Biomagnification:Biomagnification is a process in which chemical substances become more concentrated at each higher trophic level. Such chemical substances tend to be difficult to be removed from animal and plant tissues. The result is that when plants have the substance on them, they are eaten by herbivores. As each herbivore eats more of the plant, the substance accumulates in the herbivore. When the herbivores are eaten by carnivores, the substance accumulates in the carnivore. As more herbivores are eaten, the amount of the chemical substance increases in the carnivore. This scenario repeats itself at higher trophic levels, so that the top consumer has very high levels of the substance in its tissues. Often, such high levels of chemical substances causes mutations, cancers and eventually death.
1) DDT: Insecticide - Used to kill insects. So dangerous its production and use was banned decades ago. It still remains in animal tissues and is a danger for some organisms.
2) Agent Orange: Herbicide - Used to kill trees in Cambodia during the Vietnam War. Caused cancers in soldiers.
3) PCBs : Chemicals in electrical transformers, etc. Causes cancer in high concentrations.
Biomagnification of Chemicals in the Arctic (World Wildlife Fund)