Pesticide inputs into Swiss streams

A comprehensive screening of five Swiss watercourses detected 135 pesticides, many of which exceeded ecotoxicological quality criteria. At four locations, there was a high risk to aquatic organisms over several weeks, mainly due to insecticides. Input via wastewater treatment plants also contributed to pesticide pollution.

Pesticides have a wide range of uses: they are used as plant protection products (PPPs), biocides or veterinary medicines in both agriculture and urban areas. Depending on their area of application, they can enter water bodies via various pathways, thereby endangering aquatic organisms and drinking water resources. Researchers from Eawag, the VSA Water Quality Platform and the Ecotox Centre have joined forces to conduct comprehensive pesticide testing on five medium-sized watercourses and to take a closer look at the pathways through which these pesticides enter the water. The investigations were carried out as part of a special campaign by the National Water Quality Monitoring Programme (NAWA) 2023, and data from NAWA's long-term watercourse monitoring programme was evaluated to narrow down the sources.

Pesticide risks mainly from insecticides

Overall, the results of previous campaigns were confirmed: of the 253 pesticide active ingredients tested, 135 were detected, with an average of 32 substances per sample. Twenty-three of these substances exceeded the ecotoxicological quality criteria in at least one sample, meaning that harmful effects on aquatic organisms cannot be ruled out. At 4 of the 5 locations, a high risk to aquatic organisms lasting several weeks was identified.

Insecticides were primarily responsible for the risk, exceeding ecotoxicological quality criteria by more than tenfold in some cases. Five insecticides accounted for 80% of the exceedances: fipronil and the pyrethroids cypermethrin, deltamethrin, lambda-cyhalothrin and permethrin. Herbicides also contributed to the observed risk. Of the 23 critical pesticides, only six have so far been included in the Water Protection Ordinance with risk-based limit values, and only one of the five particularly risky insecticides.

Multiple pathways into water bodies

In order to reduce the entry of pesticides into water bodies, it is necessary to know where they come from and how they enter the water. In the catchment area of the five watercourses studied, there is one wastewater treatment plant in each case without a treatment stage for removing micropollutants. Samples were also taken from their effluent to quantify the proportion of pesticides entering the water bodies studied via wastewater treatment plants.

The picture that emerges is complex: the critical insecticides were introduced into the water bodies both diffusely and via wastewater treatment plants. These substances are used not only as PPPs, but also as biocides outdoors or in stables and as veterinary medicines for the treatment of farm animals and pets. Such areas of application can lead to introduction via wastewater. In the case of critical herbicides, which are only used as PPP, discharge via wastewater treatment plants played a less significant role than in the case of insecticides. Although herbicides are usually discharged diffusely, for example via runoff from fields, in certain cases, point source discharges, such as from incorrectly connected washing areas for PPP sprayers, can also lead to discharges into water bodies.

The number of exceedances involving fipronil, an insecticide used in Switzerland primarily as a veterinary medicine to treat pets against ticks and fleas, was striking. Until now, no environmental risk assessment has been required for the approval of such substances. "In order to optimise their use and minimise risks, it would make sense to change this," says Marion Junghans from the Ecotox Centre. In addition, the use of pyrethroids as biocides and veterinary medicines deserves more attention, as little is known about their pathways of entry to date.

Publications

Schorr, J., Ganz, V., Luong, K., Ceppi, E., Longree, P., Beck, B., Singer, H., Barth, S., Doppler, T.,  Junghans, M., & Holmes, B. (2025). Pestizideinträge in Fliessgewässer. NAWA Spez 2023: Wirkstoffe, Ökotoxikologisches Risiko, diffuse Eintragspfade vs. Einträge aus ARA. Aqua & Gas, 105(10), 70-78. Institutional Repository: https://www.dora.lib4ri.ch/eawag/islandora/object/eawag:35500

Barth, S., & Doppler, T. (2025). Ursachen der Pestizid-Verunreinigung. Mögliche Quellen und Eintragswege in Fliessgewässer eingrenzen. Aqua & Gas, 105(10), 80-88. Institutional Repository: https://www.dora.lib4ri.ch/eawag/islandora/object/eawag:35502

Barth, S., Doppler, T., Ganz, V., Luong, K., & Singer, H. (2025). Fipronil belastet die Fliessgewässer. Antiparasitäre Tierarzneimittel für Heimtiere als wahrscheinlichste Quelle. Aqua & Gas, 105(10), 90-95. Institutional Repository : https://www.dora.lib4ri.ch/eawag/islandora/object/eawag:35504

Contact

Ecotoxicology: Marion Junghans marion.junghans@oekotoxzentrum.ch
Chemical analysis: Heinz Singer heinz.singer@eawag.ch
Input pathways and NAWA monitoring network: Sofia Barth sofia.barth@vsa.ch

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