单项选择题

Arctic Ocean ice may hold trillions of small pieces of plastic and other synthetic trash, and they are being released into the world’s oceans as global warming melts the polar cap, researchers say. Though the finding is surprising and worrying, the possible harm to marine life is so far unknown, the authors concluded. Called micro plastics, the pollutants come mostly from debris that has broken apart, as well as from cosmetics and fibers released from washing clothes, according to the Study, which was published in the journal Earth’s Future and first reported by Science magazine.
At current melting trends, more than 1 trillion pieces 5 millimeters or smaller could wind up in the oceans during the coming decade, the authors estimate. The concentration of plastic debris is 1,000 times greater than that floating in the so-called Great Pacific Garbage Patch. The researchers based their findings on core samples of ice taken during polar expeditions in 2005 and 2010.
Rayon was the most common synthetic material discovered—54%. Though rayon is not a plastic (it’s made from wood), the authors included it "because it is a manmade semi-synthetic that makes up a significant proportion of synthetic microparticles found in the marine environment." Rayon is used in cigarette filters, clothing and personal hygiene products. Polyester (聚酯) was the next most common pollutant found in the ice (21%), followed by nylon (16%), polypropylene (聚丙烯) (3%) and polystyrene, acrylic and polyethylene (2% each).
The authors called the ice trap "a major historic global sink of man-made particulates," and said their findings "go some way to help clarify one of the most puzzling aspects of current understanding on the quantities of plastic debris reported in the oceans." As Science points out, 288 million tons of plastics were produced in 2012.
Micro plastics garbage has also been found on the shores of southernmost Chile, so the authors said it’s time to investigate the planet’s other polar region. "While multiyear sea ice makes up a smaller proportion of annual sea ice cover in the Southern Ocean, and perennial sea ice cover around Antarctica is following different trends, our finding indicate the importance of sampling ice from the Antarctic to see if it too contains micro plastics," they write.
Why does the author include "rayon" in, though it is not a plastic