"Dioxins" refers to a group of chemical compounds that share
certain chemical structures and biological characteristics.
Several hundred of these compounds exist and are members of
three closely related families: the chlorinated dibenzo-p-
dioxins (CDDs), chlorinated dibenzofurans (CDFs) and certain
polychlorinated biphenyls (PCBs). Sometimes the term dioxin is
also used to refer to the most studied and one of the most
toxic dioxins, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). CDDs
and CDFs are not created intentionally, but are produced
inadvertently by a number of human activities. Natural
processes also produce CDDs and CDFs. PCBs are manufactured
products, but they are no longer produced in the United States.
Dioxins are formed as a result of combustion processes such as
commercial or municipal waste incineration and from burning
fuels (like wood, coal or oil). The draft dioxin reassessment
makes the finding that anthropogenic emissions dominate current
releases in the United States, but acknowledges the need for
more data on natural sources. Dioxins can also be formed when
household trash is burned and as a result of natural processes
such as forest fires. Chlorine bleaching of pulp and paper,
certain types of chemical manufacturing and processing, and
other industrial processes all can create small quantities of
dioxins. Cigarette smoke also contains small amounts of dioxins.