By now even schoolchildren know that the plastics we discard every year in the millions of tons persist in the environment for hundreds of years. And we have all heard of the horrors caused by such debris in the sea: fur seals entangled by nylon nets, sea otters choking on polyethylene six-pack rings, and plastic bags or toys stuck in the guts of sea turtles. This photograph, showing plastic fragments collected in just an hour at a cove near Gloucester, Mass., hints at a lesser-known but equally disturbing story: much smaller bits of plastic that are accumulating in oceans all over the world can potentially harm marine life and possibly even human health.