EPA Updates the Environmental Impact of Methyl Bromide

Because science has fingered methyl bromide as a culprit in destroying the ozone, regulatory actions were needed to control emissions. “Although regulatory action can be difficult and confusing initially, it can lead to a better way of doing things,” said Bill Thomas, an entomologist with the U.S. Environmental Protection Agency. EPA’s Stratospheric Protection Division presented a poster update on the environmental impact of methyl bromide at the Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions, held December 7–9, 1998, in Orlando, Florida.

Under the Clean Air Act, methyl bromide had been scheduled for phaseout in the United States on January 1, 2001. However, Congress recently signed legislation to extend the use of this pesticide and gradually phase it out by 2005.

Worldwide, most of the methyl bromide used goes to fumigate soil for preplant purposes. Thomas said that the breakdown is 70 percent to fumigate soil, 16 and 8 percent to fumigate durable and perishable commodities, respectively, and 6 percent to treat structures.

“Of all the methyl bromide used, North America uses the most, at 43 percent of the total. Asia uses 24 percent and Europe, 24 percent, while the remaining 9 percent is used by Africa, South America, and Australia,” Thomas reported.

In the United States, growers use 43 million pounds of methyl bromide each year. Of that, about 35 million pounds go for soil fumigation, 5 million for postharvest uses, and 3 million for structural fumigation.

This means that 81 percent of the chemical used goes to prepare the soil for vegetables, orchards, nurseries, and other crops. Of this total, 62 percent is used for vegetables; 10 percent, orchards; 15 percent, nurseries; and 13 percent, other crops.

Postharvest uses account for 12 percent of the total U.S. methyl bromide use. Of this, 57 and 34 percent are used on perishable and durable commodities, while 9 percent is for quarantine use.

“Because most of the methyl bromide used is for soil fumigation, it is inevitable that much of it escapes into the atmosphere,” Thomas said. “We estimate that about 50 to 90 percent of the chemical used in the soil will escape into the air. From 80 to 100 percent of that used to fumigate commodities will escape.”

Once in the stratosphere, high energy radiation releases a very reactive bromine atom that destroys ozone molecules, he said. “In fact, one atom of bromine is 50 times more destructive to ozone than one atom of chlorine.”

According to atmospheric scientists, destroying stratospheric ozone molecules causes the ozone layer to thin, resulting in more ultraviolet light reaching the earth’s surface. This increases surface radiation, which is harmful to biological organisms, including plants and humans.

Therefore, since atmospheric scientists agreed that methyl bromide has an ozone depletion potential of 0.4, it was classified as a significant ozone depletor.

“Any substance with an ozone-depleting potential (ODP) of 0.2 or higher must be phased out within 7 years, under Title VI of the Clean Air Act,” Thomas reported. “In 1993, methyl bromide’s ODP was 0.7. On this basis, EPA was authorized in December 1993 to phase out use in 2001 and freeze production and importation at 1991 levels.”

But in November 1998, Congress changed these regulations to be more in line with the Montreal Protocol. The new legislation mandates that methyl bromide produced and imported will be reduced as follows:

• 25 percent in 1999,
• 50 percent in 2001,
• 70 percent in 2003,
• 100 percent in 2005.

Preshipment and quarantine use are exempt from this mandate, and critical agricultural uses will be allocated after 2005.

Like others involved in this issue, Thomas said that there is not likely to be a single, magic bullet alternative to methyl bromide. An integrated approach to pest control will be necessary by carefully considering the crop or commodity, climate, type of soil, and probably most important, the target pest.

Alternatives proposed for soil fumigation are dependent on many factors, including the pest, crop, geographic location, time of year, and soil type. Chemicals proposed as alternatives include 1,3 dichloro-propene, chloropicrin, and methyl isothiocyanate (MITC) generators such as metam sodium or dazomet. Nonchemical methods include crop rotation, organic matter, steam, solarization, and ozone.

“Proposed alternatives for commodity and structural treatment are also dependent on a wide range of factors: the commodity, the pest, storage or shipping method and the time of year, and trade requirements,” he noted. “Chemicals suggested are phosphine and sulfuryl fluoride. Nonchemical treatments are irradiation, nitrogen, carbon dioxide, and cold and heat.”

Although no single treatment has yet surfaced that can replace methyl bromide, Thomas said that “alternatives do exist and will ultimately replace methyl bromide.”

Last Updated: January 12, 1999