(E)-1,2-Difluoroethylene (HFO-1132E)

(E)-1,2-Difluoroethylene (HFO-1132E) is a colorless gas used as a refrigerant. HFO-1132E has low acute toxicity following inhalation exposure in rats and dogs. HFO-1132E caused neither cardiac sensitization in dogs nor reproductive or developmental toxicity in rats following repeated inhalation exposure. Repeated inhalation exposure for up to 13 weeks in rats resulted in degeneration of the vomeronasal organ (VNO) at all exposure levels. However, the VNO is poorly developed or absent in humans. HFO-1132E was not genotoxic in either an in vitro chromosome aberration study or in vivo (rat) or in vitro micronucleus assays although the substance was mutagenic in 4 of 5 Salmonella and E. coli strains with and without S9. In an in vivo comet assay in rats, statistically significant increases in DNA strand breaks were observed in the kidney at concentrations ≥60,000 ppm and in the liver, bladder, and lung at 120,000 ppm. An increase in hedgehog cells was also noted at these concentrations that confounded the comet response. The point of departure for the WEEL was 15,000 ppm from the 13-week inhalation study. After application of appropriate adjustment factors, an 8-h time-weighted average (TWA) WEEL value of 350 ppm was derived. This exposure limit is expected to provide a significant margin of safety against any potential adverse health effects in workers. A short-term exposure level (STEL) or skin notation is not applicable for this WEEL.