Bioaccumulation of Heavy Metals in Soil Invertebrates: Part 2: Uptake and Accumulation of Lead and Chromium by Achatina marginata (Linnaeus) and Lymnaea stagnalis (Linnaeus)

Achatina marginata and Lymnaea stagnalis were each exposed to 4.15µg/g and 8.26µg/g diet of lead and chromium respectively over a period of 28 days. Comparative accumulation studies were carried out on the edible (soft) and gut tissues of both snails. The rates of accumulation of Cr by L. stagnalis were 0.025µg/g/week and 0.084µg/g/wee in the soft tissues for the lower and higher exposure concentrations respectively. The corresponding rates in the gut were 0.290µg/g/week and 0.537µg/g/week respectively. However, lower rates of accumulation of Pb were calculated for the tissues of the same species at the two exposure levels. Higher concentrations of Cr and Pb were measured in the gut tissues than the soft tissues. The rates of accumulation of Cr by A. marginata were 0.341µg/g/week and 0.518µg/g/week for the soft tissues at the lower and higher exposure concentrations respectively while the corresponding rates for the gut were 1.347µg/g/week (lower) and 1.477µg/g/week (higher). These values are 13.6 times and 6.2 times greater than those of L. stagnalis at the lower and higher concentrations of exposure respectively. A similar trend in the bioaccumulation of Pb by A. marginata rative to L. stagnalis was also observed. Bioaccumulation rates of Pb and Cr were greater in the gut than the soft tissues for both species. The moderate accumulation factors calculated for L. stagnalis and high values for A. marginata suggest that these species can be used as indicators of metal pollution in field experiments. KEY WORDS: L. stagnalis; A. marginata ; Lead; Chromium; Bio-accumulation. Global Journal of Environmental Sciences Vol.3(1&2) 2004: 7-12