Effect of Cd on accumulation and loss of 210Po in the mussel Mytilus edulis

As a result of Po-210's previously identified association with sulphur-rich proteins, metallothioneins could have a significant effect on the behaviour and fate of Po-210 in molluscs. Starved control and cadmium-exposed mussels, Mytilus edulis, were fed Po-210-labelled algae (Isochrysis galbana) for 5 d and then allowed to depurate in clean sea water. Cadmium-exposed M. edulis accumulated less Po-210 in the digestive gland and the remainder of the tissue than control mussels, although this was due to a decrease in tissue weight. More than 40% of Po-210 was identified as being associated with high molecular weight and heat-treated cytosol proteins in M. endulis. Mussels in a starved state are known to recycle as much as 90% of their amino acids. It is proposed that Po-210 associated with these and other proteins is recycled, explaining why no significant loss of Po-210 was observed from the remainder of the tissue in either control or Cd-exposed mussels. Cadmium-induced metallothioneins had no effect on the distribution of Po-210 in M. edulis; < 5% associated with the cytosolic fraction was considered to principally contain metallothioneins. It is suggested that Po-210's apparent relationship with metallothioneins is coincidental rather than connected with its role in the regulation of metals.