Higher-tier degradation rates in water for the regulatory aquatic risk assessment of pesticides

Estimation of the degradation rate of plant protection products in water under realistic conditions is important for correct estimation of exposure concentrations for regulatory purposes. To decide whether it is worthwhile to develop a software tool enabling third parties to estimate higher-tier, realistic degradation rates in water in an automated, relatively simple way, an inventory was made. Firstly, to get insight in how often suitable, outdoor aquatic cosm studies are available in registration dossiers, and secondly, on how often higher-tier degradation rates have been used in the pesticide registration procedure at EU, zonal or national Dutch level. Information from European substance assessment reports and/or (national) product assessments was retrieved for 21 substances for which outdoor aquatic coms studies exist. For 15 substances sufficient concentrations in water and sediment were measured over time to be able to derive higher-tier degradation rates. Based on the final agreed List of EndPoints (LoEP) of the European Food Safety Authority (EFSA) Conclusion, no higher-tier degradation rates in water were used for any of the 21 substances at EU level. In the national Dutch procedure for registration of products higher-tier degradation rates have been used for three substances in the past 21 years. So higher-tier rates are relatively seldom used. As development and maintenance of a software tool to estimate the higher-tier degradation rates in an automated way requires substantial efforts, we do not recommend to develop such a tool now. In the second part of this report a brief guidance is presented on when and how higher-tier DegT50,water may be useful in the pesticide registration procedure.