Biological magnification is the increase in concentration of certain pollutants as they move up a food chain. It matters because a chemical that is barely measurable in water can become dangerous in animals at the top of the food web. Persistent pollutants such as DDT and mercury are especially important because they do not break down quickly.
This process helps explain why top predators like eagles, ospreys, tuna, and humans can face the highest toxin exposure.
Key Facts
- Biomagnification occurs when toxin concentration increases at higher trophic levels.
- Persistent pollutants resist breakdown and can remain in ecosystems for years.
- Bioaccumulation is toxin buildup within one organism over time.
- Biomagnification factor = concentration in predator / concentration in prey.
- If prey contain 0.2 ppm mercury and a predator contains 2.0 ppm, the biomagnification factor is 10.
- DDT can reduce eggshell strength in birds, while mercury can damage nervous systems.
Vocabulary
- Biological magnification
- The increase in concentration of a toxin as it passes from lower to higher trophic levels in a food chain.
- Bioaccumulation
- The gradual buildup of a substance in an organism because it is absorbed faster than it is eliminated.
- Persistent pollutant
- A chemical that remains in the environment for a long time because it does not break down easily.
- Trophic level
- A feeding position in a food chain, such as producer, primary consumer, secondary consumer, or top predator.
- Parts per million
- A unit of concentration meaning one part of a substance per one million parts of the total mixture.
Common Mistakes to Avoid
- Confusing bioaccumulation with biomagnification. Bioaccumulation happens within one organism, while biomagnification describes increasing concentration across trophic levels.
- Assuming all pollutants biomagnify. Only substances that persist, are absorbed, and are not easily excreted tend to become more concentrated in food chains.
- Thinking the largest animals always have the most toxin. Toxin levels depend more on diet and trophic level than body size alone.
- Ignoring the number of prey eaten by predators. A predator can concentrate toxins because it consumes many contaminated organisms over time.
Practice Questions
- 1 A plankton sample contains 0.04 ppm mercury, and small fish that eat the plankton contain 0.40 ppm mercury. What is the biomagnification factor from plankton to small fish?
- 2 In an aquatic food chain, water contains 0.0002 ppm DDT, plankton contain 0.01 ppm, small fish contain 0.2 ppm, and an osprey contains 4.0 ppm. How many times greater is the DDT concentration in the osprey than in the water?
- 3 Explain why banning or reducing the release of a persistent pollutant may not immediately remove the danger to top predators.