Extending the range of chemical compounds monitored in drinking water
National prevalence campaigns for emerging compounds are carried out approximately every three years by ANSES’s Laboratory for Hydrology in Nancy. They aim to improve knowledge of contamination of water resources and water treated to produce tap water. This knowledge can help those responsible for water production and distribution tdesign their water quality monitoring programmes, and regional health agencies update their safe water monitoring programmes. These data can also be used to assess population exposure to health risks from drinking tap water.
For the campaign initiated in 2019 in collaboration with regional health agencies and the Directorate General for Health (DGS), three contaminant classes were selected:
- 157 pesticides and pesticide metabolites;
- 54 explosives residues; and
- 1 solvent (1,4-dioxane).
More than 136,000 results were obtained during the campaign. Raw and treated water samples were taken at sampling points throughout France, including in France’s overseas territories, to assess water abstraction sites representing 20% of the water supply.
Pesticide metabolite chlorothalonil R471811 was frequently detected
The campaign included the sampling of 157 pesticides and pesticide metabolites, which are compounds produced from the breakdown of plant protection products. Eighty-nine of these were detected at least once in raw water and 77 times in treated water.
Among the seven "emerging" compounds that caused the 0.1 µg/litre quality limit to be exceeded, the chlorothalonil R471811 metabolite is one case that stands out. Scientists were intrigued by two things. First, this substance was found in more than half the samples, making it the most frequently detected pesticide metabolite. Second, it was found in concentrations exceeding the quality limit in more than one in three samples.
This metabolite was included in the campaign following the publication in 2019 of Swiss data indicating that it was very frequently found in drinking water in Switzerland. It is a product of the degradation of chlorothalonil – a fungicide banned in France since 2020 – in the environment. The findings show that depending on their properties, several pesticide metabolites can remain in the environment for several years after the relevant active substance has been banned.
Another chlorothalonil metabolite was found in concentrations exceeding the 0.1 µg/litre quality limit in approximately 3% of samples.
Other substances investigated
Metolachlor ESA, another pesticide metabolite, which was assessed as not relevant by ANSES in 2022, was also measured in more than half the samples, of which less than 2% were found to exceed the 0.9 µg/litre management level identified for non-relevant metabolites.
The prevalence campaign also sought to detect explosives residues and 1,4-dioxane, a substance used as a solvent. Explosives residues were found in less than 10% of the treated water samples, mainly from WWI military sites or in the vicinity of industrial weaponry facilities. These include metabolites from TNT and more recently used chemical substances. 1,4-Dioxane was found in 8% of samples.
These data are crucial for improving water quality
The results of this prevalence campaign have been shared with the regional health agencies and DGS. They provide a reliable scientific reference to update the list of chemical substances to be included in routine water quality monitoring. The authorities will also be able to establish appropriate management measures for compounds exceeding the quality limit.
What is a relevant metabolite?
According to European Directive (EU) 2020/2184, “a pesticide metabolite shall be deemed relevant for water intended for human consumption if there is reason to consider that it has intrinsic properties comparable to those of the parent substance in terms of its pesticide target activity or that either itself or its transformation products generate a health risk for consumers.”
In January 2019, ANSES proposed a method for identifying which pesticide metabolites are relevant and warrant priority attention considering potential health issues for consumers.
As a precautionary measure, in application of this method, ANSES classifies a metabolite as relevant for tap water in two cases:
- when this relevance can be established on the basis of the available scientific knowledge; and
- when essential scientific data are missing with regard to the criteria adopted by ANSES.