The accumulation of chromium by mussels Mytilus edulis (L.) as a function of valency, solubility and ligation

Mussels exposed to different forms of chromium for 4 weeks preferentially accumulated the metal in the digestive gland, irrespective of the form of chromium employed. Accumulation rates were in the following order. Cr(III)-albumen > tannery effluent Cr(III) > Cr(OH)₃ > Cr(VI) > Cr(III)-citrate. In the Cr(III)-albumen, Cr(VI) and Cr(OH)₃ exposure groups, 23, 23 and 27%, respectively, of the total chromium was found in the cytosolic fraction of the digestive gland. This cytosolic chromium component was found to be largely associated with a medium to low molecular weight fraction in the digestive gland, for both Cr(III)-albumen and Cr(VI) exposed mussels. In contrast, the majority of chromium was bound to a high molecular weight component in the gill. The results indicate that Cr(III) is generally more bio-available than Cr(VI) to Mytilus edulis, although ligation was found to be critical. Evidence is also provided to show that Cr(III) bound to proteins in tannery waste is likely to be responsible for the high levels of accumulation in the tissues of aquatic animals close to tannery effluent outfalls.