The study, which also implicates salt marshes as a source of methyl chloride, is published in the Jan. 20 issue of the journal Nature. Methyl bromide is produced naturally from oceans and plants on land. But it is also widely manufactured around the world because of its effectiveness as a pesticide against insects, nematodes, weeds, pathogens, and rodents. Methyl bromide also is generated as a by-product of leaded fuel combustion and vegetation burning.
Scientists estimate that about half escapes into the atmosphere.
In the U.S., the EPA estimates about 21,000 tons are used annually in agriculture, commodity and quarantine treatment, and structural fumigation. Because it is considered a significant ozone-depleting substance, governments have developed controls that limit methyl bromide production. Scientists have estimated that 20 percent of the methyl bromide that reaches the atmosphere can be attributed to fumigation, about 10 percent to vegetation burning, and roughly 30 percent to production from the oceans. The new study uncovers about 10 percent of the absent budget. Conducting a year-long study at Mission Bay Marsh in San Diego and San Dieguito Lagoon in Del Mar, Calif., the researchers documented significant amounts of methyl bromide and methyl chloride released to the atmosphere.