Dioxin cleanup: status and opinions.

Dioxins--toxic by-products of waste incineration and several industrial processes involving chlorine--are nearly ubiquitous throughout the industrial world, mostly in small quantities (see story, p.24). However, some 100 waste sites in the United States alone "contain serious dioxin contamination," according to a report released last month by the congressional Office of Technology Assessment. Of the 500,000 metric tons of these wastes reported to EPA, more than 98 percent consist of tainted soil -- mostly from facilities that produced chlorophenols, chlorobenzenes and chlorophenoxyl pesticides.

To date, high-temperature incineration remains the only effective technology for destroying dioxin in soil, according to the OTA report. Indeed, with properly managed incineration, "one can be assured that dioxins will be broken down" into nontoxic by-products, the report says. But this technology, requiring temperatures in excess of 1,200[degrees]C, has proved expensive, currently costing an estimated $1,200 per ton of treated wastes. And even after a dioxin destruction technique has won government approval, obtaining a permit to use it at a particular waste site can take more than a year. The result, OTA notes: "Sites with dioxin-contaminated soil have been studied for a long time, but no actual cleanup work has begun."

The OTA report highlights several promising alternatives to incineration. Base-catalyzed decomposition, for instance, uses hydrogen and temperatures of just 250[degrees]C to 350[degrees]C to remove dioxin's chlorine atoms -- and toxicity. Price: $250 to $500 per ton of wastes. Thermal gas-phase dechlorination uses temperatures at or above 850[degrees]C to encourage hydrogen reactions with organic chemicals such as dioxin--probably at a cost of $350 to $500 per ton. However, OTA observes, "In light of the relatively small number of contaminated sites, there appears to be little incentive for the private sector to [commercialize such] new technologies for destroying dioxin in soil."