Even with a small amount of unburnt tobacco clinging to it, a single cigarette butt soaked for a day is enough to turn a liter of water a sickly yellow brown and kill 50 percent of fish swimming in it. Without tobacco, it takes about 4 smoked filters to do the same job.

That's a lot of butts in a small area, and the research team that conducted the laboratory study, led by Elli Slaughter of San Diego State University, is quick to point out that no research has been done yet to test how much poison leaches from butts into ponds, lakes, streams and the ocean.

Still, humans are inadvertently carpeting the planet in cigarette butts. According to one estimate, some 4.5 trillion filters from spent smokes make their way into the environment every year.

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