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: 298-02-2; Chemical Formula: C7H17O2PS3

Previously, OSHA had no limit for phorate. The ACGIH has limits of 0.05 mg/m3 as an 8-hour TWA and 0.2 mg/m3 as a STEL for phorate, with a skin notation. The proposed PELs were 0.05 mg/m3 as an 8-hour TWA PEL, with a STEL of 0.2 mg/m3 and a skin notation; NIOSH concurs with these limits (Ex. 8-47, Table N1), which are established in the final rule. Phorate is an organophosphorus cholinesterase inhibitor that takes the form of a clear liquid and is used as an insecticide.

Phorate is a highly toxic compound in animals. Rats exposed to daily doses of phorate showed effects above 0.15 mg/kg/day but no effects below this level. The no-effect level in dogs is between 0.01 and 0.05 mg/kg/day (Gaines 1969/Ex. 1-320). The dermal LD(50) in male rats is 6.2 mg/kg and, for female rats, 25 mg/kg.

The final rule’s limits of 0.05 mg/m3 as an 8-hour TWA, supplemented by a STEL of 0.2 mg/m3 and a skin notation, are based on calculations that the no-effect level in humans would lie in the range between 0.21 and 0.7 mg/day, and that use of an appropriate safety factor would suggest an 8-hour limit of 0.05 mg/m3, with a STEL of 0.2 mg/m3, to ensure against excursions greatly in excess of the TWA limit. OSHA received no comments on phorate except those from NIOSH.

OSHA finds that these limits will protect workers exposed to phorate against cholinesterase inhibition and its associated effects, which include respiratory symptoms, nausea, confusion, and vomiting. The Agency concludes that, in the absence of any OSHA limit, phorate-exposed employees were formerly at significant risk of experiencing such effects and that establishing a PEL, STEL, and skin notation will substantially reduce these risks. OSHA finds that cholinesterase inhibition and its symptoms clearly constitute material impairments of health.

Page last reviewed: September 28, 2011