Cadmium concentrations in the freshwater mussel (Elliptio complanata) and their relationship to water chemistry

Concentrations of cadmium were determined in freshwater mussels (Elliptio complanata) from 21 small lakes in south-central Ontario. The average Cd concentrations ranged from 0.5 to 7.5 micrograms/g dry weight. A poor correlation between the concentration of Cd in lakewater and the concentration of Cd in the organisms was observed. Concentration of Cd in the sediments was not a useful predictor. Thus, it is hypothesized that the availability of the Cd varies among the 21 lakes. In an effort to test this hypothesis, the relationships between organism concentrations and water chemistry parameters that have the potential to alter Cd availability including pH, calcium (Ca), total organic carbon (TOC) and total inorganic carbon (TIC) were examined. The strongest relationship was found between Cd concentration in the mussels and water column pH, suggesting that hydrogen ions are replacing Cd ions in complexes and increasing the amount of free Cd available to the organisms. Correlations between pH and other water chemistry parameters make it difficult to test this hypothesis. A multiple regression model was developed incorporating pH, Ca, TOC, and TIC which explained 69% of the variance in Cd concentrations.