AP® Environmental Science · Unit 8 · Topic 8.8
Bioaccumulation and Biomagnification
Bioaccumulation is one organism storing a contaminant faster than it can get rid of it; biomagnification is that contaminant getting more concentrated at each step up a food chain, so top predators carry the heaviest load.
Many pollutants, like mercury and DDT, are fat-soluble and don't break down easily. An organism absorbs them from water, soil, or food faster than its body can excrete them, so the contaminant builds up in its fatty tissue over its lifetime. That buildup in a single organism is bioaccumulation. A plankton cell or a filter-feeding clam can bioaccumulate a toxin straight from the water around it without eating anything else contaminated.
Biomagnification is what happens next, across a food chain. A small fish eats thousands of plankton, each carrying a trace of mercury, and that mercury doesn't digest away — it stays locked in tissue and adds up. A bigger fish eats many small fish, inheriting all their accumulated mercury plus its own. By the time you reach a tuna or an osprey, the concentration has climbed tenfold or more at every transfer. This connects directly to the 10 percent rule of energy flow: only about 10 percent of energy passes up to the next trophic level, so an organism has to eat a huge mass of prey to get enough energy, and it swallows all of that prey's stored toxins along with it. Energy shrinks going up the chain; toxins grow. That's why the mercury warning sits on the tuna label and not the plankton — plankton hold a trace, tuna hold the sum of everything beneath them. The same math explains why apex predators and the humans who eat them face the highest poisoning risk from pollutants released far below in the water.
Key terms
- Bioaccumulation
- The buildup of a contaminant in a single organism's tissue over its lifetime, faster than the body can eliminate it.
- Biomagnification
- The increase in contaminant concentration at each successive trophic level up a food chain.
- Trophic level
- A feeding position in a food chain, such as producer, primary consumer, or top predator.
- 10 percent rule
- Only about 10 percent of energy at one trophic level transfers to the next, concentrating stored toxins in fewer, larger consumers.
Watch it explained
- How it worksWalk me through a contaminant concentrating tenfold at every step up a food chain.
- Worked exampleFind the mercury in a top predator when water holds 0.001 ppm and each level magnifies 10 times.
- Common mistakeWhy isn't bioaccumulation the same thing as biomagnification?
- Ties togetherHow does the 10 percent rule of energy flow explain why toxins concentrate upward?
Check yourself
End of topic.