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What is methyl bromide?

By Diana Matthews

The chemical formula for methyl bromide is CH3Br, meaning that it consists of a carbon atom surrounded by three hydrogens and a bromine. If the carbon were instead surrounded by four hydrogens and no bromine, it would be ordinary methane, the primary constituent of natural gas.

Hydrogen is the lightest, smallest atom; a carbon atom has 12 times the mass of a hydrogen. Bromine is a halogen, or “salt-forming” element, found in the same column of the periodic table as fluorine, chlorine and iodine; at room temperature it is a rapidly-evaporating liquid, but it seldom exists in a pure form. Instead, it is found in compounds with other elements. Some people prefer bromine to chlorine as a swimming pool sterilizing chemical.

Methyl bromide is also known as bromomethane. The N.C. Division of Air Quality classifies it as a volatile organic compound, referring to its low boiling point (about 36 degrees Fahrenheit), which is the reason for its speedy evaporation.

The News Reporter reached out to several specialists for insight on the qualities of methyl bromide.

The horticulturalist

Director Dalton Dockery, of Columbus County’s N.C. Cooperative Extension office, said that he didn’t “have a dog in the (timber fumigation) fight,” but stressed that, “I really believe in providing all the research based information so people can make informed decisions.” He offered to “speak to how it (methyl bromide) was used in farming situations.”

The compound, Dockery said, was commonly used to sterilize soil before 2005. “When we farmed, we used it to fumigate our tobacco transplant beds,” he said.

The ground would be covered with plastic and the methyl bromide gas would be injected deep into the soil and allowed to remain there for 48 hours. The plastic would then be pulled up.

Methyl bromide was a very effective pesticide at “killing everything” that was closed up with it, Dockery said.

He warned that, “If you stay in the presence of it too long or get trapped in an area where it can’t escape, like an enclosed room, etc., it can cause serious human health problems. It is odorless and tasteless. You wouldn’t know you are in the presence of it; however, companies usually put what is called a tickler in with it so if you happened to come into the presence of it, it would tickle your nose. If it wasn’t for that you would never know it was around you.”

Dockery referred The News Reporter to specialists in the state Department of Agriculture. As of press time, none of them have returned phone calls from last week, but they may feature in a coming article.

Montreal

Those farming practices had to change after the Montreal Protocol, a 2005 international agreement that put strict limits on the use of compounds that may deplete the Earth’s ozone layer, said James Sargent, a pesticide chemist based in Milwaukee, Wis.

Because methyl bromide consists of a methyl group (CH3) plus one bromine, said Sargent, it is useful for synthesizing formulas that “need an extra methyl group.” It is used to make products for health care, including prescription medications. It has been used as a sanitizer and in food processing. The leftover bromine can easily combine with other elements, including ordinary oxygen or ozone. It is CH3Br’s ability to break down and recombine with other substances that makes it both useful and a problem for the ozone layer.

Ozone in the stratosphere filters out some of the sun’s harmful ultraviolet radiation. Compounds such as chlorofluorocarbons (CFCs), Halon (a firefighting chemical) and methyl bromide all began to be phased out of everyday use at that time.

“These things were all phased out because they theoretically deplete the ozone layer, not because of toxicity to humans,” Sargent said.

Since 2005, the U.S. government’s EPA allows methyl bromide fumigation only for limited uses, including foreign produce being brought into the country and products such as logs being shipped out.

“It has many uses,” Sargent said, “because the molecule is so simple. “It’s impressive, but too much can be toxic.” The timber and produce industries use that toxicity as a weapon against insects in closed fumigation containers.

The beetle slayer

Sargent trains prospective fumigators to use methyl bromide. He did not train the certified fumigators on the Malec Brothers staff; he said that Mike Waldvogel of N.C. State University trained them.

When David Smith, Malec Brothers’ Executive for International Procurement, was scouting sites for a plant in North Carolina, he said that numerous contacts recommended Sargent as being “the best” fumigation consultant in the country. Malec Brothers brought Sargent from Milwaukee to Delco to help with logistics. He also reviewed the PowerPoint presentation that Smith showed to county government bodies in January.

Methyl bromide’s intended use on the Delco property is as a killer of beetles that live in and under the bark of pine trees.

Sargent described CH3Br as “kind of amazing” among fumigants. It spreads much more thoroughly through a space and into crevices than most other gases used to treat agricultural products, he said. “It kills fungi and spores” as well as insects, which are easier to kill; it can kill notoriously resistant bacteria such as anthrax. “After 9/11, when people were receiving anthrax in the mail, methyl bromide was one of the tactics the government was talking about using to kill it.”

Natural sources

Sargent said that methyl bromide “is produced naturally as a product of high heat combustion,” for example during grass fires and forest fires. It exists in natural gas pockets underground and is spewed into the atmosphere along with other gases such as sulfur dioxide released by volcanic eruption.

“I don’t know how much is coming out of Kilauea, but typically volcanoes produce methyl bromide,” Sargent said. “All of the oceans produce some” because the salt-forming elements, plus carbon and hydrogen, are abundant in them. “The Indian Ocean produces a high concentration of methyl bromide,” Sargent said, although no one knows why it is higher than other oceans’ production.

The gas is just slightly heavier than air (a mixture of mostly nitrogen, oxygen and carbon dioxide), said Sargent. “If there’s any air movement at all, that’s where methyl bromide goes. Typically air rises with heat, so that’s what methyl bromide does. It also diffuses very quickly. It has a very high vapor pressure, which means its molecules don’t like being next to each other and they disperse.

Sargent stressed that methyl bromide’s potential to harm humans depends on the amount of it a person is exposed to in a given space.

Sargent compared methyl bromide’s danger to humans with that of carbon monoxide, produced by burning hydrocarbons such as gasoline. “If someone closes their garage door and leaves their car running, they can die from breathing the carbon monoxide that builds up. But when firefighters come to the scene, the first thing they do is open the door.”

 

More questions

“Before the Montreal Protocol,” Sargent said, “farmers used a lot of methyl bromide on high-value crops,” including tobacco but also including many types of edible produce. North Carolina was third in the U.S. in the amount of methyl bromide used, after California and Florida.

“The farmers did it (applied the gas) themselves,” he said, “and when they removed the plastic covers they exposed themselves to more methyl bromide than the people at Malec will be exposed to. It was used for 80 years, and now we use only a tiny bit.”

The News Reporter asked Sargent whether it would be possible to confine the methyl bromide fumigation process to a closed system such as dry cleaners use to cycle and reuse volatile cleaning solutions.

Unfortunately, due to its low boiling point, methyl bromide is a gas at any temperature above 36 degrees Fahrenheit, so it would be difficult to condense and reuse.

“It is possible to pump it out and capture it in a different chamber using activated charcoal,” Sargent said. He did not think the methyl bromide could then be reused, however. The contaminated charcoal would have to be disposed of.

Could Malec Brothers fumigate the shipping containers, then leave them sealed up for their trip across the Pacific Ocean until the Chinese buyers open them? Sargent said no: International maritime law allows no containers under fumigation on board any ship.

A future article will look at the regulatory process and how Malec Brothers’ pilot program in Wilmington was set up.

For more information about methyl bromide and its planned use at the plant in Delco, attend tonight’s question-and-answer session at East Columbus High School at 6 p.m. A public comment period will begin at 7 p.m.

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