Clearance and retention of inhaled diesel exhaust particles, carbon black, and titanium dioxide in rats at lung overload conditions

Female Wistar rats were exposed 19 hrs/day, 5 days/wk for 24 months to diesel exhaust at particle concentrations of 0.8, 2.5 and 7.5 mg/cubicmetre, to 12 mg/cubicmetre of carbon black and to 10 mg/cubicmetre of TiO2; satellite groups of the latter 3 groups were removed from exposure after 18 months and inhaled clean air for a period of 6 months. Alveolar clearance of 2 superimposed tracer aerosols (AMAD: 0.3 and 3.5 mym) and the retention of inhaled materials in lungs and lung-associated lymph nodes were measured. After 18 months, lung wet weight in the 3 high exposure groups was increased 3-5-fold compared to controls. The retained masses of the test materials amounted to about 50 mg per lung and 8 mg in the lung-associated lymph nodes (LALN) in the 3 high exposure groups after 18 months. Alveolar clearance of the 0.3 mym particles was retared significantly during the study. The results indicate severe dust overload conditions.