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CHEMINFO Record Number: 614
CCOHS Chemical Name: Methyl iodide


Chemical Name French: Iodure de méthyle
Chemical Name Spanish: Yoduro de metilo
CAS Registry Number: 74-88-4
UN/NA Number(s): 2644
RTECS Number(s): PA9450000
EU EINECS/ELINCS Number: 200-819-5
Chemical Family: Halogenated aliphatic hydrocarbon / saturated halogenated hydrocarbon / halogenated alkane / haloalkane / monohaloalkane / alkyl halide / alkyl iodide
Molecular Formula: C-H3-I
Structural Formula: CH3-I


Appearance and Odour:
Colourless liquid with a sweet, pungent odour. Turns yellow, red or brown when exposed to light or moisture; lachrymator (vapour irritates the eyes and causes tears).

Odour Threshold:
Not available

Warning Properties:
POOR warning properties reported.(3)

Technical grade methyl iodide is normally at least 99% pure with copper. Iodine may be present as an impurity.(13) It is stabilized with copper.

Uses and Occurrences:
Used primarily as a methylating agent in production of pharmaceuticals (eg. quaternary ammonium compounds) and other chemicals. Sometimes used as an embedding material and reagent in microscopy; component of fire extinguishers; catalyst in production of hydrides; etching agent for micronized electronic circuits.
Produced naturally by certain marine microorganisms; atmospheric levels of 5.8-17.4 mg/m3 have been reported.(1)


Colourless liquid with a sweet, pungent odour. Turns yellow, red or brown on exposure to light or moisture. Will not burn. Can decompose at high temperatures forming toxic gases. VERY TOXIC. May be fatal if inhaled, absorbed through the skin or swallowed. CORROSIVE to the eyes, skin and respiratory tract. May cause lung injury - effects may be delayed. Central nervous system depressant. Vapour may cause headache, nausea, dizziness, drowsiness, incoordination, confusion, unconsciousness and death.


Effects of Short-Term (Acute) Exposure

Methyl iodide vapour is irritating, causing symptoms such as sore throat and coughing. There have been a few reported cases of severe effects resulting from prolonged or repeated accidental inhalation exposures (concentrations not reported).
The cases are notable because symptoms typically appeared only after a delay of hours to days, in one case after 3 consecutive weekend exposures. A person may be exposed a number of times, or for a prolonged period, before showing symptoms.(2,6,11)
Methyl iodide is a central nervous system (CNS) depressant. The symptoms resemble those of alcohol intoxication (drunkenness) and include dizziness, giddiness, slurred speech, double vision and muscular incoordination. Progression to seizures, coma and death may occur.
Severe, prolonged and possibly permanent injury to the nervous system (mental dullness, hallucination) has been reported.
High exposures may cause a life-threatening accumulation of fluid in the lungs (pulmonary edema) resulting in symptoms such as difficult and shallow breathing. The signs and symptoms of pulmonary edema can be delayed until hours or even days after the exposure.(2,6,11)
Kidney injury has also occurred resulting in decreased urinary output.

Skin Contact:
A pad soaked in methyl iodide and held against the forearm for 10 minutes produced stinging and reddening; swelling and blistering appeared several hours later.(4) Similar effects, including delayed burning, have been reported elsewhere.(11)
When methyl iodide was not held against the skin, but allowed to evaporate, no effects were observed.(4)
Methyl iodide has been given a skin notation by the ACGIH, indicating that skin absorption can significantly contribute to overall exposure.(3)

Eye Contact:
The liquid has been reported to cause redness, irritation and swelling of the eyes (conjunctivitis). Experience with human skin exposure indicates that prolonged contact could cause corrosive injury (tissue destruction).(11) In animal tests, the vapour caused irritation.(4)

No human information is available, but methyl iodide can probably cause gastric irritation and CNS depression (similar to effects of inhalation). Animal studies indicate moderate toxicity by ingestion.(1,4)

Effects of Long-Term (Chronic) Exposure

No information on chronic human exposures is available. In animal studies, chronic toxicity appears to be similar to toxicity from short-term exposures.


There is no human information available. Tumours were seen in animals following injections; this type of exposure is not directly relevant to occupational situations. The International Agency for Research on Cancer (IARC) has concluded that there is limited evidence for the carcinogenicity of methyl iodide to experimental animals.(17)

The International Agency for Research on Cancer (IARC) has concluded that this chemical is not classifiable as to its carcinogenicity to humans (Group 3).

The American Conference of Governmental Industrial Hygienists (ACGIH) has not assigned a carcinogenicity designation to this chemical.

The US National Toxicology Program (NTP) has not listed this chemical in its report on carcinogens.

Teratogenicity and Embryotoxicity:
No information available

Reproductive Toxicity:
No information available

It is not possible to conclude that methyl iodide is mutagenic. There is no human information available. Methyl iodide has been shown to interact with DNA in live animals, but mutagenic effects have not been shown. Methyl iodide caused DNA damage and mutations in short-term tests using bacteria, yeast and cultured mammalian cells.(17)

Toxicologically Synergistic Materials:
No information available

Potential for Accumulation:
There may be short-term accumulation of methyl iodide or its break-down products (delayed effects). In experimental studies, inorganic iodide was formed, was concentrated in the thyroid and was excreted in the urine.(1)


Take proper precautions to ensure your own safety before attempting rescue; e.g., wear appropriate protective equipment, use the "buddy" system. Remove source of contamination or move victim to fresh air. If breathing is difficult, oxygen may be beneficial if administered by a person trained in its use, preferably on a doctor's advice. If breathing has stopped, trained personnel should begin artificial respiration (AR) or, if the heart has stopped, cardiopulmonary resuscitation (CPR) immediately. Obtain medical attention immediately.

Skin Contact:
Avoid direct contact with this chemical. Wear chemical protective gloves, if necessary. Flush contaminated area with lukewarm, gently flowing water for at least 20-30 minutes, by the clock. If irritation persists, repeat flushing. DO NOT INTERRUPT FLUSHING. If necessary, keep emergency vehicle waiting. Under running water, remove contaminated clothing, shoes and leather goods (e.g. watchbands, belts). Transport victim to an emergency care facility immediately. Discard contaminated clothing, shoes and leather goods.

Eye Contact:
Avoid direct contact. Wear chemical protective gloves, if necessary. Immediately flush the contaminated eye(s) with lukewarm, gently flowing water for at least 20-30 minutes, by the clock, while holding the eyelid(s) open. Neutral saline solution may be used as soon as it is available. DO NOT INTERRUPT FLUSHING. If necessary, keep emergency vehicle waiting. Take care not to rinse contaminated water into the unaffected eye or onto the face. If irritation persists, repeat flushing. Quickly transport victim to an emergency care facility.

Never give anything by mouth if victim is rapidly losing consciousness, is unconscious or convulsing. Have victim rinse mouth thoroughly with water. DO NOT INDUCE VOMITING. Have victim drink 240 to 300 mL (8 to 10 oz.) of water. If vomiting occurs naturally, rinse mouth and repeat administration of water. If breathing has stopped, trained personnel should begin artificial respiration (AR) or, if the heart has stopped, cardiopulmonary resuscitation (CPR) immediately. Obtain medical attention immediately.

First Aid Comments:
Provide general supportive measures (comfort, warmth, rest).
Consult a doctor and/or the nearest Poison Control Centre for all exposures except minor instances of inhalation or skin contact.
Some recommendations in the above sections may be considered medical acts in some jurisdictions. These recommendations should be reviewed with a doctor and appropriate delegation of authority obtained, as required.
All first aid procedures should be periodically reviewed by a doctor familiar with the material and its conditions of use in the workplace.


Flash Point:
Not applicable (does not burn)

Lower Flammable (Explosive) Limit (LFL/LEL):
Not applicable

Upper Flammable (Explosive) Limit (UFL/UEL):
Not applicable

Autoignition (Ignition) Temperature:
Not applicable

Sensitivity to Mechanical Impact:
Stable material. Probably not sensitive.

Sensitivity to Static Charge:
Not sensitive. Not a flammable material.

Combustion and Thermal Decomposition Products:
Iodine and hydrogen iodide (13)

Fire Hazard Summary:
Methyl iodide is not combustible. During a fire, irritating/toxic iodine vapour and hydrogen iodide gas may be generated. The vapour formed upon decomposition at 800 deg C was less toxic than the undecomposed vapour in animal tests.(10)

Extinguishing Media:
Will not burn. Use extinguishing media appropriate for surrounding fire.

Fire Fighting Instructions:
Methyl iodide is not combustible. However, during a fire irritating/toxic gases may be generated. Evacuate area. Isolate materials not yet involved in fire and protect personnel. Move containers from fire area if it can be done without risk. Use water spray to keep fire-exposed containers cool. Use flooding quantities or water as a fog.
Do not enter without wearing specialized protective equipment suitable for the situation. Firefighter's normal protective clothing (Bunker Gear) will not provide adequate protection. A full-body encapsulating chemical protective suit with positive pressure self-contained breathing apparatus (MSHA/NIOSH approved or equivalent) may be necessary.


NFPA - Comments:
NFPA has no listing for this chemical in Codes 49 or 325.


Molecular Weight: 141.94

Conversion Factor:
1 ppm = 5.8 mg/m3; 1 mg/m3 = 0.17 ppm at 25 deg C

Physical State: Liquid
Melting Point: -67 deg C (-88 deg F)
Boiling Point: 43 deg C (109 deg F)
Relative Density (Specific Gravity): 2.28 (water = 1)
Solubility in Water: Soluble (14 g/L at 20 deg C) (1)
Solubility in Other Liquids: Very soluble in acetone, ethanol, benzene, diethyl ether and carbon tetrachloride.(1)
Coefficient of Oil/Water Distribution (Partition Coefficient): Log P(oct) = 1.51-1.69 (1)
pH Value: Not available
Vapour Density: 4.9 (air = 1)
Vapour Pressure: 400 mm Hg (53 kPa) at 25 deg C
Saturation Vapour Concentration: 526000 ppm at 25 deg C (calc.)
Evaporation Rate: No information reported, but expected to evaporate readily.


Stable material. Turns yellow, red or brown on exposure to light or moisture.

Hazardous Polymerization:
Not expected to occur.

Incompatibility - Materials to Avoid:

NOTE: Chemical reactions that could result in a hazardous situation (e.g. generation of flammable or toxic chemicals, fire or detonation) are listed here. Many of these reactions can be done safely if specific control measures (e.g. cooling of the reaction) are in place. Although not intended to be complete, an overview of important reactions involving common chemicals is provided to assist in the development of safe work practices.

STRONG OXIDIZERS - may react explosively.

SILVER CHLORITE - reaction caused explosions; immediately in the absence of solvents; delayed in the presence of solvents.(8)

TRIALKYLPHOSPHINES - in the absence of a solvent, the quaternation reaction may lead to explosions.(8)

Hazardous Decomposition Products:
Iodine, hydrogen iodide

Conditions to Avoid:
High temperatures, light, moisture.

Corrosivity to Metals:
No corrosive action in NACE tests on metals.(14)

Stability and Reactivity Comments:
Methyl iodide is a volatile, reactive substance. Reactions must be carefully controlled.(8)


LC50 (rat): 232 ppm (1350 mg/m3) (4-hr exposure) (3)
LC50 (mouse): 860 ppm (5000 mg/m3) (1-hr exposure) (4)

LD50 (oral, rat): 76 mg/kg (1); 150-220 mg/kg (4)

Eye Irritation:

A 10-minute exposure to high vapour concentrations (25000 mg/m3) caused eye irritation in rats.(4)

Skin Irritation:

Slight irritation was observed in rats following a patch test (material held against the skin). Methyl iodide allowed to evaporate freely did not produce any effects.(4)

Effects of Short-Term (Acute) Exposure:

Twenty inhalation exposures of mice to 500 mg/m3 (90 ppm) over a 30-day period (125 hrs total) did not produce any signs of toxicity. All animals died when exposed to 1000 mg/m3 (180 ppm) for 11-43 hours, or 5000-50000 mg/m3 (900-9000 ppm) for 10 minutes, or 85000 mg/m3 (15000 ppm) for 15 minutes.(4) The minimum fatal concentration after 24 hours continuous exposure was found to be 73 ppm (425 mg/m3) for mice; 54 ppm (310 mg/m3) was not toxic.(5) In a rat study, 15-minute exposures to vapour levels of 9000 mg/m3 (1590 ppm) or 16000 mg/m3 (2760 ppm) were not lethal. Exposure for 15 minutes to vapour at 22000 mg/m3 (3790 ppm) or higher, was lethal.(12) The symptoms of exposure included lachrymation (runny eyes), general discomfort, drowsiness and unconsciousness.(4) Irritation of the airways and severe lung damage (pulmonary edema) were observed in fatally exposed animals. Slight liver and kidney damage were also noted in animals that died.(4,12)

Effects of Long-Term (Chronic) Exposure:

No adverse effects were seen in rats after a 14-week exposure at 10 ppm (60 mg/m3). Eye irritation and decreased body weight were seen at 30 ppm (175 mg/m3) and 60 ppm (350 mg/m3). Death occurred after a 4-week exposure at 143 ppm (830 mg/m3).(3)

No adverse effects were seen in rats after daily oral doses of 30-50 mg/kg, 5 days/week for a month.(5)

Methyl iodide induced tumours in rats and mice following injection (a route of exposure not relevant to occupational exposures).(17) The International Agency for Research on Cancer (IARC) evaluation of the carcinogenicity of methyl iodide to experimental animals: limited evidence.(1,17)

Methyl iodide can react with DNA of live animals.(1,17)
Methyl iodide caused DNA damage and mutations in short-term tests using bacteria, yeast and cultured mammalian cells.(1,17)


Selected Bibliography:
(1) IARC monographs on the evaluation of the carcinogenic risk of chemicals to humans. Vol. 41. IARC, 1986. p. 213-227
(2) Garland, A., et al. Methyl iodide poisoning. British Journal of Industrial Medicine. Vol. 2, no. 4 (1945). p. 209-211
(3) Documentation of the threshold limit values and biological exposure indices. 6th ed. Vol. II. ACGIH, 1991. p. 1013-1014
(4) Buckell, M. The toxicity of methyl iodide : I. Preliminary survey. British Journal of Industrial Medicine. Vol. 7 (1950). p. 122-124
(5) Patty's industrial hygiene and toxicology. 3rd rev. ed. Vol. 2B. John Wiley & Sons, 1981. p. 3433-3436, 3446-3449, 3586-3601
(6) Appel, G.B., et al. Methyl iodide intoxication. Annals of Internal Medicine. Vol. 82, no. 4 (Apr. 1975). p. 534-536
(7) Forsberg, K., et al. Quick selection guide to chemical protective clothing. 4th ed. Van Nostrand Reinhold, 2002
(8) Bretherick, L. Bretherick's handbook of reactive chemical hazards. 4th ed. Butterworths, 1990. p. 6, 158-159
(9) NIOSH pocket guide to chemical hazards. NIOSH, June 1994. p. 210-211
(10) Chambers, W. An investigation of the toxicity of proposed fire extinguishing fluids. (Research report no. 23.) Medical Division, Army Chemical Corps, Oct. 1950. p. 5, 7-11, 23, 31-32, 34-35, 41-42
(11) NIOSH current intelligence bulletin 43 : Monohalomethanes. NIOSH, Sept. 27, 1984
(12) Hasegawa, H., et al. Experimental study of methyl iodide poisoning. Industrial Health. Vol. 9, no. 1-2 (1971). p. 36-45
(13) HSDB record for iodomethane. Last revision date: 92/04/01.
(14) Corrosion data survey : metals section. 6th ed. NACE, 1985. p. 82-83
(15) Emergency response planning guide. AIHA Journal. Vol. 56, no.2, 1995. p. 202
(16) European Economic Community. Commission Directive 94/69/EC. Dec. 19, 1994
(17) International Agency for Research on Cancer (IARC). IARC monographs on the evaluation of carcinogenic risks to humans. Vol. 71, parts 1, 2 and 3. Re-evaluation of some organic chemicals, hydrazine and hydrogen peroxide. World Health Organization, 1999

Information on chemicals reviewed in the CHEMINFO database is drawn from a number of publicly available sources. A list of general references used to compile CHEMINFO records is available in the database Help.

Review/Preparation Date: 1992-11-12

Revision Indicators:
Trans PEL-TWA 1993-04-01
Trans PEL comments 1993-04-01
TDG 1994-03-01
Fire fighting instructions 1994-10-01
EU class 1996-06-01
Sampling 1996-06-01
Respiratory guidelines 1996-06-01
ERPG 1996-06-01
EU risk 1996-06-01
EU safety 1996-06-01
TLV-TWA 1996-09-01
US transport 1998-03-01
Resistance of materials 1998-05-01
TLV comments 1998-08-01
Mutagenicity 2000-03-01
Animal info 2000-03-01
Bibliography 2000-03-01
Carcinogenicity 2002-02-25
WHMIS proposed classification 2002-02-25
Emergency overview 2002-02-25
TDG 2002-05-09
WHMIS detailed classification 2002-06-04
WHMIS health effects 2002-06-04
PEL-TWA final 2003-10-02
PEL transitional comments 2003-10-02
PEL-TWA transitional 2003-10-02
Resistance of materials for PPE 2004-03-10
EU classification 2005-02-06
Molecular weight 2005-09-26

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