The increasing concentration of a chemical as it moves through the links in a food chain is called

Biological Magnification

Explanation:

Organisms acquire toxic substance from the environment along with nutrients and water. Some of the toxins are metabolized and excreted, but others accumulate in specific tissues, especially fat. One of the reasons accumulated toxins are particularly harmful is that the become more concentrated in successive trophic level of the food web, this is the process of biological magnification.

Magnification occurs because the biomass at any given level is produced from a must larger biomass ingested from the level below. Thus the top-level carnivores tend to be the organism most severely affected by toxic compounds in the environment.

Examples of toxins that demonstrate biology magnification are chlorinated hydrocarbons, and many pesticides.

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