Dioxins: new attempts to smoke them out.

Dioxins appear to be raining down from the atmosphere in quantities significantly higher than can be accounted for by all the major activities known to create them, a new study finds.

Louis P. Brzuzy and Ronald A. Hites of Indiana University in Bloomington collected soils from 107 sites around the globe and analyzed them for dioxins and for furans, a group of chemicals similar to dioxins. These unintentionally produced families of chlorinated pollutants represent an almost ubiquitous toxic legacy of humanity's industrial activities.

To estimate the global load of dioxinlike compounds, the two scientists extrapolated the concentrations they measured to areas of comparable climate, geography, and economic development.

Acknowledging large uncertainties associated with their estimates, Brzuzy and Hites nonetheless conclude in the June Environmental Science & Technology that the worldwide rain of dioxins and furans onto land totals about 12,500 kilograms per year. That's roughly four times the amount suggested by estimates of emissions, which include 1,130 kg/yr from municipal waste incineration, 1,000 kg/yr from cement kilns, and 350 kg/yr from burning trees and other plants, or biomass.

This discrepancy, they say, suggests that there are major unknown sources, that diffuse sources may be larger than appreciated, or that known sources may be more variable than occasional measurements have suggested. Valerie M. Thomas of Princeton University agrees that the new inventory is suggestive of unaccounted-for sources of dioxins. However, uncertainties in both the production and the deposition of these pollutants "are still too big to conclude there is a discrepancy," she argues.

Indeed, the rates of dioxin and furan production from biomass burning that she and Thomas G. Spiro of Princeton have calculated are 10 times higher than the rates cited in the new report. If accurate, she observes, her rates alone would inflate the overall contribution of biomass to 3,500 kg/yr-doubling the Indiana team's total global estimate for dioxinlike emissions and halving that group's discrepancy between emissions and deposition.

An in-house study by the Environmental Protection Agency, also in the June Environmental Science & Technology, identifies a possible means of cutting emissions of these compounds. It shows that burning high-sulfur fuels, such as coal, along with trash can dramatically cut the creation of dioxins and furans in municipal incinerators.

The key was to roughly quintuple the sulfur typically found in materials fed into these furnaces, notes Brian K. Gullett of EPA in Research Triangle Park, N.C., a coauthor of the study. His data indicate that the extra sulfur forced the chlorine naturally present in the wastes and fuel to form primarily hydrogen chloride (HCl) rather than the molecular chlorine (Cl2) needed to build dioxins.

In some tests, burning high-sulfur fuel with simulated trash reduced an incinerator's dioxin and furan emissions by about 90 percent.