More than four years after its ban, residues of chlorothalonil persist in tap water. A report from the National Health Security Agency (ANSES) published this Thursday, April 6, focused on water samples in all departments, including overseas, in particular looking for 157 pesticides and their metabolites, i.e. components from their degradation. In particular, it demonstrates that residues of chlorothalonil, this fungicide marketed by Syngenta banned since 2019 by the European Commission, are ubiquitous in drinking water.
“These results show that, depending on their properties, certain pesticide metabolites can remain present in the environment for several years after the banning of the active substance from which they originated”, concludes ANSES. A new report which does not surprise Dominique Le Goux, in charge of the pesticides and health mission within the Eau et rivières de Bretagne association, who denounces the use of these products and pleads for measures to protect the catchment areas of drinking water, but also for a change in the agricultural model.
L’Express: A new report from ANSES demonstrates the widespread presence of pesticide residues in drinking water. Does this mean that you just have to look to find some?
Dominique Le Goux: Considering the number of pesticides on the market today, and the number of metabolites they can produce, this is to be expected. We know full well that not all pesticides and their residues are researched, because for some we did not know, until now, how to find them. Especially since not all of them fall within the framework of monitoring the sanitary control of drinking water. So when we broaden the focus and we have new laboratory techniques, it is absolutely not surprising to confirm the widespread contamination of the environment by pesticides and their metabolites.
What are metabolites?
A metabolite is a residue from the degradation of the pesticide. You have to imagine a molecule with different branches that can break and lead to “daughter” molecules originating from a “mother” molecule. It’s a form of degradation, but we don’t always know how long it can take, it depends on a certain number of elements: the sun, the temperature, the composition of the soil… and obviously the molecule itself.
Does this degradation of molecules lead to an additional difficulty in the fight and the search for traces of pesticides in water?
Yes, we know for example that metolachlor is responsible for 8 different metabolites, terbuthylazine is responsible for 9 metabolites… And it’s exponential: from the moment a pesticide is put on the market, it is possible that the ‘we then find eight or nine metabolites. Where it is problematic is that industrial manufacturers do not offer analytical methods or standards to be able to search for them. This means that if ANSES had not carried out its experiments to broaden the scope of its research, we would have remained in a form of ignorance. You also have to realize that these molecules, as they degrade, become smaller and smaller, and therefore become not only more difficult to find, but also more difficult to remove.
Which means that these molecules also persist in drinking water because it is difficult to filter them?
Presumably. For chlorothalonil and its residues, the treatment channels rely on activated carbon to filter the metabolites and this carbon must be finer and finer to capture these small molecules. This necessarily has a cost, because these activated carbon filters have to be replaced more frequently, but also because this leads to reprocessing costs behind because these processes, which are very energy-intensive, remove many minerals, and force operators to remineralize the water so that it is consumable.
This is why we must improve the quality of our raw water, that is to say upstream of treatment, to improve the quality of tap water. We cannot afford to run the risk of drinking polluted water that has been badly treated.
The report points in particular to the presence of traces of chlorothalonil, a pesticide that has been banned since 2019…
It is clear that molecules once they are banned do not disappear from the environment as if by magic. We could have expected it because we have precedents, other molecules have been banned and we see today that their metabolites are still present. We can take the example of atrazine, a herbicide which is also cited in the ANSES report, and of which we find metabolites today in waters while this product has been banned for 20 years.
We see that certain metabolites remain in “background noise”, that is to say that they remain present in the environment in small quantities, which shows that the purification of the medium takes a great deal of time. Prohibiting the product does not mean that the problems disappear, which is why from the moment a product is authorized, it is necessary to be able to monitor its future and that of its metabolites. This is not yet the case today and this should alert us to the way in which we authorize the use of certain pesticides, and as an environmental association we are asking for the banning of pesticides, so that we can enjoy clean water.
In recent years, alerts on the presence of these chemical molecules in water and in the environment have multiplied. Does this mean that we do not sufficiently control their uses?
This situation shows that from the moment we put pesticides on the market, whatever the management measures that we can put in place for their use, they will disperse in the environment, in the air, in water, or in the ground. Their use and their authorization should therefore not be taken lightly and this is also why we consider that we must move towards stopping the use of synthetic pesticides. There was a period during which we rejoiced at the chemical miracle that these substances brought to agriculture, but today we are suffering the consequences, and this for many more years. We still see it today with chlordecone in the West Indies, from the moment we used these substances they dispersed in the environment, and we have them with us for many years.
Do you think that the State is not sufficiently aware of the problem?
I have the impression that the public authorities have taken the measure of the contamination, but now we are waiting for the electroshock that would come from the State. We need stronger measures and above all structural measures that do not only concern water treatment. This means supporting the cessation of pesticide use much more seriously by supporting forms of agriculture that do without them.
The president presented a water plan recently, the question of water quality was not sufficiently addressed in your opinion?
The water plan highlighted more the quantitative question than the qualitative question of water. Of course there are things to be done on the question of the quantity of water that we will need in the future, but we also find ourselves on episodes of contamination by metabolites from certain catchments. To the point that some communities have abandoned these catchments even though we were in a situation of extreme tension on the resource. We cannot completely disconnect these two themes… The more good quality resources we have, the more chance we will have of offering the population drinking water in quantity and quality.
On several occasions this week, the Minister of Agriculture has come out against the ban on S-metolachlor, while ANSES has initiated a withdrawal procedure, what does that inspire you?
When I hear it said that technical institutes and the agricultural world have not been given enough time to change and see how we can do without these molecules, I find that to be misleading. The first plan to reduce the use of pesticides dates from 2008, and it ended in failure, just like the following ones.
I don’t think there is a strong enough will to make things happen. If there was real political will, the Minister of Agriculture would not call into question the work done by ANSES, if there was real political will, we would have worked better on the generalization and pacification of good practices that already exist in the agricultural world; and we would have thought otherwise about the types of production and forms of breeding that we should have in France. We know that the solutions exist but we do not implement them.