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Methyl bromide fumigation
Methyl bromide is used as a fumigant and pesticide. Exposure may occur during fumigation activities.
Methyl bromide is a broad-spectrum fumigant that has been used around the world since the 1930s as a pre-plant soil fumigant to control insects, pathogens, and weeds, and to control insects in buildings and in commodities. It is also used for quarantine and pre-shipment applications.
Methyl bromide is one of the very few chemicals that were approved for broad-spectrum use in agriculture and pest control. The dominant use of methyl bromide worldwide is for pre-planting soil fumigation.
Methyl bromide is the most effective soil fumigant for killing plant pests, its use is being phased out because its emissions from soil can lead to stratospheric ozone depletion. 1992, Parties to the Montreal Protocol on Substances that Deplete the Ozone Layer recognized that methyl bromide has an ozone-depleting potential (ODP); thus it is identified as an ozone-depleting substance.
The primary use of methyl bromide is as a fumigant in soil to control fungi, nematodes, and weeds; in space fumigation of food commodities (e.g., grains); and in storage facilities (such as mills, warehouses, vaults, ships, and freight cars) to control insects and rodents.
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.
The bimolecular nucleophilic substitution (S(N)2) reaction of methyl bromide and OH-in aqueous solution has been investigated using a multilayered-representation quantum mechanical and molecular mechanics methodology.
(1) Under the law, methyl bromide may only be applied by licensed applicators or those under their direct supervision. Licensed applicators must meet strict criteria governing safe handling, storage and use of the compound, which helps to reduce exposure potential.
(2) Workers involved in methyl bromide application or the removal of containment after fumigation are likely to have the highest risk of exposure, followed by those workers who first re-enter the area after fumigation. To reduce this risk, regulations restrict re-entry to application sites and require personal protective clothing and equipment for people who handle the product.
(3) Because methyl bromide is absorbed by the soil and readily dissipates in the atmosphere, bystanders such as farm workers in adjacent fields and those who live or work nearby are likely less at risk. Even so, depending on soil and weather conditions and proximity to the application site, bystanders may come into contact with residues as the compound disperses.
(4) References: www.toxipedia.org
ChEBI: A one-carbon compound in which the carbon is attached by single bonds to three bromine atoms and one hydrogen atom. It is produced naturally by marine algae.
Methyl bromide (bromomethane) is an odourless, sweetish, colourless gas, incompatible with oxidising agents and strong acids.
In ionization chambers. For degreasing wool. Extracting oils from nuts, seeds, flowers. Soil or space fumigant for insects, fungi, rodents. Methylating agent. Has been used as fire extinguishing agent.
Air & Water Reactions
Nonflammable over a wide range of concentrations in air. Slightly soluble in water (about 1.75 g/100 mL of solution at 20° C). Reacts slowly with water to give methyl alcohol and hydrobromic acid. [K-O Vol. 4].
When heated to decomposition, Methyl bromide emits toxic fumes of bromides. Hazardous polymerization may not occur.
Methyl bromide is incompatible with metals, dimethyl sulfoxide, ethylene oxide. [Lewis]. Can give flammable products if mixed with potassium hydroxide, sodium hydroxide and other strong bases. Methyl bromide in a steel tank reacted with an aluminum tube (part of the level gauge) producing methyl aluminum bromide. When the latter was subsequently exposed to air, enough heat was produced to ignite the Methyl bromide -compressed air mixture above the liquid layer. The ensuing explosion shattered the tank (also incompatible with zinc, magnesium, and alloys)[Chem. Eng. Pro. 58(8). 1962]. A reaction between Methyl bromide and dimethyl sulfoxide resulted in an explosion that shattered the apparatus [NFPA 491M. 1991].
Colorless highly toxic volatile liquid or a gas. Boiling point 3.56°C (38.41°F). Usually odorless, but has a sweetish chloroform-like odor at high concentrations. Used as an insecticide, a rodenticide, a fumigant, a nematocide, a chemical intermediate and as a fire extinguishing agent.
®; DAWSON® 100; DOWFUME®; EDCO®;
EMBAFUME®; HALON 1001®; ISCOBROME®;
KAYAFUME®; MATABROM®; METHO-GAS®; M-B-C
FUMIGANT®; R 40B1®; ROTOX®; TERABOL®;
Methyl bromide is highly toxic. Studies in humans indicate that the lung may be severely injured by the acute (short-term) inhalation of methyl bromide. Acute and chronic (long-term) inhalation of methyl bromide can lead to neurological effects in humans. Neurological effects have also been reported in animals. Degenerative and proliferative lesions in the nasal cavity developed in rats chronically exposed to methyl bromide by inhalation. Chronic inhalation exposure of male animals has resulted in effects on the testes at high concentrations. EPA has classified methyl bromide as a Group D, not classifiable as to human carcinogenicity.
Fumigant, Herbicide, Insecticide, Nematicide: The primary use of methyl bromide is as an insect
fumigant to control insects, nematodes, weeds and pathogens
in more than 100 crops and for soil, grain storage,
warehouses, mills, ships, etc. Use of methyl bromide in
the U.S. will be phased out under the requirements of the
Montreal Protocol, with some exemptions. Methyl bromide
is also used as a chemical intermediate and a methylating
agent, a refrigerant, a herbicide, a fire-extinguishing
agent, a low-boiling solvent in aniline dye manufacture,
for degreasing wool, for extracting oils from nuts, seeds,
and flowers, and in ionization chambers. It is used as an
intermediate in the manufacture of many drugs. A U.S.
EPA restricted Use Pesticide (RUP), NO INERT. Still
registered for use in the U.S. (2013). As of March
18, 2005, the use of methyl bromide in the EU was banned
for most purposes, including quarantine and pre-shipment
fumigations.Registered for use in the U.S.
Purify it by bubbling through conc H2SO4, followed by passage through a tube containing glass beads coated with P2O5. Also purify it by distillation from AlBr3 at -80o, by passage through a tower of KOH pellets and by partial condensation. [Beilstein 1 IV 68.]
Methyl bromide is a dangerous cumulative poison with delayed symptoms of central nervous system intoxication that may appear as long as several months after exposure. High concentrations can produce fatal pulmonary edema. Chronic exposure can cause central nervous system depression and kidney injury. It may cause severe and permanent brain damage. Severe neurological signs may appear when there is a sudden exposure to high concentrations following continuous slight exposure. Methyl bromide has practically no odor or irritating effects and therefore no warning, even at hazardous concentrations.