It has been determined that humans have always contained a baseline level of naturally occurring plutonium (Pu-239 and Pu-244) and fallout plutonium has contributed some plutonium to these body burdens. Total levels, however, are typically low and range from 0 to 120 mBq/ kg fresh weight of tissues (measured as Pu-239/Pu-240), depending upon the population investigated and the specific tissue analyzed. At measured levels, incidence of bone tumors is expected to be extremely low and is estimated to increase by 2 in 100 000 cases per 50 years if tissue levels were to increase by 200 times the current Pu-239 levels in humans. Furthermore, from an epide-miological point of view, links between human exposure to plutonium and human cancers at the levels measured are often confounded by factors such as cigarette smoking. Investigations into the potential for increased toxicity caused by eating contaminated marine organisms have resulted in low risk estimates because of the low level of plutonium present in the organism's tissue and the low bioavailability of plutonium when ingested.
See also: Adsorption; Atmospheric Deposition; Bioaccumulation; Bioavailability; Ecological Risk Assessment; Ecotoxicology: The Focal Topics; Ecotoxicology: The History and Present Directions; Environmental and Biospheric Impacts of Nuclear War; Environmental Impact Assessment and Application - Part 1; Environmental Impact Assessment and Application - Part 2; Exposure and Exposure Assessment; Mutagenesis; Physical Transport Processes in Ecology: Advection, Diffusion, and Dispersion; Radioactivity; Radionuclides: Their Biogeochemical Cycles and the Impacts on the Biosphere; Risk Management Safety Factor; Sediments: Setting, Transport, Mineralization, and Modeling; Transport in Porous Media; Transport over Membranes; Uranium.
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