How can pesticide residues contaminate DW?
Did you know?
The term "pesticides" used in the drinking water regulations covers a wide variety of products for use in plant protection, or for controlling pests (certain biocidal products) or parasites (veterinary and human antiparasitic drugs).
How are pesticide residues in DW regulated?
The presence of pesticides in drinking water is regulated by the European Directive, transposed into French law, which includes permanent monitoring of drinking water quality. This Directive sets quality limits for pesticides and their relevant metabolites (see explanations in the last paragraph of the article): 0.1 µg/L per individual substance (except for the more hazardous compounds aldrin, dieldrin, heptachlor and heptachlor epoxide, for which the quality limit has been set at 0.03 µg/L) and 0.5 µg/L for the sum of these compounds.
During the quality monitoring implemented by the Regional Health Agencies, pesticide residues or metabolites are sometimes detected above the quality limits. When a limit is exceeded, the regulations provide for management measures by the local health authorities (interconnection, dilution, enhanced treatment before distribution, greater protection of the resource, etc.) in order to restore the water's compliance with the quality limit within the time frames laid down by the regulations.
As the regulatory value of 0.1 µg/L is not based on a toxicological analysis or epidemiological studies, it cannot be used to assess the health risk if it is exceeded. If this limit is exceeded, maximum health values or VMAX are established and proposed as part of the collective expert appraisal work carried out by ANSES on a case-by-case basis at the request of the Directorate General for Health. These maximum health values guarantee consumer health even when the limits are exceeded. The reference to these VMAXis only intended to be used for a limited period of time during which remedial actions such as improving the quality of water from the resource, introducing DW treatments or mixing water by interconnecting networks, etc. must be implemented to restore compliance with the quality limit.
Did you know?
Unlike quality limits for other chemicals, which are usually determined on the basis of health considerations, the choice of European standards regarding pesticides is based on an ALARA position (i.e. "As Low As Reasonably Achievable") to protect water resources. The pesticide content was set at 0.1 µg/L, based on the detection threshold at the time.
At the national level, the Directorate General for Health is responsible for drawing up annual water quality reports for "pesticides and metabolites".
How are the maximum health values for pesticides and metabolites in DW determined?
Since 2007, the Agency has been regularly consulted by the DGS about establishing values on the basis of health criteria to be used in an exemption framework: maximum health values or VMAX in DW (PDF). Given the increasing number of compounds screened for, demand for the establishment of VMAX values has grown over time.
The method for establishing VMAX values, introduced at the Agency in 2007, was updated in the 2019 opinion (PDF), using the most recent national data available, such as the INCA 3 study. Since 2007, VMAX for about 200 compounds have been determined, of which about 20 have been re-assessed. These maximum health values may be revised in light of advances in scientific knowledge, in particular following the updating of toxicity reference values (TRVs). In the absence of a TRV, ANSES may not be able to provide a VMAX. In this case, the manager needs to take measures, such as applying restrictions on water use, to restore the situation to normal as quickly as possible. Where applicable, the table mentioned below states "Absence of VMAX".
View the table of maximum values (Excel) (VMAX) in drinking water (in French).
Note to the reader: VMAX are values to be used in an exemption framework, i.e. applicable for a limited period of time, and likely to evolve according to scientific knowledge. Only the opinions whose links are associated with each VMAX constitute references.
How are priority metabolites identified for DW monitoring?
As stated previously, metabolites can potentially contaminate water resources and even water supplied to consumers. The current regulatory quality limits – 0.1 and 0.5 µg/L – apply to metabolites regarded as "relevant". As the European directive does not define what is a "relevant" metabolite, the French health authorities therefore took the view that all pesticide metabolites detected in DW had to comply with the quality limit of 0.1 µg/L.
During the last decade, drinking water quality monitoring has evolved in terms of the number of substances screened for and the performance of the analytical methods. More and more active substances and metabolites are therefore being screened for and the checks are increasingly revealing situations where regulatory quality limits are exceeded, requiring management measures before the water can be distributed. At the request of the DGS, in 2019 ANSES proposed a method for identifying which pesticide metabolites warrant priority attention with regard to the health issues associated with drinking water consumption.
The approach is based on a definition of relevance to protecting consumer health. Assessing the relevance of a metabolite in DW involves several steps, including:
- analysing the potential health effects of the presence of a metabolite in terms of genotoxicity, reproductive toxicity, carcinogenicity or endocrine disruption;
- determining the potential for a pesticide metabolite to be transformed in the treatment system into a product that is hazardous to human health.
For the metabolites assessed as "relevant to drinking water", the current regulatory quality limits (0.1 µg/L and 0.5 µg/L) will continue to apply. For metabolites assessed as "not relevant to DW", the expert appraisal proposed a value of 0.9 µg/L, based on the threshold of toxicological concern, adopted by the DGS in its Instruction DGS/EA4/2020/177 of 18 December 2020 on the management of health risks in the event of the presence of pesticides and pesticide metabolites in DW, excluding packaged water.
In early 2022, the Agency had identified 20 metabolites (Excel) that are relevant to DW. This classification is likely 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 is likely to lead to a revision of the proposed method.