American Scientist

To the Editors:

Gordon Gribble’s article "Amazing Organohalogens" (July-August) gives considerable attention to natural sources of organohalogens, but leaves out a major environmental problem that may be on the horizon: The bulk of the polluting emissions of methyl bromide and some other organohalogens in the atmosphere appears to be coming from the oceans.

In 1998 the World Meteorological Organization published a report showing that almost 50 percent of the methyl bromide in the atmosphere is emitted by microorganisms in the ocean  (Report No. 44, "Scientific Assessment of Ozone Depletion"). This effect may be aggravated by the increasing use of fertilizers that release bioactive nitrogen, which reaches the oceans and effectively force-feeds the microorganisms. The amount of bioactive nitrogen doubled between 1900 and 2000, and has been increasing at an escalating rate according to a recent conference report (Science 2001 294:1268-1269). The emissions of organohalogens from the oceans are likely to be increasing at the same pace.

In addition to organohalogens, microorganisms in the ocean also emit other greenhouse gases—so the increasing release of bioactive nitrogen could be a major trigger for climate change as well as ozone depletion. The increasing level of bioactive nitrogen is also being cited as a cause of dead zones in the ocean due to microbial overgrowth. Perhaps the major environmental problem needing a call for action is the control of fertilizer nitrogen.

James A. Singmaster III
Fremont, California