The kinetics of cadmium accumulation and loss from Mytilus trossulus in the presence of marine humic substances

The accumulation and loss of cadmium (Cd) by the Baltic blue mussel Mytilus trossulus in the presence of marine humic substances (HS) was investigated under laboratory conditions. The organisms were exposed to Baltic Sea water (salinity 7.0 PSU, pH 7.9) containing cadmium (50 mu g Cd dm super(-3)) or radiocadmium (9 kBq super(115m)Cd dm super(-3)) and humic substances (0.0-7.2 mg HS dm super(-3)). Experiments were carried out in seawater at two different constant temperatures (6 degree C plus or minus 1 degree C or 15 degree C plus or minus 1 degree C). The exposure time ranged from 8 to 21 days. It was found that marine humic substances stimulate cadmium accumulation by the mussels; however, the effect was strongly modified by temperature. At 6 degree C cadmium was preferably accumulated in the gills while at 15 degree C the metal was stored mainly in the hepatopancreas. Two pools of cadmium accumulated by Mytilus trossulus were detected. Cadmium adsorbed to the shell was desorbed quickly and efficiently after the mussels, previously grown in seawater containing an elevated metal concentration (8 days, 50 mu g Cd dm super(-3) or 9 kBq super(115m)Cd dm super(-3)), had been transferred to natural seawater (60 days, 0.03 mu g Cd dm super(-3), 0 kBq super(115m)Cd dm super(-3)). The other pool of cadmium, accumulated in the soft tissue of the mussels, remained intact after depuration experiments lasting several weeks. Humic substances had no effect on the depuration of cadmium from either pool.