问题详情

Pollution occurs whenever unnatural substances are introduced into an environment. Most ocean pollution caused by humans are concentrated along the 【M1】______ coasts of continents. Lets see what some of the pollutants are. Industrial wastes sometimes get to seawater. Often, 【M2】______ these contain(concentrations)of metals and chemicals that harm organisms. Solid wastes, such as plastic bags and fishing line left lying on the beaches, can entangle in animals. Medical waste such as needles, plastic 【M3】______ tubing, and bags are a threat to both humans and animals. Pesticides, which include herbicides(weed killers) and insecticides(insect killers), used in farming reaching the ocean as runoff. They become 【M4】______ concentrating in the tissues of marine organisms. 【M5】______ Crop fertilizers and human sewage create a different kind of problem. They fertilize the water. This causes some types of algae to produce very rapidly. 【M6】______ When these algae die, theyre decomposed by huge amount of bacteria. The problem is that the bacteria use 【M7】______ up much of the oxygen in the water during respiration. However, other organisms such as fish cant get the 【M8】______ oxygen they need, and they die. Oil spills also pollute the ocean. Youve heard in the news about major oil spills caused to tanker 【M9】______ collisions, and leaks at offshore oil wells. Another source of oil pollution is oil mixed with wastewater thats pumped out of ships. In addition to these resources, oil discarded from cars and industries is 【M10】______ sometimes dumped into streams. It, too, eventually reaches the ocean.

【M1】

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