Bromomethane

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(Redirected from Methyl bromide)

The chemical compound bromomethane is an organic halogen compound with formula BrCH3. It is a colorless, nonflammable gas with no distinctive smell. Its chemical properties are quite similar to those of chloromethane. Other names for bromomethane are methyl bromide, mono-bromomethane, and methyl fume. Trade names include Embafume and Terabol.

Contents

Origin

It occurs naturally in the ocean, where it is probably formed by algae and kelp. It is manufactured for agricultural and industrial use by reacting methanol with hydrobromic acid.

Uses

Until its production and use was curtailed by the Montreal Protocol, it was widely used as a soil sterilant, mainly for production of seed. In seed production, unlike crop production it is of vital importance to avoid contaminating the crop with off-type seed of the same species. Therefore, selective herbicides cannot be used. While bromomethane is dangerous to use, it is considerably safer and more effective than the few other soil sterilants available. Its loss to the seed industry has resulted in changes to cultural practices, with increased reliance on mechanical rogueing and fallow seasons.

Bromomethane was also used as a general-purpose fumigant to kill a variety of pests including rats, insects , and fungi (and therefore also for killing 'bugs' and fungi according the IPPC esp. ISPM number 15, regulations when exporting wooden packaging to certain countries). It is also a precursor in the manufacture of other chemicals, and has been used as a solvent to extract oil from seeds and wool.

CAS # 74-83-9

Ozone depletion

Bromomethane is on the list of banned ozone-depleting subtances of the Montreal Protocol. Because bromine is 45 times more destructive to ozone than chlorine, even small amounts of bromomethane cause considerable damage to the ozone layer.

Health effects

Exposure levels leading to death vary from 1,600-60,000 ppm, depending on the duration of exposure.

The respiratory, kidney, and neurologic effects are of the greatest concern to people. No cases of severe effects on the nervous system from long-term exposure to low levels have been noted in people, but studies in rabbits and monkeys have shown moderate to severe injury.

Sources and sinks

Sources of CH3Br include oceanic production, biomass burning, leaded fuel combustion, plant and marsh emissions, and fumigation of soils, durable goods, perishables, and structures. Sinks include photochemical decomposition in the atmosphere (reaction with hydroxyl radicals (OH) and photolysis at higher altitudes), loss to soils, chemical and biological degradation in the ocean, and uptake by green plants.

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