Pesticides in surface waters: a comparison with regulatory acceptable concentrations (RACs) determined in the authorization process and consideration for regulation.

BACKGROUND: Chemical analysis of surface water conducted in European countries indicates that pesticides are often detected in surface waters. This asks regulatory authorities to consider these monitoring data while re-evaluating pesticide approval and setting appropriate risk mitigation measures. During the years 2005-2012, the cantons in Switzerland performed 345,000 pesticide measurements in surface waters. Overall, 203 approved pesticides were examined. For 60 of these substances, regulatory acceptable concentrations (RACs) were published, which were determined from ecotoxicological data in accordance with international test methods within the framework of the authorization procedure.

RESULTS: For 73 % of the 60 evaluated pesticides, the monitoring data demonstrated that no exceedance of the RAC in surface waters was found. For the 16 remaining compounds, measured environmental concentrations (MECs) were exceeding the RAC value at some sampling sites. However, the 95 percentile of the MECs of all substances analyzed were below the respective RACs. Due to the classification system of surface waters in Switzerland, it became obvious that exceedances of the RAC value occurred in small to medium surface waters. Based on these monitoring data, it can be concluded that mainly herbicides and fungicides were exceeding the RAC; for insecticides only one exceedance was determined. The findings demonstrate that in principle the pesticides are safely used. Most of the exceedances were measured in a surface water surrounded by vineyards in the canton Geneva. Therefore, risk mitigation measures were locally implemented to reduce the entry of pesticides.

CONCLUSIONS: Results suggest that a few pesticides in use might account for most of the concern for aquatic life. These pesticides with exceedances of the ecotoxicological thresholds are checked for a possible regulatory action. Implementing further risk mitigation measures might be advisable to reduce the exposure in aquatic systems. This evaluation is an ongoing process. When further RAC values are available, currently Switzerland is re-evaluating authorized pesticides, monitoring data can be evaluated accordingly.