Dismantling Dioxins

A new method for chemically treating dioxins and PCBs could help to destroy the toxic pollutants.

A New York City-based company believes it has found a way to safely and cheaply dispose of polychlorinated pollutants such as dioxins and polychlorinated biphenyls (PCBs). Its trick is to encapsulate highly reactive compounds that are already known to breakdown the pollutants, but have hitherto been too unstable for practical use.

Dioxins and PCBs are particularly persistent chemicals, which makes them very difficult to break down and dispose of. "Controlled incineration has been the most effective means of getting rid of them," says Greg Merrill, managing director of the Chlorine Chemistry Council, an industry association representing chlorine makers and a division of the American Chemistry Council in Arlington, VA.

But while incineration is the treatment of choice for high concentrations of contaminated waste, lower concentrations tend to be placed in hazardous-waste landfills, he says.

Burying it in the ground is less than ideal, says Paul Johnston, head of Greenpeace Research Laboratories at the University of Exeter, U.K. And few incinerators in the world are capable of incinerating dioxins and PCBs without the secondary formation of dioxins.

So, SiGNa Chemistry, the New York-based startup, has developed a remediation method that uses alkali metals, a group of elemental metals that include sodium and lithium, to react with and destroy the polychlorinated pollutants. While such alkali metals are usually too unstable to use for such applications--for one thing, they're explosive when mixed with water--SiGNa Chemistry's trick is to encapsulate them in a porous silica gel, explains Michael Lefenfeld, the company's founder and a chemist at Columbia University in New York City. What makes the technology effective is that the resulting powder preserves the reactivity of the alkali metal but not its volatility. "They associate to [the alkali metals], they don't chemically bond to it," says Lefenfeld.

According to the Environmental Protection Agency, other chemical treatments for breaking up PCBs exist; but they involve operating at very low temperatures, which pushes up the cost, says Lefenfeld. "We do everything at room temperature," he says. By filtering wastes like contaminated soil or sludge through a column of these powders, they've shown that it's possible to dehalogenate them. By binding to the halogen atoms--such as bromine, chlorine, iodine, and fluorine--that are present in the dioxins and PCBs, the treatment compounds break up the toxic chemicals into their harmless constituents. For example, the alkali metals bind to the chlorine atoms that hold some dioxins together, causing the dioxins to break up.