Pesticides applied onto agricultural fields are frequently found in adjacent rivers. To what extent and along which pathways they are transported is influenced by intrinsic pesticide properties such as sorption and degradation. The incomplete degradation of pesticides may lead to the formation of equally or more toxic transformation products (TPs), which additionally tend to be more stable and more mobile in the environment. Process-based environmental fate models provide the possibility of assessing the impact of agrochemical application on river contamination. Even though conceptualizations of transformation processes are available in the literature, the assessment of TP fate and export has not yet been incorporated in catchment scale models.
This talk introduces the recent progress in the modelling of pesticide TPs at catchment scale. The application of three models for an assessment of pesticides and TP river export with different complexities is presented. Issues such as conceptualizations of environmental fate processes, boundary- and initial conditions, model uncertainty and export pathways of pesticides and TPs are approached in the presented studies and limitations of model applicability are derived.