Learn More about Dioxins
Dioxins are a group of toxic chlorinated organic compounds that bioaccumulate in human beings and some animals due to their fat solubility. The most notorious of those is 2,3,7,8-tetrachlorodibenzo-p-dioxin, usually 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 commercial 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 the required number of countries. The treaty requires signatories to take steps to eliminate or minimize the sources of dioxin.
The United States Environmental Protection Agency Dioxin Reassessment is probably the most thorough review of dioxin, but other countries too have substantial research information. Australia, New Zealand and the United Kingdom all have significant research concerning body burdens and sources. Tolerable daily, monthly or annual intakes have been set by the World Health Organization and many governments. Dioxin enters the general population almost exclusively through food particularly fish, meat, and dairy products since dioxins are fat-soluble.
Occupational exposure is a risk for some in the chemical industry, or in work involving the application of chemicals, notably herbicides. Inhalation has been a problem for people living in proximity to substantial point sources where emissions are not sufficiently controlled. In many developed countries, there are now emissions regulations which have addressed some concerns but the lack of constant sampling of dioxin emissions raises concern about underestimation 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 raises 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.
Dioxins are also contained in smoke from cigarettes, in chlorine-bleached paper and residues of many chlorine pesticides. Dioxin in cigarette smoke was noted as "understudied" by the EPA in its "Re-Evaluating Dioxin" (1995). In that same document, the EPA acknowledged that dioxin is "anthropogenic" (man-made). Dioxin cannot come from the tobacco or any natural plant.
Since then, the USA categorized dioxin as a Known Human Carcinogen, and the USA signed the Stockholm Convention on POPs to globally phase out dioxin and certain other industrial pollutants. Nevertheless, chlorine tobacco pesticides and chlorine-bleached cigarette papers remain legal, with no requirement of consumer warning.
A comparison of material in two studies indicates that an uninformed, unprotected, insufficiently-warned person who smokes just 20 such contaminated products is exposed to Seven Hundred and Sixteen (716) times the US established low-threshold dose of dioxin.
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 matter.
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, especially 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.
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 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.
Excessive exposure to dioxin causes a severe form of persistent acne, known as chloracne. This is the only conclusive direct result of dioxin exposure at levels below the lethal dose.
Developmental abnormalities in the enamel of children's teeth could also be possibly correlated to dioxin exposure.
Immune systems may possibly be affected by dioxin exposure.
Endometriosis can be possibly correlated to dioxins, as can increased incidence of breast cancer. This seems to indicate that dioxins are carcinogenic. 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 research and questioning others without justified reasons.
Studies have shown it to have some significant impact on birth defects. This is because dioxin passes through the bloodstream into the baby. A few studies have revealed its effects when tumors were discovered in a newborn baby whose mother had unusually high levels of dioxin.
Other diseases are positively correlated with dioxin exposure, including diabetes.
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