Don: Not that question again, Yael. Does anyone really care whether their groceries are put in plastic or paper bags?

Y: Sure they do. In fact, the city of San Francisco has taken an interest in the predominant question all of us face when buying groceries. They've weighed the pros and cons of both paper and plastic.

D: Like what?

Y: Well, the pros for paper are that it's biodegradable and recyclable, and it's made from a renewable resource, trees.

D: Sounds good.

Y: On the other hand, making paper bags creates more air and water pollution than making plastic bags. Recycling paper requires more energy. And when paper isn't recycled, it takes up more space in landfills than plastic.

D: So plastic is better?

Y: Not so fast. Most plastic bags available are made of polyethylene, which is nonbiodegradable. Polyethylene is made from crude oil and natural gas, nonrenewable resources. Though plastic bags can be recycled, the EPA estimates that only about 5% of them are versus 21% of paper bags. When you consider that ninety percent of all grocery bags are plastic, that's a lot of bags going into landfills or worse, littered. And plastic bags have been discovered to kill animals that swallow them.

D: Paper is starting to sound like the lesser of two evils.

Y: San Francisco agrees with you. They're now requiring grocery stores to discontinue the nonbiodegradable plastic bags, and offer either paper alone or paper and biodegradable plastic.

D: Sounds like a good plan. Or better yet, I think I have one of those cloth reusable bags some place around here. Maybe I can bypass the paper or plastic question altogether.

Y: Good thinking.