1-Chloro-1,2,2,2-tetrafluoroethane (HCFC 124)
1-Chloro-1,2,2,2-tetrafluoroethane (chlorotetrafluoroethane), a non-flammable colourless gas at room temperature, is currently under development as a chlorofluorocarbon alternative and is not yet available in commercial quantities. The atmospheric degradation of chlorotetrafluoroethane will occur mainly in the troposphere by reaction with naturally occurring hydroxyl radicals. Its overall atmospheric lifetime is approximately 6.9 years and about 95% of the degradation will occur in the troposphere. Chlorotetrafluoroethane has a low calculated ozone depletion potential (ODP) of 0.022 and a global warming potential of 0.10 relative to a reference value for both indices of 1.0 for trichlorofluoromethane (CFC-11). In limited studies in rats to evaluate metabolic fate and pharmacokinetics, chlorotetrafluoroethane appears to undergo oxidative metabolism resulting in the excretion of trifluoroacetic acid and fluoride ion in the urine. Studies to assess the metabolic fate of inhaled tetrafluoroethane in rats, mice, and hamsters are currently in progress. Chlorotetrafluoroethane has a low order of acute inhalation toxicity with a 4-hour LC50 in rats between 1,283,400 and 1,674,000 mg/m3 (230,000 and 300,000 ppm). The main toxicological action of this fluorocarbon during exposure is weak anaesthesia. As with many other halocarbons and hydrocarbons, inhalation of high concentrations of chlorotetrafluoroethane, followed by an intravenous epinephrine challenge to simulate stress, can induce a cardiac sensitization response in dogs. In these experimental screening studies, cardiac sensitisation (life-threatening arrhythmia) was seen at concentrations of 146,000 mg/m3 (26,000 ppm) and above. The no-observable-effect- level was 55,800 mg/m3 (10,000 ppm). In a 2-week inhalation toxicity study, rats exposed to 558,000 mg/m3 (100,000 ppm) chlorotetrafluoroethane showed no adverse effects. In 90-day studies at concentrations as high as 279,000 mg/m3 (50,000 ppm), rats and mice showed minimal toxic effects such as slight central nervous system depression and minor blood chemistry changes. No-observable-effect level in these 90-day studies was 27,900 mg/m3 (5,000 ppm) for male rats whilst for male mice a NOEL was not achievable. For female rats and mice a NOEL of 15,000 ppm was established. A lifetime inhalation toxicity/carcinogenicity study in rats is currently in progress. No evidence of embryotoxicity or teratogenicity of chlorotetrafluoroethane was seen in developmental studies by inhalation in rats and rabbits at exposure levels as high as 279,000 mg/m3 (50,000 ppm). Minimal evidence of maternal toxicity was seen at concentrations of 83,700 mg/m3 (15,000 ppm) and above in each of these studies. Chlorotetrafluoroethane was not mutagenic either in in vitro or in in vivo studies using bacteria or yeast or mammalian cell lines or the mouse micronucleus assay. There are no reported effects of chlorotetrafluoroethane in man. An occupational exposure limit (8-hour average) of 1,000 ppm (5,580 mg/m3) is recommended by AIHA.