Measurement and application of uranium isotopes for human and environmental monitoring.

An improved method is described utilizing extraction chromatography, anion exchange, and alpha spectroscopy for measurement of uranium isotopes in human and environmental surveillance studies. These methods provide a sensitivity of approximately 0.7 mBq per isotope per sample and are generally accurate within the precision of the measurements. The extraction chromatography methods greatly simplify separation of uranium from iron in silicate matrices and provide increased sample throughput and data quality for water, soil, and air filter samples. For bioassay samples, the coprecipitation/anion exchange/alpha spectrometric methods provide rapid throughput and sufficient sensitivity to meet new analytical performance standards in human monitoring studies. In addition, the 234U:238U data can be used as a fingerprint of natural vs. anthropogenic sources of uranium. For 1995 data from our laboratory, a large percentage (79-94% by matrix) of samples appear to be of natural 234U:238U isotopic composition. For all matrices, samples with higher uranium concentration generally have more depleted isotopic composition (smaller 234U:238U). A small percentage of soil (11%), air filter (3%), urine (3%), and water (3%) samples have depleted isotopic signatures at the 95% confidence interval, indicating anthropogenic contributions of uranium to these samples.