Pesticide residues in tap water: How can we protect ourselves?

When the tap delivers more than just water

Pesticides are real polluters of our precious water. They end up in groundwater and, consequently, in our tap water. Whether they are residues of insecticides, fungicides or herbicides, they are all potentially harmful to our health.

Recently, a certain pesticide called chlorothalonil made a comeback... in our glasses of water! In the Vienne département, high levels of this pesticide briefly affected 15,000 people. Even after a ban, pesticides can resist.

What exactly do we know?

The guilty pesticide: chlorothalonil

In April, a report by the French National Health and Safety Agency (Anses) revealed that drinking water in France was contaminated with residues of chlorothalonil, a pesticide banned in Europe from 2019. These residues were detected in more than one in two samples taken throughout France, including overseas.

Le chlorothalonil is a fungicide which was widely used, particularly on cereal crops, vines and certain tubers. It was classified as a "probable carcinogen" in 2018 by the European Food Safety Authority (Efsa), but its use in France has been extended until May 2020 to clear stocks.

What are its effects on health?

The long-term health effects of chlorothalonil are not yet well known, but it has been established that it can irritate the respiratory tract, cause skin allergies and serious eye damage, and is also a marine pollutant. Animal studies also show that kidney damage is caused by its metabolites.

The main problem is that this metabolite is difficult to eliminate in water treatment plants. This difficulty has financial implications (which could lead to an increase in the price of water of around 50% in certain regions) and technical implications (depollution technologies raise the question of yields), making it difficult to return to water that complies with regulatory criteria.

Putting the danger into perspective

Please note that this is not meant to be a false alarmist, claiming that tap water in France has become unfit for consumption. It's still drinking water!

Although the toxicity of chlorothalonil to aquatic environments is well documented, the consequences for human health are less clear. The European Health Agency (Efsa) classifies it as "possibly carcinogenic". However, studies on animals have shown that large daily doses are needed to observe an initial effect on health. The presence of its residues or metabolites in water is often the result of chlorothalonil breaking down in the environment.

According to a study by the Anses hydrology laboratory (see article in the Point), the chlorothalonil residues found in drinking water are considerably lower than the maximum health values (Vmax), which is reassuring. What's more, a 2008 US study of farmers exposed to much higher levels of chlorothalonil showed no incidence of cancer. However, the presence of these residues in water is not without concern, mainly because of their persistence in the environment after the substance has been banned, as demonstrated by the numerous analyses carried out in 2020 and 2021.

How pesticides are flooding our glasses

Well, having said that, in an ideal world, we'd do without any trace of pesticides in our tap water!

But how do these pesticides end up in our glasses of water, you ask? Well, the answer lies in the journey that water takes from the sky to our taps.

France is Europe's biggest consumer of pesticides. They infiltrate the soil right up to the water table and freshwater springs.