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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.

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.

We study stationary flow in open discharge channels. A model is derived from basic principles, which is solved numerically for the water level and discharge as a function of 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.

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).

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.