Pollutants in food chains: bioaccumulation & biomagnification

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A pollutant that is **not broken down** by enzymes or decomposers, so it stays in the environment and in organisms for a long time (e.g. DDT, mercury).

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The **build-up of a pollutant inside a single organism** over time, because it is taken in faster than it can be broken down or excreted.

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The **increase in a pollutant's concentration from one trophic level to the next**, so that it is highest in the top predator.

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It is **persistent (non-biodegradable)** and **not excreted** — so it is stored (often in fat) and passed on.

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Each consumer eats **many** contaminated prey and **stores all** their pollutant, so the concentration **multiplies at each trophic level**.

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It **increases** up the chain — the opposite of energy, which decreases.

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The pollutant is **stored and passed on** (not used up or lost), whereas energy is lost as heat at each level.

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**DDT** (a pesticide) or **methyl mercury** — both are persistent and stored, not excreted.

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It biomagnified to high levels and caused **thin eggshells**, reducing breeding success and causing **population decline**.

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In **fat (fatty tissue)**, because they are often **fat-soluble** — so they are not excreted.

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Bioaccumulation is **within one organism**; biomagnification is **between trophic levels** (up the chain).

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It names the process but does not give the **cause-and-effect** — you must say it is stored and that each consumer eats many prey, so it multiplies up the chain.