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Methyl iodide

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

CAS number: 74–88–4

NIOSH REL: 2 ppm (10 mg/m3) TWA [skin]; NIOSH considers methyl iodide to be a potential occupational carcinogen as defined by the OSHA carcinogen policy [29 CFR 1990].

Current OSHA PEL: 5 ppm (28 mg/m3) TWA [skin]

1989 OSHA PEL: 2 ppm (10 mg/m3) TWA [skin]

1993-1994 ACGIH TLV: 2 ppm (12 mg/m3) TWA [skin], A2

Description of substance: Colorless liquid with a pungent, ether-like odor.

LEL: . . . Noncombustible Liquid

Original (SCP) IDLH: 800 ppm

Basis for original (SCP) IDLH: The chosen IDLH is based on the mouse 57-minute LC50 of 860 ppm [Buckell 1950 cited by Patty 1963].

Existing short-term exposure guidelines: 1991 American Industrial Hygiene Association (AIHA) Emergency Response Planning Guidelines (ERPGs):

ERPG-1: 25 ppm (60-minute)

ERPG-2: 50 ppm (60-minute)

ERPG-3: 125 ppm (60-minute)


Lethal concentration data:

Species Reference LC50 (ppm) LCLo (ppm) Time Adjusted 0.5-hr LC (CF) Derived value
Rat Bakhishev 1975 1,550 —– 30 min 1,550 ppm (1.0) 155 ppm
Mouse Buckell 1950 860 —– 57 min 1,065 ppm (1.24) 107 ppm
Rat Deichmann & Gerarde 1969 220 —– 4 hr 440 ppm (2.0) 44 ppm
Rat von Oettingen 1955 —– 3,800 15 min 3,017 ppm (0.79) 302 ppm

Other animal data: In a subchronic study, no rats died following exposures to 150 ppm for 6 hours/day for 3 days [Monsanto 1986].

Human data: None relevant for use in determining the revised IDLH.

Revised IDLH: 100 ppmBasis for revised IDLH: The revised IDLH for methyl iodide is 100 ppm based on acute inhalation toxicity data in animals [Bakhishev 1975; Buckell 1950; Monsanto 1986]. [Note: The 30-minute and 57-minute LC50 data were used rather than the 4-hour LC50 data so as not to magnify the conservatism already present in the correction factors. NIOSH recommends as part of its carcinogen policy that the “most protective” respirators be worn for methyl iodide at concentrations above 2 ppm.]


1. Bakhishev GN [1975]. Relationship between chemical structure and toxicity for some halogenated aliphatic hydrocarbons. Fiz Akt Vesh 7:35-36 (in Russian).

2. Buckell M [1950]. The toxicity of methyl iodide: I. Preliminary survey. Br J Ind Med 7:122-124.

3. Deichmann WB, Gerarde HW [1969]. Table 67. Acute inhalation toxicity of alkyl iodides. In: Toxicology of drugs and chemicals. New York, NY: Academic Press, Inc., p. 756.

4. Monsanto [1986]. Methyl iodide: pilot, 4-week, and 13-week inhalation toxicity studies in rats (ML-81-015, ML-81-084, ML-81-274). 1982-1986. [Unpublished report]. St. Louis, MO: Monsanto Company, Department of Medicine and Environmental Health.

5. Patty FA, ed. [1963]. Industrial hygiene and toxicology. 2nd rev. ed. Vol. II. Toxicology. New York, NY: Interscience Publishers, Inc., p. 1256.

6. von Oettingen WF [1955]. The halogenated aliphatic, olefinic, cyclic, aromatic, and halogenated insecticides, their toxicity and potential dangers. Washington, DC: U.S. Government Printing Office, U.S. Public Health Service Publication No. 414, pp. 30-32.