THIOGLYCOLIC ACID

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: 68-11-1; Chemical Formula: C₂H₄O₂S

OSHA had no former PEL for thioglycolic acid. The Agency proposed a 1-ppm 8-hour TWA, with a skin notation, for this colorless liquid, which has an unpleasant odor; NIOSH (Ex. 8-47, Table N1) concurred with this proposal. The 1-ppm TWA limit and the skin notation, which are the same limits as recommended by the ACGIH, are established in the final rule.

A study by the Dow Chemical Company (1973b, as cited in ACGIH 1986/Ex. 1-3, p. 571) in which thioglycolic acid was instilled into the eyes of rabbits resulted in severe conjunctival inflammation and pain, dense opacity of the cornea, and severe inflammation of the iris. These effects had not improved 14 days after exposure and washing immediately after exposure did not modify the severity of this ocular response. A single dermal application of thioglycolic acid to rabbit skin caused necrosis within five minutes and was accompanied by hyperemia and edema. The LD(50) for a 10-percent solution applied percutaneously was 848 mg/kg for rabbits (ACGIH 1986/Ex. 1-3); further studies by Dow (1973b, as cited in ACGIH 1986/Ex. 1-3, p. 571), in which female rats were fed a single oral dose of a 10-percent solution of thioglycolic acid, showed that this dose resulted in death at the level of 125 mg/kg. Autopsy revealed damage to the liver and gastrointestinal tract. Fassett (1963b, as cited in ACGIH 1986/Ex. 1-3, p. 571) reported that the oral LD(50) for undiluted thioglycolic acid in rats was 50 mg/kg, and that a 10-percent solution applied to the skin of guinea pigs caused fatalities at doses of less than 5 ml/kg. Symptoms prior to death included gasping, convulsions, and weakness.

No rulemaking participants, other than NIOSH, commented on OSHA’s proposal to establish a 1-ppm 8-hour TWA limit for thioglycolic acid. The evidence described above clearly demonstrates that this substance is a potent irritant; accordingly, OSHA finds that a limit on airborne exposure is necessary to protect workers from the risk of eye and skin irritation and systemic effects, which constitute material impairments of health. Therefore, OSHA is establishing a 1-ppm 8-hour TWA limit for this substance. In addition, the animal evidence shows that thioglycolic acid solutions readily penetrate the skin in lethal quantities (the dermal LD(50) in rabbits is 848 mg/kg). Thus, OSHA finds that a skin notation is necessary to limit dermal contract and is adding this notation to its limit for thioglycolic acid.