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Marine debris, also known as marine litter, is human-created waste that has deliberately or accidentally been released in a lake, sea, ocean or waterway. Floating oceanic debris tends to accumulate at the centre of gyres and on coastlines, frequently washing aground, when it is known as ''beach litter'' or tidewrack. Deliberate disposal of wastes at sea is called ''ocean dumping''. Naturally occurring debris, such as driftwood, are also present. With the increasing use of plastic, human influence has become an issue as many types of plastics do not biodegrade. Waterborne plastic poses a serious threat to fish, seabirds, marine reptiles, and marine mammals, as well as to boats and coasts.〔(【引用サイトリンク】title=Facts about marine debris )〕 Dumping, container spillages, litter washed into storm drains and waterways and wind-blown landfill waste all contribute to this problem. ==Types of debris== Researchers classify debris as either land- or ocean-based; in 1991, the United Nations Joint Group of Experts on the Scientific Aspects of Marine Pollution estimated that up to 80% of the pollution was land-based. A wide variety of anthropogenic artifacts can become marine debris; plastic bags, balloons, buoys, rope, medical waste, glass bottles and plastic bottles, cigarette lighters, beverage cans, polystyrene, lost fishing line and nets, and various wastes from cruise ships and oil rigs are among the items commonly found to have washed ashore. Six pack rings, in particular, are considered emblematic of the problem. The US military used ocean dumping for unused weapons and bombs, including ordinary bombs, UXO, landmines and chemical weapons from at least 1919 until 1970. Millions of pounds of ordnance were disposed of in the Gulf of Mexico and off the coasts of at least 16 states, from New Jersey to Hawaii. Eighty percent of marine debris is plastic. Plastics accumulate because they typically do not biodegrade as many other substances do. They photodegrade on exposure to sunlight, although they do so only under dry conditions, as water inhibits photolysis. In a 2014 study using computers models, scientists from the group 5 Gyres, estimate 5.25 trillion pieces of plastic weighing 269,000 tons dispersed in oceans in similar amount in the Northern and Southern Hemispheres, and one-hundredth of them in particles in the scale of a sand-size.〔(【引用サイトリンク】url=http://news.nationalgeographic.com/news/2014/12/141211-ocean-plastics-garbage-patches-5-gyres-pollution-environment/ )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「marine debris」の詳細全文を読む スポンサード リンク
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