Gammarus fossarum as a sensitive tool to reveal residual toxicity of treated wastewater effluents
Résumé
Wastewater treatment plants (WWTPs) are one of the main sources of freshwater pollution eventually resulting
in adverse effects in aquatic organisms. Treated effluents can contain many micropollutants at concentrations
often below the limit of chemical quantification. On a regulatory basis, WWTP effluents have to be non-toxic
to the aquatic environment, wherefore not only chemical abatement but also ecotoxicological evaluation through
relevant bioassays is required. Standardized bioassays currently used are often not sensitive enough to reveal a
residual toxicity in treated effluents. Therefore, attention must be paid to the development of better-adapted approaches implementing more sensitive organisms and relevant endpoints. In this study, the toxicity of two differently treated effluents (activated sludge treated effluents with and without ozonation) towards the ecologically
relevant species Gammarus fossarum was evaluated. Organism fitness traits such as reproduction and sperm DNA
integrity were followed in exposed organisms. In complement, enzymatic biomarkers were measured indicating
the presence of neurotoxic compounds (acetylcholinesterase activity), the presence of pathogens likely to increase the toxic effects of chemical compounds (phenol-oxidase activity), and the presence of toxic compounds
inducing detoxification mechanisms (glutathione-S-transferase activity). Enzymatic activities were not modified,
but significant sub-lethal effects were observed in exposed organisms. In both effluents, females showed a retarded molt cycle, a reduced fecundity and fertility, and N90% of developed embryos exhibited developmental
malformations. In addition, a slight but significant genotoxic effect was measured in gammarid sperm. In a
whole, no difference in toxicity was found between both effluents. Coupling reproduction impairment and
genotoxicity assessment in Gammarus fossarum seems to be a valuable and sensitive tool to reveal residual