A decade or so ago, scientists first discovered that tiny pieces of plastic debris discarded by human civilization - some only a few thousandths of a millimeter in size - were finding their way into the oceans. But since then, it's become increasingly apparent that microplastics, as the miniscule trash is called, represent a potentially huge threat to aquatic animals, according to an article in the July 11 edition of the journal Science.
The article, by marine scientists Kara Lavender Law of the Sea Education Association in Woods Hole, Mass. and Richard C. Thompson of the UK's Plymouth University, notes that researchers increasingly are focusing upon the danger from microplastics, because their size makes it possible for a huge range of organisms - from large marine mammals, fish and birds to zooplankton - to ingest them. (Indeed, a 2012 study found that they pose a health threat to Baleen whales.)
Photos: Life on the Ocean Floor Garbage Patch
A report issued in June by the Global Ocean Commission estimated that 10 million tons of plastic is dumped into the oceans each year. Some of the plastic is discarded into waterways and then is carried into the ocean, but it's also lost or discarded at sea by ships, the article notes.
Larger plastic items degrade to form microplastic, but some of the particles also are being put directly into the sea, because bits of cosmetic beads and clothing fibers are small enough to pass through wastewater treatment systems.
Once in the oceans, the particles are transported far and wide in a complex pattern that is difficult to predict. However, scientists have found very high concentrations in the subtropical gyres -- that is, areas where currents rotate rapidly - and in basins such as the Mediterranean.
Microplastics are themselves toxic, but they also soak up harmful chemicals that contaminate the ocean, such as DDT and PBDEs, so that they deliver a concentrated dose to the animals who ingest them. Marine scientists also worry that microplastics will end up in seafood-eating humans as well.
Video: How Much Trash is in the Ocean?
Microplastics are just one of the environmental woes afflicting the world's oceans, and pushing them perilously close to ecological collapse, according to an article published last week in Foreign Policy, a political science journal.
Solving the problem is difficult because 65 percent of the oceans are outside the territorial waters of individual nations, and have become the equivalent of a chaotic, lawless "failed state" such as Somalia on land, the Foreign Policy article argued.
Photo: Plastic bags and discarded items degrade into tiny microplastic particles, which pose an increasing threat to aquatic life. Credit: NOAA