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SWASH (Surface WAter Scenarios Help) assists the user in calculating pesticide exposure concentration in the EU FOCUS surface water scenarios. It is part of the exposure calculation procedure, being part of the obligatory evaluation procedure to place an active substance on List 1 according to EU Directive 91/414/EEC. SWASH encompasses: (i) FOCUS Drift Calculator, calculating pesticide entries through spray drift deposition, (ii) PRZM-3, calculating pesticide entries through run-off, (iii) MACRO, calculating pesticide entries through drainage and (iv) TOXSWA, calculating the behaviour of pesticides in small surface waters. It is linked to SPIN, a pesticide properties tool, and prepares input for the PRZM, MACRO and TOXSWA models. Via the SWASH shell the user can enter the shells of the other models to perform the PRZM or MACRO model runs needed to assess the fate of the substance in he FOCUS water body systems using TOXSWA.

The user-friendly shell SWASH, acronym for Surface WAter Scenarios Help, assists the user in calculating pesticide exposure concentrations in the EU FOCUS surface water scenarios. SWASH encompasses five separate tools and models: (i) FOCUS Drift Calculator, calculating pesticide entries through spray drift deposition, (ii) PRZM-3, calculating pesticide entries through run-off, (iii) MACRO, calculating pesticide entries through drainage, (iv) TOXSWA, calculating the behaviour of pesticides in small surface waters, and (v) SPIN is a central database for storage and editing of pesticide properties. The SWASH database contains information on projects and runs created by the user. This report gives a detailed description of the necessary flow of data between the various models, to make them communicate smoothly with each other. It also specifies the installation requirements for the MACRO, PRZM and TOXSWA models. The MACRO model uses an MS-Access database to store its substance and run information, while PRZM makes use of separate data files. TOXSWA uses the central SWASH database. After completing a SWASH session the user should manually perform simulations with the three individual models

Van vijf sloten verspreid liggend over Nederland, zijn de sediment eigenschappen droge bulkdichtheid, organische-stofgehalte en porositeit zijn als functie van de diepte gemeten. Het betreft hier akkerbouw- en tuinbouwgebieden. De gevonden waarden verschillen duidelijk van de gebruikte waarden voor sediment in de oppervlaktewater scenario’s, die momenteel worden ontwikkeld voor de Nederlandse registratieprocedure voor gewasbeschermingsmiddelen (die zijn overgenomen van de EU-FOCUS scenario’s).

In the Pesticide Risk Reduction Programme Ethiopia the evaluation of risks of pesticides present in drinking water for man and cattle was selected as a priority protection goal. In cooperation with the Plant Health Regulatory Department of the Ministry of Agriculture of Ethiopia and other Ethiopian stakeholders Alterra developed a procedure to assess the risks for drinking water caused by pesticides, used according to Good Agricultural Practices (GAP). To do so, ‘realistic worst case’ scenarios were developed, that intend to protect man and cattle in 99% of all possible situations in Ethiopia. For groundwater three scenarios representing wells in aquifers in the Ethiopian highlands or Rift Valley margins were developed and for surface water three scenarios representing small rivers in the highlands or temporay stagnant ponds were developed. The scenarios were linked to crops on which pesticides are used that score high on acute, chronic or local chronic risk for man. In addition other agro-environmental conditions were defined, such as precipitation, soil, and land use management. The groundwater scenarios were parameterised in the EuroPEARL metamodel to calculate leaching concentrations to groundwater, whereas the surface water scenarios make use of the runoff model PRZM, the EU-FOCUS spray drift deposition table and the surface water model TOXSWA to calculate the concentration in the small river or pond scenarios

Within the frame work of the Sino-Dutch Pesticide Environment Risk Assessment Project (PERAP) and as part of the Chinese environmental ris assessment procedures models and scenarions were developed to estimate concentrations of Plant Protection Product (PPP) leaching to the groundwater and to estimate PPP concentrations in Chinese small surface waters. Protection goals considering groundwater and surface water were defined in detail. Realistic worst-case groundwater scenario's and surface water scenarios were defined to be used in respectively a Tier 1 leaching assessment of PPP a Tier 1 assesment of the risks of PPP to aquatic ecosystems in China. Data on soil, weather, crops, irrigation and Agricultural practices were gathered for both scenario definitions. Existing models PEARL and TOXSWA were modified and parameterised for the scenarions defined.

Het TOXSWA model is uitgebreid met de beschrijving van vorming en omzetting van metabolieten in water en sediment. Op EU niveau wordt TOXSWA gebruikt in de aquatische risico beoordelingsmethodiek van bestrijdingsmiddelen om blootstellingsconcentraties te berekenen in de diverse water typen van de zogenaamde EU-FOCUS oppervlaktewater scenario’s. Voor de scenario’s met FOCUS riviertjes is er een bovenstrooms stroomgebied van 100 ha waarvan 20 ha met bestrijdingsmiddel is behandeld. Bij deze scenario’s willen we rekening houden met metabolieten die in het stroomgebied zijn gevormd. Daarom is een procedure ontwikkeld om de metaboliet concentraties en fluxen te corrigeren voor de FOCUS riviertjes, gevoed door het gedeeltelijk behandelde stroomgebied. De correctiefactoren van de procedure kunnen op twee manieren worden bepaald: (i) een simpele manier, waarbij de correctiefactor een functie is van de omzettingssnelheid van de moederstof en (ii) een meer gedetailleerde manier waarbij de correctiefactor een functie is van de omzettingssnelheid van zowel de moederstof als van de metaboliet, alsmede van de verblijftijd van de moederstof in het bovenstroomse stroomgebied.

The degradation rate of plant protection products and their transformation products in surface water and sediment may influence their concentrations in Dutch surface water. Therefore the estimation of these rates may be an important part of the assessment of the exposure of aquatic organisms. We propose a stepped sequence of studies for estimating the rate in water going from simple and conservative to more sophisticated and more realistic studies. The sequence includes: - studies on hydrolysis and photolysis; - studies with fresh surface water in the dark; - water-sediment studies in the dark or in light; - studies with algae and macrophytes; - outdoor studies in realistic surface water systems. The usefulness of these studies for the exposure assessment in Dutch surface water is discussed.

The FOCUS_TOXSWA model calculates exposure concentrations of pesticides and their metabolites in watercourses and ponds. These concentrations are used in the pesticide registration procedure at EU level. The model concepts of TOXSWA are described briefly. The input files, output files, and the use of the graphical user interface to access the input and output are described. Input data are stored in a database. Pesticide entries resulting from drainage or runoff/erosion are accessed from separate files generated by FOCUS_MACRO and FOCUS_PRZM. Substance properties are accessed from the SPIN tool/database. Instructions for simulating a water-sediment study and a multi-year run are given

SWASH (Surface WAter Scenarios Help) assists the user in calculating pesticide exposure concentration in the EU FOCUS surface water scenarios. It is part of the exposure calculation procedure, being part of the obligatory evaluation procedure to place an active substance on List 1 according to EU Directive 91/414/EEC. SWASH encompasses: (i) FOCUS Drift Calculator, calculating pesticide entries through spray drift deposition, (ii) PRZM-3, calculating pesticide entries through run-off, (iii) MACRO, calculating pesticide entries through drainage and (iv) TOXSWA, calculating the behaviour of pesticides in small surface waters. It is linked to SPIN, a pesticide properties tool, and prepares input for the PRZM, MACRO and TOXSWA models. Via the SWASH shell the user can enter the shells of the other models to perform the PRZM or MACRO model runs needed to assess the fate of the substance in he FOCUS water body systems using TOXSWA.

In the current Dutch authorisation procedure for calculating the exposure of surface water organisms to plant protection products, drift deposition is considered to be the only source for exposure of surface water organisms. Although drift can still be considered the most important source, atmospheric deposition and drainage may constitute important sources as well. Therefore, RIVM, PBL, Wageningen UR and the Board for the authorisation of plant protection products and biocides have derived a new procedure in which these two potential sources are included. The new procedure, described in this report, is restricted to downward spray applications in field crops

In the TOXSWA (TOXic substances in Surface WAters) model volatilization of pesticides from surface water is computed because it may be an important component of the mass balance of pesticides in water bodies. Here, we briefly review the physics of air-water gas exchange relevant in this context. A new parameterization of volatilization is proposed. This new TOXSWA parameterization would take into account key physical aspects of the air-water gas exchange process, while still fitting into the TOXSWA philosophy. It is recommended to cast the new parameterization into a micrometeorological framework, based on two atmospheric resistances and one aqueous resistance against gas transport. In this context, the dimensionless Henry coefficient is a crucial characteristic of the pesticides and determines whether atmospheric properties as modelled by the atmospheric resistances exert the main dynamic control on air-water gas exchange or the aqueous properties and resistance. Most pesticides will be subject to atmospherically controlled volatilization.

We study non-stationary flow in open discharge channels. A model is derived from basic principles, conservation of mass and momentum, which is solved numerically for the cross sectional area and discharge as a function of time and position along the channel. The model describes the effect of external inflow from fields adjacent to the channel. Several scenarios are calculated, both for very slowly, and more rapidly flowing water courses.

This report aims to give a general description of transformation processes for future use in the TOXSWA model. Hydrolysis, photolysis and biotic transformation are described as distinct processes, employing separate rate constants. Additionally, a way to introduce into TOXSWA the daily variation of pH and temperature is proposed.

The user-friendly shell DROPLET, acronym for DRinkwater uit OPpervlaktewater- Landbouwkundig gebruik Evaluatie Tool, assists the Dutch Board for the Authorisation of Plant Protection Products and Biocides (Ctgb) in evaluating whether pesticides may exceed the 0.1 μg/L standard in one of the Dutch surface water abstraction points for drinking water production. It operationalises the methodology developed by a Dutch expert group described in Adriaanse et al (2008). This manual explains how to use (i) SWASH to enter compound properties and application pattern, (ii) to run MACRO to calculate the drainage fluxes, (iii) to enter the deposition according to the Dutch Drift Table in TOXSWA, next (iv) to run TOXSWA to obtain an edge-of-field concentration in the FOCUS D3 ditch and finally (v) to run DROPLET to obtain the concentrations in the nine Dutch abstraction points plus the Bommelerwaard. DROPLET maintains a central database (in addition to the SWASH database) and combines the peak concentration of the FOCUS D3 ditch with intake area and compound specific factors, such as crop areas and compound degradation to calculate concentrations in the abstraction points.

A reasonably accurate estimate of the water temperature is necessary for a good description of the degradation of plant protection products in water which is used in the surface water model TOXSWA. Based on a consideration of basic physical processes that describe the influence of weather on the energy balance of natural water bodies, we propose to extend TOXSWA with a 1D bulk approach to estimate water temperature. Evaluation of such a system confirmed that it is physically realistic and yet simple, with limited data requirements. It is expected to perform reasonably well in most conditions, and fits well into the present structure of the TOXSWA model. In particular the estimation of degradation rates in shallow and turbid water will benefit from introducing the proposed system.

The TOXSWA model is used in the pesticide registration procedures in the Netherlands and the EU. This report documents the transient water flow module of TOXSWA, which simulates variable discharges and water depths in the edge-of-field ponds, ditches and streams of the EU FOCUS Surface Water Scenarios at an hourly resolution. It combines water conservation equations with water depth-discharge relations based upon weirs located downstream. In watercourses, backwater curves describe water depths as a function of distance to the weir. The water conservation equations consist of a base flow, excess water fluxes from drainage or runoff and an outflow. The conservation equations have been solved numerically using the finite difference method. A limited verification of the numerical solution has been undertaken. Example runs present model input and output Het model TOXSWA wordt gebruikt in de toelatingsprocedures van bestrijdingsmiddelen in Nederland en in de EU. Dit rapport documenteert het onderdeel van TOXSWA met een niet-eenparige (dus in de stromingsrichting veranderende) waterstroming. Dit onderdeel simuleert op uurbasis veranderende afvoeren en waterdiepten in de FOCUS Oppervlaktewater Scenario’s van de EU: meertjes, sloten en beekjes grenzend aan landbouwpercelen. Waterconserveringsvergelijkingen worden gecombineerd met afvoerformules voor benedenstrooms gelegen stuwen, die het verband tussen de afvoer en de overstorthoogte geven. In de waterlopen beschrijven stuwkrommen het verloop van de waterdiepte met de afstand tot de stuw. De waterconserverings-vergelijkingen bevatten een basisafvoer, overtollige waterfluxen door drainagebuizen of via oppervlakte-afvoer en een uitstroming. De conserveringsvergelijkingen zijn numeriek opgelost met de eindige differentiemethode. De numerieke oplossing is beperkt geverifieerd. Voorbeeldsimulaties tonen de modelinvoer en -uitvoer. We bevelen aan om de wiskundige beschrijving van de waterstroming te verbeteren door een geleidelijk veranderende en discontinue waterstromingsbeschrijving te implementeren, dus met langs de waterloop in- of uitstromend water.Trefwoorden: FOCUS oppervlaktewater scenario’s, bestrijdingsmiddelen toelating, TOXSWA, niet-eenparige waterstroming.

Our interpretation is that the reduced runoff fluxes (water and mass) of the 20 ha upstream are combined with the unchanged runoff water fluxes of the remaining 80 ha upstream catchment. This implies that the reduction factor on exposure concentrations in FOCUS streams of Step 4 FOCUS scenarios calculations compared to those of Step 3 calculations approximately equals the reduction factor applied on the runoff fluxes (water and mass of the 20 ha upstream).

Spray drift, drainage and run-off are three major routes of pesticide entry into surface waters. Using spray-drift deposition tables and the MACRO, PRZM and TOXSWA models the exposure concentrations in surface waters can be assessed. Exposure scenarios have been developed as part of an EU evaluation process

Two tiers were developed to assess the drinking water standard of 0.1 μg/L at nine locations where surface water is abstracted to produce drinking water in the Netherlands. Two tiers were developed to assess the drinking water standard of 0.1 μg/L at nine locations where surface water is abstracted to produce drinking water in the Netherlands. In Tier I, concentrations at the abstraction points are calculated on the basis of edge-of field surface water concentrations for all crops in the intake area on which the pesticide can be used. The edge-of-field concentrations are corrected to estimate the concentration at the abstraction point by factors accounting for e.g. the relative cropped area of the intake area, degradation and difference in timing of applications

The hydrological module of the model instrument Cascade describes kinetics of surface water flow in a 10 km2 catchment with a single outlet. Discharge measurements are available for calibration. The soil hydrological model SWAP is used to generate a description of drainage and infiltration. The SWQN model is used to simulate surface water flow in a detailed network representing the surface water channels and water management structures. The major terms of the surface water balance are drainage from the soil and the pump discharge at the outlet. Kinetics of cumulated discharge simulated at the outlet corresponds with cumulated discharge measured at the drainage pump. Model performance is also tested with a special simulation including a period of prolonged drought

This model calculates exposure concentrations in small watercourses or ponds; these concentrations are used in the pesticide registration procedure at EU level

The user-friendly shell SWASH, acronym for Surface WAter Scenarios Help, assists the user in calculating pesticide exposure concentrations in the EU FOCUS surface water scenarios. It is part of the exposure calculation procedure developed by the FOCUS Surface Water Scenarios Working Group, which has become part of the obligatory evaluation procedure to place an active substance on List 1 according to EU Directive 91/414/EEC. SWASH encompasses four separate tools and models: (i) FOCUS Drift Calculator, calculating pesticide entries through spray drift deposition, (ii) PRZM-3, calculating pesticide entries through run-off, (iii) MACRO, calculating pesticide entries through drainage and (iv) TOXSWA, calculating the behaviour of pesticides in small surface waters. It maintains a central pesticide properties database, prepares input for the PRZM, MACRO and TOXSWA models and then guides the user in performing the FOCUS Surface Water runs in a consistent and user-friendly way. Via the SWASH shell the user can enter the shells of the other models to perform the PRZM or MACRO model runs needed to assess the fate of the substance in the FOCUS water body systems using TOXSWA

In the Dutch registration procedure the TOXSWA model is used to calculate the exposure of aquatic organisms to the pesticides applied in agriculture. The transformation rates in water and sediment, needed as input for the computations, are not asked directly in the registration procedure. Various test guidelines for water-sediment studies are discussed; they only yield pesticide dissipation rates in water and sediment. Water-sediment studies for three compounds were simulated with TOXSWA to estimate the transformation rates from the measured data. It was found that a detailed interpretation of the experiments and reported data is crucial before the water-sediment studies can be simulated correctly. Using the model, pesticide transformation could be assigned to mainly one of the layers or to both layers. These transformation rates do not depend on system properties, such as volumes of water and sediment, nor on the surface area of their interface. The procedure has to be tested for more pesticides and studies. The factors determining microbial transformation of pesticides in aquatic systems were studied; this allows improved characterization of the systems by measurements.

The TOXSWA model calculates the acute exposure concentration and the average exposure concentrations (AECs) of pesticides in ditches after 4, 21 and 28 days. In a (global) sensitivity analysis based on the Monte Carlo method the most sensitive processparameters (pesticide properties) and the most sensitive system parameters (e.g. ditch dimensions) with respect to AECs were determined. The process parametes "transformation rate in the water layer", "coefficient for sorption to macrophytes" and "Henry coefficient" were identified as contributing most to the varation in the AECs. The full range of pesticides was characterized by these three parameters and subsequently the flow velocity, water depth and dry weight of macrophyutes were identified sas sensitive system parameters with respect to the AECs. Analytically, the water depth, bottom width of the ditch and the sorption coefficients for sorption to macrophytes and suspended solids were identified as sensitive parameters with respect to the acute exposure concentration.

The TOXSWA model describes the fate of pesticides entering field ditches by spray drift, atmospheric deposition, surface run-off, drainage or leaching. It considers four processes: transport, transformation, sorption and volatilization. Analytical andnumerical solutions corresponded well. A sample simulation showed that sorption to macrophytes can considerably reduce the concentration in the water phase. However, sorption to macrophytes leads to a slower transport and thus to longer residence times for the pesticide in the water layer. Sedimentation and resuspension of suspended solids were not considered, so that the model can only be applied for periods shorter than one month.

TOXSWA is a computer model that simulates pesticide concentrations in the water and sediment layers of a field ditch. The theoretical concepts are briefly discussed. A sample simulation is presented to guide the user in running TOXSWA. The input and output files are described. Writing the input files with the aid of a user-friendly input editor, running the program and creating the graphical output are discussed. Guidelines are given for estimating the input parameters.

Preliminary results of a differential sensitivity analysis of the TOXSWA model, without sediment layer, are presented. The most sensitive parameters are flow velocity, dispersion coefficient, Henry coefficient, biomass of macrophytes, and the sorptioncoefficient of macrophytes. First experimental results with linuron, chlorpyrifos and ethoprofos, and three aquatic macrophytes indicate that no simple relationship exists between sorption coefficients onto macrophytes and other physico-chemical quantities.

The TOXSWA model has been developed to estimate exposure concentrations of aquatic organisms to pesticides. TOXSWA describes the fate of pesticides entering field ditches by drift or atmospheric deposition, by surface run-off, or by drainage or leaching through the soil. TOXSWA considers four processes: transport, transformation, sorption and volatilization. The two mass conservation equations for the water layer and the sediment are solved with a variable weight finite-difference method. A calculation example shows that, for pesticides with high sorption capacities, sorption to macrophytes may considerably lower the exposure concentration, but the concentration will continue longer.

In the Dutch registration procedure the aquatic fate model SLOOT.BOX is used to predict exposure concentrations of pesticides in aquatic systems. In the future, SLOOT.BOX will be replaced by the TOXSWA model. In this paper model results of TOXSWA and SLOOT.BOX are compared with experimental data. Both TOXSWA and SLOOT.BOX give good predictions of the concentration in water of linuron, a herbicide with low sorption capacity. Simulation results for chlorpyrifos, an insecticide with high sorption capacity, show that TOXSWA calculations correspond better with measured concentrations. This leads to the conclusion that sorption to macrophytes needs to be included in aquatic fate models.