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Bioaccumulation and biomagnification – DDT, mercury and microplastics in a food chain

BiologyEcology & EnvironmentAges 17–18

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An aquatic food chain from plankton through small fish and large fish to a fish-eating bird takes up a persistent pollutant: fat-soluble DDT or protein-bound methylmercury. Set the water concentration, years of release, environmental half-life and number of trophic levels to see the concentration rise at each level, the biomagnification factor, eggshell thinning, and the bird population crash and recover after a ban. A Microplastics screen compares plastic particles in the gut with persistent pollutants.

Lesson: Bioaccumulation and biomagnification in food chains; pollution of ecosystems

What it shows

Bioaccumulation is the build-up of a substance in one organism because it is absorbed faster than it is lost. DDT dissolves in fat and methylmercury binds to muscle proteins; both resist breakdown and are excreted slowly. Each consumer eats many times its own mass of food, and most of that food's energy is lost in respiration, but the pollutant stays behind. The concentration therefore rises at every trophic level: biomagnification. In the 1950s–1970s DDE from DDT thinned the eggshells of ospreys, peregrine falcons and other top predators; populations recovered after bans.

How to use

Choose a Pollutant and the Number of trophic levels, then set the Water concentration during release, the Years of release and the Environmental half-life. Press Play to run 80 years, or drag the Year slider. Read the pyramid, the log graph, the bird chart and the table. Open Microplastics and move Microplastics in water to compare particles with pollutants.

Parameters you can change

  • Screen Food chain, Microplastics
  • Pollutant DDT, Methylmercury, Water-soluble chemical (for comparison)
  • Water concentration during release 0.1–50 ng/L
  • Years of release before the ban 1–40 years
  • Half-life in the environment 0.5–30 years
  • Number of trophic levels 3–5
  • Microplastic density in water 0–1000 particles/m³

Questions to explore

  1. Why can a fish-eating bird carry millions of times more DDT than the water it never drinks from?
  2. How does adding a fifth trophic level change the concentration in the top predator, and why?
  3. Why does the bird population take decades to recover after the ban, even though release stops at once?

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