HONG KONG — For bizarre items floating in the ocean, try topping this: The upper half of a set of false teeth, seen bobbing around in the South China Sea.
“I remember thinking: ‘How on earth did it get there?”’ said Lindsay Porter, a marine scientist based in the Malaysian city of Kota Kinabalu, who spotted the item from a research vessel about 200 kilometers, or 125 miles, off China in 2009.
The teeth, gripped in their plastic gums, are part of the millions of tons of plastic trash that somehow ends up in oceans around the world every year. Mostly, it is more mundane stuff, the flotsam and jetsam of everyday life: picnic plates, bottles, cigarette lighters, toys, spoons, flip-flops, condoms.
Taken together, the virtually indestructible mass is now so large that it is causing environmentalists, government officials and the plastics industry itself to sit up and take note. Many scientists believe marine plastic pollution is one of the major issues — along with climate change — facing the planet.
The problem is not the plastic itself: Even those who lobby against plastic pollution acknowledge that plastic materials help combat climate change, for example by reducing the weight — and thus fuel consumption — of vehicles, or by helping to insulate buildings.
The problem is the sheer amount of the stuff out there. Low-cost, lightweight and durable, plastic erupted onto the world stage in the 1950s. Annual production of 1.5 million tons back then has swelled to about 250 million tons now, according to the trade association PlasticsEurope .
Half of the plastic produced is used only once before being discarded. Think packaging, shampoo bottles, disposable razors, yogurt cups.
In North America and Western Europe, every single person uses about 100 kilograms of plastic every year. That figure is forecast to rise to 140 kilograms by 2015. In fast-growing Asian countries, the current average of about 20 kilograms will nearly double, to 36 kilograms, by 2015, researchers estimate.
Most of that ends up in landfills. Some is recycled. But a significant amount ends up in the sea, swept there via rivers or sewage drains, discarded on beaches or dumped from ships.
Exact figures are hard to come by, but some researchers estimate that 4.7 million tons reaches the sea each year, according to Plastic Oceans, a London-based charity that has enlisted numerous scientists to create a full-length documentary film on the topic.
Bear in mind that this stuff does not just biodegrade like food waste, wood or paper. Scientists believe it takes decades, if not centuries, for most types of plastic to degrade. That means virtually all the plastic material that has ever ended up in the ocean is still out there.
“When a plastic crate or bottle floats around in the ocean, it does not biodegrade. It only breaks into smaller and smaller pieces — which are still plastic,” said Peter Kershaw of the British marine science center Cefas, who helps advise the United Nations on marine environmental protection issues.
Some of the debris sinks to the ocean floor. Some washes back onto land, sometimes in remote and once-pristine parts of the world.
But most is gradually swept up by ocean currents, which have assembled the assorted mess into five “gyres,” or garbage patches, in the Pacific, Atlantic and Indian oceans.
Do not imagine these to be vast, tangible floating islands of trash that you can walk across. Yes, there are visible chunks of debris — some large enough to trap or choke wildlife. Mostly, however, the plastic soup consists of tiny fragments, some the size of a fingernail, some much smaller, floating on or below the surface across thousands of kilometers.
The gunk cannot be seen via satellite, making it hard for scientists to measure or track the problem. It is, however, clearly visible from up close.
“It’s kind of like chunky dust, hovering in the water. You can see the change in the texture of the water,” said Ms. Porter, a senior research scientist at the University of St. Andrews in Scotland.
“The samples taken from the sea in the middle of these gyres are a glutinous-looking mess,” said Craig Leeson, the Hong Kong-based director of the Plastic Oceans documentary.
Although these tiny fragments do not trap or choke animals the way plastic bags or abandoned nets do, they are increasingly the focus of scientific concern. Microplastics are easily swallowed and prone to absorb chemical pollutants in the sea, like pesticides, research has shown. Some scientists worry that these contaminants could end up in the food chain, the U.N. Environment Program noted in a report in February, calling for intensified research.
On the upside, plastic pollution has at least started to be recognized as a serious issue.
At a conference in Hawaii in March, plastics industry associations from around the world pledged to work with governments and nongovernmental organizations to increase research and promote efforts to recycle and prevent litter.
Still, recycling rates in many countries remain low.
The U.S. Environmental Protection Agency, for example, estimates that only 7 percent of plastics were recycled in the United States in 2009. In many developing nations, where plastics consumption is expected to rise sharply in coming years, awareness, and collection and recycling efforts, are still their infancy.
Fishing out the soupy gunk in the ocean gyres, meanwhile, is not really an option. The costs of traveling hundreds of kilometers out to sea are prohibitive, and most of the fragments are so small they cannot simply be scooped up.
The focus thus has to be on preventing new debris from getting into the oceans in the first place, said Keith Christman of the American Chemistry Council in Washington.
That means more efforts by companies to minimize packaging; more efforts by the authorities to step up collection and public awareness; and more efforts by ordinary people — yes, that is you and me — to avoid throwaway plastic products and to recycle those we do use.
As for the false teeth spotted by Ms. Porter — they will probably continue to travel the oceans for years to come.