Dioxins, aromaticity

Dioxins aromaticity, 3, 945 deprotonation, 3, 972 electronic energy levels, 3, 946 electrophilic reactions, 3, 965 half-wave potential, 3, 968... 

Another potential source for the more toxic dioxin congeners is the photoreduction of the higher chlorinated dioxins, i.e. the octa-chloro and heptacholoro congeners, to the lower chlorinated isomers. There are conflicting results concerning which positions are photo-reduced on the dioxin aromatic rings. If the 1,4,6,9-positions are most rapidly reduced, toxic tetra, penta and hexachloro isomers (2,... 

The biological properties of dioxin include an ability to bind to a protein known as the AH (aromatic hydrocarbon) receptor Dioxin IS not a hydrocarbon but it shares a certain structural property with aromatic hydrocarbons Try constructing molecular models of dioxin and anthracene to see these similarities... 

Chlorobenzenes are stable compounds and decompose slowly only under excess heating at high temperatures to release some HCl gas and traces of phosgene. It is possible, under certain limited conditions of incomplete combustion or pyrolysis, to form polychlorinated dibenzo-/)-dioxins (PCDDs) and dibenzofurans (PCDFs) from chlorobenzenes (Cm OROCARBONS and cm OROHYDROCARBONS, toxic aromatics). 

In a series of papers (175) comparing chlorination and o2oni2ation, reactive and acid dyes were readily destroyed, but direct and disperse dyes reacted more slowly o2one was more effective in some instances. Although chlorination is cheaper than o2oni2ation, the possible formation of chlorinated compounds such as dioxin and its environmental impact caimotbe overlooked (see Chlorocarbonsandchlorohydrocarbons, TOXIC AROMATICS). 

A number of airborne chemical contaminants are EDs, particularly products of combustion such as dioxins and polycyclic aromatic hydrocarbons. ... 

Halogenated chemicals Polycyclic aromatic hydrocarbons Aliphatics Substituted benzenes Halogenated aliphatics Dioxins and furans... 

The biological properties of dioxin include an ability to bind to a protein known as the AH (aromatic hydrocarbon) receptor. 

The biological activity of several halogenated herbicides in water is destroyed by ultraviolet irradiation (18). Irradiation seems to be a promising method for decontaminating small quantities of pesticides. The chemical similarity between the chlorinated dioxins and other chlo-rinted aromatic compounds suggested that if there were parallels in their photochemical behavior, sunlight might destroy dioxins in the environment. 

Industrial workers involved in chlorinated aromatic production including chlorophenol suffered dioxin-induced chloracne 2,3). Chloracne and other serious health disturbances have been attributed to polychloro-dibenzo-p-dioxins in workers involved in manufacturing 2,4,5-T 4, 5). Dioxins are toxic to chick embryos, guinea pigs, rabbits, and monkeys 6, 7, 8, 9, 10). 

Hammel KE, B Kalyanaraman, TK Kirk (1986) Oxidation of polycyclic aromatic hydrocarbons and dibenzo(p)dioxins by Phanerochaete chrysosporium ligninase. J Biol Chem 261 16948-16952. 

Other componnds have also been examined as primers for the dechlorination of hexachloro to nonachloro PCB congeners (DeWeerd and Bedard 1999) a nnmber of snbstituted brominated monocyclic aromatic componnds were examined, and 4-bromobenzoate was effective—though less so than 2,6-dibromobiphenyl. In contrast, the chlorobenzoates that are metabolites of aerobic degradation were ineffective. The positive effect of brominated biphenyls in priming the anaerobic dechlorination of CBs has also been encountered in the dechlorination of octachlorodibenzo[l,4] dioxin to the 2,3,7,8 congener indnced by 2-bromodibenzo[l,4]dioxin in the presence of (Albrecht... 

Anaerobic dehalogenation has also been observed in aromatic ethers including polychlorinated dibenzo[l,4]dioxins (Fennell et al. 2004 Yoshida et al. 2005). The anaerobic debromination of decabromodiphenyl ether is considered here since it is analogous to the dehalogenation of polyhalogenated biphenyls. 

A wide variety of xenobiotics, such as polycyclic aromatic hydrocarbons or dioxins, are analyzed in human body fluids for the investigation of environmental and occupational exposure. 

Toxic compounds polychlorinated biphenyls, polycyclic aromatic hydrocarbons, organochlorine pesticides, chlorinated pesticides, dioxins, veterinary drug residues, hormone residues, aflatoxins, toxic compounds in shellfish. Compoimds of nutritional significance in foods vitamins, fat, lipids, carbohydrates, protein, energy-calorific value, proximates, dietary fibre, ash. Other compounds hormones in blood serum... 

CRMs for Contaminants in Environmental Matrices For nearly two decades NIST has been involved in the development of SRMs for the determination of organic contaminants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and chlorinated pesticides in natural environmental matrices such as fossil fuels (Hertz et al.1980 Kline et al. 1985), air and diesel particulate material (May and Wise 1984 Wise et al. 2000), coal tar (Wise et al. 1988a), sediment (Schantz et al. 1990, 1995a Wise et al. 1995), mussel tissue (Wise et al. 1991 Schantz et al. 1997a), fish oil, and whale blubber (Schantz et al. 1995b). Several papers have reviewed and summarized the development of these environmental matrix SRMs (Wise et al. 1988b Wise 1993 Wise and Schantz 1997 Wise et al. 2000). Seventeen natural matrix SRMs for the determination of organic contaminants are currently available from NIST with certified and reference concentrations primarily for PAHs, PCBs, chlorinated pesticides, polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofiirans (PCDFs) see Table 3.11. 

Table 1 Concentrations of chlorinated polycyclic aromatic hydrocarbons (CIPAHs), polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) in ambient air, soil, and human samples collected from e-waste recycling and reference sites in China... 

Our electrostatic potential analyses of TCDD, 22-25, and a number of other dibenzo-p-dioxins have allowed us to make some generalizations about the F(r) pattern that appears to lead to high biological activity for this class of halogenated aromatics. These are listed below ... 

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