Ecological half-life of radiocesium in white-tailed deer on the Department of Energy's Savannah River Site: What can a half century of field monitoring tell us?

Abstract

This paper estimates the ¹³⁷Cs ecological half-life of white-tailed deer inhabiting the Department of Energy's Savannah River Site (SRS) based on sex and age using data collected over a 51-year time-period. With a physical half-life of 30.2 yr, the biological half-life for the deer herd is considerably shorter because of the isotope's biochemical mimicry of K+ inside the body. Leveraging this long-term dataset and robust sample size, we compared the long-term half-century estimates to shorter decadal increments. The simple exponential decay model for the entire 51-year sampling period predicted an ecological half-life of 23.15 years. When breaking the sample data into decadal increments ¹³⁷Cs body burden had complex temporal dynamics with predicted half-lives ranging from 9.25 to 32.33 years. Exponential decay for the entire 51-year sampling period for models evaluated by sex, age, sex*age to determine how these variables influence the predictability in the mean depuration rate, the ecological half-lives were between 21 and 23 years for all permutations, except for fawns that had a half-life no different than the physical half-life of the isotope itself. Differential habitat use and competition most likely explains why both yearling and adult females consistently had higher body burdens than males over the 51-year time period, showing how dynamic this radioisotope is in biological systems. This study is one of the most robust long-term datasets in the world (n = 42,412) that is specifically focused on monitoring the uptake and depuration of ¹³⁷Cs in a wild species.

Keywords: (137)Cs; Biological half-life; Deer; Department of Energy; Ecological half-life; Savannah River Site.