They include industrial chemicals like PCBs, pesticides like DDT and unwanted wastes like dioxin.
POPs are primarily products and by-products of human industry that are of relatively recent origin.
Persistent substances with this property tend to enter the air, travel long distances on air currents, and then return to earth. Persistent substances with this property tend to bioaccumulate in fatty tissues of living organisms. POPs are highly toxic. This means POPs have the potential to injure human health and the environment at very low concentrations. Some POPs at extraordinarily low concentrations can attach to intercellular receptor sites in the body and trigger a cascade of potentially harmful effects.