Ecotoxicological risk assessment linked to the discharge by hospitals of bio-accumulative pharmaceuticals into aquatic media: The case of mitotane.

The release of hospital wastewater into the urban sewer networks contributes to the general contamination of aquatic media by pharmaceutical residues. These residues include bio-accumulative pharmaceuticals that lead to increased risk for ecosystems because they can concentrate in organisms and food chains, and therefore reach toxic levels. In order to assess the ecotoxicological risks linked to this particular category of residues, we have developed a specific method, by combining a theoretical calculation of pollutant concentrations in organisms to estimate Body Residue (BR), and ecotoxicity biomarkers in fish cell lines, enabling the calculation of a Critical Body Residue (CBR). This method finally results in the calculation of a specific risk quotient (Qb=BR/CBR), characterizing the risk linked to this type of pollutant. This method was applied to mitotane, a bio-accumulative pharmaceutical typically found in hospital wastewater, in the framework of an exposure scenario corresponding to the discharge of all the hospital wastewaters into the Rhone River which flows through the city of Lyon, France. This approach leads to risk quotients (Qb and Qbg) much higher than those found with the classical approach, i.e. Q=PEC/PNEC (Predictive Environmental Concentration/Predictive Non Effect Concentration)=0.0006. This difference in the appreciation of risk is important when using cytotoxicity as the criterion for measuring the toxicity of mitotane (Qb=0.056) and it is even greater when the criterion used is genotoxicity (Qbg=6.8). This study must be now consolidated by taking the biomagnification of the pharmaceuticals into consideration.