Pesticide Leaching Research Articles

A critical review of different factors governing the fate of pesticides in soil under biochar application

Pesticides are extensively used in the modern agricultural system. The inefficient and extensive use of pesticides during the last 5 to 6 decades inadvertently led to serious deterioration of environmental quality with health risk to living organisms, including humans. It is important to use some environmentally-friendly and sustainable approaches to remediate, restore and maintain soil quality. Biochar has gained considerable attention globally as a promising soil amendment because it has the ability to adsorb and as such minimize the bioavailability of pesticides in soils. This review emphasizes the recent trends and implications of biochar in pesticide-contaminated soils, as well as highlights need of the pesticides use and associated environmental issues in context of the biochar application. The overarching aim of this review is to signify the role of biochar on primary processes such as effect of biochar on the persistence, mineralization, leaching and efficacy of pesticides in soil. Notably, the effects of biochar on pesticide adsorption-desorption, degradation and bioavailability under various operating/production conditions are critically discussed. This review delineates the indirect impact of biochar on pesticides persistence in soils and proposes key recommendations for future research which are essential for the remediation and restoration of pesticides-impacted soils.

Risk assessment of pesticide leaching into groundwater based on the results of a lysimetric experiment

Mobility of cyanthraniliprole, paclobutrazol and metribuzin was investigated on large lysimeters of the Experimental Soil Station of Moscow State University . Pesticides were applied in recommended and tenfold rates for cyantraniliprole and paclobuyrazol and recommended and eightfold rates for metribuzin. All three pesticides were detected in leachate. Cyantraniliprole was detected in most water samples analyzed. The maximum concentrations of cyanthraniliprole in the leachate were 2.6 and 12.5 µg L−1 in lysimeters with recommended and tenfold rates, respectively. Paclobutrazol was found 3 and 7 times during the year after application in the lysimeter with recommended and increased rates in concentrations up to 26 μg L−1. Used in accordance with the regulation, metribuzin in leachate was detected once, in eightfold rate - 73% of water samples; maximum concentration was 180 µg L−1. The migration risk into groundwater of all three studied pesticides is assessed as high, risk for people as low, risk for aquatic organisms as high. Risk and danger assessment based on simulation with model PEARL and mobility indexes showed high agreement with the assessment according to the experiment.

Assessment of Anions and Heavy Metals in Sediments from River Sio, Busia County, Kenya

Agricultural activities, discharge of raw sewage into farms and the rise in urbanization have greatly contributed to soil pollution. During the rainy season, surface runoff from farms find their way into water bodies and deposits these contaminants into Rivers and Lakes which poses a threat to both aquatic and terrestrial organisms that depend on that water source. The objective of this research was to determine the level of anions and heavy metals from sediments in River Sio, Busia County, Kenya. Five sediment samples were taken from five sampling points and the levels of anions and heavy metals in them determined. Anions were determined using Shimadzu 1800 UV/visible spectrophotometer while heavy metals were determined using Shimadzu 6200 flame atomic absorption spectrophotometer (AAS). Copper, lead and nickel were above the allowed WHO limits while cadmium was below detection limit. The levels of nitrates, phosphates and chlorides were higher during the wet season due to surface runoff that carried these nutrients from the farms and deposited them on the bottom of the River. The levels of heavy metals were high during the dry season due to evaporation of water from the River, leading to an increase in the analyte concentration during the dry season. High levels of copper and nickel in the sediments points to the use of herbicides and pesticides in farming and washing of vehicles and motorcycles on the banks of the River. According to Igeo nickel showed moderate pollution during the dry season. The contamination factor for lead was very high during the dry season, while pollution load index confirmed pollution due to anthropogenic activities in sampling sites 1 – 4 during the dry season and no pollution due to anthropogenic activities during the wet season. The study recommends reduced use of inorganic fertilizers in order to save the River from the danger of eutrophication. Excessive use of agrochemicals such as herbicides and pesticides should be discouraged. In addition, pesticide leaching and the level of microbes in soil and sediments should be considered for further research

How weather conditions and physico-chemical properties control the leaching of flufenacet, diflufenican, and pendimethalin in a tile-drained landscape

The input of harmful substances into surface waters are of major concern since their side effects may negatively affect the chemical state of surface waters. This study investigated the drainage loss of pesticides into surface waters in a small agricultural catchment in Northern Germany. The pesticides flufenacet, diflufenican, and pendimethalin were monitored at a daily resolution for 154 days in 2016 (dry period) and 111 days in 2017 (wet period) for two consecutive years at both field- (10 ha) and catchment-scale (100 ha). Highly contrasting weather conditions led to extremely high differences in loads between both monitoring periods. Regarding both scales and campaigns, flufenacet was released often in considerably higher amounts and faster than diflufenican and pendimethalin. The very mobile pesticide, flufenacet, is not exclusively leached during high precipitation events but also continuously discharged from soils to the drainage system during low precipitation. Pendimethalin had the lowest recovery rate in comparison to its application amount and showed a lower total loss rate than the less sorptive pesticide diflufenican. Pendimethalin and diflufenican showed high retarded loads caused by increased drainage discharge and sediment transport during late winter induced by freezing and thawing processes in the upper soil. Hence, leaching of the pesticides was controlled by the sorption properties of the investigated compounds and, to a large extent, by hydrological boundary conditions, which were highly variable from an (inter-) annual perspective. Our study identified antecedent and prevailing precipitation and soil moisture conditions as the key impact of pesticide leaching to the drainage system in the long-term.

Effect of Peat Addition on Sorption and Leaching of Triazole Fungicides in Oran Soils

In this paper, the authors treat the impact of peat amendment on sorption and leaching of fungicides penconazole and flusilazole in two Algerian topsoil samples (Misserghine and Es-Senia). The batch equilibration technique was applied for adsorption experiments, and leaching was tested through soil column simulated experiments under laboratory conditions. Adsorption data fitted well to the Freundlich and linear models, showing the higher adsorption capacity of the Es-Senia soil for both fungicides, the order of sorption being flusilazole > penconazole. Organic amendments increased the adsorption of both fungicides especially for the soil with the lower organic matter (OM) content, obtaining a good correlation of this parameter withKf,thus implying that OM is the principal soil parameter governing fungicides adsorption. Results of soil column experiments indicated that peat amendment decreased leaching of both pesticides in the soils studied. So, the use of organic addition might be an effective management practice for controlling potential pollution of penconazole and/or flusilazole to the environment.

Comparação entre índices de potencial de lixiviação para agrotóxicos utilizados na Sub-Bacia do Natuba, Vitória de Santo Antão-Pernambuco

A contaminação ambiental por agrotóxicos vem sendo crescentemente abordada por diversos autores na literatura e discutida pela sociedade civil, por causa de suas externalidades negativas. Este estudo visou calcular e comparar o potencial de lixiviação e contaminação dos princípios ativos de agrotóxicos que são utilizados na sub-bacia hidrográfica do rio Natuba, município de Vitória de Santo Antão-Pernambuco. Para tanto, utilizou-se índices que se propõem a avaliar a capacidade de um determinado princípio ativo de agrotóxico lixiviar ou ser transportado no meio ambiente, a saber: Groundwater Screening Index (GSI), Groundwater Ubiquity Score (GUS), Relative Leaching Potential Index (RLPI), Leaching IndeX (LIX), Leaching Index (LEACH) e critério da California Departament of Food and Agriculture (CDFA). Os dados dos índices GSI, GUS, LIX, LEACH e RLPI demonstraram valores semelhantes por meio da análise de variâncias, ou seja, cada índice tende a indicar, em sua faixa de valores, a mesma propensão de lixiviação do agrotóxico. Assim, ao comparar os enquadramentos de cada um dos agrotóxicos, destacaram-se, pelo risco ambiental: picloram, hexazinone, clorantraniliprole, carbofurano, thiamethoxam, 2,4 D sal dimetilamina, imidacloprido, azoxistrobina, cartape, dicloreto de paraquate. Dessa forma, deve-se evitar o uso desses ingredientes ativos e substituí-los por outros com menor potencial de lixiviação, visando à proteção da área.

Experimental and numerical study on the leaching of pesticides into the groundwater through a porous medium: Effects of transport parameters

Abstract This study aims to investigate, experimentally and numerically, the pesticide transport through the soil in unsaturated zone. The movement of pesticide is described with one dimensional model. The transport equation incorporates terms accounting for diffusion –convection, adsorption and reaction. The first objective of this work was to identifies the effects of the parameters transport such us; the dimensions first order degradation coefficient ( μ ), the peclet number ( ρ e ) and the dimensionless mass transfer coefficient (w). The evolution of pesticide concentration in function of depth and time was found by using the non-equilibrium transport model. The data obtained show the importance of the adsorbed concentration. The second objective is to find the relation between the concentration and the transport parameters because there is a difficulty of the analytical solution. The solution of the problem was carried out by a numerical approach by using the finite difference method and a Fortran program.

Leaching of Five Pesticides of Contrasting Mobility through Frozen and Unfrozen Soil

Core Ideas Significantly more pesticides leached from frozen than from unfrozen soil columns. Rapid breakthrough of pesticides indicated preferential flow in frozen soil. A strong negative correlation between Kf and leaching was observed. The effect of sorption properties is weaker in the presence of macropore flow. Macropore flow may be less important for highly mobile or highly sorbed pesticides. Field and laboratory studies show increased leaching of pesticides through macropores in frozen soil. Fast macropore flow has been shown to reduce the influence of pesticide properties on leaching, but data on these processes are scarce. The objective of this study was to investigate the effect of soil freezing and thawing on transport of pesticides with a range of soil sorption coefficients (Kf). To do this we conducted a soil column study to quantify the transport of bromide and five pesticides (2‐methyl‐4‐chlorophenoxyacetic acid, clomazone, boscalid, propiconazole, and diflufenican). Intact topsoil and subsoil columns from two agricultural soils (silt and loam) in southeastern Norway were used in this experiment, and pesticides were applied to the soil surface in all columns. Half the columns were then frozen (−3°C), and the other half were left unfrozen (4°C). Columns were subjected to repeated irrigation events where 25 mm of rainwater was applied during 5 h at each event. Irrigations were followed by 14‐d periods of freezing or refrigeration. Percolate was collected and analyzed for pesticides and bromide. Pesticide leaching was up to five orders of magnitude larger from frozen than unfrozen columns. Early breakthrough (<<1 pore volume) of high concentrations was observed for pesticides in frozen columns, indicating that leaching was dominated by preferential flow. The rank order in pesticide leaching observed in this study corresponded to the rank order of mean Kf values for the pesticides, and the results suggest that sorption plays a role in determining leaching losses even in frozen soil.

Estimating Deep Drainage Using Deep Soil Moisture Data under Young Irrigated Cropland in a Desert‐Oasis Ecotone, Northwest China

Core Ideas Deep drainage rates under young cropland in the desert‐oasis region were investigated. Deep drainage rates were estimated by a simulation approach based on deep soil moisture data. Annual deep drainage averaged 468 mm; the annual deep drainage coefficient averaged 43%. Deep drainage reduces agricultural water productivity under cropland recently converted from native desert soils (i.e., young cropland) and increases the risks of nutrient and pesticide leaching into groundwater in the desert‐oasis ecotone. However, the deep drainage rates under young cropland in these oasis environments remain unclear, especially for winter irrigation, a common practice in Northwest China. The objective of this study was to estimate the deep drainage rate using the HYDRUS‐1D model based on soil moisture data in the deep vadose zone. Soil moisture at depths ranging from 0 to 200 cm was measured using HydraProbe II soil sensors in maize (Zea mays L.) and wheat (Triticum aestivum L.) fields in 2015 and 2017, respectively. Using a novel simulation approach based on soil moisture data in the deep vadose zone, the HYDRUS‐1D model provided reliable estimates of deep drainage as confirmed by comparison with estimates from the soil water balance method and prior studies in the region. The annual deep drainage averaged 468 mm, and the annual deep drainage coefficient averaged 43% in the young croplands. The winter irrigation amount averaged 265 mm, and the deep drainage coefficient during winter averaged 21% in the young croplands. The sandy soil of the young cropland and inefficient irrigation scheduling are detrimental to water conservation, causing relatively large deep drainage losses and enhancing the risks of groundwater pollution.

Environmental risk assessment for sustainable pesticide use in coffee production

The extensive use of pesticides in agricultural practices has been associated with human health problems and environmental contamination worldwide. Brazil is the largest consumer of pesticides in the world and Espírito Santo State stands out as the second Brazilian producer of coffee. However, there is no information about environmental impact of coffee producing at Itapemirim River Basin (IRB) region, Espírito Santo State, Brazil; hence a simple and quick method using open access softwares (AGROSCRE and ARAquá Web) to estimate surface entrainment and pesticide leaching potential was carried out. AGROSCRE evaluates the contamination risk of superficial and groundwater by Active Ingredients (AIs), using GOSS Method, GUS index and US EPA criteria, while ARAquá Web estimates AI concentrations in water resources, indicating their suitability based on water quality requirements for different uses. Regarding pesticides used in coffee plantations, there is 44.7% chance of surface water and 23.7% chance of groundwater contamination. Results showed that ametryne, cyproconazole, diuron, epoxiconazole, flutriafol, triadimenol and triazophos pose contamination risk to both surface water and groundwater in the IRB region. Of these, 10.5% of the total AIs are triazoles and fall under environmental classes II and III (Product Very/Dangerous to the Environment). The AIs ametryne, thiamethoxam, iprodione, flutriafol, triazophos, endosulfan, triadimenol, cyproconazole, diuron, pendimethalin, chlorpyrifos, copper II hydroxide, etion, epoxiconazole and paraquat dichloride, were found to be potentially toxic, presenting environmental concentrations ranging from 123.40 μg L-1 to 0.14 μg L-1, which are higher than the safety standard for potable water (0.1 μg L-1). With respect to these AIs, chlorpyrifos, ethion and triazophos showed concentrations higher than EC50 values for aquatic invertebrates and ametryne and diuron for algae. Thus, local residents and environment may be at high risk of pesticide exposure, when these AIs are used in coffee plantations next to surface water or groundwater.

Modelling pesticides leaching in cropping systems: Effect of uncertainties in climate, agricultural practices, soil and pesticide properties

Modelling of pesticide leaching is paramount to managing the environmental risks associated with the chemical protection of crops, but it involves large uncertainties in relation to climate, agricultural practices, soil and pesticide properties. We used Latin Hypercube Sampling to estimate the contribution of these input factors with the STICS-MACRO model in the context of a 400 km2 catchment in France, and two herbicides applied to maize: bentazone and S-metolachlor. For both herbicides, the most influential input factors on modelling of pesticide leaching were the inter-annual variability of climate, the pesticide adsorption coefficient and the soil boundary hydraulic conductivity, followed by the pesticide degradation half-life and the rainfall spatial variability. This work helps to identify the factors requiring greater accuracy to ensure better pesticide risk assessment and to improve environmental management and decision-making processes by quantifying the probability and reliability of prediction of pesticide concentrations in groundwater with STICS-MACRO.

Health risk assessment of heavy metal contamination in groundwater of Kadava River Basin, Nashik, India

Present research work emphasizes the integrated approach of heavy metal pollution indices coupled with multivariate statistical analysis to evaluate the health risk from groundwater of the Kadava River Basin. In view of this, forty representative groundwater samples were collected from dug and bore wells during pre-monsoon seasons of 2011 from rural habitations which are actively used for drinking and irrigation. The heavy metals viz., Pb, Cd, Zn, Fe, Mn, Cr, Cu, Co and Ni were analyzed through ICP-AES and compared with the BIS standards for drinking appropriateness. The analytical results exhibited that, Pb and Ni exceeded the maximum allowable concentration in all samples; while, Cr in 95% samples and Fe in 92.5% samples found beyond the safe limits. Heavy metal contamination assessment has been performed by using Heavy metal Pollution Index (HPI), Hazard Index (HI), Heavy metal Evaluation Index (HEI) and Degree of Contamination (Cd). The HPI results depicts that, 65 and 10% groundwater samples characterizes the medium and high pollution extent class. The human exposure risk based on HI confirms that groundwater is not suitable for drinking to all age groups as the value of HI ≥ 1. HEI results shows that 82.5% groundwater samples fall in high pollution extent category and only 17.5% samples in medium pollution extent category caused due to excessive presence heavy metals. Cd result illustrates the widespread unsuitability of 97.5% groundwater samples due to high pollution load from heavy metals and 2.5% samples comes under moderate pollution extent. The correlation among the heavy metal indices depicts that HPI with HEI (r = 1) and Cd (0.825); moreover. HEI with Cd (r = 0.825) are strongly associated; hence, it confirms that, all these indices are significant to assess the heavy metal contamination risk in the study area. PCA, CA, CM and pollution indices analysis corroborate that, high contents of heavy metals in groundwater of Kadava River Basin is owed to land use pattern, intense agriculture, leaching of fertilizers and pesticides and domestic waste into the aquifer system. The outcomes of research work may help to local planners and policy makers to prevent the health risk by the implementation of appropriate monitoring and mitigation measures for contaminated aquifers.

Assessment of heavy metal pollution in a Himalayan river using multivariate statistical tools: a case study of the Kameng River in Arunachal Pradesh, India

Kameng River is a high-altitude fluvial system that originates in the snow-clad mountain ranges of the eastern Himalayas in the state of Arunachal Pradesh of India. In the present research, the spatial and seasonal distributions of selected heavy metals (Fe, Cd, Cu, Mn, Pb, Zn, and As) were studied to assess their pollution status within the river basin. This study reports the first systematic evaluation of heavy metals in the Kameng River within the geographical boundary of Arunachal Pradesh. The Kameng River is a major source of water to the indigenous communities residing within the river basin. In recent years, some serious debates have been going on the issues surrounding hydro-energy exploration in the river basin. Construction of large- and medium-scale hydroelectric projects is likely to fragment the entire river course and alter the environmental flow of the river that would invariably affect the water quality regime. In order to predict the future changes in the water quality parameters, it is important to carry out water quality studies at present. In the present study, water samples were collected from 27 locations representing four sub-watersheds within the Kameng River basin. The study revealed that the river water was polluted by Cd, Pb, Mn, and Zn with respect to the safe limit prescribed by regulatory authorities. The multivariate statistical analysis using principal component analysis (PCA) and hierarchical cluster analysis (HCA) tools suggested that the concentration of the heavy metals was primarily controlled by geochemical factors that included the dissolution of phosphate rocks, weathering of carbonate rocks, and base metal mineralization. Further, the solubility mechanics of these metals were controlled by processes of co-precipitation, adsorption, and ion precipitation on pre-existing mineral surfaces. The study also indicated the contribution of heavy metals from anthropogenic sources that primarily included the leaching of pesticides from agricultural soils. This study illustrates the successful application of multivariate statistical tools in understanding the distribution of heavy metals in river basins.

Mulch of plant residues at the soil surface impact the leaching and persistence of pesticides: A modelling study from soil columns

Crop residues left on the soil surface as mulch greatly influence the fate of pesticides in conservation agricultural practices because most of the applied pesticide is intercepted by mulch before passing to the soil. Modelling of pesticide losses from wash-off and leaching will greatly improve our understanding of the environmental consequences of pesticides in these systems. The PASTIS model, which simulates water transfer, mulch decomposition, and pesticide dynamics, was adapted in this new version to model the interactions between pesticides and mulch in order to simulate the impact of mulch on pesticide dynamic. Parameters of mulch dynamics and pesticide degradation and retention processes were estimated using independent incubation experiments. The PASTIS model was tested with experimental laboratory data that were obtained from two pesticides (Glyphosate and s-metolachlor) applied to soil columns where mulch composed of maize and dolichos was placed at the soil surface impacted by two rain intensities (a high and infrequent intensity and a light and frequent intensity). Simulations indicated good agreement between simulated and experimental values. After 1 day, 45–46% of the pesticides leached from the mulch and 54–55% remained in the mulch for both pesticides and both rain intensities. During the experiment, pesticide wash-off was greater for the high and infrequent rain (56–57%) compare to light and frequent rain (39–45%) for both pesticides. A smaller amount of S-metolachlor washed off with the light and frequent rain intensity (39%) than glyphosate (45%) because of its lower desorption rate from mulch residues. Glyphosate was more degraded (37–45%) than s-metolachlor (17–37%), which agrees with preliminary incubation experiments that were used for parameter estimation. A sensitivity analysis indicated that the saturation index of mulch at which pesticides started their diffusion in the rainwater and the time of the first rainfall were the two parameters that influenced the most output variables of our model. This study suggests that the PASTIS model developed for pesticide dissipation in mulch is a useful tool to evaluate the potential risk of pesticide leaching to the groundwater in conservation agriculture systems.

An integrated approach for assessing the migration behavior of chlorpyrifos and carbaryl in the unsaturated soil zone

ABSTRACTChlorpyrifos (O, O-diethyl O-3,5,6-trichloropyridin-2-yl phosphorothioate) and carbaryl (1-naphthyl methylcarbamate) are often applied concurrently as insecticides in food production. The aim of this study was to research their migration behavior in a real environment. We researched the leaching of both pesticides by setting up field lysimeters on a farm with the typical soil used in fruit production today. In order to analyze the variables involved in this process, we performed complementary adsorption studies, we performed complementary adsorption studies using batches and undisturbed soil laboratory columns for both compounds. The results for pesticide transport through the lysimeters showed that less than 1% of chlorpyrifos was recovered in the leachates, while almost 17% was recovered for carbaryl. Having completed the experiment in undisturbed laboratory columns, soil analysis showed that chlorpyrifos mainly remained in the first 5 cm, while carbaryl moved down to the lower sections. These results can be explained in view of the sorption coefficient values (KD) obtained in horizons A and B for chlorpyrifos (393 and 184 L kg−1) and carbaryl (3.1 and 4.2 L kg−1), respectively. By integrating the results obtained in the different approaches, we were able to characterize the percolation modes of these pesticides in the soil matrix, thus contributing to the sustainable use of resources.

Matrix Based Fertilizers Reduce Nutrient and Pesticide Leaching

Matrix Based Fertilizers Reduce Nutrient and Pesticide Leaching

Pesticide leaching by agricultural drainage in sloping, mid-textured soil conditions - the role of runoff components.

Dynamics of pesticides and their metabolites in drainage waters during baseflow periods and rainfall-runoff events (RREs) were studied from 2014 to 2016 at three small, tile-drained agricultural catchments in Bohemian-Moravian Highlands, Czech Republic. Drainage systems in this region are typically built in slopes with considerable proportion of drainage runoff originating outside the drained area itself. Continuous monitoring was performed by automated samplers, and the event hydrograph was separated using 18O and 2H isotopes and drainage water temperature. Results showed that drainage systems represent a significant source for pesticides leaching from agricultural land. Leaching of pesticide metabolites was mainly associated with baseflow and shallow interflow. Water from causal precipitation diluted their concentrations. The prerequisites for the leaching of parental compounds were a rainfall-runoff event occurring shortly after spraying, and the presence of event water in the runoff. When such situations happened consequently, pesticides concentrations in drainage water were high and the pesticide load reached several grams in a few hours. Presented results introduce new insights into the processes of pesticides movement in small, tile-drained catchments and emphasizes the need to incorporate drainage hydrology and flow-triggered sampling into monitoring programmes in larger catchments as well as in environment-conservation policy.

Meta-analysis of pesticide sorption in subsoil.

Models used to assess leaching risks generally use organic carbon partition coefficient (kOC ) values derived from batch experiments on topsoil samples to estimate pesticide sorption in subsoils of much smaller organic carbon contents. This can introduce significant errors in leaching risk calculations, because inorganic sorbents can play an important role for sorption in subsoil. The objectives of the present study were therefore to summarize the available literature data on pesticide sorption in subsoils and to test whether a simple alternative model could improve on the standard kOC approach used in risk assessment models for pesticide leaching. This model describes the sorption constant as a power law function of the organic carbon content. A database with the results of batch sorption experiments was collated from published studies that emphasized measurements in subsoils. This database contains 1029 data entries from 36 published studies with data for 29 active substances (11 nonionic compounds, 10 weak acids, 6 weak bases, one cation, and one zwitterion). The results show that whereas the constant kOC model proved to be an adequate model for 17 of the 63 individual datasets, the power law model gave acceptable fits (p < 0.05) for 60 of these cases. The exponent in the power law model varied over a wide range, from slightly negative to near unity. It also differed significantly (p = 0.015) for ionized and nonionized compounds, with median values of 0.25 and 0.55, respectively. It is concluded that the power law model could be used to parameterize subsoil sorption in regulatory leaching models, because it has widespread applicability and is simple enough for this purpose. Suitable ways of incorporating this approach in risk assessment procedures are discussed. Environ Toxicol Chem 2018;37:755-761. © 2017 SETAC.

Transport of 3,5,6-trichloro-2-pyrdionl (a main pesticide degradation product) in purple soil: Experimental and modeling

Purple soil, a loamy entisol dominating the hilly central Sichuan basin in the upper reaches of Yangtze River, is low in organic matter content and abundant in macropores that form the rapid transport network for water and solutes including pesticides. However, effects of soil's macroporosity on transport of pesticides has not been quantitatively explored and simulated at the column scale. In this study, we explore the transport of 3,5,6-trichloro-2-pyrdionl (TCP), a main pesticide degradation product, in purple soil through experiments and simulations on typical farmland categories, including rice-rape and vegetable farmland. Soil water retention characteristics (SWRCs) and physical properties are measured to learn the hydraulic parameters and porous structures of the soil. Batch experiments are conducted to obtain the adsorption coefficient of TCP on soil, and breakthrough curves of Br− (a conservative tracer) in undisturbed soil columns are applied to evaluate the hydrodynamics of TCP transport. The two-region model is used to simulate the transport processes, and the parameters are obtained by inversion simulation. It is found that TCP transport in purple soil exhibited complex patterns and is strongly affected by both chemical and physical non-equilibrium. A higher pollution risk on water body of rice-rape field is due to the stronger preferential flow and better pore connectivity despite the larger macroporosity observed in vegetable field. These results can provide useful data and modeling approach for evaluating the risk of pesticide leaching toward groundwater.

Sorption, degradation and leaching of pesticides in soils amended with organic matter: A review

The use of pesticides in modern agriculture is unavoidable because they are required to control weeds. Pesticides are poisonous; hence, they are dangerous if misused. Understanding the fate of pesticides will be useful to use them safely. Therefore, contaminations of water and soil resources could be avoided. The fates of pesticides in soils are influenced by their sorption, decomposition and movement. Degradation and leaching of pesticides are control by sorption. Soil organic matter and clay content are main soil constituents that have a high capacity for sorption of pesticides. Addition of organic maters to amend the soils is a usual practice that every year has been done in a huge area of worldwide. The added organic amendments to the soils affect the fate of pesticides in soils as well. Pesticides fates in different soils are different. The addition of organic matter to soils causes different fates for pesticides as well. It is known from the studies that sorption of non-ionic pesticides by soil in aqueous system is controlled mainly by the organic matter content of the soils. Sorption of pesticides has been reported to increase by amending soils with organic matter. In general, conditions that promote microbial activity enhance the rate of pesticides degradation, and those that inhibit the growth of microorganisms reduce the rate of degradation. Amendment of soils with organic matter may modify leaching of pesticides in soil. Some studies showed that organic matter added to soils reduced pesticides in ground water. Generally, organic amendments induces the restriction of pesticides leaching in soils.