The accumulation of metals (Cd, Cu, Pb, Zn and Ca) by two ecologically contrasting earthworm species (Lumbricus rubellus and Aporrectodea caliginosa): implications for ecotoxicological testing

The metal (Cd, Cu, Pb, Zn and Ca) concentrations in the tissues, ingesta (c rop contents) and egesta (faeces) were investigated in two physiologically contrasting earthworm species (Lumbricus rubellus and Aporrectodea caligino sa) inhabiting soils exhibiting various levels of heavy metal contamination . In addition, a complementary soil layering experiment, conducted under la boratory conditions, was undertaken to investigate whether the distribution of Pb within a soil vertical profile influenced the relative metal accumul ation patterns of these species. Generally, the Cd, Cu and Pb concentration s of field populations of A. caliginosa were significantly greater than in L. rubellus, a pattern reversed for Ca. Concentrations of Zn were significa ntly greater in A. caliginosa in soils containing the lowest Zn concentrati ons, but no species differences were apparent at high soil concentrations o f this metal. Comparisons of metal concentrations between ingesta and soils indicate that both species selectively ingest material from the soil matri x, although no significant correlations were found between tissue metal and ingesta metal concentrations. Differences in concentrations of Cd, Pb and Zn between the ingesta of the species were, however, concomitant with obser ved differences in tissue concentrations of the respective metals, which ca nnot be explained by excretion via the egesta. The soil stratification expe riment indicated that Pb distribution within a soil profile affected the pa ttern of species differences in tissue metal concentrations observed in fie ld populations. The evidence therefore suggests that the difference in diet ary intakes of these metals is an important factor in contributing to obser ved differences between these species, although other factors are also cont ributory. The observations are discussed in the context of soil hazard asse ssment monitoring, and in particular, the role of concentration factors in such applied surveys. (C) 1999 Elsevier Science B.V. All rights reserved.