Abstract
Large quantities of radionuclides released by the Fukushima nuclear power plant accident entered terrestrial and marine ecosystems. The resulting radioactive contamination of large omnivorous wild mammals such as wild boar (Sus scrofa) and Asian black bear (Ursus thibetanus) varied greatly depending on location, season, and time after the accident. Quantitative modeling of how such factors influence radionuclide burdens in these species is important for enhancing current knowledge of chronic radionuclide exposure consequences in mammalian populations, and for assessing potential human risks from consumption of contaminated animal meat. Here we modeled the time course of radioactive cesium (134Cs + 137Cs) concentrations in boar and black bears from Fukushima Prefecture over ~ 7 years after the accident, using nonlinear robust and quantile regressions and mixed-effects modeling. To estimate predictive performance, models fitted to the full data set were compared with those fitted only to the first 3.5 years of data, and tested on the last 3.5 years of data. Ecological half-lives for radioactive cesium, and magnitudes and phase shifts for sinusoidal seasonal oscillations in cesium burdens, were estimated by each analysis method for each species. These results can improve the understanding and prediction of radionuclide concentrations in large mammals that inhabit radioactively contaminated areas.
Highlights
Large quantities of radionuclides released by the Fukushima nuclear power plant accident entered terrestrial and marine ecosystems
These findings suggest that the ecological half-life values for radioactive cesium in black bears were not too different from those in wild boar, considering the large uncertainties
The differences in best-fit Q values between the 75th and 25th quantiles were similar for both species: 1.565 for boar and 1.573 for black bears. These results suggest that the magnitude of variability of radioactive cesium burdens between individuals was similar in Fukushima boar and black bear populations
Summary
Large quantities of radionuclides released by the Fukushima nuclear power plant accident entered terrestrial and marine ecosystems. All biota on contaminated land experienced chronic exposure to various forms of ionizing radiation (e.g. γ, β and α) due to irradiation from external sources as well as internal exposure from incorporation of radionuclides into the body This situation created interactions between positive and negative factors, where new habitat and resources that become available for wildlife due to reduction of human activities generated opportunities for population growth[5,6], whereas detrimental effects of radiation (e.g. impaired reproduction, genomic instability, elevated mutation rates, carcinogenesis) could cause decreased abundance or extinction[7,8]. The wild boar (Sus scrofa) is an important example of a large mammal that is useful to study in radioactively contaminated lands This widely distributed omnivorous animal is native to the areas of Europe and Asia contaminated by both the Chernobyl and Fukushima accidents. Radionuclide concentrations were measured in many boar individuals killed by these hunting programs, which provided large amounts of data on radionuclide incorporation in this species
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