Pesticides in tap water: should we worry about residues found in 20% of French people?

Metabolites, molecules resulting from the degradation of pesticides, have been discovered in the tap water of 20% of French people, at thresholds above the compliance criteria. Should we be concerned about this data? Do we know the impact of these residues on health? Are there solutions to filter them? Julie Mandret, PhD in environmental process engineering at the University of Montpellier, provides answers.

In 2021, 12 million French people in mainland France received tap water “not meeting quality criteria, regularly or occasionally”, according to data compiled by The world and France 2. In question, levels of pesticides above the alert thresholds in certain municipalities, in particular the most rural. Occitania, like all regions, is concerned, even if it is one of the good students with only 5.1% of “non-compliance”.

On June 10 in the town of Lauroux, near Lodève, residues of Anthraquinone – a chemical derivative of hydrocarbons used as an active substance in many phytosanitary products – were discovered in tap water at a rate of 0 .57 μg/L. About a hundred kilometers away, in Meynes in the Gard, it is Desethyl-Terbumeton, a herbicide used in viticulture, which exceeded the compliance threshold three times in July.

What impact on the health of the French?

Should we be concerned about these overruns? The thresholds set by the health authorities and quoted by our colleagues relate to the quality of the water. But a declaration of “non-compliance with quality requirements” does not systematically mean a risk for the consumer. The critical threshold is defined by the “maximum health value”, and exceeding it leads to an alert to consumers from the municipalities concerned.

Health authorities lack studies and data to set alert thresholds

Julie Mandret, PhD in environmental process engineering at the University of Montpellier.
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Problem, some molecules do not have “maximum health value”, explains Julie Mandret, doctor in Environmental Process Engineering at the University of Montpellier. “The health authorities lack studies and data to set the alert thresholds for certain metabolites derived from pesticides. In this case, it is the ARS who must take the decision, on a case-by-case basis, whether or not consumption of tap water if the non-compliance threshold is exceeded”.

The impact of these pesticide residues on health is still poorly known. “The long-term effects of exposure to low doses are difficult to assess”, indicates the Ministry of Health on its page dedicated to the quality of drinking water in France. But the relative researcher: “The concentration of these residues in tap water is disproportionate to the levels found directly in non-organic foods”.

Solutions, but at a price

How can we prevent these pesticide residues from ending up in tap water, knowing that the analyzes have revealed the presence of phytosanitary substances that have been banned for several years? For Julie Mandret, who works on filtration systems, it is above all necessary to act on the cause of the problem. “The more we limit the inputs in the soil, the less there will be pesticide residues to be treated at the end of the chain”, recalls the researcher.

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Pesticides, pollution: find out if the tap water in your town is of good quality

“Then, we will have to adapt our treatment plants, with the addition of a membrane or activated carbon-based filtration system, which will be able to remove these residues.” But these systems require major work on existing infrastructure, and are sometimes very energy-intensive. What suggest, if they are implemented, an increase in the price of drinking water.

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