Open burning of household waste in barrels is potentially one of the largest sources of airborne dioxin and furan emissions in the United States," said Environmental Protection Agency scientist Paul Lemieux, one of the study's co-authors.
Dioxin and furan belong to a class of compounds known to have harmful effects on laboratory animals. Scientists believe they may also pose serious danger to humans.
Lemieux and his colleagues are trying to determine how much burning in barrels contributes to dioxin and furan pollution. The study could help resolve a long-standing discrepancy reported in a 1994 EPA assessment that identified a "significant gap" between estimates of dioxin emissions and actual deposition measurements.
Emissions of dioxins and furans from burn barrels "may be an important missing link to help close the gap between measured deposition rates and the emissions inventories," the article states.
The polychlorinated compounds dioxin and furan can be created by burning common household trash at low temperatures. Years of research has determined that waste of this kind must be burned at a temperature of approximately 3000 degrees Celsius, and the resulting gases cooled to about 200 C and kept away from particulate to avoid the gas-solid reactions that create dangerous chemicals such as dioxin and furan. Household refuse can include everything from paper to plastics to metals to organic waste.
Gases created by burning such waste include carbon dioxide, water vapor and nitrogen, while the particulate may include unburned carbon and traces of metals used to make wire, plastic products or dyes. Allowing such gases and solids to intermingle at a temperature from 300 C to 350 C provides the perfect environment for the creation of dioxins and furans, said Lemieux, and "copper is believed to be the main metallic catalyst."
Another principal culprit is an unidentified chlorine source. "At this point we are not sure if the chlorine source is a solid or a gas," said Lemieux. "That is one of the pieces of the dioxin formation mechanism that is still unclear." The source of chlorine could be anything from salt to plastic polyvinyl chloride piping to bleached paper. New municipal waste incineration systems are designed to keep gases and solids from intermingling to avoid chemical reactions that create dioxin and furan.
Tests show that when trash is burned in a barrel, heat generated inside the container falls into the dioxin temperature window. "If you wanted to create dioxins, the best thing you could do would be to use a burn barrel," said Lemieux.
To determine the levels of dioxin and furan released from burn barrels, researchers from the EPA and the New York State Department of Health conducted a study at the EPA's Open Burning Test Facility in North Carolina.
In the experiment, ordinary household rubbish was incinerated in a 55-gallon drum. The mixture of trash included newspapers, books, magazines, junk mail, cardboard, milk cartons, food waste, a variety of plastics and an assortment of cans, bottles and jars. No paint, grease, oils, tires or other household hazardous wastes were burned in the test.
Emissions from the burn-barrel trash were compared with emissions from a "well-controlled incinerator performing better than the dioxin requirements set by recent EPA standards," said Lemieux. Kilogram for kilogram, "emissions from open burning are several orders of magnitude higher than for controlled combustion in a modern, clean-operating municipal waste combustor," concludes the report, "because of lower incineration temperatures and poor combustion conditions (in barrels)."
Burning trash in barrels is "potentially a major source of emissions," said Lemieux. "We think it's non-trivial, but we don't know."
"More studies are necessary to take the next step," said an EPA spokesperson, "and this step may or may not include policy."
Burning refuse in barrels is illegal in most of the U.S., but some rural municipalities still allow the practice. The EPA estimates that about three million people still dispose of their trash by burning.
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