Effect of Cd on accumulation and loss of Po-210 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 behaviou r and fate of Po-210 in molluscs. Starved control and cadmium-exposed musse ls, 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. ed ulis accumulated less Po-210 in the digestive gland and the remainder of th e tissue than control mussels, although this was due to a decrease in tissu e weight. More than 40% of Po-210 was identified as being associated with h igh molecular weight and heat-treated cytosol proteins in M. endulis. Musse ls in a starved state are known to recycle as much as 90% of their amino ac ids. 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 t he 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 prin cipally contain metallothioneins. It is suggested that Po-210's apparent re lationship with metallothioneins is coincidental rather than connected with its role in the regulation of metals.