The world’s greatest landfill is in the Pacific Ocean, it is called the great Pacific Garbage Patch and contains a mass of accumulated plastic twice the size of Texas. On atolls and islands around the area, birds die from eating plastic pieces, some of which are as small as a grain of sand, as they are mixed up with the small fish and shrimp those birds live on. Here are some photos from Midway Island.

The greatest culprits appear to be bottle caps left on beaches and cigarette lighters, but any bits of plastic that wash down stormwater drains will end up in the oceans.

http://science.howstuffworks.com/environmental/earth/oceanography/great-pacific-garbage-patch.htm