Bioaccumulation is when the concentration of chemicals increases within an organism or species. This can occur when toxic substances are ingested. These toxic substances are very difficult for organisms to excrete, therefore, accumulate in their tissues. One common pollutant that bioaccumulates is mercury, which specifically accumulates in fish. Organic compounds and metals can both bioaccumulate.
An important result of bioaccumulation is biomagnification. This describes when toxins magnify upward in the food chain—whereas bioaccumulation describes when toxins accumulate within a single organism.
Biomagnification is a very closely related idea. To learn more about it, click here.