Dioxin is the common name for 2,3,7,8-tetrachlorodibenzo-para-dioxin (
TCDD) but is also used for the structurally and chemically related pol
ychlorinated dibenzo-para-dioxins (PCDD), dibenzofurans (PCDF), and th
e coplanar polychlorinated biphenyls (PCB). There are 75 PCDD congener
s, 135 PCDF, and 209 PCB. Seven PCDD and 10 PCDF with substitutions at
the 2,3,7, and 8 positions are considered toxic, and 11 PCB have diox
in-like toxicity. The majority of toxic dioxin is and(or) has been der
ived from industrial chlorination processes, incineration of municipal
waste) and production of certain herbicides. The potential for health
risks due to the cancer-promoting, immunomodulating, and teratogenic
activities of dioxins in rodents has raised concerns over their presen
ce in the human food chain. The lipophilic nature of dioxins results i
n higher concentrations in the fat of animal and fish products, and th
eir excretion via milk secretion in dairy cattle may result in relativ
ely high concentrations of dioxin contamination in high-fat dairy prod
ucts. Surface contamination of plant foods and soil due to deposition
of atmospheric emissions may also be a significant direct source of di
oxin ingestion for livestock and thereby an indirect source of dioxin
for humans. Despite numerous epidemiological studies, dioxin has not b
een conclusively determined to be problematic for humans. Certain mana
gement practices such as trimming fat from meat, consuming low-fat dai
ry products, and simply cooking food can substantially decrease exposu
re to dioxin compounds.