PB uptake by ecologically dissimilar earthworm (Lumbricidae) species near a lead smelter in south Finland

Abstract

The number of species and individuals, and the total biomass of earthworms decreased with decreasing distance from a lead smelter in southern Finland, as the Pb load of the soil increased. In soils highly polluted with Pb significant interspecific differences were found in the Pb concentration and the Pb concentration factor of lumbricids, whereas in slightly Pb polluted ‘control’ soils there were no significant interspecific differences. Near the smelter, the Pb concentration of the endogeic Aporrectodea caliginosa was higher than in the epigeic Lumbricus rubellus and L. casteneus. Pb concentration factors of these three species were lower in the highly polluted soil than in the ‘control’ soil, indicating that they were able to regulate their Pb accumulation. Contradicting these field observations, of the worms from the ‘control’ soil but reared in highly Pb polluted soil for up to 70 days, the epigeic L. castaneus, L. rubellus and Dendrodrilus rubidus took up more Pb than did the endogeic A. caliginosa and A. rosea. They also accumulated more Pb during the rearing periods than their counterparts permanently living in the highly Pb polluted soil, indicating that besides interspecific differences in Pb accumulation there seem to be intraspecific differences as well. Acclimatization and/or genotype differences can underlie earthworms' adaptation to Pb polluted soil, where they may have dissimilar physiological pathways to cope with high soil Pb concentrations. The amount of Pb rendered available to a local food chain by a population of earthworms will depend on the ability of the worms to accumulate Pb in their tissues, which in turn, is a function of the population's history of Pb exposure. Species such as A. caligonosa, which accumulate and continuously withstand high Pb concentrations in their tissues, are most appropriate for biomonitoring.