Sources of bioavailable trace metals for earthworms from a Zn-, Pb- and Cd-contaminated soil

The sources of bioavailable metals for earthworms were investigated in a Zn-, Pb- and Cd-contaminated soil. Selective sequential extractions (SSE) of metals were performed on soil samples with different amounts of contamination and compared with the body burden concentration of metals in two earthworm species: Aporrectodea caliginosa and Lumbricus rubellus. The most labile forms (water extractable and exchangeable) of metals were poorly related with metal accumulation by the earthworms, except for Cd, whereas the moderately available forms (acid-soluble, bound to iron oxides and organic matter) were related to the pattern of metal accumulation by earthworms. This indicates that the ingestion of metals bound to soil components is likely to be a more important uptake route than the dermal uptake of dissolved ions for metals entering the body tissue of earthworms.