The former OSHA standard for tributyl phosphate was 5 mg/m3 as an 8-hour TWA. The ACGIH has a 2.5-mg/m3 TWA for tributyl phosphate, which is a clear, colorless, odorless liquid. The proposed PEL was an 8-hour TWA of 2.5 mg/m3; NIOSH (Ex. 8-47, Table N1) concurs that this limit is appropriate. The final rule establishes an 8-hour TWA PEL of 2.5 mg/m3 for tributyl phosphate.
Tributyl phosphate's toxicity affects the skin, mucous membranes, lungs, and central nervous system, and this substance is also a cholinesterase inhibitor.
A paper by Smyth and Carpenter (1944/Ex. 1-374) reported that contact with liquid tributyl phosphate caused severe eye injury and skin irritation when tested in rabbits. Chambers and Casida (1967/Ex. 1-305) found that mice injected with 1 g/kg tributyl phosphate intraperitoneally became paralyzed. A study by Vandekar (1957/Ex. 1-498) in which mice were given tributyl phosphate by gavage revealed that a dose of 80 mg/kg resulted in a one-hour period of anesthesia, and a dose of 100 mg/kg resulted in 8 to 10 minutes of anesthesia, followed by respiratory failure and death. Administered intraperitoneally to rats, tributyl phosphate inhibited cholinesterase activity and stimulated plasma beta-glucuronidase activity (Suzuki, Kikuchi, Kato et al. 1977/Ex. 1-1170). This substance did not exhibit mutagenic activity in bacterial or fruit fly assays (Hanna and Dyer 1975/Ex. 1-485).
Nausea and headache were reported by workers exposed to levels of 15 mg/m3 of tributyl phosphate (Mastromatteo 1964b, as cited in ACGIH 1986/Ex. 1-3, p. 591). No comments, other than NIOSH's, were received on this substance.
In the final rule, OSHA is reducing the 8-hour PEL from 5 mg/m3 to 2.5 mg/m3. OSHA concludes that this limit will protect workers against the significant risk of paralysis, anesthetic effects, and skin or eye irritation, all of which constitute material impairments of health that are associated with exposure to tributyl phosphate at levels above the new PEL.