Heavy metal linkages with mineral, organic and living soil compartments

For soil ecotoxicological assessment, we can observe lethal effects (on organism as presence or absence) or sublethal effects due to bioconcentrations of contaminants in organisms. This paper deals with the analysis of seven heavy metals (Cd, Cu, Fe, Mn, Ni, Pb and Zn) and Ca: (i) in soils, by three chemical extraction techniques; (ii) in earthworm tissues; (iii) the relationships between earthworm bioconcentrations and soil heavy metal contents; and (iv) the linkage of these metals with different soil components. Sixty soil sites were examined. Soil samples were analyzed by three metal extraction techniques: total, acetic acid and dethylene triamine pentacetic acid. The results of soil metal extractions have been reported in relation to total soil or to various soil fractions (organic matter, clay, silt, sand). Data were interpreted using a principal component analysis (PCA) to observe a relationship depending on soil and earthworm heavy metal contents and soil properties. The correlations between earthworm metal body burdens and soil total contents were positively significant for all metals except Fe and Ni. These correlations varied with the other soil extraction methods. The observed correlations could not be interpreted in term of simple mechanisms due, to the complexity of systems, and could not be used as a tool to predict soil biohazard. The relationships between earthworm metal bioconcentrations and the various soil metal estimations depend on many mechanisms which are discussed. The direct measurement of heavy metal concentrations in earthworm tissues is safer for ecological assessments.