Polychlorinated furans PCDD

Chlorinated micropoUutants are harmful for man and environment due to their toxicity, persistence, and bioaccumulation. Persistent compounds are very stable and difficult to get metabolized and mineralized by biological and chemical processes in the environment, and as a result, they have become ubiquitous in water, sediments, and the atmosphere bioaccumulation is the result of the lipophilicity of these compounds. Polychlorinated dibenzodioxins and -furans (PCDD/F) are not produced purposely like many of other chlorinated technical products, such as chlorinated biocides DDT, lindane, and toxaphene. The production and use of persistent organic pollutants (POPs), the dirty dozen has now been banned worldwide by the Stockholm protocol. It should be mentioned that about 3000 halogenated products have now been isolated as natural products in plants, microorganisms, and animals," but the total amount of these products is much smaller compared to xenobiotics. 

Formation of polychlorinated dibenzo(p) dioxins and furans (PCDD/PCDF) in waste combustion has received considerable attention, because dioxins even in very small concentrations are believed to be harmful to humans. Sources of PCDD/PCDF include the waste itself, gas-phase and heterogeneous reactions within the combustion zone, and catalyzed reactions in the low-temperature region downstream [352],... 

Ruokojarvi P, Ettala M, Rahkonen P, Tarhanen J, Ruuskanen J (1995) Polychlorinated Dibenzo-p-dioxins and -Furans (PCDDs and PCDFs) in Municipal Waste Landfill Fires. Chemosphere 30 1697... 

Where analytical methods are available it is largely because of a crossfertilisation of effort from well-established areas of food contaminants work. For example, the steady development since the 1960s of methods of analysis for chlorinated pesticides led to the analysis of food for polychlorinated biphenyls (PCBs) since PCBs were readily detectable by general methods used to analyse food for organochlorine pesticides. The analysis of food for chlorinated dioxins and furans (PCDDs and PCDFs) at the very low levels at which they are found in food is a more recent development, and one that is an important precedent since it arose from interest in environmental contamination rather than because of cross-fertilisation of scientific methodology from an established area of food chemistry. Although dioxins were detectable some years ago at much less sensitivity in some pesticides, it was environmental interest that led to their study at very low levels in the food chain. 

Table 8.9. Polychlorinated dibenzo-/ -dioxins/ dibenzo-/ -furans (PCDDs/PCDFs) concentrations in bird samples from different countries... 

As already introduced in Chapter 1, a widely used application of CA is the toxic equivalence factor (TEF) concept for the assessment of mixtures of polychlorinated dioxins and furans (PCDDs/Fs) (Van den Berg et al. 2006). Under the additional assumption of parallel dose-response curves, doses of specific PCDD/F isomers are all expressed in terms of the dose of a reference chemical, 2,3,7,8-... 

Dioxin A family of chemicals with related properties and toxicity. There are 75 different dioxins, or polychlorinated dibenzodioxins (PCDDs) 135 different furans, or polychlorinated dibenzofurans (PCDFs) and 209 different polychlorinated biphenyls (PCBs). Each different form is called a congener, a member of a family of compounds known chemically as dibenzo-p-dioxins. Concern about them arises from their potential toxicity as contaminants in commercial products. Tests on laboratory animals indicate that it is one of the more toxic anthropogenic (man-made) compounds a term used interchangeably with 2,3,7,8-tetrachlorodibenzo-p-dioxin or TCDD Disease prevention Measures used to prevent a disease or reduce its severity Dispersoids The particles of a dispersion... 

These chemicals have received intense international attention in recent years because of their ubiquity, persistence, high bioaccumulation potential and harmful biological effects. Under the Stockholm Convention on POPs (see Chapter 1), 12 chlorinated chemical substances have been banned or severely restricted. These include dioxins and furans (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, PCDD/Fs),... 

In response to the continuing discovery of the persistence, bioaccumulative properties, and toxicity of POPs, regional, national and international policies ban the intentional production of compounds, such as polychlorinated biphenyls (PCBs), several organochlo-rine pesticides, such as mirex and dieldrin, and the brominated flame retardants poly-brominated diphenyl ethers (penta-BDE and octa-BDE, and most recently, deca-BDE). Policies and programs have also targeted the unintentional production and release of POPs such as polychlorinated dibenzodioxins and furans (PCDD/Fs). Evidence of the success of these policies has been seen in immediate reductions of air concentrations, followed by declining concentrations in water bodies, soils, biota and our food supplies... 

Many of the toxic and biological effects induced by polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and PCBs such as carcinogenesis, reproductive disturbances and immunotoxic effects are believed to be mediated via the hepatic cytosolic aryl hydrocarbon receptor (Ah receptor) [254,255]. Based on in vitro and in vivo studies, the toxicity of individual organochlorines have been determined relative to 2,3,7,8-tetrachlorodibenzo-p -dioxin (TCDD) and expressed as toxic equivalency factors (TEFs) [254, 256]. In addition to PCDD/F, structurally related PCBs and PCNs bind to the Ah receptor. After binding to the Ah-receptor, the receptor-ligand complex is transferred into the nucleus where it binds to specific DNA sequences and causes transcription of structural genes, which in turn causes synthesis of various cytochrome P4501A1-dependent enzymes such as ethoxyresorufin O-deethylase (EROD) and aryl hydrocarbon hydroxylase (AHH). TEFs for PCNs have been estimated from enzyme-induction assays of EROD and AHH [10, 257] and Luciferase assays in rat cells [12] cf. Table 4. 

Fig. 7.25 Chemical structures of the contrasting persistent organic pollutants (POPs), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and furans (PCDDs/PCDFs), p,p -dichlorodiphenyl trichloroethane (DDT) and hexachlorocyclohexane (HCH). Symbols x and y indicate the possible number of chlorines attached to the ring structures.

In June 1997, an expert meeting was organized by the World Health Organization (WHO) to reach a consensus about TEFs for human and wildlife of polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) and PCBs. " " Twenty-nine congeners of these compound classes were... 

Dioxins are a family of the most toxic chlorinated organic compounds known to science, numbering around 75 dioxins and 135 related furans. These can cause cancer and are ECD for humans, even at very low exposure levels, since minute amounts, can bio-accumulate due to their ease of solubility in body fat (dioxins are hydrophobic, water-hating and lipophilic, fat-loving ). Number and position of chlorine atoms in the molecule has a considerable effect on toxicity, and 17 dioxins are classed as highly toxic. These include polychlorinated dioxins (PCDD) and dibenzofurans (PCDF) which are by-products of the chlorine bleaching of paper, the burning of chlorinated hydrocarbons (such as pentachlorophenol, PCB, and PVC) and the incineration of municipal/medical... 

A large number of pubUcations have resulted from research on environmental appHcations of GC-MS. The compounds most commonly analyzed include alkanes, PAHs, pesticides, volatile organic compounds (VOCs) including off-flavor and water disinfection by-products (DBPs), PCBs, polychlorinated dibenzo-p-dioxins, and furans (PCDDs/Fs), as well as other ED chemicals such as phthalates and short ethoxy alkylphenol ethoxylate. GC-MS is also the technique of choice for the analysis of emerging contaminants, such as polybrominated diphenyl ethers (PBDEs) or polychlorinated alkanes, as well as for the analysis of some pharmaceuticals and organo-metallic compounds. 

MS has been the leading technique used in dioxin analysis. Until the 1990s, ultratrace determinations of polychlorinated dibenzo-p-dioxins and furans (PCDDs/Fs) were routinely performed using GC-HRMS, operating in the El mode (electron energy... 

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