4,4′-THIOBIS

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: 96-69-5; Chemical Formula: C₂₂H₃₀O₂S

OSHA formerly regulated 4,4′-thiobis under the Agency’s generic total particulate limit of 15 mg/m³ TWA. The ACGIH limit is 10 mg/m³ as an 8-hour TWA, the limit established by the ACGIH for all of the nuisance dusts. OSHA proposed a 10-mg/m³ total particulate TWA limit and a 5-mg/m³ respirable fraction PEL for 4,4′-thiobis, and these limits are established in the final rule. NIOSH (Ex. 8-47, Table N4) concurs with the selection of these limits. 4,4′-Thiobis is a light gray to tan powder with a slightly aromatic odor.

In a 30-day study, rats fed diets of 500 ppm 4,4′-thiobis exhibited normal weight gain; those rats fed five times this amount exhibited enlarged livers and a reduced rate of weight gain (Lefaux 1968/Ex. 1-814). In a 90-day study reported by the same author, rats fed 50 ppm showed no toxic effects, but male rats fed 500 ppm ate and grew at a slightly lower rate. No pathologic changes were observed in the 500-ppm-dosed rats. A dose of 5 g/kg of 4,4′-thiobis proved lethal to rats, with the predominant symptom being gastroenteritis. NIOSH was the only commenter on this substance.

In the final rule, OSHA is establishing exposure limits of 10 mg/m³ TWA (total particulate) and 5 mg/m³ TWA (respirable fraction) for 4,4′-thiobis. The Agency concludes that these limits will protect workers from the significant risk of material health impairment, in the form of eye, skin, and other physical irritation, which is associated with exposure to this substance.