Prompted in large part by concern over dioxin emissions, cities around the globe have been tightening regulations on municipal incinerators. Largely ignored have been rural households that burn their garbage in a barrel out back. A new federal study now indicates that just a handful of such fires can spew as much dioxin as a large municipal incinerator does.

The results also reveal that per pound of trash burned, avid recyclers spew the most dioxins.

These toxicants, last year formally designated human carcinogens (SN: 5/15/99, p. 309), are slated to be banned from production, even accidental, under a pair of developing United Nations treaties (SN: 7/4/98, p. 6).

Trash burning is policed at state and local levels. In recent years, many regulators have called an Environmental Protection Agency hotline requesting data on pollution emitted by the open burning of trash. Two studies had examined burning but had yielded few reliable data, notes Paul M. Lemieux, a chemical engineer who led the new testing by EPA at its lab in Research Triangle Park, N.C.

His team collaborated with New York officials who had characterized the trash generated by households that did and didn't avidly recycle. The EPA scientists then compiled equal-weight batches of trash simulating those two waste streams. To imitate the typical practice, Lemieux's team burned trash in 55-gallon barrels with ventilation holes punched near the bottom.

On average, burning each kilogram of a recyclers' trash created 264 micrograms of dioxins, 44 times more than did an equivalent quantity of trash from nonrecycling households. Lemieux credits the difference to the higher proportion of chlorine and metals in the recyclers' trash-key ingredients in the recipe for cooking up dioxins.

In fact, it would take only two to three avid recyclers burning 1.5 kg of trash on any given day to match the daily dioxin output of a well-run municipal incinerator serving the needs of up to 120,000 households, Lemieux and his colleagues observe in the Feb. 1 ENVIRONMENTAL SCIENCE & TECHNOLOGY.

Charged with tallying U.S. dioxin data, David H. Cleverly of the EPA in Washington, D.C., has applied Lemieux's data to a rough estimate of the U.S. households not subject to bans on residential burning. Backyard burning, he speculates, might annually "add 800 grams [of dioxins] to our national inventory, which is now about 3,000 grams from all sources. So it could, potentially, be a big deal."

Lemieux's data also "imply we should be thinking about what's in the waste stream that is causing dioxins to form rather than just trying to manage municipal incinerators to form less dioxin," says environmental scientist Valerie M. Thomas of Princeton University.

Chemist Pat Costner of Greenpeace International in Eureka Springs, Ark., agrees. Since creating dioxins requires chlorine, she argues, "we should move away from chlorine-containing materials"-such as the polyvinyl chloride plastic that Lemieux identified as the likely primary source of the dioxin in the trash he burned. -J. Raloff