Dioxin is a general term for a large group of toxic compounds with similar molecular structures that contain carbon, oxygen, hydrogen and chlorine atoms. The degree of toxicity varies greatly among dioxins and is determined by the number of the chlorine atoms and their positions in the dioxin molecule.
Although small amounts of dioxins are produced naturally by forest fires, the main sources are human activities, particularly the burning of municipal, hospital and household waste and automobile emissions. Small amounts are also contained in cigarette smoke.
Dioxins have high chemical stability and are thus very resistant to breakdown in both the environment and the human body. They are easily absorbed and stored in fat cells and accumulate in the food chain. In general, the higher an animal is in the food chain, the greater will be its concentration of dioxins. Humans, at the top of that chain, ingest dioxins primarily from animal fats, especially those in fish, milk and meat. Among the health problems that dioxins can cause are skin lesions, liver damage, interference with hormones, reproductive and developmental problems, damage to the immune system and cancer.