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

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.