title: Biopersistence of inhaled organic and inorganic fibers in the lungs of rats.
abstract: Fiber dimension and durability are recognized as important features in influencing the development of pulmonary carcinogenic and fibrogenic effects. Using a short-term inhalation bioassay, we have studied pulmonary deposition and clearance patterns and evaluated and compared the pulmonary toxicity of two previously tested reference materials, an inhaled organic fiber, Kevlar para-aramid fibrils, and an inorganic fiber, wollastonite. Rats were exposed for 5 days to aerosols of Kevlar fibrils (900-1344 f/cc; 9-11 mg/m3) or wollastonite fibers (800 f/cc; 115 mg/m3). The lungs of exposed rats were digested to quantify dose, fiber dimensional changes over time, and clearance kinetics. The results showed that inhaled wollastonite fibers were cleared rapidly with a retention half-time of < 1 week. Mean fiber lengths decreased from 11 microns to 6 microns over a 1-month period, and fiber diameters increased from 0.5 micron to 1.0 micron in the same time. Fiber clearance studies with Kevlar showed a transient increase in the numbers of retained fibrils at 1 week postexposure, with rapid clearance of fibers thereafter, and retention half-time of 30 days. A progressive decrease in the mean lengths from 12.5 microns to 7.5 microns and mean diameters from 0.33 micron to 0.23 micron was recorded 6 months after exposure to inhaled Kevlar fibrils. The percentages of fibers > 15 microns in length decreased from 30% immediately after exposure to 5% after 6 months; the percentages of fibers in the 4 to 7 microns range increased from 25 to 55% in the same period.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Central Research and Development, Haskell Laboratory for Toxicology and Industrial Medicine, E. I. du Pont de Nemours and Co., Newark, Delaware 19714.
authors.forename: D B
authors.initials: DB
authors.lastname: Warheit
authors.forename: M A
authors.initials: MA
authors.lastname: Hartsky
authors.forename: T A
authors.initials: TA
authors.lastname: McHugh
authors.forename: K A
authors.initials: KA
authors.lastname: Kellar
mesh_terms: D000280:Administration, Inhalation; D000818:Animals; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry / Q000166:cytology; D017610:Calcium Compounds / Q000493:pharmacokinetics*; D008168:Lung / Q000378:metabolism*; D008297:Male; D008657:Metabolic Clearance Rate; D011108:Polymers / Q000493:pharmacokinetics*; D051381:Rats; D017640:Silicates / Q000493:pharmacokinetics*
chemical_list: D017610:Calcium Compounds; C039578:Kevlar Aramid fibers; D011108:Polymers; D017640:Silicates; C031293:calcium silicate