The opinion deals with situations involving the simultaneous presence of several pesticides and relevant pesticide metabolites in water intended for human consumption in the event of non-compliance with regulatory limit values.

The Directorate-General for Health recommends applying the following calculation formula proposed by the French Food Safety Agency: the sum of the ratios between the concentrations detected and the maximum health values (Vmax) established by the French National Agency for Food, Environmental and Occupational Health Safety (Anses) must not exceed 1 (S(Ceau/Vmax) < 1).

The High Council for Public Health (HCSP) opinion is sought on the use in this formula, in the absence of Vmax, of the transitional health values of the German federal environmental agency Umweltbundesamt (UBA).

The HCSP indicates that this formula can be used with several Vmax, but specifies that beyond the formula, a critical examination of the overall quality of the water concerned must be carried out before applying the formula, as its validity decreases with the number of metabolites detected, due to possible interactions. The HCSP indicates that this formula should only be used with a single provisional health value, as it is impossible to add them together, as they are derived from a probabilistic approach.

The HCSP also recommends that a "consensus group" be set up as a matter of urgency to establish a strategy for managing contamination by mixtures of pollutants and to consider the multiple exposure of populations through media other than water (air, food…).

This opinion concerns a formula to assist in the management of “relevant” pesticide metabolites, but attention must also be paid to "non-relevant" metabolites in view of the development of scientific knowledge on the subject and their impacts.