(MENAFN- Swissinfo) A pesticide cocktail can be found in Swiss streams and rivers. A new national study has detected 135 pesticides in five streams. Some 23 of them in concentrations that pose a risk to fish, insect larvae and other organisms. This content was published on October 2, 2025 - 09:21 3 minutes Keystone-SDA

• Deutsch de Forscher finden 135 Pestizide in Schweizer Bächen und Flüssen Original Read more: Forscher finden 135 Pestizide in Schweizer Bächen und Flüsse
• Español es Un equipo de investigación encuentra 135 pesticidas en ríos suizos Read more: Un equipo de investigación encuentra 135 pesticidas en ríos suizo

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These results from three special studies by the National Surface Water Quality Monitoring Programme (Nawa) were published in Thursday's issue of the specialist journal Aqua&Gas.

The 23 pesticides with concentrations that are hazardous to aquatic organisms, including highly effective insecticides in particular, exceeded so-called ecotoxicological quality criteria, in some cases by a factor of ten and in individual cases even by a factor of more than a hundred, over a period of several weeks.

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The current Water Protection Ordinance sets ecotoxicological limits for only 19 pesticides. The new study shows that this does not cover all substances that pose a risk to water bodies.

From fields and sewage treatment plants

The researchers were also able to determine the origin of the substances more precisely. According to the study, herbicides mainly enter rivers via rainwater from fields.

Many critical insecticides, such as fipronil from flea and tick products for pets, also enter streams via wastewater treatment plants. The active ingredient can adhere to hands, animal hair and textiles and thus enter the wastewater treatment plant and watercourses during washing, explained the aquatic research institute Eawag in a press release on the studies published on its website.

The research was done in collaboration with the cantons and the Federal Office for the Environment (FOEN), Federal Aquatic Institute (Eawag), the VSA Water Quality Platform and the Ecotox Centre. They investigated the water quality in the Surb (Unterehrendingen, Aargau), the Petite Glâne (Bussy, Fribourg), the Ron (Hochdorf, Lucerne), the Halbach (Hallau, Schaffhausen) and the Scairolo (Barbengo, Ticino). At all sites, fortnightly composite samples were taken both from the rivers and from treated wastewater from the sewage treatment plants in order to better understand the origin and pollution pathways of the substances. The researchers searched for a total of 253 pesticides.

Translated from German by DeepL/jdp

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