Bioaccumulation of 137Cs in anuran larvae utilizing a contaminated effluent canal on the U.S. Department of Energy's Savannah River Site

Abstract

As a result of activities such as nuclear weapons testing, nuclear power generation and waste disposal, and nuclear accidents, radiocesium (137Cs) is a widely distributed radio-contaminant of concern that readily accumulates in exposed wildlife. Although bioaccumulation of 137Cs is an important factor for understanding its fate within the environment, there are currently limited data available on bioaccumulation patterns of 137Cs in amphibians, despite their widespread distribution and potential to transport contaminants between aquatic and terrestrial ecosystems. Therefore, the objective of this study was to determine the amount of time necessary for anuran larvae experimentally placed in a contaminated system to reach a steady-state whole-body 137Cs concentration, and to determine the threshold at which that steady-state 137Cs concentration occurred for tadpoles within our study system. By restricting uncontaminated bullfrog (Lithobates catesbeianus) larvae to three experimental enclosures located along a137Cs contaminated effluent canal on the U.S. Department of Energy's Savannah River Site, we modeled 137Cs uptake through time using the von Bertalanffy modification of the Richards Model. The results of our modified Richards Model indicate that bullfrog tadpoles achieved steady-state 137Cs concentrations of 3.68–4.34 Bq/g137Cs dry whole-body weight after 11.63–15.50 days of exposure among sampling sites, with an average of 3.94 Bq/g after 14.07 days exposure. Radiocesium accumulation in bullfrog tadpoles was more rapid than that reported for other biota studied from other contaminated systems, likely due to incidental ingestion of sediments and a diet consisting of periphyton and other items that accumulate high levels of 137Cs. Given their rapid accumulation of 137Cs and inability to leave aquatic environments prior to metamorphosis, our data suggest amphibian larvae may be useful indicators for monitoring 137Cs distributions and bioavailability within aquatic systems.