Methyl bromide sources

Methyl bromide is nonflammable over a wide range of concentrations in air at atmospheric pressure and offers practically no fire hazard. With an intense source of ignition, flame propagation within a narrow range from 13.5 to 14.5% by volume has been reported. The material has no flash point. Thermal decomposition in a glass vessel begins somewhat above 400°C. 

Anbar, A. D., Y. L. Yung, and F. P. Chavez, Methyl Bromide Ocean Sources, Ocean Sinks, and Climate Sensitivity, Global Biogeochem. Cycles, 10, 175-190(1996). 

Some HAPs impact not only the troposphere but also the stratosphere. The most obvious example is highly toxic methyl bromide, CH3Br, used as a soil fumigant as well as for treatment of buildings for termites. As discussed in Chapter 12, this is a significant source of stratospheric bromine and hence contributes to stratospheric ozone depletion. Its continued use has been controversial and is being phased out (e.g., see Thomas, 1996 Ristaino and Thomas, 1997 and Duafala, 1996). 

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). 

Varner RK, Crill PM, Talbot RW (1999) Wetlands A Potentially Significant Source of Atmospheric Methyl Bromide and Methyl Chloride. Geophys Res Lett 26 2433... 

Pilinis C, King DB, Saltzmann ES (1996) The Oceans A Source or a Sink of Methyl Bromide Geophys Res Lett 23 817... 

Lee-Taylor JM, Holland EA (2000) Litter Decomposition as a Potential Natural Source of Methyl Bromide. J Geophys Res 105 8857... 

Varner R. K., Grill P. M., and Talbot R. W. (1999) Wetlands a potentially significant source of atmospheric methyl bromide and methyl chloride. Geophys. Res. Lett. 26, 2433-2436. 

Some halocarbons are produced by both natural and industrial sources. Unfortunately, the few data concerning the magnitude of the natural sources are conflicting. For example, based on measured concentrations of methyl bromide in the sea and troposphere, Singh et al. (6) estimated that the net annual global flux from ocean to air is about 0.3 teragrams (1 Tg is 1 X 1012 g). This net emission is much larger than that derived from human activities (0.05-0.08 Tg per year) (7, 8). On the other hand, Penkett and co-workers (7) concluded that human activities were the main source of methyl bromide. 

A mitigating factor in this process are the various cellular DNA repair enzyme systems which may remove the chemically induced lesion before or after DNA replication. A number of these which actively repair damage as a result of short-chained alkylation, much as would be expected to occur as a result of exposure to the genotoxic pesticides methyl bromide or ethylene dibromide, are listed in Table 2. However, the activity of repair enzyme systems does represent a saturable process and in some instances may itself be the source of errors in DNA base sequences, possibly by an inducible error-prone DNA repair enzyme system analogous to the so-... 

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