They're everywhere -- so much a part of the landscape that you may have to focus for a moment to even notice them. Trillions of cigarette butts are flicked and stomped to the ground each year, often by people who would never think of themselves as littering. Contrary to popular belief, cigarette filters are not biodegradable. They're made from cellulose acetate, a plastic that absorbs tobacco "tar" and eventually breaks down in the environment, but never loses its toxicity and can poison essential links int he aquatic food chain.