May 1994
Immediately Dangerous to Life or Health Concentrations (IDLH)

CAS number: 72–43–5

NIOSH REL: None established; NIOSH considers methoxychlor to be a potential occupational carcinogen as defined by the OSHA carcinogen policy [29 CFR 1990].

Current OSHA PEL: 15 mg/m3 TWA

1989 OSHA PEL: 10 mg/m3 TWA

1993-1994 ACGIH TLV: 10 mg/m3 TWA

Description of substance: Colorless to light-yellow crystals with a slight, fruity odor.

LEL: . . Unknown

Original (SCP) IDLH*: No Evidence [*Note: “Effective” IDLH = 7,500 mg/m3 — see discussion below.]

Basis for original (SCP) IDLH: ACGIH [1971] stated that methoxychlor has a very low toxicity. The available toxicological data indicate that an acute exposure to a high concentration of methoxychlor would not result in death or in any irreversible health effects. For this draft technical standard, therefore, respirators have been selected on the basis of the assigned protection factor afforded by each device. However, for some particulate substances for which no evidence of an IDLH exists, the determination of allowable respiratory protection based on protection factors may result in the assignment of respirators for concentrations that are not likely to be encountered in the occupational environment. Therefore, for all such particulate substances, it has been arbitrarily determined that only the “most protective” respirators are permitted for use in concentrations exceeding 500 ´ the OSHA PEL (500 ´ 15 mg/m3 is 7,500 mg/m3).

Short-term exposure guidelines: None developed


Lethal dose data:

Species Reference Route LD50




Adjusted LD Derived value
Rat CDC 1956 oral 5,000 ----- 35,000 mg/m3 3,500 mg/m3
Mouse Coats et al. 1977 oral 1,000 ----- 7,000 mg/m3 700 mg/m3
Rabbit Kenaga & Morgan 1978 oral >6,000 ----- >42,000 mg/m3 >4,200 mg/m3

Human data: It has been reported that 6,430 mg/kg is the estimated fatal oral dose [AAPCO 1966]. [Note: An oral dose of 6,430 mg/kg is equivalent to a worker being exposed to about 300,000 mg/m3 for 30 minutes, assuming a breathing rate of 50 liters per minute and 100% absorption.]

Revised IDLH: 5,000 mg/m3

Basis for revised IDLH: The available toxicological data contain no evidence that an acute exposure to a high concentration of methoxychlor would impede escape or cause any irreversible health effects within 30 minutes. However, the revised IDLH for methoxychlor is 5,000 mg/m3 based on being 500 times the OSHA PEL of 10 mg/m3 (500 is an assigned protection factor for respirators and was used arbitrarily during the Standards Completion Program for deciding when the "most protective" respirators should be used for particulates). [Note: NIOSH recommends as part of its carcinogen policy that the "most protective" respirators be worn for methoxychlor at any detectable concentration.]


1. AAPCO [1966]. Pesticide chemicals official compendium. Topeka, KS: Association of the American Pesticide Control Officials, Inc., p. 750.

2. ACGIH [1971]. Methoxychlor (2,2-bis-p-methoxy phenyl-1,1,1-trichloroethane). In: Documentation of the threshold limit values for substances in workroom air. 3rd ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, pp. 152-153.

3. CDC [1956]. Clinical memoranda on economic poisons. Atlanta, GA: Communicable Disease Center, Bureau of State Services, Public Health Service, U.S. Department of Health, Education, and Welfare, Public Health Service Publication No. 476, pp. 33-38.

4. Coats JR, Metcalf RL, Kapoor IP [1977]. Effective DDT analogues with altered aliphatic moieties. Isobutanes and chloropropanes. J Agri Food Chem 25:859-868.

5. Kenaga EE, Morgan RW [1978]. Commercial and experimental organic insecticides (1978 revision). Entomological Society of America Special Publication 78-1:16.

Page last reviewed: December 4, 2014