day observation period, and there were no biologically significant effects on body weight. Although there were some statistically significant variations in hematologic and clinical-chemistry measures examined, including thyroxine (T4) and T4-binding globulin, all were within historical and biologic limits and were considered unrelated to treatment.

Groups of five male and five female Sprague-Dawley rats were given a single whole-body inhalation exposure to CF3I at 0.0%, 10.0%, 12.8%, 20.0%, or 32.0% (0, 100,000, 128,000, 200,000, or 320,000 ppm) for up to 4 h (Ledbetter 1994). All rats exposed to 32.0% test material died within 20 min of the start of exposure. However, hydrogen fluoride at 7 ppm had contaminated the test gas, and that necessitated the installation of a potassium hydroxide scrubber for the later 20.0% exposure. All male and female rats exposed to 20.0% CF3I died within 20 min of the start of exposure. A new sample of test material was used for the 10.0% and 12.8% exposures. Within 30 min of the start of exposure, all male and female rats exposed to 10.0% CF3I became unconscious or semiconscious, and they had limb twitching for the remainder of exposure. After cessation of exposure, the rats awakened after about 3 min. Male and female rats exposed to 12.8% CF3I appeared to enter a deep sleep and remained there until the end of exposure. All male and female rats exposed to 10.0% or 12.8% CF3I survived the 2-wk observation period, and no other clinical signs of toxicity were noted. At necropsy, the rats exposed to 32.0% test material had dark red and puffy lungs that were consistent with hydrogen fluoride exposure. Rats exposed at 20.0% had puffy lungs that were much less red than the 32.0% animals. The lungs of two male rats exposed to 12.8% CF3I had slight redness or red foci, but no other treatment-related effects were noted in the remaining rats. Given the animal responses seen at 12.8%, the responses seen at 20.0% and 32.0% may have been indicative of CF3I toxicity with little contribution from HF.

Ledbetter (1994) also conducted a nose-only 15-min exposure to 24.2% or 28.8% CF3I with groups of five male and five female Sprague-Dawley rats. All the female rats and two male rats died during exposure to 28.8% CF3I; no female rats and one male rat died during exposure to 24.2% CF3I. All surviving rats were shaky when removed from the exposure chamber, but they recovered within minutes. On the basis of the results, the authors calculated a 15-min CF3I LC50 (the concentration of a substance that is estimated to be lethal to 50% of the test animals) of 27.4%. Typically, three concentrations are used for the determination of LC50. However, the authors reasoned, and the subcommittee concurs, that the steepness of the LC50 curve between the two exposure concentrations made it unnecessary



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