Abstract
ABSTRACT
In separate inhalation investigations, rodents (Wistar rats, Fischer-344 rats, Syrian golden hamsters, NMRI and C57BL mice) were exposed to various dusts such as test toner (polymer pigmented with carbon black), polyvinyl chloride, carbon black, diesel exhaust and two crystalline forms of titanium dioxide (anatase and rutile). The animals inhaled various concentrations (0.8 to 64 mg/m3) of these particles for up to 2 years.
Alveolar clearance retardation was detectable above a retained pulmonary burden of 0.5 mg per rat lung, and a substantial decrease in the clearance rate (about a factor of 6) was observed following heavy dust loading, exceeding 10 mg dust per rat lung. Above a threshold lung burden, signs of lung overloading persisted 15 months after cessation of exposure in F-344 rats. Retardation of alveolar clearance was also observed in hamsters, commencing at higher lung burdens (normalized to lung weight) than in rats. At high dust exposure levels, persistent pulmonary inflammation was present in both species. In rats the concentration of lavagable cells remained constant, with decreased macrophages and increased polymorphonuclear neutrophils (PMN) noted, while in hamsters, the cell count increased substantially in both macrophages and PMN's. A retarded particle clearance was also observed in mice at a lung burden above 1 mg/lung.
These results, accompanied by published accounts, indicate that the lung overloading phenomenon is noted among a variety of species and materials. It is generally observed upon exceeding a threshold lung burden with particles of low solubility and low acute toxicity for considerable periods of time.
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