Methods for toxicity assessment of contaminated soil by oral or dermal uptake in land snails: metal bioavailability and bioaccumulation.

Using two biological characteristics of the land snail (subspecies Helix aspersa aspersa and Helix aspersa maxima), i.e., soil eating and crawling on wet surfaces, methods were developed to assess the bioavailability of heavy metals (Cd, Cr, Pb, and Zn) from soil and aqueous leachates of soil. Measurement of heavy-metal concentrations in soil, leachates, and soft tissues of snails showed that contamination from ingested soil is the major route for metal uptake. Generally, the concentrations of metals were greater in the viscera than in the foot and rose with the proportion of spiked soil (Sl) in the diet. After ingestion of soil, bioaccumulation factors in the viscera were over two for Cd (3.5-27) and Zn (1.7-4.4) for both subspecies but were below one for Cr (0.04-0.6, except for H. aspersa maxima: 1.21) and Pb (0.02-0.23). Contamination by leachate Sl mainly caused accumulation of Cr in the tissues. Determining the metal burden per snail enables an estimation to be made of the risk of secondary poisoning encountered by predators. The present study provides data on the bioavailability of metals in soils and on the relationships between bioaccumulation and sublethal effects.