Bioaccumulation

Chemicals that dissolve readily in fat and resist breakdown are the likeliest to accumulate. They settle in fatty tissue and remain for long periods. Persistent organic pollutants and some heavy metals such as mercury are well-known examples, although the mechanisms differ between organic chemicals and metals.

Bioaccumulation can lead to biomagnification, where concentrations rise at each step of a food chain. Small organisms take up the chemical, fish eat many of them, and birds or mammals eating the fish end up with the highest levels. This is why a chemical present at very low levels in water can still harm top predators.

Assessment relies on several tools. Laboratory or measured data on bioconcentration factors, the octanol-water partition coefficient used as a screening indicator, and persistence information are used together. None of them alone settles the question, and the SDS may report only some.

Bioaccumulation matters to people who handle chemicals because it drives disposal rules. A substance that accumulates cannot simply be diluted down the drain, since dilution does not stop uptake by organisms.