Science Fair Project Encyclopedia
Dioxins form a family of toxic chlorinated organic compounds that bioaccumulate in humans and wildlife due to their fat solubility. The most notorious of those is 2,3,7,8-tetrachlorodibenzo-p-dioxin, often abbreviated as TCDD. The isomers containing chlorine in the 2, 3, 7, and/or 8 positions are the most toxic isomers and the ones which bioaccumulate. Dioxins are a byproduct only, with no industrial uses.
Dioxins and other Persistent Organic Pollutants (POPs) are subject to the Stockholm Convention. This convention will come into effect as it has been ratified by sufficient countries, the last being Russia. The treaty obliges signatories to take measures to eliminate where possible, and minimize where not possible to eliminate, all sources of dioxin.
The United States Environmental Protection Agency Dioxin Reassessment is possibly the most comprehensive review of dioxin, but other countries now have substantial research. Australia, New Zealand and the United Kingdom all have substantial research into body burdens and sources. Tolerable daily, monthly or annual intakes have been set by the World Health Organization and a number of governments. The most prominent source of dioxin for humans is the food chain, particularly meat, dairy and fish products. Occupational exposure is an issue for some in the chemical industry, or in the application of chemicals, notably herbicides. Inhalation has been a problem for people living near substantial point sources where emissions are not adequately controlled. In many developed nations there are now emissions regulations which have alleviated some concerns, although the lack of constant sampling of dioxin emissions causes concern about the understatement of emissions. In Belgium, through the introduction of a process called AMESA , constant sampling showed that periodic sampling understated emissions by a factor of 30 to 50 times. Few facilities have constant sampling.
Most controversial is the US EPA assessment's (draft) finding that any reference dose that were to be set would be far below current average intakes.
Children are passed substantial body burdens by their mothers, and breast feeding increases the child's body burden. Children's body burdens are often many times above the amount implied by tolerable intakes which are based on body weight. Breast fed children usually have substantially higher dioxin body burdens than non breast fed children until they are about 8 to 10 years old. The WHO still recommends breast feeding for its other benefits.
Dioxins are produced in small concentrations when organic material is burned in the presence of chlorine, whether the chlorine is present as chloride ions or as organochlorine compounds, so they are widely produced in many contexts such as:
- trash burn barrels;
- incinerators for municipal waste;
- iron ore sinter plants;
- incinerators for clinical waste; and
- facilities of the non-ferrous metal industry.
In incineration, dioxins can also reform in the atmosphere above the stack as the exhaust gases cool through a temperature window of 600 to 200°C. The most common method of reducing dioxins reforming or forming de novo is through rapid (30 millisecond) quenching of the exhaust gases through that 400°C window. Chemical Engineering, December 2002 has a detailed article on this issue.
Dioxins are also generated in reactions that do not involve burning — such as bleaching fibers for paper or textiles, and in the manufacture of chlorinated phenols, particularly when reaction temperature is not well controlled. Affected compounds include the wood preservative pentachlorophenol, and also herbicides such as 2,4-dichlorophenoxyacetic acid (or 2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Higher levels of chlorination require higher reaction temperatures and greater dioxin production. See Agent Orange for more on contamination problems in the 1960s.
Dioxins are present in minuscule amounts in a wide range of materials used by humans — including practically all substances manufactured using plastics, resins or bleaches. Such materials include tampons, and a wide variety of food packaging substances. The use of these materials means that all modern humans receive (at least) a very small daily dose of dioxin—however, it is disputed whether such exceptionally tiny exposures have any clinical relevance. It is even controversially discussed if dioxins might have a non-linear dose-response curve with beneficial health effects in a certain lower dose range, a phenomenon called hormesis.
Dioxins build up in living tissue (bioaccumulate) over time, so even small exposures can accumulate to dangerous levels.
Endometriosis can be possibly correlated to dioxins , as can increased incidence of breast cancer. This seems to indicate that dioxins are carcinogenic in nature. Animal studies seem to support claims of its carcinogenic nature, but other human studies find no such results. The classification of dioxins as carcinogens has recently been questioned , a standpoint that has been rebutted in a later review article as ignoring important studies and questioning others without justified reasons .
Studies have shown it to have no significant impact on birth defects.
Other diseases are positively correlated with dioxin exposure, including diabetes.
Some groups dispute some or all of these claims. Some claim that dioxins are not as harmful as previously thought.
Studies of dioxins effects
US veterans' groups and Vietnamese groups, including the Vietnamese government, have convened scientific studies to explore their belief that dioxins were responsible for a host of disorders, including tens of thousands of birth defects in children, amongst Vietnam veterans as well as an estimated one million Vietnamese, through their exposure to Agent Orange during the Vietnam War, which was found to be highly contaminated with TCDD. The most recent study, paid for by the National Academy of Sciences, was released in an April 2003 report.
The Center for Disease Control found that dioxin levels in Vietnam veterans  were in no way atypical when compared against the rest of the population. The only exception existed for those who directly handled Agent Orange. These were members of Operation Ranch Hand. Long term studies of the members of Ranch Hand have thus far uncovered a possibility of elevated risks of diabetes.
Dioxin exposure incidents
Large amounts of dioxin were released in an industrial accident at Seveso in 1976, although no human fatalities or birth defects occurred. In 1978, dioxin was one of the contaminants that forced the evacuation of the Love Canal neighborhood of Niagara Falls, New York. Dioxin also caused the 1983 evacuation of Times Beach, Missouri.
Parts of the Spolana chemical plant in Neratovice , Czechoslovakia, were heavily contaminated by dioxins in the 1960s, when the herbicide 2,4,5-T (also a component of Agent Orange) was produced there. Workers in this factory were exposed to high concentrations of dioxins at that time. Dozens of them fell seriously ill. A possibly large amount of dioxins was flushed from the factory into the Labe river during the 2002 European flood . No direct consequences of this incident have thus far been recorded.
In a 2001 case study , physicians reported clinical changes in a 30 year old woman who had been exposed to a massive dosage (144,000 pg/g blood fat) of dioxin equal to 16,000 times the normal body level; the highest dose of dioxin ever recorded in a human. She suffered from chloracne, nausea, vomiting, epigastric pain, loss of appetite, leukocytosis, anemia, amenorrhoea and thrombocytopenia. However, other notable laboratory tests, such as immune function tests, were relatively normal. The same study also covered a second subject who had received a dosage equivalent to 2,900 times the normal level, who apparently suffered no notable negative effects other than chloracne. These patients were provided with olestra to accelerate dioxin elimination.
A notable individual case of dioxin poisoning, Ukrainian politician Viktor Yushchenko was exposed to the second-largest measured dose of dioxins in 2004, according to the reports of the physicians responsible for diagnosing him. This is the first known case of a single high dose of pure TCDD dioxin poisoning. Experts say that it could take two to three years for the disfigurement of his face to clear up.
- "Dioxins and Dioxin-like Compounds in the Food Supply: Strategies to Decrease Exposure", a 2003 report by the National Academy of Sciences
- "Rhodes Remediation" Website about remediation of dioxin contaminated Homebush Bay and land in Rhodes, a suburb of Sydney, NSW, Australia. Union Carbide was the polluter.
- "Assesment of the Health Risks of Dioxins", a 1998 report by the World Health Organisation.
- Environment and Health 5:87 The risks of dioxin to human health (Review article) Re-evaluation of the health hazards posed by dioxins
- Ind. Health 41(3): 149-157 (2003) Impact of Agent Orange exposure among Korean Vietnam veterans. Scientific article that corroborates the increased risk of diabetes among Korean Vietnam veterans.
- Env. Health Persp. 109(8): 865-869 (2001) Severe 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) Intoxication: Clinical and Laboratory Effects. Case study of a TCDD poisoning.
- Regulatory Toxicology and Pharmacology 38(3): 378-388 (2003) Dioxin and cancer: a critical review. Review article that questiones the carcinogenity of dioxins.
- Environmental Health Perspectives 112(13): 1265-1268 (2004) Dioxin Revisited: Developments Since the 1997 IARC Classification of Dioxin as a Human Carcinogen. Review article that provides evidence for the carcinogenity of dioxins.
- Treatment of dioxin poisoning with olestra.
- Assessment of the health risk of dioxins 1998 by the WHO and the IPCS (pdf).
- A summary of the previous report by the industry lobbying group GreenFacts.
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