Adaptation by an urban population of the snail Helix aspersa to a diet contaminated with lead

Two populations of the garden snail Helix aspersa, from an urban car park and from a semi-rural site, were fed a diet containing 500 microg g(-1) of Pb as PbSO(4). After 2 days, half of each population was removed to a Pb-free diet and half continued on the dosed food, both for 64 days. The snails from the contaminated site had a significantly lower uptake of Pb compared with those from the rural, uncontaminated site. The car park snails also lost Pb more rapidly from their tissues. A second experiment evaluated the effect of a previous exposure to a high Pb diet on Pb uptake. The results suggest that the differences between the two populations are not due to a physiological adaptation, but rather that the car park snails represent an ecotype adapted to a high Pb diet.