EFFECT OF TOTAL CADMIUM AND ORGANIC COMPLEXING ON THE UPTAKE OF CADMIUM BY THE BRINE SHRIMP, ARTEMIA-FRANCISCANA

The effect of total cadmium and organic complexing on the rate of cadm ium uptake by the brine shrimp, Artemia franciscana has been studied i n chemically defined saltwater solutions. The uptake of cadmium from s olution by the laboratory-reared brine shrimp displays saturable uptak e kinetics. Uptake of cadmium is linear in time up to a total cadmium concentration of 200 mu moll(-1) and saturates above 800 mu moll(-1). Complexation of cadmium with organic ligands decreases the uptake of t he metal by the brine shrimp. This is in agreement with the view that the availability of cadmium to aquatic organisms is related to the act ivity of the free cadmium ion in the solution. There is no evidence th at the direct uptake of cadmium complexes is important in determining uptake of cadmium. Cadmium uptake is not, however, a mere function of the free cadmium ion activity in the solution, i.e., cadmium uptake ra tes may differ by an order of magnitude for the same free cadmium ion activity depending on the complexation conditions. In addition to cont rolling the free cadmium ion activity, the role of organic ligands in metal ion buffering and metal ion masking appear important factors in determining the availability of the metal to the organism.