Respiratory tract clearance of 14C-labeled diesel exhaust compounds associated with diesel particles or as a particle-free extract.

Radiolabeled diesel exhaust particles or dichloromethane extracts of these particles were intratracheally instilled (10 mg) into Fischer-344 rats and the clearance of 14C radioactivity was measured. Approximately 88% of the 14C radioactivity associated with the particles was soluble in dichloromethane. The clearance of 14C radioactivity from lungs occurred in two phases. The initial, more rapid phase of lung clearance of both particle-associated 14C radioactivity (Particle 14C) and extract-associated 14C radioactivity (Extract 14C) was very similar (t 1/2 approximately equal to 3 hr). However, the second phase of lung clearance of the remaining Particle 14C was much slower (t 1/2 approximately equal to 25 days) than the second phase of lung clearance of the Extract 14C (t 1/2 approximately equal to 2.9 days). Tracheal clearance rates of 14C radioactivity from both instillation studies were both rapid and similar (t 1/2 approximately equal to 10-12 hr). These results indicate that diesel engine exhaust particles reduce the lung clearance rate of the organic compounds associated with these particles. These studies also point to the possibility that the rate limiting step in the lung clearance of organic compounds associated with inhaled diesel exhaust particles may be the rate at which they dissociate from these particles in vivo. This is because the long-term clearance rate of the particle-associated organic compounds was shown here to be much slower than that of the same organic compounds in a particle-free form but not as slow as the lung clearance rate reported for diesel exhaust core particles (T.L. Chan, P.S. Lee, W.E. Hering, J. Appl. Toxicol. 1, 77-82 (1981].(ABSTRACT TRUNCATED AT 250 WORDS)