How water quality standards for pesticides affect the classification of the chemical status of rivers

Abstract

Awareness of the presence of high concentrations of pesticides in Swiss rivers has increased in the last decade. Since 2017, the Federal Department of the Environment, Transport, Energy and Communications is planning to introduce new regulatory acceptable concentrations for surface water of 38 organic pesticides. Based on pesticide concentration analyses carried out in a small agricultural catchment in the canton of Vaud, over the 2005–2015 period, we review the impacts of this legislative revision on the chemical status of rivers. A first comparison between the historical standard (0.1 μg/L) and revised water quality criteria (WQC) highlights that standards are raised for 12 pesticides and lowered for 25 pesticides, sometimes with very high ratios. Risk coefficients were computed based on the historical standard and revised WQC to determine the chemical status of the river. The worst‐case value was retained to define this status. Individual risk coefficients indicate that more pesticides meet the revised WQC than the historical one, leading to very different chemical status. According to the historical standard, the chemical status of the Boiron River is defined as moderate to poor, and the main problem is the presence of herbicides. According to the revised WQC, the chemical status is good, and periodically moderate or poor. Ninety percent of the pesticides identified had a low to very low ecotoxicological risk coefficient. Other issues related to insecticides were identified. Based on these results, we discuss the importance of the standard chosen when defining regulatory acceptable concentrations. This article is categorized under: Water and Life > Conservation, Management, and Awareness Science of Water > Water Quality Engineering Water > Sustainable Engineering of Water

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