USTUR Researcher Studies Uranium Hexafluoride Inhalation

USTUR researcher, Maia Avtandilashvili, published a study on the long-term retention of uranium hexafluoride in a USTUR donor. Registrant 1031 was exposed to UF₆ during an explosion, and died decades after the accident.

Tissues collected at autopsy were acid digested, and the resulting acid solutions were analyzed using inductively coupled mass spectrometry (ICP-MS). ICP-MS not only quantifies the amount of uranium present in a sample; it provides the ²³⁵U/²³⁸U and ²³⁴U/²³⁸U isotopic ratios. These ratios revealed that the Registrant was exposed to slightly-enriched uranium. This was surprising given that he was thought to have been exposed to natural uranium. The tissue analysis also found that enriched uranium remained in the Registrant’s lungs and lymph nodes (plot at right) at the time of death, and there was a higher concentration of uranium in his lymph nodes than in his lungs at the time of death. Both of these observations are inconsistent with the assumption that he inhaled pure ‘soluble’ (Type F) material, as is recommended for UF₆.

Dr. Avtandilashvili estimated the uranium intake by simultaneously fitting urinalysis results and the amount of uranium that remained in major target organs (lungs, skeleton, liver, kidneys) at the time of death. She accomplished this using the Integrated Modules for Bioassay Analysis (IMBA) Professional Plus software. Both conventional and Bayesian statistical methods were used to estimate the intake. The conventional maximum likelihood analysis resulted in an estimated uranium intake of 79 mg, consisting of 86% soluble and 14% insoluble material. The Bayesian analysis resulted in an estimated intake of 160 mg, and lung dissolution parameters were consistent with an inhalation of soluble uranium that had a small but significant insoluble component.

This work was published in the Journal of Radiological Protection in 2015, and was presented at both the 2013 Health Effects of Incorporated Radionuclides (HEIR) conference and the 2015 Health Physics Society (HPS) meeting.

Journal of Radiological Protection paper
HEIR presentation
HPS Presentation

References

1. ICRP. Human respiratory tract model for radiological protection. Oxford: Elsevier Science; ICRP Publication 66; Ann ICRP 24 (1-3); 1994.
2. ICRP. Dose coefficients for intakes of radionuclides by workers. Oxford: Elsevier Science; ICRP Publication 68; Ann. ICRP 24 (4); 1994.