The term dioxins refers to chlorinated hydrocarbons containing
a dibenzo-p-dioxin structure (two benzene rings conjoined at
their para carbons by two oxygen molecules). The nomenclature
for chlorinated dibenzodioxins (CDD) is based on the
number and position of the chlorine molecules and include
mono- (MCDD), di- (DCDD), tri- (TrCDD), tetra- (TCDD),
penta- (PeCDD), hexa- (HxCDD), hepta- (HpCDD), and octachlorinated
(OCDD) congeners. There are 75 congeners in
total. The 2,3,7,8-tetrachlorodienzo-p-dioxin (2,3,7,8-TCDD)
congener is the most familiar congener due in part to its toxicity
in animal models, its widespread distribution and persistence
in the environment, its bioaccumulation potential, and
because most data pertain to this congener. Dioxins in pure
form are colorless solids and are formed as combustion products.
Dioxins may be formed during the combustion of organic
material in the presence of halogens, especially chlorine (and
bromine), during waste incineration and forest fires. They also
occur as contaminants in herbicides.
Dioxin was a contaminant of Agent Orange and possibly
responsible for some of the adverse health effects associated
with exposure to the defoliant. Dioxin was the poisoning agent
in a high-profile political incident in 2004. Dioxin was ultimately
identified as the cause of the disfiguring acne-like skin
(chloracne) condition suffered by Ukrainian opposition leader
Viktor Yushchenko a few months prior to the first presidential
election. The suspicion was that the dioxin was placed into
soup consumed by Mr Yushchenko. The acne-like skin condition
is a recognized hallmark of dioxin poisoning in humans.
The actual intake of dioxin in this incident is unknown.
