Every time he uses the potent pesticide methyl bromide to kill the worms on his walnuts, farmer Mark Gibson worries that he is also destroying a small chunk of the planet's ozone layer.
It bothers him, too, that when he releases the poison from his fumigation shed across the street from Calaveras Elementary School, the toxic gas could pose a danger to schoolchildren. But for Gibson and a lot of farmers like him, methyl bromide is a matter of economic survival.
One of the most widely used pesticides on Earth, it is applied on crops from alfalfa to wheat and is touted for helping turn California strawberries into a $450-million industry. In cities, the odorless and highly poisonous gas is also the chemical of choice for ridding homes of termites.
But from rural Hollister to the United Nations, pressure is mounting to ban the pesticide with the discovery that it is one of the most potent causes of ozone depletion in the upper atmosphere, breaking down ozone about 40 times as quickly as the better-known chlorofluorocarbons, or CFCs.
Use of methyl bromide as a pesticide is responsible for as much as 10% of the annual depletion of the ozone layer, much of it over the Northern Hemisphere, said Susan Solomon, a senior scientist at the National Oceanic and Atmospheric Administration Aeronomy Laboratory in Colorado.
Experts believe that depletion of the planet's protective ozone layer will cause major increases in skin cancer and a variety of other environmental problems.
Methyl bromide, in use for 60 years, also has a checkered history of causing deaths in homes, evacuations in farming communities, and, some experts suspect, birth defects.
For farmers such as the bearded, bespectacled Gibson, the sudden campaign on a variety of fronts to ban methyl bromide is disconcerting, given the lack of a good substitute for the chemical.
"Being a practical man," Gibson said, "we're going to do what we have to do. We will continue to use methyl bromide and hope they will come up with an alternative."
In Monterey, the Air Resources Board is trying to reduce emissions of the gas from Gibson's fumigation chamber and 30 others like it. In Sacramento, the Legislature is considering a bill to ban the chemical because it is lethal in small doses.
In the nation's capital, prompted by environmental groups such as the Natural Resources Defense Council, the Environmental Protection Agency is considering banning methyl bromide because of its destructive effect on the ozone layer. In Geneva, a U.N. study group recently added the pesticide to its list of ozone depleting chemicals that should be banned by 1995.
And the nations that signed the 1990 Montreal Protocol, a treaty restricting CFCs and other ozone-depleting chemicals, are scheduled to consider the fate of methyl bromide when they meet in Copenhagen in November.
"We've got to figure out something to take its place because it's going to be gone," said Stan Prochaska, a spokesman for the U.S. Department of Agriculture. "How far down the road are we talking? That's what is being negotiated."
The chemical industry is fighting back with a $3-million campaign to keep the pesticide in use, arguing that banning it would result in catastrophic crop losses and economic disruption around the world.
"We estimate that its value to world trade is in excess of $50 billion," said David Bouchard, chairman of a newly formed industry coalition called the Methyl Bromide Working Group.
Manufacturers of the chemical are finding high-level allies within the Bush Administration, where a battle has broken out over the chemical's future.
The EPA will soon recommend that the chemical be phased out of use, spokesman Dave Ryan said. But at the Department of Agriculture, top officials argued in a recent letter to the EPA that eliminating methyl bromide "would not be in the best interests of the nation's agriculture, consumers or the economy."
Harry Mussman, a high-ranking USDA official, estimated that crop loss caused by the immediate ban of methyl bromide could be $500 million a year. "It would be much better to move much more slowly," he said. "There's too much at stake."
To farmers and the pest control industry, methyl bromide is a valuable pesticide because of its versatility in killing a wide range of bugs and its ability to penetrate hard surfaces such as walls and walnuts. The fumigant is most commonly used to sterilize soil before planting, to fumigate produce after harvest, and to kill termites in buildings.
With soil fumigants such as DBCP and EDB banned amid concerns about cancer and ground-water contamination, methyl bromide has become increasingly popular with farmers. Instead of percolating into the water supply like some pesticides, methyl bromide rises into the atmosphere.
California is the largest market in the world for methyl bromide, using twice as much of the chemical as it did seven years ago. The state's use is more than 20 million pounds--about a seventh of the 140 million pounds the industry estimates is manufactured worldwide each year.
The biggest consumer in California is the pest control industry, which uses more than 5 million pounds each year to kill dry-wood termites--about 60% of that in Los Angeles County alone.
Although methyl bromide is generally mixed with the tear gas chloropicrin as a warning agent, its use as a structural fumigant comes at a high cost: It has killed at least 16 people who entered treated residences in the last decade, accounting for nearly all of California's pesticide deaths during that time.
The pesticide's danger as a lethal poison was underscored this year in Redwood City when residents of a downtown apartment building were allowed to re-enter their homes after the building had been tented and fumigated.
One resident, Gary Barthold, 37, was carried out the next day suffering from stomach pains and seizures. He died 16 days later of methyl bromide poisoning.
Barthold's death was apparently the first case in which the victim was a resident who had been given permission to return to a treated building. Most often, those who have died have been burglars or homeless people who entered tented buildings.
Authorities believe that after Barthold returned to his apartment, the chemical desorbed from the saturated walls and furniture and reached toxic levels within the living area. Three months after he died, the state adopted stricter standards for the re-entry of treated structures. San Mateo Dist. Atty. James P. Fox is considering filing charges in the case.
In agriculture, methyl bromide is often injected into the soil, which is covered with tarps to keep the gas from escaping, to kill nematodes, weeds and other pests. In some cases, the pesticide has leaked out prematurely, causing scores of people to become ill and thousands to flee their homes.
In the San Joaquin Valley town of Ceres, 35 people sought medical aid and 1,500 were evacuated from their homes in 1984 after the chemical was improperly applied in a spice field. More than 1,200 people were forced to flee their homes in Fremont three years later when the pesticide drifted off a gladiolus field.
Methyl bromide also is widely used to fumigate a large variety of products bound for international shipment--including the walnuts that come from Gibson Farms in Hollister. Experts say the chemical poses no danger to people who consume treated produce. However, fumigation is conducted in gas chambers that are scattered around the countryside and largely unregulated. Afterward, the gas is released into the air.
Methyl bromide is a man-made and a naturally occurring substance. In nature, it is produced primarily in the oceans by algae. The commercial product is manufactured by mining ancient brine deposits that are found in only a few places in the world, including Arkansas and the Dead Sea.
In the United States, all methyl bromide is produced in Arkansas by two companies, Great Lakes Chemical and Ethyl Corp., which are responsible for about half of the world's production.
At first, scientists questioned whether bromides found in the atmosphere were the result of the biological process or pesticide use. But researchers recently found that the amount of methyl bromide in the atmosphere is higher over the Northern Hemisphere, where most of the pesticide is used, and lower over the Southern Hemisphere, where the ocean's surface area is significantly greater.
National Oceanic and Atmospheric Administration scientists estimate that about 25% of the destructive bromides in the atmosphere stem from man-made methyl bromide, Solomon said.
Some environmentalists put the number at 50% or more. Industry spokesmen question whether any of the man-made chemical reaches high enough into the atmosphere to destroy ozone.
"I have uncertainties about the effect of man-made methyl bromide," said David Riggs, manager of the California Strawberry Advisory Board. "More research needs to be done, particularly given the impact its banning would have on world food production."
Environmentalists argue that eliminating the use of methyl bromide could lead to an almost immediate improvement in the condition of the ozone layer.
Unlike CFCs, which keep destroying ozone for decades once they reach the upper atmosphere, the faster-acting bromides last about two years. Thus, within two years, a ban on methyl bromide could produce up to a 10% reduction in the rate of ozone depletion, they say.
"If we can eliminate the use of methyl bromide internationally," said Arcata environmentalist Patricia Clary, a leader in the burgeoning movement to ban the pesticide, "I think we can have such an effect on ozone depletion that millions of lives will be affected."
Methyl Bromide at a Glance
Methyl bromide, a common pesticide, has been identified by some scientists as a major cause of ozone depletion in the atmosphere. Used in residential termite fumigation and in agriculture, it has also been blamed for 16 deaths in California in the last decade, has caused evacuations of farming communities and is suspected of causing birth defects. Here are some statistics on its use: METHYL BROMIDE IN CALIFORNIA
1985: 10.7 million pounds
1986: 12.9 million pounds
1987: 13.7 million pounds
1988: 16.8 million pounds
1989: 15.2 million pounds
1990: 20.1 million pounds TOP FIVE USES IN 1990
Structural pest control: 5.2 million pounds
Strawberries: 4.3 million pounds
Nursery stock: 2.4 million pounds
Grapes and raisins: 2 million pounds
Nuts: 1.1 million pounds SOURCE: California Department of Pesticide Regulation