Long-term trends of pesticides in Norwegian agricultural streams and potential future challenges in northern climate

Effective plant protection practices and use of chemical pesticides are a prerequisite for maintaining yields of sufficient quality and quantity in conventional agriculture today. Despite regulatory efforts to ensure safe use, reports have indicated that residual amounts of pesticides and their metabolites occur in surface and ground water and may have non-target effects on aquatic organisms. The objective of the present study was to identify environmental challenges of pesticide use in the northern climate by evaluating long-term pesticide monitoring data compiled by the Norwegian Agricultural Environmental Monitoring Programme. Pesticide use data and pesticide concentrations measured in stream water from six small agricultural catchments in Norway were analysed. Observed trends in pesticide detection frequencies, measured concentrations and cumulative risk from the six monitoring sites were compared. The results demonstrated the need for continued focus on the herbicides metribuzin and aclonifen, and potential concerns regarding use of the fungicide prothioconazole and the insecticide imidacloprid. The six monitoring sites represented the diversity of intensively cropped areas in Norway and differed with respect to estimated cumulative risk. Vegetable and potato cropping areas showed not only the highest level of total environmental risk, but also a statistically significant decreasing trend over the monitoring period. Cereal cropping areas exhibited no statistically significant time-dependent trends in the studied parameters but did show an increase in fungicide use that requires continued attention. The need for risk assessment of mixture toxicity effects and improved monitoring strategy is also discussed. In conclusion, the present results imply that the current global focus on multiple stressors and mixture toxicity of pesticides in stream water is equally relevant in cold climatic conditions.