The effect of a "Nuisance" dust inhalation on lung clearance

For particles which show low solubility and/or slight biological effects a general threshold limit is applied in the occupational field, e.g. 6 mg/cubic meters (FRG) and 5 mg/cubic meters (USA). The test materials were titanium dioxide (rutil), PVC powder and iron powder with mass median aerodynamic diameters of 1.2, 1.3 and 5 micrometers. 60 female Fischer rats (F344) per concentration group were explosed nose only 5 hours/day, 5 days/week for 8 months. 1, 3 and 6 months after begin of exposure 8 animals of each group additionally inhaled a test aerosol of Fe-59 labelled ironoxide particles for 1 hour. 1, 3, 6 and 8 months after beginning of inhalation and 1 and 3 months after the end of inhalation 4 animals per group were sacrified and the lung burden was determined. The lung burden increased up to about 0.5, 1.5 and 4 mg Ti02 per lung for the 3.2, 8 and 20 mg/cubic meters concentration groups after 8 months of titanium dioxide inhalation. The long-term clearance half time for the an imals of the high TiO2 concentration increased significantly (about 20%) 3 and 6 months but not 1 month after beginning of inhalation. For the groups exposed to the low and middle TiO2 concentration no relevant difference to the control group was found at any time. The effect 2 months after end of 8 months inhalation was the same. With PVC and iron dust the study is not complete. The animals, which inhaled the high PVC concentration, had a significant deceleration of long-term clearance already 1 month after beginning of inhalation