The next hurdle in ozone repair.

• Author: O'Meara, Molly
• Position: Ozone depletion due to the use of methyl bromide

Early this year, after heated debate, California lawmakers postponed a ban on the use of the pesticide methyl bromide. The issue was safety: activists cited nearly 300 poisoning cases as reason to allow the ban to go into effect in March, as was required under California law, barring a clean bill of health from the long-delayed and still incomplete toxicology studies. But the controversy may mark the beginning of a much broader political battle over a planned global phaseout of the chemical for a different reason: methyl bromide is damaging the upper atmosphere's ozone layer, which shields the earth's surface from excess ultraviolet light. The bromine in methyl bromide is 50 times more efficient at destroying ozone than the chlorine in chloroflurocarbons (CFCs), the best known ozone-depleting compounds, which once had a wide range of industrial applications (See "The Refrigerator Revolution," September/October 1996).

Methyl bromide has been used as a pesticide since the 1930s. About 76 thousand tons of it are sold worldwide every year, mostly for soil fumigation. Pesticide use accounts for the bulk of methyl bromide emissions from human activities, but the chemical is also released through the burning of biomass such as fuel wood, and through the combustion of leaded gasoline. Methyl bromide is also produced by the oceans, but these emissions are not well understood and it is possible that the oceans are absorbing more of the material than they release.

Initial international efforts under the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer focused on longer-lived ozone destroying substances, such as the formerly ubiquitous CFCs. Atmospheric chlorine levels have consequently begun to decline, but bromine levels continue to rise. At present, methyl bromide is thought to be causing 5 to 10 percent of observed ozone loss; if emissions continue to grow at current rates, the figure may rise to 17 percent by 2000. Thus, scientists consider the phasing out of methyl bromide as the next major step in repairing the ozone layer. Under the protocol, industrialized countries have agreed to halt production by 2010, although the United States will ban production in 2001 under its Clean Air Act.

Many farmers fear these bans because methyl bromide is an extremely versatile pesticide. In the United States, the chemical is used on more than 100 crops, for nearly every kind of pest: insects, parasitic worms, rodents, weeds, fungi, and...