Residues of plant protection products, i.e. their active substances as well as their degradation products, occur at over half of the groundwater monitoring sites across Switzerland. In intensive arable farming areas, residues of plant protection products are detected at over 90% of the monitoring sites.
According to the Waters Protection Ordinance (WPO), groundwater should generally contain no persistent synthetic substances. For groundwater that is used for drinking water or is intended as such, there is also a limit value ('numerical requirement') of 0.1 micrograms per litre (µg/l) for active substances of plant protection products. In addition, the groundwater – after basic treatment, where appropriate – must meet the requirements of legislation on foodstuffs. This legislation also prescribes a maximum value of 0.1 µg/l for metabolites of plant protection products classified as relevant in the context of the approval procedure.
Metabolites of plant protection products widespread
In recent years, the concentrations of active substances of plant protection products have exceeded the limit value at around 2% of the NAQUA monitoring sites. Their degradation products, known as metabolites, have also been widely detected in elevated concentrations. They exceeded the concentration of 0.1 μg/l at around 20% of the monitoring sites; this is the limit value for metabolites considered as relevant in regards to drinking water.
The three active substances of plant protection products that exceeded the limit value at multiple monitoring sites every year between 2014 and 2017 are bentazon, metolachlor and atrazine. After the approval of atrazine was revoked in 2007, the concentrations of this substance in groundwater are by now gradually decreasing.
On the contrary, the concentrations of various metabolites of metolachlor have risen in recent years. In 2017, four metabolites of this herbicide were found in groundwater in concentrations above 0.1 μg/l.
Metabolites of the beet herbicide chloridazon are also widespread in groundwater. In particular, the metabolite desphenyl chloridazon is widely found in groundwater in concentrations of more than 0.1μg/l.
Furthermore, metabolites of the fungicide chlorothalonil were detected for the first time in groundwater in Switzerland during a NAQUA pilot study in 2017. Current evidence suggests that the metabolites chlorothalonil R471811 and chlorothalonil R417888 occur frequently in elevated concentrations in groundwater on the Swiss Plateau. In December 2019, the Federal Food Safety and Veterinary Office has classified all chlorothalonil metabolites as relevant in regards to drinking water. All NAQUA monitoring sites are currently investigated in detail.
Pflanzenschutzmittel-Metaboliten im Grundwasser (PDF, 2 MB, 29.11.2019)Ergebnisse aus der NAQUA-Pilotstudie "Screening". Artikel in "Aqua & Gas" Nr. 11/2019.
Monitoring von PSM-Rückständen im Grundwasser (PDF, 7 MB, 30.06.2017)Zahlen und Fakten der Nationalen Grundwasser-Beobachtung NAQUA. Artikel in "Aqua & Gas" Nr. 6/2017.
Arzneimittel und Pestizide im Grundwasser (PDF, 3 MB, 24.02.2009)gwa 2007/3: 187-196 (german, french)
Last modification 12.02.2020