Pesticides in tap water: how are controls carried out 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 exceedances of drinking water quality thresholds for pesticides and their "metabolites"; this term refers to the by-products of pesticides, resulting from their evolution over time.
Julie Mendret, University of Montpellier and Alice Schmitt, University of Montpellier
On February 15, 2023, ANSES announced that it was initiating a procedure to withdraw S-metolachlor from the market, a herbicide substance whose metabolites are responsible for major groundwater pollution in France. Its metabolites, in particular metolachlor-ESA, metolachlor-OXA, and metolachlor-NOA, are reportedly present in French groundwater at concentrations exceeding the quality limit set by European legislation.
This worrying situation calls for a review of how drinking water is monitored in France.
Mainly used for agricultural purposes in rural areas, pesticides, once spread, diffuse into the soil and can lead to the contamination of underground resources. They can also spread into surface waters (rivers, lakes, etc.) through soil erosion or runoff during rainy periods.
However, the water used to produce our tap water is collected from these same sources. It is therefore potentially polluted by pesticides. For this reason, tap water in France is subject to regular health monitoring.
Water monitored at several levels
This monitoring consists of surveillance, carried out by the person morally responsible for the production or distribution of water, as well as health checks, carried out by 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 actors, local authorities, healthcare professionals, and associations all interact with it. It acts as a point of reference for the prefecture's decision-making in the field of health and carries out water quality checks on its behalf.
Samples are taken at the source (i.e., from the aquifer or river, at the point of collection before treatment), at the outlet of the treatment plant, and at the point of distribution (i.e., at the tap).
The parameters measured and the frequency of sampling are specified by decree and depend on the control points. At the distribution point, for example, nitrate and iron levels are checked, as well as the presence ofE. coli. Medicines are not currently subject to these controls.
Samples are taken and analyses carried out by laboratories approved by the Department of Health for water quality control. These laboratories must comply with analysis methods and achieve a certain level of "analytical performance," i.e., produce consistent and reliable results.
Indeed, the validity of the data produced is closely linked to the reliability of the analyses, and developing a specific analysis technique for each substance can be a long and laborious process. In particular, the detection limit for a compound must be below the regulatory value in order for its analysis to be interpreted. This requires particularly accurate 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 carried out by laboratories that have proven their competence.
The cost of testing means choices have to be made
With regard to pesticides, more than 1,000 substances are currently authorized and used on crops in France. In addition, 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 tested for has been increased since the end of 2020, it is not currently feasible to analyze all of these substances due to cost and resource constraints.
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For this reason, the Directorate-General for Health specifies that it is necessary to target these pesticide tests in water intended for consumption based on their likelihood of presence and the risks to human health.
The choice of molecules to be tested for is made by the ARS based on local agricultural activities, cultivated areas, and 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 Brittany, around 200 pesticides and metabolites have been investigated since the beginning of 2021.
The frequency of inspections depends on the flow rate of the catchment and the size of the population served, with variations ranging from 0 inspections per year to more than 800, as indicated by the data provided by the AIDA website. The Ministry of Health then makes the results of the ARS health inspections available.
How are regulatory values for pesticides established?
The "quality limit" refers to the maximum concentration of pesticides present in drinking water permitted by law under normal circumstances. It is 0.1 micrograms per liter for individual substances and 0.5 µg/l for the sum of measured pesticides and metabolites, with the exception of molecules considered more dangerous, 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 pollute certain soils and water resources.
Unlike the standards set for other pollutants, this regulatory standard, defined by a European directive published in 1998, is not based on toxicological criteria, but on the detection limits of the analytical equipment available at the time.
More specifically, with regard to pesticides and their metabolites, the European Commission follows the ALARA principle ( as low as reasonably achievable): it therefore suggests maintaining their concentrations at the lowest level that can reasonably be achieved in order to protect resources.
It is therefore not a health standard and does not mean that the water is unfit for consumption when this value is exceeded.
Exceeding regulatory standards
The limit beyond which exposure to the molecule is considered dangerous is defined by the maximum health value, known as Vmax.
The Vmax is set by ANSES as follows: each compound is assigned 10% of a toxicological reference value via 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 is linked to the water we drink (according to ANSES, this figure drops to 5% in France), while food accounts for 80% of this exposure; the rest comes from our environment, via the air we breathe, for example.
The Vmax has no legal value and can sometimes be much higher than the regulatory value for the reasons explained above: the ALARA principle is applied in order to protect the environment and as a precautionary principle for our health.
These Vmax values have a limited use of nine years, during which so-called remediation measures (improving the quality of the water resource, implementing treatments, for example) must be implemented.
Only exceeding the Vmax leads to immediate restrictions on tap water consumption.
Compliance with the Vmax therefore allows water to be distributed even when it exceeds the legal standard for pesticides. In the latter case—i.e., when the regulatory value is exceeded but not the Vmax—local authorities apply for an exemption in order to continue distributing this non-compliant water, and new regulatory thresholds are then established for a period of three years, renewable once.
These exceptional values can be several dozen times higher than the initial regulatory values and are established so as not to cut off the water supply to thousands of people.
The procedures for informing the public by town halls are described in Article D1321-104 of the Public Health Code: the town hall must display the results of water testing within two working days of receiving them, except in emergency situations where measures are taken to inform users as soon as possible and offer temporary solutions, such as distributing bottled water.
When the Vmax has not yet been established by ANSES, particularly due to a lack of scientific data, restrictions on use are applied, or a transitional health value may be defined by the DGS and submitted to the High Council for Public Health (HCSP) for its opinion.
On June 15, 2022, an instruction from the Department of Health established a transitional health value of 3µg/L following the recommendations of the HCSP.
It is therefore this value that now applies for the implementation of water consumption restriction measures.
A lack of data on pesticide metabolites
Still from a regulatory perspective, pesticide metabolites present in drinking water are classified into two categories, depending on their level of danger: "relevant" and "irrelevant."
According to ANSES, a pesticide is considered relevant to water intended for human consumption "when there is reason to believe that it (or its transformation products) could pose an unacceptable health risk to consumers."
Depending on the category in question, the limit values in drinking water differ. Relevant metabolites are subject to the same quality limit of 0.1 µg/l as pesticides, while non-relevant 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. Added to this is a lack of data and studies on these products, making it impossible to know their real impact on health.
This is why, in the fall of 2022, S-metolachlor metabolites were already making headlines: after reassessing their relevance, their limit was raised to 0.9 µg/l, making water that had been deemed unfit for consumption in certain French municipalities drinkable again, without any change in its quality. These changes are a source of confusion for consumers and may, justifiably, raise doubts about the quality of their tap water.
What options are available to limit contamination?
A first option for limiting drinking water contamination logically involves limiting inputs at the source by ending the widespread use of pesticides. However, the issue of persistent organic pollutants, which can remain in the environment for years or even decades, remains.
There is also a curative solution, which would involve adapting existing treatment processes. The typical conventional process currently in place is generally not sufficient to eliminate all pesticides. To achieve this, a multi-barrier approach must be adopted, adding several treatments to the conventional stages.
One example is the combination of powdered activated carbon and ultrafiltration (a membrane technique), which appears to be effective for removing pesticides and their metabolites.
Membranes could thus find their place in water purification processes. In particular, nanofiltration can remove a large number of pesticides, as is the case in Mery-sur-Oise, where the water purification plant has been using 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 approach should be taken?
While drinking bottled water should not be a systematic solution due to its catastrophic environmental impact and possible health risks linked to the consumption of plastic micro-particles and plasticizers, it can nevertheless be a solution in the event of contamination of your water supply network.
However, although bottled water is subject to health checks by the ARS(Regional Health Agencies), microplastics and plasticizers are not included in the list of parameters tested for...
Julie Mendret, Senior Lecturer, HDR, University of Montpellier and Alice Schmitt, Postdoctoral researcher in process engineering, European Institute of Membranes, University of Montpellier
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