Plastic bags are a favorite of grocers because of their price, around 2 cents per bag, compared with 5 cents for paper. Used widely since the 1970s, environmentalists now estimate that between 500 billion to a trillion bags are produced annually worldwide. Made from fossil fuel-based polymers, the bags are virtually indestructible, taking years to break down and commonly ending up in landfills.

Grocers say they are not deaf to the public's concern about litter, and some have implemented recycling programs, and many also sell reusable bags, made from canvas or recycled plastic.

In Utah, Smith's Food and Drug this month began selling reusable shopping bags, including insulated ones for hot and cold foods. The bags look like canvas but are actually made of polypropylene, a form of plastic that is nontoxic, washable and water-repellent.

Regular bags cost 79 cents. Insulated bags cost $1.99. The chain, owned by Cincinnati-based Kroger Co., claims one reusable bag can fit more groceries than three plastic bags.

Smith's has also placed recycling barrels for plastic grocery bags in stores.

Albertsons sells reusable canvas bags that cost 99 cents. They have been available in Utah stores since September.

Whole Foods plans to stop offering plastic bags by April 22 — Earth Day — following a trial run at two of its Austin, Texas, stores, Lowery said. Shoppers will still be able to get recycled paper bags, bring their own, or buy reusable bags in the store for 99 cents. About 10,000 reusable bags were sold at the Texas stores since the change went into effect in December.

But given the choice, many customers still go for the plastic, said Barry Scher, spokesman for Giant Food, owned by Amsterdam-based Royal Ahold NV. Giant is pushing customers to recycle bags using in-store bins.

"In the United States, we are a throwaway society, but we are going to try to change that thought process," he said.

Another option is plastic bags that are compostable, often made of starches that will break down over time. But their cost — around 10 cents to 15 cents each — means most grocers won't buy them. The San Francisco ban, for example, allows for the use of compostable bags, but most stores have just switched to paper, according to the California Grocers Association.

The plastics industry argues that the shift to paper is actually worse for the environment. To make paper bags, trees must be cut down. And it takes seven fuel-burning trucks to ship paper bags to retailers, compared with just one for the same amount of plastic bags, according to the Plastics Division of the industry group American Chemistry Council.

"Plastic bags are a very good environmental choice," said Keith Christman, senior director of packaging for the group.