LONG-TERM LUNG CLEARANCE OF AU-195-LABELED TEFLON PARTICLES IN HUMANS

Ten healthy males inhaled monodisperse Teflon particles (geometric dia meter 3.6 mu m, aerodynamic diameter 5.3 mu m) labeled with Au-195 (ha lf-life 183 days). The leakage of Au-195 from the particles in vitro i n water was less than 0.2% per year. Retention over the thorax was fol lowed for about 900 days using two separate detector systems. One syst em consisted of four Ge detectors placed close to the front of the che st over the upper and lower regions of the lungs. The other system con sisted of three NaI crystals placed in a ring around the thorax at som e distance from the chest wall. Activities of Au-195 in feces (24- or 48-h samples) could be measured as long as activities in the thorax co uld be measured. For the period 7-250 days, the half-times were simila r for the two detectors, on the average 740 days for the NaI detectors and 680 days for the Ge detectors. The average half-times estimated f rom measurements from about 250 days to about 900 days were 1750 days with the NaI detectors and 880 days with the Ge detectors. Clearance c urves constructed front measurements from feces agreed very well with clearance measured with the NaI detectors. The excretion via feces was well described by a power function with days after exposure as base. This total clearance from the thoracic region, was slower than in earl ier studies. No activity could be measured in the urine. The measureme nts with the two detector systems show that a translocation within the thoracic region occurred. This might be explained by transportation o f particles from the lung parenchyma to the regional lymph nodes. The accumulation of particles in the regional lymph nodes was tentatively calculated on the basis of that assumption.