Benefit of ecotoxicological bioassays in the evaluation of a biological treatment of PAHs polluted soil

Abstract

The performance of a biological treatment of a PAH-contaminated soil was evaluated with respect to its physicochemical and ecotoxicological properties. After six months, the biological treatment led to an significant reduction of 2- and 3-ring PAHs and to a lesser extent to 4-ring PAHs. As a consequence a significant decrease of the acute ecotoxicity was observed passing from highly ecotoxic before treatment to non-ecotoxic according to Lactuca sativa seedling and growth inhibition test and Eisenia fetida mortality test. This could be related to the bioavailability of PAHs. Indeed, tests performed on aqueous leachates of the soil showed a strong decrease of 2- and 3-ring PAHs correlated with a significant reduction of acute and chronic ecotoxicity responses. The biological treatment led to the mutagenicity reduction and the genotoxicity disappearance in the leachate. Thus, bioassays are complementary to chemical analyses to evaluate the efficiency of a bioremediation process and to evaluate the bioavailability of the organic pollutants as the total concentration of a contaminant is not the only criterion to consider. The comparison of the ecotoxic responses allowed us to underline the best sensitivity of the earthworm, Microtox, Alga and Ames bioassays among the tested set. These bioassays could thus be good candidates to build a toxicity evaluation procedure for PAHs contaminated/ remediated soils.