Methyl iodide

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)

ACUTE TOXICITY DATA:

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 ppm Basis 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.]

REFERENCES:

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.