Paper ALIMENTARY TRACT ABSORPTION (f, VALUES) FOR RADIONUCLIDES IN LOCAL AND REGIONAL FALLOUT FROM NUCLEAR TESTS Shawki A. Ibrahim,* Steven L. Simon,’ André Bouville,’ Dunstana Melo,’ and Harold L. Beck* located in equatorial waters in the Pacific. During roughly the same period (1951-1958), the U.S. also conducted 119 nuclear tests at the Nevada Test Site Abstract—This paper presents gastrointestinal absorption fractions (f, values) for estimating internal doses from local and regional fallout radionuclides due to nuclear tests. The choice of f, values are based on specific circumstances of weaponstest conditions and a review of reported f, values for elements in different physical and chemical states. Special attention is given to fallout from nuclear tests conducted at the Marshall Islands. We makea distinction between the f, values for intakes of radioactive materials immediately after deposition (acute intakes) and intakes that occur in the course of months and years after deposition, following incorporation into terrestrial and aquatic foodstuffs (chronic intakes). Multiple f, values for different circumstances where persons are exposed to radioactive fallout (e.g., local vs. regional fallout and coral vs. continental tests) are presented when supportive information is available. In somecases, our selected f, values are similar to those adopted by the International Commission on Radiological Protection (ICRP) (e.g., iodine and most actinides). However, f, values for cesium and strontium derived from urine bioassay data of the Marshallese population are notably lower than the generic f, values recommended by ICRP, particularly for acute intakes from local fallout (0.4 and 0.05 for Cs andSr, respectively). The f, values presented here form the first complete set of values relevant to realistic dose assessments for exposure to local or regional radioactive fallout. Health Phys. 99(2):233-251; 2010 (NTS) (U.S. DOE 1988). All together, over 500 atmo- spheric nuclear weaponstests took place at varioussites around the world from 1945 to 1980 (Beck and Bennett 2002). These tests resulted in the deposition of significant quantities of radioactive debris to the local, regional and global environments resulting in human health consequences that have ensued over the decades since (Simon 1997; Simon et al. 2006). Since nuclear testing ceased, a number of dose reconstruction assessments have been conductedfor specific populations (Becketal. 2006). Depending on the level of detail considered and the degree of realism sought in assessment calculations, dose estimation parameters may require evaluation and interpretation based on the available historical data for each assessment. The assessment of internal dose from the ingestion of radionuclides for the general public requires knowledge on the fraction of the radioactive material absorbed from the alimentary tract to blood, using a model parameter usually termed the “f, value.” Literature information for f, values vary significantly depending on the origin of the measurements or assumptions made about the chemical and physical properties of the ingested form in addition to other biological and environmental factors. Metabolic investigations on radionuclide uptake using soluble compoundsused in laboratories and some industries often produced higher f, values compared to other less soluble forms in both animal and humanstudies. Typically, the International Commission on Radiological Protection (ICRP) and other radiation protection organizations tend to adopt conservative f, values to ensure a margin of safety for protection of humans exposedto a wide range of radionuclide forms in the workplace and to members of the public. The Key words: fallout; Marshall Islands; radionuclide; nuclear weapons INTRODUCTION From 1946 through 1958, 66 nuclear weaponstests were conducted by the U.S. in or near the Marshall Islands * Department of Environmental and Radiological Health Sci- ences, Colorado State University, Fort Collins, CO; * Division of Cancer Epidemiology and Genetics, National Cancer Institute, Na- tional Institutes of Health, Bethesda, MD; * New York City, NY. For correspondence contact: Steven L. Simon, National Cancer Institute, National Institutes of Health, 6120 Executive Blvd., Bethesda, MD 20892, or email at ssimon@mail.nih.gov. (Manuscript accepted 5 June 2009) 0017-9078/10/0 Copyright © 2010 Health Physics Society use of generic f, values, however, may not be desir- able in dose reconstructions, particularly where “best DOI: 10.1097/HP.0b013e3 18 1b186ff 233