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HYDROFLUOROCARBON-404A 42 Toxicity Information Acute Toxicity Groups of six male rats were exposed for 4 hr (nose only) to HFC-143a at concentrations of 97,000 or 540,000 parts per million (ppm) (Brock et al. 1996). No deaths occurred during exposure or during the 14-day post-exposure observation period. No clinical signs attributed to HFC-143a were observed. Slight-to-moderate body-weight losses were observed in both exposure groups on the day following exposure, but normal weight gains were observed through the remainder of the study. Thus, the 4-hr LC50 (concentration causing death in 50% of test animals) for rats is considered to be greater than 540,000 ppm. The LC50 value of HFC-143a in mice is reported to be greater than 500,000 ppm (Nikijenko and Tolgskaya 1965, as cited in AIHA 1996). Cardiac Sensitization Brock et al. (1996) evaluated the cardiac-sensitization potential of HFC-143a in an epinephrine challenge test. An intravenous control injection of epinephrine (2-12 µg/kg) was administered to groups of six beagle dogs that were subsequently exposed for 10 min to HFC-143a at concentrations ranging from 50,000 to 300,000 ppm via single-pass-through face mask. Five minutes after initiating vapor exposure, a challenge concentration of epinephrine (same as the pre-test concentration) was administered. Evidence of cardiac sensitization was determined if multiple ectopic beats (more than five beats) or ventricular fibrillation, which could be fatal, was evident. No cardiac- sensitization responses were observed at HFC-143a concentrations of 50,000 to 250,000 ppm. At 300,000 ppm, two of five dogs were considered to have exhibited cardiac sensitization. Subchronic Toxicity Four groups of rats (10 of each sex) were exposed nose-only for 6 hr per day, 5 days per week for 4 weeks to HFC-143a at 0, 2,000, 10,000, or 40,000 ppm (Brock et al. 1996). Clinical signs, body weights, food consumption, clinical pathology, organ weights, and tissue histopathology were evaluated. Premature deaths in three rats from different exposure groups were consid
