Aromatic halogen compounds polybrominated biphenyls

BFRs are one of the last classes of halogenated compounds that are still being produced worldwide and used in high quantities in many applications. In order to meet fire safety regulations, flame retardants (FRs) are applied to combustible materials such as polymers, plastics, wood, paper, and textiles. Approximately 25% of all FRs contain bromine as the active ingredient. More than 80 different aliphatic, cyclo-aliphatic, aromatic, and polymeric compounds are used as BFRs. BFRs, such as polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), and tetrabromobisphenol A (TBBPA), have been used in different consumer products in large quantities, and consequently they were detected in the environment, biota, and even in human samples [26, 27]. 

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. 

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. 

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... 

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