Win some, lose some

Experts debate the phasing out of methyl bromide, a chemical with potent ozone-depleting qualities

Published: Sunday 31 January 1999

to the dismay of many environmentalists, it seems that a potent ozone-depleting pesticide scheduled for a gradual phase-out would be retained after all.

us researchers have found that emissions of the agricultural fumigant gas methyl bromide could be reduced to what they claim are insignificant levels by applying composted manure and a novel plastic cover to soil before the gas is injected. The manure expedites the breakdown of the gas to harmless products such as methyl alcohol and bromide ions dissolved in water.

Methyl bromide gas is used to kill pests, like nematodes and fungi, and weeds before crops such as tomatoes and flowers are planted. Although used worldwide, the gas is scheduled for a gradual phase-out in industrialised nations by 2005 because it depletes stratospheric ozone. The phase-out deadline was recently postponed from 2001 to 2005 due to lack of effective alternatives.

Now, researchers at the us Department of Agriculture ( usda ) say farmers across the world may not need to stop the gas at all. While this announcement has been welcomed by the farming community, environmentalists are adamant that methyl bromide should go. "It's unrealistic to think that there would be the level of control to reduce emissions to zero," says a spokesperson for the San Francisco-based Pesticide Action Network. "The chemical is going to be phased out and research efforts should focus on alternatives." But usda researchers are pressing ahead with their new plan. "I think it is possible to use methyl bromide with nearly zero emissions," says Scott Yates of the usda 's Agricultural Research Service in Riverside, California. Earlier in 1998, Yates and his colleagues reported that methyl bromide emissions could be cut significantly using a new, highly impermeable plastic instead of polyethylene tarpaulins that most us farmers use ( Geophysical Research Letters , Vol 25, p 1633).

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