E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Publication Date: 9/93
TRADE OR OTHER NAMES
Trade or common names of methyl bromide containing products include:
Brom-o-Gas, Celfume, Embafume, MB, MeBr, Methogas, Profume, Terr-o-Gas, and
EPA has proposed restrictions on methyl bromide, as well as a schedule of
phaseout by the year 2000. Methyl bromide is considered an ozone depleting
chemical and thus falls under the Clean Air Act with an ozone depletion
potential of 0.2%.
The methyl bromide phaseout is due to action under the Clean Air Act, not
FIFRA. 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 phaseout of ozone depleters depend on the
availability of alternative products (16).
Methyl bromide is most often used as a gas 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 United States goes into
pesticidal formulations. Nonpesticidal uses include degreasing wool and
extracting oils from nuts, seeds and flowers. Methyl bromide is also a
methylating agent in the chemical industry. In the past, it was used as a
refrigerant and as a fire-extinguishing agent in aircraft. The chemical name
for this fumigant is bromomethane.
Methyl bromide is a Restricted Use Pesticide (RUP) because of its high
acute toxicity to applicators. Restricted Use Pesticides may be purchased and
used only by certified applicators.
Methyl bromide, labeled with a DANGER signal word, is an extremely toxic
vapor. In humans, methyl bromide is readily absorbed through the lungs. Most
problems occur as a result of inhalation. About 1,000 human poisoning
incidents caused by methyl bromide exposure have been documented, with effects
ranging from skin and eye irritation to death. Most fatalities and injuries
occurred when methyl bromide was used as a fumigant.
Inhalation of 1,600 ppm for 10-20 hours, or 7,900 ppm for 1.5 hours is
lethal to humans (8). The lowest inhalation level found to cause toxicity in
humans is 35 ppm in air.
Methyl bromide is a dangerous cumulative poison. First symptoms often
are due to damage to the nervous system, and may be delayed from 48 hours to
as long as several months after exposure. This delay, combined with methyl
bromide's lack of odor, means that the victim may not realize that exposure is
occurring until much time has passed.
Symptoms of poisoning vary widely. Soon after inhalation of large doses,
symptoms may include headache, dizziness, nausea, chest and abdominal pain,
and a dry throat. Three to 12 hours after vapor inhalation, symptoms include
slurred speech, blurred vision, temporary blindness, mental confusion, and
sweating. More severe symptoms may include lung swelling; congestion;
hemorrhaging of the brain, heart, and spleen; severe kidney damage; and
numbness. Death may occur within 1-30 hours, usually from respiratory
Although skin absorption is not an important route for methyl bromide
intoxication, the skin is affected by contact with this chemical. Methyl
bromide can cause enormous blisters that are rarely deep enough to destroy the
entire skin layer. Small amounts of skin or eye contact brings on shortness
of breath and itching. If absorbed through the skin, nausea and vomiting may
result. Clothing that can not "breathe" may delay the evaporation of the
pesticide from the skin. Continued contact with skin can cause death.
Ingestion of methyl bromide may cause hand tremors, and convulsions.
The inhalation LC50 for rats is 3,120 ppm/15 minutes (7), 2,700 ppm/30
minutes, and 1,164 ppm/60 minutes. For guinea pigs, it is 300 ppm/9 hours and
it is 2,000 ppm/11 hours in the rabbit (7). The rat LD50 administered in
liquid is 20 mg/L (11). The dermal LD50 for rabbits is 15 ppm.
Common animal responses to high doses often include lung irritation,
fluid accumulation in the lungs, paralysis, and kidney, liver, and nervous
system damage (9).
Chronic exposures to methyl bromide can cause dizziness, vision and
hearing disturbances, depression, confusion, hallucinations, euphoria,
personality changes, and irritability. If exposure is severe enough, lung
irritation followed by lung swelling and bronchial pneumonia may occur (7).
No reproductive problems involving methyl bromide have been observed in
test animals, though few experiments have been performed.
Inhalation of methyl bromide for 6-7 hours per day during gestation was
reported to cause no birth defects on rabbits and rats (7).
The overall scientific evidence indicates that methyl bromide is a
mutagen, but that its potential to cause genetic mutations is relatively low
(13). Mutagenic effects were seen in a mouse cell test and two different
tests on bacteria (2). In addition, fruit flies showed mutagenic effects as
did human white blood cells (6). However, rat liver cells did not display
mutagenicity after exposure to methyl bromide (2).
Methyl bromide is considered to be a potent cell growth stimulant and is
thus a potential promoter of cancerous growth. 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. The mortality rate for this cancer was significantly higher than
In another study, methyl bromide induced tumors in the stomach of the rat
(2). The chemical was given through the stomach in an oil solution for 90
days. In 13 of 20 rats given high doses, malignant growths developed quickly
and in high numbers near the site of application. Some tumor growth was
observed in rats given much lower doses. No effects were seen in rats exposed
to very low doses of methyl bromide for 90 days (2). Due to a very limited
amount of information on the cancer causing effects on humans the EPA has
determined that the compound is not classifiable.
Chronic low level exposure causes depression of the central nervous
system, injury to the kidneys, and may cause respiratory problems, and
irritate the skin and eyes. Methyl bromide and its constituents appear to
concentrate in the central nervous system. This chemical can affect muscle
control and behavior. Other targets of the fumigant are the heart, nasal
cavities, adrenal gland, and the testis (14).
Fate in Humans and Animals
The major route of absorption of methyl bromide vapors is through the
lungs. Some of the compound is excreted through the lungs as unchanged methyl
bromide, but a significant amount also undergoes metabolic decomposition. The
primary breakdown product is the bromide ion, which is detectable in the blood
and tissues and is excreted in the urine. Organic bromides also appear in
stomach fluids and mucous.
In humans, methyl bromide's half-life in blood is about 12 days (11). As
a result, the toxic effects of methyl bromide can be delayed or prolonged.
Additionally, once in a cell, this chemical inactivates many enzyme systems,
so prolonged small doses can cause severe toxicity.
Methyl bromide is moderately toxic to aquatic organisms. Acute toxicity
for some freshwater fish may occur at concentrations of 11 ppm and around 12
ppm for saltwater fish (7). However, when applied properly, methyl bromide is
not expected to enter surface waters via run-off or erosion, and thus poses
little risk to aquatic species. It is not highly toxic to most plants.
The amount of bromide ion, the metabolite of methyl bromide, in residues,
is proportional to the protein content of the crop. Higher levels of the
bromide ion will most likely be found in high-protein plants.
When used as a soil fumigant, only a small amount of methyl bromide is
transformed into the bromide ion while much of the gas enters the atmosphere.
Transformation of methyl bromide into bromide increases as the amount of
organic matter in the soil increases. The rate of degradation in fumigated
soil is 6-14% per day at 20 degrees C. More leaching occurs in a sandy versus
a loamy soil.
Methyl bromide run-off from fields into surface waters is rare due to the
way this chemical is normally applied. If it contacts surface waters, the
average half-life for methyl bromide under field conditions has been
calculated to be 6.6 hr at 11 degrees C. Another study showed the half-life
in water to be 20 days at 25 degrees C in a neutral solution (9). Methyl
bromide quickly evaporates at temperatures ordinarily encountered in
Some methyl bromide is vaporized during chemical manufacturing and
processing operations. It can also enter the environment through auto exhaust
(when used as a gas additive) and may play a role in ozone depletion. Bromide
compounds have been shown to have destructive effects on the ozone layer.
PHYSICAL PROPERTIES AND GUIDELINES
Methyl bromide is a colorless gas or volatile liquid which is usually
odorless, but has a sweet, chloroform-like odor at high concentrations.
Since the chemical is a gas at ordinary temperatures, it is compressed
and applied as a liquid. Methyl bromide is not spontaneously combustible, but
it poses a hazard when exposed to sparks or flame. Although stable under
normal temperatures and pressures, when heated to decomposition, methyl
bromide emits highly toxic and corrosive fumes of bromides.
This compound presents a severe explosion hazard when combined with
aluminum, magnesium, or zinc. Delayed explosions may occur in the presence of
dimethyl sulfoxide. A vigorous reaction occurs when it is mixed with strong
oxidizers or ethylene oxide (5).
|NOEL: ||16 ppm on rats, rabbits, guinea pigs, and monkeys (7).
|TOL: ||odorless at low concentrations; no odor until at a very high concentration (above TLV) so odor is a poor warning signal.
|PEL: ||20 ppm in the air (4).
|TLV: ||5 ppm skin
|TWA: ||5 ppm skin
|RfD: ||1.4 x 10 to the minus 3 mg/kg/day
|CAS #: ||74-74-83-9
|Solubility in water: ||Methyl bromide is considered very slightly soluble in water. 1.34 g/100g (25 degrees C); 1.75 g/100g (20 degrees C, 748 mm Hg) (12)
|Solubility in solvents: ||Easily miscible with ethanol, ether, carbon disulfide, chloroform; freely soluble in benzene, carbon tetrachloride.
|Melting point: ||93.6 degrees C (12)
|Boiling point: ||3.56 degrees C (at 760 torr) (12)
|Vapor pressure: ||1250 mg Hg (at 20 degrees C) (5); 1824 mm at 25 degrees C (3)
|Kow: ||1.69 (1971 med); 109 (1979 mth)
Great Lakes Chemical Corporation
P.O. Box 2200
West Lafayette, Indiana 47906
Review by Basic Manufacturer:
Comments solicited: October, 1992
American Conference of Governmental Industrial Hygienists. Threshold
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Methylbromide: Carcinogenic Effects in the Rat Forestomach. Toxicology and
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Occupational Health Guidelines for Methyl Bromide.
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