The distribution of cadmium, copper, lead, zinc and calcium in the tissues of the earthworm Lumbricus rubellus sampled from one uncontaminated and four polluted soils

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Abstract
The tissue distribution of Cu, Cd, Pb, Zn, and Ca in the earthworm Lumbricus rubellus living in non-polluted and heavy-metal polluted soils was investigated. Cd, Pb and Zn were primarily accumulated within the posterior alimentary canal. As the whole-worm Pb burden increased, the proportion of the metal accumulated within this tissue fraction increased. A similar pattern was found for Zn. By contrast, 70%–76% of the Cd burden was found in the posterior alimentary canal, irrespective of the whole-worm Cd content. The accumulation of Cd, Pb and Zn primarily in the posterior alimentary canal prevents dissemination of large concentrations of these metals into other earthworm tissues, and may thus represent a dextoxification strategy based on accumulative immobilisation. Cu was distributed fairly evenly in the tissue fractions investigated. There was no evidence of sequestration of this metal. The apparent lack of a detoxification strategy may contribute to the well-known susceptibility of earthworms to low environmental Cu concentrations. Indeed, earthworms from the site of highest soil Cu (Ecton) were markedly smaller than those from the other sites sampled. The highest Ca concentrations were found in the anterior alimentary canal, and were related to calciferous gland activity. A large proportion of Ca was also stored as a physiologically available pool in the posterior alimentary canal. Despite huge variations in soil Ca concentrations, the body wall Ca levels were fairly similar in L. rubellus from all the study sites. Thus, L. rubellus may become physiologically adapted to soils of exceptionally low Ca concentration. The observations are discussed in the context of the merits of analysing specific tissues, rather than whole organisms, for the purpose of monitoring metal bioaccumulation.