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Dioxins Dioxin is the common name used to refer to the chemical 2,3,7,8-tetrachlorodibenzo-p-dioxin or TCDD. In addition to dioxin itself there are other compounds, such as the polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and some polychlorinated biphenyls (PCBs), that have similar structures and activity as dioxin. These are often commonly referred to as dioxin-like compounds or "dioxins". Dioxins are chemical contaminants that have no commercial usefulness by themselves. They are formed during combustion processes, such as waste incineration, forest fires and backyard trash burning, and during manufacturing processes such as herbicide manufacture and paper manufacture. PCBs can be transported by various environmental media, including air and water, spreading contamination to other areas. Wildlife and people are constantly exposed to dioxins through ingestion of dioxins that are present at low levels as environmental contaminants in food. Although they are at low levels in food , some dioxins are very slowly removed from the body and therefore they accumulate in fat tissue. In laboratory animals, dioxins are highly toxic, cause cancer, and alter reproductive, developmental and immune function. The way in which dioxin affects cells is similar in some way to the way in which hormones such as estrogen work. Dioxin enters a cell and binds to a protein present in cells known as the Ah receptor. The receptor when bound to dioxin can then bind to DNA and alter the expression of some genes. This can lead to alterations in the level of specific proteins and enzymes in the cell. While it is not known exactly how changes in the levels of these different proteins cause the toxicity of dioxin, it is believed by most scientists that the initial binding of dioxin the Ah receptor is the first step. (Summary from: US National Institute of Health, National Institute of Environmental Health Sciences (NIEHS). Dioxin Research at the National Institute of Environmental Health Sciences (NIEH). 2/28/2006). Organophosphates These pesticides affect the nervous system by disrupting the enzyme that regulates acetylcholine, a neurotransmitter. Most organophosphates are insecticides. They were developed during the early 19th century, but their effects on insects, which are similar to their effects on humans, were discovered in 1932. Some are very poisonous (they were used in World War II as nerve agents). However, they usually are not persistent in the environment (1). (1) US Environmental Protection Agency. Types of Pesticide - Chemical Pesticides. Summary from: US National Institute of Health, National Institute of Environmental Health Sciences (NIEHS). Dioxin Research at the National Institute of Environmental Health Sciences (NIEH). 2/28/2006). Hydrocarbons Hydrocarbons are compounds that contain only carbon and hydrogen. They are classified as aliphatic or aromatic. Aliphatic hydrocarbons are not linked together to form a ring. Compounds include the alkanes, alkenes, and alkynes, and substances derived from them by replacing one or more hydrogen atoms by atoms of other elements or groups of atoms. Aromatic hydrocarbons have elements linked together in rings. Polycyclic aromatic hydrocarbons (PAHs) Polycyclic aromatic hydrocarbons (PAHs) are a family of chemical compounds made up of carbon and hydrogen atoms, with a molecular structure consisting of at least two fused aromatic rings, each with five or six carbon atoms. The PAH family includes about 100 substances, differing in the number and position of their rings. PAHs are generally formed from the incomplete combustion of organic matter. Today, most of the PAHs present in the environment come from human activities. PAHs can enter the aquatic environment directly, through industrial and municipal effluents, accidental crude oil spills and PAH emissions from creosote treated materials used in water (for example, on pilings). Nearly all types of organic fuel combustion can produce PAHs. The most important sources are the incomplete combustion of fossil fuels from domestic heating systems and transportation (car exhaust fumes), garbage incineration, aluminum reduction smelting for aluminum production, catalytic cracking of crude oil and coal liquefaction and gasification. All these human activities release PAHs into the atmosphere, where they tend to adhere to particles in suspension, some of which will enter the aquatic environment through atmospheric fallout. Owing to their low solubility and high affinity for particulate matter, PAHs are not usually found in water in notable concentrations. Their presence in surface water or groundwater is an indication of a source of pollution. Polybrominated diphenyl ethers (PBDE) Polybrominated diphenyl ethers (PBDE) are a class of widely used fire retardants most commonly employed in building materials, textiles, furnishings, electronics, and plastics. Because they are physically combined (not chemically bound) with materials, PBDEs can migrate out of products over time and into the environment. Environmental release of PBDEs occurs in production waste streams, municipal waste incineration and treatment, and from landfills. PBDEs accumulate in fat tissue, and have been detected in tissues of humans and both aquatic and terrestrial wildlife. Because of their tendency to be stored in the tissue of plants and animals, PBDEs are passed through the food chain, putting top predators at greater risk of higher exposures. Monitoring studies indicate that PBDE concentrations in soil, sediment, humans, and wildlife are increasing. A retrospective study of herring gull eggs collected from the Great Lakes from 1981 to 2000 found that concentrations increased exponentially, with a doubling time of 2-3 years (Norstrom et al 2002). Research into the effects of wildlife exposure to PBDEs has just begun. While PBDEs do not appear to be acutely toxic, early studies have found effects to physiological and reproductive parameters in the lab. More research is required to determine the effects of chronic exposure to environmentally-relevant levels of these contaminants in the field. Norstrom R.J., M. Simon, J. Moisey, B. Wakeford, and D.V.C. Weseloh. 2002. Georgaphic distribution (2000) and temporal trends (1981-2000) of brominated diphenyl ethers in Great Lakes herring gull eggs. Environmental Science and Technology 36:4783-4789. Acute Toxicity: The ability of a substance to cause severe biological harm or death soon after a single exposure or dose. Also, any poisonous effect resulting from a single short-term exposure to a toxic substance. EPA — Terms of Environment: Glossary, Abbreviations and Acronyms
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