Determination of pulmonary deposition, translocation and clearance using neutron activation techniques

Neutron activation provides a sensitive technique to estimate pulmonary deposition, translocation and clearance of inhaled particles. Talc and fly ash were irradiated in an integrated neutron flux of or approximately 10(16) n/cm2. Radionuclides were induced by (n, gamma) reactions on major an minor elements in the dusts. Hamsters received a single nose-only exposure to the dusts. Groups of 4 to 6 animals were than serially sacrificed at intervals up to 4 months postexposure. Lungs, other tissues of interest and excreta were collected for gamma-ray analysis. Limit of detection for the isotopes 60Co or 46Sc was or approximately 0.1 dpm, facilitating detection of 10(-11) gram quantities of these elements. Analyzing for more than one radionuclide and comparing their ratios in the bulk dust to those in the tissue or excreta indicated whether a radionuclide leached from the particle or represented particles in the tissue samples. Six to 8% of the inhaled talc were deposited in the alveoli; its biological half-life in the lung was 7 to 10 days. Alveolar clearance was essentially complete 4 months postexposure. No translocation of talc to liver, kidneys, ovaries of other parts of the body was found. Picogram quantities of 60Co found in the urine probably represented leached 60Co, absorbed in the gastrointestinal tract. Two to 3% of the inhaled fly ash were initially retained in the respiratory tract. Estimated biological half-lives were 3 and 35 days for airways and alveoli, respectively. After 99 days the mean lung burden had decreased to about 10% of its initial value; extrapolation suggests near-complete pulmonary clearance at about 200 days postexposure.