Methyl bromide is a fumigant (poison gas) used principally in farming and storage and transport of commodities. It is one of only two methods so far approved for treatment of wood prior to international shipment (the other being heat treatment) under ISPM 15.
Methyl bromide has various unfortunate health effects, such as toxicity to non-target species, including the workers that apply the product and people living in communities nearby. Methyl bromide is also one of the chemicals that damages the ozone layer, and of those that have not yet been completely phased out, is now the largest problem. Because of this, methyl bromide was singled out for elimination globally by 2005 as part of the Montreal Protocol.
The United States, under the leadership of the Bush Administration, stopped the rapid trend toward elimination of methyl bromide. The United States is now only making extremely modest (on the order or 5-15%) progress in use reductions each year.
One voice giving testimony against more rapid progress has been Steven Hamilton, Executive Director of the Urban Environmental Affairs Council.
Use in tobacco
Methyl bromide is a highly toxic fumigant used in the tobacco industry to control an insect called "cigarette beetle." It has no warning properties, such as smell, taste or color. According to a tobacco industry document about the chemical,"When heated to decomposition, [methyl bromide] emits highly toxic fumes of bromides." Of course, this would describe the fate of any residues remaining on tobacco leaves that makes it into cigarettes. It also says that the most significant route of exposure of methyl bromide is through the lungs. A 1984 Philip Morris internal memo reveals concern within Philip Morris about use of this potent chemical poison:
Recently, there have been more rumblings about methyl bromide at the EPA, and I enclose a portion of the letter ... which was sent by the Natural Resources Defense Council, Inc ... On page 2, ... the Council makes some statement about methyl bromide's toxicity. I bring this to your attention to focus once again on the need to remove methyl bromide from our tobacco processing operations." 
An October, 1983 memo reveals just how toxic methyl bromide is, and just how much of it is present in tobacco after fumigation. Note that the threshold limits stated in this paper are probably limits of methyl bromide gas in ambient air, while the amount noted on tobacco are on or within the tobacco leaf itself:
Methyl bromide is a widely used fumigant with known alkylating and methylating properties. The most significant route of exposure is inhalation, although serious skin burns may occur from prolonged contact. Exposure at high concentrations will produce lung irritation with congestion and edema which may develop into bronchial pneumonia. Threshold concentrations from prolonged and repeated exposures result in nervous system disorders - including excitation, convulsions and most typically paralysis of the extremities. Because methyl bromide has no odor or irritating effects, and therefore no warning, hazardous concentration can readily be attained. The threshold limit of methyl bromide has been set at 5 ppm (20 mg/m3). Methyl bromide has been shown to be mutagenic and genotoxic in a variety of assay systems.
- Disaster hazard for methyl bromide is 'Dangerous' according to Sax, when heated to decomposition, it emits highly toxic fumes of bromides. * A limit of 15 ppm is recommended to prevent serious neurotoxic effects and pulmonary edema ...
- Methyl bromide is responsible for more deaths in recent years among occupationally exposed persons than all of the more publicized organophosphate groups of insecticides (Casarett, Toxicology 1973, Pg. 444)...
- Methyl bromide is readily absorbed through the lungs and excreted predominantly through the lungs as unchanged methyl bromide.... * Significant changes in monoamines, particularly norepinephrine, were seen in the brains of rats exposed to methyl bromine gas for 24 hours or 3 weeks continuously. Methyl bromine produced remarkable reduction in the norepinephrine contents of the hypothalamus and cortex at 100 ppm or higher levels.
RESIDUE LEVELS IN FUMIGATED TOBACCO
- Strip tobacco ... exposed to vacuum fumigation with methyl bromide ... showed inorganic bromide residues of 212-480 ppm. The untreated control tobacco strips showed bromide residues of 72 to 91 ppm. Tobacco ... fumigated twice during a three day period showed residue values ranging from 257 ppm of inorganic bromide following the first gassing, and 505 ppm after second gassing. (Confidential, unpublished report, Manzelli, A., 'Vacuum Chamber Fumigation of Tobacco with Methyl Bromide for the Control of Cigarette Beetle, ...1973)