Pesticides in groundwater

Pesticides exceed the limit value of 0.1 micrograms per litre at 1 to 2% of monitoring sites every year. In addition, pesticide degradation products (known as metabolites) occur in concentrations of more than 0.1 micrograms per litre at one in three groundwater monitoring sites across Switzerland. Metabolites significantly impair the quality of groundwater, particularly on the Swiss Plateau.

Under the Waters Protection Ordinance (WPO), groundwater should generally not contain any persistent synthetic substances. For groundwater used for drinking water or intended for such use, there is also a limit value ('numerical requirement') of 0.1 micrograms per litre (µg/l) for pesticides. 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 pesticide metabolites classified as relevant for drinking water in the authorisation procedure.

Pesticides exceed the limit value at 1 to 2% of the NAQUA National Groundwater Monitoring sites per year. This percentage has remained largely unchanged for more than 10 years. In recent years, elevated concentrations were mostly due to bentazone. Groundwater resources in karst areas of the Jura are particularly sensitive to pesticide pollution, where these substances can exceed the limit value for a short time, but in some cases substantially.

NAQUA - Pesticides and metabolites in groundwater 2007–2022 (PDF, 222 kB, 26.04.2024)

Metabolites are widespread

In intensively used agricultural areas, metabolites, i.e. pesticide degradation products, are widespread and regularly detected in concentrations of more than 0.1 μg/l. On the Swiss Plateau, metabolites exceed the value of 0.1 μg/l at more than 60% of monitoring sites. Nationwide, every third NAQUA monitoring site is affected.

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A total of 21 metabolites of 12 active substances currently exceed the value of 0.1 μg/l.

NAQUA – Pesticides and metabolites in groundwater 2022 (PDF, 229 kB, 26.04.2024)

Metabolites of the fungicide chlorothalonil are particularly widespread in groundwater. In arable farming areas, they occur at 80% of measuringthe monitoring sites points in concentrations above 0.1 μg/lexceed the value of 0.1μg/l at more than 80% of monitoring sites. Throughout the country, every third monitoring site is affected.

Chlorothalonil

Metabolites of the herbicides chloridazon and metolachlor also exceed the value of 0.1 μg/l both repeatedly and widely. The metabolites of chloridazon occurred in elevated concentrations at 13 to 16% of the monitoring sites per year over the last 5 years, the metabolites of metolachlor at 5 to 6% of the monitoring sites.

The metabolites of dimethachlor, for which a nationwide analysis was launched in 2021, also affect groundwater quality at numerous monitoring sites. They exceed the value of 0.1 μg/l at 3% of monitoring sites at a national scale.

Pesticide metabolites in groundwater 2013 to 2022 — Number of monitoring sites per pesticide active substance at which a metabolite of this active substance exceeds the value of 0.1 μg/l. For each active substance, the metabolite that usually occurs in the highest concentrations is taken into account. Metabolites are considered if national data of more than 500 monitoring sites are available. Metabolites of several active substances might be present at one monitoring site. Data: NAQUA.

In recent years, the concentrations of the metabolites of atrazine and dichlobenil have slowly decreased. The reason for this is the ban on these pesticides in 2007 and 2013 respectively. In 2020, the authorisation for chloridazon was also withdrawn and the use of chlorothalonil was banned. Since 2023, farms receiving direct payments under the Proof of Ecological Performance (PEP), are only allowed to use metolachlor and dimethachlor in exceptional cases, i.e. with special authorisation.