Polyhalogenated aromatic chemicals

A particular instance of iron overload being associated with liver injury, with free radicals again being implicated, is the hepatic porphyria and hepatocarcinoma induced by polyhalogenated aromatic chemicals. This is described separately below. 

Polyhalogenated Aromatic Chemicals, Iron and hepatic Porphyria... 

Murk, A.J., T.J. Boudewijn, P.L. Meininger, A.T.C. Bosveld, G. Rossaert, T. Ysebaert, P. Meire, and S. Dirksen. 1996. Effects of polyhalogenated aromatic hydrocarbons and related contaminants on common tern reproduction integration of biological, biochemical, and chemical data. Arch. Environ. Contam. Toxicol. 31 128-140. 

Dioxins (PCDDs) and furans (PCDFs) are polyhalogenated aromatic hydrocarbons of high toxicity. There are a total of 210 different congeners 75 dioxin congeners and 135 furan congeners, of which 17 are potentially toxic. Dioxins and furans are now found prevalent in air, water, and soil in almost all natural environments. PCDD/Fs are strongly bound to organic matter, where half-life in soil has been estimated at 10-20 years (Ryan et al., 1987). PCDD/Fs enter the environment primarily as unintentional byproducts of combustion and chemical processes. 

In retrospect, the development and standardization of S-9 has centered around a limited number of chemical types, i.e., iV-nitrosamines, aromatic amines, and polycyclics. Accordingly, the ability of microbial systems supplemented with S-9 to detect these chemicals has been rather consistent. However, the converse also appears true chemicals, other than those types with which the testing has been standardized, that are metabolized in vivo to their active forms are not as consistently detected in such in vitro testing. While further discussion of this point is reserved for later, suffice it here to note that, in general, poorly activated types include azonaphthol dyes carbamyl and thiocarbamyl compounds phenyls polyhalogenated aromatics, cyclics, and aliphatics benzodioxoles and symmetrical hydrazines. 

Quite extensive investigations have been directed to the biodegradation of heterocyclic aromatic compounds since a number of these are constituents of crude oil and creosote (Sundstrom et al. 1986 Herod 1998), some are used as agrochemicals, and many of them are important chemical intermediates. On the other hand, the polyhalogenated dibenzo-l-4-dioxins and dibenzofurans that have not been deliberately produced may be said to have achieved notoriety. Reference may be made to a more extensive review (Neilson and Allard 1998). 

The purpose of this chapter is to give an overview of the chemical and biological processes that control the reactivity of Fe(II) in heterogeneous aqueous systems with respect to pollutant transformation. To this end, we will evaluate data collected in various laboratory systems as well as field studies. Two classes of model compounds with complementary properties will be used to monitor the reactivity of Fe(II) species in the various systems. Nitroaromatic compounds (NACs) primarily served to characterize the systems in terms of mass and electron balances. Reduction of NACs by Fe(II) species results in only a few major products (aromatic amines and hydroxy-lamines) which can be easily quantified by standard HPLC-UV methods in the low liM range. Polyhalogenated aliphatic compounds (PHAs) were used if little perturbation of the systems in terms of electron transfer to the organic substrates was crucial. Reduction of PHAs requires fewer electrons than nitro reduction and PHAs can be quantified by standard GC-ECD methods in the low ppb range. 

Chlorinated paraffins are claimed to be one of the lowest cost FRs besides the hydrated metal oxides. They can be used with antimony oxide as FRs in unsaturated polyester resin systems. Special grades have been developed by Dover Chemical in its Hordaresin and Chlorez ranges for flame retarding high-impact polystyrene, offering an absence of polyhalogenated biphenyls or dioxins, low cost, improved melt flow, and better UV stability than aromatic brominated FRs. They are also used in rubber compounds, where they can also improve tensile and tear properties of neoprene, SBR, and nitrile, and in EPDM rubber for electrical or roofing products. 

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