Purpose and issues
Persistent organic pollutants (POPs) are complex molecules which, unlike other pollutants, are not defined by their chemical composition (since they are so varied) but rather by four properties they have in common. They possess toxic properties, resist degradation, bioaccumulate, and are transported through air, water and migratory species across international boundaries. The definition of POPs is therefore strictly regulatory. All POPs are organic compounds; they are often simply termed pesticides, PCBs, or dioxins (see below).
World Health Organization (WHO)