Estimating degradation rates in outdoor stagnant water by inverse modelling with TOXSWA: a case study with prosulfocarb

The regulatory risk assessment of pesticides requires the assessment of exposure of aquatic ecosystems in small surface waters adjacent to agricultural fields. This exposure is predicted using simulation models, for which an important input parameter is the degradation rate in water. In regulatory dossiers, the decline rate in water from outdoor mesocosms is often available, but this rate encompasses more processes than degradation. Therefore, a procedure was designed for estimating the degradation rate in water that was suitable for mesocosm studies with limited datasets, e.g. datasets lacking site-specific sorption coefficients and relevant sediment properties. The procedure, based upon inverse modelling with TOXSWA, has been tested on a dataset for prosulfocarb in stagnant ditches