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98-732: The United States discovered 2,4-dichlorophenoxyacetic acid (2,4-D) during World War II. It was recognized as toxic and was combined with large amounts of water or oil to function as a weed-killer. Army experiments with the chemical eventually led to the discovery that 2,4-D combined with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) yielded a more potent herbicide. Some batches of 2,4,5-T manufactured for Rainbow Herbicide use were later found to have been contaminated with synthesis-byproduct dioxins including 2,3,7,8-tetrachlorodibenzodioxin (TCDD). Work by researcher Alvin Lee Young identifies examples of Agent Pink and Agent Green containing as much as double

196-424: A chemical compound ; the concept is most readily understood when considering pure chemical substances . It follows from their being composed of fixed proportions of two or more types of atoms that chemical compounds can be converted, via chemical reaction , into compounds or substances each having fewer atoms. A chemical formula is a way of expressing information about the proportions of atoms that constitute

294-419: A solid-state reaction , or the electron transfer reaction of reactive metals with reactive non-metals, such as halogen gases. Ionic compounds typically have high melting and boiling points , and are hard and brittle . As solids they are almost always electrically insulating , but when melted or dissolved they become highly conductive , because the ions are mobilized. An intermetallic compound

392-474: A broad class of compounds that vary widely in toxicity, the concept of toxic equivalency factor (TEF) has been developed to facilitate risk assessment and regulatory control. TEFs exist for seven congeners of dioxins, ten furans and twelve PCBs. The reference congener is the most toxic dioxin TCDD which per definition has a TEF of one. In essence, multiplying the amount of a particular congener with its TEF produces

490-543: A common mechanism of action via the aryl hydrocarbon receptor (AHR), but their potencies are very different. This means that similar effects are caused by all of them, but much larger doses of some of them are needed than of TCDD. Binding to the AHR as well as persistence in the environment and in the organism depends on the presence of so-called "lateral chlorines", in case of dioxins and furans, chlorine substitutes in positions 2,3,7, and 8. Each additional non-lateral chlorine decreases

588-412: A continuous three-dimensional network, usually in a crystalline structure . Ionic compounds containing basic ions hydroxide (OH ) or oxide (O ) are classified as bases. Ionic compounds without these ions are also known as salts and can be formed by acid–base reactions . Ionic compounds can also be produced from their constituent ions by evaporation of their solvent , precipitation , freezing ,

686-516: A disputed marginal case. A chemical formula specifies the number of atoms of each element in a compound molecule, using the standard chemical symbols with numerical subscripts . Many chemical compounds have a unique CAS number identifier assigned by the Chemical Abstracts Service . Globally, more than 350,000 chemical compounds (including mixtures of chemicals) have been registered for production and use. The term "compound"—with

784-444: A meaning similar to the modern—has been used at least since 1661 when Robert Boyle's The Sceptical Chymist was published. In this book, Boyle variously used the terms "compound", "compounded body", "perfectly mixt body", and "concrete". "Perfectly mixt bodies" included for example gold, lead, mercury, and wine. While the distinction between compound and mixture is not so clear, the distinction between element and compound

882-469: A member of the basic helix-loop-helix / Per-Arnt-Sim (bHLH/PAS) family of transcription factors , and it acts to modify transcription of a number of genes (see figure). AH receptor activity is necessary for normal development and many physiological functions. Mice lacking the AH receptor (knockouts) are sick with cardiac hypertrophy, liver fibrosis, reproductive problems, and impaired immunology. The AH receptor

980-566: A particular chemical compound, using chemical symbols for the chemical elements, and subscripts to indicate the number of atoms involved. For example, water is composed of two hydrogen atoms bonded to one oxygen atom: the chemical formula is H 2 O. In the case of non-stoichiometric compounds , the proportions may be reproducible with regard to their preparation, and give fixed proportions of their component elements, but proportions that are not integral [e.g., for palladium hydride , PdH x (0.02 < x < 0.58)]. Chemical compounds have

1078-496: A positively charged cation . The nonmetal will gain the electrons from the metal, making the nonmetal a negatively charged anion . As outlined, ionic bonds occur between an electron donor, usually a metal, and an electron acceptor, which tends to be a nonmetal. Hydrogen bonding occurs when a hydrogen atom bonded to an electronegative atom forms an electrostatic connection with another electronegative atom through interacting dipoles or charges. A compound can be converted to

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1176-479: A result of these concerns, incineration processes have been improved with increased combustion temperatures (over 1,000 °C (1,830 °F)), better furnace control, and sufficient residence time allotted to ensure complete oxidation of organic compounds. Incineration or "coprocessing" of municipal and solid industrial wastes in cement kilns is another proven source of PCDD/F compounds despite extreme high temperatures 1,400–1,500 °C (2,550–2,730 °F), posing

1274-423: A result. The wood preservative pentachlorophenol often contained dioxins and dibenzofurans as impurities. The Stockholm Convention banned the production and use of dioxins in 2001. PCDD/F-compounds were never synthesized for any purpose, except for small quantities for scientific research. Small amounts of PCDD/Fs are formed whenever organics, oxygen and chlorine are available at suitable temperatures. This

1372-402: A risk in countries where coprocessing is increasingly employed as a primary waste management strategy if appropriate environmental monitoring and controls are not put in place. Ideally, an incineration process oxidizes all carbon to CO 2 and converts all chlorine to HCl or inorganic chlorides prior to the gases passing through the temperature window of 400-700 °C where PCDD/F formation

1470-713: A single dose, high concentrations are found in the liver, but in a few days, adipose tissue will predominate. In rat liver, however, high doses cause induction of CYP1A2 enzyme, and this binds dioxins. Thus, depending on the dose, the ratio of fat and liver tissue concentrations may vary considerably in rodents. Dioxins have no common uses. They are manufactured on a small scale for chemical and toxicological research, but mostly exist as by-products of industrial processes such as chlorine bleaching of paper pulp , pesticide manufacture, and combustion processes such as incineration . The defoliant Agent Orange contained trace amounts of dioxin impurities and caused severe health issues as

1568-447: A solid state dependent on how low the temperature of the environment is. A covalent bond , also known as a molecular bond, involves the sharing of electrons between two atoms. Primarily, this type of bond occurs between elements that fall close to each other on the periodic table of elements , yet it is observed between some metals and nonmetals. This is due to the mechanism of this type of bond. Elements that fall close to each other on

1666-665: A thorough benefit/risk analysis is needed before setting limits, in order to avoid increased other risks or lost benefits. The uncertainty and variability in the dose–response relationship of dioxins in terms of their toxicity, as well as the ability of dioxins to bioaccumulate , have led WHO experts to recommending very low tolerable daily intake (TDI) of dioxin, 1-4 pg/kg body weight per day, i.e. 7x10 to 2.8x10 g per 70-kg person per day, to allow for this uncertainty and ensure public safety in all instances. Authorities have then set weekly or monthly intake levels that equal to TDIs around 2 pg/kg. Because dioxins are eliminated very slowly,

1764-469: A unique and defined chemical structure held together in a defined spatial arrangement by chemical bonds . Chemical compounds can be molecular compounds held together by covalent bonds , salts held together by ionic bonds , intermetallic compounds held together by metallic bonds , or the subset of chemical complexes that are held together by coordinate covalent bonds . Pure chemical elements are generally not considered chemical compounds, failing

1862-445: Is a central theme. Quicksilver ... with Aqua fortis will be brought into a ... white Powder ... with Sulphur it will compose a blood-red and volatile Cinaber. And yet out of all these exotick Compounds, we may recover the very same running Mercury. Boyle used the concept of "corpuscles"—or "atomes", as he also called them—to explain how a limited number of elements could combine into a vast number of compounds: If we assigne to

1960-403: Is a type of metallic alloy that forms an ordered solid-state compound between two or more metallic elements. Intermetallics are generally hard and brittle, with good high-temperature mechanical properties. They can be classified as stoichiometric or nonstoichiometric intermetallic compounds. A coordination complex consists of a central atom or ion, which is usually metallic and is called

2058-414: Is augmented by metal catalysts such as copper. The optimal temperature range is 400 °C (752 °F) to 700 °C (1,292 °F). This means that formation is highest when organic material is burned in less-than-optimal conditions such as open fires, building fires, domestic fireplaces, and poorly operated and/or designed solid waste incinerators. Historically, municipal and medical waste incineration

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2156-432: Is based on inappropriate activation of a physiologically important receptor, and therefore dose-response must be carefully considered. Inappropriate stimulation of many receptors leads to toxic outcomes, e.g. overdose of vitamin A leads to inappropriate activation of retinoid receptors resulting in e.g. malformations, and overdoses of corticosteroids or sex hormones lead to a multitude of adverse effects. Therefore, it

2254-520: Is cancer promotion. A mixture of PCBs such as Aroclor may contain PCB compounds which are known estrogen agonists but are not classified as dioxin-like in terms of toxicity. Mutagenic effects have been established for some lower chlorinated chemicals such as 3-chlorodibenzofuran, which is neither persistent nor an AH receptor agonist. High doses . The symptoms reported to be associated with dioxin toxicity in animal studies are incredibly wide-ranging, both in

2352-464: Is concentration in breast milk measured over decades. In many countries the concentrations have decreased to about one tenth of those in the 1970s, and the total TEQ concentrations are now of the order of 5-30 pg/g fat (please note the units, pg/g is the same as ng/kg, or the non-standard expression ppt used sometimes in the United States). The decrease is due to strict emission controls and also to

2450-464: Is evidence on human carcinogenicity. Increases in cancer have been modest, in fact reaching statistical significance has been difficult even after high accidental or occupational exposures like in Yusho and Yucheng poisonings, Seveso accident, and combined occupational cohorts. Therefore, controversies on cancer risk at low population levels of dioxins are understandable. The problem with IARC evaluations

2548-503: Is extremely slow. This results in biological half-lives of several years for all dioxins. That of TCDD is estimated to be 7 to 8 years, and for other PCDD/Fs from 1.4 to 13 years, PCDFs on average slightly shorter than PCDDs. In mammals, dioxins are found mostly in fat. Concentrations in fat seem to be relatively similar, be it serum fat, adipose tissue fat, or milk fat. This permits measuring dioxin burden by analysing breast milk. Initially, however, at least in laboratory animals, after

2646-715: Is hoped to increase the reliability of risk assessment. Recently also developmental effects have been reassessed by the Contamination Panel of the European Food Safety Agency (EFSA). They propose decreasing the tolerable weekly intake (TWI) from 14 pg/kg to 2 pg/kg. This is likely to cause another controversy before being accepted by European countries. Dioxin intake and levels in breast milk in 1970s and 1980s were 5 to 10 times higher than presently, and very few effects have been found, possibly mild developmental effects on teeth. All dioxin-like compounds share

2744-618: Is important to separate the effects of low doses causing activation of the receptor around the physiological range from the effects of high toxic doses. This is all the more important because of large differences in exposures even among human beings. Western populations today are exposed to dioxins at doses leading to concentrations of 5 to 100 picograms/g (as TEQ in body fat), and the highest concentrations in accidental or deliberate poisonings have been 10,000 to 144,000 pg/g leading to dramatic but not lethal outcomes. The most relevant toxic outcomes of dioxins both in humans and animals are cancer and

2842-449: Is likely that the TDI for other population groups could be higher. One important cause for differences in different assessments has been carcinogenicity. If the dose-response of TCDD in causing cancer is linear, it might be a true risk. If the dose-response is of a threshold-type or J-shape, there is little or no risk at the present concentrations. Understanding the mechanisms of toxicity better

2940-493: Is neutral overall, but consists of positively charged ions called cations and negatively charged ions called anions . These can be simple ions such as the sodium (Na ) and chloride (Cl ) in sodium chloride , or polyatomic species such as the ammonium ( NH 4 ) and carbonate ( CO 3 ) ions in ammonium carbonate . Individual ions within an ionic compound usually have multiple nearest neighbours, so are not considered to be part of molecules, but instead part of

3038-461: Is possible. These substances cannot easily form organic compounds, and HCl is easily and safely neutralized in the scrubber while CO 2 is vented to the atmosphere. Inorganic chlorides are incorporated into the ash. Scrubber and particulate removal systems manage to capture some of the PCDD/F which forms even in sophisticated incineration plants. These PCDD/Fs are generally not destroyed but moved into

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3136-478: Is relevant in toxicology for two very different reasons. First, it induces several enzymes important in the metabolism of foreign substances, so called xenobiotics . These include both oxidative phase I enzymes and conjugative phase II enzymes, e.g. CYP 1A2, CYP1B1, CYP2S1, CYP2A5, ALDH3, GSTA1, UGT1A1, UGT1A6, UGT1A7 and NQO1. This is in essence a protective function preventing toxic or carcinogenic effects of xenobiotics, but in some conditions it may also result in

3234-567: Is that they only assess hazard, i.e. carcinogenicity at any dose. It is likely that there is a practical safe threshold for the non-genotoxic dioxins, and the present population levels do not possess any risk of cancer. There is thus some agreement on that cancer risk is taken care of as well, if daily intake limits are set to protect from developmental effects. Among fishermen with high dioxin concentrations in their bodies, cancer deaths were decreased rather than increased. All this means that in case of important beneficial food items and breast feeding

3332-643: Is the cause of the other. The main problem is that similar associations can be found with many quite different POPs, which have only long half-lives and tendency to accumulate in lipids in common. This suggests that they may all be related to diet and obesity which are by far the most common causes of type 2 diabetes. Over the years there have been speculations on various effects of dioxins on endometriosis , sexual development, liver function , thyroid hormone levels, white blood cell levels, immune functions, and even learning and intelligence. While some of these effects might be possible after heavy exposures (like in

3430-639: Is therefore not a compound. A compound can be transformed into a different substance by a chemical reaction , which may involve interactions with other substances. In this process, bonds between atoms may be broken and/or new bonds formed. There are four major types of compounds, distinguished by how the constituent atoms are bonded together. Molecular compounds are held together by covalent bonds ; ionic compounds are held together by ionic bonds ; intermetallic compounds are held together by metallic bonds ; coordination complexes are held together by coordinate covalent bonds . Non-stoichiometric compounds form

3528-491: The European Food Safety Agency (EFSA) recommended decreasing tolerable weekly intake (TWI) levels based on the Russian children study. This recommendation can be challenged, because it does not properly consider competing risks following from lost benefits of important and healthy food items such as certain fish. TWI levels are not applied for breast feeding, because benefits of breast milk are judged to be far more important than

3626-768: The University of the Philippines College of Forestry, and was also described in a 1969 issue of The Philippine Collegian , the college's newspaper. Super or enhanced Agent Orange was tested by representatives from Fort Detrick and Dow Chemical in Texas, Puerto Rico, Hawaii, and later in Malaysia, in a cooperative project with the International Rubber Research Institute. Picloram in Agent White and Super-Orange

3724-411: The body burden accumulated during the whole lifetime is high compared with daily doses, and occasional modest exceedances of limit values do not change it much. Therefore, long-term intake is much more important than daily intake. Specifically, the TDI has been assessed to guarantee the safety of children born to mothers exposed to such a daily intake of dioxins all their lifetime prior to pregnancy. It

3822-452: The coordination centre , and a surrounding array of bound molecules or ions, that are in turn known as ligands or complexing agents. Many metal-containing compounds, especially those of transition metals , are coordination complexes. A coordination complex whose centre is a metal atom is called a metal complex of d block element. Compounds are held together through a variety of different types of bonding and forces. The differences in

3920-485: The fly ash . Catalytic systems have been designed which destroy vapor-phase PCDD/Fs at relatively low temperatures. This technology is often combined with the baghouse or SCR system at the tail end of an incineration plant. The European Union limit for concentration of dioxin-like compounds in the discharged flue gas is 0.1 ng/Nm³ TEQ. Both in Europe and in U.S.A., the emissions have decreased dramatically since

4018-569: The food chain . They are eliminated very slowly in animals, e.g. TCDD has a half-life of 7 to 9 years in humans. Incidents of contamination with PCBs are often reported as dioxin contamination incidents since these are of most public and regulatory concern. There are 75 possible congeners of polychlorinated dibenzo -p- dioxins, but only 7 of them have affinity for the aryl hydrocarbon receptor (AH receptor) and are toxic via this mechanism. The crucial structures are so called lateral chlorines in positions 2,3,7, and 8. These 4 chlorines also make

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4116-938: The liver , thymus , and other organs. Some effects such as thymic atrophy are common in many species, but e.g. liver toxicity is typical in rabbits. Low doses . Very few signs of toxicity are seen in adult animals after low doses, but developmental effects may occur at low dioxin levels, including foetal , neonatal , and possibly pubescent stages. Well established developmental effects are cleft palate , hydronephrosis , disturbances in tooth development and sexual development , and endocrine effects. Surprisingly, enzyme induction, several developmental effects and aversion to novel foods occur at similar dose levels in animals that respond differently to acute high-dose toxicity. Therefore, it has been suggested that dioxin effects be divided to type I effects (enzyme induction etc.) and type II effects (lethality, liver damage, anorexia, and tumour promotion). The reason may be different requirements of

4214-449: The oxygen molecule (O 2 ); or it may be heteronuclear , a chemical compound composed of more than one element, as with water (two hydrogen atoms and one oxygen atom; H 2 O). A molecule is the smallest unit of a substance that still carries all the physical and chemical properties of that substance. An ionic compound is a chemical compound composed of ions held together by electrostatic forces termed ionic bonding . The compound

4312-497: The 11,712,860 U.S. gal (44,338,000 L; 9,753,000 imp gal) of Agent Orange (both versions) used from 1965 to 1970. Agent White started to replace Orange in 1966; 145,239,853 U.S. gal (549,792,650 L; 120,937,476 imp gal) of White were used. The only agent used on a large scale in an anti-crop role was Agent Blue, with 142,166,656 U.S. gal (538,159,330 L; 118,378,504 imp gal) used. The bombardment occurred most heavily in

4410-436: The 1980s, by even 90% (see Figure). This has also led to decreases in human body burdens, which is neatly demonstrated by the decrease of dioxin concentrations in breast milk . With the substantial decrease of emissions from municipal waste incinerators, other potentially large sources of dioxin-like compounds, for example from forest and wild fires, have increased relative to industrial sources. They are however not included in

4508-841: The AH receptor requires a planar (flat) structure, only PCB congeners that can rotate freely along the C—C axis between the rings can attach the receptor. Substituents in ortho-positions 2 and 6 prevent rotation and thus hinder the molecule from assuming a planar position. Mono-ortho congeners (one Cl in 2, 2', 6, or 6') have minimal activity. No significant dioxin-like activities have been noticed, if there are two or more o-chlorines. Brominated dioxins and biphenyls have similar properties, but they have been studied much less. Many natural compounds have very high affinity to AH receptors. These include indoles, flavones, benzoflavones, imidazoles and pyridines. These compounds are metabolized rapidly, but continuous intake from food may cause similar receptor activation as

4606-401: The AHR. Some toxic effects (especially of PCBs) may be independent of the AHR, and those are not taken into account by using TEQs. TEFs are also approximations with certain amount of scientific judgement rather than scientific facts. Therefore, they may be re-evaluated from time to time. There have been several TEF versions since the 1980s. The most recent re-assessment was by an expert group of

4704-506: The Arctic. Only a minor portion of PCBs in mixtures are dioxin-like. Other sources of PCDD/F include: Improvements and changes have been made to nearly all industrial sources to reduce PCDD/F production. In waste incineration, large amounts of publicity and concern surrounded dioxin-like compounds during the 1980s-1990s continues to pervade the public consciousness, especially when new incineration and waste-to-energy facilities are proposed. As

4802-896: The Corpuscles, whereof each Element consists, a peculiar size and shape ... such ... Corpuscles may be mingled in such various Proportions, and ... connected so many ... wayes, that an almost incredible number of ... Concretes may be compos’d of them. In his Logick , published in 1724, the English minister and logician Isaac Watts gave an early definition of chemical element, and contrasted element with chemical compound in clear, modern terms. Among Substances, some are called Simple, some are Compound ... Simple Substances ... are usually called Elements, of which all other Bodies are compounded: Elements are such Substances as cannot be resolved, or reduced, into two or more Substances of different Kinds. ... Followers of Aristotle made Fire, Air, Earth and Water to be

4900-459: The Earth. Other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which changes the ratio of elements by mass slightly. A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. A molecule may be homonuclear , that is, it consists of atoms of one chemical element, as with two atoms in

4998-583: The Seveso disaster), these claims are only based on potential exposures of population, not supported by actual measurements of dioxin concentrations. E.g. absorption from bleached tampons claimed to be associated with endometriosis is insignificant compared with daily dioxin intake from food. Dioxins are well established carcinogens in animal studies, although the precise mechanism is not clear. Dioxins are not mutagenic or genotoxic . The United States Environmental Protection Agency has categorised dioxin, and

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5096-683: The TCDD concentrations observed in Agent Purple or Agent Orange. This is a list of the different types of agents used, their active ingredients, and the years they were being used during the Vietnam War as follows: In Vietnam, the early large-scale defoliation missions (1962–1964) used 8,208 U.S. gal (31,070 L; 6,835 imp gal) of Agent Green, 122,792 U.S. gal (464,820 L; 102,246 imp gal) of Agent Pink, and 14,500 U.S. gal (55,000 L; 12,100 imp gal) of Agent Purple. These were dwarfed by

5194-524: The Truth ;; tho' they are not all agreed ... Compound Substances are made up of two or more simple Substances ... So a Needle is simple Body, being made only of Steel; but a Sword or a Knife is a compound because its ... Handle is made of Materials different from the Blade. Any substance consisting of two or more different types of atoms ( chemical elements ) in a fixed stoichiometric proportion can be termed

5292-481: The U.S. government and the manufacturers of the chemical. Dioxins and dioxin-like compounds Dioxins and dioxin-like compounds ( DLCs ) are a group of chemical compounds that are persistent organic pollutants (POPs) in the environment . They are mostly by-products of burning or various industrial processes or, in the case of dioxin-like PCBs and PBBs , unwanted minor components of intentionally produced mixtures. Some of them are highly toxic, but

5390-505: The World Health organization in 2005. Greenpeace and some other environmental groups have called for the chlorine industry to be phased out. However, chlorine industry supporters say that "banning chlorine would mean that millions of people in the third world would die from want of disinfected water". Sharon Beder and others have argued that the dioxin controversy has been very political and that large companies have tried to play down

5488-469: The absolute and relative significance of dairy products and meat have decreased due to strict emission controls, and brought about the decrease of total intake. E.g. in the United Kingdom the total intake of PCDD/F in 1982 was 239 pg/day and in 2001 only 21 pg/day (WHO-TEQ). Since the half-lives are very long (for e.g. TCDD 7–8 years), the body burden will increase almost over the whole lifetime. Therefore,

5586-507: The actual amount or concentration of a congener by its TEF, the product is the virtual amount or concentration of TCDD having effects of the same magnitude as the compound in question. This multiplication is done for all compounds in a mixture, and these "equivalents of TCDD" can then simply be added, resulting in TEQ, the amount or concentration of TCDD toxicologically equivalent to the mixture. The TEQ conversion makes it possible to use all studies on

5684-588: The amount toxicologically equivalent to TCDD, and after this conversion all dioxin-like congeners can be summed up, and the resulting toxicity equivalent quantity (TEQ) gives an approximation of toxicity of the mixture measured as TCDD. Dioxins are virtually insoluble in water but have a relatively high solubility in lipids . Therefore, they tend to associate with organic matter such as plankton, plant leaves, and animal fat. In addition, they tend to be adsorbed to inorganic particles, such as ash and soil. Dioxins are extremely stable and consequently tend to accumulate in

5782-484: The area of the Ho Chi Minh Trail . The rainbow herbicides damaged the ecosystems and cultivated lands of Vietnam, and led to buildup of dioxins in the regional food chain. About 4.8 million people were affected. The environmental destruction caused by this defoliation has been described by Swedish Prime Minister Olof Palme , lawyers, historians and other academics as an ecocide . In addition to testing and using

5880-409: The background levels of dioxins. They do not reach concentrations causing typical dioxin-like toxicity, however. The aryl hydrocarbon receptor (AH receptor) is an ancient receptor, and its many functions have been revealed only recently. It is an over 600-million-year-old protein occurring in all vertebrates, and its homologs have been discovered in invertebrates and insects. It is classified as

5978-572: The best proven effect is chloracne. The suspected effects in adults are liver damage, and alterations in heme metabolism, serum lipid levels, thyroid functions, as well as diabetes and immunological effects . Low exposures. Effects after low exposures such as from food have been difficult to prove. Levels of dioxins in contemporary population are 5 to 20 pg/g (TEQ in fat) and 50 to 100 pg in older people or at least 1000 times lower than those in poisonings (see above). Tooth deformities have been considered plausible after long breast-feeding, when

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6076-408: The best studied TCDD to assess the toxicity of a mixture. This is most useful in regulatory work, but it can also be used in scientific studies. This resembles the common measure of all alcoholic drinks: beer, wine and whiskey can be added together as absolute alcohol, and this sum gives the toxicologically meaningful measure of the total impact. The TEQ only applies to dioxin-like effects mediated by

6174-543: The city. The highest TCDD levels were found in children, up to 56,000 pg/g fat. Acute effects were limited to chloracne, although many animals such as rabbits died after eating contaminated grass. Dental aberrations were found after 25 years in persons exposed as children, and a slightly increased cancer risk was confirmed 35 years later. In line with animal studies, developmental effects may be much more important than effects in adults. These include disturbances of tooth development, and of sexual development. An example of

6272-476: The concentrations may increase five to tenfold from age 20 to age 60. For the same reason, short term higher intake such as after food contamination incidents, is not crucial unless it is extremely high or lasts for several months or years. The highest body burdens were found in Western Europe in the 1970s and early 1980s, and the trends have been similar in the U.S. The most useful measure of time trends

6370-452: The congeners persistent, because they prevent microbial degradation. Additional chlorines make the compounds less potent, but basically the effects remain the same although at higher doses. There are 135 possible dibenzofurans, and 10 in which the lateral chlorines are dioxin-like. There are 209 PCB compounds. Analogously to PCDDs at least two lateral chlorines in each ring in positions 3,4, and/or 5 are needed for dioxin-like activity. Because

6468-408: The control of concentrations in food. In the U.S. young adult female population (age group 20–39), the concentration was 9.7 pg/g lipid in 2001-2002 (geometric mean). Certain professions such as subsistence fishermen in some areas are exposed to exceptionally high amounts of dioxins and related substances. This along with high industrial exposures may be the most valuable source of information on

6566-416: The developmental effects on offspring. Both have been documented at high doses, most accurately in animal experiments. As to developmental effects there is an agreement that the present dioxin levels in many populations are not very far from those causing some effects, but there is not yet consensus on the safe level. As to cancer, there is a disagreement on how to extrapolate the risk from high toxic doses to

6664-473: The dioxin concentrations were high in 1970s and 1980s. When the concentrations decreased during 1990s and 2000s, the effects were no longer seen. According to a study in Russia, sperm counts in 18-19 year old young men were lower when dioxin levels were higher at the age of 8 to 9 years. This was in industrial environments causing relatively high exposures to boys as well as their mothers. The contamination panel of

6762-400: The fixed ratios. Many solid chemical substances—for example many silicate minerals —are chemical substances, but do not have simple formulae reflecting chemically bonding of elements to one another in fixed ratios; even so, these crystalline substances are often called " non-stoichiometric compounds ". It may be argued that they are related to, rather than being chemical compounds, insofar as

6860-405: The formation of tumours caused by other factors, and adversely affect the normal mechanisms for inhibiting tumour growth. Some researchers have also proposed that dioxin induces cancer progression through a very different mitochondrial pathway. As with many toxic endpoints of dioxin, a clear dose–response relationship is difficult to establish. After accidental or high occupational exposures there

6958-508: The four Elements, of which all earthly Things were compounded; and they suppos'd the Heavens to be a Quintessence, or fifth sort of Body, distinct from all these : But, since experimental Philosophy ... have been better understood, this Doctrine has been abundantly refuted. The Chymists make Spirit, Salt, Sulphur, Water and Earth to be their five Elements, because they can reduce all terrestrial Things to these five : This seems to come nearer

7056-629: The health risks of dioxins. Dioxins are absorbed well from the digestive tract if they are dissolved in fats or oils (e.g. in fish or meat). On the other hand, dioxins tend to adsorb tightly to soil particles, and absorption may be quite low: 13.8% of the given dose of TEQs in contaminated soil was absorbed. The same features causing persistence of dioxins in the environment also cause very slow elimination in humans and animals. Because of low water solubility, kidneys cannot excrete them in urine as such. They must first be metabolised to more-water-soluble metabolites, but that metabolism, especially in humans,

7154-631: The herbicides in Vietnam, Laos, and Cambodia, the US military also tested the "Rainbow Herbicides" and many other chemical defoliants and herbicides in the United States, Canada, Puerto Rico, Korea, India, and Thailand from the mid-1940s to the late 1960s. Herbicide persistence studies of Agent Orange and Agent White were conducted in the Philippines. The Philippine herbicide test program was conducted in cooperation with

7252-548: The hormone dehydoepiandosterone (DHEA), which has a role in the determination of male or female sex characteristics. There have been thousands of documented instances of health problems and birth defects associated with rainbow herbicide exposure in Vietnam, where tested levels remain high in the soil, water, and atmosphere, decades after initial exposure. Soldiers exposed to Rainbow Herbicides in Southeast Asia reported long-term health effects, which led to several lawsuits against

7350-424: The mixture of substances associated with sources of dioxin toxicity as a "likely human carcinogen". The International Agency for Research on Cancer has classified TCDD as a human carcinogen (class 1) on the basis of clear animal carcinogenicity and limited human data, and subsequently also 2,3,4,7,8-PCDF and PCB 126 as class 1 carcinogens. The mechanism is thought to be mainly promotion, i.e. dioxins can accelerate

7448-616: The most prominent symptom was chloracne after initial stomach pain indicating hepatitis and pancreatitis . These episodes show that a human being is not as sensitive as the most sensitive animals, since the doses must have been up to 25 μg/kg. Two serious food contamination accidents were caused by PCB oils used in heat exchangers. The PCB oil leaked to rice bran oil consumed by thousands of people in Japan ( Yusho disease 1968) and Taiwan ( Yu-cheng disease 1979). The toxic effects have been attributed to dioxin-like PCBs and PCDFs. Their daily intake

7546-536: The periodic table tend to have similar electronegativities , which means they have a similar affinity for electrons. Since neither element has a stronger affinity to donate or gain electrons, it causes the elements to share electrons so both elements have a more stable octet . Ionic bonding occurs when valence electrons are completely transferred between elements. Opposite to covalent bonding, this chemical bond creates two oppositely charged ions. The metals in ionic bonding usually lose their valence electrons, becoming

7644-654: The potency, but qualitatively the effects remain similar. Therefore, a simple sum of different dioxin congeners is not a meaningful measure of toxicity. To compare the toxicities of various congeners and to render it possible to make a toxicologically meaningful sum of a mixture, a toxicity equivalency (TEQ) concept was created. Each congener has been given a toxicity equivalence factor (TEF). This indicates its relative toxicity as compared with TCDD. Most TEFs have been extracted from in vivo toxicity data on animals, but if these are missing (e.g. in case of some PCBs), less reliable in vitro data have been used. After multiplying

7742-469: The present low exposures. While the affinity of dioxins and related industrial toxicants to the Ah receptor may not fully explain all their toxic effects including immunotoxicity, endocrine effects and tumor promotion , toxic responses appear to be typically dose-dependent within certain concentration ranges. A multiphasic dose–response relationship has also been reported, leading to uncertainty and debate about

7840-445: The production of reactive metabolites that are mutagenic and carcinogenic. This enzyme induction can be initiated by many natural or synthetic compounds, e.g., carcinogenic polycyclic hydrocarbons such as benzo (a) pyrene , several natural compounds, and dioxins. Secondly, AH receptors are involved in the activation or silencing of genes that lead to the toxic effects of high doses of dioxins. Because TCDD at high doses can influence

7938-458: The remote risks of dioxins. A general conclusion may be that safety margins are not very great concerning developmental effects, but toxic effects are not likely at the present population levels of dioxins. A number of cross-sectional studies have shown associations between type 2 diabetes and several POP compounds including dioxins. Such observational studies cannot prove causality, i.e. there may be an association which does not prove that one

8036-444: The same species, with the most notable disparity being between the seemingly similar species of hamster and guinea pig . The oral LD 50 for guinea pigs is as low as 0.5 to 2 μg/kg body weight, whereas the oral LD 50 for hamsters can be as high as 1 to 5 mg/kg body weight. Even between different mouse or rat strains there may be tenfold to thousandfold differences in acute toxicity. Many pathological findings are seen in

8134-439: The scope of the biological systems affected and in the range of dosage needed to bring these about. Acute effects of single high dose dioxin exposure include reduced feed intake and wasting syndrome , and typically a delayed death of the animal in 1 to 6 weeks. By far most toxicity studies have been performed using 2,3,7,8-tetrachlorodibenzo- p -dioxin . The LD 50 of TCDD varies wildly between species and even strains of

8232-441: The seriousness of the problems of dioxin. The companies involved have often said that the campaign against dioxin is based on "fear and emotion" and not on science. Most intake of dioxin-like chemicals is from food of animal origin: meat, dairy products, or fish predominate, depending on the country. The daily intake of dioxins and dioxin-like PCBs as TEQ is of the order of 100 pg/day, i.e. 1-2 pg/kg/day. In many countries both

8330-570: The total inventory due to uncertainties in available data. A more recent study on the environmental effects of accidental fires, including forest fires , estimated the emissions from dioxins (PCDD/Fs) to be about equivalent to those from traffic and municipal waste combustion. Chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities ) containing atoms from more than one chemical element held together by chemical bonds . A molecule consisting of atoms of only one element

8428-426: The toxicity among them varies 30,000-fold. They are grouped together because their mechanism of action is the same. They activate the aryl hydrocarbon receptor (AH receptor), albeit with very different binding affinities, leading to high differences in toxicity and other effects. They include: Dioxins have different toxicity depending on the number and position of the chlorine atoms. Because dioxins refer to such

8526-566: The transactivation domain structure of the AH receptor for different genes. Some of these low-dose effects can in fact be interpreted as protective rather than toxic (enzyme induction, aversion to novel foods). High doses. Toxicity of dioxins at high doses has been well documented after accidents, deliberate poisonings, food contamination episodes, and high industrial exposures. Three women in Vienna, Austria, were poisoned with large doses of TCDD in 1998. The highest concentration of TCDD in fat tissue

8624-517: The transcription of perhaps hundreds of genes, the genes crucial for the multitude of toxic effects of dioxins are still not known very well. Binding of dioxin-like compounds to the AH receptor has made it possible to measure total dioxin-like activity of a sample using CALUX (Chemical Activated LUciferase gene eXpression) bioassay. The results have been comparable to TEQ levels measured by much more expensive gas chromatography-high resolution mass spectrometry in environmental samples. Dioxin toxicity

8722-591: The true role of dioxins in cancer rates. The endocrine disrupting activity of dioxins is thought to occur as a down-stream function of AH receptor activation, with thyroid status in particular being a sensitive marker of exposure. TCDD, along with the other PCDDs, PCDFs and dioxin-like coplanar PCBs are not direct agonists or antagonists of hormones, and are not active in assays which directly screen for these activities such as ER-CALUX and AR-CALUX. These compounds have also not been shown to have any direct mutagenic or genotoxic activity. Their main action in causing cancer

8820-494: The two or more atom requirement, though they often consist of molecules composed of multiple atoms (such as in the diatomic molecule H 2 , or the polyatomic molecule S 8 , etc.). Many chemical compounds have a unique numerical identifier assigned by the Chemical Abstracts Service (CAS): its CAS number . There is varying and sometimes inconsistent nomenclature differentiating substances, which include truly non-stoichiometric examples, from chemical compounds, which require

8918-455: The types of bonds in compounds differ based on the types of elements present in the compound. London dispersion forces are the weakest force of all intermolecular forces . They are temporary attractive forces that form when the electrons in two adjacent atoms are positioned so that they create a temporary dipole . Additionally, London dispersion forces are responsible for condensing non polar substances to liquids, and to further freeze to

9016-421: The variability in their compositions is often due to either the presence of foreign elements trapped within the crystal structure of an otherwise known true chemical compound , or due to perturbations in structure relative to the known compound that arise because of an excess of deficit of the constituent elements at places in its structure; such non-stoichiometric substances form most of the crust and mantle of

9114-588: The variation in responses is clearly seen in a study following the Seveso disaster indicating that sperm count and motility were affected in different ways in exposed males, depending on whether they were exposed before, during or after puberty. In occupational settings many symptoms have been seen, but exposures have always been to a multitude of chemicals including chlorophenols , chlorophenoxy acid herbicides , and solvents . Therefore, definitive proof of dioxins as causative factors has been difficult to obtain. By far

9212-763: The water table and have built up in the tissues of local fauna. However, the contamination has begun to deteriorate, and the forest canopy has regrown somewhat since the Vietnam War. Dioxins are endocrine disruptors and may have effects on the children of people who were exposed. Rainbow herbicides and other dioxin-like compounds are endocrine disruptors, and evidence suggests that they continue to have long-term health consequences many years after exposure. Because they mimic, or interfere with, hormonal function, adverse effects can include problems with reproduction, growth and development, immune function, and metabolic function. As an example, dioxins and dioxin-like compounds influence

9310-418: Was 144,000 pg/g, the highest ever reported in human beings. The main feature was chloracne , a serious skin disease. The victim survived, and other symptoms were modest after initial gastrointestinal symptoms and amenorrhea . Another acute incident was the deliberate poisoning of Victor Yushchenko , then presidential candidate of Ukraine, in 2004. TCDD concentration in fat was 108,000 pg/g. Also in this case

9408-557: Was contaminated by hexachlorobenzene (HCB) a dioxin-like carcinogen. The Canadian government also tested these herbicides and used them to clear vegetation for artillery training. A 2003 study in Nature found that the military underreported its use of rainbow herbicides by 2,493,792 U.S. gal (9,440,030 L; 2,076,516 imp gal). Vietnam remains heavily contaminated by dioxin -like compounds, which are classified as persistent organic pollutants . These compounds remain in

9506-526: Was the most important source of PCDD/Fs. PCB-compounds , always containing low concentrations of dioxin-like PCBs and PCDFs, were synthesized for various technical purposes (see Polychlorinated biphenyls ). They have entered the environment through accidents such as fires or leaks from transformers or heat exchangers, or from PCB-containing products in landfills or during incineration. Because PCBs are somewhat volatile, they have also been transported long distances by air leading to global distribution including

9604-562: Was up to 100,000 times higher than average intake presently. There were many skin problems, chloracne, swelling of eyelids, and hypersecretion of Meibomian glands in the eyes. Babies born to Yusho and Yu-cheng mothers were smaller than normal, they had dark pigmentation and sometimes teeth at birth and tooth deformities. Foetal deaths and miscarriages were common. Perhaps the best known dioxin accident occurred in Seveso, Italy, in 1976. A tank of chlorophenols released its contents to air including many kilograms of TCDD, and contaminated much of

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