Aromatic halogen compounds polychlorinated biphenyls

The quantitative environmental analysis of surfactants, such as alcohol ethoxylates, alkylphenol ethoxylates (APEOs) and linear alkylbenzene sulfonates (LASs), is complicated by the presence of a multitude of isomers and oligomers in the source mixtures (see Chapter 2). This issue bears many similarities to the quantitation problems that have occurred with halogenated aromatic compound mixtures, e.g. polychlorinated biphenyls (PCBs) [1]. 

Such xenobiotics as aliphatic hydrocarbons and derivatives, chlorinated ahphatic compounds (methyl, ethyl, methylene, and ethylene chlorides), aromatic hydrocarbons and derivatives (benzene, toluene, phthalate, ethylbenzene, xylenes, and phenol), polycyclic aromatic hydrocarbons, halogenated aromatic compounds (chlorophenols, polychlorinated biphenyls, dioxins and relatives, DDT and relatives), AZO dyes, compounds with nitrogroups (explosive-contaminated waste and herbicides), and organophosphate wastes can be treated effectively by aerobic microorganisms. 

This technology has been used to treat polychlorinated biphenyls (PCBs), halogenated and nonhalogenated solvents, semivolatile organic compounds (SVOCs), polynuclear aromatic hydrocarbons (PAHs), pesticides, herbicides, fuel oils, benzene, toluene, ethylbenzene, and xylenes (BTEX), and mercury. This system has also treated Resource Conservation and Recovery Act (RCRA) hazardous wastes such as petroleum refinery wastes and multisource leachate treatment residues to meet RCRA Land Disposal Restrictions (LDR) treatment standards. 

Aromatic compounds are especially stable and are, therefore, important persistent pollutants. They include the polyaromatic hydrocarbons (PAHs), and may be halogenated, such as the polychlorinated biphenyls (PCBs) and many pesticides. Also included are the substituted benzenes, such as phenol. A large body of literature has examined aromatic radiation chemistry [22— 38]. The discussion that follows examines benzene and substituted benzenes as a model for the radiolysis of more complicated aromatic compounds. 

The photocatalytic degradation of chlorophenols on ZnO has also been demonstrated [127]. The photocatalytic degradation of other chlorinated aromatic compounds [127], phenol [128-134], fluorinated aromatic compounds [135], and other substituted phenols and aromatic compounds [Izumi 1981, 738 Matthews 1984, 2386 Abdullah 1990, 2099 [136-141] have been demonstrated. The degradation of halogenated aromatic pollutants such as polychlorinated biphenyls (PCBs) [142] and polybrominated dibenzofiirans [143] has also been attempted. 

From these inventories and data, it is clear that society is facing an enormous problem of contamination. Many of the polluting compounds that are continuously dispersed are products of industrial activities such as phenols and halogenated phenols, polycyclic aromatic hydrocarbons (PAH s), endocrine disruptive chemicals (EDC), pesticides, dioxins, polychlorinated biphenyls (PCB s), industrial dyes, and other xenobiotics. In this chapter, we critically review the literature information on the enzymatic transformation of these polluting xenobiotics. This work is focused on peroxidases as enzymes able to transform a variety of pollutant compounds with the aim to reduce their toxicity and their environmental impact. 

It is well known that immunosuppression is caused by a variety of hydrocarbons such as benzene, polycyclic aromatic hydrocarbons and halogenated aromatic hydrocarbons. Thus, human exposure to polychlorinated biphenyls (PCBs) in Japan (Yusho accident) and China has been associated with increased respiratory infections and decreased levels of immunoglobulins in serum. In animals exposed to these compounds there is atrophy of both primary and secondary lymphoid organs, lower circulating immunoglobulins and decreased antibody responses after exposure to antigens. Similarly, the exposure of both humans and farm animals to polybrominated biphenyls, which occurred in Michigan in 1973, resulted in depressed immune responses. 

A further example for the analysis of trace levels of pollutants is the determination of polychlorinated dibenzo-dioxins and polychlorinated dibenzofurans in milk. The method includes gel permeation chromatography, alumina cleanup, and porous graphitized carbon chromatography, followed by analysis by GC/high-resolution MS. Moreover, the potential of porous graphitic carbon as an HPLC adsorbent for the isolation of halogenated aromatic compounds has been demonstrated by the fractionation of polychlorinated biphenyls (PCBs), chlorinated pesticides, polychlorinated dibenzo-p-dioxins (PCDDs), and... 

Polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) are chemically classified as halogenated aromatic hydrocarbons. The chlorinated and brominated dibenzodioxins and dibenzofurans are tricyclic aromatic compounds with similar physical and chemical properties, and both classes are similar structurally. Certain of the PCBs (the so-called coplanar or mono-ortho coplanar congeners) are also structurally and conformationally similar. The most widely studied of these compounds is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). This compound, often called simply dioxin, represents the reference compound for this class of compounds. The structure of TCDD and several related compounds is shown in Figure 4.1. 

This study was undertaken to test the ability of our previous molecular connectivity models to accurately predict the soil sorption coefficients, bioconcentration factors, and acute toxicities in fish of polycyclic aromatic hydrocarbons (PAHs), alkylbenzenes, alkenylbenzenes, chlorobenzenes, polychlorinated biphenyls, chlorinated alkanes and alkenes, heterocyclic arid substituted PAHs, and halogenated phenols. Tests performed on large groups of such compounds clearly demonstrate that these simple nonempirical models accurately predict the soil sorption coefficients, bioconcentration factors, and acute toxicities in fish of the above compounds. Moreover, they outperform traditional empirical models based on 1-octanol/ water partition coefficients or water solubilities in accuracy, speed, and range of applicability. These results show that the molecular connectivity models are a very accurate predictive tool for the soil sorption coefficients, bioconcentration factors, and acute toxicities in fish of a wide range of organic chemicals and that it can be confidently used to rank potentially hazardous chemicals and thus to create a priority testing list. ... 

Many commercial products are complex chemical or physical mixtures. In some cases the use of the type of search scheme described above is not always useful. Sometimes, all that is required is a broad based characterization or a generic identity in terms of a product type. A good example is a polychlorinated biphenyl (a PCB), such as the Arochlor 1254 shown in Figure 8. This time the identification of the individual component polychlorinated compounds would not be useful. Therefore in this case a normal absolute scoring scheme is preferred where the material is treated as a single entity. The computer interpretation (Table 6) accurately classifies the sample as an aromatic material with multiple halogen (ring) substituents. 

Aryl halides tend to be chemically unreactive and include persistent environmental pollutants such as dichloro-diphenyl-trichloroethane (DDT), polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and polybrominated diphenyl ethers (PBDEs). Many studies of the photochemistry of halogenated aromatic compounds have been stimulated by environmental concerns, the goal often being to understand whether photolysis is an important sink for these compounds in natural waters - or in the atmosphere.The photochemistry of aryl halides causes problems in this context because many aryl halides have minimal absorption in the region of the tropospheric solar spectrum (>295 nm), and experiments at environmentally irrelevant wavelengths such as 254 nm are... 

---