Chronic toxicity and oncogenicity bioassay of inhaled ethylene in Fischer-344 rats.

The toxicity and oncogenicity of inhaled ethylene was determined in Fischer-344 rats. Nine hundred and sixty animals were randomly divided into four groups of one hundred twenty animals of each sex and were exposed 6 hr/day, 5 days/week, for up to 24 months to concentrations of ethylene in air of 0, 300, 1000, or 3000 ppm. The maximum tolerated dose was not used as concentrations above 3000 ppm were considered hazardous because of the risks associated with ethylene's explosive properties. The calculated time-weighted average concentrations for the 24 months of exposure were 0.0, 301, 1003, and 3003 ppm, respectively. Randomly selected animals were necropsied and examined after 6, 12, and 18 months of exposure. All surviving rats were necropsied at 24 months. A complete selection of tissues and organs from all animals in the control and 3000-ppm groups were examined for microscopic lesions. All animals were examined for clinical changes throughout the course of the study and selected animals were used to determine ophthalmologic or hematologic effects and for clinical blood chemistry or urinalysis effects. There were 151 unscheduled deaths (15.7% of 960 animals). There was no difference in mortality between groups during the 2-year study. Gross examination of rats dying during the study, or of those that were sacrificed as scheduled, did not reveal any lesions attributable to ethylene exposure. Histologically, a variety of proliferative, degenerative, and inflammatory lesions were observed in both the control and 3000-ppm groups. These lesions were typical of those seen in this strain of animal and were considered unrelated to ethylene exposure.(ABSTRACT TRUNCATED AT 250 WORDS)