Degradation Of Pesticides In Soil Research Articles

Development of a new test design to investigate the degradation of pesticides in soil under sunlight conditions

Pesticides applied to soil surface are subject to photodegradation if the parent molecule is sensitive to UV-light absorption. Photodegradation studies are therefore mandatory for the registration of plant protection products to provide data on the degradation rate and on the nature of photoproducts formed. In general, sunlight is simulated in these studies with xenon lamps, e.g., a Suntest® device. Surface application on very thin soil layers followed by direct irradiation is common practice, but the control of the boundary conditions, i.e. soil temperature and moisture, to maintain the structure and viability of the soil is challenging. A homogeneous and stable soil microclimate is crucial to compare the degradation data of the test item from the irradiated soil samples to the dark controls as well as to the results from the aerobic soil metabolism study. After trying different scale-up test systems with the UV-sensitive herbicide imazamox as comparative test item, a new soil photolysis test system was developed which is manageable in the laboratory and enables a more favorable management of the boundary conditions, especially with regard to the soil moisture and temperature. For this, the solar simulator SolarConstant® 1200, equipped with metal halide lamps Radium HRI-TS 1000W/D/S/PRO, was installed by Atlas Ametek (Germany) in a temperature controllable walk-in incubation chamber with aluminum racks and reflectors to minimize diffuse light and to maintain a homogenous temperature of 22(± 1)°C within the irradiated soil. Borosilicate glass vessels with an inner diameter of 10 cm and a maximum height of 9 cm, covered by quartz glass, were used for the incubation of the applied soil under light. Contrary to the imazamox degradation half-lives obtained with the Suntest® test system, where an unusual slower degradation was observed under light compared to the dark controls, the results from the new SolarConstant® study design showed the expected faster degradation under light. Hence, it can be concluded that the experimental boundary conditions of the new test system are more suitable to maintain the viablity of the irradiated soil. Since no adjustments of the soil water content were needed, compared to daily water adjustments for thin soil layers incubated under a Suntest®, drying–wetting cycles are eliminated and microbial-induced soil processes are maintained.

Phages in vermicomposts enrich functional gene content and facilitate pesticide degradation in soil

Organic fertilizer microbiomes play substantial roles in soil ecological functions, including improving soil structure, crop yield, and pollutant dissipation. However, limited information is available about the ecological functions of phages and phage-encoded auxiliary metabolic genes (AMGs) in orga9nic fertilizers. Here we used a combination of metagenomics and phage transplantation trials to investigate the phage profiles and their potential roles in pesticide degradation in four organic fertilizers from different sources. Phage annotation results indicate that the two vermicomposts made from swine (PV) and cattle (CV) dung had more similar phage community structures than the swine (P) and cattle (C) manures. After vermicomposting, the organic fertilizers (PV and CV) exhibited enriched phage-host pairings and phage AMG diversity in relative to the two organic fertilizers (P and C) without composting. In addition, the number of broad-host-range phages in the vermicomposts (182) was higher than that in swine (153) and cattle (103) manures. Notably, phage AMGs associated with metabolism and pesticide biodegradation were detected across the four organic fertilizers. The phage transplantation demonstrated that vermicompost phages were most effective at facilitating the degradation of pesticide precursor p-nitrochlorobenzene (p-NCB) in soil, as compared to swine and cattle manures (P < 0.05). Taken together, our findings highlight the significance of phages in vermicompost for biogeochemical cycling and biodegradation of pesticide-associated chemicals in contaminated soils.

Potential Applications of Chitosan-Coated Zinc Oxide Nanoparticles for Degrading Pesticide Residues in Environmental Soils

The precipitation process was applied to synthesize chitosan-coated zinc oxide nanoparticles (chitosan-ZnO NPs). Then, various characterization tools were used such as XDR, SEM, TEM, FTIR, and EDX. The use of these 50 nm chitosan-ZnO NPs in soil decontamination of thifluzamide and difenoconazole pesticide residues is being investigated. In two distinct soils, the effect of catalytic decontamination on pesticide residues was examined (sandy loam and sandy clay soils). The studies required two sets of pesticide concentrations. One set of samples was added to the chitosan-ZnO NPs catalyst, and the other set was studied without the addition of a catalyst. Photocatalytic studies were conducted under the sunlight in July. The soil samples were hand-spread in a glass dish to a height of 5 mm and sprayed with an aqueous solution of pesticide. From 8 a.m. to 5 p.m., these samples were exposed to sunlight in October 2021. We found that the best concentration of catalyst was 0.05%. The acquired samples were quantified using validated Ultra-Fast Liquid Chromatography (UFLC) with Photo Diode Array (PDA) detection. Kinetic parameters such as rate constant k and the degradation rate of pesticides DT50 have been calculated using Pesticide Residue Dissipation Data. The findings showed that the tested fungicides degenerate according to pseudo-first-order kinetics. Based on the findings, we concluded that photocatalytic degradation of pesticides in soils are faster than photolysis.

Evaluation of temperature corrections for pesticide half-lives in tropical and temperate soils.

Temperature is a key factor that influences pesticide degradation. Extrapolating degradation half-lives (DT50) measured at a given temperature to different temperatures remains challenging, especially for tropical conditions with high temperatures. In this study, the use of the standard Arrhenius equation for correcting temperature effects on pesticide degradation in soils was evaluated and its performance was compared with that of alternative Arrhenius-based equations. To do so, a database of 509 DT50 values measured between 5 and 35°C for 32 pesticides on tropical and temperate soils was compiled for the first time through an extensive literature search. The temperature correction models were fitted to the database using linear mixed regression approaches that included soil type and compound effects. No difference in the temperature dependence of DT50 between tropical and temperate soils was detected, regardless of the model. A comparison of the prediction performances of the models showed that constant activation energy (Ea) cannot be considered valid for the whole range of temperatures. The classical Arrhenius equation with an Ea of 65.4kJ.mol-1, as recommended by the European Food Safety Authority (EFSA), was shown to be valid for correcting the DT50 only for temperatures ranging from 5 to 20°C. However, for temperatures greater than 20°C, which are common in tropical environments, the median Ea was significantly lower at 10.3kJ.mol-1. These findings suggest the need to adapt the standard temperature correction of the European pesticide risk assessment temperature procedure when it is applied in tropical settings.

Effects of the presence of triclocarban on the degradation and migration of co-occurring pesticides in soil

Triclocarban (TCC), a bactericide widely used in personal care products, is frequently detected in soil and surface water, which may affect the environmental behavior of other environmental pollutants by changing the community structure of environmental microorganisms. This work evaluated the effects of TCC on the degradation and migration of seven herbicides and five fungicides in soil under co-occurrence conditions. TCC significantly increased the persistence of the pesticides in soil, and this effect increased with TCC concentration. For example, the half-life of metolachlor, atrazine, metribuzin, and metamitron increased 44%, 38%, 153%, and 33%, respectively, with 10 mg/kg TCC and increased 60%–640% with 100 mg/kg TCC. After 90 days, the residue of the pesticides in soil treated with TCC was significantly elevated relative to the control. TCC treatment could also increase the potential leaching risk of the herbicides in the soil, as indicated by an increased Groundwater Ubiquity Score (GUS) index. The reduced abundance of soil bacteria by TCC might be an essential reason for the impacts on the environmental behavior of the pesticides. This study confirmed that TCC could slow down the degradation of pesticides in soil, increase their persistence and even affect the leaching behavior, thus influencing the risks of the pesticides to the environment.

Gene-Centric Model Approaches for Accurate Prediction of Pesticide Biodegradation in Soils.

Pesticides are widely used in agriculture despite their negative impact on ecosystems and human health. Biogeochemical modeling facilitates the mechanistic understanding of microbial controls on pesticide turnover in soils. We propose to inform models of coupled microbial dynamics and pesticide turnover with measurements of the abundance and expression of functional genes. To assess the advantages of informing models with genetic data, we developed a novel "gene-centric" model and compared model variants of differing structural complexity against a standard biomass-based model. The models were calibrated and validated using data from two batch experiments in which the degradation of the pesticides dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) were observed in soil. When calibrating against data on pesticide mineralization, the gene-centric and biomass-based models performed equally well. However, accounting for pesticide-triggered gene regulation allows improved performance in capturing microbial dynamics and in predicting pesticide mineralization. This novel modeling approach also reveals a hysteretic relationship between pesticide degradation rates and gene expression, implying that the biodegradation performance in soils cannot be directly assessed by measuring the expression of functional genes. Our gene-centric model provides an effective approach for exploiting molecular biology data to simulate pesticide degradation in soils.

Exogenous salicylic acid mitigates the accumulation of some pesticides in cucumber seedlings under different cultivation methods.

Salicylic acid (SA) is a crucial signal molecule and phytohormone, regulating the biotic and abiotic stress responses as well as plant development. In this research, we comparatively examined the effects of exogenous SA on the behaviors of thiamethoxam (THIM), hymexazol (HMI) and chlorantraniliprole (CAP) in cucumber planting systems under soil pot and hydroponic cultivation. The cucumber seedlings were transplanted into soil or nutrient solution containing a target pesticide (1mg/kg) or a target pesticide with SA (1mg/kg) after the fourth leaf emerged. We examined the behaviors of pesticides both the SA treated and nontreated plants by analyzing cucumber root, stem and leaf samples taken on the 0-21 days following the root treatment. The root concentration factor (RCF), bioconcentration factor (BCF) and translocation factors (TFstem and TFleaf) were calculated for the comparison of the differences in the behaviors of pesticides. We found that the accumulation behaviors of pesticides in planting systems were related to the physicochemical properties of pesticides, exogenous SA and cultivation methods. Exogenous SA had a certain promoting effect on the degradation of pesticides in soil and nutrient solution, resulting in reduced half-lives. SA was able to block the accumulation of pesticides in roots and leaves and alleviated the accumulation ability of roots, the bioconcentration ability of plants, and the translocation ability from roots to leaves. Interestingly, SA had more distinct effects on the behaviors of pesticides under hydroponic experiments than under soil pot experiments. Furthermore, the behaviors of clothianidin (CLO), the main metabolite of THIM, were also assessed, indicating that THIM was mainly metabolized to CLO in leaves and stems, and SA facilitated this process. Our findings suggest that SA has a certain regulatory effect on the accumulation of pesticides in plants, and SA-blocked pesticide accumulation is practically rewarding for improving food safety.

Solarization-based pesticide degradation results in decreased activity and biomass of the soil microbial community

Pesticides are chemical compounds, mostly synthetic, which are used widely in agricultural fields to prevent and to control pests and soil-borne diseases. The synthetic nature of these compounds makes some of them non-biodegradable and they may accumulate in harmful concentrations in soils. Solarization seems to be a non-chemical strategy that could enhance pesticide degradation in soils. Here, we evaluate the combined impact of pesticides and solarization on the microbial community of a Mediterranean soil. For this purpose, enzyme activities, basal respiration, and the biomass and composition of the microbial community (through analysis of phospholipid fatty acids, PLFAs) were evaluated in solarized and non-solarized soils, in a 90-day greenhouse experiment with a combination of different pesticides. The degradation of the pesticides in the solarized soils was 30% greater than in non-solarized samples. However, solarization also affected the soil microbial community. The soil respiration was lowest in solarized samples without pesticides, while the enzyme activities were greater in non-solarized samples (with and without pesticides). Both the bacterial and fungal PLFA contents declined in solarized samples. The G+/G− ratio was highest in the solarized samples without pesticides and in the non-solarized samples with pesticides. Considering such impacts on the soil microbial community and the relationship of soil microbes with soil ecosystem services, the utilization of solarization must be carefully considered when adopting strategies for pesticide degradation in Mediterranean soils.

An assessment of environmental and toxicological risk to pesticide exposure based on a case-based approach to computing

Pesticide environmental fate and toxicity depends on its physical and chemical features, the soil composition, soil adsorption, as well as residues that may be found in different soil slots. Indeed, pesticide degradation in soil may be influenced by either biotic or abiotic factors. In addition, the toxicity of pesticides for living organisms depends on their adsorption, distribution, biotransformation, dissemination of metabolites together with interaction with cellular macromolecules and excretion. Biotransformation may result in the formation of less toxic and/or more toxic metabolites, while other processes determine the balance between toxic and a nontoxic upcoming. Aggregate exposure and risk assessment involve multiple pathways and routes, including the potential for pesticide residues in food and drinking water, in addition to residues from pesticide use in residential and non-occupational environments. Therefore, this work will focus on the development of a decision support system to assess the environmental and toxicological risk to pesticide exposure, built on top of a Logic Programming approach to Knowledge Representation and Reasoning, complemented with a Case Based attitude to computing. The proposed solution is unique in itself, once it caters for the explicit treatment of incomplete, unknown, or even self-contradictory information, either in terms of a qualitative or quantitative setting.

Fine scale spatial variability of microbial pesticide degradation in soil: scales, controlling factors, and implications.

Pesticide biodegradation is a soil microbial function of critical importance for modern agriculture and its environmental impact. While it was once assumed that this activity was homogeneously distributed at the field scale, mounting evidence indicates that this is rarely the case. Here, we critically examine the literature on spatial variability of pesticide biodegradation in agricultural soil. We discuss the motivations, methods, and main findings of the primary literature. We found significant diversity in the approaches used to describe and quantify spatial heterogeneity, which complicates inter-studies comparisons. However, it is clear that the presence and activity of pesticide degraders is often highly spatially variable with coefficients of variation often exceeding 50% and frequently displays non-random spatial patterns. A few controlling factors have tentatively been identified across pesticide classes: they include some soil characteristics (pH) and some agricultural management practices (pesticide application, tillage), while other potential controlling factors have more conflicting effects depending on the site or the pesticide. Evidence demonstrating the importance of spatial heterogeneity on the fate of pesticides in soil has been difficult to obtain but modeling and experimental systems that do not include soil's full complexity reveal that this heterogeneity must be considered to improve prediction of pesticide biodegradation rates or of leaching risks. Overall, studying the spatial heterogeneity of pesticide biodegradation is a relatively new field at the interface of agronomy, microbial ecology, and geosciences and a wealth of novel data is being collected from these different disciplinary perspectives. We make suggestions on possible avenues to take full advantage of these investigations for a better understanding and prediction of the fate of pesticides in soil.

Pesticide relevance and their microbial degradation: a-state-of-art

The extensive use of pesticide causes imbalance in properties of soil, water and air environments due to having problem of natural degradation. Such chemicals create diverse environmental problem via biomagnifications. Currently, microbial degradation is one of the important techniques for amputation and degradation of pesticide from agricultural soils. Some studies have reported that the genetically modified microorganism has ability to degrade specific pesticide but problem is that they cannot introduce in the field because they cause some other environmental problems. Only combined microbial consortia of indigenous and naturally occurring microbes isolated from particular contaminated environment have ability to degrade pesticides at faster rate. The bioaugumentation processes like addition of necessary nutrients or organic matter are required to speed up the rate of degradation of a contaminant by the indigenous microbes. The use of indigenous microbial strains having plant growth activities is ecologically superior over the chemical methods. In this review, we have attempted to discuss the recent challenge of pesticide problem in soil environment and their biodegradation with the help of effective indigenous pesticides degrading microorganisms. Further, we highlighted and explored the molecular mechanism for the pesticide degradation in soil with effective indigenous microbial consortium. This review suggests that the use of pesticide degrading microbial consortia which is an eco-friendly technology may be suitable for the sustainable agriculture production.

Correction to Modeling Spatial Variation in Microbial Degradation of Pesticides in Soil

Correction to Modeling Spatial Variation in Microbial Degradation of Pesticides in Soil

Modeling Spatial Variation in Microbial Degradation of Pesticides in Soil

Currently, no general guidance is available on suitable approaches for dealing with spatial variation in the first-order pesticide degradation rate constant k even though it is a very sensitive parameter and often highly variable at the field, catchment, and regional scales. Supported by some mechanistic reasoning, we propose a simple general modeling approach to predict k from the sorption constant, which reflects bioavailability, and easily measurable surrogate variables for microbial biomass/activity (organic carbon and clay contents). The soil depth was also explicitly included as an additional predictor variable. This approach was tested in a meta-analysis of available literature data using bootstrapped partial least-squares regression. It explained 73% of the variation in k for the 19 pesticide-study combinations (n = 212) in the database. When 4 of the 19 pesticide-study combinations were excluded (n = 169), the approach explained 80% of the variation in the degradation rate constant. We conclude that the approach shows promise as an effective way to account for the effects of bioavailability and microbial activity on microbial pesticide degradation in large-scale model applications.

Measurements and modeling of pesticide persistence in soil at the catchment scale

Degradation of pesticides in soils is both spatially variable and also one of the most sensitive factors determining losses to surface water and groundwater. To date, no general guidance is available on suitable approaches for dealing with spatial variation in pesticide degradation in catchment or regional scale modeling applications. The purpose of the study was therefore to study the influence of various soil physical, chemical and microbiological characteristics on pesticide persistence in the contrasting cultivated soils found in a small (13 km 2) agricultural catchment in Sweden and to develop and test a simple model approach that could support catchment scale modeling. Persistence of bentazone, glyphosate and isoproturon was investigated in laboratory incubation experiments. Degradation rate constants were highly variable with coefficients of variation ranging between 42 and 64% for the three herbicides. Multiple linear regression analysis and Mallows Cp statistic were employed to select the best set of independent parameters accounting for the variation in degradation. Soil pH and the proportion of active microorganisms (r) together explained 69% of the variation in the bentazone degradation rate constant; the Freundlich sorption co-efficient (K f) and soil laccase activity together explained 88% of the variation in degradation rate of glyphosate, while soil pH was a significant predictor (p < 0.05) for isoproturon persistence. However, correlations between many potential predictor variables made clear interpretations of the statistical analysis difficult. Multiplicative models based on two predictors chosen ‘a priori’, one accounting for microbial activity (e.g. microbial respiration, laccase activity or the surrogate variable soil organic carbon, SOC) and one accounting for the effects of sorption on bioavailability, showed promise to support predictions of degradation for large-scale modeling applications, explaining up to 50% of the variation in herbicide persistence.

Microbial Aspects of Accelerated Degradation of Metam Sodium in Soil

Preplant soil fumigation with metam sodium is used worldwide to control soilborne diseases. The development of accelerated degradation of pesticides in soil, including metam sodium, results in reduced pesticide efficacy. Therefore, we studied microbial involvement in accelerated degradation of methyl isothiocyanate (MITC) following repeated soil applications of the parent compound, metam sodium. MITC degradation was reduced in soil with a history of metam sodium applications following sterilization, indicating the key role of microorganisms in accelerated degradation. Accelerated degradation of MITC was induced by inoculation of soil with no previous application of metam sodium with soil with a history of metam sodium applications. We developed a method to extract the active microbial fraction responsible for MITC degradation from soil with a history of metam sodium applications. This concentrated soil extract induced accelerated degradation of MITC when added to two different soils with no previous application of metam sodium. An extensive shift in total bacterial community composition in concentrated soil extracts occurred after a single metam sodium application. Two Oxalobacteraceae strains, MDB3 and MDB10, isolated from Rehovot soil following triple application of metam sodium rapidly degraded MITC in soil with no previous application of metam sodium. Polymerase chain reaction-denaturing gradient gel electrophoresis analysis of bacterial community composition showed relative enrichment of MDB3 following metam sodium application, suggesting its potential in situ involvement in accelerated degradation development in Rehovot soil. Responses of resident Oxalobacteraceae community members to metam sodium applications differed between Rehovot and En Tamar soils. Isolate MDB10 did not induce accelerated degradation of MITC in En Tamar soil and, with the slow dissipation of MITC, soil suppressiveness of accelerated degradation is suggested. The isolation and identification of MITC-degrading bacteria might be helpful in developing tools for managing accelerated degradation.

Overcoming of soil contamination with pesticides in forest nurseries using the activity of microorganisms

The use of pesticides during cultivation of pine seedlings in forest nurseries results in the formation two phenotypes of teratomorph seedlings - conditionally normal and abnormal. Growing forest cultures from teratomorph seedlings leads to their low survival rate. It is known that pesticides and their metabolic products can remain in soil for many years. It is therefore impossible to rely only on natural degradation of pesticides in soil. A promising way of removing pesticides from soil is their microbiological decomposition. This method is preferable because there is a meliorative organic substance not far from forest nurseries - i.e. forest litter rich in microorganisms. The purpose of these experiments was to examine the influence of forest litter applied on pesticide decomposition in soil and morphology of pine seedlings. The rates of forest litter that were most effective in decomposition of pesticides and the activity of microbial communities in litter, depending on forest stand structure, were determined. Estimation of that action was based on the morphology of seedlings (rate of pine seedlings with normal, conditionally normal and abnormal phenotypes), intensity of CO2 emission from soil and catalase activity, which correlates with the number of soil microorganisms. The results of these experiments showed the most effective activity of forest litter at the application rate of 20 kg/m2. The number of seedlings with normal phenotype rose from 32% up to 40%. Besides, it was noted that saprophytes were most effective in pine forest litter, which is characterized by a more acid reaction of soil solution, while most others were rich in fungi. The highest number of normal phenotype seedlings, intensity of CO2 emission and activity of soil catalase were correlated with the microbiological activity of the applied pine forest litter.

Modelling pesticide volatilization after soil application using the mechanistic model Volt'Air

Volatilization of pesticides participates in atmospheric contamination and affects environmental ecosystems including human welfare. Modelling at relevant time and spatial scales is needed to better understand the complex processes involved in pesticide volatilization. Volt'Air-Pesticides has been developed following a two-step procedure to study pesticide volatilization at the field scale and at a quarter time step. Firstly, Volt'Air-NH 3 was adapted by extending the initial transfer of solutes to pesticides and by adding specific calculations for physico-chemical equilibriums as well as for the degradation of pesticides in soil. Secondly, the model was evaluated in terms of 3 pesticides applied on bare soil (atrazine, alachlor, and trifluralin) which display a wide range of volatilization rates. A sensitivity analysis confirmed the relevance of tuning to K h . Then, using Volt'Air-Pesticides, environmental conditions and emission fluxes of the pesticides were compared to fluxes measured under 2 environmental conditions. The model fairly well described water temporal dynamics, soil surface temperature, and energy budget. Overall, Volt'Air-Pesticides estimates of the order of magnitude of the volatilization flux of all three compounds were in good agreement with the field measurements. The model also satisfactorily simulated the decrease in the volatilization rate of the three pesticides during night-time as well as the decrease in the soil surface residue of trifluralin before and after incorporation. However, the timing of the maximum flux rate during the day was not correctly described, thought to be linked to an increased adsorption under dry soil conditions. Thanks to Volt'Air's capacity to deal with pedo-climatic conditions, several existing parameterizations describing adsorption as a function of soil water content could be tested. However, this point requires further investigation. Practically speaking, Volt'Air-Pesticides can be a useful tool to make decision about agricultural practices such as incorporation or for the estimation of overall pesticide volatilization rates, and it holds promise for time specific dynamics.

Dissipation of acephate, chlorpyrifos, cypermethrin and their metabolites in a humid‐tropical vegetable production system

High amounts of insecticides are often used in intensive tropical vegetable production systems. Their persistence and residues in vegetables and soils need to be studied to ensure food safety and environmental stability. The dissipation of acephate, chlorpyrifos, cypermethrin and their metabolites was studied in green mustard [Brassica juncea (L.) Coss.] and soils. Two treatments, Impact 75 (acephate) and Agent 505 (cypermethrin plus chlorpyrifos), were applied 4 times at weekly intervals. Dissipation of acephate, chlorpyrifos and cypermethrin in green mustard and topsoils followed first-order kinetics, with half-lives of between 1.1 and 3.1 days in green mustard and between 1.4 and 9.4 days in topsoils (26 degrees C). Higher vapour pressure of insecticides and higher rainfall appeared to stimulate dissipation from the vegetable, with least effect of rainfall on chlorpyrifos. Dissipation rates in the vegetable were faster or similar (cypermethrin) to rates observed for temperate areas. Preharvest intervals of 13, 4 and 3 days were required for acephate, chlorpyrifos, cypermethrin and their metabolites to comply with the tolerance levels. The pesticide dissipation rates in soils varied by less than a factor of 3 between sites. The metabolites methamidophos and TCP derived from acephate and chlorpyrifos amounted to less than 10 and 25% by mass of the parent compounds in soils. Vegetable shading possibly retarded pesticide degradation in soil. The dissipation of pesticides and their metabolites in the vegetable was rapid and faster than the dissipation in temperate climates. The degradation rates of pesticides in the soil were equal to or slightly faster than the degradation rates in temperate soils.

Impact of pesticides on soil microbiological parameters and possible bioremediation strategies

Intensive agriculture is spectacularly successful since last couple of decades due to the inputs viz; fertilizers and pesticides along with high yielding varieties. The mandate for agriculture development was to feed and adequate nutrition supply to the expanding population by side the agriculture would be entering to into new area of commercial and export orientation. The attention of public health and proper utilization natural resources are also the main issues related with agriculture development. Concern for pesticide contamination in the environment in the current context of pesticide use has assumed great importance [1]. The fate of the pesticides in the soil environment in respect of pest control efficacy, non-target organism exposure and offsite mobility has been given due consideration [2]. Kinetics and pathways of degradation depend on abiotic and biotic factors [6], which are specific to a particular pesticide and therefore find preference. Adverse effect of pesticidal chemicals on soil microorganisms [3], may affect soil fertility [4] becomes a foreign chemicals major issue. Soil microorganisms show an early warning about soil disturbances by foreign chemicals than any other parameters.But the fate and behavior of these chemicals in soil ecosystem is very important since they are degraded by various factors and have the potential to be in the soil, water etc. So it is indispensable to monitor the persistence, degradation of pesticides in soil and is also necessary to study the effect of pesticide on the soil quality or soil health by in depth studies on soil microbial activity.The removal of metabolites or degraded products should be removed from soil and it has now a day's primary concern to the environmentalist. Toxicity or the contamination of pesticides can be reduced by the bioremediation process which involves the uses of microbes or plants. Either they degrade or use the pesticides by various co metabolic processes.

Adsorption and degradation of four acidic herbicides in soils from southern Spain

Pesticide degradation and adsorption in soils are key processes determining whether pesticide use will have any impact on environmental quality. Pesticide degradation in soil generally results in a reduction in toxicity, but some pesticides have breakdown products that are more toxic than the parent compound. Adsorption to soil particles ensures that herbicide is retained in the place where its biological activity is expressed and also determines potential for transportation away from the site of action. Degradation and adsorption are complex processes, and shortcomings in understanding them still restrict the ability to predict the fate and behaviour of ionisable pesticides. This paper reports the sorption and degradation behaviour of four acidic pesticides in five soils from southern Spain. Results are used to investigate the influence of soil and pesticide properties on adsorption and degradation as well as the potential link between the two processes. Adsorption and degradation of four acidic pesticides were measured in four soils from Spain characterised by small organic matter (OM) contents (0.3-1.0%) and varying clay contents (3-66%). In general, sorption increased in the order dicamba < metsulfuron-methyl < 2,4-D < flupyrsulfuron-methyl-sodium. Both OM and clay content were found to be important in determining adsorption, but relative differences in clay content between soils were much larger than those in OM content, and therefore clay content was the main property determining the extent of herbicide adsorption for these soils. pH was negatively correlated with adsorption for all compounds apart from metsulfuron-methyl. A clear positive correlation was observed for degradation rate with clay and OM content (P < 0.01), and a negative correlation was observed with pH (P < 0.01). The exception was metsulfuron-methyl, for which degradation was found to be significantly correlated only with soil bioactivity (P < 0.05). Both OM and clay content were found to be important in determining adsorption, but relative differences in clay content between soils were much larger than those in OM content, and therefore clay content was the main property determining the extent of herbicide adsorption for soils of this type. pH was negatively correlated with adsorption for all compounds apart from metsulfuron-methyl. The contrasting behaviour shown for these four acidic pesticides indicates that chemical degradation in soil is more difficult to predict than adsorption. Most of the variables measured were interrelated, and different behaviours were observed even for compounds from the same chemical class and with similar structures.