如标题可以参考下列原文 A third factor for some substances is bioaccumlation, in which some molecules are absorbed and stored in specific organs or tissues at higher than normal levels. As a consequence, a chemical found at a fairly low concentration in the environment can build up to a harmful level in certain organs and tissues. A related factor is biomagnification, in which levels of some potential toxins in the environment become magnified as they pass through food chains and webs. Organisms at low trophic levels might ingest only small amounts of a toxin, but each animal on the next trophic level up that eats many of those organisms will take in increasingly larger amounts of that toxin. Examples of chemicals that can be biomagnified include long-lived, fat-soluble organic compounds such as DDT, PCBs (oily chemicals used in electrical transformers), and some radioactive isotopes (such as strontium-90) 大家考试加油! --

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