Bromomethane

Bromomethane, commonly known as methyl bromide, is an organobromine compound with formula CH3Br. This colorless, odorless, nonflammable gas is produced both industrially and biologically. It has a tetrahedral shape and it is a recognized ozone-depleting chemical. It was used extensively as a pesticide until being phased out by most countries in the early 2000s. Bromomethane originates from both natural and human sources. In the ocean, marine organisms are estimated to produce 56,000 tonnes annually. It is also produced in small quantities by certain terrestrial plants, such as members of the family Brassicaceae. It is manufactured for agricultural and industrial use by treating methanol with bromine in the presence of sulfur or hydrogen sulfide: 6 CH3OH + 3 Br2 + S → 6 CH3Br + 2 H2O + H2SO4 In 1999, an estimated 71,500 tonnes of synthetic methyl bromide were used annually worldwide. 97% of this estimate was used for fumigation purposes, whilst 3% was used for the manufacture of other products. Moreover, 75% of the consumption used to take place in developed nations, led by the United States (43%) and Europe (24%). Asia and the Middle East combined to use 24% whereas Latin America and Africa had the lowest usage at 9%. Until its production and use was curtailed by the Montreal Protocol, bromomethane was widely applied as a soil sterilant, mainly for production of seed but also for some crops such as strawberries and almonds. In commercial large-scale monoculture 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. Although bromomethane is dangerous, it is considerably safer and more effective than some other soil sterilants. Its loss to the seed industry has resulted in changes to cultural practices, with increased reliance on soil steam sterilization, mechanical roguing, and fallow seasons. Bromomethane was also used as a general-purpose fumigant to kill a variety of pests including rats and insects.