The Role of Helix aspersa as a Major Herbivore in the Transfer of Lead Through a Polluted Ecosystem

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Abstract
H. aspersa, Mueller was studied as a major herbivore in an ecosystem contaminated with Pb. An artificial food was used to test diet selection according to Pb or Ca levels and to construct a budget of Pb uptake and loss, at various doses. Dosed agar gels containing PbSO4 and CaSO4 were presented to juvenile snails. No preference for or aversion to Pb and Ca-rich food is demonstrated. The rates of uptake of Pb by H. aspersa are comparable to those estimated by extraction with 10% acetic acid. Tissue and fecal concentrations are related to dietary consumption, and evidence suggests that tissue turnover of the metal increases with consumption. The proportion of Pb available to other trophic levels in either the tissues or the feces rises with the snail''s consumption of the metal. Comparisons are made with snails from a contaminated car-park. A range of ecological and physiological factors are known to make the concentrations of Pb in snails time-dependent. H. aspersa may therefore serve to ''buffer'' the supply of Pb to other trophic levels.