Burning exposed trash pollutes soil. (Dioxin Dumps).

In poor urban areas of underdeveloped countries, people frequently set fire to refuse that accumulates along streets and in unofficial dumps. Research now suggests that this form of trash incineration leaves behind prodigious quantities of dioxins and related compounds, which other studies have shown can cause cancer and damage the liver and immune system.

As a consequence, open trash piles may expose people who live in the vicinity and scavenging animals to serious health risks, says Shinsuke Tanabe of Ehime University in Matsuyama, Japan. Other scientists note that the combustion products could be dispersing across borders on wind currents.

The chemicals can move from soil to body tissues by several means. They may be attached to dust that's kicked up and inhaled by animals

and people. The substances may also be consumed accidentally or enter the body through the skin.

At open trash-burning sites in Cambodia, Vietnam, the Philippines, and India, Tanabe and his colleagues set out to measure five polychlorinated dibenzo-p-dioxins (dioxins) and eight related compounds mostly in the category of polychlorinated dibenzofurans (furans). Studies in industrialized nations have implicated ash and gases from municipal trash incinerators as sources of these chemicals. Furthermore, because open fires typically burn at lower temperatures than incinerators do, they're more likely to produce the compounds.

Tanabe's team tested 48 soil samples from five dumps where trash had been burned. The researchers also tested 13 soil samples from locales at least 30 kilometers from these dumpsites.

Soil from the dumps had much higher concentrations of the dioxins and furans than the other sites did. For example, at a dump in Phnom Penh, Cambodia, concentrations of 9 of the 10 studied dioxins and furans were at least 100 times greater than they were in soil away from the dump. The chemicals' concentrations in soil at this site and one in Hanoi, Vietnam, exceeded a threshold that in the United States and Japan triggers government intervention, Tanabe and his colleagues report in an upcoming issue of Environmental Science and Technology.

The study didn't include enough soil samples to give a reliable estimate of the magnitude of the problem caused by these dumps, says Karl-Werner Schramm, a dioxin researcher at the Institute of Ecological Chemistry in Neuherberg, Germany. Nevertheless, Schramm adds, the work supports a relationship between the incineration of junk and environmental problems.

This study appears to be the first to document that common methods of trash elimination in Asia are creating hazardous environmental concentrations of dioxins and related contaminants, says Johan Nouwen, who studies soil pollutants at the research institute Vito in Mol, Belgium. Trash burning "also could be an important problem in African and South American developing countries," he says.

Because diseases unrelated to pollution keep life expectancy short in many poor countries, the newly documented threat may not become a high-priority health issue for the countries studied, Nouwen adds. However, air currents can carry dioxins and furans across national borders, so the health implications of small-scale trash burning deserve international attention, he says.