ACCUMULATION OF ZN, CU, PB AND CD IN THE GARDEN SNAIL (HELIX-ASPERSA)- IMPLICATIONS FOR PREDATORS

Accumulation of Zn, Cu, Pb and Cd was studied in snails fed for 120 da ys on diets contaminated with each metal separately and with all metal s mixed together. The concentrations of Zn in food were in the range 3 9 to 12 200 mg kg(-1), Cu 9-1640 mg kg(-1), Pb 0.4-12 700 mg kg(-1), a nd Cd 0.16-146 mg kg(-1) on a dry weight basis. At the highest concent rations of all metals the consumption rates decreased significantly. F or the remaining concentrations, Zn and Cu were accumulated in soft ti ssue in proportion to their concentrations in food. The lowest treatme nts of Pb and Cd did not cause any increase in soft tissue concentrati ons of these metals but at average treatments, a clear increase was ob served. Copper was accumulated especially efficiently, exceeding conce ntrations in food throughout the whole range of treatments. Except for the lower end of experimental treatments, Zn was accumulated approxim ately in direct proportion to its concentration in the diet. Lead was the most efficiently regulated metal, with soft tissue concentrations always substantially lower than in food. Approximately 60% of Zn, 90% of Cu, 43% of Pb and 68% of Cd on average was assimilated from food. T he assimilation efficiency of food alone was ca 74%. The concentration s of metals in shells increased significantly with exposure, but (with one exception) the concentrations in shells did not exceed 5% of thos e found in soft tissue. We argue that snails are more important as age nts of food-chain transport of Cu and Cd, than of Zn or Pb. Our result s indicate also that snails are not able to deposit significant quanti ties of metals in their shells, at least during the time scale of our laboratory experiment.