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: 111-76-2; Chemical Formula: C4H9OCH2CH2OH
OSHA's former permissible exposure limit for 2-butoxyethanol, one of the family of substances known as the glycol ethers, was 50 ppm as an 8-hour TWA, with a skin notation. The ACGIH has a limit of 25 ppm TWA, also with a skin notation, for this colorless liquid with a mild ether odor. The proposed PEL was 25 ppm as an 8-hour TWA, and this limit is established by the final rule. The skin notation is retained. NIOSH (Ex. 8-47, Table N1) concurs with the 25-ppm limit for 2-butoxyethanol.
2-Butoxyethanol has long been known to be toxic, with early studies indicating that a single seven-hour exposure to 700 ppm was lethal to laboratory animals (Werner, Mitchell, Miller, and von Oettingen 1943a, as cited in ACGIH 1986/Ex. 1-3, p. 71). Exposures near the lethal level caused systemic toxicity in the form of hemoglobinuria and lung, kidney, and liver changes. Carpenter, Pozzani, Weil, and associates (1956/Ex. 1-303) reported hemolytic anemia and increased fragility of the red blood cells in rats repeatedly exposed to 2-butoxyethanol at 320 ppm for five weeks. However, repeated exposure for 12 weeks at 400 ppm was only slightly injurious to dogs (Werner, Mitchell, Miller, and von Oettingen 1943b, as cited in ACGIH 1986/Ex. 1-3, p. 71).
Humans appear to be less susceptible to butoxyethanol poisoning than experimental animals. In humans, several single 8-hour exposures at levels of 200 ppm and 100 ppm caused urinary excretion of butoxyacetic acid; these subjects experienced irritation and discomfort after these exposures (Carpenter, Pozzani, Weil et al. 1956/Ex. 1-303). A recent study has confirmed that the increased erythrocyte osmotic fragility observed in rats exposed to many of the glycol ethers is a very sensitive indicator of toxicity and correlates with the development of hemoglobinuria at higher exposure levels (Moffett, Linnett, and Blair 1976, as cited in ACGIH 1986/Ex. 1-3, p. 71). These findings indicate that the no-effect level in animals is approximately 25 ppm. The ACGIH suggests that 2-butoxyethanol's toxicity may be more likely to occur as a result of skin absorption than as a consequence of inhalation (ACGIH 1986/Ex. 1-3, p. 71).
The Independent Lubricant Manufacturers (Ex. 3-830) objected to the establishment of a PEL for 2-butoxyethanol on the basis of a 25-ppm no-effect level in animals, particularly when the evidence suggests that humans may be less susceptible than animals to the effects of this substance (Ex. 3-830, p. 5). In response to this comment, OSHA notes that Patty's Industrial Hygiene and Toxicology (3rd rev. ed., Clayton and Clayton 1982) states that "the lowest concentration of ethylene glycol butyl ether vapor considered to be unpleasant and therefore disagreeable was 40 ppm" (Vol. 2C, p. 3939). This level is below OSHA's former PEL of 50 ppm, and the Agency thus believes that its former standard for 2-butoxyethanol was too high.
OSHA concludes that the former PEL of 50 ppm was insufficiently protective against the risk of 2-butoxyethanol's irritant, hematological, and other potential systemic effects, which constitute material health impairments. The limit of 25 ppm included in the final rule will reduce this significant risk to a level below that at which these toxic effects have been observed in animals and humans. This lower limit will also prevent the discomfort experienced by workers at exposure levels of 40 ppm. The skin notation is retained because of 2-butoxyethanol's ability to be absorbed dermally in toxic quantities (2-butoxyethanol's dermal LD(50) in rabbits is 490 mg/kg [RTECS 1988]).
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