Pulmonary Toxicity of Inhaled Polypropylene Fibers in Rats

This study was initiated to assess the pulmonary toxicity ofpolyolefin fiber composed of polypropylene in male Fischer 344rats after 90 days of inhalation exposure. To increase fiberrespirability in the rodent, polypropylene fibers were size-selectedbefore aerosolization to have a geometric mean diameter of 1.6m (46% <1 µm) and a geometric mean length of 30.3 µm.Three groups of animals were exposed in nose-only inhalationchambers, 6 hr/day, 5 days/week, for 90 days to 15, 30, or 60mg/m³ of polypropylene, or filtered air (negative control).Microscopic examination of the polypropylene fiber-exposed lungsrevealed that, at all time points examined in the study, therewas a dose-dependent increase in pulmonary macrophages. Theseminimal or mild increases in cellularity appeared to be reversible,especially at the lower doses 30 days post exposure. No fibrosiswas observed in any of the groups. A strong correlation wasfound between the external exposure concentration, the timeexposure, and the lung fiber burden. The number of partiallydegraded (segmented) fibers within the lung increased with theexposure concentration and period of exposure, as well as withthe period of recovery after termination of exposure at 90 days.Fibers were recovered from exposed lungs using a hypochloritedigestion technique.