Sensitivity of water and sediment concentrations to pesticide parameters in a pond and a small stream simulated by the TOXSWA model

A sensitivity analysis has been performed for the TOXSWA model, which simulates pesticide behaviour in surface waters. For 11 pesticide input parameters, including degradation rates, sorption coefficients, saturated vapor pressure and solubility, the influence on predicted peak concentrations in water (PECwat) and sediment (PECsed), as well as Time-Weighted Averages in water (TWA7 and TWA28) have been evaluated. Advanced global sensitivity methods, including Saltelli’s Sobol sequence for sampling input parameters, were applied to ponds and streams, representing low and high flow systems, respectively. Results show that sorption coefficients are the most sensitive parameters for TWA concentrations in ponds. In addition, degradation rates are sensitive parameters. The findings refine our understanding of pesticide behaviour, enabling more targeted parameterisation, and can contribute to improving guidance for regulatory exposure assessments. Compared to prior analyses, this study incorporates variable hydrology and sediment concentrations. It is recommended to extend the analysis to system parameters and pesticide entries.