LAND POLLUTION (GM HETTIARACHCHI, SECTION EDITOR) Pesticide Pollution in Agricultural Soils and Sustainable Remediation Methods: a Review Shixian Sun 1 & Virinder Sidhu 2 & Yuhong Rong 3 & Yi Zheng 1,4 # Springer International Publishing AG, part of Springer Nature 2018 Abstract An increasing number of pesticides have been used in agriculture for protecting the crops from pests, weeds, and diseases but as much as 80 to 90% of applied pesticides hit non-target vegetation and stay as pesticide residue in the environment which is potentially a grave risk to the agricultural ecosystem. This review gives an overview of the pollution in agricultural soils by pesticides, and the remediation techniques for pesticide-contaminated soils. Currently, the remediation techniques involve phys- ical, chemical, and biological remediation as well as combined ways for the removal of contaminants. The microbial functions in rhizosphere including gene analysis tools are fields in remediation of pesticide-contaminated soil which has generated a lot of interest lately. However, most of those studies were done in greenhouses; more research work should be done in the field conditions for proper evaluation of the efficiency of the proposed techniques. Long-term monitoring and evaluation of in situ remediation techniques should also be done in order to assess their long-term sustainability and practical applications in the field. Keywords Pesticides . Agricultural soil . Pollution . Sustainable remediation Introduction Pesticides have been present as an essential part of agriculture and have played a decisive role in protecting crops and live- stock from yield reductions for many decades. Pesticide ap- plication is still considered the most effective and accepted means for plant crop protection from pests [79]. However, as little as 1% of an applied pesticide reaches the target pest and the remainder ends up in soil, water, and air, ultimately enter- ing our food chain and affecting non-target species including humans [63, 86], flora and fauna, and soil enzyme activity [21, 28]. As much as 80 to 90% of pesticides that are applied to crops hit non-target vegetation directly, or can drift or volatil- ize from the treated area off-site and contaminate air, soil, and non-target plants. About 80% of all applied pesticides could be detected, with half of these residues found as transforma- tion products (TPs) with a persistence of more than a decade. Forty-seven percent of the TPs were detected in the top soils of Switzerland where Bparent compound^ was applied [25]. Groundwater may be polluted by pesticides via leaching [93]. Pesticides pose a huge risk to human beings indirectly, via food chain and contamination of natural resources. For exam- ple, pesticide pollution has been implicated in the rise of Bcancer villages^ which stem from the mortality rate of cancer being significantly higher than average because of widespread pesticide use [64]. Migrant workers and their offspring have exhibited negative and latent health effects stemming from chronic exposure to pesticides and their lingering persistence in the environment, especially the endocrine disruptor com- pounds (EDC) often leading to an increased risk of obesity and neurological issues [82, 96]. Chlorpyrifos, an organo- phosphate neurotoxic insecticide, poses a significant risk to children’ s intelligent quotients (IQs) via contamination of food crops [31]. Benfuracarb is cytotoxic to human cells [24]. Anticholinesterase pesticide poisoning is associated with an increased risk of hypothyroidism [38, 39]. This article is part of the Topical Collection on Land Pollution * Yi Zheng zhengyi–[email protected] 1 Faculty of Landscape Architecture, Southwest Forestry University, Kunming 650224, People’ s Republic of China 2 Department of Civil, Environmental and Ocean Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA 3 Landscape Architecture College, Southwest Forestry University, Kunming 650224, People’ s Republic of China 4 Yunnan Provincial Department of Education, Kunming 650223, People’ s Republic of China Current Pollution Reports https://doi.org/10.1007/s40726-018-0092-x
Pesticide Pollution in Agricultural Soils and Sustainable Remediation Methods: a Review
Jan 02, 2023
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Pesticide Pollution in Agricultural Soils and Sustainable Remediation Methods: a ReviewPesticide Pollution in Agricultural Soils and Sustainable Remediation Methods: a Review
Shixian Sun1 & Virinder Sidhu2
& Yuhong Rong3 & Yi Zheng1,4
# Springer International Publishing AG, part of Springer Nature 2018
Abstract An increasing number of pesticides have been used in agriculture for protecting the crops from pests, weeds, and diseases but as much as 80 to 90% of applied pesticides hit non-target vegetation and stay as pesticide residue in the environment which is potentially a grave risk to the agricultural ecosystem. This review gives an overview of the pollution in agricultural soils by pesticides, and the remediation techniques for pesticide-contaminated soils. Currently, the remediation techniques involve phys- ical, chemical, and biological remediation as well as combined ways for the removal of contaminants. The microbial functions in rhizosphere including gene analysis tools are fields in remediation of pesticide-contaminated soil which has generated a lot of interest lately. However, most of those studies were done in greenhouses; more research work should be done in the field conditions for proper evaluation of the efficiency of the proposed techniques. Long-term monitoring and evaluation of in situ remediation techniques should also be done in order to assess their long-term sustainability and practical applications in the field.
Keywords Pesticides . Agricultural soil . Pollution . Sustainable remediation
Introduction
Pesticides have been present as an essential part of agriculture and have played a decisive role in protecting crops and live- stock from yield reductions for many decades. Pesticide ap- plication is still considered the most effective and accepted means for plant crop protection from pests [79]. However, as little as 1% of an applied pesticide reaches the target pest and the remainder ends up in soil, water, and air, ultimately enter- ing our food chain and affecting non-target species including humans [63, 86], flora and fauna, and soil enzyme activity [21,
28]. As much as 80 to 90% of pesticides that are applied to crops hit non-target vegetation directly, or can drift or volatil- ize from the treated area off-site and contaminate air, soil, and non-target plants. About 80% of all applied pesticides could be detected, with half of these residues found as transforma- tion products (TPs) with a persistence of more than a decade. Forty-seven percent of the TPs were detected in the top soils of Switzerland where Bparent compound^ was applied [25]. Groundwater may be polluted by pesticides via leaching [93].
Pesticides pose a huge risk to human beings indirectly, via food chain and contamination of natural resources. For exam- ple, pesticide pollution has been implicated in the rise of Bcancer villages^which stem from the mortality rate of cancer being significantly higher than average because of widespread pesticide use [64]. Migrant workers and their offspring have exhibited negative and latent health effects stemming from chronic exposure to pesticides and their lingering persistence in the environment, especially the endocrine disruptor com- pounds (EDC) often leading to an increased risk of obesity and neurological issues [82, 96]. Chlorpyrifos, an organo- phosphate neurotoxic insecticide, poses a significant risk to children’s intelligent quotients (IQs) via contamination of food crops [31]. Benfuracarb is cytotoxic to human cells [24]. Anticholinesterase pesticide poisoning is associated with an increased risk of hypothyroidism [38, 39].
This article is part of the Topical Collection on Land Pollution
* Yi Zheng zhengyi–[email protected]
1 Faculty of Landscape Architecture, Southwest Forestry University, Kunming 650224, People’s Republic of China
2 Department of Civil, Environmental and Ocean Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA
3 Landscape Architecture College, Southwest Forestry University, Kunming 650224, People’s Republic of China
4 Yunnan Provincial Department of Education, Kunming 650223, People’s Republic of China
Aims and Scope
The aim of this review is to highlight pesticide pollution of arable soils, appraise the techniques used to clean the pesticide pollutants from farmland soils, and evaluate the mechanisms underpinning the remediation of contaminated farmland soils. Knowledge of the effects of soil pollutants will enhance an understanding of the increased threat by agro-chemicals, es- pecially by pesticides, which can probably be used as a refer- ence by practitioners who will work on the restoration of con- taminated farmland soils. This review summarizes and evalu- ates (1) the recent research on pesticide residue in farmland soils and (2) established remediation strategies and mecha- nisms, especially regarding pesticide contaminants. Other
contaminants and media other than farmland soils (e.g., groundwater) are outside the scope of this review.
Agricultural Soils Polluted by Pesticides
Agricultural chemicals consist of pesticides and fertilizers. In modern agricultural systems, pesticides are defined as special bioactivators, also known early on as economic poisons in the USA [122, 123]. Pesticides are mostly or- ganic chemicals used in agricultural systems. Pesticides are comprised of insecticides, bactericides, and herbicides according to their functions. Based on the chemical struc- ture, they include organo-phosphorus, organo-chlorines, nitrogen-benzenes, phenols, metallo-organics, and other compounds. The increasing use of pesticides has been one of the major non-point sources of pollution in agri- culture [66]. Seventy percent of pesticides used in agri- culture enter the soils leading to farmland soil pollution by the pesticide residues [108]. In recent years, herbicides represented 30–40% of all pesticides used in agriculture, and in the last 10 years, the area of chemical weed control has increased to 31 million ha−2 in China [106]. In the global pesticide market, insecticides and bactericides make up 30 and 26%, respectively, of the pesticide usage in agriculture in 2014 [128].
The adverse effects of pesticides have been increasing due to the improper use of pesticides induced by a lack of aware- ness and pesticide overuse which has been reported in rice, cotton, maize, and wheat production [45]. Pesticides affect soil quality and agricultural production in various ways. An increase in the concentration of herbicides above their recom- mended field application rates could change the growth and activities of microorganisms, influencing nutrient cycling in soil [20]. It has been reported that prodiamine, indaziflam, and isoxaben reduced root mass of hybrid Bermuda grass relative to non-treated plants and these pre-emergent herbicides re- duced the accumulation of macro- and micro-nutrients such as phosphorus (P), sulfur (S), potassium (K), magnesium (Mg), and manganese (Mn) in the foliar tissues of the affected plants [11].
The use of insecticides (acetamiprid and carbofuran) at field application rates in the groundnut fields stimulated the activities of enzymes (arylamidase and myrosinase); however, higher concentrations of these pesticides were toxic to the enzyme activities in black and red clay soils [71]. Sulfur is an essential nutrient for agricultural crop production; pesti- cides influence agricultural production by changing the avail- ability of specific nutrients [105]. The application of monocrotophos significantly changed the rate of sulfur oxida- tion in black and red soils in India with enhancing sulfur oxidation after 7 and 14 days of pesticide application alone or in combination with mancozeb in the black soil [105].
Curr Pollution Rep
Different Types of Pesticides in the Environment
Organophosphorus pesticides (OPs) are an increasing concern due to a potential risk to wildlife and human health, and they are among the most frequently detected pesticides in contaminated soils [8]. In the agricultural soils of the Yangtze River Delta of China, 93% of soil samples contained OPs, with total concen- trations of nine OPs ranging from < 3 to 521 ng g−1 dry weight, with a mean of 65 ng g−1 [80]. The organochlorine pesticides (OCs), many of them listed as persistent organic pollutants (POPs) and prohibited for use, were still detected in soils and air because of their persistence in the environment [33]. In the testing of soil samples, 14 OCs with an average of 57 ng g−1
were found in the soils of Wangyanggou River in Shijiazhuang City, China and 2,2-bis(4-chlorophenyl)-1,1,1-trichloroethane pesticides (DDTs) were the dominant compounds in surface water, sediments, soils, and maize seeds [120]. All 45 soil sam- ples from the vegetable fields in Wuhan, Yichang, and Xiangyang (Hubei Province) contained P,P′-DDT and P,P′- DDE as the main contaminants [121]. Three types of OCs were detected in all soil samples from the upper reaches of Haihe River with a total concentration of OCs as 139 ng g−1 and average of 40 ng g−1 DDTs and their metabolites 1-chloro- 2,2-bis(4′-chlorophenyl)ethylene (DDMU), dodecyl-beta-D- maltoside (DDM), benzene-1,2-dicarboxylicaciddibutylester (DBP) and hexachlorocyclohexane pesticides (HCHs) were the main pollutants in the soil as a combination of their early usage and new input in some areas [83].
Anti-cholinestearase pesticides, including organophos- phates and carbamates are the most common cause of pesti- cide poisoning in the world [37, 57]. Some POP pesticides, such as endosulfan, pose an environmental risk in agricultural soils through the practice of straw incorporation and sedimen- tation, even though the main risk in the Breceiving-retention- release^ route is the atmosphere [74]. The fungicide cyazofamid has a short life in differently textured agricultural soils and therefore has little chance of contaminating ground- water [102]. OCs and their metabolites pose a grave risk in agricultural soils as OCs were detected in 27 of 29 soil sam- ples tested in Turkey and ranged from 6 to 1090 μg kg−1 dry soil in areas where OCs were heavily used between the 1940s and 1980s in Turkey [2]. 4,4′-DDE was present above the acceptable risk levels in the agricultural soils of Mersin District in Turkey [2].
Sometimes, obsolete pesticides pollute the agricultural and surrounding soil because of improper disposal and persistence in the environment. Some banned chlorinated pesticides have been quantified in surface soils and raw foods (meat, dairy, and plants) from four rural areas of Tajikistan from 2011 to 2014. DDTwas consistently measured as the highest individ- ual pesticide at each of the four sampling areas, along with gluconodeltalactone (BHC) isomers and endosulfan [9]. Some disposed POPs including 4500 dumps of obsolete pesticides
decreased to 1033 with huge efforts in Ukraine by the end of 2014 [51]. However, the Polygon site remains contaminated and requires further assessment and remediation because of hexachlorobenzene (HCB) waste [51].
In the last two decades, pesticides have posed a threat to the inhabitants and livestock of the White Nile and Gezira states because of unprotected stocking and agricultural systems [76]. In China (Inner Mongolia), 21 OCPs were detected in agricul- tural soils (102 ng g−1) and pastoral areas (0.2–24 ng g−1) with HCHs and DDTs being the main contaminants [127]. In the soils supporting different types of vegetation, the largest res- idues of OCPs, HCHs, and DDTs were present in vegetables, watermelon patches, and soybean fields [127]. The OC resi- dues were higher in agricultural soils as compared to pastoral areas [127]. Therefore, barring conventional detection, geno- mic tools were used for assessing the effects of pesticides on agro-ecosystems [43]
Remediation of Pesticide-Contaminated Agricultural Soils
General Remediation Techniques for Organic Chemicals
Remediation methods include (1) ex situ method, in which contaminated soil is excavated and transported to another lo- cation for treatment, (2) on-site, in which contaminated soil is excavated and treated on-site before returning to the original state, and (3) in situ, in which the contamination is treated on- site without excavating and removing the contaminated soil [88]. The selection of remediation method is dependent upon whether the pesticide contamination is localized or diffused in the agricultural soils [73]. Ex situ methodwas commonly used as the soil remediation method earlier, but it has several draw- backs including the high cost of soil excavation and transport in addition to destroying the ecosystem. Therefore, in situ restoration has become the key focus recently [116].
Polluted soil can be remediated using physical, chemical, and biological techniques [26, 44]. These relevant techniques are (1) bioremediation, (2) phytoremediation, (3) chemical ox- idation, (4) surfactant extraction, (5) electrokinetic remedia- tion, and (6) thermal desorption. Although, the physical and chemical techniques are suitable for the remediation of pesticide-contaminated agricultural soil. However, those tech- nologies are mainly used for industry-impacted soil, seldom recommended for remediation of the extensive areas of agri- cultural soil that are contaminated by organic chemicals, be- cause physical and chemical techniques require high equip- ment and treatment costs and may lead to damage of the bio- logical and chemical qualities of soil [58, 107]. Compared with physical and chemical remediation, bioremediation, phytoextraction and phytovolatilization are biological
Curr Pollution Rep
approaches used to remove and detoxify organic contaminants in agricultural soils [59, 78, 124]. Bioremediation alone was usually unable to remove persistent and highly toxic contam- inants from agricultural soil within a shorter time [38, 39]. However, bioremediation enhanced by surfactants is a prom- ising technology for improving the bioavailability and remov- al efficiency of organic pollutants in agricultural soil [46, 77, 109, 117, 125, 126]. This list does not include all remediation strategies, but rather, it focuses on some established ap- proaches that have accompanying literature assessing the soil properties. Even though these techniques are used for pesticide remediation, the primary application may be for other types of contaminants such as electrokinetic remediation, which is pri- marily applied to remediate heavy metal contamination of soils. Thus, information provided in this review may be appli- cable beyond pesticide contamination of agricultural soils.
Remediation Technologies for Pesticides
Bioremediation reduces pesticide contamination of agricultural soils by improving natural biodegradation processes via meta- bolic activities of microorganisms, and it is becoming popular for being an efficient, cost-effective, and environment-friendly in situ treatment [88, 92]. Pesticide contamination of agricul- tural soils represents non-point source contaminants and ex situ chemical remediation technologies have been used earlier [73]. However, chemical remediation methods are unrealistic for diffused pollution of agricultural soils by pesticides. Instead, in situ bioremediation can be a better treatment [118]. Bioremediation involves phytoremediation and microbial re- mediation. Phytoremediation of pesticides from soil is based upon plant uptake, vegetation degradation, volatilization, and combined degradation by root exudates and rhizosphere mi- croorganisms [62]. The degradation rate of deltamethrin in soil had a direct relationship with microbial activity in soil [42]. Bacterial populations with P450 cytochrome genes positively influenced the aerobic bioremediation of pesticides [22]. Vetiver (Chrysopogon zizanoides) is suitable for phyto- stabilization of moderately dioxin-contaminated sites [71].
Electrokinetic soil flushing (EKSF) is used for the remedia- tion of soils polluted with different contaminants [111]. When the polluted soil is subjected to an electric field between anodes and cathodes, the contaminants in the soil can be removed or transferred into the flushing fluid that can then be treated or mobilized via electro-osmosis, electromigration, and electro- phoresis. The EKSF process used for the removal of pesticides from contaminated soils has become a hot topic of discussion in the remediation community [115] and has recently been com- bined with other remediation technologies such as bioremedi- ation and permeable reactive barriers [89, 111]. Several studies have described the rhizoremediation of polychlorinated biphe- nyls (PCBs), dioxins, decabromodiphenyls, phenanthrene, pyrene, and heavy metals [31, 34, 98, 114]. The use of a
combination of plant species and microbial strains has brought the spotlight on remediation [114].
Sustainable Remediation Methods for Agricultural Soils
For agricultural soils polluted by pesticides, most in situ sus- tainable remediation technologies can be used. There is a con- siderable impetus to develop bioremediation technologies as well as combined technologies for use such as rhizosphere re- mediation, fertilized-assisted remediation, and rhizoremediation combined with microbial remediation. The key enzymes and fungi which are helpful in pesticide removal along with poten- tial interactions with other soil microorganisms should be researched further in the future of rhizosphere remediation tech- nology [68]. An increasing research focus is on the combined techniques for remediation such as electrokinetic remediation with biological permeable reactive barriers for the remediation of soil polluted by insoluble organics [69]. Ultrasound-assisted soil washing has been combined with bioaugmentation for the remediation of soil polluted by polycyclic aromatic hydrocar- bons (PAHs) and heavy metals [14]. Tourmaline catalyzed Fenton-like reaction (TCFR) combined with Phanerochaete chrysosporium (TCFR + P) was used for the removal of polybrominated diphenyl ethers (PBDEs) in field soil micro- cosms [52]. Nanoremediation [zero valent iron nanoparticles (nZVI)] combined with electrokinetics was used for the remov- al of PCBs from soil, with the removal rate increasing from 20% to > 75% in contaminated soils [29]. Fenton-like oxidation combined with soil washing can potentially be an approach for the remediation of soil contaminated by PCBs [65].
Anaerobic or facultative anaerobic microflora and phytoremediation have been combined for treating the soil contaminated by POPs (DDTs and trifluralin) [41]. Gene tools were used for biomineralization of soil contaminated with pesticides [23]. Microbes and transgenic plants can also be used for the remediation of pesticide-contaminated soils [40].
Discussion
As Table 1 shows, some physical remediation technologies were used for the removal of pesticide-contaminated soil, such as electrokinetic soil fences (EKF) [89], electrokinetic soil flushing [89, 90, 101], soil washing, and solar-powered elec- trokinetic remediation [104]. The major mechanism of those technologies was that the pesticide was removed from the contaminated soil to the flushing fluids through adsorption, desorption, and volatilization. Some chemical remediation technologies, such as enhanced electrokinetic-Fenton [10], advanced oxidation process [86], and photo-degradation [84] were used for pesticide-contaminated soil through special chemical reactions (abiotic degradation). Both physical and
Curr Pollution Rep
Table 1 Current research work on the remediation and efficiency of treatment strategies of pesticide-polluted soils (2015–2017)
Remediation methods Pesticide and efficiency of treatment Reference
Advanced biodegradation Biochar resulted in significant reduction in soil DDT levels and soil microbial activity after 60 days.
[30]
Advanced oxidation process 86–88% degradation efficiency was achieved in about 3.5 h under UV light or enhanced sunlight; 99.86% of degradation was achieved in UV/TiO2/K2S2O8 system in the same irradiation time.
[86]
Bioaugmentation 95% of initial spiked terbuthylazine (TBA) was removed from soil microcosms upon bioaugmentation with ammonium-grown Arthrobacter aurescens TC1 inocula dur- ing the first 3 days. Around 70% on average of initial TBA remained in the non-bioaugmented control soil during the 14 days.
[101]
Electrokinetic soil fences (EKF) An extra 26.8% of oxyfluorfen was removed with surfactant (calcium dodecyl benzene sulfonate).
[89]
Electrokinetic soil flushing (EKSF) More than 80% of pesticide (30 mg/kg) was eliminated, 2, 4-D was removed by 95% after 15 days of treatment.
[101]
Electrokinetic soil flushing (EKSF) 50% of the initial 2, 4-D from the soil was eliminated; 25% remained in the soil, and the remaining 25% was volatilized after 40 days treated by the electrolyte wells.
[89]
Electro-remediation More than 22% of the spiked (20 mg kg−1) 2, 4-D transported to the flushing fluids, 57% of removal of 2, 4-D by volatilization. The main mechanism for the 2, 4-D’s removal was volatilization.
[90]
Enhanced electrokinetic-Fenton A maximum of 67% of the triazoles from a real vineyard soil (north-west of Spain) was degraded by enhanced electrokinetic-Fenton treatment after 27 days.
[10]
[99]
Microbial degradation Rhizobacteria were isolated from Okra (Abelmoschus esculentus L.); S10 and S20 had the maximum pesticide tolerance for bifenthrin pesticide degradation.
[75]
[12]
[13]
[32]
Microbial degradation The morphological, biochemical and 16S rRNA gene sequence analysis confirmed that the isolated bacterium for dichlorvos degradation is Pseudomonas stutzeri smk.
[48]
Microbial degradation Cyhalothrin and other pyrethroids could be degraded by Bacillus thuringiensis and some metabolites were identified and degradation pathway by cleavage of both the ester linkage and diary bond in a microorganism.
[54]
Microbial degradation Bacteria and putative genes confirmed pentachlorophenol (PCP) dechlorination and phenol degradation accomplished in segments 0–565 cm and 0–865 cm, respectively, contributing to a high PCP mineralization rate of 3.8665 μM d 611.
[55]
Microbial degradation Strain JPL-2 was isolated; the chain length of the alcohol moiety strongly affected the hydrolysis activity of the FeH (100 mg L−1) toward aryloxyphenoxy propanoate (AOPP) herbicides.
[61]
Microbial degradation Cypermethrin-degrading Bacillus strain SG2 was isolated which degraded the compound up to 81.6% within 15 days under standard growth conditions in minimal medium.
[81]
Microbial…
Shixian Sun1 & Virinder Sidhu2
& Yuhong Rong3 & Yi Zheng1,4
# Springer International Publishing AG, part of Springer Nature 2018
Abstract An increasing number of pesticides have been used in agriculture for protecting the crops from pests, weeds, and diseases but as much as 80 to 90% of applied pesticides hit non-target vegetation and stay as pesticide residue in the environment which is potentially a grave risk to the agricultural ecosystem. This review gives an overview of the pollution in agricultural soils by pesticides, and the remediation techniques for pesticide-contaminated soils. Currently, the remediation techniques involve phys- ical, chemical, and biological remediation as well as combined ways for the removal of contaminants. The microbial functions in rhizosphere including gene analysis tools are fields in remediation of pesticide-contaminated soil which has generated a lot of interest lately. However, most of those studies were done in greenhouses; more research work should be done in the field conditions for proper evaluation of the efficiency of the proposed techniques. Long-term monitoring and evaluation of in situ remediation techniques should also be done in order to assess their long-term sustainability and practical applications in the field.
Keywords Pesticides . Agricultural soil . Pollution . Sustainable remediation
Introduction
Pesticides have been present as an essential part of agriculture and have played a decisive role in protecting crops and live- stock from yield reductions for many decades. Pesticide ap- plication is still considered the most effective and accepted means for plant crop protection from pests [79]. However, as little as 1% of an applied pesticide reaches the target pest and the remainder ends up in soil, water, and air, ultimately enter- ing our food chain and affecting non-target species including humans [63, 86], flora and fauna, and soil enzyme activity [21,
28]. As much as 80 to 90% of pesticides that are applied to crops hit non-target vegetation directly, or can drift or volatil- ize from the treated area off-site and contaminate air, soil, and non-target plants. About 80% of all applied pesticides could be detected, with half of these residues found as transforma- tion products (TPs) with a persistence of more than a decade. Forty-seven percent of the TPs were detected in the top soils of Switzerland where Bparent compound^ was applied [25]. Groundwater may be polluted by pesticides via leaching [93].
Pesticides pose a huge risk to human beings indirectly, via food chain and contamination of natural resources. For exam- ple, pesticide pollution has been implicated in the rise of Bcancer villages^which stem from the mortality rate of cancer being significantly higher than average because of widespread pesticide use [64]. Migrant workers and their offspring have exhibited negative and latent health effects stemming from chronic exposure to pesticides and their lingering persistence in the environment, especially the endocrine disruptor com- pounds (EDC) often leading to an increased risk of obesity and neurological issues [82, 96]. Chlorpyrifos, an organo- phosphate neurotoxic insecticide, poses a significant risk to children’s intelligent quotients (IQs) via contamination of food crops [31]. Benfuracarb is cytotoxic to human cells [24]. Anticholinesterase pesticide poisoning is associated with an increased risk of hypothyroidism [38, 39].
This article is part of the Topical Collection on Land Pollution
* Yi Zheng zhengyi–[email protected]
1 Faculty of Landscape Architecture, Southwest Forestry University, Kunming 650224, People’s Republic of China
2 Department of Civil, Environmental and Ocean Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA
3 Landscape Architecture College, Southwest Forestry University, Kunming 650224, People’s Republic of China
4 Yunnan Provincial Department of Education, Kunming 650223, People’s Republic of China
Aims and Scope
The aim of this review is to highlight pesticide pollution of arable soils, appraise the techniques used to clean the pesticide pollutants from farmland soils, and evaluate the mechanisms underpinning the remediation of contaminated farmland soils. Knowledge of the effects of soil pollutants will enhance an understanding of the increased threat by agro-chemicals, es- pecially by pesticides, which can probably be used as a refer- ence by practitioners who will work on the restoration of con- taminated farmland soils. This review summarizes and evalu- ates (1) the recent research on pesticide residue in farmland soils and (2) established remediation strategies and mecha- nisms, especially regarding pesticide contaminants. Other
contaminants and media other than farmland soils (e.g., groundwater) are outside the scope of this review.
Agricultural Soils Polluted by Pesticides
Agricultural chemicals consist of pesticides and fertilizers. In modern agricultural systems, pesticides are defined as special bioactivators, also known early on as economic poisons in the USA [122, 123]. Pesticides are mostly or- ganic chemicals used in agricultural systems. Pesticides are comprised of insecticides, bactericides, and herbicides according to their functions. Based on the chemical struc- ture, they include organo-phosphorus, organo-chlorines, nitrogen-benzenes, phenols, metallo-organics, and other compounds. The increasing use of pesticides has been one of the major non-point sources of pollution in agri- culture [66]. Seventy percent of pesticides used in agri- culture enter the soils leading to farmland soil pollution by the pesticide residues [108]. In recent years, herbicides represented 30–40% of all pesticides used in agriculture, and in the last 10 years, the area of chemical weed control has increased to 31 million ha−2 in China [106]. In the global pesticide market, insecticides and bactericides make up 30 and 26%, respectively, of the pesticide usage in agriculture in 2014 [128].
The adverse effects of pesticides have been increasing due to the improper use of pesticides induced by a lack of aware- ness and pesticide overuse which has been reported in rice, cotton, maize, and wheat production [45]. Pesticides affect soil quality and agricultural production in various ways. An increase in the concentration of herbicides above their recom- mended field application rates could change the growth and activities of microorganisms, influencing nutrient cycling in soil [20]. It has been reported that prodiamine, indaziflam, and isoxaben reduced root mass of hybrid Bermuda grass relative to non-treated plants and these pre-emergent herbicides re- duced the accumulation of macro- and micro-nutrients such as phosphorus (P), sulfur (S), potassium (K), magnesium (Mg), and manganese (Mn) in the foliar tissues of the affected plants [11].
The use of insecticides (acetamiprid and carbofuran) at field application rates in the groundnut fields stimulated the activities of enzymes (arylamidase and myrosinase); however, higher concentrations of these pesticides were toxic to the enzyme activities in black and red clay soils [71]. Sulfur is an essential nutrient for agricultural crop production; pesti- cides influence agricultural production by changing the avail- ability of specific nutrients [105]. The application of monocrotophos significantly changed the rate of sulfur oxida- tion in black and red soils in India with enhancing sulfur oxidation after 7 and 14 days of pesticide application alone or in combination with mancozeb in the black soil [105].
Curr Pollution Rep
Different Types of Pesticides in the Environment
Organophosphorus pesticides (OPs) are an increasing concern due to a potential risk to wildlife and human health, and they are among the most frequently detected pesticides in contaminated soils [8]. In the agricultural soils of the Yangtze River Delta of China, 93% of soil samples contained OPs, with total concen- trations of nine OPs ranging from < 3 to 521 ng g−1 dry weight, with a mean of 65 ng g−1 [80]. The organochlorine pesticides (OCs), many of them listed as persistent organic pollutants (POPs) and prohibited for use, were still detected in soils and air because of their persistence in the environment [33]. In the testing of soil samples, 14 OCs with an average of 57 ng g−1
were found in the soils of Wangyanggou River in Shijiazhuang City, China and 2,2-bis(4-chlorophenyl)-1,1,1-trichloroethane pesticides (DDTs) were the dominant compounds in surface water, sediments, soils, and maize seeds [120]. All 45 soil sam- ples from the vegetable fields in Wuhan, Yichang, and Xiangyang (Hubei Province) contained P,P′-DDT and P,P′- DDE as the main contaminants [121]. Three types of OCs were detected in all soil samples from the upper reaches of Haihe River with a total concentration of OCs as 139 ng g−1 and average of 40 ng g−1 DDTs and their metabolites 1-chloro- 2,2-bis(4′-chlorophenyl)ethylene (DDMU), dodecyl-beta-D- maltoside (DDM), benzene-1,2-dicarboxylicaciddibutylester (DBP) and hexachlorocyclohexane pesticides (HCHs) were the main pollutants in the soil as a combination of their early usage and new input in some areas [83].
Anti-cholinestearase pesticides, including organophos- phates and carbamates are the most common cause of pesti- cide poisoning in the world [37, 57]. Some POP pesticides, such as endosulfan, pose an environmental risk in agricultural soils through the practice of straw incorporation and sedimen- tation, even though the main risk in the Breceiving-retention- release^ route is the atmosphere [74]. The fungicide cyazofamid has a short life in differently textured agricultural soils and therefore has little chance of contaminating ground- water [102]. OCs and their metabolites pose a grave risk in agricultural soils as OCs were detected in 27 of 29 soil sam- ples tested in Turkey and ranged from 6 to 1090 μg kg−1 dry soil in areas where OCs were heavily used between the 1940s and 1980s in Turkey [2]. 4,4′-DDE was present above the acceptable risk levels in the agricultural soils of Mersin District in Turkey [2].
Sometimes, obsolete pesticides pollute the agricultural and surrounding soil because of improper disposal and persistence in the environment. Some banned chlorinated pesticides have been quantified in surface soils and raw foods (meat, dairy, and plants) from four rural areas of Tajikistan from 2011 to 2014. DDTwas consistently measured as the highest individ- ual pesticide at each of the four sampling areas, along with gluconodeltalactone (BHC) isomers and endosulfan [9]. Some disposed POPs including 4500 dumps of obsolete pesticides
decreased to 1033 with huge efforts in Ukraine by the end of 2014 [51]. However, the Polygon site remains contaminated and requires further assessment and remediation because of hexachlorobenzene (HCB) waste [51].
In the last two decades, pesticides have posed a threat to the inhabitants and livestock of the White Nile and Gezira states because of unprotected stocking and agricultural systems [76]. In China (Inner Mongolia), 21 OCPs were detected in agricul- tural soils (102 ng g−1) and pastoral areas (0.2–24 ng g−1) with HCHs and DDTs being the main contaminants [127]. In the soils supporting different types of vegetation, the largest res- idues of OCPs, HCHs, and DDTs were present in vegetables, watermelon patches, and soybean fields [127]. The OC resi- dues were higher in agricultural soils as compared to pastoral areas [127]. Therefore, barring conventional detection, geno- mic tools were used for assessing the effects of pesticides on agro-ecosystems [43]
Remediation of Pesticide-Contaminated Agricultural Soils
General Remediation Techniques for Organic Chemicals
Remediation methods include (1) ex situ method, in which contaminated soil is excavated and transported to another lo- cation for treatment, (2) on-site, in which contaminated soil is excavated and treated on-site before returning to the original state, and (3) in situ, in which the contamination is treated on- site without excavating and removing the contaminated soil [88]. The selection of remediation method is dependent upon whether the pesticide contamination is localized or diffused in the agricultural soils [73]. Ex situ methodwas commonly used as the soil remediation method earlier, but it has several draw- backs including the high cost of soil excavation and transport in addition to destroying the ecosystem. Therefore, in situ restoration has become the key focus recently [116].
Polluted soil can be remediated using physical, chemical, and biological techniques [26, 44]. These relevant techniques are (1) bioremediation, (2) phytoremediation, (3) chemical ox- idation, (4) surfactant extraction, (5) electrokinetic remedia- tion, and (6) thermal desorption. Although, the physical and chemical techniques are suitable for the remediation of pesticide-contaminated agricultural soil. However, those tech- nologies are mainly used for industry-impacted soil, seldom recommended for remediation of the extensive areas of agri- cultural soil that are contaminated by organic chemicals, be- cause physical and chemical techniques require high equip- ment and treatment costs and may lead to damage of the bio- logical and chemical qualities of soil [58, 107]. Compared with physical and chemical remediation, bioremediation, phytoextraction and phytovolatilization are biological
Curr Pollution Rep
approaches used to remove and detoxify organic contaminants in agricultural soils [59, 78, 124]. Bioremediation alone was usually unable to remove persistent and highly toxic contam- inants from agricultural soil within a shorter time [38, 39]. However, bioremediation enhanced by surfactants is a prom- ising technology for improving the bioavailability and remov- al efficiency of organic pollutants in agricultural soil [46, 77, 109, 117, 125, 126]. This list does not include all remediation strategies, but rather, it focuses on some established ap- proaches that have accompanying literature assessing the soil properties. Even though these techniques are used for pesticide remediation, the primary application may be for other types of contaminants such as electrokinetic remediation, which is pri- marily applied to remediate heavy metal contamination of soils. Thus, information provided in this review may be appli- cable beyond pesticide contamination of agricultural soils.
Remediation Technologies for Pesticides
Bioremediation reduces pesticide contamination of agricultural soils by improving natural biodegradation processes via meta- bolic activities of microorganisms, and it is becoming popular for being an efficient, cost-effective, and environment-friendly in situ treatment [88, 92]. Pesticide contamination of agricul- tural soils represents non-point source contaminants and ex situ chemical remediation technologies have been used earlier [73]. However, chemical remediation methods are unrealistic for diffused pollution of agricultural soils by pesticides. Instead, in situ bioremediation can be a better treatment [118]. Bioremediation involves phytoremediation and microbial re- mediation. Phytoremediation of pesticides from soil is based upon plant uptake, vegetation degradation, volatilization, and combined degradation by root exudates and rhizosphere mi- croorganisms [62]. The degradation rate of deltamethrin in soil had a direct relationship with microbial activity in soil [42]. Bacterial populations with P450 cytochrome genes positively influenced the aerobic bioremediation of pesticides [22]. Vetiver (Chrysopogon zizanoides) is suitable for phyto- stabilization of moderately dioxin-contaminated sites [71].
Electrokinetic soil flushing (EKSF) is used for the remedia- tion of soils polluted with different contaminants [111]. When the polluted soil is subjected to an electric field between anodes and cathodes, the contaminants in the soil can be removed or transferred into the flushing fluid that can then be treated or mobilized via electro-osmosis, electromigration, and electro- phoresis. The EKSF process used for the removal of pesticides from contaminated soils has become a hot topic of discussion in the remediation community [115] and has recently been com- bined with other remediation technologies such as bioremedi- ation and permeable reactive barriers [89, 111]. Several studies have described the rhizoremediation of polychlorinated biphe- nyls (PCBs), dioxins, decabromodiphenyls, phenanthrene, pyrene, and heavy metals [31, 34, 98, 114]. The use of a
combination of plant species and microbial strains has brought the spotlight on remediation [114].
Sustainable Remediation Methods for Agricultural Soils
For agricultural soils polluted by pesticides, most in situ sus- tainable remediation technologies can be used. There is a con- siderable impetus to develop bioremediation technologies as well as combined technologies for use such as rhizosphere re- mediation, fertilized-assisted remediation, and rhizoremediation combined with microbial remediation. The key enzymes and fungi which are helpful in pesticide removal along with poten- tial interactions with other soil microorganisms should be researched further in the future of rhizosphere remediation tech- nology [68]. An increasing research focus is on the combined techniques for remediation such as electrokinetic remediation with biological permeable reactive barriers for the remediation of soil polluted by insoluble organics [69]. Ultrasound-assisted soil washing has been combined with bioaugmentation for the remediation of soil polluted by polycyclic aromatic hydrocar- bons (PAHs) and heavy metals [14]. Tourmaline catalyzed Fenton-like reaction (TCFR) combined with Phanerochaete chrysosporium (TCFR + P) was used for the removal of polybrominated diphenyl ethers (PBDEs) in field soil micro- cosms [52]. Nanoremediation [zero valent iron nanoparticles (nZVI)] combined with electrokinetics was used for the remov- al of PCBs from soil, with the removal rate increasing from 20% to > 75% in contaminated soils [29]. Fenton-like oxidation combined with soil washing can potentially be an approach for the remediation of soil contaminated by PCBs [65].
Anaerobic or facultative anaerobic microflora and phytoremediation have been combined for treating the soil contaminated by POPs (DDTs and trifluralin) [41]. Gene tools were used for biomineralization of soil contaminated with pesticides [23]. Microbes and transgenic plants can also be used for the remediation of pesticide-contaminated soils [40].
Discussion
As Table 1 shows, some physical remediation technologies were used for the removal of pesticide-contaminated soil, such as electrokinetic soil fences (EKF) [89], electrokinetic soil flushing [89, 90, 101], soil washing, and solar-powered elec- trokinetic remediation [104]. The major mechanism of those technologies was that the pesticide was removed from the contaminated soil to the flushing fluids through adsorption, desorption, and volatilization. Some chemical remediation technologies, such as enhanced electrokinetic-Fenton [10], advanced oxidation process [86], and photo-degradation [84] were used for pesticide-contaminated soil through special chemical reactions (abiotic degradation). Both physical and
Curr Pollution Rep
Table 1 Current research work on the remediation and efficiency of treatment strategies of pesticide-polluted soils (2015–2017)
Remediation methods Pesticide and efficiency of treatment Reference
Advanced biodegradation Biochar resulted in significant reduction in soil DDT levels and soil microbial activity after 60 days.
[30]
Advanced oxidation process 86–88% degradation efficiency was achieved in about 3.5 h under UV light or enhanced sunlight; 99.86% of degradation was achieved in UV/TiO2/K2S2O8 system in the same irradiation time.
[86]
Bioaugmentation 95% of initial spiked terbuthylazine (TBA) was removed from soil microcosms upon bioaugmentation with ammonium-grown Arthrobacter aurescens TC1 inocula dur- ing the first 3 days. Around 70% on average of initial TBA remained in the non-bioaugmented control soil during the 14 days.
[101]
Electrokinetic soil fences (EKF) An extra 26.8% of oxyfluorfen was removed with surfactant (calcium dodecyl benzene sulfonate).
[89]
Electrokinetic soil flushing (EKSF) More than 80% of pesticide (30 mg/kg) was eliminated, 2, 4-D was removed by 95% after 15 days of treatment.
[101]
Electrokinetic soil flushing (EKSF) 50% of the initial 2, 4-D from the soil was eliminated; 25% remained in the soil, and the remaining 25% was volatilized after 40 days treated by the electrolyte wells.
[89]
Electro-remediation More than 22% of the spiked (20 mg kg−1) 2, 4-D transported to the flushing fluids, 57% of removal of 2, 4-D by volatilization. The main mechanism for the 2, 4-D’s removal was volatilization.
[90]
Enhanced electrokinetic-Fenton A maximum of 67% of the triazoles from a real vineyard soil (north-west of Spain) was degraded by enhanced electrokinetic-Fenton treatment after 27 days.
[10]
[99]
Microbial degradation Rhizobacteria were isolated from Okra (Abelmoschus esculentus L.); S10 and S20 had the maximum pesticide tolerance for bifenthrin pesticide degradation.
[75]
[12]
[13]
[32]
Microbial degradation The morphological, biochemical and 16S rRNA gene sequence analysis confirmed that the isolated bacterium for dichlorvos degradation is Pseudomonas stutzeri smk.
[48]
Microbial degradation Cyhalothrin and other pyrethroids could be degraded by Bacillus thuringiensis and some metabolites were identified and degradation pathway by cleavage of both the ester linkage and diary bond in a microorganism.
[54]
Microbial degradation Bacteria and putative genes confirmed pentachlorophenol (PCP) dechlorination and phenol degradation accomplished in segments 0–565 cm and 0–865 cm, respectively, contributing to a high PCP mineralization rate of 3.8665 μM d 611.
[55]
Microbial degradation Strain JPL-2 was isolated; the chain length of the alcohol moiety strongly affected the hydrolysis activity of the FeH (100 mg L−1) toward aryloxyphenoxy propanoate (AOPP) herbicides.
[61]
Microbial degradation Cypermethrin-degrading Bacillus strain SG2 was isolated which degraded the compound up to 81.6% within 15 days under standard growth conditions in minimal medium.
[81]
Microbial…
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