Deposition and clearance of inhaled diesel exhaust particles in the respiratory tract of Fischer rats.

The fate of inhaled diesel particles was determined in male Fischer 344 rats using radioactive tracers of 131Ba and 14C. Test animals were exposed in a 'nose-only' inhalation chamber for 40-45 min to diluted diesel exhaust generated from diesel engines burning type 2D diesel fuel containing either 131Ba labelled barium dodecylbenzene sulfonate or 14C labelled n-hexadecane. Immediately after exposure, the deposition efficiency of inhaled diesel particles in the respiratory tract was determined to be 15 +/- 6% by external gamma counting of 131Ba and 17 +/- 2% by liquid scintillation counting of 14C in the lung tissue samples. Elimination of the particles was observed by measuring the 131Ba activity in which 40% of the initial deposition was excreted in the feces via the GI tract in 4 days. The long-term retention was determined with the 14C tag in the insoluble 'core' of the diesel particles. Two distinct phases of clearance were evident in the experimental data collected up to 105 days. Clearance half-times of 1 day and 62 days were found for mucociliary and alveolar clearance, respectively. A small fraction of the particles, about 6% of the initial deposition, was found in the mediastinal lymph nodes after 28 days. This demonstrated that the lymphatic system was also involved in the removal of diesel particles from the pulmonary airways.