Retention and dosimetry of 106Ru inhaled along with inert particles by Fischer-344 rats

This study was done to provide data useful for predicting the deposition, retention and radiation dose patterns for humans who might be exposed to an aerosol containing 106RuO4 and respirable particles. Ruthenium-106 tetroxide was introduced into air containing inert particles. The inert particles were monodisperse. 0.69 micrometer diameter fused aluminosilicate and very small residue particles from nebulized droplets. A complex exposure atmosphere resulted. In addition to condensation of 106RuO4 on pre-existing particles, self-nucleation occurred, presumably resulting from the formation of RuO2. It appears there was a significant amount of 106RuO4 present in the inhalation exposure system. When a group of Fischer-344 rats inhaled this exposure atmosphere, approx. 12% of the initial body burden reached the pulmonary region of the respiratory tract. Of the remaining 88% of the initial burden, 60% was deposited in the upper respiratory tract, 10% in the tracheobronchial region and 18% was external contamination, primarily on the nares and head skin. Most of the initial body burden was cleared via the gastrointestinal system and excreted via feces. Clearance of 106Ru from the pulmonary region had an effective half-time of approx. 30 days and was predominantly by dissolution. Relative radiation doses accumulated to 100 days after inhalation exposure, normalized to a lung dose of 1.0, were nasopharyngeal mucosa, 11; trachea and larynx, 5; lower large intestine, 5; upper large intestine, 2; liver, 0.9; and kidneys, 0.9. Other tissues and organs received lesser relative doses. Comparable results are predicted for man inhaling a similar exposure atmosphere, which could be encountered under certain circumstances in nuclear industry operations.