Some aspects of the uptake and metabolism of cadmium and zinc by the freshwater mussel 'Anodonta anatina' (L.)
The use of mussels as indicators of pollution in fresh- and seawater was reviewed and the ability of the freshwater mussel 'Anodonta anatina' to absorb Cadmium-115m and zinc-65 from its environment was studied. The uptake was studied when the metals were available in solution only and in the algal food supply. A higher accumulation occurred in the tissues when the metals were available in the food and they were concentrated up to 2x10[sup]3 times for zinc-65 and 1x10[sup]3 times for cadmium-115m above the levels found in the water. Those tissues with large surface areas in contact with the water (i.e. the gills and the mantle) and those involved with processing food (i.e. the digestive gland and kidney) were found to take up the tracers most rapidly. The muscular tissues took up the least amount of tracers. The uptake into the tissues from each source was compared and the metabolic consequences discussed. Depuration of the metals from the tissues was studied when the mussels were placed in uncontaminated water. Although the total body burdens of the tracers declined, a loss was not recorded for all the tissues. For some tissues, notably the digestive gland and the adductor muscles with cadmium-155m and the gonad and kidney with zinc-65, a continued uptake was recorded. It was concluded that permanent binding sites for the metals might exist in some tissues. The fate of cadmium in the tissues was studied. Cadmium was found to be located in the cytosol and associated with low molecular weight proteins. These proteins were found to have low aromatic amino acid and high cysteine content as indicated by their absorption characteristics at 280 and 250 nm respectively. These properties together with the demonstrated heat stability indicated that the cadmium-binding proteins in 'Andonta' are similar to metallothioneins indentified in other species.