Metabolites of the fungicide chlorothalonil pollute the groundwater in large areas with more than 0.1 micrograms per litre. Metabolites are present in these concentrations in more than half of the cantons. The Swiss Plateau, which is used intensively for agriculture, is the main region affected.
Chlorothalonil, a plant protection product substance, has been used in Swiss agriculture since the 1970s. After the FSVO reassessed this substance with regard to its potential health risk, attention has focused on chlorothalonil metabolites in drinking water.
As 80% of drinking water in Switzerland is extracted from groundwater and because these substances are extremely difficult to remove during drinking water treatment, groundwater quality with regard to these substances is very important.
Groundwater that is used as drinking water or which is intended for this purpose must meet the requirements of foodstuffs legislation after basic treatment procedures have been carried out (Waters Protection Ordinance WPO). The maximum values specified in the DWBSO (Federal Department of Home Affairs (FDHA) Ordinance of 16 December 2016 on Drinking Water and Water in Public Baths and Shower Facilities) therefore also apply as limit values (numerical requirement of the WPO) for groundwater.
For metabolites of plant protection products that are classified as relevant in regards to drinking water, a limit of 0.1 micrograms per litre applies.
Metabolites of the plant protection product chlorothalonil were detected in groundwater for the first time in 2017 during a pilot study of the NAQUA National Groundwater Monitoring which is operated by the FOEN in close cooperation with the cantonal authorities. The Swiss Federal Institute of Aquatic Science and Technology (Eawag) analysed hundreds of substances in samples taken from 31 specific monitoring sites using a complex, specially developed procedure.
In 2018, these trace-analysis tests were extended to further monitoring sites. A national data set from the NAQUA monitoring sites is now available for one of the chlorothalonil metabolites (R417888) for 2019.
More than half of cantons affected
Several chlorothalonil metabolites are present in concentrations exceeding 0.1 micrograms per litre in groundwater. In particular, the two metabolites R471811 and R417888 contaminate the groundwater in many areas of the Swiss Plateau used for agriculture. Values of over 0.1 micrograms per litre have been detected in the cantons of Aargau, Bern, Basel-Landschaft, Fribourg, Geneva, Jura, Lucerne, Schaffhausen, Solothurn, Thurgau, Ticino, Vaud, Valais, Zug and Zurich. Evidence of the metabolites R419492, R611968, SYN507900 and SYN548580 has also been found at some monitoring sites.
The metabolite chlorothalonil R417888, for which most data is currently available, exceeds 0.1 micrograms per litre in groundwater of the Swiss Plateau at over 20% of the monitoring sites.
The groundwater is even more severely polluted by the metabolite chlorothalonil R471811, which displays the highest concentration per monitoring site. The concentration of this metabolite is well in excess of 1 microgram per litre at some monitoring sites. Although no nationwide data set currently exists for this metabolite, the level of chlorothalonil R471811 can be estimated based on chlorothalonil R417888: Chlorothalonil R471811 may exceed 0.1 micrograms per litre at over half of all NAQUA monitoring sites on the Swiss Plateau. Based on the tests currently being carried out on this metabolite, a complete data set from the approximately 550 NAQUA monitoring sites will be available in summer 2021.
As the renewal of groundwater takes a relatively long time and the chlorothalonil metabolites are very persistent, it can be assumed that these contaminants significantly impair groundwater for many years.
Groundwater quality on site
All data gathered as part of the NAQUA national groundwater monitoring are made available to the cantonal authorities. The water suppliers concerned are also informed about the results. The cantonal authorities are responsible for providing detailed information on groundwater quality of a specific region or location. The water suppliers inform their customers about the quality of the local drinking water.
The NAQUA national groundwater monitoring project records the condition and evolution of groundwater nationwide and enables the effectiveness of the measures to be assessed. In close cooperation with the cantonal authorities, NAQUA monitors the quality and quantity of groundwater at over 600 monitoring sites and reports on long-term changes.
Specific analysis of individual pollutants or pollutant groups is also carried out through pilot studies and thus the need for their inclusion in the long-term monitoring is assessed.
Last modification 09.02.2021