| dc.description |
Groups of rats were exposed 6 h per day, 5 days per week for 12 weeks as follows: (1) control (filtered air); (2) TiO<sub>2</sub>-F (∼250 nm particle size); (3) TiO<sub>2</sub>-D (∼20 nm particle size); and (4) SiO<sub>2</sub> (cristobalite, 800 nm particle size). At the end of exposure, retained lung burdens were 6.62 and 5.22 mg for TiO<sub>2</sub>-F and TiO<sub>2</sub>-D, respectively, and 0.34 mg for SiO<sub>2</sub>. Inflammatory parameters in lung lavage fluid (cells, protein, enzymes) were highly increased in the SiO<sub>2</sub> and TiO<sub>2</sub>-D group and only moderately in the TiO<sub>2</sub>-F group. Long-term lung clearance of <sup>85</sup>Sr test particles, instilled or inhaled at the end of the dust exposures, was significantly prolonged in the SiO<sub>2</sub> and TiO<sub>2</sub>-D groups by factors of 28 and 8 and only moderately by a factor of 2 in the TiO<sub>2</sub>-F group compared to control. Pulmonary retention of TiO<sub>2</sub>-D particles was likewise highly increased whereas TiO<sub>2</sub>-F retention was less prolonged despite a slightly higher initial lung dust burden. We conclude, that inhalation of ultrafine particles of nuisance dusts can lead to increased pulmonary toxicity and that TLVs should be revised to take this into account. |
