A gray whale that washed up on a Puget Sound beach last year has become Exhibit A in the debate over whether to ban plastic bags in Seattle.

Environmentalists point to the contents of the dead whale's stomach, itemized in a necropsy, as a compelling argument that the thin-film carryout shopping bags should be outlawed. The inedible trash that the whale had ingested included sweatpants, a golf ball, surgical gloves, small towels and more than 20 plastic bags.

"While it's true we don't know what killed the whale, I think we can all agree those plastic bags don't belong there," said Dan Kohler, regional director of Environment Washington, which — along with several other environmental groups including People for Puget Sound and the Sierra Club — supports the city's proposed ban on plastic bags as a way to protect the Sound and marine wildlife.

But opponents of the ban, including the plastics industry and some independent grocery stores, say plastic bags represent a fraction of the litter that ends up in the water. What's more, they argue, plastic bags are convenient, reusable and recyclable.

"The hysteria around this issue is remarkable," said Michael Johnson, inside-sales manager for Poly Bag in Tacoma, which makes plastic bags and packaging. "If we're using the itemized list of things that ended up in the whale's stomach, I'd like to see all those other things banned as well."

The Seattle City Council will hold a public hearing Monday night on the proposal to ban plastic carryout bags from grocery and retail stores. The bill also would impose a nickel fee on paper bags to offset the higher cost of paper to stores and to remind shoppers to bring in reusable bags.

The bill, modeled on one adopted earlier this year in Bellingham, still allows plastic bags for produce, bulk foods and meat. It also allows them for takeout food from restaurants and for the patrons of food banks and farmers' markets. Low-income people using their state Basic Food cards would be exempt from the 5-cent fee.

Environmental advocates and others have deluged Seattle City Council members with more than 500 emails and letters in support of the proposed ban. In contrast, the council has received 20 letters in opposition, said the bill's sponsor, Councilmember Mike O'Brien.

O'Brien acknowledges that plastic bags may not be the greatest threat to marine life, but he said banning them is one more step in eliminating unnecessary waste and protecting the environment.

A 2008 survey by Seattle Public Utilities, which manages solid-waste programs for the city, found that Seattle used 292 million plastic bags a year, but recycled only 13 percent of them.

"Banning plastic bags is part of the broader initiative to reduce waste. Plastic bags provide minutes of convenience for us as consumers, but they stay in the environment for hundreds of years," O'Brien said.

The ban picked up a key endorsement recently when the Northwest Grocery Association, which represents Safeway, QFC and Fred Meyer stores across the state, said it supported Seattle's proposed ordinance. Joe Gilliam, president of the association, said the plastics industry hasn't come up with a solution for the problem of plastic litter.

"In Seattle, on a roadside or a waterway, the plastic-bag litter is visible. People want to do something about it," Gilliam said.

He said a typical large grocery store goes through a million plastic bags in a year. Shifting to paper bags, without charging the proposed nickel fee, would cost his members about $60,000 a year. In a business with a small profit margin, he said, "that's a big hit."

The organization stayed neutral on the city's 2008 proposed 20-cent fee on both plastic and paper bags, which was rejected by voters the following year. The current proposal, he said, avoids bureaucracy, bans plastic bags outright, and helps stores offset the costs of paper.

"The model Seattle has adopted is the best I've seen," Gilliam said.

Not all stores agree. Jan Gee, president of the Washington Food Industry Association, which represents 480 independent grocery stores statewide, calls the ban punitive. She said paper bags take up more room and require checkout stands to be retrofitted. She said people can be educated to recycle plastic bags and to bring reusable ones, rather than being legally compelled.

"If people understood it's a problem, they'd change their behavior," she said.

Some bookstore owners are concerned about customers not being able to protect their purchases, particularly in a rainy climate. J.B. Dickey, owner of Seattle Mystery Bookshop downtown, said if someone has just bought a stack of paperbacks, or a signed edition of a hardback, they don't want the books to get wet. And, he said, many of his patrons are tourists who don't travel with reusable bags.

"Ideally, it's a good idea to get rid of as much plastic as possible. But there are places where it's useful and necessary," Dickey said.

Local plastics manufacturers say a ban would hurt their business. Ken Holmes, marketing director for American Plastic Manufacturing in South Seattle, which employs 20 people, calls the proposed ordinance a "feel good" measure that would eliminate only a small source of pollution. He noted that paper bags consume more resources and cost more to manufacture and transport than plastic bags.

But those who study plastics in the marine environment say they are finding their way even into birds and animals that live far from urban centers.

Anne Murphy, executive director of the Port Townsend Marine Science Center, said researchers examining seagull boluses — regurgitated, walnut-size pellets of indigestible materials — found that more than 12 percent contained thin plastic film.

Murphy said the samples were taken from nesting birds on Protection Island, an uninhabited national wildlife refuge in the Strait of Juan de Fuca. She said plastic is shiny and mimics the food birds, fish and mammals may eat. And as it floats in the water, she said, it can get coated with other petroleum-based contaminants, making it even more harmful to ingest.

"Our marine wildlife is facing some pretty horrendous issues. Human-sourced, disposable plastic debris is one thing we can do something about," she said.

Lynn Thompson: 206-464-8305 or lthompson@seattletimes.com. On Twitter @lthompsontimes.