Entry and toxicity of organic pesticides and copper in vineyard streams: Erosion rills jeopardise the efficiency of riparian buffer strips

The present study was performed to characterise in-stream pesticide exposure within the Palatinate vineyard region in south-west Germany, evaluate the influence of buffer strip widths and identify mitigation measures for the relevant entry pathways. In-stream water and sediment samples that were taken at nine sampling sites of different buffer widths following intense rainfall, and edge-of-field runoff that were sampled in erosion rills were analysed regarding 28 active ingredients of pesticides including copper. In-stream samples contained a mix of 8 ± 4 pesticide compounds, resulting in total pesticide concentrations of 1.4-8.9 μg l⁻¹ for water and 16-670 μg kg⁻¹ dw for sediment. Following an exceptional rainfall event with a previous 34-day drought period, pesticide concentrations reached 7.0-83.4 μg l⁻¹. Fungicides were the most important pesticides found and were significantly correlated with the pesticide application frequency and rate. The calculated toxicity values per sample (TU_max) indicated that both organic pesticides and copper concentrations likely cause ecotoxicological effects in the field. The buffer strip width was of little importance for pesticide in-stream concentrations because pesticide entry occurred mainly via the field path network and erosion rills. Pesticide in-stream concentrations were significantly and positively correlated with the concentrations detected in erosion rills (R² = 0.56). As possible risk mitigation measures, we suggest the implementation of grassed field paths and vegetated ditches or wetlands.