Pesticide Leaching Models Research Articles

GIMMI: Geographic Information and Mathematical Models Inter-operability

GIMMI 2 GIMMI IST-2001-34245 receives funding under the EU IST program. 2 project, started in April 2002, aims at bridging the gap of communication in the pesticide impact assessment domain between data providers (soil, meteorology, agronomy, pesticide experts), scientists (chemists, geologists, modellers and academic institutions), service providers (local and central governments, public administration bodies, private chemical industries manufacturing pesticides) and final users (agronomists, consultants and even citizens). This can be achieved by allowing the inter-operability via Web of Geographic Information Systems (GIS), environmental protection data and service (e.g. mathematical models) providers physically distributed, by providing the proper IT structures to represent and manage temporal knowledge, and by integrating state-of-the-art legacy systems for document management and report generation. The main results of GIMMI will be an open Web brokerage system supporting different web-services such as: On-line Data Access to seek and drill down into huge amount of distributed Geographic Information; On/Off-line Simulations allowing inter-relation of distributed databases to run mathematical models. “Open systems” means that new data and service providers can easily be integrated in the running system while remaining autonomous. The validation scenario chosen for GIMMI is the field of pesticides impact assessment in agriculture practices and Land Protection, by the adoption of four alternative EC-validated pesticide leaching models.

The potential steroid hormone contribution of farm animals to freshwaters, the United Kingdom as a case study

The combined farm animal population is considerably larger than the human one in the United Kingdom, implying a possibly important contribution to the environmental load of steroid hormones entering water. To make comparisons on the amount of steroid hormones produced by the different livestock, information was gathered on the structure of the UK farm animal populations and the amount of hormones excreted by animals at each of their life stages. An individual normalised dairy cow excretes two orders of magnitude more, and a normalised pig excretes more than one order of magnitude more steroid oestrogens than a normalised human. In terms of excretion, the combined farm animal population (including sheep and poultry) probably generates around four times more oestrogens than the human population in the UK. The biggest contributor on the animal side is the relatively small dairy cow population. If steroid oestrogens behave like herbicides, in which a worst case loss to surface waters is around 1%, then it could be argued that farm animals are responsible for 15% of all the oestrogens in UK waters. When simulations were made with the MACRO pesticide leaching model, predicted concentrations for field drains failed to exceed 1 ng/L. The rapid biodegradation rates, and high sorption rates taken from the literature and used in the model suggested less than 0.001% of oestrogens would reach the field drains. This survey suggests that direct excretion of steroid hormones by animals into water courses, or discharges from farmyard drains, are likely to be more important sources of contamination rather than via normal agricultural scenarios.

A spatialising tool to simulate pesticide fate in the unsaturated zone on a catchment scale

A tool has been designed to calculate the leaching potential of pesticide on a catchment scale using the one-dimensional pesticide leaching model MACRO. The tool is able to collect the input data of the study area in a grid with homogeneous cells and prepare spatially distributed data required by MACRO. Successively, the tool can run multiple MACRO simulations for each cell of the grid and organise output reports following the user's preference, as well as generate output files compatible with GIS and other environmental software applications. The tool was tested to simulate the behaviour in the unsaturated zone of water and pesticide isoproturon used on winter wheat at 1.75 kg ha -1 of active ingredient in a German study area for 10 years of meteorological data and for different crop-soil combinations. Maps of isoproturon concentration in the liquid phase were created using the spatialised output data from the tool.

Simulation of pesticide leaching in a cracking clay soil with the PEARL model

Testing of pesticide leaching models is important to increase confidence in their use in pesticide registration procedures world-wide. The chromatographic PEARL model was tested against the results of a field leaching study on a cracking clay soil with a tracer (bromide), a mobile pesticide (bentazone) and a moderately sorbing, persistent pesticide (imidacloprid). Input parameters for water flow and solute transport were obtained from site-specific measurements and from literature. The model was tested using a stepwise approach in which each sub-model was sequentially and separately tested. Uncalibrated simulations for the water flow resulted in moisture profiles that were too wet. Calibration of the hydraulic relationships resulted in a good description of the moisture profiles. Calibration of the dispersion length was necessary to obtain a good description of bromide leaching. The calibrated dispersion length was 61 cm, which is very long and indicates a large non-uniformity of solute transport. The half-life of bentazone had to be calibrated to obtain a good description of its field persistence. The calibrated half-life was 2.5 times shorter than the half-life derived from the laboratory studies. Concentrations of bentazone in drain water and groundwater were described reasonably well by PEARL. Although measured and simulated persistence of imidacloprid in soil corresponded well, the bulk of the imidacloprid movement was overestimated by PEARL. However, imidacloprid concentrations in drain water were underestimated. In spite of the extensive calibration of water flow and tracer movement, the behaviour of the moderately sorbing pesticide imidacloprid could not be simulated. This indicates that the convection-dispersion equation cannot be used for accurate simulation of pesticide transport in cracking clay soils (even if extremely long dispersion length is used). Comparison of the model results from a poorly sorbed chemical (bentazone) and a moderately sorbed chemical (imidacloprid) were useful in defining the limitations of using a chromatographic flow model to simulate the effects of preferential flow.

An improved description of pesticide volatilization: refinement of the pesticide leaching model (PELMO).

The consideration of pesticide volatilization from soil surfaces as an integral component of pesticide fate models is of importance, especially as part of the Predicted Environmental Concentrations (PEC) models used in the registration procedures for pesticides. The Pesticide Leaching Model (PELMO), which is used in the European registration process, was modified to allow for a reliable prediction of volatilization from soil. The previous PELMO version was upgraded by improving the spatiotemporal discretization at the soil surface, improving the empirical description of temperature dependence of Henry's law constants and including increased sorption of pesticides in dry soils. Comparison of predictions with experimental findings revealed the improvements of PELMO to contribute to a more realistic reflection of measurements, particularly at initial stages of the studies. The broad range of literature values of Henry's law constants was shown to have a significant effect on predicted volatilization fluxes. As a main refinement, the tendency of pesticides toward enhanced volatilization under moist conditions was correctly calculated by the improved model. Variations between model predictions and measurements were due to a lack of experimental data on soil sorption under dry conditions and indicated the need for further calibration of the model. The description of water content in the top layer was subject to uncertainty, which was exemplified by an overestimation of soil moisture during the last days of the field study. Thus, future model improvement will be dependent on experimental support to obtain more detailed information on soil-air-water partitioning of pesticides in the top soil layer.

Preferential flow of bromide, bentazon, and imidacloprid in a Dutch clay soil.

Leaching to ground water and tile drains are important parts of the environmental assessment of pesticides. The aims of the present study were to (i) assess the significance of preferential flow for pesticide leaching under realistic worst-case conditions for Dutch agriculture (soil profile with thick clay layer and high rainfall) and (ii) collect a high-quality data set that is suitable for testing pesticide leaching models. The movement of water, bromide, and the pesticides bentazon [3-isopropyl-1H-2, 1,3-benzothiadiazine-4(3H)-one-2,2-dioxide] and imidacloprid [1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine] was monitored in a clay soil for about 1 yr. The 1.2-ha field was located in the central part of the Netherlands (51 degrees 53' N, 5 degrees 43' E). The soil was a Eutric Fluvisol cropped with winter wheat (Triticum aestivum L.). Tile drains were present at a 0.8- to 0.9-m depth and the ground water level fluctuated between a 0.5- and 2-m depth. All chemicals were applied in spring. None of the soil concentration profiles showed bimodal concentration distributions. However, for each substance the highest concentration in drain water was found in the first drainage event after its application, which indicates preferential flow. This preferential flow is probably caused by permanent macropores that were present in the 0.3- to 1.0-m layer. At the time of the first drainage event, the drain water concentration of each substance was about an order of magnitude higher than its ground water concentration. Thus, the flux concentrations in drain water proved to be a more sensitive detector of preferential flow than the resident concentrations in the soil profile and the ground water.

Issues of replicability in Monte Carlo modeling: a case study with a pesticide leaching model.

Sensitivity and uncertainty analyses based on Monte Carlo sampling were undertaken for various numbers of runs of the pesticide leaching model (PELMO). Analyses were repeated 10 times with different seed numbers. The ranking of PELMO input parameters according to their influence on predictions for leaching was stable for the most influential parameters. For less influential parameters, the sensitivity ranking was severely influenced by the seed number used. For uncertainty analyses, probabilities of exceeding a particular concentration were significantly influenced by the seed number used in the random sampling of values for the two parameters considered, even for those cases in which 5,000 model runs were undertaken (coefficient of variation of 10 replicated analyses, 5%). A decrease in the variability of exceedance probabilities could be achieved by further increasing the number of model runs. However, this may prove to be impractical when complex deterministic models with a relatively long running time are used. Attention should be paid to replicability aspects by modelers when devising their approach to assessing the uncertainty associated with the modeling and by decision makers when examining the results of probabilistic approaches.

Predicting and Measuring Environmental Concentration of Pesticides in Air after Soil Application

Pesticides can volatilize into the atmosphere, which affects the air quality. The ability to predict pesticide volatilization is an essential tool for human risk and environmental assessment. Even though there are several mathematical models to assess and predict the fate of pesticides in different compartments of the environment, there is no reliable model to predict volatilization. The objectives of this study were to evaluate pesticide volatilization under agricultural conditions using malathion [ O,O-dimethyl-S-(1,2-dicarbethoxyethyl)-dithiophosphate], ethoprophos (O-ethyl S,S-dipropylphosphorodithioate), and procymidone [N-(3,5-dichlorophenyl)-1,2-dimethylcyclopropane-1,2-dicarboximide] as test compounds and to evaluate the ability of the Pesticide Leaching Model (PELMO) to calculate the predicted environmental concentrations of pesticides in air under field conditions. The volatilization rate of procymidone, malathion, and ethoprophos was determined in a field study during two different periods (December 1998 and September 1999) using the Theoretical Profile Shape (TPS) method. The experiments were performed on bare silty soil in the Bologna province, Italy. Residues in the air were continuously monitored for 2 to 3 wk after the pesticide applications. The amount of pesticide volatilized was 16, 5, and 11% in December 1998 and 41, 23, and 19% in September 1999 for procymidone, malathion, and ethoprophos, respectively. In both these experiments, the PELMO simulations of the concentration of ethoprophos and procymidone were in good agreement with the measured data (factor +/- 1.1 on average). The volatilization of malathion was underestimated by a factor of 30 on average. These results suggest that volatilization described by PELMO may be reliable for volatile substances, but PELMO may underpredict volatilization for less-volatile substances.

Sensitivity analyses for four pesticide leaching models.

Sensitivity analyses using a one-at-a-time approach were carried out for leaching models which have been widely used for pesticide registration in Europe (PELMO, PRZM, PESTLA and MACRO). Four scenarios were considered for simulation of the leaching of two theoretical pesticides in a sandy loam and a clay loam soil, each with a broad distribution across Europe. Input parameters were varied within bounds reflecting their uncertainty and the influence of these variations on model predictions was investigated for accumulated percolation at 1-m depth and pesticide loading in leachate. Predictions for the base-case scenarios differed between chromatographic models and the preferential flow model MACRO for which large but transient pesticide losses were predicted in the clay loam. Volumes of percolated water predicted by the four models were affected by a small number of input parameters and to a small extent only, suggesting that meteorological variables will be the main drivers of water balance predictions. In contrast to percolation, predictions for pesticide loss were found to be sensitive to a large number of input parameters and to a much greater extent. Parameters which had the largest influence on the prediction of pesticide loss were generally those related to chemical sorption (Freundlich exponent nf and distribution coefficient Kf) and degradation (either degradation rates or DT50, QTEN value). Nevertheless, a significant influence of soil properties (field capacity, bulk density or parameters defining the boundary between flow domains in MACRO) was also noted in at least one scenario for all models. Large sensitivities were reported for all models, especially PELMO and PRZM, and sensitivity was greater where only limited leaching was simulated. Uncertainty should be addressed in risk assessment procedures for crop-protection products.

Using a linked soil model emulator and unsaturated zone leaching model to account for preferential flow when assessing the spatially distributed risk of pesticide leaching to groundwater in England and Wales

Although macropore flow is recognized as an important process for the transport of pesticides through a wide range of soils, none of the existing spatially distributed methods for assessing the risk of pesticide leaching to groundwater account for this phenomenon. The present paper presents a spatially distributed modelling system for predicting pesticide losses to groundwater through micro- and macropore flow paths. The system combines a meta version of the mechanistic, dual porosity, preferential flow pesticide leaching model MACRO (the MACRO emulator), which describes pesticide transport and attenuation in the soil zone, to an attenuation factor leaching model for the unsaturated zone. The development of the emulator was based on the results of over 4000 MACRO model simulations. Model runs describe pesticide leaching for the range of soil types, climate regimes, pesticide properties and application patterns in England and Wales. Linking the MACRO emulator to existing spatial databases of soil, climate and compound-specific loads allowed the prediction of the concentration of pesticide leaching from the base of the soil profile (at 1 m depth) for a wide range of pesticides. Attenuation and retardation of the pesticide during transit through the unsaturated zone to the watertable was simulated using the substrate attenuation factor model AQUAT. The MACRO emulator simulated pesticide loss in 10 of 12 lysimeter soil–pesticide combinations, for which pesticide leaching was shown to occur and also successfully predicted no loss from 3 soil–pesticide combinations. Although the qualitative aspect of leaching was satisfactorily predicted, actual pesticide concentrations in leachate were relatively poorly predicted. At the national scale, the linked MACRO emulator/AQUAT system was found to predict the relative order of, and realistic regional patterns of, pesticide leaching for atrazine, isoproturon, chlorotoluron and lindane. The methodology provides a first-step assessment of the potential for pesticide leaching to groundwater in England and Wales. Further research is required to improve the modelling concept proposed. The system can be used to refine regional groundwater monitoring system designs and sampling strategies and improve the cost-effectiveness of the measures needed to achieve ‘good status’ of groundwater quality as required by the Water Framework Directive.

Parameterisation, evaluation and comparison of pesticide leaching models to data from a Bologna field site, Italy.

Effective prediction of pesticide fate using mathematical models requires good process descriptions in the models and good choice of parameter values by the user. This paper examines the ability of seven pesticide leaching models (LEACHP, MACRO, PELMO, PESTLA, PLM, PRZM and VARLEACH) to describe an arable field environment where sunflowers are grown in the Po Valley, northern Italy. Two pesticides were considered, aclonifen and ethoprophos. The models were evaluated in terms of their ability to reproduce field data of soil water content and pesticide residues in the soil and ground water. The evaluation was based on a combination of calibrated and uncalibrated runs. The results from the models were compared with each other to explore the differences between the models. The models varied in their ability to predict soil water content in the summer: the capacity models PRZM, PELMO and VARLEACH predicted less drying than MACRO, PESTLA, PLM and LEACHP. The models varied in their ability to simulate the persistence of the pesticides in the soil. Differences in the simulated pesticide degradation rate were observed between the models, due to variations in the simulated soil water content and soil temperature, and also differences in the equation linking degradation rate to soil water content. There were large differences among the predictions of the models for the mean leaching depth of ethoprophos. PRZM, PELMO, PESTLA and LEACHP all showed similar mean leaching depth to each other, whereas VARLEACH predicted lower ethoprophos mobility and PLM and MACRO predicted greater mobility. All the models overpredicted dispersion of ethoprophos through the soil profile, as compared to the field data. None of the models was able to simulate the field data of rapid leaching of pesticide to ground water except PLM after calibration of the percentage of macropores in the mobile pore space. More work is required in the parameterisation of macropore flow for those models that include this process.

Calibration of pesticide leaching models: critical review and guidance for reporting

Calibration of pesticide leaching models may be undertaken to evaluate the ability of models to simulate experimental data, to assist in their parameterisation where values for input parameters are difficult to determine experimentally, to determine values for specific model inputs (e.g. sorption and degradation parameters) and to allow extrapolations to be carried out. Although calibration of leaching models is a critical phase in the assessment of pesticide exposure, lack of guidance means that calibration procedures default to the modeller. This may result in different calibration and extrapolation results for different individuals depending on the procedures used, and thus may influence decisions regarding the placement of crop-protection products on the market. A number of issues are discussed in this paper including data requirements and assessment of data quality, the selection of a model and parameters for performing calibration, the use of automated calibration techniques as opposed to more traditional trial-and-error approaches, difficulties in the comparison of simulated and measured data, differences in calibration procedures, and the assessment of parameter values derived by calibration. Guidelines for the reporting of calibration activities within the scope of pesticide registration are proposed.

Modelling the leaching and drainage of pesticides in the Netherlands: the GeoPEARL model

A one-dimensional pesticide leaching model, PEARL, in combination with a geographical information system was used to calculate the leaching potential of pesticides into local surface waters and the regional groundwater. Calculations were performed for6405 plots, which are unique combinations of spatially distributed model inputs. To have the seepage and drainage fluxes correctly described, the model was loosely coupled with a regional groundwater model. Simulations were carried out for four pesticides with different properties. Results showed that, generally, the average fluxes of pesticide into local surface waters were higher than the average fluxes of pesticide into the regional groundwater. Discharge by rapid drainage mechanisms (i.e. tube drainage and surface drainage) dominated. For the four pesticides, different spatial patterns of leaching and discharge by drainage water were predicted. It was shown that the spatial pattern was affected by a large number of interacting processes, and that the relative importance of these processes differed between the four example pesticides. This should be kept in mind when applying the USES system, which describes the leaching of pesticides on the basis of a limited number of pesticide parameters. Frequency distributions of the leaching concentration were compared with results from the first tier of the Dutch pesticide registration procedure, which comes down to the application of a single standard scenario. For two pesticides, the first tier was not strict enough. It was shown that it is not possible to find one single standard scenario, which applies to the full range of registered pesticides. This means that the number of standard scenarios should be increased. Direct application of a regional-scalemodel, however, is to be preferred, because it provides the user with frequency distributions and gives information about areas of safe usage.

Ability of three pesticide leaching models to simulate summer crops in a Mediterranean scenario

Capacite de trois modeles de lessivage des pesticides a simuler une culture d'ete dans un scenario mediterraneen. La capacite de prevoir le devenir de pesticides dans un scenario du sud de l'Italie a ete testee pour trois modeles de lessivage des pesticides (PLM), VARLEACH, PELMO et PESTLA, en utilisant un jeu de donnees prealablement obtenu dans une experience au champ. Les mesures de l'evapotranspiration reelle dans une experience au champ a necessite le calage des trois modeles (PLM) pour la composante hydrologique dans le scenario etudie, dans lequel l'evapotranspiration etait tres elevee durant les mois chauds. Alors que PELMO et PESTLA ont ete cales facilement, VARLEACH n'a pas donne de resultats satisfaisants, peut-etre a cause de ses deficiences intrinseques. Apres calage, les trois modeles PLM ont bien simule les mouvements de deux herbicides imazethapyr et bentazone selon le profil du sol. L'accord pourrait etre fortuit pour VARLEACH, puisqu'il ne simule pas correctement le mouvement d'eau et d'ion bromure (ion non interferent). PESTLA simule bien la quantite totale d'herbicide lessivee au-dessous de 80 cm de profondeur, domaine dans lequel VARLEACH et PELMO ont echoue. Les trois modeles PLM cales pourraient etre utilises pour effectuer des simulations dans des conditions climatiques semblables a celles de l'experience.

Simulation of pesticide leaching at Vredepeel and Brimstone farm using the macropore model PLM

The distributions of bromide, bentazone and ethoprophos in the light-textured and unstructured soil at Vredepeel was simulated using the Pesticide Leaching Model (PLM). Distributions of all compounds were satisfactorily simulated using the data provided and without calibration. Since bromide is used as a tracer of water movement, this agreement indicates that PLM was able to model the movement and dispersion of water in the soil profile. However traces of bromide that remained near the soil surface were not predicted. Although PLM was designed to simulate concentrations of pesticide that reach drainage waters by preferential flow in structured soils, the model was still able to predict the distribution of the large proportion of bentazone and ethoprophos that remained in the topsoil at Vredepeel. The soil at Brimstone farm is a very highly structured, heavy, cracking-clay soil. PLM was used to simulate concentrations of isoproturon measured in samples of drainage water taken from the site. Simulated concentrations similar to those measured were obtained but only after extensive calibration of the model.

Movement of water, bromide and the pesticides ethoprophos and bentazone in a sandy soil: the Vredepeel data set

The aim of this study was to collect a data set suitable for testing pesticide leaching models in the case of a Dutch sandy soil with a shallow groundwater table. The movement of water, bromide ion and the behaviour of the pesticides ethoprophos and bentazone was studied. The substances were applied after sowing winter wheat in autumn 1990. This late application time is unusual for bentazone: it was selected on scientific grounds (without agricultural purpose). Rainfall, groundwater level and soil temperature were monitored continuously at the experimental field (80 m long and 54 m wide) until spring 1992. Soil profiles were sampled at 1, 103, 278 and 474 days after application (16 profiles at each date). In the laboratory, pesticide transformation rates were measured with soil material from 0–25, 50–100 and 100–200 cm depth. Sorption isotherms were measured with material from 0–25 cm depth. Concentration profiles showed that mobility increased in the sequence ethoprophos — bentazone — bromide ion. Ethoprophos movement was limited to the top 25 cm layer whereas bentazone leached to below 1 m depth. At the end of the study, the concentrations of ethoprophos and bentazone were below the detection limit (0.2–2 μg dm −3) in all soil layers between 25 and 120 cm depth. Recommended values for the most important input parameters of pesticide leaching models are presented.

Comparing and evaluating pesticide leaching models: results for the Tor Mancina data set (Italy)

This paper describes the results of an evaluation of pesticide leaching modelling, using data collected on four lysimeters in Italy. The experimental data were collected during a 3 year period at Tor Mancina (Rome, Italy), on a clay-loam calcareous soil. Monitored variables are the soil water drainage, the bromide leaching and the metolachlor leaching. Two different irrigation schedules were considered in the experimental design. The models inadequately described the monitored breakthrough of water, bromide and pesticide. Poor modelling performance was firstly attributed to an inappropriate model structure, poorly representing the specific conditions of Mediterranean soils. In particular, the models did not allow to represent correctly the preferential flow that was observed during some of the flow events. Secondly, deficiencies were identified in the calibration procedures, and the application of a well defined modelling practice. The lack of such a good modelling practice induced user subjectivity in the estimation of the model parameters, which had an impact on the modelling results.

Application of pesticide leaching models to the Vredepeel dataset: II Pesticide fate

The performance of nine deterministic, one-dimensional, dynamic pesticide leaching models with different complexity was evaluated using a field experiment with bentazone and ethoprophos on a humic sandy soil with a shallow groundwater table. All modelers received an extensive description of the experimental data. Despite this fact, the interpretation of the experimental data was ambiguous, leading to tremendous user-dependent variability of selected model inputs. Together with the fact that most modelers calibrated at least part of their model, the possibility for evaluating model concepts was limited. In the case of bentazone, most model predictions were within the 95% confidence intervals of the observations. In the case of ethoprophos, model performance was often poor due to the ignorance of volatilization, kinetic sorption and adaptation of the microbial population. Most models were calibrated using on-site measured data, limiting the possibility for extrapolation for policy-oriented applications.

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.

Evaluation of pesticide dynamics of the WAVE-model

A validation study of the physical based pesticide leaching model WAVE is presented. The model considers a mechanistic description of 1-D water, solute and heat transport. Linear sorption isotherms and first order degradation sub-models are used to simulate pesticide sorption and transformation. The first order degradation rates are reduced when temperature and moisture stress in the soil profile occur. The model is conceived to describe pesticide fate within rigid mineral soils. Model tests were therefore done using data collected at a sandy (Vredepeel) and a loamy soil (Weiherbach). Both field data and lysimeter data were used to evaluate the performance to describe water, bromide, ethoprophos, bentazone and isoproturon transport in soil. The evaluation procedure presented by Vanclooster et al. (Agric. Water Mgmt., Vol. 44, pp. 1–19) was completely adopted. The measured soil moisture in the sandy soil could only successfully be described after calibrating the hydraulic functions using field observed soil moisture profiles. In addition, the predicted balance terms, such as the soil water drainage, were subject to a lot of uncertainty. Bromide transport in the sandy soil was poorly described with the equilibrium solute transport model. Anomalies were also observed when simulating the transport of the inert tracer in the lysimeter at the loamy site. The fate of the weakly sorbing bentazone component was appropriately described at the Vredepeel field site. However, the retardation of the strongly sorbing ethoprophos and isoproturon components was poorly simulated. Further, the pesticide dissipation varied considerably in time, which could not be accounted for with the first order degradation model. The need for model calibration illustrates the constraints when using mechanistic models such as WAVE to predict field scale pesticide fate and transport. The adoption of a mechanistic model for registration purposes may therefore be subjected to a lot of uncertainty. In addition, processes affecting pesticide fate and transport are still poorly represented within the model. Deficiencies are related to the description of non-linear sorption, time dependent pesticide degradation, and pesticide volatilisation. Future developments with the model should therefore envisage to improve the parametrisation reduce the output uncertainty, and improve process descriptions of essential processes.