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(21-28) Combined ecological risk of pesticide use in the netherlands. de Zwart, Dick*,1, Vonk, Marijke1, van de Meent, Dik1, 1 RIVM, Bilthoven, The Netherlands ABSTRACT- Starting from a 500 * 500 meter grid GIS-map of the 71 major crop types grown in the Netherlands, a GIS-map was produced of the combined ecological risk in Dutch ditches that are directly exposed to spray drift of a about 250 pesticides. This is accomplished by combining the crop map with the following types of databases: (1) the percentage of any of the pesticides applied to individual types of crop in general farmers practice, (2) the total yearly amount used of individual pesticides, (3) the percentage of drift transfer per unit area of adjacent surface water, depending on the type of crop and the pesticide, (4) a standard estimate of application frequency per pesticide and type of crop, (5) The average depth of ditches in the Netherlands. This combination of data yields a GIS-map of predicted maximum surface water concentrations for the 250 pesticides. The combined toxic risk, in terms of the multi-substance Potentially Affected Fraction of Species (msPAF, %) is subsequently calculated. Single-compound risks are quantified using Species Sensitivity Distributions (SSDs) for each compound. Combined risk is calculated using toxicology-based additivity principles. The implications of the predicted risk for species in the field were assessed by statistically calculating the relationship between the risk and the occurrence of aquatic species in the field. A significant association between toxic risk and species occurrence was demonstrated. Key words: Pesticides, SSD, GIS |
