Uptake and excretion of 60Co by black bullheads Ictalurus melas (Rafinesque)

Black bullheads were able to accumulate 60Co from water. During uptake the gills contained from 19% to 30% of the whole-body 60Co activity. After 3 days of 60Co uptake the flesh accounted for 16% of the total activity. Fish that were dosed in a single feeding lost 95.5% of the initial activity in one day of excretion whereas fish that were exposed in 60Co-dosed water lost 28% of the initial activity during the first day of excretion. Elimination of 60Co after intake from water or from food occurred in three components. The initial rapid loss of activity after uptake from food had a biological half-life of 1.5 days, compared to 3.4 days for the initial component after uptake via water. The intermediate components had biological half-lives of 35 and 40.5 days, respectively, after water uptake and after food uptake. The third components in both cases had long, undetermined biological half-lives. Radiocobalt and stable cobalt analyses showed that the blood and blood-rich organs, particularly the kidney, were principal sites of cobalt concentration.