Pesticides in tap water

After they have been applied, a small fraction of plant protection products are released into the environment. Their active substances can then degrade into metabolites depending on their characteristics and the physico-chemical conditions they encounter in the soil.

Plant protection substance residues and the metabolites generated can therefore make their way into soil, surface and groundwater, sediment, plants and the atmosphere. Once they are present in water resources, in the absence of a suitable treatment system, they can potentially be transferred into the water supplied to consumers.

Firstly, the degradation of metabolites is taken into account when assessing and authorising active substances, and secondly, plant protection products are regularly re-assessed, taking new knowledge and methodologies into account.

In addition, the European Drinking Water Directive provides for close monitoring of drinking water quality. This monitoring also covers pesticide active substances and their metabolites in drinking water. European Directive 1998/83 EC, which is being replaced by Directive 2020/2184/EC, has been implemented in French law.

During the quality monitoring carried out by the Regional Health Agencies (ARSs), pesticide residues or metabolites are sometimes detected above the quality limits. In such situations, the regulations provide for management measures at the request of the local health authorities, to restore the water's compliance with the quality limit within the time frames specified in the regulations. Different measures can be taken depending on the context and may include increased protection of the resource, interconnections between different raw water resources, dilution, or reinforced treatment of the supplied water.

Causes of limits being exceeded due to the use of plant protection products can also be identified, and lead to specific measures.

When the water quality limit is exceeded, even though this limit is not an indicator of a health risk, it becomes a priority to prevent any risk to consumers. To this end, at the request of the DGS, ANSES establishes exceptional maximum health values (Vmax) to guarantee consumer health even when quality limits are exceeded.

These Vmax values act as a temporary benchmark while solutions are implemented to remedy the exceeded quality limit. The duration of this temporary situation is set by the regulations.

The maximum health values are determined based on the toxicity reference values (TRVs) for the active substances or metabolites, considering that a person's exposure through the water they consume should not exceed 10% of the TRV.

To ensure the greatest possible safety, the Vmax is established with a view to protecting heavy consumers of tap water and takes lifelong consumption of water into account.

These maximum health values may be updated in light of advances in scientific knowledge, in particular when TRVs are updated, or when calculation methods are revised. For example, the method for establishing Vmax values, introduced at the Agency in 2007, was updated in a 2019 opinion (PDF), using recent national data such as those from the INCA 3 study.

Since 2007, Vmax values for around 200 compounds have been determined, of which about 20 have also been re-assessed. To date, for the substances concerned by the 0.1 µg/L limit, the Vmax values determined are all above this quality limit.

During the last decade, drinking water quality monitoring has evolved in terms of the performance of the analytical methods. In addition, more and more active substances and metabolites are being screened for. Lastly, the uses of plant protection products are also changing over time. This change is due on the one hand to plant protection practices and needs, and on the other to developments in the number and diversity of authorised substances. For some uses, this may lead to a restriction in the choice of available products or an increase in the volume of use of certain active substances.

Through a combination of these different factors, the monitoring reveals a greater number of situations where the regulatory quality limits are exceeded than in the past, requiring management measures to restore the quality of the water supply.

According to European Directive (EU) 2020/2184, "A pesticide metabolite shall be deemed relevant for water intended for human consumption if there is reason to consider that it has intrinsic properties comparable to those of the parent substance in terms of its pesticide target activity or that either itself or its transformation products generate a health risk for consumers".

When a metabolite is considered relevant for drinking water, it must be subject to the same vigilance and the same regulatory measures as an active substance found in tap water.

As the criteria and assessment procedures for establishing the relevance of pesticide metabolites in drinking water have not been defined at European level, it is up to each country to determine them. In France, it is ANSES that assesses whether or not a metabolite is relevant for drinking water.

At the request of the DGS, in January 2019, ANSES proposed a method for identifying which pesticide metabolites are relevant and warrant priority attention with regard to the health issues for consumers.

The methodology adopted by ANSES applies only to drinking water: it focuses on protecting human health from the risks associated with the ingestion of metabolites in tap water. In particular, it should not be confused with the methodology for assessing the relevance of plant protection product metabolites in groundwater. In principle, this methodology is used in the European assessment of plant protection products to safeguard the health of the population and the environment, and is based on different calculation methods and courses of action.

As a precautionary measure, in application of this method, ANSES classifies a metabolite as relevant for tap water in two cases:

• when this relevance can be established on the basis of the available scientific knowledge;

when essential scientific data are missing with regard to the criteria adopted by ANSES.

Directive (EU) 2020/2184 states that "Member States shall define a guidance value to manage the presence of non-relevant metabolites of pesticides in water intended for human consumption".

In its opinion of 30 January 2019, ANSES therefore proposed a value of 0.9 µg/L in drinking water as an action threshold for metabolites classified as non-relevant.

On the basis of current knowledge, this value is intended to ensure that lifelong exposure to these substances does not pose a health risk to consumers. It also assumes possible effects that could not be assessed due to a lack of data, in particular toxic effects on reproduction and carcinogenic effects.

Like all ANSES opinions, those responding to formal requests from the DGS on metabolites provide scientific benchmarks for the decision-makers responsible for ruling on management measures.

In the method established in 2019, ANSES's assessment mainly draws on criteria of genotoxicity, toxicity to reproduction, carcinogenicity or endocrine disruption. Thus, a pesticide metabolite is considered relevant if it meets at least one of the following criteria, considered in this order:

• It has pesticidal activity or the absence of such activity has not been demonstrated;
• It has genotoxic potential or the absence of such potential has not been demonstrated;
• It has a proven toxic effect on reproduction or carcinogenicity, or the associated active substance has been classified in Group 1A or 1B by the IARC;
• It has proven potential for endocrine disruption or the associated active substance is identified as having such potential;
• It can be transformed into a product that is harmful to human health during the drinking water treatment steps.

The classification of a metabolite is liable to change as new scientific knowledge is acquired regarding the criteria on which this classification is based: re-assessment of active substances, new data available, etc. A metabolite may therefore change from being relevant to non-relevant, or vice versa.

In early 2022, the Agency classified eight relevant metabolites out of the 20 metabolites assessed (Excel). This classification is liable to change with the acquisition of new scientific knowledge: re-assessment of active substances, new data available, etc. Similarly, advances in knowledge and/or the revision of assessment methods could lead to a revision of the proposed method for assessing relevant metabolites.