RADIATION DOSES TO MEMBERS OF THE U.S. POPULATION FROM UBIQUITOUS RADIONUCLIDES IN THE BODY: PART 3, RESULTS, VARIABILITY, AND UNCERTAINTY

Abstract

This paper is Part 3 of a three-part series investigating effective dose rates 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 (238)U series (14 nuclides), the actinium series (headed by (235)U; 11 nuclides), and the (232)Th series (11 nuclides); primordial radionuclides (87)Rb and (40)K; cosmogenic and fallout radionuclides (14)C and (3)H; and purely anthropogenic radionuclides (137)Cs-(137m)Ba, (129)I and (90)Sr-(90)Y. This series of papers explicitly excludes intakes from inhaling (222)Rn, (220)Rn, and their short-lived decay products; it also excludes intakes of radionuclides in occupational and medical settings. In this work, it is assumed that instantaneous dose rates in target organs are proportional to steady-state radionuclide concentrations in source regions. Part 1 reviewed, summarized, characterized, and grouped all published and some unpublished data for U.S. residents on ubiquitous radionuclide concentrations in tissues and organs. Part 2 described the methods used to organize the data collected in Part 1 and segregate it into the ages and genders defined by the study, including 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 dose rates 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 dose rates using ICRP tissue-weighting factors recommended in 1977, 1990, and 2007, are then calculated, and an upper bound of variability of the effective dose rate 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 effective dose rate is estimated to be 337 μSv y(-1) (CV = 0.65, geometric mean = 283 μSv y(-1), geometric standard deviation s(G) = 1.81) using 2007 ICRP tissue-weighting factors. This result is between the National Council on Radiation Protection and Measurements' 1987 estimate of 390 μSv y(-1) (using 1977 w(T)s) and its 2009 estimate of 285 μSv y(-1) (using 2007 w(T)s) and is higher than the United Nations Scientific Committee on the Effects of Atomic Radiation's 2000 estimate of 310 μSv y(-1) (using 1990 w(T)s). 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.