The shell as a site of lead deposition inHelix aspersa

Abstract

Snails from a contaminated urban car park were fed an experimental diet for 64 days. One group received a high Pb diet for the duration, and another group were removed from the high Pb diet after two days. Shells were analyzed at various intervals to measure Pb uptake and loss. Regression analysis of twenty-eight shells for each treatment suggests that the weight of Pb in the shell increased linearly with time, but loss from the shell was correlated with soft tissue Pb levels. The shells of fourteen snails from an uncontaminated site accumulated Pb less quickly on the high Pb diet, and had lower Mg and Ca concentrations. All snails lost Mg from the shell following the initial dose, possibly as part of a detoxification mechanism for heavy metals. The shell may lose Pb over a number of days, serving as a short-term sink for Pb which it releases when soft tissue concentrations fall.