Ecological effects of pesticide use in the Netherlands: Modeled and observed effects in the field ditch

Through the application of Sensitivity Distributions for aquatic species (SSD), in combination with rules for mixture toxicity calculation, the modeled exposure is transformed to a risk estimate for the species assemblage in the aquatic ecosystem. The risk is expressed as the proportion of species likely to be suffering any effect from the exposure. In the summary of the risk maps, the majority of predicted effects is observed to be caused by the pesticide application practice in growing potato crops: 95% of the predicted risk is caused by only 7 of the 261 pesticide ingredients. The maximum local risk of pesticide use is estimated to affect about 50% of species. For the purpose of validation, local toxic risk estimates were compared to observed species composition in field ditches using simple statistical methods (regression analysis). However, the number of field observations was not sufficient enough to generate quantitative results. The unexplained variability in the biotic field data collected by a range of non-aligned monitoring networks does not allow highly significant conclusions. Nevertheless, there is a weak indication that the predicted risks are associated to biodiversity changes in field-exposed communities.