An international treaty had banned the popular pesticide methyl bromide for depleting the ozone layer.
Soil scientists at the U.S. Salinity Laboratory in Riverside, California, measured methyl bromide emissions from Brassica plants, a family that includes broccoli, cabbage, and other important crops.
The removal of methyl bromide (CH3Br) from streams of dry and humid air was investigated using coconut shell carbon impregnated with triethylene diamine (TEDA).
The mass-to-charge ratios of the molecule ion peaks corresponded to a loss of methyl bromide (MeBr) from one chain end and concomitant cyclisation to give a lactone end group.
The air measurement verified a methyl bromide concentration from 2.5 to 200 ppm (mean: 125 ppm with 2.5-200 ppmin-maxax) in the storage room between the packing materials five days after the incidence.
For the primary buffer distance used in this analysis (5 km), the estimated median amounts of methyl bromide use ranged from 6,010 to 8,201 kg, and the 95th percentile values ranged from 53,685 to 68,893 kg.
An agriculture department spokesman said all flower consignments were fumigated with methyl bromide before being released from quarantine.
Not only had the risk from methyl bromide diminished, he said, but most of the substitutes offered to it pose bigger environmental dangers.
In a related effort, the American Farm Bureau, Florida State officials and other lobbying groups wrote members of Congress this week seeking an amendment that would allow the use of methyl bromide to rise 20percentt from the amount currently permitted under federal law and the treaty.
