavailability of both lead and

cadmium. Chemical reaction between the phosphate and lead possibly resulted in the

formation of lead pyromorphites similar to highly insoluble lead phosphates thereby

decreasing its bioavailability in soils. The carbonate content in the agricultural lime also

seemed to play a key role in the chemical stabilization of both lead and cadmium in the

soils and helped consequently in decreased availability of these metals,/

Chapter-4 Remediation of Heavy Metal Infested Coffee ...shodhganga.inflibnet.ac.in/bitstream/10603/86487/11/11_chapter 4.pdf · Remediation of Heavy Metal Infested Coffee Growing

Documents