Assessment Of Physico-Chemical And Biokinetic Properties Of Uranium Peroxide Hydrate UO4

Abstract

Comprehensive studies on the radiotoxicological risk of an intermediate compound UO4, which is not specified in ICRP Recommendations, were motivated by its increased use in the nuclear fuel cycle and the lack of information such as physico-chemical and biokinetic properties. The aim of this work was to give an experimental basis for assessing the appropriate limits on intake for workers exposed to UO4 and to provide guidance for the interpretation of personal monitoring data. Particle size measurement of the UO4 dust indicated a geometric diameter D of 0.5 microm, which corresponds to an activity median aerodynamic diameter (AMAD) of 1.1 microm. In vitro experiments conducted in culture medium showed that UO4 is a soluble compound with 66.2% dissolved in 1.9 d and 33.8% in 78 d. Results of dissolution obtained with macrophages showed a significant decrease of 50% at 1 d in terms of solubility. Biokinetic data in the rat obtained from two in vivo studies involving intratracheal instillation in rats indicated half-times in the lung of 0.5 d (96.6%) and 27 d (3.4%) for an initial lung deposit (ILD) of 195 microg, and 1.2 d (90.3%) and 38 d (9.7%) for an ILD of 7.6 microg. Absorption parameters to blood as defined in the ICRP Publication 66 human respiratory tract model were calculated with the specific software GIGAFIT and led to the rapid fraction fr (0.800 to 0.873), the rapid rate sr (0.525 to 0.928 d(-1)), and the slow rate ss (1.57 x 10(-2) to 2.42 x 10(-3) d(-1)). Effective dose coefficients by inhalation for this UO4 compound using the in vivo experimental results were calculated to be between 0.52 and 0.70 x 10(-6) Sv Bq(-1). Comparison of these values with effective dose coefficients defined in ICRP Publication 68 for workers showed that UO4 could be considered as a fast soluble compound of Type F.

Distribution and Genotoxic Effects After Successive Exposure to Different Uranium Oxide Particles Inhaled by Rats

“…In our study, the UO 4 biokinetics after single UO 4 inhalation (AcUO4 group) agreed with previous UO 4 instillation studies (Ansoborlo et al, 1998;Houpert et al, 1999;Chazel et al, 2001). A rapid clearance of U from lungs resulted partly from its translocation to the blood, and U was subsequently excreted in the urine.…”

“…A rapid clearance of U from lungs resulted partly from its translocation to the blood, and U was subsequently excreted in the urine. Both our inhalation study and a previous instillation study, with comparable lung deposit (around 200µg), showed a UO 4 peak in kidneys of about 15% of the intake, at 3 days postexposure (Ansoborlo et al, 1998). The previous UO 2 exposures apparently modify the early UO 4 biokinetics in kidneys without modifying the day of appearance of the UO 4 peak in kidneys.…”

“…UO 2 is a subproduct of the enrichment process of U for radioactive fuel, while UO 4 is a subproduct of the reprocess steps of fuel after its use in nuclear reactor. UO 2 is considered by ICRP to be a very insoluble compound (absorption type S), while UO 4 is much more soluble (Ansoborlo et al, 1998) and considered as absorption type F. Due to this difference in solubility, their behavior and biokinetics in the organism are very different, with a long biological half-time for UO 2 staying in lungs and a rapid elimination of UO 4 from the lungs to the blood. The UO 2 characteristics were: insoluble depleted U; specific alpha activity = 13.10 3 Bq g −1 ; isotopic composition by mass: 238 U = 99.75%, 235 U = 0.24%, 234 U = 0.001%, 236 U < 0.0003%, 232 U < 0.00001%.…”

In vitro dissolution studies of uranium bearing material in simulated lung fluid

“…Ansoborlo et al (1998a) used two different media (Gamble's solution and culture medium) for the solubility tests. The dissolution rate for the slow fraction of the material in Gamble's solution (an alternative to simulated lung fluid) was lower by a factor of 30.…”

An automatic video instillator for intratracheal instillation in the rat

“…1 For pulmonary toxicity studies, specialized equipment that includes aerosol generators, airflow monitoring instruments, exposure chambers, exhaust systems and often analytical chemical support is required in order to deliver known amounts of the test compound into the lungs. Consequently, the need for this equipment increases the cost and technical complexity of such studies.…”