---

The information in this profile may be out-of-date. It was last revised in 1996. EXTOXNET no longer updates this information, but it may be useful as a reference or resource.

Please visit the National Pesticide Information Center (NPIC) to find updated pesticide fact sheets. If you don't find a fact sheet related to your question, feel free to call 1-800-858-7378. NPIC is open five days a week from 8:00am to 12:00pm Pacific Time.

---

E X T O X N E T

Extension Toxicology Network

Pesticide Information Profiles

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.

EXTOXNET primary files maintained and archived at Oregon State University

Revised June 1996

Methyl bromide; Bromomethane

Tradenames: Trade or common names of methyl bromide containing products include: Brom-o-Gas, Bromomethane, Celfume, Embafume, Haltox, MB, MeBr, Methogas, Profume, Terr-o-Gas, and Zytox.

Regulatory Status: Methyl bromide is a highly toxic compound in EPA Toxicity Class I. Labels for products containing it must bear the Signal Word DANGER. Methyl bromide is a Restricted Use Pesticide (RUP). RUPs may be purchased and used only by certified applicators.

EPA has expressed concerns and proposed restrictions on methyl bromide due to concerns over its potential to destroy ozone. Ozone-depleting chemicals fall within the scope of the Clean Air Act. Unlike FIFRA, the Clean Air Act does not contain a risk/benefit balancing process that would allow retention of essential or high benefit uses, nor does the listing and phase-out of ozone depleters depend on the availability of alternative products.

Chemical Class: Not Available

Introduction: Methyl bromide is chiefly used as a gas soil fumigant against insects, termites, rodents, weeds, nematodes, and soil-borne diseases. It has been used to fumigate agricultural commodities, grain elevators, mills, ships, clothes, furniture, and greenhouses. About 70% of methyl bromide produced in the U.S. goes into pesticidal formulations.

Formulation: Methyl bromide is chiefly used as a gas soil fumigant against insects, termites, rodents, weeds, nematodes, and soil-borne diseases.

Toxicological Effects:

• Acute toxicity: Since bromomethane is a gas at ambient temperatures, the most significant route of exposure is inhalation [188]. The reported 1-hour inhalation LC50 in rats is 4.5 mg/L, and the 11-hour LC50 in rabbits is 8 mg/L [8]. Inhalation of 6 mg/L for 10 to 20 hours, or 30 mg/L for 1.5 hours is lethal to humans [8]. The compound is readily absorbed through the lung alveoli (gas exchange regions). Methyl bromide can be highly irritating to the mucous membranes of the eyes, airways, and skin with contact [17]. About 1000 human poisoning incidents caused by methyl bromide exposure have been documented, with effects ranging from skin and eye irritation to death [17]. Most fatalities and injuries occurred when methyl bromide was used as a fumigant. The lowest inhalation level found to cause toxicity in humans is 0.14 mg/L in air [17]. A typical delay in onset of symptoms following exposure combined with an odor threshold (level at which most people can smell it) well-above the level at which toxic effects occur, means that the victim may not realize a harmful exposure is occurring until it is too late [17]. Initial acute effects may include headache, dizziness, nausea or vomiting, chest and abdominal pain, and irritated eyes, nose, and throat [188]. With sufficient exposure, symptoms of slurred speech, blurred vision, temporary blindness, mental confusion, and sweating may occur [188]. More severe symptoms at even higher doses may include lung swelling; congestion; hemorrhaging of the brain, heart, and spleen; severe kidney damage; and numbness, tremors, and convulsions [188]. The nervous effects observed in lab animals included degeneration of key nerve cells in various portions of the brain and peripheral nervous system [188]. Death may occur from respiratory failure [188]. The rat oral LD50 (bromomethane administered as a liquid, or in solution) is 214 mg/kg [1], also indicating moderate to high toxicity.
• Chronic toxicity: Chronic exposure to methyl bromide can cause extensive damage to neurons (nerve cells) involved in cognitive processes and physical coordination or muscular control [188]. These effects were seen in rats exposed to 0.51 to 1.3 mg/L 6 hours per day for 5 days [188]. Rats exposed to 65 ppm over 4 weeks for an average of 7 hours per day for 4 to 5 days did not show neurological effects, but this level of exposure did result in severe, in some cases irreversible, neurological effects in rabbits over a similar time period [188]. Exposure levels of 0.1 mg/L over 8 months (7.5 hours per day, 4 days/week) did not produce observable neurotoxicity [188]. The symptoms of chronic exposure may include dizziness, vision and hearing disturbances, depression, confusion, hallucinations, euphoria, personality changes, and irritability [8]. A chronic pneumonia-like syndrome may become apparent after repeated exposure to sufficient levels [8]. Other targets of the fumigant identified through long-term animal studies are the heart, adrenal gland, and the testis [189].
• Reproductive effects: No reproductive efffects were seen in rats exposed to up to 0.3 mg/L for 7 hours/day, 5 days a week, for 3 weeks prior to mating and during gestation [188]. This suggests that methyl bromide does not cause reproductive effects.
• Teratogenic effects: No teratogenic efffects were seen in rats exposed to up to 0.3 mg/L for 7 hours/day, 5 days a week, for 3 weeks prior to mating and during gestation [188]. This evidence indicates that bromomethane is unlikely to cause teratogenic effects.
• Mutagenic effects: Mutagenic effects were seen in mouse cell cultures, mutagenicity assays with bacteria, and in in human white blood cells [190]. Rat liver cells did not display increased rates of mutation after exposure to methyl bromide [190]. Methyl bromide is considered to be weakly mutagenic [188].
• Carcinogenic effects: In one study of industrial workers exposed to various brominated compounds, exposure to methyl bromide was suggested as the possible common factor in two fatal cases of testicular cancer, but other exposures could not be ruled out [189]. In a rat study, methyl bromide given at 50 mg/kg/day by stomach tube for 90 days (gavage) induced stomach tumor increases [188,190]. It appeared that the cancerous growth was due to severe localized cellular injury, with subsequent increased cell reproduction to repair tissue damage amplifying the natural incidence of mutant or abnormal cells [188]. This is not likely to occur at low doses. Thus, the data are inconclusive.
• Organ toxicity: Acute exposure primarily damages the lung and results in nervous system effects; chronic exposure may cause damage to the central nervous system, kidneys, and lungs. Other targets of the fumigant are the heart, nasal cavities, adrenal gland, and the testis.

• Fate in humans and animals: The major route of absorption of methyl bromide vapors is through the lungs [188]. Some of the compound is excreted through the lungs as unchanged methyl bromide, but a significant amount also undergoes metabolic decomposition [32]. The primary breakdown products are the bromide ion and methanol, which are detectable in the blood and tissues and are excreted in the urine [32]. Organic bromides (formed by reaction of bromide ion with molecular carbon centers in biomolecules) also appear in stomach fluids and mucus. In humans, methyl bromide's half-life in blood is about 12 days [32]. As a result, the toxic effects of methyl bromide can be delayed or prolonged [32]. Additionally, once in a cell, this chemical inactivates many enzyme systems, so prolonged small doses can cause severe toxicity [32].

Ecological Effects:

• Effects on birds: Bromomethane is most likely to be in vapor form, and unless birds are in the fumigation area, during the fumigation, they are unlikely to be exposed .
• Effects on aquatic organisms: Methyl bromide is moderately toxic to aquatic organisms. Acute toxicity in freshwater fish (bluegill sunfish) occurs at concentrations of 11 mg/L and in saltwater fish (tidewater silversides) at about 12 mg/L [8].
• Effects on other organisms: It is not toxic to bees [1].

Environmental Fate:

• Breakdown in soil and groundwater: Methyl bromide quickly evaporates at temperatures ordinarily encountered in fumigating, but some may be entrapped in soil micropores following application [11]. Methyl bromide is moderately persistent in the soil environment, with a field half-life of between 30 and 60 days; a representative half-life is estimated to be about 55 days [11]. Transformation of methyl bromide into bromide increases as the amount of organic matter in the soil increases. It is soluble in water and very poorly sorbed by soils. Some leaching may occur if bromomethane is entrapped in soil micropores following fumigation; the rate of degradation for retained bromomethane in fumigated soil is 6 to 14% per day at 20 C [11].
• Breakdown in water: Methyl bromide quickly evaporates at temperatures ordinarily encountered in fumigating; therefore run-off from fields into surface waters is very rare. If it does contact surface waters, the average half-life for methyl bromide under field conditions has been calculated to be 6.6 hours at 11 C [8]. Another study showed the half-life in water to be 20 days at 25 C in a neutral solution [8].
• Breakdown in vegetation: The amount of bromide ion (the metabolite of methyl bromide) taken up from the soil, is proportional to the protein content of the crop. Higher levels of the bromide ion will most likely be found in high-protein plants [8].

Physical Properties:

• Appearance: Methyl bromide is a colorless gas or volatile liquid which is usually odorless, but has a sweet, chloroform-like odor at high concentrations [1].
• Chemical Name: bromomethane [1]
• CAS Number: 74-83-9
• Molecular Weight: 94.94
• Water Solubility: 13,400 mg/L at 25 C [1]
• Solubility in Other Solvents: easily miscible with ethanol, ether, aromatic carbon disulfide, and ketones [1]
• Melting Point: -93.6 C [1]
• Vapor Pressure: 227,000,000 mPa @ 25 C [1]
• Partition Coefficient: Not Available
• Adsorption Coefficient: 22 [11]

Exposure Guidelines:

• ADI: 1.0 mg/kg/day (as bromide ion) [12]
• MCL: Not Available
• RfD: 0.0014 mg/kg/day [13]
• PEL: 80 mg/m3 (ceiling) [14]
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

Great Lakes Chemical Corporation
One Great Lakes Blvd.
P.O. Box 2200
West Lafayette, IN 47906

• Phone: 317-497-6204
• Emergency: 501-862-5141
  

References:

References for the information in this PIP can be found in Reference List Number 10

DISCLAIMER: The information in this profile does not in any way replace or supersede the information on the pesticide product labeling or other regulatory requirements. Please refer to the pesticide product labeling.