Cadmium turnover in minnows (phoxinus phoxinus) preexposed to waterborne cadmium

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Abstract
The radioactive isotope 109Cd 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 109Cd exposure (3 nM Cd). The effect of preexposure on the turnover of 109Cd 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 109Cd turnover was a decreased uptake of 109Cd into the gills. In the gill tissue, the 109Cd was retained by Cd binding ligands mainly in the cytosolic fraction. Preexposure decreased the percentage of 109Cd 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 109Cd 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 109Cd, while the gills, head and skin eliminated tracer during the 64‐d post‐tracer exposure period. The 109Cd 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.

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