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 (crop contents) and egesta (faeces) were investigated in two physiologically contrasting earthworm species (Lumbricus rubellus and Aporrectodea caliginosa) inhabiting soils exhibiting various levels of heavy metal contamination. In addition, a complementary soil layering experiment, conducted under laboratory conditions, was undertaken to investigate whether the distribution of Pb within a soil vertical pro®le in ̄uenced the relative metal accumulation patterns of these species. Generally, the Cd, Cu and Pb concentrations of ®eld populations of A. caliginosa were signi®cantly greater than in L. rubellus, a pattern reversed for Ca. Concentrations of Zn were signi®cantly greater in A. caliginosa in soils containing the lowest Zn concentrations, but no species differences were apparent at high soil concentrations of this metal. Comparisons of metal concentrations between ingesta and soils indicate that both species selectively ingest material from the soil matrix, although no signi®cant 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 observed differences in tissue concentrations of the respective metals, which cannot be explained by excretion via the egesta. The soil strati®cation experiment indicated that Pb distribution within a soil pro®le affected the pattern of species differences in tissue metal concentrations observed in ®eld populations. The evidence therefore suggests that the difference in dietary intakes of these metals is an important factor in contributing to observed differences between these species, although other factors are also contributory. The observations are discussed in the context of soil hazard assessment monitoring, and in particular, the role of concentration factors in such applied surveys. # 1999 Elsevier Science B.V. All rights reserved.