Specifics and challenges of assessing exposure and effects of pesticides in small water bodies

Small water bodies (SWB) are freshwater ecosystems of high ecological relevance. However, they receive considerably higher inputs of pesticides compared to larger water bodies owing to their close connection to adjacent agricultural fields in combination with their low water volume or discharge. Monitoring of the pesticide contamination of lentic and lotic SWB is a challenging task as various spatial and temporal factors affect pesticide’s maximum peak concentrations in the water bodies. We present an overview of the major challenges that can complicate the detection of exceedances of regulatory acceptable concentrations. Pesticide data from streams encompassed by the Danish pesticide monitoring program show that the highest pesticide concentrations are found in SWB. A ditch monitoring in a German orchard reveals that event-driven sampling following spray application outperforms the widely used automatic water sampling at fixed intervals, and we therefore suggest that the latter should replace the former in SWB. Furthermore, we suggest that gathering of quantitative data on pesticide pollution of lentic SWB should be given priority in future research.