Cadmium Speciation in Aquatic-Life Flow-Through Bioassay Diluters

A framework of cadmium speciation studies is described for flow-through minidiluter bioassay systems which employs Lake Superior water containing added concentrations of calcium carbonate alkalinity, Aldrich humic acid, and/or <2 μm suspended Lake Superior red clay. Aspects of the flow-through diluter function were qualitatively related to major changes in the observed Cd2+ concentration as a function of time and water-quality chemical variables. Red clay caused the greatest change, since it markedly accelerated the rate of loss of Cd2+ from Lake Superior water containing added CaCO3. This acceleration factor was highly sensitive to other variables such as pH and humic acid. In addition, ion selective electrode (ISE) potentiometry, dialysis, and membrane filtration were employed to formulate an ionic chemical equilibria model designed to describe dissolved cadmium specie concentrations. A linear regression of Cd2+ concentrations, measured in situ with the ISE, with the corresponding calculated Cd2+ concentrations (n = 84), gave the relationship (νg/L) of, https://www.w3.org/1998/Math/MathML" display="block"> MODEL = 0.90 · ISE + 0.6 with a correlation coefficient of 0.988.