To what extent are Swiss surface waters and groundwater contaminated with pesticides?
Numerous federal, cantonal and academic studies have shown that the concentrations of pesticides in many surface waters in agricultural areas are sufficiently high to pose risks to aquatic organisms. In 2017, for example, scientists from Eawag and the Ecotox Centre analysed water samples collected from five small streams in agricultural catchments. They concluded that risks of toxicity to sensitive aquatic organisms could not be excluded in any of the streams investigated, with exposure lasting for several months. In addition, more than 35 different active ingredients were found in half of the samples. Although the streams studied are situated in intensively used catchments, they are by no means unusual for Switzerland. It can therefore be assumed that these findings from 2017 are still relevant today. In 2019, pesticides were also detected in stream sediments.
- Eawag News, 12 December 2020: Ecotoxicological effects of pesticides in stream sediments
- Eawag News, 2 April 2019: Excessive levels of plant protection products in small streams
- Aqua & Gas article, 12/2019: Écotoxicité des sédiments de ruisseaux. Les pesticides présents dans les sédiments ont des effets sur les organismes benthiques (includes German summary)
- Aqua & Gas article,11/2019: Geringe Konzentrationen mit grosser Wirkung. Nachweis von Pyrethroid- und Organophosphatinsektiziden in Schweizer Bächen im pg l–1-Bereich : (includes French summary)
- Aqua & Gas article, 4/2019: Ökotoxikologische Untersuchungen: Risiko von PSM bestätigt
- Aqua & Gas article, 4/2019: Anhaltend hohe PSM-Belastung in Bächen
- Aqua & Gas article, 3/2014: Über 100 Pestizide in Fliessgewässern
- Zurich Cantonal Office for Waste, Water, Energy and Air (AWEL), 2018: Gesamtüberblick Gewässerqualität im Kanton Zürich
- Canton of Vaud, 2018: De source sûre. La qualité des cours d’eau vaudois.
Pesticide residues (i.e. active ingredients and metabolites) occur in groundwater at over 50 per cent of the NAQUA National Groundwater Monitoring sites across Switzerland. In intensively farmed areas, residues are detected at over 90 per cent of NAQUA sites.
What risks do the concentrations measured pose to aquatic organisms?
Ecotoxicological studies show that pesticides can adversely affect the reproduction, development and health of microorganisms, plants and animals. Pesticides thus threaten biodiversity.
Are all pesticides equally toxic to aquatic organisms?
No. Pesticides vary widely in their toxicity to aquatic organisms, as do the amounts applied. A low‑toxicity substance applied in large quantities may have the same environmental impact as a highly toxic substance used in small quantities. However, whether significant quantities of a substance can enter waterbodies will also depend on its properties; for example, it is important how rapidly a substance is degraded in soil.
The revised Waters Protection Ordinance which came into effect on 1 April 2020 takes variable toxicity into account and introduces stricter limits for pesticides of particular concern.
- Federal Office for the Environment: media release on the adoption of stricter limits for pesticides in the revised Waters Protection Ordinance, 18 February 2020 (available in French / German / Italian)
Why can certain substances still be detected in groundwater years after their use has been banned?
Groundwater is only slowly replenished. In addition, substances take a long time to break down in low‑temperature groundwater, and there is a lack of microorganisms contributing significantly to pesticide degradation. In some cases, substances or their metabolites stored in the soil are only slowly leached into groundwater. Thus, for example, metabolites of the herbicide atrazine are still found in groundwater today, even though it has been banned in Switzerland since 2012.
Have all pesticides been covered by the studies performed to date?
No. Around 300 active ingredients for pesticides are currently authorised. Only about 50 have to be included in routine cantonal monitoring. While many cantons monitor a larger number of substances, the entire range is almost never covered. In addition, for certain substances, analytical methods have only recently been developed – e.g. for pyrethroids (potent synthetic insecticides). Moreover, the use of composite samples (usually collected over a 2-week period) means that short-term peak concentrations are hardly ever recorded.
Why do the concentrations determined in the authorisation procedure differ from the limits specified in the waters protection legislation?
In the authorisation procedure, modelling is used to assess whether a pesticide poses risks to aquatic organisms. From the risk assessment, so-called regulatory acceptable concentrations (RAC) are derived. Pesticides are only authorised if they are not expected to cause any “unacceptable adverse effects” on aquatic organisms. (Pesticides Ordinance (PSMV) Art. 1 purpose clause)
In contrast, the waters protection legislation specifies the maximum concentrations which may actually occur in the environment so that pesticides “do not detrimentally affect the reproduction, development and health of sensitive plants, animals and microorganisms” (WPO, Annex 2).
Could the contamination problem be solved by banning substances of particular concern?
Studies carried out by Eawag from 2012 to 2017 showed that, for at least 30 substances, the risks are so high that inputs to waterbodies should be markedly reduced. Whenever substances of particular concern are banned, it must be ensured in particular that this does not lead to increased use of an alternative substance creating new problems.
Under the pesticide-related measures developed for Switzerland’s agricultural policy after 2022 (AP22+), the use of substances of particular concern is to be excluded from the direct payments system or prohibited altogether.
What are Swiss policymakers doing to protect natural waters?
Particularly when groundwater (the main source of drinking water) is affected, measures are taken – e.g. the ban on chlorothalonil.
To ensure compliance with legally specified limits over the long term, the Action Plan on risk reduction and sustainable use of plant protection products was adopted by the Federal Council in 2017. Since then, numerous measures have been initiated, with the following goals:
- reducing pesticide emissions by 25 per cent in the medium term
- promoting alternatives to chemical plant protection
- halving the risks currently associated with plant protection products and markedly reducing contamination with metabolites
As the active ingredients of pesticides are sometimes highly persistent and groundwater is only replenished slowly, anticipatory measures are particularly important. The effects of a ban are often only fully apparent years or decades after it has been introduced.