Twelve healthy non-smoking male volunteers inhaled monodisperse 1 and 4 μm diameter fused aluminosilicate particles labelled with strontium-85 and yttrium-88, respectively. Retention was followed for at least a year (372-533 days). Approximately 7% of the initial lung deposit of 1 μm particles and 40% of that of the 4 μm particles were associated with a distinct rapid clearance phase. These figures correspond closely to the calculated tracheo-bronchial deposits, indicating insignificant rapid pulmonary clearance. Retention of the remaining material (R(t)) generally followed a two-component exponential function, the phases having half-times of the order of tens of days and several hundred days, respectively. At 350 days after inhalation, R(t) averaged 46 ± 11% (x ± SD) for the 1 μm particles and 55 ± 11% for the 4 μm particles. Retention of the 1 μm particles by each subject was correlated with that of 4 μm particles. Estimated lung dissolution rates based on urinary excretion were 7 × 10-4 and 2 × 10-4 per day for the 1 and 4 μm particles, respectively. The estimated rate of clearance of particles from the pulmonary region to the gastro-intestinal tract fell from an initial value of 4 × 10-3 per day to about 1 × 10-3 per day at and beyond 200 days after inhalation.
Bibliographical noteFunding Information:
Technical assistance was provided by Mrs A. J. Murfitt and Mrs S. Quant. Mr S. F. Barry carried out the multiple linear regression analysis. Medical examinations and lung function tests were carried out by Dr J. C. Evans, Medical Advisor, AERE Harwell. The work was partially supported by the CEC under Contracts 182-BIO-UK and BIO-D-489-UK.