Fate of inhaled fly ash in hamsters

To determine pulmonary deposition, translocation, and clearance of inhaled fly ash, hamsters received a single 95-min nose-only exposure to neutron-activated fly ash. Over a period of 99 days postexposure, the hamsters were sacrificed in groups of six animals. Lungs, liver, kidneys, decapitated and skinned carcass, pelt, head, gastrointestinal tract, urine, and feces were collected for analysis of the radionuclide tracers ⁴⁶Sc, ⁵⁹Fe, and ⁶⁰Co by γ-ray spectrometry. The fly ash burden estimates as determined by the radionuclides ⁴⁶Sc and ⁵⁹Fe are in good agreement for the majority of samples analyzed. Such close agreement indicates fly ash particulate levels in the lungs, carcass, head, pelt, GI tract, and feces rather than leached radionuclides. Relative to the ⁴⁶Sc and ⁵⁹Fe-based estimates, fly ash deposition estimates obtained with the isotope ⁶⁰Co were appreciably lower for the lungs and appreciably higher for one or more sacrifice times for carcass, liver, head, pelt, and urine samples. This indicates that ⁶⁰Co (and thus the element cobalt) selectively leached from fly ash deposited in the deep lung, translocated to other sites, and was excreted in the urine. An estimated average of 63 μg fly ash, or 2 to 3% of the inhaled fly ash, was initially retained in the respiratory tract. The estimated biological half-times of the fly ash were 2.6 and 34.5 days, probably for the airways and for the deep lung, respectively. After 99 days, the mean lung burden had decreased to about 10% of its initial value.