Long-term lung clearance of 195Au-labeled teflon particles in humans

Ten healthy males inhaled monodisperse Teflon particles (geometric diameter 3.6 microns, aerodynamic diameter 5.3 microns) labeled with 195Au (half-life 183 days). The leakage of 195Au from the particles in vitro in water was less than 0.2% per year. Retention over the thorax was followed for about 900 days using two separate detector systems. One system consisted of four Ge detectors placed close to the front of the chest over the upper and lower regions of the lungs. The other system consisted of three NaI crystals placed in a ring around the thorax at some distance from the chest wall. Activities of 195Au in feces (24- or 48-h samples) could be measured as long as activities in the thorax could be measured. For the period 7-250 days, the half-times were similar 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 from measurements from about 250 days to about 900 days were 1750 days with the NaI detectors and 880 days with the Ge detectors. Clearance curves constructed from 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 earlier studies. No activity could be measured in the urine. The measurements with the two detector systems show that a translocation within the thoracic region occurred. This might be explained by transportation of 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.