Pesticides in Tap Water: How Are Tests Conducted in France?
In September 2022, the magazine *Complément d’enquête* (France 2) and the daily newspaper *Le Monde* revealed that in 2021 in France, 12 million people had been affected by instances where drinking water quality thresholds for pesticides and their “metabolites”—a term referring to the byproducts of pesticides resulting from their breakdown over time—had been exceeded.
Julie Mendret, University of Montpellier and Alice Schmitt, University of Montpellier
On February 15, 2023, ANSES announced that it was initiating a procedure to remove S-metolachlor from the market, a herbicide whose metabolites are responsible for significant groundwater contamination in France. Its metabolites—notably metolachlor-ESA, metolachlor-OXA, and metolachlor-NOA—are reportedly present in French groundwater at concentrations exceeding the quality limit set by European legislation.
This alarming situation calls for a reexamination of how drinking water testing is conducted in France.
Pesticides, which are primarily used for agricultural purposes in rural areas, seep into the soil once applied and can lead to the contamination of groundwater. They can also, through soil erosion or runoff during rainfall, enter surface waters (rivers, lakes, etc.).
However, the water used to produce our tap water is drawn from these same sources. It is therefore potentially contaminated by pesticides. For this reason, tap water in France is subject to regular health monitoring.
Water Quality Monitoring at Multiple Levels
This monitoring consists of surveillance, carried out by the entity responsible for water production or distribution, as well as health inspections, conducted by the regional health agencies (ARS), in accordance with the provisions of the Public Health Code and European Directive 98/83/EC.
The ARS oversees the entire healthcare system at the regional level. Public entities, local governments, healthcare professionals, and nonprofit organizations all interact with it. It serves as the point of contact for the prefecture’s decision-making on health matters and conducts water quality inspections on its behalf.
Samples are taken at the source (i.e., from the aquifer or river, at the intake point before treatment), at the outlet of the treatment plant, and at the point of distribution (i.e., at the faucet).
The parameters measured and the frequency of sampling are specified by an executive order and vary depending on the monitoring points. At the distribution point, for example, tests are conducted to check nitrate and iron levels, as well as for the presenceof E. coli. Medications are not currently included in these tests.
Sampling and analysis are conducted by laboratories accredited by the Ministry of Health for water quality testing. These laboratories must follow established analytical methods and meet a certain level of “analytical performance,” meaning they must produce consistent and reliable results.
Indeed, the validity of the data produced is closely linked to the reliability of the analyses, and developing an analytical technique specific to each substance can be a long and laborious process. In particular, a compound’s limit of detection must be below the regulatory threshold to make it possible to interpret the results of its analysis. This requires highly precise analytical instruments.
In addition, other compounds present in the water sample may also interfere with the analysis of the target parameter. For this reason, analyses should only be conducted by laboratories that have demonstrated their competence.
The cost of testing means we have to make choices
With regard to pesticides, more than 1,000 substances are currently authorized and used on crops in France. Furthermore, certain pesticides and their “metabolites” can persist in the environment for several decades and must therefore continue to be monitored even long after they have been banned.
Although the number of pesticides and metabolites being tested has been increased since late 2020, it is not currently feasible, due to cost and resource constraints, to analyze all of these substances.
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For this reason, the Directorate General for Health states that it is necessary to prioritize testing for pesticides in water intended for human consumption based on the likelihood of their presence and the risks to human health.
The ARS selects the target compounds based on local agricultural activities, cultivated areas, and the quantities of pesticides sold. On average, 170 pesticides and metabolites are tested for, with considerable variations from one region to another.
In the Grand Est region and in Brittany, testing for approximately 200 pesticides and metabolites has been underway since early 2021.
The frequency of testing depends on the flow rate of the water source and the size of the population served, with variations ranging from 0 tests per year to more than 800, as indicated by these data provided by the AIDA website. The Ministry of Health then makes the results of the ARS water quality tests available.
How are regulatory limits for pesticides established?
The “quality limit” refers to the maximum concentration of pesticides in drinking water permitted by law under normal circumstances. It is 0.1 micrograms per liter for each individual substance and 0.5 µg/L for the total of all measured pesticides and metabolites, with the exception of molecules considered more hazardous, for which the quality limit is set at 0.03 µg/L: aldrin, dieldrin, heptachlor, and heptachlor epoxide.
Classified as “persistent organic pollutants” and banned in France since the 1990s, these molecules continue to contaminate certain soils and water resources.
Unlike the standards set for other pollutants, this regulatory standard—established by a European directive issued in 1998—is not based on toxicological criteria, but on the detection limits of the analytical instruments available at the time.
More specifically, with regard to pesticides and their metabolites, the European Commission follows the principle known as ALARA ( as low as reasonably achievable): it therefore recommends keeping their concentrations at the lowest level that is reasonably achievable in order to protect resources.
This is therefore not a health standard, and exceeding this value does not mean that the water is unfit for consumption.
Exceeding Regulatory Standards
The threshold beyond which exposure to the molecule is considered hazardous is defined by the maximum health limit, known as Vmax.
ANSES sets the Vmax as follows: each compound is assigned 10% of a toxicological reference value based on dietary water exposure (assuming that a 60-kg individual consumes 2 liters of water per day throughout their lifetime).
The WHO estimates that 10% of our chronic exposure to pesticides comes from the water we drink (according to ANSES, this figure drops to 5% in France), while food accounts for 80% of this exposure; the remainder comes from our environment, such as the air we breathe.
The Vmax has no legal significance and may sometimes be much higher than the regulatory limit for the reasons explained above: the ALARA principle is applied to protect the environment and as a precautionary measure for our health.
These Vmax permits are valid for a limited period of nine years, during which so-called remediation measures (such as improving the quality of the water source and implementing treatment methods) must be carried out.
Only exceeding the Vmax results in immediate restrictions on tap water consumption.
Compliance with the Vmax therefore allows for the distribution of water even when it exceeds the legal limit for pesticides. In the latter case—that is, when the regulatory limit is exceeded but not the Vmax—local authorities apply for an exemption to continue distributing this non-compliant water, and new regulatory thresholds are then established for a period of 3 years, renewable once.
These temporary limits may be several dozen times higher than the original regulatory limits and are set to prevent the water supply from being cut off to thousands of people.
The procedures for providing information to the public by municipal governments are described in Article D1321-104 of the Public Health Code: The local government must post the results of water quality tests within two business days of receiving them, except in emergency situations, in which case measures are taken to inform users as soon as possible and to offer temporary solutions, such as the distribution of bottled water.
When ANSES has not yet established the Vmax—particularly due to a lack of scientific data— usage restrictions are applied, or a transitional health-based limit may be defined by the DGS and submitted to the High Council for Public Health (HCSP) for its opinion.
On June 15, 2022, a directive from the Ministry of Health established a transitional health standard of 3 µg/L in accordance with the recommendations of the HCSP.
This value is therefore now used as the basis for implementing water use restrictions.
A lack of data on pesticide metabolites
From a regulatory standpoint, pesticide metabolites found in drinking water are classified into two categories based on their level of hazard: “relevant” and “irrelevant.”
According to ANSES, a pesticide is considered relevant to water intended for human consumption “whenever there is reason to believe that it (or its degradation products) could pose an unacceptable health risk to consumers.”
Depending on the category in question, the limit values in drinking water vary. Relevant metabolites are subject to the same quality limit of 0.1 µg/l as pesticides, while irrelevant metabolites are subject to a limit of 0.9 µg/l.
Deciding whether a pesticide should be classified as “relevant” is far from easy, as this definition leaves considerable room for interpretation. Compounding this is a lack of data and studies on these products, which makes it impossible to determine their actual impact on health.
That is why, by the fall of 2022, S-metolachlor metabolites had already become a topic of discussion: following a reassessment of their relevance, the limit for these metabolites was lowered to 0.9 µg/l, thereby making water that had previously been deemed unfit for consumption in certain French municipalities safe to drink again—even though its quality had not actually changed. These changes are a source of confusion for consumers and may, quite understandably, raise doubts about the quality of their tap water.
What options are available to limit the spread of infection?
One obvious option for limiting contamination of drinking water is to reduce inputs at the source by ending the widespread use of pesticides. However, the issue of persistent organic pollutants remains, as these can linger in the environment for years or even decades.
There is also a remedial solution, which would involve adapting existing treatment processes. In fact, the typical conventional process currently in place is generally insufficient to remove all pesticides. To achieve this, a so-called “multi-barrier” approach must be adopted by adding several treatment steps to the standard process.
One example is the combination of powdered activated carbon and ultrafiltration (a membrane-based technique), which appears to be effective for removing pesticides and their metabolites.
Membranes could thus be used in water treatment processes. In particular, nanofiltration can remove a large number of pesticides, as is the case in Mery-sur-Oise, where the water treatment plant has incorporated a nanofiltration process since 1999. Only membranes that comply withthe decree of June 22, 2012—which guarantees their safety—may be used in the production of water intended for human consumption.
What should we do?
While drinking bottled water should not be a routine solution due to its catastrophic environmental impact, as well as potential health risks associated with the ingestion of plastic microplastics and plasticizers, it can nevertheless be a solution in the event of contamination of your municipal water supply.
However, while bottled water is subject to health inspections by the ARS, microplastics and plasticizers are not included on the list of parameters tested for…
Julie Mendret, Associate Professor, HDR, University of Montpellier and Alice Schmitt, Postdoctoral Researcher in Process Engineering, European Membrane Institute, University of Montpellier
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