enlarge Gordon Chibroski/Staff Photographer

Kevin Roche, general manager of ecomaine, searches household trash piles for compact fluorescent light bulbs at the ecomaine dumping station in Portland. The energy-saving bulbs also contain traces of toxic mercury.

In the past three years, Mainers have put millions of energy-efficient compact fluorescent light bulbs into their homes. About a thousand more are installed in the state every day.

It’s been an environmental success story, reducing global warming pollution as well as saving consumers millions of dollars in reduced electricity bills.

But the popularity of the bulbs also is growing cause for concern at places such as ecomaine , the Portland-based incinerator that is the end of the line for the region’s household waste.

Each of the bulbs contains a trace amount of toxic mercury. And if enough of them get thrown into the trash and brought to the incinerator after they burn out, they could add up to a big new problem for Maine’s environment and the publicly owned waste agency.

“We wholeheartedly support compact fluorescents,” said Kevin Roche, general manager at ecomaine. “Now we have to make sure the residents don’t throw them in the trash.”

Ecomaine is sizing up the looming problem this summer as part of a $25,000 study of mercury sources and control options. Meanwhile, it hopes the state’s light bulb recycling program and education efforts head off the problem at the waste basket.

Maine and other states have been heavily promoting the new bulbs because they are four to six times more efficient than the old-fashioned incandescent lamps. In the past 12 months, Efficiency Maine incentives helped sell 1.1 million bulbs, more than a 20 percent increase from the year before, said Fred Bever, spokesman for the Maine Public Utilities Commission, which operates the Efficiency Maine program.

And that adds up to big reductions in pollution and electricity costs. The average Maine home now has seven energy-efficient compact fluorescent light bulbs, and stands to save nearly $400 in electricity costs before they burn out and need to be replaced, according to a state report released earlier this year.

Each bulb also contains about 4 or 5 milligrams of mercury, however. Mercury is a neurotoxin that can build up in the food chain and is the reason children and pregnant women are advised not to eat fish pulled from Maine’s lakes and streams.

A variety of items – including fluorescent tubes, thermometers, thermostats and button cell batteries – carry mercury through the waste stream to ecomaine, as well as other incinerators and landfills. The publicly owned waste agency spends $270,000 a year on carbon that it injects into its smokestack to capture 90 percent to 95 percent of the mercury vapors before they spew into the air and settle into lakes or streams.

But ecomaine may have to do even more because of tightening state restrictions on mercury. In 2010, the annual limit for emissions will drop from 35 pounds to 25 pounds. And, while ecomaine has reduced its discharges to about 25 pounds a year, according to Roche, it may now be facing a new wave of mercury as the energy-efficient bulbs start burning out in the next few years.

“We don’t want any additional sources,” he said. “We’re trying to ensure that the amount goes down.”

Ecomaine knows the oldest fluorescent bulbs are already coming in with the trash. But the real concern is what will happen starting in a few years when millions of them start to burn out. “We don’t know what the residents are going to do with the bulbs,” Roche said.

It is illegal in Maine to knowingly throw away the light bulbs or other items that contain mercury. Each community is required to have a plan for recycling them, although the systems vary widely.

Some charge fees, and some require residents to hold onto items for periodic hazardous-waste pickups.Simply putting the bulbs in with other recyclable items won’t work because they can break, releasing...