Transfer of cadmium in a phytoplankton-oyster-mouse food chain

The trophic transfer of cadmium (Cd) was studied in a phytoplankton-oyster-mouse food chain. Phytoplankton, grown in a continuous culture chemostat system containing CdCl₂ plus the isotope¹⁰⁹Cd, accumulated 70% of the total supplied cadmium. Oysters filtered out 85 to 95% of the phytoplankton. The rate of oyster Cd accumulation at 15 C increased linearly with seawater Cd concentration according to: y=0.066X – 0.15 (n =12, r=0.96); where X=g Cd/L seawater (between 2 and 22) and y=g Cd/g dry wt oyster/ day. About 59% of the Cd accumulated by the oysters came from the phytoplankton food source and 41% from the cadmium dissolved in the water. Sixty-one percent of the total supplied cadmium was retained in the whole soft body of the osyters. Mice fed 0.4 g of oyster-bound Cd per g of diet, retained 0.83% of the dietary cadmium consumed. Mouse kidney retention for organic oyster-bound cadmium was 0.14%. Extrapolation of these results to human risk assessment indicates that moderate consumption of oysters, which are not highly contaminated with cadmium, poses no significant health risk in terms of elevating kidney cadmium levels.