Open access publications in the SLU publication database

Environmental monitoring reveals that pesticides enter surface waters regularly in Sweden. Mitigating measures against point sources and spray drift have successfully reduced concentrations, but pesticide concentrations still sometimes exceed ecotoxicological guideline values. Additionally, the EU directives for water (2000/60/EC) and for sustainable use of pesticides (2009/128/EC), and the regulation regarding placing plant protection products on the market (EC 1107/2009) stipulate that mitigation strategies should be developed against diffuse sources, such as surface runoff and drainage. The current project is a knowledge compilation to support authorities in the implementation of runoff mitigation in regulatory and subsidy systems. The project lists a number of mitigation measures: vegetated buffer strips, wetlands, ditch management, integrated pest management and other management strategies to reduce the risk of runoff transport of pesticides. The focus is on vegetated buffer strips. The project has also evaluated the validity for Swedish conditions of the PRZM-in-FOCUS R1 scenario for assessing risk of pesticide concentrations exceeding the ecotoxicological guideline values due to pesticide transport through runoff. In Sweden, the majority of surface runoff occurs during snowmelt, when pesticide loss is unlikely. The temporal and spatial frequency of runoff events during the growing season and the amount of pesticides transported in this way are currently unknown. Phosphorous models estimate that up to 33% of total yearly water flow enters water courses as surface runoff in the worst cases and around 10% on average, but the lack of data for calibration renders these estimates highly uncertain. Field data from a drained silt loam (considered 95-percentileworst-case for runoff under Swedish conditions) suggest 35-50% of total monthly water flow during summer (May-September) occurs through surface runoff. Thus, surface runoff may contribute considerably to pesticide transport locally, but is still considered unlikely to be of major importance on a national level, although data is lacking to confirm this assumption. Therefore, local adaptation of mitigation measures is deemed a more efficient strategy for Sweden, than general solutions, such as mandatory buffer strips along all water courses. This would also simplify links with other environmental mitigation measures e.g. for nutrients and biodiversity, as well as increase the acceptance among farners. The PRZM-in-FOCUS R1 scenario greatly overestimated the risks for runoff and erosion for Sweden, due to more extreme soil and weather conditions than are realistic for Sweden. Thus, alternative solutions for assessing pesticide runoff risks in Sweden are suggested: 1) developing a Swedish scenario for the PRZM model, 2) developing the Swedish groundwater scenario for the MACRO-in-FOCUS model to include runoff estimation, and 3) establishing a system for local runoff mitigation that is reliable enough to justify the assumption that pesticides will rarely enter surface waters through runoff. It is strongly suggested that research and monitoring projects are supported to provide a better database on which to build risk assessment scenarios and risk management strategies.