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Sensitivity analysis of the aquatic pesticide fate models in SYNOPS and their parametrization for Switzerland

de Baan, Laura
The Science of the total environment 2020 v.715 pp. 136881
climate, drainage, models, pesticide application, pesticides, risk, risk reduction, runoff, soil, surface water, Germany, Switzerland
The model SYNOPS was developed to calculate national risk indicators for assessing the aquatic and terrestrial risk potential of pesticides in Germany. For Switzerland, a national aquatic risk indicator is currently being developed based on SYNOPS. It aims at evaluating long-term trends in aquatic risks based on changing pesticide usage and risk mitigation measures. In a first step, parameters of the fate models of SYNOPS were parametrized for the Swiss geographical context. Apart from data about pesticides and their specific usage, SYNOPS requires information about climate, soil and site-specific properties and crop stage. Based on these inputs, SYNOPS calculates the predicted environmental concentrations (PEC) of pesticides in water bodies and the associated exposure-toxicity-ratios (i.e., risks). To consider the effects of risk mitigation measures in risk indicators, a realistic representation of the contribution of different routes of entry (run-off, erosion, drainage, drift) is essential. To parametrize SYNOPS, a sensitivity analysis of the aquatic transport and fate models of SYNOPS was conducted: realistic ranges of Swiss-specific parameters and their combinations were defined and used as input for the sensitivity analysis. The impacts of input parameters on total PEC values and on the contribution of different routes of entry were analyzed. The sensitivity analysis revealed that slope and KOC were the parameters with the highest impact on pesticide concentration and that run-off was the dominant route of entry in most tested scenarios. From over 40,000 tested environmental scenarios, a reduced set of 75–113 environmental scenarios was finally selected, which predicted similar PEC values and comparable contributions of different routes of entry compared with the full set. With the parametrization and reduction of used environmental scenarios, fate calculations became more efficient and realistic for Swiss conditions. The findings of this study provide a solid basis for developing a national aquatic risk indicator using SYNOPS.