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: 121-45-9; Chemical Formula: (CH3O)3P

OSHA previously had no limit for trimethyl phosphite. The proposed PEL was an 8-hour TWA of 2 ppm and NIOSH (Ex. 8-47, Table N1) supported this proposal. The final rule establishes this limit. The ACGIH limit for this substance is a 2-ppm 8-hour TWA. Trimethyl phosphite is a colorless liquid with a pungent odor.

Trimethyl phosphite’s toxic effects include lung, skin, and eye irritation. In a chronic inhalation study of rats, Levin and Gabriel (1973/Ex. 1-746) found that exposure to trimethyl phosphite at concentrations of 500 (+ or -) 75 ppm for 7.5 hours daily, five days/week for eight weeks caused an adverse effect on body weight and, at necropsy, revealed evidence of severe pulmonary and cutaneous pathology. At exposures of 600 ppm for six hours/day, five days/week for four weeks, 70 percent of the rats died, and 10 percent of those exposed even at 300 ppm on the same regimen died (Mobil Oil Corporation 1979, as cited in ACGIH 1986/Ex. 1-3, p. 609).

Rats exposed at 100 ppm showed signs of eye irritation, and at 300 to 600 ppm, mild to severe cataracts developed. At doses of 164 mg/kg, trimethyl phosphite caused gross abnormalities in the offspring of treated rats (Mobil Oil Corporation 1979, as cited in ACGIH 1986/Ex. 1-3, p. 609). Skin contact with trimethyl phosphite produced severe skin irritation in rabbits, and instillation in the eyes of rabbits caused temporary swelling and irritation but no permanent effects (Fassett 1963c/Ex. 1-1148).

In a group of 179 workers exposed to average concentrations of trimethyl phosphite of between 0.3 and 4 ppm, no ocular changes were observed (Mobil Chemical Company 1980, as cited in ACGIH 1986/Ex. 1-3, p. 609).

OSHA is establishing an 8-hour TWA PEL of 2 ppm for trimethyl phosphite. The Agency concludes that this limit will protect workers against the significant risk of eye damage, skin irritation, and upper respiratory tract irritation, all of which constitute material health impairments that are potentially associated with exposures to this substance at levels above the new PEL.

Page last reviewed: September 28, 2011