Biomagnification is the increasing concentration of a non-biodegradable pollutant in organisms at successively higher trophic levels of a food chain. Top predators therefore receive the highest pollutant concentrations and often experience the greatest harm.
How Biomagnification Occurs
Non-biodegradable pollutants such as polychlorinated biphenyls (PCBs) are not readily broken down by biological processes. If they are also persistent and fat-soluble, they can remain in body tissues rather than being excreted.
- A small concentration of a pollutant enters an ecosystem, perhaps through industrial wastewater.
- Producers or small consumers absorb the pollutant from water or food.
- The pollutant accumulates in their tissues because uptake occurs faster than removal.
- A predator consumes many contaminated organisms, receiving all the pollutants stored in their tissues.
- Repeated feeding causes the pollutant concentration to increase at each trophic level.
For example, contaminated phytoplankton may be eaten by zooplankton, which are eaten by small fish, then larger fish, and finally fish-eating birds or humans. Even when the water contains little PCB, a top predator can receive a damaging concentration through its diet.
| Process | Meaning |
|---|---|
| Bioaccumulation | Pollutant concentration increases within one organism over time. |
| Biomagnification | Pollutant concentration increases between successive trophic levels. |
The common misconception is that these terms are interchangeable. Bioaccumulation occurs within an individual; biomagnification occurs along a food chain.
PCBs can disrupt reproduction, development and immune function. Their effects also have an environmental justice dimension because communities relying heavily on contaminated fish may face disproportionate exposure despite contributing little to the pollution.
Exam Technique
This is core SL and HL content in IB ESS subtopic 2.2, Energy and biomass in ecosystems. For an “explain” question, give the causal sequence: persistence, storage in tissues, consumption of many contaminated prey, and increasing concentration at higher trophic levels. Name a pollutant such as PCB, DDT or mercury, and do not confuse biomagnification with bioaccumulation.