Plastic waste now accounts for nearly 80 percent of all of the garbage in the world's oceans.  Photos of fish or other sea life caught in plastic six pack rings or the remains of sea birds that starved to death because their plastic-choked bellies couldn't absorb real nutrition are now ubiquitous on the Internet.  But what about the plastic you can't see?

Plastic waste breaks down into smaller and smaller particles.  Sweden's Lund University conducted one of the first investigations on how nano-sized plastic particles adversely impact the food chain.

"Not very many studies have been done on this topic before.  Plastic particles of such a small size are difficult to study," says Karin Mattsson of Lund University's Department of Biochemistry and Structural Biology.  "We tested how polystyrene plastic particles of different sizes, charge and surface affect the zooplankton Daphnia.  It turned out that the size of the nanoparticles that were most toxic to the Daphnia in our study was 50 nanometers," she added.

Zooplankton like Daphnia sit near the bottom of the food chain, serving as food many other aquatic animals.  And thus their fate is important to the creatures higher up the ladder.  Lund found that fish which ate Daphnia containing nanoplastics experienced a change in their predatory behavior and poor appetite.  Researchers also noted that the nanoparticles had the ability to cross biological barriers, such as the intestinal wall and brain.

"Although in our study we used much larger amounts of nanoplastic than those present in oceans today, we suspect that plastic particles may be accumulated inside the fish.  This means that even low doses could ultimately have a negative effect," said Ms. Mattsson.

Plastic breaks down very slowly in nature.  But once that degradation reaches the microscopic level, it's incredibly difficult to remove from rivers and streams, lakes and oceans.