Increasingly, researchers are realizing that cigarettes are as much an environmental problem as they are a health issue. Walk along a beach or around a busy city and you step on a lot of cigarette butts, thrown carelessly to the ground. By one estimate, up to 6 trillion cigarette butts get flicked onto the ground and into the global environment every year. They’re one of the most common forms of the world’s litter, making up 25 to 50 percent of all trash collected from roads and streets.