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Scientists develop methyl bromide alternative

An Alabama Agricultural Experiment Station (AAES) researcher has reformulated a chemical used as the inflation-triggering agent in automobile airbags into a highly effective, environmentally friendly agricultural pesticide that will give farmers a viable alternative to methyl bromide, a widely used but soon-to-be-banned farm chemical.

Auburn University plant pathologist and Distinguished University Professor Rodrigo Rodriguez-Kabana said the liquid formulation of sodium azide he has developed, presently known as SEP-100, significantly outperforms ozone-depleting methyl bromide in controlling weeds, diseases and harmful, root-eating nematodes. And as an unexpected bonus, the liquid sodium azide, which is applied to soil before planting through drip irrigation systems under plastic tarps, actually enhances the environment.

"As sodium azide decomposes in the soil, it breaks down into fertilizer and leaves the soil healthier than it was before the sodium azide was applied," Rodriguez-Kabana says. Furthermore, he adds, while methyl bromide kills all nematodes and insects, "good" and "bad" in the soil, sodium azide does not harm beneficial nematodes and insects.

Methyl bromide, which is injected as a gas into the soil before planting, is a broad-spectrum soil fumigant that fruit and vegetable growers, ornamental plant and tree nurseries, forest seedling nurseries and sod producers worldwide have relied on exclusively for decades. The chemical will be banned in the United States and other developed countries effective Jan. 1, 2005, because it destroys the earth's protective ozone layer.

Before phase-out of methyl bromide began in 1998, U.S. farmers were using an estimated 21,000 tons annually to fumigate soil before planting crops.

As early as the 1970s, Rodriguez-Kabana's concern over growers' sole reliance on one chemical prompted him to do preliminary research, which indicated that granular sodium azide held potential as an alternative to methyl bromide. To a world that assumed methyl bromide was here to stay, however, that research got little attention and no funding.

With the 2005 ban mandated in the early 1990s under the international Montreal Protocol, finding replacements for methyl bromide became a research priority worldwide, as experts warned that, unless cost-effective replacements for methyl bromide were found, the ban would cost U.S. growers almost $500 million a year in lost production.

Convinced by his 1970s investigations that sodium azide had strong potential as a replacement and aware that most methyl bromide users now have sub-surface water delivery systems known as drip irrigation, Rodriguez-Kabana resumed his research. The result: a liquid sodium azide formulation that could be delivered into the soil via drip irrigation systems.

Much of Rodriguez-Kabana's research to date has been funded by the nation's sole sodium azide manufacturer, American Pacific (AmPac), which is seeking additional uses for the airbag chemical.

Rodriguez-Kabana, whom the U.S. Environmental Protection Agency formally recognized in 1997 for his leadership in coordinating the global effort to find methyl bromide replacements, says Auburn University has applied for two patents on sodium azide: one for the new liquid formulation of the chemical, which previously was marketed only in granular form, and the other for the chemical's soil-enhancement properties.

Meanwhile, AmPac is pursuing EPA registration for the product. Rodriguez-Kabana said the methyl bromide replacement could be on the market as early as the 2004 growing season for a limited number of crops. Approval of Auburn's patent applications, which are now under review in the U.S. Patent Office, will insure that when sodium azide becomes available commercially, Auburn University will earn royalties on the sales.

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