Collection of sediment samples on the Hoobach (Schaffhausen). (Photo: Andri Bryner, Eawag)
In small watercourses in Swiss agricultural catchments, pesticides pose an ecotoxicological risk. This was demonstrated by studies carried out in 2015 and 2017 under the National Surface Water Quality Monitoring Programme (NAWA SPEZ), where pesticide concentrations exceeded environmental quality standards for most of the study period. Depending on their physicochemical properties (low water solubility, high organic carbon adsorption), pesticides may also bind to stream sediments, potentially harming benthic organisms. Sediments are an integral part of aquatic ecosystems, serving as a habitat and spawning site for many aquatic organisms and playing a vital role in the nutrient cycle. However, they also act as a sink for contaminants such as metals, persistent organic pollutants and pesticides. Little is known about the concentrations or toxic effects of pesticides in sediments in Switzerland. For this reason, in parallel with the 2017 NAWA SPEZ study of five small streams, the Ecotox Centre assessed sediment quality in samples collected on a monthly basis between March and October from the Chrümmlisbach (canton of Bern), Weierbach (Basel-Landschaft), Le Bainoz (Fribourg), Hoobach (Schaffhausen) and Eschelisbach (Thurgau).
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