Groundwater heavily polluted by pesticides

Concentrations of several chlorothalonil degradation products In the groundwater of the Central Switzerland exceed the limit value of 0.1 micrograms per litre on a large scale. This thereby represents significant contamination, as the Federal Office for the Environment announced on Tuesday.

The chlorothalonil plant protection agent has been used in Swiss agriculture since the 1970s. The federal government has recently described chlorothalonil as "probably carcinogenic" and has banned its use by early 2020.

In December 2019, the Federal Food Safety and Veterinary Office (BLV  Bundesamt für Lebensmittelsicherheit und Veterinärwesen) classified all degradation products (metabolites) of chlorothalonil as relevant with regard to drinking water. A maximum value of 0.1 micrograms per litre for drinking water therefore applies to these substances, which, in this case, is also the limit value for groundwater.

Great importance for drinking water
The Federal Office for the Environment (Bafu) has now carried out a first nationwide assessment of the pollution in groundwater. The state of groundwater is of great importance with regard to these substances, writes the Bafu. After all, 80 percent of the drinking water in Switzerland is extracted from groundwater, and these substances can only be removed with a very great effort during treatment.

As the groundwater only renews itself relatively slowly, and the metabolites of chlorothalonil are extremely long-lived, it can be assumed that these contaminants will continue to affect groundwater quality to a greater extent for some years to come.

Almost half of cantons affected
Studies from 2017 and 2018 allow for a first nationwide assessment of groundwater pollution. According to these results, several chlorothalonil metabolites have polluted the groundwater on a large scale in many agricultural areas of Central Switzerland.

Values of more than 0.1 micrograms per litre can be found in the cantons of Aargau, Bern, Fribourg, Geneva, Lucerne, Schaffhausen, Solothurn, Thurgau, Ticino, Vaud, Zug and Zurich. Cantonal specialist agencies and water suppliers are currently carrying out extensive own analyses of potentially affected water reservoirs.

Detailed information on groundwater quality on site or in individual municipalities is the responsibility of the cantonal specialist agencies, and water suppliers inform consumers about the quality of drinking water.