Publications by the PEARL team

The following papers were published by the PEARL team.

2008

Details Uncertainty and sensitivity analysis of GeoPEARL
Details Spatial moment analysis of transport of nonlinearly adsorbing pesticides using analytical approximations
Details Revised proposal for the risk assessment of persistence of plant protection products in soil
Details Evaluation of the 2006 proposal for risk assessment of persistence of plant protection products in soil

2007

Details Simulation of Pesticide Leaching in the Field and in Zero-Tension Lysimeters
Details Conceptual model for improving the link between exposure and effects in the aquatic risk assessment of pesticides
Details Including spatial variability in Monte Carlo simulations of pesticide leaching
Details The consequences of interpolating or calculating first on the simulation of pesticide leaching at the regional scale

2006

Details Mapping Ground Water Vulnerability to Pesticide Leaching with a Process-Based Metamodel of EuroPEARL
Details Volatilisation of the pesticides chlorpyrifos and fenpropimorph from a potato crop

2005

Details Simulation of pesticide leaching in a cracking clay soil with the PEARL model
Details Pesticide Transport in the Groundwater at the National Scale: Coupling an Unsaturated Zone Model with a Groundwater Flow Model
Details Measured and computed volatilisation of the fungicide fenpropimorph from a sugar beet crop.

2004

Details Influence of dispersion length on leaching calculated with PEARL, PELMO and PRZM for FOCUS groundwater scenarios.
Details On the use of unsaturated flow and transport models in nutrient and pesticide management.
Details Computations on the volatilisation of the fungicide fenpropimorph from plants in a wind tunnel.
Details Assessment of the pesticide leaching risk at the Pan-European level. The EuroPEARL approach.
Details Pesticide Transport in the Groundwater at the National Scale: Coupling an Unsaturated Zone Model with a Groundwater Flow Model
Details The GeoPEARL model: Part II. User guide and model description update

2003

Details The GeoPEARL model: Description, applications and manual
Details Assessing the Risk of Pesticide Leaching at the Pan-European Level.
Details Comparison of GeoPEARL with the Single Scenario Approach in Pesticide Registration and Policy Evaluation.
Details Development of an Environmental Indicator that can be used on National and Regional Scales.
Details Effective approaches for predicting environmental concentrations of pesticides: the APECOP project
Details Incorporating macropore flow into FOCUS PEC Models.
Details Improvement of concepts for pesticide volatilisation from bare soil in PEARL, PELMO and MACRO models.
Details Methodological Approach for Evaluating First Tier PEC Groundwater Scenarios Supporting the Prediction of Environmental Concentrations of Pesticides at the European Scale.
Details Pesticide volatilisation from plants: Improvement of the PEARL, PELMO and MACRO models.

2002

Details Emissions of pesticides to the environment. Evaluation of the policy goals of the Long-Term Crop Protection Plan
Details Nationwide assessments of non-point source pollution with field-scale developed models: The pesticide case.
Details Modelling the Leaching and Drainage of Pesticides in the Netherlands: The GeoPEARL model.
Details Role of dispersion in interpretation of differences between FOCUS leaching models (pdf only).

2000

Details Manual of FOCUS PEARL version 1.1.1
Details A European test of pesticide leaching models: Methodology and Recommendations.
Details Application of pesticide leaching models to the Vreedepeel dataset: I. Water, solute and heat transport.
Details Movement of water, bromide and the pesticides ethoprophos and bentazone in a sandy soil: The Vreedepeel data set.

1999

Details Modelling Non-Point Source Pollutants in Soils (PhD thesis).

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Uncertainty and sensitivity analysis of GeoPEARL
(2008)

F. van den Berga, D.J. Brusb, S.L.G.E. Burgersa, G.B.M. Heuvelinka, J.G. Kroesa, J. Stoltea, A. Tiktakc, and F. de Vriesa

a) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands
b) Biometris, PO Box 47, 6700 AA Wageningen, Netherlands
b) Netherlands Environmental Assessment Agency (PBL),PO BOX 303, 3720 AH Bilthoven, Netherlands
Alterra report 1330, PBL report 500123001, Wageningen, Bilthoven, Netherlands

In the environmental assessments by the Netherlands Environmental Assessment Agency (PBL), the GeoPEARL model is used to calculate the leaching of pesticides to the groundwater at the national scale. In this study, the propagation of errors resulting from the use of a simplified spatial schematisation as well as that of uncertainties in the GeoPEARL input to the predicted leaching concentrations were investigated. Computations using GeoPEARL with the standard schematisation were compared with those obtained with a schematisation at a higher spatial resolution. For all three pesticides considered the nationwide spatial frequency distribution of the median annual leaching concentration (PEC50) and the spatial 90th percentile of the PEC50 (SP90) were hardly affected by spatial aggregation of soil type within larger spatial units. For the assessment of the propagation of uncertainties in the input, only soil properties and the most important pesticide properties, i.e. half-life in soil (DT50) and the coefficient for the sorption on organic matter (Kom) were considered. First, the uncertainties in the soil data and the pesticide were quantified. Next, a regular grid sample of points covering the whole of the agricultural area in the Netherlands was randomly selected. At the grid nodes, realisations from the probability distributions of uncertain inputs were generated and used as input to a Monte Carlo uncertainty propagation analysis. Uncertainties in DT50 and to a lesser extent Kom contributed most to the uncertainty in PEC50 and SP90. The uncertainty about the PEC50 at point locations is greater than that about the SP90. When taking the uncertainties into account, the SP90 of the leaching concentration shifted towards greater values. Recommendations are made for further improvement of the model predictions, in particular by reducing the uncertainty in DT50.

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Revised proposal for the risk assessment of persistence of plant protection products in soil
(2008)

A.M.A. van der Lindena, J.J.T.I. Boesten, b, T.C.M. Brockb, G.M.A. van Eekelenc, M.M.S. ter Horstb, F.M.W. de Jonga, M.H.M.M. Montfortsa, and J.W. Polc

a) RIVM, PO Box 1, 3720 AA Bilthoven, Netherlands
b) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands
c) CTGB, Wageningen, Netherlands
RIVM report 601712003, RIVM, Bilthoven, Netherlands

This report gives revised guidance for the environmental risk assessment of persistency of plant protection products in soil where European legislation is absent.

This report considers three protection goals for soils: 1) protection of soil functions relevant to agricultural production, 2) protection of the structure of agro-ecosystems, and 3) protection of the structure of soil ecosystems in general. Existing guidance at the EU level considers the first protection, so this is not elaborated upon in this report. For the two other protection goals, the report proposes decision schemes in which both exposure and ecotoxicological effects are assessed in a tiered approach. The evaluation is triggered when the half-life of a substance in soil exceeds a value of 90 respectively 180 days.

In line with the European regulations on plant protection products, the guidance considers all relevant scientific information. The revised proposal provides points of departure for further guidance development at the European level

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Evaluation of the 2006 proposal for risk assessment of persistence of plant protection products in soil
(2008)

A.M.A. van der Lindena, J.J.T.I. Boesten, b, T.C.M. Brockb, G.M.A. van Eekelenc, M.M.S. ter Horstb, F.M.W. de Jonga, M.H.M.M. Montfortsa, and J.W. Polc

a) RIVM, PO Box 1, 3720 AA Bilthoven, Netherlands
b) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands
c) CTGB, Wageningen, Netherlands
RIVM report 601712002, RIVM, Bilthoven, Netherlands

This report describes the evaluation of the 2006 proposal for the risk assessment of persistence of plant protection products in soil. The proposal considered three protection goals and proposed tiered assessment and decision schemes for each protection goal. The three schemes appeared to be consistent, both internally and with each other. It was found that both pore water concentrations and total content have to be considered in the soil risk assessment.

The evaluation has been performed for five substances with all available information from both registration dossiers and open literature. Nevertheless, insufficient information was available to evaluate all aspects of the proposal. In practice this means that pesticide industry has to provide additional information for many dossiers. Furthermore, it was found that existing information often needs to be re-interpreted and a need for standardisation of evaluation of terrestrial (semi-)field experiments was observed. The proposal would require specific expertise and investments of evaluating authorities as well as stakeholders.

To better understand fate and effects of persistent substances, it is recommended to investigate the behaviour of substances in the field over longer periods, to perform exposure concentration measurements while performing ecotoxicological tests, to develop protocols for testing effects on fungi, and to gain the necessary experience on the conduct and interpretation of (semi-)field studies with respect to the relation between exposure and effects of plant protection products

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Spatial moment analysis of transport of nonlinearly adsorbing pesticides using analytical approximations
(2008)

Wim H.J. Beltmana, Jos J.T.I. Boestena, and Sjoerd E.A.T.M. van der Zeeb

a) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands
b) Soil Physics, Ecohydrology and Groundwater Management Group, Wageningen University, Wageningen, Netherlands
Water Resources Research 44(W05417):1-12

Analytical approximations were derived for solute transport of pesticides subject to Freundlich sorption, and first-order degradation restricted to the liquid phase. Solute transport was based on the convection-dispersion equation (CDE) assuming steady flow. The center of mass (first spatial moment) was approximated both for a non-degraded solute pulse and for a pulse degraded in the liquid phase. The remaining mass (zeroth spatial moment) of a linearly sorbing solute degraded in the liquid phase was found to be a function of only the center of mass (first spatial moment) and the Damk÷hler number (i.e., the product of degradation rate coefficient and dispersivity divided by flow velocity). This relationship between the zeroth and first spatial moments was shown to apply to nonlinearly sorbing pulses as well. The mass fraction leached of a pesticide subject to Freundlich sorption and first-order degradation in the solution phase only was found to be a function of the Damk÷hler number and of the dispersivity, so independent of sorption. Hence perceptions of the effects of sorption on pesticide leaching should be reconsidered. These conclusions equally hold for other micropollutants that degrade in the solution phase only.
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Simulation of Pesticide Leaching in the Field and in Zero-Tension Lysimeters
(2007)

Jos J.T.I. Boestena

a) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands
Vadose Zone Journal 6:793-804

Zero-tension lysimeters play an important role in groundwater risk assessments for pesticides in the European Union. In these assessments, measured lysimeter leachate concentrations are usually used directly for decision making. When doing so, one assumes (i) that the lysimeter bottom boundary condition itself did not lead to underestimating field leaching concentrations, (ii) that the number of application years and the duration of the lysimeter study were adequate to measure the maximum concentration in time, and (iii) that the pesticide-lysimeter system considered was sufficiently vulnerable with respect to leaching. These assumptions were tested using simulations with a Darcian water flow model combined with a chromatographic pesticide leaching model. The scenario consisted of a layered light-textured soil cropped with cereals and of multiyear weather data. The groundwater level in the field usually fluctuated between 0.7 and 2.5 m depth. The lysimeter bottom boundary condition resulted in pesticide leaching concentrations lower than those calculated for the field system. Simulations showed that a lysimeter study of 2 yr was too short to measure the maximum leaching concentration for pesticides with organic-matter/water distribution coefficient values exceeding 40 L/kg. The probability that a lysimeter study results in a leaching concentration below 0.1 microgram/litre by a coincidental favorable combination of pesticide-soil parameters was assessed by Monte Carlo simulations. This probability exceeded 20% for pesticides that would give leaching concentrations of 1 microgram/litre under field conditions. Therefore, it is advisable that for each lysimeter study, modeling be used to assess the likelihood that the leaching concentration would be below 0.1 microgram/litre, considering all relevant systematic and random factors.
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Conceptual model for improving the link between exposure and effects in the aquatic risk assessment of pesticides
(2007)

Jos J.T.I. Boestena, H. Koeppb, Paulien I. Adriaansea, Theo C.M. Brocka, V.E. Forbesc

a) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands
b) Office for Consumer Protection and Food Safety, Messeweg 11/12, D-38104 Braunschweig, Germany
c) cCentre for Integrated Population Ecology, Department of Life Sciences and Chemistry, Roskilde University, PO Box 260, DK-4000 Roskilde, Denmark
Ecotoxicology and Environmental Safety 66(3):291-308

Assessment of risks to aquatic organisms is important in the registration procedures for pesticides in industrialised countries. This risk assessment consists of two parts: (i) assessment of effects to these organisms derived from ecotoxicological experiments (=effect assessment), and (ii) assessment of concentration levels in relevant environmental compartments resulting from pesticide application (=exposure assessment). Current procedures lack a clear conceptual basis for the interface between the effect and exposure assessments which may lead to a low overall scientific quality of the risk assessment. This interface is defined here as the type of concentration that gives the best correlation to ecotoxicological effects and is called the ecotoxicologically relevant concentration (ERC). Definition of this ERC allows the design of tiered effect and exposure assessments that can interact flexibly and efficiently. There are two distinctly different exposure estimates required for pesticide risk assessment: that related to exposure in ecotoxicological experiments and that related to exposure in the field. The same type of ERC should be used consistently for both types of exposure estimates. Decisions are made by comparing a regulatory acceptable concentration (=RAC) level or curve (i.e., endpoint of the effect assessment) with predicted environmental concentration (=PEC) levels or curves (endpoint of the exposure assessment). For decision making based on ecotoxicological experiments with time-variable concentrations a tiered approach is proposed that compares (i) in a first step single RAC and PEC levels based on conservative assumptions, (ii) in a second step graphically RAC and PEC curves (describing the time courses of the RAC and PEC), and (iii) in a third step time-weighted average RAC and PEC levels.
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Including spatial variability in Monte Carlo simulations of pesticide leaching
(2007)

Bertrand Letermea, Marnik Vancloostera, Anthonius M.A. van der Lindenb Aaldrik Tiktakc and Mark D.A. Rounsevella

a) Universite catholique de Louvain, Louvain-la-Neuve, Belgium
b) RIVM, PO Box 1, 3720 BA Bilthoven, Netherlands
c) MNP, PO BOX 303, 3720 AH Bilthoven, Netherlands

Environ Science and Technology 41(21):7444-7450

A methodology is developed to quantify the uncertainty in a pesticide leaching assessment arising from the spatial variability of non-georeferenced parameters. A Monte Carlo analysis of atrazine leaching is performed in the Dyle river catchment (Belgium) with pesticide half-life (DT50) and topsoil organic matter (OM) content as uncertain input parameters. Atrazine DT50 is taken as a non-georeferenced parameter, so that DT50 values sampled from the input distribution are randomly allocated in the study area for every simulation. Organic matter content is a georeferenced parameter, so that a fixed uncertainty distribution is given at each location. Spatially variable DT50 values are found to have a significant influence on the amount of simulated leaching. In the stochastic simulation, concentrations exist above the regulatory level of 0.1 microgram per litre, but virtually no leaching occurs in the deterministic simulation. It is axiomatic that substance parameters (DT50, sorption coefficient, etc.) are spatially variable, but pesticide registration procedures currently ignore this fact. Including this spatial variability in future registration policies would have significant consequences on the amount and pattern of leaching simulated, especially if risk assessments are implemented in a spatially distributed way.
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The consequences of interpolating or calculating first on the simulation of pesticide leaching at the regional scale
(2007)

Bertrand Letermea, Marnik Vancloostera, Anthonius M.A. van der Lindenb Aaldrik Tiktakc and Mark D.A. Rounsevella

a) Universite catholique de Louvain, Louvain-la-Neuve, Belgium
b) RIVM, PO Box 1, 3720 BA Bilthoven, Netherlands
c) MNP, PO BOX 303, 3720 AH Bilthoven, Netherlands

Geoderma (137):414-425

We analysed different approaches to process soil information when simulating pesticide leaching to groundwater at the regional scale. The first approach, calculate alone (CA), consisted of the model application on point data followed by the aggregation of the results to the regional scale. Two further approaches were used to generate spatial output and differed by interpolating after or before the model run on point support (calculate first, interpolate later; CI vs. interpolate first, calculate later; IC). The three approaches were tested with both a linear (modified Attenuation Factor, AF) and a non-linear leaching model. The non-linearity of GeoPEARL appeared to produce differences between CI and IC that did not occur in the linear model. The results also suggested that the relevance of either CI or IC is dependent on the available input information. Finally, different ways to estimate the prediction precision of the three approaches are discussed.
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Mapping Ground Water Vulnerability to Pesticide Leaching with a Process-Based Metamodel of EuroPEARL
(2006)

Aaldrik Tiktaka, Jos J.T.I. Boestenb, Anthonius M.A. van der Lindenc, and Marnik Vancloosterd

a) MNP, PO Box 303, 3720 AH Bilthoven, Netherlands
b) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands
c) RIVM, PO Box 1, 3720 BA Bilthoven, Netherlands
d) Universite catholique de Louvain, Louvain-la-Neuve, Belgium

J. Environ. Qual. (35):1213-1226

To support EU policy, indicators of pesticide leaching at the European level are required. For this reason, a metamodel of the spatially distributed European pesticide leaching model EuroPEARL was developed. EuroPEARL considers transient flow and solute transport and assumes Freundlich adsorption, first-order degradation and passive plant uptake of pesticides. Physical parameters are depth dependent while (bio)-chemical parameters are depth, temperature, and moisture dependent. The metamodel is based on an analytical expression that describes the mass fraction of pesticide leached. The metamodel ignores vertical parameter variations and assumes steady flow. The calibration dataset was generated with EuroPEARL and consisted of approximately 60 000 simulations done for 56 pesticides with different half-lives and partitioning coefficients. The target variable was the 80th percentile of the annual average leaching concentration at 1-m depth from a time series of 20 yr. The metamodel explains over 90% of the variation of the original model with only four independent spatial attributes. These parameters are available in European soil and climate databases, so that the calibrated metamodel could be applied to generate maps of the predicted leaching concentration in the European Union. Maps generated with the metamodel showed a good similarity with the maps obtained with EuroPEARL, which was confirmed by means of quantitative performance indicators.
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Volatilisation of the pesticides chlorpyrifos and fenpropimorph from a potato crop
(2006)

Minze Leistraa, Johan H. Smelta, J. Hilbrand Weststrateb, Frederik van den Berga and Rene Aalderinka

a) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands

b) TNO, PO Box 342, 7300 AH Apeldoorn, Netherlands

Environ. Sci. & Technol. (40):96-102

Volatilization of pesticides from crops in the field can be an important emission pathway. In a field experiment with characterization of meteorological conditions, the pesticides chlorpyrifos and fenpropimorph were sprayed onto a potato crop, after which concentrations in the air and on/in the plants were measured. Rates of volatilization were estimated with the aerodynamic profile (ADP), energy balance (EB), relaxed eddy accumulation (REA), and plume dispersion (PD) methods. The volatilization rates obtained with the ADP and EB methods were similar, while some rates obtained with the REA and PD methods in the initial period were lower. Cumulative volatilization of chlorpyrifos during daylight hours (ADP and EB methods) was estimated to be about 65% of the dosage. By far the majority of this volatilization occurred in the first few days. Competing processes at the plant surface had a considerable effect on the dissipation of fenpropimorph, so cumulative volatilization during daylight hours was estimated to be only 7% of the dosage. Plant surface residues were higher than would correspond with the volatilization rate, indicating that penetration into the leaves had occurred.
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Simulation of pesticide leaching in a cracking clay soil with the PEARL model
(2005)

Scorza Junior RP and Jos Boestena

a) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands

Pesticide Management Science (61):432-448

Testing of pesticide leaching models is important to increase confidence in thei r 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.
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Pesticide Transport in the Groundwater at the National Scale: Coupling an Unsaturated Zone Model with a Groundwater Flow Model
(2005)

Aaldrik Tiktaka, Ton van der Lindenb, and Gerard Uffinkb

a) MNP, PO Box 303, 3720 AH Bilthoven, Netherlands
b) RIVM, PO Box 1, 3720 BA Bilthoven, Netherlands

In: N.R. Thomson (ed). Bringing groundwater quality research to the watershed scale. IAHS Publ. 297, 2005, 441-448.

Evaluation of the leaching potential of a pesticide and its metabolites is a crucial part of European registration procedures. So far, these procedures consider the movement into the shallow groundwater only. An important question is whether processes in the saturated zone can reduce the concentration in deeper aquifers to levels below a target value, for instance the drinking water limit. To investigate this problem, a spatially distributed model of pesticide leaching from soils was combined with a regional-scale groundwater flow and transport model. The combined model was used to simulate the concentration of a commonly used mobile herbicide in deeper aquifers. Results indicate that the herbicide concentration in the shallow groundwater often exceeds the target value. Due to dispersion, concentrations generally decrease with depth, but the reduction in concentrations is not sufficient to lower the concentration below the drinking water limit of 0.1 ug/L.
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Measured and computed volatilisation of the fungicide fenpropimorph from a sugar beet crop
(2005)

Minze Leistra, Johan H. Smelt and Erik van den Berg.a

a) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands

Pesticide Management Science (61):151-158

Depending on their vapour pressure, volatilisation can be one of the main pathways of emission of pesticides into the environment. The volatilisation of fenpropimorph was studied in a field experiment in which the fungicide was sprayed onto a sugar beet crop. Volatilisation rates were calculated by measuring the concentration gradient in air, using the Aerodynamic and Bowen Ratio methods. A simplified computation model was used to simulate pesticide volatilisation, together with the concurrent processes of penetration into the plant leaves and phototransformation. Input data for the model had already been obtained by carrying out a wind-tunnel study with fenpropimorph, whereby field conditions were imitated. The computations yielded a reasonable description of the level and rate of decline of fenpropimorph volatilisation in the first 4 h after spraying. The continued volatilisation 2 and 3 days after spraying could be described by assuming that a fraction of the deposit was poorly exposed with comparatively low rates of the decline processes. In the first 3 days, penetration of fenpropimorph into the plant leaves was computed to be the main route for the pesticide (52% of the dosage), with substantial contributions from volatilisation (12%) and phototransformation (11%). The computation model can be developed further as a tool for extrapolating results on volatilisation from small-scale experiments to field conditions, but this requires more information on the effect of environmental conditions on the model parameters.
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Influence of dispersion length on leaching calculated with PEARL, PELMO and PRZM for FOCUS groundwater scenarios
(2004)

Jos Boestena

a) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands

Pesticide Management Science (60):971-980

Harmonisation of the assessment of pesticide leaching to groundwater for EU registration is desirable to minimise confusion in the decision-making process at EU level. Recently, the FOCUS groundwater scenarios have been developed for three chromatographic models (PEARL, PELMO and PRZM) to increase this harmonisation. This study investigates the role of dispersion parameterisation in explaining the cause of the differences in pesticide leaching calculated by these models. PEARL describes dispersion via a physical parameter, ie the dispersion length. PELMO and PRZM simulate dispersion via a numerical procedure which generates an effective dispersion length equal to 0.5 times the thickness of the numerical compartments. The hypothesis was tested that the difference in the dispersion length input parameter (ie 5 cm for PEARL and about 2.5 cm for PELMO and PRZM) is amajor cause of the difference in calculated leaching. It was tested whether results of PEARL calculations with a dispersion length of 2.5 cm corresponded much better to results of PELMO or PRZM than results of PEARL calculations with a dispersion length of 5 cm. This was done by calculations for one substance and all nine FOCUS scenarios and by calculations for a range of substances and two FOCUS scenarios (Chateaudun and Sevilla). All calculations were for winter wheat and an application at 1 day before emergence. Both tests showed that reduction of the dispersion length from 5 to 2.5cm in PEARL led to amuch better correspondence between PEARL and either PELMO or PRZM. Hence the hypothesis was supported. It is likely that harmonisation of the dispersion length in the FOCUS groundwater scenarios would reduce the differences in calculated leaching between PEARL and PELMO or PRZM considerably for part of these scenarios. Published in 2004 for SCI by John Wiley & Sons, Ltd.
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Computations on the volatilisation of the fungicide fenpropimorph from plants in a wind tunnel
2004

Minze Leistraa and Andre Woltersb

a) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands
b) Institute of chemistry and dynamics of the geosphere IV: Agrosphere, Forschungszentrum Julich GmbH, 52425 Julich, Germany

Water, Air and soil pollution (157):133-148

Volatilisation of pesticides from plants is one of the main pathways for their emission to the environment. A simplified computation model was set up to simulate this volatilisation, including penetration into plants and photochemical transformation as competing processes. Previous wind tunnel experiments using plants sprayed with 14C-labelled fenpropimorph were simulated using the model . Volatilisation could be simulated by diffusion through a laminar air-boundary layer, with a thickness in the range of 0 .5-1.0 mm. Rate coefficients of 1.74.8 d-1 had to be used to simulate the penetration of fenpropimorph into different plant species. The rate of phototransformation was lowest when the incoming air stream was filtered through activated carbon, thus minimising the formation of hydroxyl radicals by sunlight. The simulations enabled us to estimate model parameters that could neither be derived from laboratory studies nor could be obtained with pesticide (non-labelled) in the field.
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Assessment of the pesticide leaching risk at the Pan-European level.
The EuroPEARL approach.
2004

Aaldrik Tiktaka, Danielle S. de Niea, Juan D. Pineros Garcetb, Arwyn Jonesc and Marnik Vancloosterb

a) RIVM, PO Box 1, 3720 BA Bilthoven, Netherlands
b) Universite Catholique de Louvain-la-Neuve, Croix du Sud 2 Bte. 2, Louvain-la-Neuve, Belgium
c) JR-Environmental Institute, Via Fermi 1, 21020 Ispra, Italy

Journal of Hydrology (289):222-238

Contamination of the groundwater is an important side-effect of the usage of plant protection products in agriculture. Today, the use of plant protection products that potentially contaminate the groundwater is banned by registration procedures at both the European level (Council Directive 91/414/EEC), and the level of individual member states. The Directive places great importance on the use of models to calculate Predicted Environmental Concentrations (PECs) as a basis for assessing the environmental risks. In the first tier of the current procedure, point scale leaching models are combined with a limited number of worst-case scenarios to assess PEC groundwater in Europe. An alternative procedure would be to use spatially distributed leaching models. Such models provide policy makers with a wealth of additional information, allowing identification of high and low risk areas in terms of spatially varying environmental and land use properties. In this study, such a spatially distributed leaching model, the EuroPEARL model, was implemented to assess the leaching risk of plant protection products at the Pan-European scale. This model is one of the products that has been delivered within the framework of the APECOP project (FP5-QLK-1999-01238), which is a European project supporting the harmonised registration of plant protection products in Europe. Simulations were performed for 1062 unique combinations of Soil Mapping Unit, Climate Zone and Country. Soil properties, including soil horizon designations, were obtained from the Soil Profile Analytical Database of Europe. Daily weather data were obtained from the MARS database. Other data like irrigation data, crop data and product properties have been compiled from various sources, such as inventories, field-studies and the literature. The 1062 unique combinations together represent 75% of the total agricultural area of the European Union. Austria, Sweden and Finland could not be included in the simulations, because there was insufficient soil profile information for these countries. Results are presented with a resolution of 10x10 km2, which is the highest justifiable resolution based on the EU soil map 1:1,000,000. The Pan-European results confirm that the predicted leaching concentration generally increases with precipitation and irrigation and decreases with increasing organic matter content. Because of the strong sensitivity of the leaching concentration to soil properties, there is a strong variability of the calculated leaching concentration at relatively short distances. Results further indicate that due to large irrigation amounts combined with large temporal variation of rainfall in the Southern European countries, the trend in the calculated leaching risks from North to South was less than expected. This implies that areas of high leaching risk ("hotspots") as assessed by means of the EuroPEARL model occur in all countries of the European Union, including the Southern European countries.
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On the use of unsaturated flow and transport models in nutrient and pesticide management
2004

Marnik Vancloostera, Jos Boestenb, Aaldrik Tiktakc, Nick Jarvisd, Joop Kroesb, R. Munoz-Carpenae, B.E. Clothierf and S.R. Greenf

a) Universite catholique de Louvain, Louvain-la-Neuve, Belgium (vanclooster@geru.ucl.ac.be)
b) Alterra, Wageningen, the Netherlands
c) RIVM, PO BOX 1, 3720 BA Bilthoven, the Netherlands
d) Sveriges Lantbruksuniversitet, Uppsala, Sweden
e) University of Florida Agricultural and Biological Engineering Department, 18905 SW 280 Street, Homestead, FL 33031-3314, US
f) HortResearch, Private Bag 11 030, Palmerston North, New Zealand

In: R.A. Feddes, G.H. de Rooij and J.C. van Dam (eds.) Unsaturated-zone modelling. Progress, chalanges and applications. Wageningen UR Frontis series Volume 6, Kluwer Academic Publishers, Dordrecht, the Netherlands, pp. 331-361.

Nutrient and pesticide emissions from agricultural land significantly impact surface and groundwater resources all over the world. These emissions should therefore be controlled by an appropriate management of agricultural practices. Effective agricultural management builds on a thorough understanding of the fate and behavior of nutrients and pesticides in the soil-crop system. Unsaturated flow and transport models may therefore be used as tools to predict fate and behavior of chemicals in soil, supporting decision making in the area of nutrient and pesticide management. In this paper, we show how flow and transport models are introduced in the nutrient and pesticide management decision-making process. Examples are given of the use of flow and transport models in (i) field-scale nutrient and pesticide management; (ii) the identification and evaluation of fertilization and pesticide application practices supporting the implementation of regional-scale environmental management plans; and (iii) the registration of plant-protection products. Examples are selected across different eco-regions elucidating the generality of the presented approaches. Particular emphasis is put on (i) the limitations of the current modeling approaches for management applications, (ii) the handling of uncertainty in the data flow, (iii) the problems associated with the estimation of the required modeling data and parameters, and (iv) the transfer of scientific know-how into operational decisionmaking tools. Opportunities are presented for improving the process descriptions, the data generation methods, and the modeling practice. Finally, threats are summarized on the use of flow and transport models in future nutrient and pesticide management studies.
Details Full paper

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Pesticide Transport in the Groundwater at the National Scale: Coupling an Unsaturated Zone Model with a Groundwater Flow Model
2004

Aaldrik Tiktaka, Ton van der Lindena and Gerard Uffinka

a) RIVM, PO BOX 1, 3720 BA Bilthoven, the Netherlands

Proceedings of the COST 296 action in Louvain-la-Neuve

Evaluation of the leaching potential of a pesticide and its metabolites is a crucial part of European registration procedures. So far, these procedures consider the movement into the shallow groundwater only. An important question is whether processes in the saturated zone can reduce the concentration in deeper aquifers to levels below a target value, for instance the drinking water limit. To investigate this problem, a spatially distributed model of pesticide leaching from soils was combined with a re-gional-scale groundwater flow and transport model. The combined model was used to simulate the concentration of a commonly used mobile herbicide in deeper aquifers. Results indicate that the her-bicide concentration in the shallow groundwater often exceeds the target value. Due to dispersion, concentrations generally decrease with depth, but the reduction in concentrations is not sufficient to lower the concentration below the drinking water limit of 0.1 ug/L.
Details Full paper

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The GeoPEARL model: Part II. User guide and model description update
2004

Aaldrik Tiktaka, Ton van der Lindena, Jos Boestenb, Roel Kruijneb and Daniel van Kraalingenb

a) RIVM, PO BOX 1, 3720 BA Bilthoven, the Netherlands
b) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands

RIVM report 716601008, RIVM, Bilthoven, the Netherlands, pp. 82

Recently, the Netherlands has adopted a new decision tree for evaluating the leaching potential of pesticides, specifically to see if the concentration in groundwater exceeds the EU drinking-water limit of 0.1 ug/L. The spatial criterion in the new decision tree states that the long-term average concentration of a pesticide or its relevant metabolites should not exceed the drinking-water limit for at least 90% of the surface area where the pesticide is potentially used. A spatially distributed model, 'GeoPEARL', has been developed to scientifically test the above criterion. GeoPEARL will play a key role in the new Dutch decision tree. The aim of this report is to provide a guideline on the use of GeoPEARL, with special emphasis on the Dutch registration procedure. This report should be used in combination with RIVM report no. 601450019, which describes the new decision tree and the role of GeoPEARL in this tree. Background information, including the theory behind the model, can be found in the earlier RIVM report, no. 716601007.
Details To the report
Details More information about GeoPEARL.

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Nationwide assessments of non-point source pollution with field-scale developed models:
The pesticide case

Aaldrik Tiktaka, Jos Boestenb and Ton van der Lindena

a) RIVM, PO Box 1, 3720 BA Bilthoven, Netherlands
b) Alterra Green World Research, PO Box 47, 6700 AA Wageningen, Netherlands

In: G.J. Hunter and K. Lowell (Eds.). Proceedings of the 5th International Symposium on Spatial Accuracy Assessment (Accuracy 2002), Melbourne, July 2002, pp. 17-30.

The use of nationwide models of non-point source pollutants in soils is now common practice. Most of these models have originally been developed at the field-scale. An integrated approach (a 'research chain') is presented, and applied to the modelling of pesticide leaching in the Netherlands. The research chain consists of five steps, i.e. (i) problem definition, selection of model approach and model building, (ii) applica-tion of the model to a number of field-plots, (iii) scale transfer, including process aggregation and data aggregation, (iv) regional-scale model appli-cation, and (v) analysis and presentation of results. It was shown that some of the steps of the research chain could not be completely carried out. In this particular study, regional-scale model validation and uncer-tainty analysis were hampered by lack of data. Probably the most impor-tant part of the research chain is the phase of scale transfer. It was shown that in the pesticide leaching study data aggregation was more appropriate than process aggregation (model simplification). Data were aggregated by stratifying the input-data and by setting up procedures in which specific model-inputs were derived from generally available data sources.
Details More information about GeoPEARL.
Details Full paper (pdf, 625K).
Details More details in the PhD thesis of Tiktak (pdf, 1,5M).

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The GeoPEARL model: Description, applications and manual
2003

Aaldrik Tiktaka, Ton van der Lindena and Jos Boestenb

a) RIVM, PO Box 1, 3720 BA Bilthoven, Netherlands
b) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands

RIVM report 716601007/2003, RIVM, Bilthoven, the Netherlands, pp. 79.

The GeoPEARL model presented here is a spatially distributed model describing the fate of pesticides in the soil-plant system. The model calculates the drainage of pesticides into local surface waters and their leaching into the regional groundwater. Set up to simulate the behaviour of a wide range of pesticides (e.g. volatile substances and substances showing soil-dependent sorption constants and transformation rates), GeoPEARL plays an important role in the evaluation of such Dutch pesticide policy plans as the 'Multiyear Crop Protection Plan' and the plan for 'Sustainable Crop Protection'. The report contains a number of examples of applications using pesticides with different properties. Generally, results showed the average fluxes of pesticide into local surface waters to be higher than the average fluxes of pesticide to the regional groundwater, with rapid drainage mechanisms (i.e. tube drainage and surface drainage) dominating. These observations should be taken seriously, since pesticides lost through these routes contaminate local surface waters directly. GeoPEARL has also been used to verify the current Dutch Pesticide Authorisation procedure. This procedure starts by applying PEARL to a single site, which, for leaching, is assumed to represent realistic worst-case conditions. Results of GeoPEARL showed, however, that the leaching potential of individual pesticides peaked in different regions, indicating that no such single site exists. The conclusion was that the single-site approach could give erroneous results, unless additional precautionary measures were taken while selecting the pesticide input parameters. Discussion on what these conditions should be can be avoided by opting for direct application of GeoPEARL in preference to the single-site approach.<
Details To the report
Details More information about GeoPEARL.

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Assessing the Risk of Pesticide Leaching at the Pan-European Level.
2003

Aaldrik Tiktaka, Danielle de Niea, Juan Pineros Garcetb, Arwyn Jonesc and Marnik Vancloosterb

a) RIVM, PO Box 1, 3720 BA Bilthoven, Netherlands
b) UCL-Louvain la Neuve, Belgium
c) JRC-Ispra, Italy

In: A.A.M. Del Re, E. Capri, L. Padovani, M. Trevisan (Eds.). Pesticide in air, plant, soil & water system. Proceedings of the XII international Symposium Pesticide Chemistry, June 4-6, 2003, Piacenza, Italy, pp. 941-950.

Contamination of the groundwater is an important side-effect of the usage of pesticides in agriculture. Today, the use of pesticides that potentially contaminate the groundwater is banned by registration procedures at both the European level (Council Directive 91/414/EEC), and the level of individual member states. The Directive places great importance on the use of models to calculate Predicted Environmental Concentrations (PECs) as a basis for assessing the environmental risks. In the current procedure, models are applied to a limited number of point locations. These point locations are assumed to represent realistic worst case conditions. An alternative is to use a spatially distributed model. Such a model provides policy makers with a wealth of additional information, particularly high and low risk areas. In this study, the EuroPEARL model was used to establish th e pesticide leaching risk in the European Union. This model is one of the products that has been delivered within the framework of the APECOP project, which is a European project supporting the harmonised registration of pesticides in Europe. Simulations were performed for 1062 unique combinations of Soil Mapping Unit, Climate Zone and Country. Soil properties, including soil horizon designations, were obtained from the Soil Profile Analytical Database of Europe. Daily weather data were obtained from the MARS database. Other data like irrigation data, crop data and pesticide properties have been compiled from various sources, such as inventories, field-studies and the literature. The 1062 unique combinations together represent 75% of the total agricultural area of the European Union. Austria, Sweden and Finland could not be included in the simulations, because there was insufficient soil profile information for these countries. Results are presented with a resolution of 10x10 km2, which is the highest justifiable resolution based on the EU soil map 1:1,000,000. Results indicate that the leaching concentration generally increases with precipitation and irrigation and decreases with increasing organic matter content. Because of the strong sensitivity of the leaching concentration to soil properties, there is a strong variability of the calculated leaching concentration at relatively short distances. Results further indicate that due to large irrigation amounts combined with large temporal variation of rainfall in the Southern European countries, the trend in the calculated leaching risks from North to South was less extreme then expected. This implies that areas of high leaching risk ('hotspots') as assessed by means of the EuroPEARL model occur in all countries of the European Union, including the Southern European countries. The practical consequence of this study is that protection of groundwater bodies should be given political priority in all countries of the European Union.
Details Full text (pdf, 426K).
Details Presentation (pps, 3MByte).

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Comparison of GeoPEARL with the Single Scenario Approach in Pesticide Registration and Policy Evaluation.
2003

Ton van der Lindena, Aaldrik Tiktaka, Jos Boestenb and Roel Kruijneb

a) RIVM, PO Box 1, 3720 BA Bilthoven, Netherlands
b) Alterra Green World Research, PO Box 47, 6700 AA Wageningen, Netherlands

In: A.A.M. Del Re, E. Capri, L. Padovani, M. Trevisan (Eds.). Pesticide in air, plant, soil & water system. Proceedings of the XII international Symposium Pesticide Chemistry, June 4-6, 2003, Piacenza, Italy, pp. 499-506.

Several countries use one or a few scenarios to evaluate the leaching of pesticides. This, however, can be too strict for some substances while being too lenient for others, because of the wide ranges in pesticide properties. In a GIS approach the variability is explicitly taken into account and more accurate results are expected. This research has been carried out to compare the two approaches. The PEARL model was used to calculate the leaching in 8 FOCUS scenarios and the Dutch standard scenario (NLS). A number of pesticides was included, covering wide ranges in properties. The spatially distributed model GeoPEARL was used to calculate the 90th percentile leaching concentrations for the Netherlands, taking into account information on a.o. soil properties and climatic conditions. None of the scenarios is capable of representing realistic worst-case conditions in the Netherlands for the broad range of pesticides. Six FOCUS scenarios appear to be more vulnerable. Using the FOCUS approach, the NLS and GeoPEARL results agree well, except for volatile and acidic substances. When using single applications, NLS-results appear to be lower: the ratio (GeoPEARL/NLS) ranges from 1 to 385. We conclude that tools such as GeoPEARL should replace single scenarios in evaluation studies.
Details Full text (pdf, 78K).

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Development of an Environmental Indicator that can be used on National and Regional Scales.
2003

John Deneera, Ton van der Lindenb, Robert Luttikb and Rob Smidta

a) Alterra Green World Research, PO Box 47, 6700 AA Wageningen, Netherlands
b) RIVM, PO Box 1, 3720 BA Bilthoven, Netherlands

In: A.A.M. Del Re, E. Capri, L. Padovani, M. Trevisan (Eds.). Pesticide in air, plant, soil & water system. Proceedings of the XII international Symposium Pesticide Chemistry, June 4-6, 2003, Piacenza, Italy, pp. 641-648.

The use and emission of pesticides as a result of their agricultural use has been reduced substantially in the Netherlands over the last 10 years. A new governmental program, which was introduced in the Netherlands in 2001, encourages growers to achieve an even further reduction of the emission of pesticides. In order to monitor the results of this program, a tool is being developed which can give an accurate description of the emissions and fate of pesticides and their environmental effects. This tool, the Dutch National Environmental Indicator, is intended to calculate emissions of pesticides, and evaluate results of policy, over the period from 1998 - 2010. The indicator calculates emissions into several environmental compartments (surface water, ground water, soil, non-agricultural soil and atmosphere) from agriculture, horticulture and glasshouses. Ecotoxicological consequences of these emissions are judged by comparing predicted environmental concentrations (PEC) and acute and chronic toxicity data for aquatic, soil and terrestrial organisms. One of the aims during development of the indicator was to incorporate the possibility to perform calculations on a detailed geographical scale, taking into account differences between regions which may affect the emission and fate of pesticides. To this end the Netherlands were divided into approx. 136,000 geographical units (cells), for each of which information about crop areas, soil characteristics (density, organic matter, acidity), average air temperature and the presence or absence of surface water is available. Calculations are performed for each of these cells separately, which results in a very detailed picture of the emissions of pesticides over the Netherlands. Emissions are calculated using detailed agricultural information like total yearly sales, the weekly use of active ingredients in approx. 50 distinguishable crops and the areas used for each of the crops. Much of this information is updated on a yearly basis. Moreover, information about the implementation of several emission reducing techniques, such as the use of special nozzles during spraying and the presence of buffer zones, is also included and updated whenever new results from national surveys become available. Whenever possible, calculations make use of procedures and data which are used in EU registration procedures (Pearl, Pestla, TOXSWA). The presentation will give an outline of the information necessary to perform such detailed calculations, and will describe in some detail some of the emission routes included in the indicator. Some results of emission calculations will be presented, demonstrating the use of the indicator for evaluating policy.
Details Full text (pdf, 537K).

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Effective approaches for predicting environmental concentrations of pesticides: The APECOP project.
2003

Vanclooster, M.a, Armstrong, A.j, Baouroui, F.i, Bidoglio, G.i, Boesten, J.J.T.I.b, Buraeul, P.d, Capri, E.f, De Nie, D.h, Fernandez, E.e, Jarvis, N.c, Jones, A.i, Klein, M.g, Leistra, M.b, Linnemann, V.d, Pineros Garcet, J.D.a, Smelt, J.H.b, Tiktak, A.h, Trevisan, M.f, Van den Berg, F.b, Van der Linden, A.M.A.h, Vereecken, H.d, Wolters, A.d

a) Universite catholique de Louvain, Louvain-la-Neuve, Belgium (vanclooster@geru.ucl.ac.be)
b) Alterra Green World Research, Wageningen, the Netherlands
c) Sveriges Lantbruksuniversitet, Uppsala, Sweden
d) Forschungszentrum Jülich GmBH, Jülich, Germany
e) Consejo Superior de Investigaciones Cientificas, Seville, Spain
f) Instituto di chimica Agraria ed Ambientale, Universita Cattolica des Sacro Cuore, Piacenza, Italy
g) Fraunhofer - Gesellschaft zur Förderung der angewandten Forschung München, e.V., Schmallenberg, Germany
h) Rijksinstituut voor Volksgezondheid en Milieu, Bilthoven, the Netherlands
i) Joint Research Centre (EC-JRC): Environment Institute, Ispra, Italy.
j) ADAS, United Kingdom

In: A.A.M. Del Re, E. Capri, L. Padovani, M. Trevisan (Eds.). Pesticide in air, plant, soil & water system. Proceedings of the XII international Symposium Pesticide Chemistry, June 4-6, 2003, Piacenza, Italy, pp. 923-931.

Environmental fate modelling is now actively used for the registration of plant protection products (PPPs). Yet, to be efficient in a harmonised registration process, the quality of PEC modelling needs to be assured. Quality assurance of mathematical modelling implies the validation, documentation and maintenance of the modelling codes and scenarios. The FOrum for the Co-ordination of pesticide fate models and their USe (FOCUS) defined the procedures for realising tier 1 PEC groundwater calculations for active substances at the pan-European level. The FOCUS working groups also identified a range of uncertainties related to the validity of the leaching models and scenarios. To mitigate some of these problems, the EU project APECOP (Effective approaches for predicting environmental concentrations of pesticides) was designed. The major objective of the project is to improve modelling concepts for PEC groundwater and air, and to increase the validity status of the modelling codes. In addition a methodology was developed and implemented to evaluate the representativity of the current tier 1 groundwater scenarios such as recommended by the FOCUS groundwater scenarios working group. In this paper, we summarise the methodologies that were used in this project. More detailed information is given in the subsequent papers.
Details Full text (pdf, 78K).
Details Apecop final report (pdf, 2.8 MB).

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Methodological Approach for Evaluating First Tier PEC Groundwater Scenarios Supporting the Prediction of Environmental Concentrations of Pesticides at the European Scale.
2003

Pineros Garcet, J.D..a, Vanclooster, M.a, Tiktak, A.b, De Nie, D.Sb and Jones, A

a) Universite catholique de Louvain, Louvain-la-Neuve, Belgium (vanclooster@geru.ucl.ac.be)
b) RIVM, PO BOX 1, 3720 BA Bilthoven, the Netherlands
c) Joint Research Centre (EC-JRC): Environment Institute, Ispra, Italy.

In: A.A.M. Del Re, E. Capri, L. Padovani, M. Trevisan (Eds.). Pesticide in air, plant, soil & water system. Proceedings of the XII international Symposium Pesticide Chemistry, June 4-6, 2003, Piacenza, Italy, pp. 951-962.

Within the framework of the harmonised registration of plant protection products (PPPs) at the EU-scale, environmental fate models are nowadays combined with a series of scenarios to predict the environmental concentrations of PPPs in the different environmental compartments. At present, harmonised procedures and scenarios for assessing the predicted environmental concentration (PECs) of pesticides in groundwater have been implemented through the FOCUS working groups. The effectiveness and efficiency of the risk assessment procedures will thereby strongly depend on the validity of the environmental fate model and on the validity of the selected scenarios. In contrast to the validation of environmental fate models itself, little attention has been devoted so far to the validation of scenarios.

Within this paper we present a methodological approach for validating scenarios within the framework of risk assessment. The approach was developed within the framework of the EU-FP5 research project APECOP (Effective approaches for predicting environmental concentrations of pesticides) and helps to determine the validation status of the FOCUS groundwater scenarios, as presently used in the higher tier harmonised registration of pesticides at the EU level. Validation encompasses the comparison of PECs to groundwater as obtained using the most detailed modelling approach that currently can be implemented at the Pan-European scale with the results obtained from FOCUS PECs.
Details Full text (pdf, 131K).

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Improvement of concepts for pesticide volatilisation from bare soil in PEARL, PELMO and MACRO models.
2003

F. van den Berga, A. Woltersb, N. Jarvisc, M. Kleind, J.J.T.I. Boestena, M. Leistraa, V. Linnemannb, J.H. Smelta and H. Vereeckenb

a) Alterra Green World Research, PO Box 47, 6700 AA Wageningen, Netherlands
b) Forschungszentrum Juelich GmbH, Juelich, Germany
c) Swedish Institute of Agricultural Science, Dept. of Soil Sciences, PO BOX 7072, 75007 Uppsala, Sweden.
d) Fraunhofer Institute for Molecular Biology and Applied Ecology, PO BOX 1260, 57377 Schmallenberg, Germany.

In: A.A.M. Del Re, E. Capri, L. Padovani, M. Trevisan (Eds.). Pesticide in air, plant, soil & water system. Proceedings of the XII international Symposium Pesticide Chemistry, June 4-6, 2003, Piacenza, Italy, pp. 973-983.

Volatilisation is an important process to be considered when predicting the fate of a pesticide after its application to soil. At present, this emission pathway has not been described adequately in pesticide fate models used to calculate environmental concentrations as needed in the current EU risk assessment procedure under Council Directive 91/414. Moreover, little attention has been given to the concentration of pesticides in air. To remedy this, a project was started to include or improve the description of volatilisation process in the PEARL, PELMO and MACRO models. Datasets for volatilisation under field conditions were collected and described and process studies were done in the laboratory to assess the effects of soil moisture and other environmental factors on volatilisation. Concepts to describe the volatilisation from soil surfaces were developed or improved and implemented in the models. First tests were done using measured volatilisation rates in the field to check whether the improved models could predict leaching better than the reference models. The inclusion of a description for the increase in the sorption coefficient at low soil water contents resulted in a better description of the volatilisation under dry soil surface conditions. Hourly input is needed to describe adequately the volatilisation process, particularly during the first day after application.
Details Full text (pdf, 134K).

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Pesticide volatilisation from plants: Improvement of the PEARL, PELMO and MACRO models.
2003

A. Woltersa, M. Leistrab, V. Linnemanna, J.H. Smeltb, F. van den Bergb, M. Kleinc, N. Jarvisd, J.J.T.I. Boestenb and H. Vereeckena

a) Forschungszentrum Juelich GmbH, Juelich, Germany
b) Alterra Green World Research, PO Box 47, 6700 AA Wageningen, Netherlands
c) Fraunhofer Institute for Molecular Biology and Applied Ecology, PO BOX 1260, 57377 Schmallenberg, Germany.
d) Swedish Institute of Agricultural Science, Dept. of Soil Sciences, PO BOX 7072, 75007 Uppsala, Sweden.

In: A.A.M. Del Re, E. Capri, L. Padovani, M. Trevisan (Eds.). Pesticide in air, plant, soil & water system. Proceedings of the XII international Symposium Pesticide Chemistry, June 4-6, 2003, Piacenza, Italy, pp. 985-994.

Simulation of volatilisation from plants is an important part in pesticide fate models, especially for the models used to predict the concentrations of pesticides in the environment in the registration procedures. Recent efforts to harmonise registration procedures for pesticides in the European Union necessitated the development and implementation of suitable volatilisation modules within the framework of the EC project APECOP (Effective Approaches for Assessing the Predicted Environmental Concentration of Pesticides). An empirical description to estimate the cumulative volatilisation of pesticides during seven days after application to crops was included in MACRO. A mechanistic approach using a laminar air-boundary layer concept for the consideration of volatilisation from plant surfaces was developed and calibrated on the basis of a series of wind-tunnel studies performed under well-defined conditions. The description was implemented in PELMO (Pesticide Leaching Model). When key parameters had been calibrated (thickness of air-boundary layer, phototransformation and penetration into the leaves), the approach was able to simultaneously estimate volatilisation of pesticides form plants and soil. For a more appropriate reflection of field conditions, the advanced volatilisation module to be included in PEARL (Pesticide Emission Assessment at Regional and Local Scales) could replace the concept of the laminar boundary layer with the improved description of aerodynamic and boundary-layer resistances in air.
Details Full paper (pdf, 167K).

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Incorporating macropore flow into FOCUS PEC Models.
2003

N. Jarvisa, J.J.T.I Boestenb, R. Hendriksb, M. Kleinc, M. Larsboa, S. Rouliera, F. Stenemoa and A. Tiktakd

a) Swedish Institute of Agricultural Science, Dept. of Soil Sciences, PO BOX 7072, 75007 Uppsala, Sweden.
b) Alterra Green World Research, PO Box 47, 6700 AA Wageningen, Netherlands
c) Fraunhofer Institute for Molecular Biology and Applied Ecology, PO BOX 1260, 57377 Schmallenberg, Germany.
d) RIVM, PO BOX 1, 3720 BA Bilthoven, the Netherlands

In: A.A.M. Del Re, E. Capri, L. Padovani, M. Trevisan (Eds.). Pesticide in air, plant, soil & water system. Proceedings of the XII international Symposium Pesticide Chemistry, June 4-6, 2003, Piacenza, Italy, pp. 963-972.

Macropore flow can strongly influence leaching of pesticides in the unsaturated zone, but this process has until now played only a limited role in exposure assessments. This paper describes efforts to incorporate descriptions of macropore flow into the exposure assessment models PEARL and PELMO, recommended for use in pesticide registration in the EU. We also outline improvements made to an existing macropore flow model (MACRO), including upgraded numerical routines, new processes (e.g. tillage, kinetic sorption), and an inbuilt inverse modeling capability (SUFI) to help parameterization. Simulations made with the macropore flow version of PELMO and the existing FOCUS version of the model are compared with measurements of pesticide leaching made in two clay soils (Lanna, Andelst). Results show that the functional description of macropore flow included in PELMO appears promising, and should be further tested on additional high quality datasets. Use of SUFI to estimate parameters in MACRO 4.3 and 5.0 for the Lanna dataset, showed that the effects of differences in parameter optimisation methods were overshadowed by differences between models in process descriptions and numerical methods. Despite the comprehensive nature of the dataset, one important parameter regulating the strength of macropore flow could only be identified with a large uncertainty
Details Macropore flow in PEARL.
Details Full text (pdf, 136K).

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Emissions of plant protection products to the environment. Evaluation of the policy goals of the Long-term Crop Protection Plan
2002

Danielle de Nie (Eds.)

RIVM report 716601004, RIVM, Bilthoven, The Netherlands, pp. 160

The long-term crop protection programme (MJP-G) of the Netherlands aimed for the period 1990 - 2000 a.o. at 50 to 90 % reduction of emissions of plant protection products to the environment. The success of the emission reduction part of this plan was evaluated by calculating emissions to air, surface water, soil and groundwater for the reference period and the year 2000. Reductions were estimated to be 79 % (aim: at least 75 %) for emissions to soil and groundwater, 54 % (aim: at least 50 %) for emissions to air and 79 % (aim: at least 90 %) for emissions to surface water. The emissions to air constitute over 95% of total emitted amounts. This report presents technical backgrounds, boundary conditions and calculation methods. As compared to the interim evaluation in 1995, several calculations methods have changed significantly. For the calculation of emissions to air, new information has become available so that it is now possible to account for direct emission of droplets to air and interactions of the plant protection products with soil and crop. The leaching and drainage is calculated directly for the most important substances, while in the interim evaluation an overall distribution was calculated. Drift to surface water and non-target areas is now based on an extended database on drift measurements and includes drift reduction measures. Emissions for the reference period and for 1995 have been recalculated with the new calculation procedures to make a proper evaluation of the reduction percentages possible.
Details More information about GeoPEARL.
Details Full paper (pdf, 2,5MB).

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Modelling the Leaching and Drainage of Pesticides in the Netherlands: The GeoPEARL model
2002

Aaldrik Tiktaka, Danielle de Niea, Ton van der Lindena and Roel Kruijneb

a) RIVM, PO Box 1, 3720 BA Bilthoven, Netherlands
b) Alterra Green World Research, PO Box 47, 6700 AA Wageningen, Netherlands

Published in Agronomie (22) 2002, page 373-387

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 for 6405 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-scale model, however, is to be preferred, because it provides the user with frequency distributions and gives information about areas of safe usage.
Details More information about GeoPEARL.
Details Full paper (pdf, 1,4MB).

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Manual of FOCUS PEARL version 1.1.1
2002

Aaldrik Tiktaka, Erik van den Bergb, Jos Boestenb, Daniel van Kraalingenb, Minze Leistrab and Ton van der Lindena

a) RIVM, PO Box 1, 3720 BA Bilthoven, Netherlands
b) Alterra, PO Box 47, 6700 AA Wageningen, Netherlands

RIVM report 711401008/2000, RIVM, Bilthoven, the Netherlands, pp. 142.

The PEARL model is used to evaluate the leaching of pesticide to the groundwater in support to the Dutch and European pesticide registration procedures. PEARL is an acronym for Pesticide Emission Assessment at Regional and Local scales. The model is a joint product of Alterra Green World research and the National Institute of Public Health and the Environment, and it has replaced the models PESTLA and PESTRAS since June 1st, 2000. Model and data can be accessed through a user-friendly Graphical User Interface for Windows 95/98/NT. All data are stored in a relational database. Both the Dutch standard scenario and the European standard scenarios as suggested by the FOCUS modeling working group can be accessed through the User Interface. This report gives a description of the processes and parameters included in PEARL version 1.1. It also contains a description of the Pearl User Interface and the input and output files. The Dutch standard scenario is described briefly.
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Details More information about FOCUS groundwater.

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A European Test of Pesticide Leaching Models:
Methodology and major Recommendations
2002

Marnik Vancloostera and others..

a) UCL, Louvain-la-Neuve, Place Croix du Sud 2, BP2,1348 Louvain-la-Neuve, Belgium


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, solutes, 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 analyses. 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 the water transport, solute transport, heat transport and pesticide transport in soils, a stepwise evaluation procedure was followed. Splitting up the experimental dataset enabled us to quantify the calibration capability and the prediction capability of the models. The simulation were performed by different model users enabling us to characterise output variability in terms of user dependent interpretation of the model inputs and parameters. Recommendation are formulated for improving the quality of modelling datasets, and the process description of water, solute, heat and pesticide 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. (C) 2000 Elservier Science BV.
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Movement of water, bromide and the pesticides ethoprophos and bentazone in a sandy soil:
The Vreedepeel data set.
2002

Jos Boestena and Johan Smelta


a) Alterra Green World Research, PO Box 47, 6700 AA Wageningen, Netherlands.


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 later application time is unusual for bentazone: it was selected on scientific grounds (without agricultural practice). 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 each date). In the laboratory, pesticide transformation rates were measured with soil material from 0-25 cm, 50-100 cm and 100-200 cm depth. Sorption isotherm 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 concentration of bentazone and ethoprophos were below the detection limit (0.2 to 2 ug dm-3) in all soil layers between 25 and 120 cm depth. Recommended values for the most important parameters of pesticide leaching models are presented. (C) 2000 Elservier Science BV.
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Application of pesticide leaching studies to the Vreedepeel dataset:
I. Water, solute and heat transport
2002

Marnik Vancloostera and Jos Boestenb

a) UCL, Louvain-la-Neuve, Place Croix du Sud 2, BP2,1348 Louvain-la-Neuve, Belgium
b) Alterra Green World Research, PO Box 47, 6700 AA Wageningen, Netherlands


The performance of 10 deterministic one-dimensional dynamic pesticide leaching models with different complexity was evaluated using data collected on a humic sandy soil with a shallow gruondwater table in the Netherlands. Both mechanistic models, based on the solution of the governing equations and functional, more empirical models were considered. Simulation were carried out by 18 modellers allowing the characterisation of model performance in terms of user specific model parameterisation. Both uncalibrated and calibrated results are presented which demonstrate the impact of model calibrations on model results. In this paper, the ability of the models to correctly describe the physical transport mechanisms is evaluated, while in a second paper the potential of the model to represent pesticide fate correctly will be assessed. (C) 2000 Elsevier Science B.V.
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Application of pesticide leaching studies to the Vreedepeel dataset:
II. Water, solute and heat transport
2002

Aaldrik Tiktaka

a) RIVM, PO Box 1, 3720 BA Bilthoven, Netherlands


The performance of nine deterministic, one-dimensional, dynamic pes-ticide 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 exten-sive description of the experimental data. Despite this fact, the inter-pretation of the experimental data was ambiguous, leading to tremen-dous 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 per-formance 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. (C) 2000 Elsevier Science B.V.
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Modeller Subjectivity in estimating Pesticide Parameters for Leaching Models
using the same Laboratory Data Set
2002

Jos Boestena

a) Alterra Green World Research, PO Box 47, 6700 AA Wageningen, Netherlands


User-dependent subjectivity in the process of testing pesticide leaching models is relevant because it may result in wrong interpretation of model results. About 20 modellers used the same data set to test pesticide leaching models. The data set included laboratory studies on transformation and sorption of ethoprophos and bentazone in soil from the top 25 cm, at two or three temperatures. All modellers received the data from these two studies without guidance for deriving the model input paramters. The modellers were asked to provide the values of the half-lives and sorption coefficients which the model considered. The half-life of ethoprophos ranged from 92 to 346 days with an average of 191 days and a coefficient of variation of 29%. The half-life of bentazone ranged from 33 to 204 days with an average of 83 days and a coefficient of variation of 46%. The linear and Freundlich sorption coefficients of ethoprophos ranged from 1.7 to 4.3 dm3 kg-1 with an average of 3.4 dm3 kg-1 and a coefficient of variation of 21%. The linear and Freundlich sorption coefficients of bentazone ranged from 0.08 to 0.14 dm3 kg-1 with an average of 0.11 dm3 kg-1 and a coefficient of variation of 13%. This variability caused by the interpretation of the modeller is so large that it overrules conceptual differences between the models in many cases. The most important cause of the variability in the half-lives was the expert judgement involved in establishing the relationship between transformation rate and soil temperature. Differences in fitting procedures played only a minor role for the half-lives but they were an important cause of the variability in the linear sorption coefficient. Some recommendantions are proposed to reduce the effect of user-subjectivity on modelling results in future model tests. (C) 2000 Elsevier Science B.V.
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Modelling Non-Point Source Pollutants in Soils:
Applications to the Leaching and Accumulation of Pesticides and Cadmium.
2002

Aaldrik Tiktaka

a) RIVM, PO Box 1, 3720 BA Bilthoven, Netherlands


The general objective of the present study was to contribute to a justified application of plot-scale developed models of non-point source pollutants on a regional-scale. Two environmental issues were studied, i.e. the leaching of pesticides to the shallow groundwater and the accumulation of cadmium in the topsoil and leaching into the groundwater. These two issues were chosen because they required entirely different model approaches. Pesticide leaching was calculated with a detailed, numerical, multi-layer model with a high temporal resolution (PESTRAS). Processes included were transient flow, convection, hydrodynamic dispersion, equilibrium sorption, degradation, uptake by plant roots and volatilization. In the heavy metal accumulation study two models were used: A comprehensive, multi-layer, numerical model (METRAS), which was applicable at the plot-scale, and a simple analytical, one-layer model with a lower temporal resolution (SOACAS), which was used for the regional-scale assessments. Processes included in SOACAS are steady-state waterflow, convection, equilibrium sorption, complexation, and plant-uptake. A general procedure was outlined for the development and evaluation of regional-scale models of non-point source pollut-ants in soil (chapter 1). The following major stages were distin-guished: problem definition, selection of model approach and model building (chapter 1), application and evaluation of the model at a number of field-plots (chapter 2), change in spatial-scale, including upscaling, data-aggregation and process-aggregation (chapter 3), regional-scale model application and evaluation (chapters 3 and 4), and presentation of results (chapter 3).
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