Methyl bromide (MB) is an odorless, colorless gas at normal temperatures and pressures, very potent and very toxic fumigant. The chemical name (IUPAC) is bromomethane, and it is classified as an alkyl bromide. Under moderate pressure, the gas can be liquified and is normally supplied and transported as a liquid in pressurized cylinders. The cylinders range from about 10 to 200kg in content, and sometimes in larger containers and small pressurized disposable steel cans typically of 0.5 to 1kg capacity each. The specific gravity at 0ºC and 760 mm Hg is 1.732, with a vapor density of ~3.27, boiling point of 3.6ºC (38.5ºF), vapor pressure at 20ºC of 1400 mm/Hg (at 40ºC it is 2600 mm/Hg), and the viscosity is 0.22 centistokes at 0ºC. Methyl bromide is readily soluble in lower alcohols, ethers, esters, ketones, halogenated hydrocarbons, aromatic hydrocarbons, and carbon disulfide.
Methyl Bromide for controlled uses is produced in two Article 5 (1) (developing) countries (China and Romania) and four non-Article 5 (1) (developed) countries (France, Israel, Japan and USA). However, the vast quantity of methyl bromide is manufactured by four companies: two located in the US State of Arkansas, one in Israel (Dead Sea Bromine), and one European (Altafino). These companies utilize naturally occurring bromide salts which are either contained in underground brine deposits (as is the case with Arkansas), or in highly concentrated above ground sources like the Dead Sea. Methyl bromide is often produced as a by-product of other bromide manufacturing processes.
Apart from being a toxic chemical fumigant, methyl bromide contributes significantly to the destruction of earth’s stratospheric ozone layer, a protective shield that filters out harmful ultraviolet (UV) radiation from the sun. The bromines contained in methyl bromide are fifty times more destructive to ozone than the chlorine found in Chlorofluorocarbons (CFCs). Methyl Bromide has a substantial ozone-depleting potential, with a best estimate of the ODP at 0.6 (maximum limits of estimate 0.3 to 0.9). The ozone layer is vital to life on earth. The effect of ozone depletion is particularly significant in Australia, where one in two people will be affected by ultraviolet-B (UVB) damage to skin at some stage of their lives. Excessive exposure to UV-B radiation is linked to skin cancer and eye disease in humans, suppression of the immune system in living organisms, damage to proteins and DNA, and decreases in agricultural and marine productivity. Human exposure to high concentrations of methyl bromide have resulted in central nervous system and respiratory system failure, as well as specific and severe deleterious actions on the lungs, eyes, skin and human deaths. United Nations Scientific Panel estimated Methyl bromide as being responsible for 5-10% of worldwide ozone depletion.
Uses of Methyl Bromide
MB can be divided into the following use categories:
- as a preplant treatment against insect, nematode and fungal pests and for weed control in production of cut flowers, strawberries, cucurbits, tomatoes, peppers and eggplant;
- as a replant treatment for vines or deciduous fruit trees against 'replant disease';
- as a treatment of seed beds principally against fungi for production of a wide range of seedlings, notably tobacco;
- as a treatment to ensure production of pest-free propagation stock, e.g. strawberry runners.
- as a treatment against insect pests for cereal grains and similar commodities in storage to restrict damage to the commodity and at point of import or export as quarantine, phytosanitary or contractual measures;
- to control pests of dried fruit and nuts in storage and trade;
- as a quarantine measure for treatment of exported or imported timber and wooden pallets, principally against insects and some fungal pests.
- as a phytosanitary or quarantine treatment against insect pests in many fresh fruit, vegetables and cut flowers in export trade.
In structures and transport:
- as a treatment for food facilities, flour mills and other buildings against established insect infestations;
- as a treatment of ships and freight containers, either empty or containing durable cargo, against rodents and insect pests, often as a quarantine or contractual measure.