CADMIUM TURNOVER IN MINNOWS (PHOXINUS-PHOXINUS) PREEXPOSED TO WATERBORNE CADMIUM

The radioactive isotope Cd-109 was used to study the turnover of Cd in minnows (Phoxinus phoxinus) preexposed to waterborne Cd. Three groups of fish were preexposed to 3 nM Cd for 0, 30 and 91 d before a 24-h Cd-109 exposure (3 nM Cd). The effect of preexposure on the turnover of Cd-109 in the fish was studied during a 64-d post-tracer exposure period at 3 nM Cd. The major effect of Cd preexposure on the Cd-109 turnover was a decreased uptake of Cd-109 into the gills. In the gill tissue, the Cd-109 was retained by Cd binding ligands mainly in the cytosolic fraction. Preexposure decreased the percentage of Cd-109 retained in a cytosolic high-molecular-weight fraction at the end of the tracer exposure. At the same time, an increased percentage of tracer was retained in a low-molecular-weight cytosolic fraction with high Cd-109 content (Cd-BP), probably metallothionein (MT). This effect was not caused by an increased MT content in the preexposed fish. The liver, kidney, muscle and bone accumulated Cd-109, while the gills, head and skin eliminated tracer during the 64-d post-tracer exposure period. The Cd-109 elimination and accumulation were not altered by the Cd preexposure. A large part of the tracer accumulated in the liver and kidney was detected in the Cd-BP fraction, and the MT content in the organs was not altered by the preexposure.