Scientists say: Biomagnify

A little weed killer can mushroom into a lot as it moves up the food chain

bald eagle

Bald eagles ate fish and other animals contaminated with the toxic insect killer DDT. In time, the eagles “biomagnified” this pollutant in their bodies, which sometimes harmed their eggs.

Yathin S Krishnappa/Wikimedia Commons

Biomagnify  (verb “BY-oh-MAG-nih-fye”), or Biomagnification (noun, “BY-oh-mag-nih-fih-CAY-shun”)

The growing buildup of pollutants in the bodies of animals as they eat contaminated food. For example, there might be low levels of the insect killer DDT in the water. Fish cannot break down DDT. So the chemical will stay in the fish. If a bald eagle eats a lot of these fish, the DDT can build up — or biomagnify — in the eagle. High concentrations of DDT make eagle eggs very thin. Scientists have shown that biomagnification of DDT is partly responsible for making bald eagles — the American emblem — endangered. Banning DDT in 1970 helped the eagles stage a comeback.

In a sentence

Spiders eat many insects that have been exposed to harmful chemicals. The more insects they eat, the more pollutants in those insects may biomagnify in the spiders.

Follow Eureka! Lab on Twitter

Power Words

biomagnification   A process by which the concentration of a chemical increases in predatory animals as they dine on contaminated prey.  

DDT  (short for dichlorodiphenyltrichloroethane) This toxic chemical was for a time widely used as an insect-killing agent. It proved so effective that Swiss chemist Paul Müller received the 1948 Nobel Prize (for physiology or medicine) just eight years after establishing the chemical’s incredible effectiveness in killing bugs. But many developed countries, including the United States, eventually banned its use for its poisoning of non-targeted wildlife, such as birds.

endangered   An adjective used to describe species at risk of going extinct.

food chain (also known as a food web  )  The network of relationships among organisms sharing an ecosystem. Member organisms depend on others within this network as a source of food.

pollutant  A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.

predator  (adjective: predatory) A creature that preys on other animals for most or all of its food.

species  A group of similar organisms capable of producing offspring that can survive and reproduce.

Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

More Stories from Science News Explores on Ecosystems