M11 AM Using Stable Isotopes in Ecotoxicology
Monday, 14 November 2005: 8:00 AM - 11:40 AM in 343-344

(PET-1117-834808) Stable isotopes provide evidence for the biomagnification of radiocesium in a contaminated aquatic environment.

Peters, E¹, Jagoe, C², Unrine, J², Romanek, C², Rosales, Y¹, Batts, R¹, Brant, H², ¹ Chicago State University, Chicago, IL, USA² Savannah River Ecology Lab, Aiken, SC, USA

ABSTRACT- Anthropogenic radionuclides can be released to the environment during nuclear power generation or through the production, testing or use of nuclear weapons. Evaluation of risks associated with radionuclide contamination requires understanding their movement, accumulation, and retention in the environment. Among fission products, radiocesium (especially the longer-lived ¹³⁷Cs), is important because it is a biochemical analog of potassium and can accumulate in the soft tissues of organisms. Unlike other fission products (and most metals), radiocesium appears to biomagnify. This observation is controversial because, while some studies have found biomagnification of radiocesium, others have not, or have even reported decreased concentrations at higher trophic positions. The available data suggest that the potential for biomagnification varies among environments and may be related to trophic complexity. However, few prior studies of radiocesium have used objective, unambiguous methods to quantify trophic relationships or differences in diet among the organisms sampled. To investigate biomagnification of ¹³⁷Cs, we employed stable isotope ratios of C and N as indicators of trophic position and carbon source in biota from Pond B on the Savannah River Site, a nuclear production facility in South Carolina, USA, that was contaminated with ¹³⁷Cs in the 1960s.We collected plants, aquatic invertebrates and fishes from Pond B over a two-year period, and measured ¹³⁷Cs concentrations, ¹⁵N, and ¹³C. Aquatic plants contained relatively low concentrations of ¹³⁷Cs. Among fishes, ¹³⁷Cs concentrations increased by a factor of 4.5 (95% C.I. 3.5 to 5.9) per trophic level, assuming a shift in ¹⁵N of about 3.5‰ per trophic level. The best regression model of ¹³⁷Cs concentration (R² = 0.46) incorporated both ¹⁵N and ¹³C as predictors. As assimilation efficiencies of ¹³⁷Cs and K are comparable, both the bioaccumulation and biomagnification of ¹³⁷Cs likely result from slower whole-body elimination rates of ¹³⁷Cs than for K.

Key words: radiocesium, biomagnification, trophic transfer, stable isotopes