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Effects of dioxins


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The chlorinated dibenzo-p-dioxins are a class of compounds that are loosely referred to as dioxins. There are 75 possible dioxins. The one with four chlorine atoms at positions 2, 3, 7 and 8 of the dibenzo-p-dioxin chemical structure is called 2,3,7,8- tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). It is a colorless solid with no known odor. 2,3,7,8-TCDD does not occur naturally nor is it intentionally manufactured by any industry, except as a reference standard. It can be inadvertently produced in very small amounts as an impurity during the manufacture of certain herbicides and germicides and has been detected in products of incineration of municipal and industrial wastes. At the present time, 2,3,7,8-TCDD is not used for any purpose than scientific research.


From now on, we are going to speak many times about the dioxin 2,3,7,8-TCDD, because it is one of the more common dioxins, and maybe the most dangerous of them. But many other dioxins can appear during the following processes. The most toxic member of the dioxin family is PCDD and it is mostly from studies on this compound that we know about the mechanism of the other chemicals in the same group (Silbergeld & Gasiewicz, 1989).


Exposure Pathways


The main environmental sources of polychlorinated dioxins (PCDD) are:

  • Use of herbicides containing 2,4,5-Trichlorophenoxy acids (2,4,5-T)
  • Production and use of 2,4,5-Trichlorophenol in wood preservatives
  • Production and use of hexachlorophene as a germicide
  • Pulp and paper manufacturing plants
  • Incineration of municipal and certain industrial wastes
  • Small amounts formed during the burning of wood in the presence of chlorine
  • Accidental transformer/capacitor fires involving chlorinated benzenes and biphenyls
  • Exhaust from automobiles powered with leaded gasoline
  • Improper disposal of certain chlorinated chemical wastes  

Exposure pathways are:

  • Skin contact with surfaces such as soil and vegetation contaminated by the chemical
  • Skin contact and inhalation of wood dusts from use of pentachlorophenol-treated woods
  • Inhalation of air near improperly maintained dump sites or municipal incinerators
  • Consumption of fish and cow's milk from contaminated areas
  • Consumption of breast milk containing PCDD by babies
  • Minute exposure from the use of paper towels, napkins, coffee filters, computer papers, and other contaminated paper products 

According to one estimate of ambient exposure, breathing air constitutes 2 percent, drinking water less than 0.01 percent, and consuming foods 98 percent of the total human exposure to PCDD. No estimate of relative intake of PCDD due to skin absorption is available.


PCDD produces a range of toxic effects:


  • Lethal effects: animals die from a wasting disease in two to six weeks at levels ranging from 1 ug/kg to 5000 ug/kg
  • Immune system damage at similar levels in all animals examined, because of damage to the thymus gland causing changes in cell immunity: especially likely in children
  • Damage to other organs such as liver, kidney and digestive tract
  • Reproductive effects: miscarriage, sterility
  • Birth defects, including neurological effects
  • Cancer: most potent cancer promoter known, also evidence of some tumour initiation; animal carcinogen
  • Chloracne - persistent skin eruptions in humans and some animals  

Health Effects


Chloracne is a skin disease, often accompanied by severe disfiguration, severe joint pain, headaches, fatigue, irritability and chronic weakness; and it can persist in the body for at least 30 years after exposure (Kimbrough & Grandjean, 1989). No-one disputes that it is caused by dioxin-like compounds, but it is not an infallible marker of dioxin exposure (Gough, 1991).


There is suggestive evidence that PCDD causes liver damage in humans, as indicated by an increase in levels of certain enzymes in the blood, although these effects might also have resulted from the concomitant exposure to the chemicals contaminated with PCDD or to the solvents in which these chemicals are usually dissolved.


Animal studies have demonstrated severe liver damage in some species. There is suggestive evidence that PCDD causes loss of appetite, weight loss, and digestive disorders in humans, although these effects might also have resulted from the concomitant exposure to the chemicals contaminated with PCDD or to the solvents in which these chemicals are usually dissolved. Animal exposure to PCDD results in severe loss of body weight prior to death.


Although not demonstrated in humans, in animal studies PCDD produced toxicity to the immune system. This toxicity can result in greater susceptibility to infection.


Although not demonstrated in humans, in some animal species exposure to PCDD resulted in adverse reproductive effects including spontaneous abortions. The monkey is very sensitive to this toxic property of PCDD. Although not demonstrated in humans, in some animal species exposure to PCDD during pregnancy resulted in malformations in the offspring. Low levels of PCDD have been detected in human milk, but the effects on infants and children are unknown.


The human evidence for PCDD alone is inadequate to demonstrate or reflect a carcinogenic hazard, although certain herbicide mixtures containing a PCDD as an impurity provide limited evidence of causing cancer in exposed humans.


Based on the positive evidence in animal studies, PCDD is probably carcinogenic in humans.


Everyone in industrialized countries has a potent mixture of dioxins, furans, co-planar PCBs, PCNs and other similar compounds stored and accumulated in their bodyfat. This chemical concoction of compounds in our bodies is likely to add together, making up a total dioxin-like toxicity: dioxins plus PCBs is equivalent to more dioxins.


In addition to these dioxin and dioxin-like molecules, we must also be concerned with other organochlorine compounds in our bodies which are not part of this family but are likely to interact with it. We do not know enough at present about these compounds which include pesticides such as DDT.


2,3,7,8-PCDD (often known simply as PCDD) is known for its lethal effects at very low concentrations: a millionth of a gram will kill a guinea pig.


Neurological Effects


Proper development of the nervous system is critical for early learning and can provoke significant consequences for the health of individuals.

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