Systemic absorption of americium from nasal airways of dogs exposed intranasally to nitrate and oxide aerosols

This study quantitated the amount of 241Am that was systemically absorbed after deposition on the nasal airway surfaces. Four dogs each were exposed to one of two polydisperse aerosols, AmO2 Or Am(NO3). Only the nasal airways were exposed using an isolation technique developed by Whaley et. in which aerosol was brought into the nasal airways via the nares and exhausted through the mouth in a closed system. To allow for correction of the amount of 241Am absorbed into blood that was due to clearance of aerosol from the nasal airways, swallowing and subsequent absorption through the gut, a second isotope, 243Am, was administered intragastrically in the same physicochemical form as 241Am. Each animal was sacrificed 24 h after exposure. Based on preliminary results obtained by gamma counting the biological samples, the fractional absorption of Am to blood from aerosol deposited on the nasal airway surfaces was 0.014 for the nitrate exposed group and 0.0016 for the oxide-exposed group. These values are 7- and 60-fold less than the value of 0.10 assumed for Am as a ICRP class W compound. (author)