Biomagnification is the increase in toxin concentration as pollutants move up a food chain. It matters because small amounts of pollution in water or soil can become dangerous in predators, including fish-eating birds and humans. Many of these toxins are persistent, meaning they do not break down quickly in the environment.
This process helps explain why pollution can harm organisms far from the original source.
Key Facts
- Biomagnification occurs when toxin concentration increases at higher trophic levels.
- Bioaccumulation happens within one organism over time, while biomagnification happens across a food chain.
- Persistent organic pollutants and heavy metals are common biomagnifying toxins.
- Toxin concentration can be estimated with concentration = toxin mass ÷ organism mass.
- If plankton contain 0.01 ppm mercury and small fish concentrate it 10 times, the fish contain 0.1 ppm mercury.
- Top predators often have the highest toxin levels because they eat many contaminated prey over their lifetimes.
Vocabulary
- Biomagnification
- The increase in concentration of a toxin at higher levels of a food chain.
- Bioaccumulation
- The buildup of a substance inside an organism over time as it takes in more than it can eliminate.
- Persistent pollutant
- A pollutant that remains in the environment for a long time because it breaks down slowly.
- Trophic level
- A feeding position in a food chain, such as producer, primary consumer, or top predator.
- Parts per million
- A unit of concentration equal to one part of a substance per one million parts of the mixture.
Common Mistakes to Avoid
- Confusing bioaccumulation with biomagnification: bioaccumulation occurs within one organism, while biomagnification occurs as toxins move upward through multiple trophic levels.
- Assuming all pollutants biomagnify: only substances that are persistent, difficult to excrete, and often fat soluble tend to increase strongly in food chains.
- Thinking the largest organism always has the highest toxin level: trophic position and diet matter more than body size, so a smaller top predator can be more contaminated than a larger herbivore.
- Ignoring concentration units: ppm, ppb, and mass per kilogram are not interchangeable unless converted correctly.
Practice Questions
- 1 A lake contains algae with 0.02 ppm of a pesticide. Zooplankton that eat the algae have 0.2 ppm, and small fish that eat the zooplankton have 2.0 ppm. By what factor does the pesticide concentration increase from algae to small fish?
- 2 A bird eats 50 small fish in a week. Each fish has 0.04 mg of mercury stored in its tissues. If the bird retains 80 percent of that mercury, how many milligrams of mercury are added to the bird that week?
- 3 Explain why a warning about mercury is often aimed at people who eat large predatory fish rather than people who eat algae or small plankton-feeding fish.