Chapter 02 · Nature, land & waterWater, Waste & Pollution
Bioaccumulation
Definition
The process by which chemicals accumulate in a living organism when the rate of uptake — from water, food, sediment or air — exceeds the rate of elimination. It concerns especially persistent, fat-soluble substances (methylmercury, PCBs, DDT and other persistent organic pollutants) that the body cannot readily break down or excrete. Bioaccumulation within one organism is distinct from biomagnification: the increase in concentration from one trophic level to the next up a food chain.
References
Definitions of both processes; fat-solubility mechanism; mercury example; DDT and PCB cases.
POPs behaviour; food-web transfer from phytoplankton up trophic levels.
Overview
What it means
The two processes compound: a pollutant that bioaccumulates in plankton and small fish biomagnifies to concentrations in predatory fish, birds and humans that can be orders of magnitude higher than in the surrounding water — the mechanism behind fish-consumption advisories for mercury and the eggshell-thinning crisis caused by DDT.
Legacy pollutants banned decades ago still circulate through food webs because persistence is what makes them accumulate.
How it is used
Bioaccumulation potential is a core screening criterion in chemical regulation — the "B" in PBT (persistent, bioaccumulative, toxic) assessment under regimes such as REACH and the Stockholm Convention. Monitoring programmes measure tissue concentrations in indicator species.
Why it matters
Bioaccumulation is why dilute pollution is not safe pollution: substances released at trace levels can concentrate to harmful doses in wildlife and people, particularly communities dependent on fish. It underpins the regulatory logic of eliminating persistent chemicals at source.