Biological magnification often refers to the method whereby certain substances like pesticides or heavy metals work their way into lakes, rivers and therefore the ocean, then move up the food chain in progressively greater concentrations as they're incorporated into the diet of aquatic organisms like zooplankton, which successively are eaten perhaps by fish, which then may be eaten by bigger fish, large birds, animals, or humans. The substances become increasingly concentrated in tissues or internal organs as they move up the chain. Bioaccumulants are substances that increase in concentration in living organisms as they absorb contaminated air, water, or food because the substances are very slowly metabolized or excreted.