Ecological half-life of Cs-137 in fish from a stream contaminated by nuclear reactor effluents

Radiocesium (Cs-137) concentrations were determined during 1974, 1981 and 1 998 for seven species of fish inhabiting a stream (Steel Creek) contaminate d by effluents from a nuclear reactor to examine the decline of this radion uclide in a natural ecosystem. Median Cs-137 concentrations were highest in Micropterus salmoides (largemouth bass) during each year of the investigat ion (1974 = 6.67 Bq g(-1) dry wt. of whole body; 1981 = 3.72 Bq g(-1) 1998 = 0.35 Bq g(-1)), but no patterns of differences were observed among Aphred oderus sayanus (pirate perch), Esox americanus (redfin pickerel), Lepomis a uritus (redbreast sunfish), L. gulosus (warmouth), L. punctatus (spotted su nfish), and Notropis cummingsae (dusky shiner). Results demonstrated a rapi d decline in Cs-137 within fish from Steel Creek during the 24-year period. For example, Cs-137 concentrations in all fish species declined significan tly among years, even after accounting for radioactive decay. The observed percent declines in Cs-137 concentrations of individual species were 3-4 ti mes greater between 1974 and 1981 compared to that expected by physical dec ay alone, and 2-3 times greater during 1981-1998. Ecological half-lives (EH Ls) of Cs-137 in fish ranged from 4.43 years in A. sayanus to 6.53 years in L. gulosus. The EHL for Cs-137 in all fish species combined was 5.54 years . Current levels of Cs-137 in fish from Steel Creek (1.16 Bq g(-1) dry wt, of whole body to below detection limits) indicate that the consumption of f ish from this ecosystem poses little risk to humans and sensitive wildlife species. These results demonstrate the importance of incorporating the conc ept of ecological half-life into determinations concerning the length and s everity of potential risks associated with radiocontaminants. (C) 2000 Else vier Science B.V. All rights reserved.