Bromomethane , commonly known as methyl bromide , is an organobromine compound with the formula CH 3 Br . This colourless, odorless, flammable gas is produced both industrially and organically. It has a tetrahedral shape and is a recognized ozone-depleting chemical. It was widely used as a pesticide until it was phased out by most countries in the early 2000s .
Event and construction
Bromomethane is produced from both natural and human sources. In the ocean, marine organisms are estimated to produce 56,000 tonnes annually. [6] It is also produced in small amounts by some 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: [5]6 CH 3 OH + 3 Br 2 + S → 6 CH 3 Br + 2 H 2 O + H 2 SO 4
Use
In 1999, an estimated 71,500 tons of synthetic methyl bromide were used annually worldwide. [7] Of this estimate, 97 % was used for fumigation purposes, while 3% was used for the manufacture of other products. In addition, 75% of consumption was in developed countries led by the United States (43%) and Europe (24%). Asia and the Middle East combined used 24% while 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, primarily for the production of seeds, but also for some crops such as Strawberry [8]and almonds. In commercial large-scale monoculture seed production, unlike crop production, it is extremely important to avoid off-type contaminating the crop with seeds of the same species. Therefore, selective herbicides cannot be used. Although bromomethane is dangerous, it is significantly safer and more effective than some other soil bactericides. Its damage to the seed industry has resulted in a change in cultural practices, including increased reliance on soil steam sterilization, mechanical turbidity and fallow weather. Bromomethane was also used as a general purpose smoker to kill a variety of pests including rats and insects. Bromomethane has poor fungicide properties. Bromomethane is only allowed under fumigation (heat treatment is not the only feed) under ISPM 15 when ISPM 15 compliant countries are approved for solid wood packaging (forklift pallets, crates, bracing) export regulations. Bromomethane is used to prepare golf courses, especially to control Bermuda grass. The Montreal Protocol stipulates that the use of bromomethane will be phased out.
Bromomethane is also a precursor in the manufacture of other chemicals as a methylating agent. Bromomethane was once used in specialized fire extinguishers, prior to the advent of the less toxic halogen, as it is electrically non-conductive and leaves no residue. It was mainly used for electrical substations, military aircraft and other industrial hazards. It was never as popular as other agents due to its high cost and toxicity. Bromomethane was used from the 1920s to the 1960s, and continued to be used in aircraft engine fire suppression systems into the late 1960s.
Alternative
Alternatives to bromomethane are currently in use in agriculture and further alternatives are in development, including propylene oxide and furfural. [10]
Australia
In Australia, bromomethane is the Department of Agriculture and Water Resources’s preferred smoker for most organic goods imported into Australia. [11] The department conducts methyl bromide fumigation certification for both domestic and foreign fumigators, who can then fumigate containers earmarked for Australia. A list of alternative fumigants is available for goods imported from Europe (known as the BICON database), where methyl bromide fumigation is banned. [12] Alternatively, the department allows containers from Europe to be fumigated with methyl bromide upon arrival in Australia.
New Zealand
In New Zealand, bromomethane is used as a smoker for whole logs destined for export. Environmental groups and the Green Party oppose its use. [13] [14] In May 2011 the Environmental Risk Management Authority (ERMA) introduced new regulations for its use that restrict the level of public exposure to fumigant, determine minimum buffer zones around fumigation sites, -Provide notification to nearby residents and require users to monitor air quality during fumigation and report to ERMA each year. All methyl bromide fumigation must use recapture technology by 2021. [15]
United States of america
In the United States bromomethane is regulated as a pesticide under the federal Insecticide, Fungicide, and Rodenticide Act (FIFRA; 7 USC 136 et sec.) and as a hazardous substance under the Resource Conservation and Recovery Act (RCRA). ; 42 USC 6901 et sec.), and subject to reporting requirements under the Emergency Planning and Community Right to Know Act (EPCRA; 42 USC 11001 et seq.). US Clean Air Act (CAA; 42 USC 7401 et seq.). A 1998 amendment (PL 105–178, Title VI) dated the Clean Air Act phase with the Montreal Protocol. [16] [17] While the Montreal Protocol has severely restricted the use of bromomethane internationally, the United States has successfully lobbied for significant-use exemptions. [18]Severe use exemptions allow the United States to continue using MeBr entirely as long as it is prescribed [19]
In 2004, more than 7 million pounds of bromomethane were applied in California. Applications include tomato, strawberry, and ornamental shrub growers, and fumigation of ham/pork products. Solid wood packaging (forklift pallets, crates, bracing) and treatment of packaged goods exported to ISPM 15 countries (to include Canada in 2012) are also exempt.
Chile
It has phased out use in traditional agriculture in 2015, with exemptions of 100% pure formulations that continue and are used extensively in the quarantine pest control and pre-shipment of the fruit export industry.
Health effects
Brief exposure to high concentrations and prolonged inhalation of low concentrations are problematic. [21] The exposure level for death varies from 1,600 to 60,000 ppm depending on the duration of exposure (since comparable exposure levels of 70 to 400 ppm of carbon monoxide cover the same spectrum of illness/death ). Concentrations in the range of 60,000 ppm can be fatal immediately, while toxic effects may be present after prolonged exposure to concentrations below 1,000 ppm.
“Recommended TLV-TWA of 1 ppm (3.89 mg/m3) for occupational exposure to methyl bromide” -ACGIH 8-hour time-weighted average. Dangerous to immediate life or health concentration by NIOSH: “The modified IDLH for methyl bromide is 250 ppm based on acute inhalation toxicity data in humans [Clark et al. 1945]. This is a conservative approach due to the lack of relevant acute toxicity. There may be value. Data for workers exposed to concentrations higher than 220 ppm. [Note: As part of its carcinogen policy, NIOSH recommends that the “most protective” respirator for methyl bromide be the “most protective” respirator for any detection. Be worn at the eligible concentration.] “The concentration detectable by the dredger tube is 0.5 ppm.
Respiratory, renal and neurological effects are of greatest concern.
The treatment of wooden packaging requires a concentration of up to 16,000 ppm.
NIOSH considers methyl bromide a potential commercial carcinogen as defined by the OSHA carcinogen policy [29 CFR 1990]. “Methyl bromide showed a significant dose-response relationship with prostate cancer risk.” [22]
Extreme risk
Manifestations of toxicity after exposure may include latent periods of several hours, followed by symptoms such as nausea, abdominal pain, weakness, confusion, pulmonary edema and seizures. Individuals who survive the acute phase often require long-term recovery. Persistent neurological defects such as asthenia, cognitive impairment, optical atrophy and paresthesia are often present after moderate to severe poisoning. Blood or urine concentrations of inorganic bromide, a bromomethane metabolite, are useful in confirming the diagnosis of poisoning in hospitalized patients or in aiding in forensic investigations of a case of fatal overdose.
