Pesticide Transport In Soils Research Articles

Spatial Control of Microbial Pesticide Degradation in Soil: A Model-Based Scenario Analysis.

Microbial pesticide degraders are heterogeneously distributed in soil. Their spatial aggregation at the millimeter scale reduces the frequency of degrader–pesticide encounter and can introduce transport limitations to pesticide degradation. We simulated reactive pesticide transport in soil to investigate the fate of the widely used herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) in response to differently aggregated distributions of degrading microbes. Four scenarios were defined covering millimeter scale heterogeneity from homogeneous (pseudo-1D) to extremely heterogeneous degrader distributions and two precipitation scenarios with either continuous light rain or heavy rain events. Leaching from subsoils did not occur in any scenario. Within the topsoil, increasing spatial heterogeneity of microbial degraders reduced macroscopic degradation rates, increased MCPA leaching, and prolonged the persistence of residual MCPA. In heterogeneous scenarios, pesticide degradation was limited by the spatial separation of degrader and pesticide, which was quantified by the spatial covariance between MCPA and degraders. Heavy rain events temporarily lifted these transport constraints in heterogeneous scenarios and increased degradation rates. Our results indicate that the mild millimeter scale spatial heterogeneity of degraders typical for arable topsoil will have negligible consequences for the fate of MCPA, but strong clustering of degraders can delay pesticide degradation.

Modelling Water and Pesticide Transport in Soil with MACRO 5.2: Calibration with Lysimetric Data

Assessing the risk of using pesticides for the environment in general, and for groundwater in particular, necessitates prediction of pesticide migration. For this purpose, mathematical models of pesticide behavior are utilized, which must be parameterized and calibrated based on experimental data to make them perform properly. The behavior of the pesticide cyantraniliprole was examined in a long-term lysimetric experiment. The MACRO 5.2 dual porosity model was calibrated based on the percolate and the levels of pesticides in the soil profile and percolate. Despite employing experimentally verified soil parameters and pedotransfer functions (PTF), the model must be calibrated for percolation. This is due to the model’s properties as well as the complexity of the soil as an object of study, and its pore space, which is subject to daily and annual fluctuations. It is the parameters that describe the structure of the pore space that need to be calibrated. Calibrating for pesticide concentrations required a minor revision of the sorption and transformation rates, as well as an increase in the dispersivity and ASCALE values.

Coupling HYDRUS-1D with ArcGIS to estimate pesticide accumulation and leaching risk on a regional basis

HYDRUS-1D is a well-established reliable instrument to simulate water and pesticide transport in soils. It is, however, a point-specific model which is usually used for site-specific simulations. Aim of the investigation was the development of pesticide accumulation and leaching risk maps for regions combining HYDRUS-1D as a model for pesticide fate with regional data in a geographical information system (GIS). It was realized in form of a python tool in ArcGIS. Necessary high resolution local soil information, however, is very often not available. Therefore, worldwide interpolated 250-m-grid soil data (SoilGrids.org) were successfully incorporated to the system. The functionality of the system is shown by examples from Thailand, where example regions that differ in soil properties and climatic conditions were exposed in the model system to pesticides with different properties. A practical application of the system will be the identification of areas where measures to optimize pesticide use should be implemented with priority.

Spatiotemporal sensitivity analysis of vertical transport of pesticides in soil

Environmental fate and transport processes are influenced by many factors. Simulation models that mimic these processes often have complex implementations, which can lead to over-parameterization. Sensitivity analyses are subsequently used to identify critical parameters whose uncertainties can be further reduced or better described and prediction variability minimized. In this study, a variance decomposition based global sensitivity analysis technique (Sobol’ method) is conducted based on estimated concentrations in vertical soil compartments using the Pesticide Root Zone Model (PRZM). Daily simulations are performed that explore the input parameter space. Estimated concentrations are compared to data collected over the course of a growing season from an experimental site in Georgia. Our results suggest that model sensitivity is conditional and should be examined at appropriate spatial and temporal resolution to avoid omitting important parameters. This approach can yield a better understanding about the interplay between sensitivity/uncertainty and model dynamics in non-monotonic, non-linear systems.

Effects of nano-SiO2 on the adsorption of chiral metalaxyl to agricultural soils

The application of nanotechnology in agriculture, pesticide delivery and other related fields increases the occurrence of engineered nanoparticles (ENPs) in soil. Since ENPs have larger surface areas and normally a high adsorption capacity for organic pollutants, they are thought to influence the transport of pesticides in soils and thereafter influence the uptake and transformation of pesticides. The adsorption pattern of racemic-metalaxyl on agricultural soils including kinetics and isotherms changed in the presence of nano-SiO2. The adsorption of racemic-metalaxyl on agricultural soil was not enantioselective, in either the presence or the absence of SiO2. The adsorption of racemic-metalaxyl on SiO2 decreased to some extent in soil-SiO2 mixture, and the absolute decrease was dependent on soil properties. The decreased adsorption of metalaxyl on SiO2 in soil-SiO2 mixture arose from the competitive adsorption of soil-dissolved organic matter and the different dispersion and aggregation behaviors of SiO2 in the presence of soil. Interactions between SiO2 and soil particles also contributed to the decreased adsorption of metalaxyl on SiO2, and the interactions were analyzed by extended Derjaguin–Landau–Verwey–Overbeek theory. The results showed that the presence of nano-particles in soils could decrease the mobility of pesticides in soils and that this effect varied with different soil compositions.

Degradation and Downward Movement of Lindane in Soil Under Cultivated Field Conditions

Transport of pesticides in soil is important because it determines the extent to which pesticides reach groundwater. Many investigators have studied in a qualitative manner the tendency of insecticides to move by leaching through the soil by developing a mathematical expression. Little attention has been given to the actual formulation of such a model particularly under cultivated field conditions. The investigations described in this paper presented quantitative data which has indicated the relative importance of the factors which must be considered in predicating pesticide movement under cultivable field conditions. The data on residues of lindane in soil under cropped conditions showed the highly persistence nature of the pesticide. The movement of lindane being a matter of inches rather than feet holds good with the present experimental findings though the experiment was carried out in a sandy loam soil with very little organic carbon and clay contents.

Ethoprophos fate on soil–water interface and effects on non-target terrestrial and aquatic biota under Mediterranean crop-based scenarios

The present study aimed to assess the environmental fate of the insecticide and nematicide ethoprophos in the soil–water interface following the pesticide application in simulated maize and potato crops under Mediterranean agricultural conditions, particularly of irrigation. Focus was given to the soil–water transfer pathways (leaching and runoff), to the pesticide transport in soil between pesticide application (crop row) and non-application areas (between crop rows), as well as to toxic effects of the various matrices on terrestrial and aquatic biota. A semi-field methodology mimicking a “worst-case” ethoprophos application (twice the recommended dosage for maize and potato crops: 100% concentration v/v) in agricultural field situations was used, in order to mimic a possible misuse by the farmer under realistic conditions. A rainfall was simulated under a slope of 20° for both crop-based scenarios. Soil and water samples were collected for the analysis of pesticide residues. Ecotoxicity of soil and aquatic samples was assessed by performing lethal and sublethal bioassays with organisms from different trophic levels: the collembolan Folsomia candida, the earthworm Eisenia andrei and the cladoceran Daphnia magna. Although the majority of ethoprophos sorbed to the soil application area, pesticide concentrations were detected in all water matrices illustrating pesticide transfer pathways of water contamination between environmental compartments. Leaching to groundwater proved to be an important transfer pathway of ethoprophos under both crop-based scenarios, as it resulted in high pesticide concentration in leachates from Maize (130µgL−1) and Potato (630µgL−1) crop scenarios, respectively. Ethoprophos application at the Potato crop scenario caused more toxic effects on terrestrial and aquatic biota than at the Maize scenario at the recommended dosage and lower concentrations. In both crop-based scenarios, ethoprophos moved with the irrigation water flow to the soil between the crop rows where no pesticide was applied, causing toxic effects on terrestrial organisms. The two simulated agricultural crop-based scenarios had the merit to illustrate the importance of transfer pathways of pesticides from soil to groundwater through leaching and from crop rows to the surrounding soil areas in a soil–water interface environment, which is representative for irrigated agricultural crops under Mediterranean conditions.

Evaluation of the Environmental Impact of Pesticides by Application of Three Risk Indicators

This study compares three pesticide-risk indicators: 1) the environmental impact quotient (EIQ), 2) the toxicity, human health, and persistency hazard rating system (THP), and 3) the pesticide environmental risk indicator (PERI) to evaluate the environmental impacts of active ingredients in pesticides. Environmental risk scores were obtained and evaluated for commonly used pesticides in Kumluca region of Turkey. The risk scores of EIQ and THP were in good agreement. This study provides an example applicable in other areas where environmental measurements of pesticides are either unaffordable or not physically feasible. The selected pesticide risk indicators are easily applied and helpful tools for pest management practitioners. However, site specific components (surface runoff, particle transport processes, and spatial variability of pesticide transport in soil) and exposure of consumers to pesticide residues are missing in the selected indicators. Forensic methods and approaches could be applied in conjunction with existing indicator models to better understand pesticide fate and transport and improve their selection and application pattern.

A critical review of the influence of effluent irrigation on the fate of pesticides in soil

The impact of effluent irrigation on the transformation and mobility of organic contaminants is poorly understood. The objectives of this review paper are: (i) to discuss the fundamental processes influencing the transformation and transport of pesticides in soil; (ii) to present a critical analysis of the impact of effluent irrigation on the transformation and transport of pesticides in soils; (iii) to suggest research areas that need attention. Effluent irrigation affects the fate of pesticides through its direct effect on the transformation and transport of pesticides that are already present at the irrigation sites, and its indirect effect on soil properties that are important in controlling the transformation and transport of organic contaminants. It has often been noticed that the effluent-derived dissolved organic matter (DOM) facilitates the movement of soil-borne pesticides by forming soluble pesticide complexes, and enhances their biodegradation by providing energy sources for the microorganisms that are involved in pesticide degradation. However, the results of field and laboratory experiments that examined the effect of effluent irrigation on the fate of pesticides are inconsistent; in some cases reduced mobility resulting from enhanced pesticide sorption has been observed, but enhanced pesticide mobility has also been reported. The inconsistency may be related to the inherent spatial variability of soil properties and/or the heterogeneity of effluent quality. For example, effluents vary in the nature and concentration of DOM that play a vital role in the degradation, sorption and transport behaviour of pesticides. Similarly, they vary in the concentrations of solvents and surfactants that have been shown to impact sorption and transport of organic contaminants. Field-based investigations on the impact of effluent irrigation on pesticide fate coupled with an accurate characterisation of the effluent are urgently required to assess the long-term risk associated with effluent irrigation in relation to pesticide transformation and transport.

Comparison of Pesticide Transport Processes in Three Tile‐Drained Field Soils Using HYDRUS‐2D

The purpose of this study was to assess the transport of the herbicide bentazone [3‐(1‐methylethyl)‐1H‐2,1,3‐benzothiadiazin‐4(3H)‐one 2,2‐dioxide] in three contrasting tile‐drained cultivated field soils subject to otherwise similar experimental conditions. Observed drain discharge rates and chemical concentrations in the drainage water reflected the different transport processes at the three sites in the same area of northeastern France: a sandy loam site (Villey), a silt loam site (Bouzule‐1), and a silty clay site (Bouzule‐2). The sandy loam site showed very little tile drainage (240 m3 ha−1) during the 100‐d study in the spring of 2002, as well as low chemical losses in the drainage water (0.16% [v/v] of the applied amount). While little drainage was observed also for the silty clay soil (175 m3 ha−1), observed pesticide losses were considerably larger (1.25% of the applied amount). The silt loam soil, in comparison, showed much more drainage (521 m3 ha−1) and the highest chemical loads in the drainage water (2.7% of the applied amount). Numerical simulations of drain discharge with the HYDRUS‐2D variably saturated flow and solute transport model compared well with the observed data for the relatively homogeneous sandy loam (Villey) and the silt loam (Bouzule‐1) soils. The saturated hydraulic conductivity of the bottom layer in both cases was key to correctly predicting the drainage fluxes. Accurate predictions of the silty clay field data (Bouzule‐2) could be obtained only when the soil hydraulic functions were modified to account for preferential flow through drying cracks near the soil surface. Chemical concentrations could be better described using a dual‐porosity (mobile–immobile water type) transport model for all three soils, including the sandy loam. Results indicate that water and pesticide transport in soils is governed by site‐specific processes. Optimal use of the HYDRUS‐2D flow and transport model allowed a reasonable description of the field‐scale pesticide processes using only a limited number of adjustable parameters.

A comparison of non-linear least square and GLUE for model calibration and uncertainty estimation for pesticide transport in soils

The problems of calibrating soil hydraulic and transport parameters are well documented, particularly when data are limited. Programs such as CXTFIT, UUCODE and PEST, based on well established principles of statistical inference, will often provide good fits to limited observations giving the impression that a useful model of a particular soil system has been obtained. This may be the case, but such an approach may grossly underestimate the uncertainties associated with future predictions of the system and resulting dependent variables. In this paper, this is illustrated by an application of CXTFIT within the generalised likelihood uncertainty estimation (GLUE) approach to model calibration which is based on a quite different philosophy. CXTFIT gives very good fits to the observed breakthrough curves for several different model formulations, resulting in very small parameter uncertainty estimates. The application of GLUE, however, shows that much wider ranges of parameter values can provide acceptable fits to the data. The wider range of potential outcomes should be more robust in model prediction, especially when used to constrain field scale models.

Dynamics of Pesticides in Potato Crops

This study investigated the behavior of pesticides commonly used on potato in a part of northwestern Spain with a large area devoted to this crop. Experimental potato plots were treated with commercial formulations of two insecticides, a nematicide, a herbicide, and a combination of two fungicides, and the concentrations of the active ingredients were monitored throughout the growing season in the 0-1 and 1-15 cm soil layers, in water dripping off the potato plants, and in the potatoes themselves. The technique used for pesticide determination was gas chromatography with mass selective detection. For potato analyses, pesticide extraction was optimized. The only pesticide ever detected in potato tubers was metalaxyl, the concentration of which never exceeded half the maximum residual limit even when it was applied several times more often than is officially recommended for potato crops. Metalaxyl was also the only pesticide detected in wash-off, apparently due to its being more soluble in water than the other pesticides applied to the growing plants. A mathematical model of pesticide transport in soil was fitted to the experimental data using the program HYDRUS-1D.

Construction and Evaluation of a Humic Acid Column: Implication for Pesticide Risk Assessment

In this paper, humic acid (HA), known to play a large role in the binding and transport of pesticides in soil, was immobilized on a chromatographic support. Then, the association of some herbicides and rodenticides with the main soil component HA was examined using this novel chromatographic column. It appeared that HA has a lower affinity for neutral than for charged pesticides. Moreover, the influence of various parameters was investigated on the pesticide retention in order to providevaluable information about both the binding mechanism and the utilization conditions of the HA column. For all the pesticides studied, a change was clearly vizualized in the HA-pesticide association mechanism at a critical value of the Na+ concentration in the bulk solvent, x(c), equal to 0.6 M. Around this value, the HA structure balanced between a flexible linear conformation for x < x(c) and a random coil form for x > x(c). This work confirmed the conformation change on HA immobilized on silica. As well, only for the charged pesticides, it was clearly pointed out that below a Na+ concentration equal to 0.3 M, the pesticide binding to HA decreased when the salt concentration was enhanced due to an ion pair formation and a competition effect between the sodium cation and pesticide to bind to the HA molecule. Furthermore, it was established that the HA column was stable during an extended period of time, indicating that the HA column could soon become very attractive to determine the risk assessment of pesticides.

Simulation of 2,4-d herbicide transport through the unsaturated zone using an analytical model

Pesticide movement through the unsaturated zone of the subsurface environment is a complex process. Agricultural practices, soil properties, and climatic conditions among others, constitute the most important aspects to be considered. To simulate the transport and fate of the herbicide 2,4-D under real agricultural conditions, the Hantush–Mariño (1996) model has been applied. The model is a physically based analytical model that simulates pesticide transport in soils and groundwater. In the unsaturated zone, the model simulates one-dimensional pesticide movement based on the concept of complete mixing, adsorption, volatilization, and degradation. Linear equilibrium liquid–vapor partition is considered based on Henry's law and linear equilibrium adsorption is assumed for sorption and desorption in soil. The simulation model is applied to a study area located in a newly built golf course (Baix Emporda-Gerona, Spain), where 2,4-D is currently applied. Results show that with current agricultural practices, 2,4-D can be still detected at a depth of 2 m at concentrations greater than 0.1 µg/L.

A Multivariate Adaptive Regression Splines Model for Simulation of Pesticide Transport in Soils

In this study, an innovative and intelligent computing regression algorithm, multivariate adaptive regression splines (MARS), was applied to simulate pesticide transport in soils. Using a divide-and-conquer method, the algorithm classifies the training data into several groups, in each of which a regression line or hyperplane is fitted. Compared to other intelligent computing technologies, MARS is fast, flexible, and capable of determining the important sequence of inputs to the output. This study evaluated MARS by applying it to simulate pesticide concentration levels at different soil depths and at various times. The model inputs included the number of days after pesticide application, accumulated rainfall, accumulated potential evapotranspiration, accumulated soil temperatures at depths of 100 mm in the morning as well as in the afternoon, and tillage practices. Several MARS models were developed to simulate the concentration levels of atrazine, deethylatrazine, and metolachlor at depths of 0–75 and 75–150 mm, respectively. The performance of MARS was compared to that of artificial neural networks (ANNs) using standard errors and correlation coefficients of linear regression. The results show the strong potential of MARS to be applied to agriculture as a regression technology.

COUPLING DIAZINON VOLATILIZATION AND WATER EVAPORATION IN UNSATURATED SOILS: I. WATER TRANSPORT

Volatilization of pesticides from soil is one of the key processes causing transport of chemicals to non-target areas. This study focuses on how water transport in the surface soil affects volatilization of pesticides. Volatilization of soil-incorporated diazinon [O, O diethyl O-(2-isopropyl-4-methyl-6-pyrimidinyl) phosphorothioate] was measured under different initial soil-water contents and soil-water evaporation conditions. These conditions were varied by passing wet air and dry N2 alternately across the soil surface. When dry sweep gas (N2) was used in high initial water content columns, diazinon volatilization was accelerated as a result of appreciable upward water flow. When upward water flow was insufficient to meet evaporative demand, soil-water content at the soil surface was quickly reduced below a threshold, and diazinon volatilization started to decrease exponentially because of diazinon adsorption on the dry soil surfaces. When the sweep gas was switched to humidified air, the soil surface adsorbed water and diazinon volatilization increased dramatically. A numerical model was developed to simulate pesticide transport in soil for isothermal conditions. The calculated and measured diazinon volatilization fluxes agreed well, but the model overestimated diazinon concentrations in the deeper depths of the soil significantly.

A European test of pesticide-leaching models: methodology and major recommendations

Testing of pesticide-leaching models is important in view of their increasing use in pesticide registration procedures in the European Union. This paper presents the methodology and major conclusions of a test of pesticide-leaching models. Twelve models simulating the vertical one-dimensional movement of water, solute, heat, and, in particular, pesticides, through the soil profile were used by 36 different modellers. The adopted modelling codes differ in terms of modelling concepts and modelling hypothesis. Modellers were affiliated to industry and to the scientific community as well. Four quality datasets were identified to perform the analysis. The dataset included field and lysimeter data, collected in the Netherlands, Germany, Italy and the UK. As well, non-structured as structured soils were available in the dataset. To elucidate the ability to model correctly water transport, solute transport, heat transport and pesticide transport in soils, a stepwise evaluation approach was followed. Splitting up the experimental dataset enabled us to quantify the calibration capability and the prediction capability of the models. The simulations were performed by different model users enabling us also to characterise output variability in terms of user dependent interpretation of the model input and parameters. Recommendations are formulated for improving the quality of modelling datasets, and the process description of water, solute, and heat transport in a pesticide-leaching model, plus the process description of pesticide fate. Application of the principles of good modelling practice (GMP) is briefly described.

Study of the behaviour of azinphos-methyl in a clay mineral by batch and column leaching

Research efforts dealing with the processes affecting the transport of pesticides in soils are needed in order to prevent further damage of surface and groundwater reserves. Although organic matter has been recognised as the most important contributor to the adsorption of non-ionic organic pesticides in soils, in some cases clay minerals may have an important role in the retention of these compounds. The present study was designed to improve the knowledge of the behaviour of azinphos-methyl in soils. Coefficients from adsorption isotherms and HPLC analysis of soil column leachates were used in this work for predicting pesticide mobility in soils. The studied clay mineral was a Spanish bentonite with a predominant montmorillonite fraction. The results showed that azinphos-methyl was adsorbed on the clay mineral and demonstrated the catalytic effect of bentonite on the hydrolysis of the pesticide.

Patterns of groundwater concentration and fate of lindane in an irrigated semiarid area in Argentina

AbstractThe pattern of lindane breakthrough to groundwater and its mobilization thereafter were observed in a semiarid irrigated agricultural basin in southern Argentina. The pesticide half‐life in the unsaturated vadose zone and the realized Koc were estimated through parameter optimization techniques on the basis of an ad hoc developed fugacity model, and two existing models of the transport of pesticides in soils (RITZ, PRZM2). Although the estimated half‐life values are in agreement with values reported in the literature for other areas, the Koc was lower than usually reported, indicating that the adsorption of the pesticide is controlled by the kinetics of soil water infiltration. The lindane concentration and groundwater conductivity fields over an area of about 2,700 km2 were compared and similarities between the transport of the pesticide and soluble soil salts were inferred. These showed that lindane is transported dissolved in the upper aquifer and can accumulate at exfiltration areas at 10 to 30 km from the sites of its application. The relevance of considering the kinetic constraints imposed by the hydraulic conductivity of the soil profile and the partition with the soil organic matter are highlighted in relation to the prediction of pesticide environmental fate.

Solute Transport in Soils Under Conditions of Variable Flow Velocities

Temporal and spatial variabilities of flow distribution significantly influence solute transport in soils. This laboratory study was designed to investigate the effects of temporal variation in flow velocity on pesticide transport in soils. Two pesticides, metribuzin (weakly adsorbed) and atrazine (moderately adsorbed), were chosen along with the following two soils: Cecil (&lt;2 mm) and Sharkey (2–4 mm). Several tritium pulses were introduced into packed soil columns (15 or 30 cm in length) under different flow velocities to obtain velocity‐dependent dispersion coefficients (D). Subsequently, several atrazine and metribuzin pulses were introduced under conditions of constant and variable velocities. For each experiment, changes in flow velocity were stepwise using a piston flow pump and were carried out during pulse application and leaching. For constant and variable flow velocity experiments, approximately similar pulse volumes and average flow velocities were maintained. Values of D versus pore water velocity (ν) from tritium breakthrough curves (BTCs) were well described using a linear equation for both soils. Identical BTCs for metribuzin were observed under conditions of constant or variable flow velocities in the Cecil soil column. However, metribuzin transport in the Sharkey soil was significantly influenced by velocity variations. Atrazine transport in the Sharkey soil was also significantly affected by variations in flow velocity. We further examined the error when an average rather than actual velocity distribution was used in BTC representation. The resulting experimental BTCs (concentration versus velocity‐averaged pore volume) exhibited early arrival and the appearance of multiple peaks. Moreover, predictions of such BTCs based on the convective‐dispersive equation were not successful. We concluded that actual water velocity distributions should be used in BTC representation, and, whenever possible, the use of an average velocity should be avoided.