BOSTON -- What happens to the trash once it leaves your home is a hot topic in Massachusetts that could get a lot hotter. The Department of Environmental Protection may decide to lift a ban on new incinerators. But few can seem to agree if burning your trash is good or bad for the environment.

Incinerators convert trash into energy in every part of the state. There are seven waste to energy facilities -- Wheelabrator owns three and Covanta Energy owns four.

"We're great on emissions, we are good for the climate, it's a better way to handle solid waste," said Covanta Chief Sustainability Officer Paul Gilman.

But more than 20 environmental groups are pushing hard to make sure the moratorium on building new incinerators is not lifted.

"Incinerators emit more carbon dioxide than coal-fired plants, for example, or gas-fired or oil-fired," said Lynn Pledger, of the Sierra Club.

"That is false, it's not correct," said Gilman.

The science is clear on this: Incinerators of today have decreased their emissions dramatically. But along with CO2, incinerator stacks still emit carbon monoxide, nitrous oxide, mercury and other pollutants. Critics say that's a threat to public health.

"There's no avoiding that. You can't destroy matter. Those toxins have to go somewhere," said Pledger.

When Team 5 Investigates asked Gilman if Covanta's technology was emissions-free, he admitted it was not, but said "It is a safe technology."

Waste to energy facilities cut down on the need for garbage landfills. But they create their own landfills, made up of the ash residue after burning.

"The trash just doesn't disappear," said Brent Baeslack, who lives near the Covanta facility in Haverhill. He's concerned about toxins in the ash.

"They are persistent. And they build up in things such as fish and people who get exposed to it," said Baeslack.

But management at waste to energy facilities insisted the ash landfills are safe, and stressed they are monitored by the companies and regulated by the Department of Environmental Protection and the EPA.

"We have some of the most stringent regulations in Massachusetts in terms of their operation and environmental impact," said DEP commissioner Laurie Burt.

But there have been recent violations at waste to energy facilities.

Team 5 Investigates learned that in 2007, before Covanta bought the facility in Agawam, the DEP cited and fined the facility for excessive emissions of mercury.

In 2008, Covanta's Pittsfield facility was cited for exceeding the allowable dioxin emission rate by nearly 350 percent.

"We do have some misses, we've seen some equipment go down, all of those incidences are self-reported," said Gilman.

A big debate for the DEP as it considers whether to allow more incinerators is how they affect recycling efforts. Critics say burning trash undermines what the DEP calls its mantra: reduce, reuse, recycle.

"It's a delicate balance," said Burt. "You don't want to have the waste to energy be in competition with recycling."

Some long-term contracts require trash quotas. If towns under-produce, they are still charged.

"Our community doesn't have as much of an incentive to recycle," said Baeslack.

The trash at the Haverhill's Covanta facility showed plenty of recyclable material in the mix about to burn. The DEP told Team 5 all the waste to energy facilities combined convert less than 25 percent of the waste to electricity.

"You don't need a hungry incinerator needing to burn up all that trash," said Pledger.

Waste to energy industry proponents told Team 5 Investigates that short of exporting garbage or expanding polluting landfills, burning waste is the best and safest alternative.

No matter how recycling is done, there's always going to be some trash that needs to go to an incinerator or a landfill. In the next few weeks, the DEP will decide which direction Massachusetts should go. In the meantime, a bill is pending that would permanently ban new incinerators.

In a statement to Team 5, a Covanta Energy spokesman added "typically emissions from our US energy from waste facilities routinely fall 60-80 percent below permitted levels, and that they remain "committed to this goal and to continuous improvement."

"We employ 'best practices' with respect to environmental monitoring and management. We invest in employee training and advanced technological systems to improve our performance," the company said.