Biodiversity Int J. DOI: Download PDF. Persistent, bioaccumulative and toxic chemicals PBTs are substances that can build up to levels that can be harmful to human and ecological health.
These contaminants may travel long distances in the atmosphere and can move readily from land to air and water. The accumulation of such chemicals in organisms from the surrounding environment through absorption, ingestion and inhalation may cause severe health issues. Dioxin is formed as an unintentional by-product of many industrial processes involving chlorine such as waste incineration, chemical and pesticide manufacturing, treatment of hazardous material and pulp and paper bleaching.
The potential for health risks due to the cancer-promoting, immunomodulating and teratogenic activities of dioxins in rodents has raised concerns over their presence in the human food chain. There is an urgent need of taking attention on sources of emission of dioxin and its mitigation measures.
In this chapter, the sources, its origin and toxicity assessment of dioxin has been presented along with 3 case studies. Keywords: dioxin, epa, toxic equivalents, bioaccumulation, immunoglobulin.
The term dioxin refers to a group of chemical compounds sharing certain similar structures and biological characteristics. Dioxin compounds are not created intentionally, but are formed inadvertently by a number of human and natural activities.
These activities include combustion and incineration, forest fires, chlorine bleaching of pulp and paper, certain types of chemical manufacturing and processing and other industrial processes. One form, 2,3,7,8-tetra-chlorodibenzo-p-dioxin 2,3,7,8-TCDD is considered the most toxic form. It is also the most studied form. Bioaccumulation is the accumulation of chemicals in organisms from the surrounding environment through absorption, ingestion and inhalation. Because of this, they are more prevalent in animals with body fat, soils and sediments than they are in water.
The same goes for other wildlife. Dioxin works its way to the top of the food chain. Any one particular member of the same chemical family, e. Group of structurally related chemicals that have the same degree of chlorination.
For example, there are eight homologues of CDDs, monochlorinated through octochlorinated. Substances that belong to the same homologous class. For example, there are 22 isomers that constitute the homologues of TCDDs.
Denoted by unique chemical notation. For example, 2,4,8,9-tetrachlorodibenzofuran is referred to as 2,4,8,9-TCDF. The majority of toxic dioxin is and has been derived from industrial chlorination processes, incineration of municipal waste and production of certain herbicides. Dioxin is formed as an unintentional by-product of many industrial processes involving chlorine such as waste incineration, chemical and pesticide manufacturing and pulp and paper bleaching.
Dioxin is formed by burning chlorine-based chemical compounds with hydrocarbons. The major source of dioxin in the environment comes from waste-burning incinerators of various sorts and also from backyard burn-barrels. Dioxin pollution is also affiliated with paper mills which use chlorine bleaching in their process and with the production of Polyvinyl Chloride PVC plastics and with the production of certain chlorinated chemicals like many pesticides.
The major sources of dioxin are in our diet. Since dioxin is fat-soluble, it bioaccumulates, climbing up the food chain. In fish, these toxins bioaccumulate up the food chain so that dioxin levels in fish are , times that of the surrounding environment. Dioxin is released by paper mills, by metal smelters, by many chemical plants, by many pesticide factories and by all incinerators. The destruction of hazardous waste in cement kilns, including chlorinated hydrocarbons have been analyzed by many researchers and found more than In the preheater region red , raw meal is added, heated with the hot gas coming from rotary kiln and calcination occurs in this region.
The organic material present in the raw meal, volatilize in the preheater zone and become available in the gas stream. Usually there is enough chlorine present in the raw meal to maintain the formation reactions of the chlorinated organic compounds chlorophenols, chlorobenzene etc. The temperature and oxygen concentration may also be responsible for the formation of dioxins in APCD.
APCD such as electrostatic precipitator ESP is used in cement industries to remove the particulate matter from the flue gas. This particulate matter may adsorb some dioxins on their surfaces. In modern preheater kilns, the emission is lower because of lower temperature of APCD.
The raw gases from the rotary kilns go through the preheater then through raw mill dryer to heat the raw meal, enter into APCD and then stack gas. Karstensen et al. Cement kiln dust CKD containing adsorbed dioxins collected and reintroduced into the process along with raw meal.
Once dioxins are produced, they will circulate between gaseous and particle adsorbed form. Homologue profile provides the information about the relative proportions of mono to Oct-chlorinated compounds and simply described as a single number indicating the average degree of chlorination.
Some studies show that homologue profile differs if there are changes in fuel composition and combustion conditions. The lipophilic nature of dioxins results in higher concentrations in the fat of animal and fish products and their excretion via milk secretion in dairy cattle may result in relatively high concentrations of dioxin contamination in high-fat dairy products.
Surface contamination of plant foods and soil due to deposition of atmospheric emissions may also be a significant direct source of dioxin ingestion for livestock and thereby an indirect source of dioxin for humans. Despite numerous epidemiological studies, dioxin has not been conclusively determined to be problematic for humans.
Certain management practices such as trimming fat from meat, consuming low-fat dairy products and simply cooking food can substantially decrease exposure to dioxin compounds. The EPA report confirmed that dioxin is a cancer hazard to people. In , the International Agency for Research on Cancer IARC , part of the World Health Organization, published their research into dioxins and furans and announced on February 14, , that the most potent dioxin, 2,3,7,8-TCDD, is a now considered a Group 1 carcinogen, meaning that it's a known human carcinogen.
In addition to cancer, exposure to dioxin can also cause severe reproductive and developmental problems at levels times lower than those associated with its cancer causing effects. Dioxin is well-known for its ability to damage the immune system and interfere with hormonal systems.
Dioxin exposure has been linked to birth defects, inability to maintain pregnancy, decreased fertility, reduced sperm counts, endometriosis, diabetes, learning disabilities, immune system suppression, lung problems, skin disorders, lowered testosterone levels and much more.
A very large proportion of dioxin comes from human sources. Counting around the carbon rings, those with chlorines at positions 2, 3, 7, and 8 are toxic see figure 1. The dioxin-like PCBs have both biphenyl rings in the same plane flat appearance , which allows them to act like dioxins in the body. PCBs are manufactured products, but they are no longer produced in the United States.
The most studied and most toxic of all dioxins is 2,3,7,8-tetrachlorodibenzo-p-dioxin. Pure dioxin looks like white crystalline needles. In the environment, however, it generally is dispersed and attached to soil and dust particles and is invisible to the eye. Industrial activities: Dioxin is not produced or used commercially in the United States.
It is a contaminant formed during the production of some chlorinated organic compounds, including a few herbicides such as Silvex. Over the past decade, EPA and industry have been working together to dramatically reduce the production of dioxin and its release to the environment.
Although environmental levels of dioxins have decreased in the last 30 years, dioxins are extremely persistent compounds and break down very slowly. In fact, a large part of current exposures to dioxins in the United States is due to releases that occurred decades ago e.
Even if all human-generated dioxins were eliminated, low levels of naturally produced dioxins would remain. EPA and its government partners are looking for ways to further reduce dioxins entering the environment and to reduce human exposure to them.
Burning: Combustion processes such as waste incineration commercial or municipal or burning fuels like wood, coal or oil form dioxins. Dioxins are formed as a result of combustion processes such as The report also acknowledges the need for more data on natural sources, such as forest fires, that can form dioxins.
Bleaching: Chlorine bleaching of pulp and paper and other industrial processes can create small quantities of dioxins in the environment. Learn more about dioxin in drinking water from this table of regulated drinking water contaminants.
Dioxins are highly toxic and can cause cancer, reproductive and developmental problems, damage to the immune system, and can interfere with hormones. Dioxins can cause developmental problems in children, lead to reproductive and infertility problems in adults, result in miscarriages, damage the immune system, and interfere with hormones. Exposure to dioxins has widespread effects in nearly every vertebrate species, at nearly every stage of development, including in the womb.
Dioxins are a family of compounds that share distinct chemical structures and characteristics. Numerous dioxin-like compounds have been identified that are considered to have significant toxicity and can cause disease. The singular term dioxin refers to the most toxic compound, TCDD. NIEHS researchers continue to explore the detailed chemical pathway through which dioxin damages the body, but scientists are now confident that the first step takes place when dioxin binds to an intracellular protein known as the aryl hydrocarbon receptor AhR.
When that happens, the AhR can alter the expression, or function, of certain genes. The resulting cellular imbalance leads to a disruption in normal cell function and ultimately adverse health effects.
About compounds in the environment act on the body through the AhR receptor. Public health officials around the world are concerned about the combined effects of multiple chemicals that activate the AhR, and are developing health standards that take into account the fact that people are exposed to mixtures of DLCs, not just one at a time.
The public health threats posed by dioxins were highlighted dramatically in the public consciousness in the late s and early s. Newspapers and television broadcasts were full of stories about ailing veterans who had been exposed to dioxins through Agent Orange, an herbicide and defoliant used in the Vietnam War.
Research supported by NIEHS and many others, examining the link between dioxin and serious illnesses, has helped lead the U.
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