It seems that cigarette butts are often found in the stomachs of sea turtles. The filtered ends do not degrade; consequently, they get to the sea in other ways than being directly flicked into the waves. Many of the butts survive a journey through sewer drains and end up in the sea. Of course the filters themselves are toxic.
I had the sad mental picture of a large, unsuspecting marine turtle seeing what it assumed was some sort of tasty meal. Although hardly an ardent environmentalist, I couldn't shake the notion that we, as humans, can really screw up nature. In a more positive light, we also try to help it along at times.