What is Biomagnification? - Definition & Examples

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  • 0:00 What Is Biomagnification?
  • 1:11 Chemicals in the Environment
  • 2:10 Cases of Biomagnification
  • 5:08 Lesson Summary
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Lesson Transcript
Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Expert Contributor
Matthew Bergstresser

Matthew has a Master of Arts degree in Physics Education. He has taught high school chemistry and physics for 14 years.

Have you ever heard the phrase, 'you are what you eat'? In this lesson we will explore just how true that statement is, especially when it comes to chemicals and toxins from the environment.

What Is Biomagnification?

Let's say you are a bird of prey, a soaring hawk whose favorite meal is snakes. Snakes are so tasty! They're also fun to catch and you're quite good at it. You don't think much about snakes other than this, but you should. What that snake has eaten, and what its food has eaten, affects you in important ways. Biomagnification, which is the increase in concentration of toxins up the food chain, especially affects you.

Chemicals and toxins accumulate more and more as you move up the food chain, because they do not get broken down in the body. So you may think you are a hawk that just likes to eat snakes, but when you eat a snake, you also eat all of the mice, frogs, and other things that snakes find tasty. And while the small mice and frogs may only have small amounts of chemicals or toxins in their systems, a snake might eat 10 mice and 20 frogs before you get to it. Meaning, you absorb the chemicals and toxins of 10 mice, 20 frogs, and a snake into your own tissues.

Chemicals in the Environment

What exactly are these things you're taking into your body? They come in a variety of shapes and sizes. They could be things like mercury, lead, and other heavy metals. Other environmental-related chemicals include Polychlorinated Biphenyls (PCBs), found in things like motor oil, plastics, and even tape; Polycyclic Aromatic Hydrocarbons (PAHs), from burning carbon-containing compounds such as wood and gasoline; and even pharmaceuticals, such as ibuprofen and birth control that go through people's bodies and end up in waste water.

As you can see, things that can biomagnify cut a wide swath. Anything that gets into biological tissue, that isn't normally there, has the potential to accumulate and magnify as it moves up the food chain. Some things are more harmful than others, but it's still important to take note that they can become problematic the further up they go.

Cases of Biomagnification

We haven't always been acutely aware of biomagnification. It took a few severe situations for people to realize the effect our products have on wildlife and sometimes ourselves. Here are a few examples.

Birds and DDT

One of the most famous cases of biomagnification is the one involving DDT, which is a pesticide that was historically used for mosquito control, as well as on agricultural crops, and bird eggs. DDT was widely used starting in the mid-40s, but was banned in the United States in 1972 because of its harmful effects on wildlife.

When birds take up DDT into their bodies, it becomes difficult for them to absorb calcium, necessary to produce strong eggshells. Birds that have accumulated DDT in their bodies produce eggs with very thin shells, which can often break before they hatch. As a bird of prey, you may only lay a few eggs at a time. And if you lay only three eggs and two of them break, then your population shrinks pretty quickly. This is exactly what happened to the birds of prey during the widespread use of DDT.

Mercury and Fish

Mercury, a liquid element on the periodic table that is highly toxic, is one of those toxins that gets a lot of attention because it can eventually make its way into human tissue. The most prominent way this occurs is through fish and other seafood. Mercury exists in ocean sediments and in the water, and may be taken up by plants and plankton. Small marine animals come along and eat these plants and plankton, and then bigger marine animals eat those animals, and so on.

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Additional Activities

Biomagnification in the Ocean

In this lesson we learned that toxins are ingested or absorbed by animals and passed through the food chain. The oceans contain a wealth of life, from tiny plankton to gargantuan whales. The food webs in the oceans are complex. Follow the steps to make a bio pyramid that we can then use to trace toxins through a food chain. Let's work on an activity to visually represent how this process occurs and what the results of it are.


  1. Draw as large of a equilateral triangle as you can on a piece of paper.
  2. Draw 4 horizontal lines equally spaced in your triangle. This should give you five areas in the triangle.
  3. In the bottom-most area, write phytoplankton, cyanobacteria and algae.
  4. In the next area up, write zooplankton, snails and urchins.
  5. Up one more row, write sea stars and sardines.
  6. In the next area up, write herring and mackerel.
  7. In the top part of the triangle, write tuna.

Follow-Up Questions

  1. Why do you think the planktons are in the largest section of the pyramid and the tuna is in the smallest section of the period?
  2. Let's say each zooplankton eats 0.00000001 gram of microplastic and there are 100,000,000 zooplankton in 1 cubic meter of water. How many grams of microplastics have been eaten by the zooplankton in the 1 cubic meter of water?
  3. Ten sardines eat all of the zooplankton in the 1 cubic centimeter of water. How much microplastics are in one sardine?
  4. A single herring eats 300 sardines (assume the sardines have the same amount of microplastic in them). How much microplastic is now in the herring?
  5. Let's say the apex predator tuna eats 100 herring in a day. How much microplastic is in the tuna?
  6. Write out a paragraph explaining the calculations you just made in questions 2-5 and be sure to include the word biomagnification.

Answers to Questions 2-5

2. 1 g

3. 0.1 g per sardine

4. 30 g

5. 3000 g = 3 kg. A tuna can have a mass of about 700 kg, so this is about 0.4% of its body mass.

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