Two-week aerosol inhalation study in rats of ethylene oxide/propylene oxide copolymers

Previous studies have shown that aerosols of an ethylene oxide/propylene oxide copolymer (UCON 50-HB-5100) produced an inflammatory response in lungs of rats in short-term repeated exposures at relatively low concentrations. This study was carried out on related polyalkylene glycols (EO/PO copolymers) to determine if similar effects would occur upon short-term repeated exposure. Rats were treated by whole body liquid droplet aerosol exposures of six hours per day, five days per week for two consecutive weeks to each of five EO/PO copolymers. The exposure level for the positive control (UCON 50-HB-5100) was 55 mg/m3, while the remaining 4 test copolymers were evaluated at 100 mg/m3. Each exposure group consisted of ten male albino rats. After three exposures, nine of ten rats exposed to UCON 50-HB-5100, and six of ten rats exposed to UCON 50-HB-2000 had died. At necropsy, congestion, consolidation and red discoloration of the lungs were noted. A moderate to severe alveolitis, characterized by intraalveolar edema, hemorrhage and fibrin deposition, was observed after five days of exposure. At necropsy, these rats exhibited elevated lung weights and similar macroscopic and microscopic lesions. Rats exposed to the other test materials (UCON 75-H-1400, Pluronic L17R1, Pluronic L31, and Pluronic L64) survived with essentially no signs of toxicity through the ten exposure days. Body weights, organ weights, hematological evaluation, pharmacotoxic signs, and macroscopic and microscopic evaluation after necropsy were similar between groups and when compared to the negative control group. Only a slight alveolitis was noted after two weeks of exposure which subsided by two-weeks post exposure.