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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 meter (FRG) and 5 mg/cubic meter (USA). In this study the effect on lung retention and lung clearance of three typical "inert" dusts, titanium dioxide (rutil), PVC powder and iron powder was determined. Female Fischer rats (F344) were exposed nose-only 5 hours/day, 5 days/week at aerosol concentrations of 3.2, 8 and 20 mg/cubic meter up to 8 months. 1, 3 and 6 months after beginning of exposure 8 animals of each group inhaled additionally a test aerosol of Fe-59 labelled iron oxide particles and in some cases also Sr-85 labelled polystyrene particles. For lung clearance measurement the decrease of x-activity in the thoracic area of these animals was monitored for 85 days. Chronic exposure was continued during this time. Recovery of the lung clearance was investigated two months after ending of exposure. Lung retention of inhaledpartic les was determined at various times during and after ending of exposure. The lung burden after 8 months of exposure has been about 7 mg for PVC, 4 mg for titanium dioxide and 0.6 mg for iron powder at the highest concentration. The PVC dust inhalation caused a severe retardation of the long-term lung clearance of labelled polystyrene particles at the medium and high concentration. For iron powder and titanium dioxide inhalation only in the high concentration group a small retardation of lung clearance was detected.