8.7 Persistence, Bioaccumulation, and Biomagnification

Persistence: pollutants that don't break down

Persistence describes how resistant a chemical is to degradation. Persistent pollutants (like DDT, PCBs, and heavy metals) resist breakdown by sunlight, water, or microbes, so they remain in the environment for decades. Because they don't degrade quickly, persistent pollutants keep accumulating in soil, water, and living tissue, increasing their chances of causing long-term ecological and health harm.

Bioaccumulation: building up in one organism

Bioaccumulation is the buildup of a substance (often fat-soluble toxins) within an individual organism over its lifetime because the substance is absorbed faster than it's excreted or metabolized. Fat tissue often stores these chemicals. Organisms exposed to persistent pollutants over long lifespans, like fish, accumulate higher concentrations than what's found in surrounding water or food.

Biomagnification: increasing up the food chain

Biomagnification is the increase in concentration of a pollutant at each successive trophic level of a food chain, since predators eat many contaminated prey and concentrate the toxin further. Top predators (eagles, humans, orcas) suffer the highest doses. Classic example: DDT biomagnified in food chains, thinning eggshells and nearly wiping out bald eagle populations.

Key terms

Persistence

The resistance of a chemical to breaking down (degrading) in the environment, allowing it to remain for long periods.

Bioaccumulation

The buildup of a substance within an individual organism over its lifetime, often because it's absorbed faster than excreted.

Biomagnification

The increase in pollutant concentration at each successive trophic level in a food chain.

Why do fat-soluble toxins biomagnify?

They aren't easily excreted and accumulate in fatty tissue, becoming more concentrated as predators eat many contaminated prey.

DDT and bald eagles

DDT biomagnified up the food chain, causing eggshell thinning in bald eagles (top predators) and population decline.

Try an AP-style question

What is bioaccumulation?

1. Toxins breaking down quickly
2. Toxins increasing up the food chain
3. Toxins leaving the body fast
4. Toxins building up in one organism over time