A persistent organic pollutant (POP) is a toxic chemical that resists environmental breakdown, travels long distances, and accumulates in living tissue, increasingly concentrated up the food chain. The notorious examples, DDT, PCBs, dioxins, and brominated flame retardants, are fat-soluble, so they lodge in adipose tissue and magnify from plankton to predatory fish to humans, with Arctic communities and heavy fish consumers showing the highest body burdens. Health concerns include endocrine disruption, immune effects, and cancer. The Stockholm Convention coordinates global phase-outs, and levels of legacy POPs in breast milk and food have fallen markedly where bans bit. Food safety monitoring continues through surveillance of fish, dairy, and meat, since complete elimination takes decades. POPs are the reason dietary advice sometimes limits oily fish from contaminated waters despite its nutritional value.