Fumigation methyl bromide

The primary use for methyl bromide is in the extermination of insect and rodent pests. Methyl bromide is used in space and stmctural fumigation except in California. The material is suitable for the fumigation of food commodities such as dried fmits, grain, flour, and nuts, and the faciHties in which these foods are processed or stored, as weU as for tobacco and many kinds of nursery stock. The usual dosage is 2—4 kg/28 m for 12—24 h. In soil fumigation methyl bromide controls weed seeds, nematodes, wireworms, and soil fungi. The usual dosage is 0.5—1 kg/9 m for 24 h at 16°C and above (82). 

About 10% is marketed ia elemental form. Eighteen percent is converted to ethylene dibromide [106-93 ] for use ia gasoline and 30% is used ia fire retardants. Fifteen percent is used as a soil fumigant methyl bromide [74-83-9]. Other commercial forms are alkaU metal bromides, ammonium bromide [12124-97-9] and hydrobromic acid [10035-10-6],... 

Due to its gaseous nature it may have an effect on the stratospheric ozone layer [281, 402, 404]. After injection into soil for fumigation, methyl bromide rapidly diffuses through the soil pore space to the soil surface and then into the atmosphere [159,162,163,405,406]. Since a plastic sheet typically covers the soil surface, the rate of emission into the atmosphere depends upon the thickness and density of the plastic, if other conditions are the same [159, 406]. Other routes of disappearance from soil include chemical hydrolysis, methylation to soil organic matter through free radical reactions, and microbial degradation [ 136,159,405,407]. Several reports appeared on the study of the microbial transformations of methyl bromide, summarized as follows ... 

Starratt AN, Bond EJ. 1988. In vitro methylation of DNA by the fumigant methyl bromide. J Environ Sci Health [B] 23 513-524. 

Second, reaction 8.9 and other relevant reactions appear to occur preferentially on available solid surfaces, which are often ice crystals but may also be particles of sulfate hazes from volcanic eruptions or human activity. Third, volatile bromine compounds are even more effective (via Br atoms) than chlorine sources at destroying ozone methyl bromide is released into the atmosphere naturally by forest fires and the oceans, but anthropogenic sources include the use of organic bromides as soil fumigants (methyl bromide, ethylene dibromide) and bromofluorocarbons as fire extinguishers (halons such as CFsBr, CF2BrCl, and C2F4Br2). 

Consider the reversible transformation of the soil fumigant methyl bromide (CH3Br) to methyl chloride (CH3C1) in aqueous solution (a nucleophilic substitution reaction, see Chapter 13) ... 

Host of the cyclic organohalogen pesticides studied are known or suspect animal carcinogens. The alkyl halide fumigants (methyl bromide, EDB, DBCP) are alkylating agents and mutagens, with adverse reproductive effects as well. 

Halogenated aliphatics Fumigants Methyl Bromide, EDB, DBCP... 

Goldman, L.R., Mengle, D., Epstein, D.M. (1987). Acute symptoms in persons residing near a field treated with the soil fumigants methyl bromide and chlorpicrin. West. J. Med. 147 95-8. 

For some pesticide compounds, such as dini-troaniline herbicides (Weber, 1990), phototransformation occurs primarily in the vapor phase, rather than in the dissolved or sorbed phases. Perhaps the most environmentally significant pesticide phototransformation in the atmosphere, however, is the photolysis of the fumigant methyl bromide, since the bromine radicals created by this reaction are 50 times more efficient than chlorine radicals in destroying stratospheric ozone (Jeffers and Wolfe, 1996). Detailed summaries of the rates and pathways of phototransformation of pesticides and other organic compounds in natural systems, and discussions of the physical and chemical factors that influence these reactions, have been presented elsewhere (e.g., Zepp et al, 1984 Mill and Mabey, 1985 Harris, 1990b). 

As a soil fumigant methyl bromide leaves no toxic residue in soils. The volatile gas rises into the atmosphere. Methyl bromide is an ozone-depleting substance. Although methyl bromide is very soluble in water, its high vapor pressure in various soil types indicates a low tendency to adsorb to soils and rapid evaporation. Methyl bromide has a half-life in air estimated from 0.3 to 1.6 years. Degradation is primarily due to photolysis. In soils, the half-life is 0.2-0.5 days. In water, a half-life of 3 h was calculated. 

Use Manufacture of ethylene dibromide (antiknock gasoline), organic synthesis, bleaching, water purification, solvent, intermediate for fumigants (methyl bromide), analytical reagent, fireretardant for plastics, dyes, pharmaceuticals, photography, shrink-proofing wool. 

Fumigation Methyl bromide, Vikane (sulfuryl fluoride), phosphine... 

Although useful in agriculture as a soil fumigant, methyl bromide is an ozone-depleting chemical, and its production is being phased out. The industrial preparation of methyl bromide is from methanol, by reaction with hydrogen bromide. Write a mechanism for this reaction and classify it as S l or 8 2. 

The two gaseous AIs in use today are methyl bromide and sulfuryl fluoride. 1,3-Dichloropropylene is also discussed here due to this liquid s very high vapor pressure and the use of 1,3-dichloropropyl-ene as a fumigant. Methyl bromide is used as a fumigant for rodents and insects in stored grain, and injected into the soil for the control of nematodes, weed seeds, fungi, and insects. Neither product utilizes surfactants in their delivery or application. A mixture of methyl bromide with chloropicrin,... 

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