Occurrence of calcium concretions in various tissues of freshwater mussels, and their capacity for cadmium sequestration

Abstract

The freshwater unionids Anodonta anatina, Anodonta cygnea and Unio pictorum were examined with respect to the distribution of calcium concretions among the various organs, and to a possible role of concretions in heavy metal detoxification. Gills of all three species contain large amounts of concretions, up to 55% of the tissue dry weight in A. cygnea. Smaller amounts are present in the mantle and the midgut gland, and also in granulocytes. The other organs, including the kidney, are practically devoid of concretion material. By electron-microprobe analysis, the concretions appear to be of the phosphatic type, and also contain manganese, iron and zinc. When animals were exposed to CdCl2, cadmium was bound to the concretion fraction of the various organs. But, in almost all cases, Cd concentrations in the concretion material were lower than those in the whole organ. Furthermore, the contribution of the concretion fractions in Cd accumulation decreased over the course of exposure. It is concluded that calcium (pyro)phosphate concretions do not function as preferential sequestration sites for cadmium.