Bioaccumulation of 137Cs and 60Co by a tropical marine teleost Epinephelus sp.

As part of a project on the behaviour of radionuclides released by the Angra Nuclear Power Station in the marine environment, laboratory experiments were performed to study cesium and cobalt accumulation by juvenile groupers (Epinephelus sp.). The fishes were kept in aquariums equipped with gravel-bed filters spiked with 60Co (150 KBq/l) and 137Cs (75 KBq/l). Uptake was only via water since the fishes received only non-radioactive food during the 4 months of experiment. Cesium accumulation in muscle was higher than in any other organ, reaching concentration factors (CFs) of 5 (fresh weight basis). Cobalt, in contrast, was concentrated mostly in the liver, gut and skin and scales. Cobalt CF in muscle tissue was 8 x 10(-2), lower than any previously reported figure. Chromatographic analysis of the water at the beginning and end of the experiment showed that cobalt had been completely converted from 60CoCl2 to non-cationic forms, most probably through complexation with organic ligands, mediated by the intense microbial activity of the filter bed. This conversion apparently enhanced cobalt bioavailability since a second experiment performed with this aged seawater yielded CFs for muscle tissue higher by a factor of 2.5.