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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: 34590-94-8; Chemical Formula: CH3OC3H6OC3H6OH
H.S. No. 1149

OSHA formerly had an 8-hour TWA limit of 100 ppm for dipropylene glycol methyl ether (DPGME), with a skin notation. The ACGIH recommends a TLV-TWA of 100 ppm and a TLV-STEL of 150 ppm, with a skin notation, for this colorless liquid with a mild, pleasant, ethereal odor and a bitter taste. OSHA proposed to retain the 8-hour permissible exposure limit of 100 ppm TWA, to add a 150-ppm STEL, and to retain the skin notation for dipropylene glycol methyl ether. NIOSH (Ex. 8-47, Table N1) concurs that these limits are appropriate, and the final rule establishes these limits.

Intact dogs receiving intravenous injections of DPGME exhibited central nervous system depression and died as a result of respiratory failure (Shideman and Procita 1951/Ex. 1-667). Rowe and associates (1954/Ex. 1-435) reported a single acute oral LD(50) for rats of 5.4 ml/kg. Even at the highest levels tested (not further specified), no single application of DPGME to the skin of rabbits was lethal, although some narcosis and transient weight loss did occur. However, a significant number of deaths occurred in a group of rabbits treated with 65 repeated dermal applications containing DPGME concentrations of 3 ml/kg or higher during a 90-day period. Four animal species, including the monkey, were exposed repeatedly to seven-hour daily inhalation exposures of between 300 and 400 ppm DPGME; the animals exhibited narcosis and changes in the lung and liver (Rowe, McCollister, Spencer et al. 1954/Ex. 1-435).

Humans inhaling DPGME concentrations of 300 to 400 ppm judged this level to be very disagreeable, but 100 ppm was tolerable and, in the opinion of the authors, was unlikely to produce organic injury (Rowe, McCollister, Spencer et al. 1954/Ex. 1-435). Patch tests on the skin of 250 human subjects produced neither irritation nor sensitization (ACGIH 1986/Ex. 1-3, p. 221). Humans exposed to DPGME vapor concentrations at levels between 50 to 2000 ppm experienced eye, nose, and throat irritation before the onset of CNS impairment, which occurred at 1000 ppm in one of two subjects (Stewart, Baretta, Dodd, and Torkelson 1970/Ex. 1-379).

NIOSH (Ex. 150, Comments on Dipropylene Glycol Monomethyl Ether) reported that it is developing a criteria document on the glycol ethers; NIOSH submitted recent toxicity data on DPGME, including the following: rats and mice inhaling concentrations of 50, 140, or 330 ppm DPGME six hours/day for nine days showed increased liver weights (at 50 and 140 ppm for the rat and at 330 ppm for the mouse), but no effects were observed when rats inhaled 15, 50, or 200 ppm DPGME six hours/day, five days/week for 13 weeks (Landry and Yano 1984, as cited in Ex. 150). NIOSH also reported results of a 1985 study by Miller et al. indicating that DPGME is metabolized via the same routes to the same types of metabolites - propylene glycol, and sulfate and glucuronide conjugates of DPGME - as previously identified for PGME (1-methoxy-2-propanol) (Miller, Hermann, Calhoun et al. 1985, as cited in Ex. 150). The Landry and Yano study (1984, as cited in Ex. 150) further indicated that at the concentrations tested, DPGME exerted no teratogenic or reproductive effects (NIOSH/Ex. 150, Comments on Dipropylene Glycol Monomethyl Ether).

The ARCO Chemical Company (Ex. 3-740) questioned the appropriateness of a skin notation for this substance. In response to ARCO, the Agency notes that DPGME, applied essentially according to the Draize method, is absorbed in sufficient quantities through rabbit skin to cause transient narcosis, although the absorption rate was not considered acutely dangerous (Patty's Industrial Hygiene and Toxicology, 3rd rev. ed., Vol. 2C, p. 3990, Clayton and Clayton 1982). Topical administration of 10 mg/kg DPGME five times per week for 13 weeks to shaved rabbit skin caused six deaths among seven animals (Chemical Hazards of the Workplace, 2nd ed., p. 221, Proctor, Hughes, and Fischman, 1988). To date, there are no human data demonstrating that dermal contact with DPGME is without a significant adverse health risk; therefore, in accordance with the policy described in Section VI.C.18, OSHA finds that the available evidence does not meet the criterion for deleting an existing skin notation.

In the final rule, OSHA is retaining a PEL of 100 ppm TWA and adding a STEL of 150 ppm for dipropylene glycol methyl ether; the skin notation is retained. The Agency concludes that this combined limit will substantially reduce the significant risks of central nervous system effects and irritation, which constitute material health impairments, that exist when workers are exposed to DPGME for short periods above the 100-ppm PEL.