Backyard trash burning has been illegal in Maine for more than four years, but in many small towns, an old metal drum filled with smoldering household garbage is still a common sight.

In rural parts of the state, where a landfill could be 20 miles away and municipalities don’t have the funds to send a garbage truck to every home, this Maine ethic of “do it yourself” is having serious environmental consequences, said Andrea Lani, of the state Department of Environmental Protection’s air bureau.

State and federal environmental officials throughout the Northeast have recently joined forces to quantify the problem and educate the public by signing a joint resolution titled “Don’t Trash Our Air,” she said.

Most states, including nearby New Hampshire and Vermont, have restrictions, if not outright bans on backyard trash burning. But throughout the region, illegal burning in hundreds of backyard barrels, wood stoves and fireplaces continues.

In 1997, four years before the Maine law went into effect, a DEP study indicated that one in 58 households – 1.72 percent of all homes – burned trash, disposing of 21 tons of waste daily. In rural Aroostook County, the practice peaked, with 2.4 percent of all households reporting a burn barrel.

The department is currently working with an environmental group to update its data, but anecdotal information suggests that many people continued burning despite the 2001 law, Lani said.

“People think, ‘It’s going to get burned [in a municipal incinerator] anyway – I might as well do it in my yard.’ But it’s not the same,” she said Friday.

An incinerator burns trash at more than 1,800 degrees, with a precise balance of oxygen to optimize combustion. In a burn barrel, the trash is often damp to begin with, and with wind drafts moderating the flame, incineration tends to be at a very low temperature, producing a great amount of soot and allowing toxic chemicals to survive the burning intact.

And incinerators are required to install pollution control equipment in an attempt to capture the soot and chemicals that are produced.

According to a study conducted by environmental officials in New York state, burning 10 pounds of trash in an open barrel produces the same amount of air pollution as burning 400,000 pounds of trash in a modern incinerator.

That pollution can contain particulate matter that can irritate lungs, cause asthma attacks and contribute to smog. But it’s the invisible pollutants that prompt the biggest health concerns:

. When No. 3 plastic – also known as polyvinyl chloride, or PVC – is burned, the smoke contains dioxins and furans, chemicals that can accumulate in rivers and the fish that swim in them, eventually contributing to cancer in humans.

A recent federal Environmental Protection Agency study indicated that more dioxins and furans were produced by backyard trash burning between 2002 and 2004 than from all other sources combined, including paper mills, municipal incinerators, electric utilities and vehicles.

Under the right conditions, burning PVC can also produce poisonous chlorine gas – a chemical that was used as a nerve agent during World War I.

. When some types of pressure-treated lumber are burned, the smoke and ash can contain arsenic or chromium, elements that can be poisonous when they accumulate in the body.

Arsenic is of particular concern in Maine, as some parts of the state naturally have high arsenic levels in the water because of the mineral content of the soil.

. Burning of some bleached papers, many synthetic paints and dyes (even in the small amounts that are applied to wood or paper) and household items like batteries and small electronics can produce a stew of chemicals, including heavy metals like mercury, lead and cadmium that remain in the smoke and the ash, and can contaminate groundwater – particularly when the ash is dumped on the ground. To avoid this same pollution, the state requires that municipal incinerator ash be disposed of in highly regulated landfills.

In coming months, the Maine DEP will work with other states, the EPA and environmental groups to create an inventory of backyard trash burning and the effects of its pollution, as well as develop new strategies for enforcing the state ban and educating the public.

For information, visit the DEP Web site at http://state.me.us/dep/air/backburn.htm.