Biokinetics of radiocobalt in the asteroid Asterias rubens (Echinodermata) : Sea water and food exposures

The biokinetics of cobalt-57 uptake and loss in the asteroid, Asterias rubens, were examined. Exposures were conducted directly via seawater and through ingestion of radiolabelled food. Results showed that uptake from seawater followed first-order linear kinetics. Uptake was determined to be dependent upon body compartment, with the aboral part of the body wall concentrating super(57)Co to the greatest extent. Cobalt-57 taken up directly from seawater was released following exponential loss kinetics that were characterized by an estimated biological half-life of 27 d. Via diet, the highest proportion of super(57)Co was found in the pyloric caeca. The turnover time of dietary super(57)Co was twice as rapid as that following direct uptake from seawater.