Metabolism and Dosimetry of 106Ru Inhaled As 106RuO4 by Beagle Dogs

Abstract

Ruthenium-106 is a fission product radionuclide present in large quantities in the nuclear fuel cycle. Humans have been exposed accidentally to vaporized '"Ru, probably ImRuO4, a highly reactive vapor form that can diffuse readily through porous barriers. This report provides metabolism and dosimetry data for inhaled ruthenium developed from studies in Beagle dogs that were exposed by inhalation to '"Ru04. Twenty-six dogs were exposed nose-only to '"Ru04 and sacrificed at times from 2 hr to 512 days after inhalation exposure. Ninety-nine percent of the initial body burden was retained with an effective half-time of 1.2 days, 0.7% with a half-time of 14 days and 0.3% with a half-time of 170 days. Initial deposition was primarily in the nasopharyngeal and tracheobronchial regions. Results for deposition and retention of '"Ru inhaled as '"Ru04 in dogs were similar to what has been observed for humans. The data for dogs were used to develop a model to predict potential radiation exposure patterns for humans after inhalation exposure to '"Ru04. The model indicates that for humans the nasopharyngal region, lower large intestine, and tracheobronchial epithelium would receive approx. 36, 13 and 10 times, respectively, the dose to 500 days after inhalation exposure to '"Ru04 that the lung would receive. The nasopharyngal region should be considered the critical region for inhalation exposures to '"Ru04.

ICRP Publication 137: Occupational Intakes of Radionuclides: Part 3

“…Assuming these values, dissolution parameter values fitted here (i.e. by the Task Group) for 106 RuO 4 inhaled by rats (with regional deposition of 99.8% in extrathoracic airways and 0.2% in the alveolar-interstitial region) were f r = 0.92, s r = 0.35 d –1 , and s s = 0.01 d –1 . (27) Snipes (1981) followed the biokinetics of 106 Ru for 512 d after inhalation of 106 RuO 4 by dogs. In a complementary experiment, the biokinetics of 106 Ru were followed for 5 d after ingestion of 106 RuO 2 by dogs; fractional absorption was estimated to be approximately 0.005.…”

“…(27) Snipes (1981) followed the biokinetics of 106 Ru for 512 d after inhalation of 106 RuO 4 by dogs. In a complementary experiment, the biokinetics of 106 Ru were followed for 5 d after ingestion of 106 RuO 2 by dogs; fractional absorption was estimated to be approximately 0.005.…”

“…Autoradiographs showed that ruthenium dispersion in the turbinates and lymph nodes was relatively uniform; only single tracks were observed with no indication of focal accumulation, supporting the view that the ruthenium was in a bound form rather than a particulate form. Based on the results of a study of 106 RuO 4 inhaled by dogs (Snipes, 1981), bound state parameter values for ruthenium of f b = 0.05 and s b = 0.1 d –1 were chosen here. (58) There is experimental evidence that ruthenium in soluble form deposited in the conducting airways is retained in a bound state. It is therefore assumed here that these bound state parameter values apply throughout the respiratory tract (ET 2 , BB, bb, and AI regions).…”

Retention and Dosimetry of 106Ru Inhaled Along With Inert Particles by Fischer-344 Rats

“…This '"Ru release appeared to have been as RuO,, but the deposition and retention patterns did not appear to be similar to what was observed in rats or Beagle dogs exposed to '"RuO,vapor (Ru79;Ru80;Sn81). Since the '"Ru was released into room air, it was likely to have mixed and interacted with pre-existing particles.…”

“…Inhaled ruthenium tetroxide deposits primarily in the upper respiratory tract and clears from the body relatively quickly via the gastrointestinal tract (Ru80;Sn81;We76). It delivers the highest radiation doses to the mucosa of the upper respiratory tract and large intestine (Ru80;Sn81). Ultrafine particles formed as condensation aerosols deposit more efficiently in the deep lung than micrometer-sized particles (Wo8 1).…”