1,2,4-TRICHLOROBENZENE

OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.

CAS: 120-82-1; Chemical Formula: C₆H₃Cl₃

OSHA formerly had no limit for 1,2,4-trichlorobenzene and proposed to establish a limit of 5 ppm as a ceiling for this substance. NIOSH (Ex. 8-47, Table N1) concurred with this proposal. The final rule establishes this limit, which is consistent with the ACGIH recommendation. 1,2,4-Trichloro-benzene is a colorless, stable liquid at room temperature, with an odor similar to that of o-dichlorobenzene.

The inhalation toxicity of 1,2,4-trichlorobenzene was studied by Treon (1950, as cited in ACGIH 1986/Ex. 1-3, p. 593), who determined that the target organs of exposure in cats, dogs, rats, rabbits, and guinea pigs included the liver, kidneys, ganglion cells at all brain levels, and mucous membranes. Irritation of the lungs and changes in respiration were seen in animals that later died as a result of exposure. Brown, Muir, and Thorpe (1969/Ex. 1-537) reported that 1,2,4-trichlorobenzene’s single-dose oral LD(50) is 756 mg/kg for rats and 766 mg/kg for mice. The acute percutaneous LD(50) for rats was 6139 mg/kg. Sublethal doses administered repeatedly to guinea pigs caused liver damage; acute and short-term (15 six-hour exposures to 70 to 200 ppm) inhalation studies failed to kill these animals (Gage 1970/Ex. 1-318). In a separate study reported on by Rowe (1975, as cited in ACGIH 1986/Ex. 1-3, p. 593), 20 male rats, 4 rabbits, and 2 dogs were exposed at levels of 30 or 100 ppm 1,2,4-trichlorobenzene for seven hours/day, five days/week, for a total of 30 exposures in 44 days. No adverse effects were detected in exposed animals belonging to 30 species as a result of exposure to 30 ppm, with the exception of an elevation of urinary porphyrins in the rats at days 15 and 30 of exposure. A second inhalation study was performed with 1,2,4-trichlorobenzene administered seven hours/day, five days/week for 26 consecutive weeks (Coate, Schoenfisch, Busey, and Lewis 1977, as cited in ACGIH 1986/Ex. 1-3, p. 593). Thirty rats, 16 rabbits, and 9 monkeys, all males, were exposed at 0, 25, 50, or 100 ppm. Microscopic changes were seen in the parenchymal cells of the livers and kidneys of all rats after weeks 4 and 13 of exposure to 1,2,4-trichlorobenzene, but no adverse effects were seen in any of the other species.

In workers, exposure to 1,2,4-trichlorobenzene caused dermal irritation, which may have been attributable to the defatting action of this chemical (Powers, Coate, and Lewis 1975/Ex. 1-658), and in some cases, exposure levels of 3 to 5 ppm caused eye and throat irritation (Rowe 1975, as cited in ACGIH 1986/Ex. 1-3, p. 593). NIOSH was the only rulemaking participant to submit comments on 1,2,4-trichlorobenzene.

The Agency concludes that the PEL being established today will protect workers from the risk of eye, throat, and dermal irritation associated with exposure to this substance; these adverse effects represent material impairments of health. To afford workers this protection, OSHA is promulgating a ceiling limit of 5 ppm for 1,2,4-trichlorobenzene.