Last reviewed 4 Nov 2026 · 2 min read
1. Definitions
| Term | Meaning |
|---|---|
| Bioaccumulation | Build-up of a substance in one organism over its lifetime, because intake is faster than excretion or breakdown |
| Bioconcentration | Uptake directly from water (e.g. through gills) to a level higher than in the water |
| Biomagnification (biological magnification) | Increase in concentration from one trophic level to the next along a food chain — highest in top predators |
2. Which pollutants magnify?
Substances that are:
- Persistent — not easily broken down (non-biodegradable).
- Fat-soluble (lipophilic) — stored in fatty tissue, not excreted in urine.
- Biologically active — toxic at low levels.
Examples: DDT and other organochlorine pesticides, PCBs, dioxins, methyl mercury, lead, cadmium.
3. Classic examples
Worked ExampleDDT in an aquatic food chain
Water ≈ 0.000003 ppm → zooplankton ≈ 0.04 ppm → small fish ≈ 0.5 ppm → large fish ≈ 2 ppm → fish-eating birds ≈ 25 ppm. The concentration rises about a million times from water to birds. In birds DDT disturbs calcium metabolism → thin eggshells that break — this caused the decline of eagles, ospreys and pelicans (described in Rachel Carson's Silent Spring, 1962).
| Case | Pollutant | Effect |
|---|---|---|
| Minamata disease (Japan, 1950s) | Methyl mercury in fish from industrial waste | Nervous-system damage |
| Itai-itai disease (Japan) | Cadmium | Painful bone and kidney damage |
| Endosulfan in Kasaragod (Kerala) | Aerial spraying of the pesticide on cashew plantations | Birth defects and illness; banned by the Supreme Court in 2011 |
| PCBs in marine mammals | Industrial chemicals | Immune and reproductive problems |