A cement plant near Kingston wants permission from the province to incinerate tires, arguing it is less harmful to the environment than burning coal.

Lafarge Canada has applied for a permit to burn thousands of tonnes of waste, including tires and non-recyclable materials, from Ontario, Quebec and eight U.S. states.

Environmental groups are criticizing the proposal, saying similar experiments in the United States resulted in emissions with higher levels of heavy metals.

"You can have hot temperatures in something like a cement kiln, but that's never going to destroy metals," said Dr. Elaine MacDonald, a scientist with the Sierra Legal Defence Fund.

"When you're putting in different kinds of fuels like tires, you're going to get different things coming out of the stack."

MacDonald says the environmental group has been studying tire incineration over the past few years.

It says heavy-metal emissions skyrocketed at plants in Quebec and the U.S. after they began burning tires for fuel.

Lafarge officials say the group's information is false.

"I will categorically say tires and the other alternative fuels have been proven safe and our emissions will stay the same or improve as a result of this project," said Rob Cumming, a senior official at Lafarge's Bath plant.

He argues it's an ideal time to dispose of tires by burning them, since the demand for recycled tires has fallen.

According to provincial law, there must be a hearing on the application if an incineration project uses an amount of waste equivalent to that typically generated by 1,500 or more people.

Lafarge's proposal is close to that threshhold, but the Sierra Legal Defence Fund is asking the provincial government to force a review.

Landfills have been a hot topic in Ottawa recently.

Waste Management of Canada Corp., the company that takes in half of the city's waste at the Carp Road landfill, has been under harsh criticism by both citizens and city officials over its plan to triple its size.