A survey of uranium and thorium background levels in water, urine, and hair and determination of uranium enrichments by ICP-MS

Sandia National Laboratories collects bioassay samples to monitor individuals for possible exposure to uranium and thorium as part of ongoing medical surveillance of employees. The current analytical methods involve separation chemistry and alpha-spectrometry for isotopic measurements or kinetic phosphorescence analysis for total uranium. There are several areas where this monitoring can be improved (e.g., analysis times and accurate isotopic ratio measurements). In addition, in case of accidents or exposure to people who are not routinely monitored, the optimum window for collecting bioassay samples may be missed. An example of this scenario is the recent concern over the exposure of civilians to depleted uranium from military ammunition in Kosovo and Kuwait. For these cases, hair may be an alternative bioassay. Analytical procedures utilizing an inductively coupled plasma mass spectrometer (ICP-MS) have been developed that have simplified sample processing and improved the isotopic ratio measurements. The focus of this study is to survey the background levels for U-235, U-236, U-238, and Th-232 isotopes in hair, urine, and drinking water which could be used to determine action levels for follow-up monitoring. In addition, variations of U-238 to U-235 mass ratio for the background samples are measured. The analytical procedures, achieved detection limits, observed background distributions, and the results of uranium isotope ratio tests are presented.