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: 72-43-5; Chemical Formula: C16H15Cl3O2

OSHA formerly applied its generic 15-mg/m3 TWA limit for particulates to methoxychlor. The ACGIH recommends a limit of 10 mg/m3 TWA for this white crystalline solid. This is the limit that was proposed for the total particulate of methoxychlor, and the final rule establishes this limit. NIOSH (Ex. 8-47, Table N4) concurs with the selection of these limits.

The reported oral LD(50) for methoxychlor in rats is 6000 mg/kg (Lehman 1954, as cited in ACGIH 1986/Ex. 1-3, p. 364). Lehman also determined that 100 ppm for two years is the lowest dietary level producing no effect in rats; this corresponds to a level of 350 mg/man/day (Lehman 1954, as cited in ACGIH, 1986/Ex. 1-3, p. 364). Results of another dietary study indicated that rats fed 200 ppm methoxychlor for two years were not affected in terms of growth or survival (Hodge, Maynard, and Blanchet 1952/Ex. 1-488). Tegeris and co-workers (1966/Ex. 1-389) reported that dogs fed 1 g/kg daily for six months showed weight loss; most animals died within nine weeks when the dietary level was increased to 2 g/kg daily (Tegeris, Earl, Smalley, and Curtis 1966/Ex. 1-389). Morgan and Hickenbottom (1978/Ex. 1-351) reported that male Holtzman rats fed 10, 40, 160, or 640 mg/kg for 24 hours showed no liver abnormalities. Extrapolating from animal data, Lehman (1954) estimated the dose levels that would produce toxic effects in humans as follows: the fatal oral dose would be 450 grams; adverse health effects would occur at 6430 mg/kg orally; and 2414 mg/kg is the level at which dermal effects would be predicted to occur (Lehman 1954, as cited in ACGIH 1986/ Ex. 1-3, p. 364).

NIOSH concurs with these limits (Ex. 8-47, Table N4) but recommends that methoxychlor also be designated as a potential occupational carcinogen. However, OSHA notes that both IARC and NCI find the evidence for the carcinogenicity of methoxychlor in animals to be inadequate (Dangerous Properties of Industrial Materials, 7th ed., p. 1326, Sax and Lewis 1989). The Agency will continue to monitor the scientific evidence for this substance in the future. No other comments on methoxychlor were received by OSHA.

In the final rule, OSHA is reducing the existing 15-mg/m3 8-hour TWA limit for methoxychlor to 10 mg/m3 (total particulates) to reduce the significant health risks to systemic toxicity, which constitutes a material impairment of health. OSHA also notes that cancer may be an exposure effect of methoxychlor.

Page last reviewed: September 28, 2011