Zinc and cadmium body burdens in terrestrial oligochaetes: Use and significance in environmental risk assessment

Uptake and elimination kinetics of zinc and cadmium were studied in the oligochaetes Enchytraeus albidus and Eisenia fetida. Even at the highest exposure concentrations where E. fetida survived, the internal zinc concentration was still regulated to a constant level. Enchytraeus albidus could not regulate the internal zinc concentration as well, and the body burden increased after exposure to high zinc concentrations. After transfer to clean soil, the internal zinc concentration dropped back to the control level within a few weeks. For both species, internal cadmium concentrations did not reach equilibrium during the uptake experiments. The internal concentrations causing 50% reduction in cocoon production for E. fetida exposed to cadmium varied between different soil types, indicating that no fixed critical body burdens exist. For both zinc and cadmium, bioaccumulation factors decreased with increasing soil metal concentrations. Bioaccumulation factors may therefore be poor indicators of environmental risk. Their dependence on the total soil concentration makes bioaccumulation factors also unsuitable for assessing the influence of soil characteristics on the bioavailability of metals in contaminated field soils. For the same reason, uptake rate constants are probably not suited for this purpose.