Methyl Bromide

Methyl bromide is packaged as a liquid under pressure in either small cans or in various sizes of steel cylinders. It has a density of approximately 3.3 times that of air and, as a result, should be used with fans to prevent stratification, resulting in fumigation failures in the higher portion of the area. To prevent some of this phenomenon from occurring, it is usually recommended that the product be released near top of the site to be fumigated whether it is a silo or mill. If fans are not employed, there is a possibility that the upper portion of the site will not be successfully fumigated. If bagged commodities are to be fumigated under a tarpaulin or in a truck or container, the entry tube should be leakproof and a pan should be placed under the end of the tube so that no liquid methyl bromide is allowed to come into contact with the bagged commodity, which can result in staining.

The properties of methyl bromide that must be considered prior to fumigation are as follows.

1. Its density is such that fans should be used to recirculate the gas for even distribution.

2. A heat exchanger may be necessary to properly vol-atize the methyl bromide.

3. Methyl bromide is nonflammable but can result in the formulation of hydrobromic acid when open flames are present. Hydrobromic acid can be corrosive.

4. Methyl bromide can be sorbed under certain condition and can react chemically with certain compounds resulting in damage or bad odors. These materials include certain foodstuffs, rubber goods, furs, leather goods, woolens, rayons, various paper products, photographic chemicals, cinder blocks, charcoal or any material that contains active sulfur compounds.

5. Methyl bromide can effect germination of seeds and should be used for this purpose with caution.

6. Methyl bromide does have a true CT product, and fumigation usually can be completed in 12-24 h depending on dosage.

7. Normally fumigation with methyl bromide is not recommended when the commodity temperature is lower than 15.5°C (60°F).

8. Following fumigation, aeration must continue until the level of methyl bromide is below 5 ppm. If the level exceeds this amount, then proper respiratory equipment must be worn.

9. Repeated fumigations with methyl bromide can result in residues exceeding tolerances established by federal agencies for various commodities.

Finally, it should be noted that methyl bromide is odorless and proper measuring instrumentation is required to measure concentration. The halide detector is not sensitive enough to be used to determine levels suitable for reentry into an aerated facility. Aeration may have to be prolonged due to sorption of methyl bromide to commodities or materials in the structure. Fans will help in the aeration process. The half-life of methyl bromide can be 15-18 months depending on climatic conditions.

Toxicology

Methyl bromide is known to be a chronic toxic chemical, that is, the effects due to exposure are cumulative and are not reversible. Major studies such as chronic toxicity, teratology, pharmacokinetics, and mutagenicity are being conducted to fill data gaps for regulatory purposes.

Methyl bromide is known to be a chronic toxic chemical, as the effects due to exposure are cumulative and not reversible. Consumption of methyl bromide from fumigated food has been estimated at 0.00125 mg/kg/day in the average diet. Wilson et al. (4) fed dogs a diet containing 0.270.28 mg/kg/day methyl bromide over a period of a year. No adverse effects were observed, indicating it did not present a significant health hazard to humans. Another recent feeding trial on rats and rabbits conducted by Kaneda et al. (5) concluded that methyl bromide was not fetotoxic or teratogenic to rat and rabbit fetuses up to dose levels of 30 and 10 mg/kg/day, respectively. Nevertheless, the use of methyl bromide as a fumigant was banned by the Montreal Protocol (an international treaty) as of 2001 because it is an ozone depleter. This could have a significant effect on Florida's horticultural industry unless alternative methods are found (6,7).

Respiratory Protection

If application is made inside a structure, then an air pack must be worn for any level above 5 ppm. This same restriction applies to aeration.

Alternatives to Methyl Bromide

A number of alternative methods are being explored for possible implementation prior to the ban on methyl bromide in 2001. Warner (8) suggested a combination of moist heat and controlled atmosphere as an alternative quarantine treatment for codling moth in fruit. Subjecting apples, pears, and cherries to 113-117°F (45-47°C) would be adequate to destroy the codling moth larvae. Storing the fruit in a controlled atmosphere of 0.5 % oxygen and 15%

carbon dioxide shortened the heating time at 117°F needed to kill the larvae by as much as one half or two-thirds compared to just heating alone. Warner (9) also recommended irradiation as an alternative quarantine treatment to fumigation with methyl bromide for cherries. Irradiation up to 50 krad did not have a detrimental effect on the quality of the fruit. A recent study by Sholberg (10) used short chain organic acids (acetic, formic, and proprionic) as fu-migants against postharvest decay by fungal pathogens. All three acids reduced decay in citrus by Penicillium dig-itatum from 86% to 11% and decay in pome fruit by P. ex-pansum from 98% to 14%, 4%, and 8%, respectively. It is clear that alternative methods to fumigants will soon be implemented before the ban on methyl bromide comes into force.

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