Influence of aquatic humus and pH on the uptake and depuration of cadmium by the Atlantic salmon (Salmo salar L.).

Uptake and release of cadmium by Atlantic salmon at the concentrations near the background values for fresh water have been studied using cadmium labelled with Cd-109. Cumulation constant and biological half-time of release were established for different concentrations of humus and values of pH. The uptake is strongly dependent on the concentration of humus, showing a pronounced maximum at a DOC concentration of 2.7 mg/l. Release of cadmium is relatively slow, the biological half-time exceeds one year in the water without humic substances. Calculated bioconcentration factors range from 130 to several thousands, which may explain the wide differences of bioconcentration factor reported for natural systems. A general equation enabling calculation of bioconcentration factors for various conditions has been derived. An attempt is done to discuss the results from the point of view of physico-chemical forms of cadmium in respective waters. The amount of cadmium adsorbed on the surface of the fish was proved to be insignificant when compared with total concentration of cadmium bioaccumulated in the fish.