Dioxins are a group of chemical compounds sharing the basic structure of two benzene molecules linked by two oxygen atoms.  Dioxins are created in combustion processes.  Poor combustion conditions increase dioxin production.  Another significant source of dioxin creation is the high temperature processing of metals. 

Dioxins deposit from polluted air onto animal feed crops.  When animals consume these contaminated feeds the dioxins are stored in their bodies.  Dioxins are fat-soluble.  These pollutants are therefore stored in fat tissue.

2,3,7,8-Tetrachlorodibenzo-p-dioxin is listed by the National Toxicology Program as Known to Be a Human Carcinogen (NTP, 2005).  It is suspected that all dioxins and dioxin-like compounds, including furans and certain PCBs are human carcinogens.  Dioxins cause cancer by acting as promoters of the process whereby malignant tumors are formed.  Promotion involves the accelerated development of cells that have lost the ability to control cell division.

The United States Environmental Protection Agency (US EPA) has been working on a reassessment of dioxin exposure and adverse health effects since the early 1990s (US EPA, 2003).  Dietary surveys conducted by the United States Food and Drug Administration (US FDA) provide an estimate of American consumption of animal fat.  Limited testing of animal fat foods has generated data for estimating dioxin levels in these foods.  The dioxin reassessment reports an average dioxin intake rate of 1 pg dioxin TEQ per kg body weight per day.  Over ninety-five percent of dioxin exposure is a result of consumption of animal fat.

Dioxin exposure cancer risk has been quantified in numerous epidemiological studies focused upon cancer cases recorded among pesticide factory workers and veterans of the Vietnam War involved in the aerial spraying of defoliants contaminated with dioxins.  EPA sets forth a dioxin cancer risk factor of 1.0 X 10 E-3 in its reassessment.  Using this cancer risk factor and the rate of intake stated above the cancer risk of dioxin exposure for the average American is 1 in 1000.

Reducing consumption of animal fat foods decreases dioxin exposure.  All of these foods contain animal fat that is contaminated with dioxins:  milk, cheese, ice cream, beef, pork, chicken, eggs and fish.  Two percent milk contains half as much dioxin as whole milk.  The dioxins are present in the animal fat part of the food.

References:

NTP.  “Report on Carcinogens, Eleventh Edition”; U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program, 2005; http://ntp.niehs.nih.gov/ntpweb/index.cfm?objectid=035E5806-F735-FE81-FF769DFE5509AF0A

US EPA. “Exposure and Human Health Reassessment of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds”, 2003; http://www.epa.gov/ncea/pdfs/dioxin/nas-review/