OSHA formerly had a ceiling limit of 10 ppm for 1,1-dichloro-1-nitroethane. The ACGIH has a TLV-TWA of 2 ppm for this colorless liquid. The proposed PEL was an 8-hour TWA of 2 ppm, with which NIOSH (Ex. 8-47, Table N1) concurs. The final rule establishes the 2-ppm 8-hour TWA PEL for 1,1-dichloro-1-nitroethane.
Toxicity data on 1,1-dichloro-1-nitroethane are largely derived from the 1945 studies conducted by Machle and co-workers (Ex. 1-349). These scientists reported that both rabbits and guinea pigs died from inhaling vapors at 100 ppm for six hours; at a concentration of 60 ppm, the animals survived a two-hour exposure. Four-hour inhalation exposures at 34 ppm and six-hour daily exposures at 25 ppm for a total of 204 hours also did not kill rabbits or guinea pigs. Skin and mucous membrane irritation were not produced at the 25-ppm exposure level. At survival concentrations, the primary targets of toxicity were the lungs, which showed edema, congestion, hemorrhage, and acute bronchitis. At lethal exposures, these investigators observed acute myocardial degeneration with interstitial edema, cloudy swelling of the liver with cellular degeneration, and tubular degeneration and interstitial edema of the kidney, as well as edema of the tufts of the glomeruli and kidney necrosis. The compound was also found to be a severe skin irritant when two applications were applied on two successive days (Machle, Scott, Treon et al. 1945/Ex. 1-349). The ACGIH (1986/Ex. 1-3, p. 188) states that dichloronitroethane is more toxic than the nonchlorinated nitroalkanes. The Workers Institute for Safety and Health (Ex. 116) questioned OSHA's selection of an 8-hour TWA rather than ceiling limit for this substance. In response, OSHA notes that the final rule's lower TWA limit is protective because the health effects of concern do not occur at the peak exposures that would be permitted by the revised 8-hour TWA PEL.
In the final rule, OSHA is establishing a PEL of 2 ppm TWA for 1,1-dichloro-1-nitroethane. The Agency concludes that this limit will protect workers against the significant risk of irritation, lung injury, and liver and kidney damage, all material health impairments that are associated with exposures at levels above the revised PEL.