The effect of chelating agents on the uptake and accumulation of cadmium by Mytilus edulis

The uptake, storage and excretion of cadmium by the common mussel Mytilus edulis (L.) has been studied at sub-lethal concentrations using the radioactive isotope ^115mCd as a marker. After an initial lag period, the uptake at low concentrations in sea water is linear with time and directly proportional to the sea water concentration, with a maximum concentration factor of 165 at 0.7 g Cd/ml sea water. A decrease occurs at higher concentrations indicating saturation of the available binding capacity. Prior complexation of the cadmium with either EDTA, humic and alginic acids or pectin doubles both the rate of accumulation and the final tissue concentrations (order: kidneyviscera>gillsmantle>muscle) and eliminates the lag period, suggesting that ionic cadmium must first be complexed before uptake can occur. A mechanism for this effect, which may involve thionein, is described. The rate of excretion of cadmium is 18 times slower than that of uptake, with the major route via the kidney but not via the byssal threads as with particulate iron. The need to detoxify and store cadmium by an immobilization mechanism is a consequence of this slower rate of elimination.