Dioxin Contamination of Food

Dioxin is a generic name used to describe a family of compounds known as chlorinated dibenzo-p-dioxins. The most notable, most studied, and most toxic chemical in this family is 2,3,7,8-tetrachlorodibenzo-p-dioxin, or 2,3,7,8-TCDD, most commonly referred to as TCDD. TCDD is colorless and odorless (1). Dioxins bioaccumulate in the food chain and the major route of human exposure is by eating fish, meat, and dairy products that have been exposed. Fetuses and nursing infants are at particular risk of exposure because of TCDDs accumulation in breast milk (1).

Studies with laboratory animals have shown TCDD to be extremely toxic and the most potent carcinogen ever tested under laboratory conditions for some species of animals (1). However, the effects in humans exposed to TCDD have been more difficult to ascertain. Because of this, animal studies have been used as the basis of most risk assessments for dioxins (1).

Although dioxins do occur naturally, they are not intentionally manufactured by industry. They occur as a contaminant in the manufacturing process of certain chlorinated organic intermediates and products, such as chlorinated phenols (1). TCDD is a by-product formed during the manufacture of 2,4,5-trichlorophenol, which was used in the manufacture of the bactericide, hexachlorophene, and the herbicide, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Various formulations of 2,4,5-T have been used extensively for weed control on roads, crops, rangelands, and roadways throughout the world. A combination of the herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-T, called Agent Orange, was used for defoliation and crop destruction by the American military in the Vietnam War (1).

2,4,5-T can no longer be used legally in the United States and pentachlorophenol (a wood preservative) and hexachlorophene have been restricted in their uses (1). Dioxins have been released to the environment during the manufacturing, use, and disposal of these chemicals, and are also formed during the chlorine bleaching processes used by pulp and paper mills. They also enter the environment in waste water effluent from these plants(1). The primary mechanism by which dioxin-like compounds enter the terrestrial food chain is via atmospheric deposition (2). Dioxin and related compounds enter the atmosphere directly through air emissions or indirectly, for example, through volatilization from land or water or from resuspension of particles. Deposition can occur directly on to soil or on to plant surfaces. Another source of dioxin production in the past has been the burning of leaded gasoline(1).

Certain segments of the population may be exposed to additional increments of exposure by being in proximity to point sources or because of dietary practices. The levels of dioxin and related compounds in the environment and in food in the U.S. are based on relatively few samples and must be considered uncertain (2). However, they seem consistent with levels measured in studies in Western Europe and Canada.

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Here are some very informative external links that pertain to Dioxins in food:


1. Congressional Testimony, Public Health Implications of Dioxins, Testimony by Barry L. Johnson, Ph.D. June 10, 1992. URL: http://atsdr1.atsdr.cdc.gov:8080/test-06-10-92.html

2. Norman Petersen, Food Safety Including Dioxin URL: http://www.epa.gov/oppeinet/oppe/futures/risk/crexamples/examples/Arizona/humhlth/food/dioxin.txt.html

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This Page prepared by B.T. Johnson, December 1997 UCD EXTOXNET FAQ Team.