The influence of thermal desorption on genotoxicity of multipolluted soil

A multipolluted soil sampled from a former coking plant in Lorraine (France) was evaluated for its genotoxic effects on coelomocytes of the Eisenia fetida earthworm using the comet assay. The biological efficiency of thermal desorption of the contaminated soil was also investigated. The untreated polluted soil was shown to be genotoxic to earthworms. Although thermal desorption reduced the concentration of PAHs by 94% (Sigma(16 PAHs)=1846 and 101 mg/kg before and after thermal desorption, respectively), the treatment did not eliminate the genotoxicity of soil pollutants to earthworms but increased it. The concentration of non-volatile metals did not change after thermal desorption. Among metals found in the treated soil, cadmium, chromium and nickel could explain the genotoxicity of the contaminated soil after thermal desorption. The treatment could increase the bioavailability and genotoxicity of heavy metals, through a modification of the soil's organic matter, the speciation of heavy metals and their binding to organic matter. This study underlines the importance of measuring biological effects, in order to evaluate the risk associated with formerly contaminated soils and the efficiency of remediation.