OSHA formerly had an 8-hour TWA PEL of 10 ppm TWA for p-tert-butyl- toluene; the Agency proposed to retain this limit and to supplementit with a 20-ppm STEL. The ACGIH has a TLV-TWA of 10 ppm and aTLV-STEL of 20 ppm for this substance. The final rule adopts a STEL of 20 ppmto supplement OSHA's 10-ppm 8-hour TWA PEL for p-tert-butyltoluene. NIOSH (Ex. 8-47, Table N1) concurs with the selection of these limits. p-tert-Butyltoluene is a colorless liquid with an aromatic,gasoline-like odor.
p-tert-Butyltoluene has been shown to have varying degrees of toxicity, depending on route of administration. It is slightly toxic on ingestion, and minimally toxic through skin exposure, but moderately toxic when inhaled (Hine, Ungar, Anderson et al. 1954/Ex. 1-983). Repeated exposures in animals have shown liver and kidney changes and microscopic degenerative hemorrhages in the spinal cord and brain, even at relatively low concentrations. The chief acute effects in animals are central nervous system depression and respiratory irritation; in rats exposed for one to seven hours daily over a 26-week period, 25 ppm daily appeared to be the no-observed-adverse-effect level (Gerarde 1960a, as cited in ACGIH 1986/Ex. 1-3, p. 85).
In humans, Hine, Ungar, Anderson et al. (1954/Ex. 1-983) observed nasal irritation, nausea, malaise, headache, and weakness associated with exposure to p-tert-butyltoluene at unspecified levels. These authors also noted cardiovascular effects, as well as effects on the central nervous system, the skin, and the respiratory tract. Half of the subjects exposed to p-tert-butyltoluene developed tremor and anxiety, and 25 percent of exposed individuals showed evidence of chemical contact irritation of the respiratory tract (Hine, Ungar, Anderson et al. 1954/Ex. 1-983).
OSHA is retaining its 8-hour TWA of 10 ppm and adding a STEL of 20 ppm for p-tert-butyltoluene. The Agency concludes that a STEL as well as a TWA will protect workers against the significant risks of central nervous and cardiovascular system effects, as well as those of irritation and nausea, all of which constitute material impairments to health that are potentially associated with short-term (one to seven hours) exposures to this substance at levels above the 8-hour TWA.