Caractérisation du potentiel toxique des eaux urbaines par bioessais - Cas de l'agglomération parisienne

In a regulatory framework, water quality is often assessed by comparing concentrations of individual substances with thresholds such as environmental quality standards. This approach, although robust, presents some limitations. Information on the presence of contaminants alone is not sufficient to quantify the impact or toxic potential of these waters; the information remains "individual" at the level of substances for which sufficient ecotoxicological data exist, without allowing the potential cocktail effect to be assessed. Bioassays are global and integrated methods that provide information on the toxic potential of the sample under consideration and even on the specific toxicity of certain groups of substances. Our approach therefore consisted in monitoring the toxic potential of various urban water samples (hospital effluent, wastewater at the outlet of two sub-basins of the City of Paris, wastewater at the inlet of a wastewater treatment plant and treated water, combined sewer overflows) using three panels: General toxicity (8 bioassays on algae, bacteria, fungi and human cells), Genotoxicity (3 bioassays on bacteria and human cells), Endocrine disruption (6 bioassays on human cells). The results show that combined sewer overflows bring excess toxicity to the receiving environment. Indeed, all the dimensions of toxicity have, at one time or another, been observed in the emissaries as a whole. The comparison between the inlet and outlet of wastewater treatment plants seems to indicate that the reduction found for the physico-chemical parameters is not observed for toxicity indicators. However, further studies on these types of samples are required to confirm, or not, this trend.