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  3. Keep Our Seas Clean By the year 2050 it is estimated that the world’s population could have increased to around 12 billion.

Keep Our Seas Clean By the year 2050 it is estimated that the world’s population could have increased to around 12 billion.

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问题                             Keep Our Seas Clean
    By the year 2050 it is estimated that the world’s population could have increased to around 12 billion. Of these, some 60 percent will live within 60 km of the sea. The agricultural and industrial activities required to support this population will increase the already significant pressures on fertile coastal areas. Death and disease caused by polluted coastal waters costs the global economy US$12.8 billion a year. Plastic waste kills up to 1 million sea birds, 100,000 sea mammals and countless fish each year.
Pollution & the sea—like oil and water
    One significant impact of human activity is marine pollution. The most visible and familiar is oil pollution caused by tanker accidents and tank washing at sea, and in addition to the gross visible short-term impacts, severe long-term problems can also result. In the case of the Exxon Valdez which ran onto a shore in Alaska in 1989, biological impacts from the oil spill can still be identified 15 years after the event. The Prestige which sank off the Spanish coast late in 2002, resulted in huge economic losses as it polluted more than 100 beaches in France and Spain and effectively destroyed the local fishing industry.
    Despite the scale and visibility of such impacts, the total quantities of pollutants entering the sea from the long line of catastrophic oil spills appeared small compared with those of pollutants introduced directly and indirectly from other sources (including domestic sewage, industrial discharges, leakages from waste tips, urban and industrial run-off, accidents, spillages, explosions, sea dumping operations, oil production, mining, agriculture nutrients and pesticides, waste heat sources, and radioactive discharges).
    Land based sources are estimated to account for around 44 percent of the pollutants entering the sea and atmospheric inputs account for an estimated 33 percent. By contrast, transport on the sea accounts for 12 percent.
Dawn of the dead: Creeping dead zones
    The impacts of pollution vary. Nutrient pollution from sewage discharges and agriculture can result in unsightly and possibly dangerous "blooms" of algae (藻类) in coastal waters. As these blooms die and decay they use up the oxygen in the water. This has led, in some areas, to "creeping dead zones" (CDZ), where oxygen dissolved in the water falls to levels unable to sustain marine life. Industrial pollution also contributes to these dead zones.
Gone fission (裂变)
    Radioactive (放射性的) pollution has many causes, including the normal operation of nuclear power stations, but by far the single biggest sources of man-made radioactive elements in the sea are the nuclear fuel reprocessing plants at La Hague in France and at Sellafield in the UK. Waste released from them has resulted in the widespread pollution of living marine resources over a wide area; radioactive elements traceable to reprocessing can be found in seaweeds as far away as the West Greenland Coast.
Heavy metal
    Trace metal pollution from metal mining, production and processing industries can damage the health of marine plants and animals and render some seafoods unfit for human consumption. The contribution of human activities can be very significant: the amount of mercury introduced to the environment by industrial activities is around four times the amount released through natural processes such as weathering and erosion (腐蚀).
    The input of man-made chemicals to the oceans potentially involves an overwhelming number of different substances. 63,000 different chemicals are thought to be in use worldwide with 3,000 accounting for 90 percent of the total production amount. Each year, anywhere up to 1,000 new synthetic chemicals may be brought onto the market. Of all these chemicals some 4,500 fall into the most serious category. These are known as persistent organic pollutants (POPs). They’re resistant to breakdown and have the potential to accumulate in the tissues of living organisms (all marine life), causing hormone disruption which can, in turn, cause reproductive problems, induce cancer, suppress the immune system and interfere with normal mental development in children.
    POPs can also be transported long distances in the atmosphere and deposited in cold regions. As a result, Inuit populations who live in the Arctic a long distance from the sources of these pollutants are among the most severely influenced people on the planet, since they rely on fat-rich marine food sources such as fish and seals. POPs are also thought to be responsible for some polar bear populations failing to reproduce normally.
Are you eating fish ’n’ POPs tonight?
    Scarily, seafoods consumed by people living in warm and mild regions are also affected by POPs. Oily fish tend to accumulate POPs in their bodies and these can be passed to human consumers. When oily fish are rendered down into fish meal and fish oils and subsequently used to feed other animals, then this too can act as a pathway to humans. Farmed fish and shellfish, dairy cattle, poultry and pigs are all fed fish meal in certain countries, and so meat and dairy products as well as farmed and wild fish can act as further sources of these chemicals to humans.
Pollution superhighway—North and Baltic Seas
    The North and Baltic Seas also contain some of the world’s busiest shipping lanes. 200,000 ships cross the North Sea every year. Many goods transported by ships are hazardous (half the goods carried at sea can be described as dangerous) and loss of dangerous cargoes can result in damage to the marine environment. Chemical tank washings, discharge of oily wastes and wash waters are all significant sources of marine pollution.
    In addition there is always the risk of a major oil spill, a risk made worse by the fact that some of the tankers that routinely travel through still have only one body-frame or have other technical defects and crews who are poorly educated. In November 2002, the Prestige oil tanker went down off the coast of Spain with 70,000 tons of oil on board which polluted 2,890 km of coastline. A few days earlier it had been crossing the Baltic.
Solutions
    Some sources of pollution have been brought under control by international legislation.
    Countries which signed the London Convention have agreed to stop the dumping of radioactive and industrial waste at sea. The OSPAR Convention regulates marine pollution in the North East Atlantic Region while countries which signed the Stockholm Convention have committed themselves to the phase out of a number of persistent organic pollutants. Within the European Community, the Water Framework Directive may be expected to bring further reductions in polluting inputs, although it will be over a very long time frame. The additional benefit of the new EU REACH (Registration Evaluation and Authorisation of Chemicals) initiative, which aims to regulate the production and use of dangerous chemicals at source, remains to be seen.
In warm and mild regions, farmed fish and shellfish are also affected by POPs because they ______
选项
答案are fed fish meal
解析 空白处应为动词(词组)，在句中充当原因状语从句的谓语成分。结合该段标题和其他句子的内容，可推断该段末句中的these chemicals指的就是POPs．该句中的so表明养殖的鱼类和贝壳类都会受POPs的影响是因为这些养殖水产are all fed fish meal，因此空白处应填写are(all)fed fish meal。
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