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  3. The amount of floating plastic trapped in a north Atlantic current system hasn’t got any bigger in 22 years, despite more and mo

The amount of floating plastic trapped in a north Atlantic current system hasn’t got any bigger in 22 years, despite more and mo

admin2013-09-07  41
问题     The amount of floating plastic trapped in a north Atlantic current system hasn’t got any bigger in 22 years, despite more and more plastic being thrown away. Since 1986 students taking samples of plankton(浮游生物)in the Atlantic and Caribbean Oceans have also noted when their nets caught plastic litter. Kara Lavender and colleagues at the Sea Education Association in Woods Hole, Massachusetts, analysed the data, and found that of 6136 samples recorded, more than 60 per cent included pieces of plastic, typically just millimetres across. The areas of highest plastic concentration are within the north Atlantic sub-tropical gyre(环流), where currents gather the litter.
    Lavender and her team were surprised to find that the amount of floating plastic had not increased in the gyre. Although it has been illegal since the 1970s for ships to throw plastic overboard, Lavender thinks that the overall rate of plastic rubbish reaching the ocean will have increased, given the fivefold increase in global production of plastic since 1976. "Where the extra plastic is going is the big mystery," she says. Plastic resists bio-degradation and can last decades or more in the ocean. Eventually sunlight and wave motion break it into smaller pieces, which can be harmful to marine life—blocking the stomachs of fish and seabirds, for example.
    Some experts suggest that the plastic might be degrading into pieces small enough to pass through the 0.3-millimetre-mesh nets used in the study, or becoming coated in biofilms and sinking out of range of the nets. However it is unclear why the rate of degradation during the study period should have increased to offset the extra plastic going into the ocean. Lavender says it is unlikely that ocean currents are pushing plastic out of the gyre, although Simon Boxall of the National Oceanography Centre in Southampton, UK, who wasn’t involved in the study, disagrees. He says the Atlantic gyre has an exit strategy in the form of the Gulf Stream. We’ve seen high levels of plastic in the Arctic." he says.
    Wherever it is going at the moment, the plastic on our oceans will eventually be broken down into microscopic pieces and individual molecules whose environmental effect is unknown. "The million-dollar question is, is it causing any damage?" says Boxall.
    "When plastic particles get so small are they just like fibre going through the system? Some studies suggest that persistent chemicals in newer plastics function as endocrine(内分泌)disruptors and simulated hormones." And this fine-grained plastic is very long-lived. "The depressing thing is it’s likely to remain in the oceans essentially forever," says Lavender.
Kara Lavender and her colleagues had analyzed 6136 samples of
选项 A、plankton
B、floating litter
C、plastic litter
D、nets
答案A
解析 解题关键在于弄清6136 samples中的samples指的是什么。答案通常要在前面找．第2句提到学生采集的是samples of plankton。可见，第3句中提到的data就是关于plankton的数据，6136 samples应该就是6136 samples of plankton。选A。
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