Measurement of Uranium Isotope Ratios in Keratinous Materials: A Noninvasive Bioassay for Special Nuclear Material

Hair, toenail, and fingernail are noninvasive, integrative biological monitors routinely used to assess mineral intake.(1-4) In this study, we demonstrate the feasibility of distinguishing between exposure to natural, depleted, and enriched U by measuring the U-235/U-238, U-234/U-238 and U-236/U-238 ratios in the hair, fingernails, and toenails of occupationally exposed workers and control volunteers. The exposure history of cases and controls to non-natural U was assessed through voluntary self-reporting using a simple questionnaire. The measured U isotope ratios and U concentration in the hair, toenail, and fingernail of cases were compared to a nonexposed control group. No difference was observed in the uranium concentration between the two groups. Significant differences between the cases and the control group were observed in the U-235/U-238 and U-236/U-238 isotope ratios but not the U-234/U-238. This is the first time that hair, fingernail, and toenail have been demonstrated to be sensitive to occupational exposure to enriched and depleted U, a result with significant implications for proliferation compliance monitoring.