Module 3: Toxicology - Section 19: Dioxin Toxicity

TOX 19.1: Introduction

INTRODUCTION:

Dioxin is one of 75 isomers of polychlorinated dibenzo-p-dioxins (PCDD). It is not a commercial product but instead is only a by-product of other manufacturing.

Its toxicity varies depending upon the isomer - 2,3,7,8-tetrachlorodibenzo-p-dioxin is by far the most toxic of PCDD’s. Its toxicity varies with the position and number of chlorine atoms. Dioxins bind tightly to soil. It does not migrate (groundwater contamination unlikely). Dioxin is broken down by ultraviolet light - half life 1-3 years, and is stable to heat, acids and alkali. It is virtually insoluble in water (2 x 10^-4 ppm). It is slightly soluble in fats. Uptake by plants from soil is highly unlikely. (No detectable amounts of dioxin has been found in grain and soybeans.)

Sources of dioxin are:

• Minute levels from production of hexachlorophene and herbicide 2,4,5- trichlorophenoxyacetic acid (2,4,5-T) - (.01 to 6 ppm).
• Burning, especially incomplete burning of wastes containing chlorine, such as polyvinyl chloride (PVC).
• Exhaust of coal burning power plants and diesel engines.
• Natural sources - volcanoes, fires.

The organochlorines such as dioxin and DDT’s are lipophyllic, solid synthetic compounds which are non-volatile. Exposure to these compounds in the environment may occur in air through particulate phase from combustion sources, (incinerators), to a very limited extent through water through adsorbtion to soil particulate or more typically through dietary fat consumption with bioaccumulation up the food chain.

Human Exposure occurs in the following circumstances:

• Accidents at chemical manufacturing plants.
• Occupational exposure to herbicides - applicators (Air Force personnel with Agent Orange).
• Contamination of general environment - improper waste disposal - local residents exposed to low doses.
• Very, very low levels of dioxin contamination present everywhere due to herbicides, solvents, burning of wastes.

Known health effects in humans are:

Chloracne - a skin disorder, reversible.
• General "not feeling well" syndrome (sleeplessness, headache, nausea, irritability).
• Reports but not confirmed of soft-tissue sarcoma, birth defects of offspring of Vietnam veterans, changes in metabolic measurements.
• No known human deaths.

Effects on lab animals include severe blood chemistry changes, liver damage, skin disorders, lung lesions, loss of weight and death. It is also, an animal carcinogen affecting numerous sites including liver and thyroid.

The specific role in carcinogenesis is not known and may act as a co-carcinogen or even an anti-carcinogen. It is not mutagenic in mammals. It causes birth defects and fetal deaths in many animal species if exposure of high levels of dioxin during critical periods of fetal development.

There is no scientific evidence that  sperm cells are affected by dioxin.  

REFERENCES:

1. Edmonds LD, Layde PM, James LM, et al. Congenital malformations surveillance: Two American systems. Int J Epid 1981;10:247-52.
2. Environmental Protection Agency. Environmental monitoring at Love Canal. Three volumes. Washington, U.S. Government Printing Office, Document No. EPA-600/4-82-030a, 1982.
3. Heath CW Jr. Field epidemiologic studies of populations exposed to waste dumps. Environ Health Perspect 1983;48:3-7.
4. Heath CW Jr, Nadel MR, Zack MN Jr, et al. Cytogenetic findings in persons living near the Love Canal, JAMA 1984;251:1437-40.
5. Janerich DT, Burnett WS, Feck G, et al. Cancer incidence in the Love Canal area. Science 1981;192:1404-7.
6. Kim CS, Narang R, Richards A, et al. Love Canal: chemical contamination and migration. Proceedings of National Conference on Management of Uncontrolled Hazardous Waste Sites, Environmental Protection Agency, 1980, pp 192-19.
7. Paigen B. Testimony before the Subcommittees on Environmental Pollution and Resource Protection of the Committee on Environment and Public Works, United States Senate, 96th Congress, U.S. Government Printing Office, Serial No. 96-H9, Part 1, 1979, pp 140-61.
8. Picciano D. Pilot cytogenetic study of the residents living near Love Canal, a hazardous waste site. Mammalian Chromosome Newsletter 1980;19:86-93.
9. Vianna NJ. Adverse pregnancy outcomes--potential endpoints of human toxicity in the Love Canal. Preliminary results. Proc 10th Ann NYSDH Birth Defects Symp, in Human Embryonic and Fetal Death, 1980, ed by Porter IH, Hook EP, pp 165-68.
10. Vianna NJ, Polan AK, Ragal R, et al. Adverse pregnancy outcomes in the Love Canal area. Manuscript released by NYSDH 23 June 1980.
11. Warburton D, Fraser FC. Spontaneous abortion risks in man--data from reproductive histories collected in a medical genetics unit. Am J Hum Genet 1963;16:1-8.
12. Wolff S. Love Canal revisited (editorial). JAMA 1984;251:1464.

Postgraduate Diploma in Occupational Health (DOH) - Modules 3: Occupational Medicine & Toxicology (Basic) by Profs Mohamed Jeebhay and Rodney Ehrlich, Health Sciences UCT is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License. Major contributors: Mohamed Jeebhay, Rodney Ehrlich, Jonny Myers, Leslie London, Sophie Kisting, Rajen Naidoo, Saloshni Naidoo. Source available from here. For any updates to the material, or more permissions beyond the scope of this license, please email healthoer@uct.ac.za or visit www.healthedu.uct.ac.za. Last updated Jan 2007.
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