The Science of a Banned Pesticide

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The February 2006 (vol. 2, issue 20) Scientist contains a letter to the editor from ACSH Advisor S. Fred Singer, of the Science and Environmental Policy Project, who notes some of the forgotten science in the debate about mandating that industry phase out the fumigant methyl bromide:

¢ About two-thirds of the methyl bromide entering the atmosphere is of natural origin, mainly from the oceans.

¢ The atmospheric lifetime of methyl bromide is only a few months. This has two important consequences: First, most of it is destroyed before it can reach the stratosphere, where it can attack the ozone layer. This is especially true for human-produced methyl bromide, which first has to travel from mid-latitudes to the equator before being transported into the stratosphere. Second, if ever a problem is found, production can be turned off and anthropogenic methyl bromide would disappear from the atmosphere within a year or two.

By contrast, chlorofluorocarbons have lifetimes of decades or a century.

¢ New data from ice cores show that atmospheric methyl bromide started to increase more than a century ago, long before it was manufactured and used commercially. Other measurements show that rice paddies in Asia are a source of the chemical, suggesting that rice cultivation to feed a growing population could be an important human-related source.

¢ Finally, I know of no measurements that show a gradual increase of bromine in the stratosphere. This would indicate that the human component is still insignificant.