Dioxin Fact Sheet

Source of Exposure

TCDD is formed during the synthesis of the trichlorophenol precursor 2,4,5-trichloroanisole. This makes it a possible contaminant in any trichlorophenol herbicide. In vietnam the mixture known as "Agent Orange" was a mixture of 2,4-D and 2,4,5-T but it contained anywhere from 1 - 47 ppm of TCDD as a contaminant. Presently the TCDD content is regulated in 2,4,5-T at 0.1 ppm or less. The ratio of the LD50 of 2,4,5-T to the LD50 of dioxin is 630,000 for female guinea pigs. The feto toxic concentration of dioxin in rats is only 1/400 of the maternal LD50 and only 1/4aaaaaa of the LD50 of 2,4,5-T.

Disposition

Patterson and coworkers reported that inividuals occupationally exposed to trichlorophenol in manufacturing had maximum adipose levels of TCDD in the low ppb (1000 ppt) range. An oral dose of 105 ng (1.14 ng/kg) of TCDD has been reported by Poiger and Schlatter to produce concentrations of TCDD in adipose tissue in the low ppt range. TCDD levels in adipose tissue of Vietnam Veterans heavily exposed 15 to 20 previously to Agent Orange were reported to range between 10 to 150 ppt (10 - 150 pg/gm).

Toxic Levels

In laboratory animals TCDD is fatal in the order of 1 to 100 m g/kg. The effects in man, based on occupational exposures and industrial accidents, include; chloracne, porphyria, liver damage, polyneuropathies, and psychiatric disturbances. Estimated serum levels of TCDD consistent with production of clinically observable chloracne has been reported to be in excess of 100 ppt.

References

IARC: Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man. Vol. 15, Some Fumigants, the Herbicides 2,4-D and 2,4,5-T, Chorinated Dibenzodioxins and Miscellaneous Industrial Chemicals. International Agency for Research on Cancer, Lyon, France, 1977.

Young, A.L.; Calcagne, J.A.; Thalken, C.E.; and Tromblay, J.W.; The Toxicology, Environmental Fate and Human Risk of Herbicide Orange and Its Dioxin. USAF OEHL Technical Report 78-92. National Technical Information Service (AD-A062-143), U.S. Department of Commerce, Springfield, Va., 1978.

Kociba, R.I.; Keyes,, D.G.; and Beyer, J.E.; Results of a two year chronic toxicity and oncogenicity study of 2,3,7,8-tetrachlorodibenzo-p-dioxin in rats. Toxicol.Appl.Pharmacol., 46:279-303, 1978.

Van Miller, J.P.; Lalich, J.J.; and Allen, J.R.: Incrased incidence of neoplasm in rats exposed to low levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin. Chemosphere, 6:537-544, 1977.