Radiation Doses to Members of the U.S. Population from Ubiquitous Radionuclides in the Body: Part 3, Results, Variability, and Uncertainty

This paper is part three of a three-part series investigating annual effective doses to residents of the United States from intakes of ubiquitous radionuclides, including radionuclides occurring naturally, radionuclides whose concentrations are technologically enhanced, and anthropogenic radionuclides. The radionuclides of interest are the 238U series (14 nuclides), the actinium series (headed by 235U; 11 nuclides), and the 232Th series (11 nuclides); primordial radionuclides 87Rb and 40K; cosmogenic and fallout radionuclides 14C and 3H; and purely anthropogenic radionuclides 137Cs-137mBa, 129I and 90Sr-90Y. This series of papers explicitly excludes intakes from inhaling 222Rn, 220Rn, and their short-lived decay products; it also excludes intakes of radionuclides in occupational and medical settings. Part one reviewed, summarized, characterized, and grouped all published and some unpublished data for U.S. residents on ubiquitous radionuclide concentrations in tissues and organs. Part two described the methods used to organize the data collected in part one and segregate it into the ages and genders defined by the study, imputed missing values from the existing data, apportioned activity in bone, and imputed activity in hollow organ contents and the remainder of the body. This paper estimates equivalent doses to target tissues from source regions and maps target tissues to lists of tissues with International Commission on Radiation Protection (ICRP) tissue-weighting factors or to surrogate tissue regions when there is no direct match. Effective doses, using ICRP tissue-weighting factors recommended in 1977, 1990, and 2007, are then calculated, and an upper bound of variability of the effective dose is estimated by calculating the average coefficients of variation (CV), assuming all variance is due to variability. Most of the data were for adult males, whose average annual effective dose is estimated to be 337 (micro)Sv y-1 (CV = 0.65, geometric mean = 283 (micro)Sv y-1, geometric standard deviation sG = 1.81) using 2007 ICRP tissue-weighting factors. This result is between the National Council on Radiation Protection and Measurements 1987 estimate of 390 (micro)Sv y-1 (using 1977 wTs) and its 2009 estimate of 285 (micro)Sv y-1 (using 2007 wTs) and is higher than the United Nations Scientific Committee on the Effects of Atomic Radiation's 2000 estimate of 310 (micro)Sv y-1 (using 1990 wTs). The methods and software developed for this project are sufficiently detailed and sufficiently general to be usable with autopsy data from any or all countries.