OSHA formerly had no established limit for catechol. The ACGIH has a TLV-TWA of 5 ppm. The proposed PEL was 5 ppm as an 8-hour TWA, and NIOSH (Ex. 8-47, Table N1) concurs with this limit, which is established in the final rule. In addition, the Agency has added a skin notation for this substance, in accordance with its policy on skin designations, as discussed in Section VI.C.18. Catechol is a colorless crystalline solid that sublimes readily and thus occurs in the vapor state at room temperature.
Catechol is approximately 1.1 to 2.2 times more toxic than phenol, depending on the route of exposure (Industrial Bio-Test Laboratories 1974, as cited in ACGIH 1986/Ex. 1-3, p. 112). The oral LD(50) in rats is 300 mg/kg, or approximately half that of phenol. Percutaneous toxicity for catechol in rabbits is 800 mg/kg, only slightly greater than the value for phenol. OSHA notes that phenol has a skin designation and that catechol's dermal LD(50) in rabbits of 0.8 g/kg places this substance in the category of "toxic" by the percutaneous route of administration, as discussed in Section VI.C.18. In addition, the Agency is concerned by reports of central nervous system effects (i.e., convulsions) in humans as a result of skin absorption that are "more marked" than those produced by phenol (Deichmann and Keplinger 1981, in Patty's Industrial Hygiene and Toxicology, 3rd rev. ed., Vol. 2A, p. 2586). OSHA is therefore adding a skin notation to the final limit for catechol to protect workers from the serious CNS effects that may potentially occur from percutaneous absorption of this substance. Eye and nose irritation, as well as muscular spasms and tremor, have been observed in rats at a concentration of 2800 mg/m3 catechol, indicating that the acute respiratory toxicity of catechol is approximately one-third that of phenol (Industrial Bio-Test Laboratories 1974, as cited in ACIGH 1986/Ex. 1-3, p. 112). Metabolic data indicate that the urinary elimination rate of catechol in rabbits is only 10 percent that of phenol (Williams 1959/Ex. 1-1176). In mice, catechol is easily absorbed through the skin and gastrointestinal tract (Forsyth and Quesnel 1957/Ex. 1-978). Additional data document a variety of dermal, respiratory, and systemic toxicities that are closely analogous to those of phenol in their metabolic actions (Harold, Nierenstein, and Roaf 1910/Ex. 1-1111; Dietering 1938/Ex. 1-1019; Cushny et al. 1940, as cited in ACGIH 1986/Ex. 1-3, p. 112).
Exposure to catechol causes an increase in blood pressure, and, at high doses, kidney damage, eczematous dermatitis, and systemic illness (Harold, Nierenstein, and Roaf 1910/Ex. 1-1111; Dietering 1938/Ex. 1-1019; Cushny et al. 1940, as cited in ACGIH 1986/Ex. 1-3, p. 112). OSHA received no comments, except for those from NIOSH, on catechol.
In the final rule, OSHA is establishing a permissible exposure limit of 5 ppm as an 8-hour TWA for this substance, with a skin notation. The Agency concludes that these limits will protect workers against the significant risks of dermal, upper respiratory tract, convulsions, and central nervous system effects (i.e., convulsions), all of which constitute material impairments of health that are potentially associated with exposure to catechol at levels above the new PEL.