"Remember when everyone used to smoke in restaurants?" Ned Lightner asked recently.

He had been talking about his work with Ban the Bag in Belfast, a volunteer movement to do away with single-use plastic bags in the city. There was plenty to say about plastic in the environment, but it was the sort of conversation that drifted easily to precedents — other changes that once seemed unthinkable but had quickly become the new normal.

Lightner was never a smoker, but until earlier this year when he enrolled in the Penobscot Bay Stewards Program, his awareness of the harm that plastic caused in the environment was similar to a smoker's sense of his own deteriorating health. He knew something bad was probably happening, but he didn't know exactly what.

In the month-long course — a joint offering of Maine Coastal Program of the State Planning Office and Belfast Bay Watershed Coalition — he learned that plastic bags don't decompose much in the amount of time that can be observed by humans, but they fairly quickly fall apart in certain conditions.

In Penobscot Bay, a bag might be bashed to pieces until it is small enough to be sucked up by filter-feeding bivalves like the ones Lightner had been blissfully enjoying for years.

He was alarmed to learn the mussels he had enjoyed as the unspoiled fruits of Maine's coastal wilderness might be, in some small part, made of plastic. The bay water itself, while less composed of chicken fat than it had once been, was also found to be speckled with the shopping bags. A study found that a typical liter of water from Penobscot Bay contained 17 pieces of plastic.

Lightner and five other alums of the Penobscot Bay Stewards Program spent the summer and fall researching how to get rid of the flimsy and ubiquitous bags that were causing the problem. This week, they presented the City Council with a recommendation for an ordinance that would ban them.

Seven other Maine municipalities — Falmouth, Freeport, Kennebunk, Portland, South Portland, Topsham and York — have enacted some version of a plastic bag ordinance. Each has taken a slightly different approach to the challenge of reducing plastic bag use without crippling businesses and forcing shoppers to carry their groceries by the armload.

Freeport, Kennebunk and York banned all single-use plastic bags, but not paper ones. Portland, South Portland and Falmouth still allow all types of single-use bags but require retailers to charge 5 cents for them. Here, the rule applies only to merchants whose food sales account for more than 2 percent of gross revenue.

In Falmouth, the bag ban only applies to stores with more than 10,000 square feet of floor space, but excludes restaurants, dry cleaners and horticultural nurseries. In York and Kennebunk, commercial establishments may not use single-use plastic bags, but nonprofits and religious organizations may.

As the Belfast group learned, some towns tried to define single-use bags by the thickness of the plastic. Meanwhile, the term "reusable" was popping up on bags that clearly were not.

Ban the Bag in Belfast ultimately recommended that the City Council enact a full ban on single-use plastic bags with a six-month delay after the ordinance is adopted to give retailers time to make the transition.

According to the group, 600 million single-use plastic bags are used in Maine every year and only about 5 percent of those are recycled.

In Belfast, the transfer station used to collect the bags for recycling, but manager Sandy Carey said people threw so much other trash in the barrel with the bags that the whole thing was usually contaminated and had to be thrown out.

Now transfer station employees send people to Hannaford — where many single-use bags originate, and where the store has set up a recycling receptacle.

Hannaford spokesman Eric Blom said the company doesn't take a position on plastic bag ordinances. "We'll make it work for our customers, whatever the community decides," he said.

Blom noted that Hannaford was early to offer reusable bags and has tried to promote them. In Kennebunk and York, where single-use bags are now banned, Blom said the company has seen an increase in use of paper bags, "which do have some environmental implications."

Compared to plastic bags, Blom said, it takes four times as many truckloads to get the same number of paper bags to a Hannaford store.

Ban the Bag in Belfast members aren't expecting to solve to the earth's environmental problems, but they believe every small step helps.

Lightner said the transition would probably be hard, but it would be worth it.

"There was a time when nobody recycled," he said. "Now it's like a part of our life that we recycle."

The City Council on Nov. 15 discussed the proposal but did not take action. Councilors generally wanted more public input and felt the proposal needed to be more broadly publicized. They spoke of holding a public hearing after the holidays, on January 5.

Ban the Bag in Belfast is hosting an educational presentation at Belfast Free Library on Thursday, Dec. 1, at 6:30 p.m. with Sarah Wakeman from the Natural Resources Council of Maine and Madelyn Woods, a marine research coordinator with the Marine Environmental Research Institute in Blue Hill.