Biphenyls, toxicity

PCBS (polychlorinated biphenyls) Toxic synthetic chemicals with excellent heat resistance and low electrical conductivity properties. Now little used but considerable quantities remain in old electrical equipment. Produces dioxins and polychlorinated dibenzo-furans when burned below 1200°C. PCBs are toxic and bio-accumulative. 

Kannan, N., S. Tanabe, M. Ono, and R. Tatsukawa. 1989. Critical evaluation of polychlorinated biphenyl toxicity in terrestrial and marine mammals increasing impact of non-ortho and mono-ortho coplanar polychlorinated biphenyls from land to ocean. Arch. Environ. Contam. Toxicol. 18 850-857. 

Polychlorinated biphenyls are stiU used in large quantities in electrical and condenser technology. One of the main members of this group of substances is perchlorobiphenyl (PCB). In fires involving polychlorinated biphenyls, toxic dioxins can be released. Biphenyls lead to powerful induction of the cytochrome P-450 system. Following exposure, biphenyls can be detected in adipose tissue and breast milk. Severe cases of liver damage, including fatalities, have been reported. 

Chakraborty D, Bhattacharyva A, Chatterjee J, et al. 1978. Biochemical studies on polychlorinated biphenyl toxicity in rats Manipulation by vitamin C. Int J Vitam Nutr Res 48 22-31. 

Truelove J, Grant D, Mes J, et al. 1982. Polychlorinated biphenyl toxicity in the pregnant Cynomolgus monkey A pilot study. Arch Environ Contam Toxicol 11 583-588. 

In another similar study for ME (Venkatachalam et al. 2008), palladium-based nanoparticles immobilized in polymeric matrices were applied to the reductive dechlorination of 3,3, 4,4 -tetrachlorobiphenyl (PCB77) at room temperature. Two different dechlorination platforms were evaluated using (1) Pd nanoparticles within conductive polypyrrole films or (2) immobilized Fe/Pd nanoparticles within PVDF MF membranes. The results indicated the removal of chlorine atoms from PCB77, which led to the formation of lower chlorinated intermediates and, ultimately, biphenyl. Toxicity associated with vascular dysfunction by PCB77 and biphenyl was compared using cultured endothelial cells. The data strongly suggest that the... 

Polychlorinated biphenyls Toxicity, aquatic biota, wildlife... 

Ei ivironrr lent Absence of toxic compounds such as polychlorinated biphenyls (PCB s)... 

Biphenyl is defined as a toxic chemical under, and subject to, reporting requirements of Section 313 of Tide 111 of the Superfund Amendments and Reauthori2ation Act (SARA) of 1986 and 40 CFR, Part 372 under the name biphenyl. It is identified as a ha2ardous chemical under criteria of the OSHA Ha2ard Communication Standard (29 CFR 1910.1200). 

Although biphenyl and the terphenyls fall under the ha2ardous chemical criteria of the OSHA Ha2ard Communications Standard, the products themselves are fairly low in toxicity and do not constitute a serious industrial ha2ard. Some relevant exposure and toxicity data are summari2ed in Tables 5 and 6. 

See Biphenyl AND TBRPHENYLs Cid,orocarbons and cid,orohydrocarbons, toxic aromatics. 

In earlier editions of the Eniyclopedia there have been articles covering the properties, manufacture, capacities, etc, of polychlorinated biphenyls (PCBs), chlorinated naphthalenes, benzene hexachloride, and chlorinated derivatives of cyclopentadiene. These materials are no longer in commercial use because of their toxicity. However, they stiU impact on the chemical industry because of residual environmental problems. Their toxicity and environmental impact are discussed (see Cm.OROCARBONSANDCm.OROHYDROCARBONS, TOXIC aromatics). 

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) ai e toxic compounds of anthropogenous origin, able to accumulate in tissues of alive organisms and to cause different diseases. These compounds ai e the most dangerous for aquatic ecosystems as they easily adsorb in sludge and ai e included in food chains of biota. Humans consume PCBs and OCPs mostly with fish. 

Until the 1970s the chemical used as the impregnating and dielectric medium for capacitor units was PCB (polychlorinated biphenyl) liquid. It was found to be toxic and unsafe for humans as well as contamination of the environment. For this reason, it is no longer used. The latest trend is to use a non-PCB, non-toxic, phenyl xylyl ethane (PXE-oil), which is a synthetic dielectric liquid of extremely low loss for insulation and impregnation of the capacitor elements or to use mixed polypropylene or allpolypropylene (PP) liquids as the dielectric. A non-oil dielectric, such as epoxy resin, is also used. 

PCBs and PCTs are particularly troublesome liquids because of their toxicity and persistence in the environment. They are defined as polychlorinated biphenyls, polychlorinated terphenyls, monomethyl-dibromo-diphenyl metliane, monomethyl-dichloro-diphenyl metliane or monomethyl-tetrachlorodiphenyl methane. With low electrical conductivity and heat resistance they found wide use as dielectric fluids and were formerly used as hydraulic fluids. PCBs have not been made in the UK since 1977 and whilst most new uses for the substance are banned in most countries, around two-thirds of the 1.5 million tonnes manufactured in Europe and the US prior to 1985 still remain in equipment such as transformers. PCTs have been used in the past in a restricted range of specialist industrial applications. 

Polychlorinated biphenyls (PCBs) Highly toxic organic compounds used in the electrical industry, use of w hich is now restricted. 

J. C. Duinker, D. E. Schult and G. Petiick, Multidimensional gas chromatography with electi on capture detection for the deteimination of toxic congeners in polycWorinated biphenyl mixture . Anal. Chem. 60 478-482 (1998). 

Dioxins are prominent members of the class of polychlorinated hydrocarbons that also includes diben-zofuran, biphenyls and others. Dioxins are highly toxic environmental contaminants. Like others small planar xenobiotics, some dioxins bind with high affinity to the arylhydrocarbon (Ah) receptor. Dioxins activate the receptor over a long time period, but are themselves poor substrates for the enzymes which are induced via the Ah-receptor. These properties of the dioxins and related xenobiotics may be important for the toxicity of these compounds. Dioxins like 2,3,7,8-tetrachloro-p-dibenzodioxin can cause persistent dermatosis, like chloracne and may have other neurotoxic, immunotoxic and carcinogenic effects. 

Except for polybrominated biphenyls (PBB), a limited number of studies regarding the toxicity of aromatic brominated compounds has been performed. Some experiments suggest a moderate acute toxicity of these compounds (ref. 1). 

Among aromatic bromine derivates, only polybrominated biphenyl is known to have a porphyrogenic effect (ref. 24). From scarce data about the toxicity of 4 and 5 porphyrogenic activity in the case of repeated administration could be expected (refs. 25,26). No data are available concerning the remaining compounds. 

Pijnenburg, A., Everts, J., and de Boer, J. et al. (1995). Polybrominated biphenyl and diphe-nylether flame retardants analysis, toxicity, and environmental occurrence. Reviews in Environmental Contamination and Toxicology. 141, 1-26. 

There is a vast range of aqueous organic pollutants with a wide toxicity profile. Some, e.g. polychlorinated biphenyls, certain herbicides, fungicides and pesticides, and organo-mercury compounds, are persistent and may bioaccumulate in the food chain. Trace contaminants such as sodium chloride, iron and phenols (especially if chlorinated) may also impart a taste to water. Typical consent levels for industrial discharges are provided in Table 13.10. 

Mixed cultures of organisms that were isolated from sediments contaminated with PCBs and polybrominated biphenyls (PBBs) were shown to debrominate PBBs under anaerobic conditions (Morris et al. 1992), and the dominant congener—2,2, 4,4, 5,5 (245-245)-hexabromobiphenyl—could be successively debrominated to 2,2 -dibromobiphenyl. However, in sediments from the most heavily contaminated site containing contaminants in addition to PBBs, very little debromination occurred and the recalcitrance was attributed to the toxicity of the other contaminants (Morris et al. 1993). 

Bedard DL, JE Quensen III (1995) Microbial reductive dechlorination of polychlorinated biphenyls. In Microbial transformation and Degradation of Toxic Organic Chemicals (Eds LY Yonng, CE Cemiglia), pp. 127-216. Wiley-Liss, New York. 

The structural range of industrially important representatives of these groups is enormous, and includes chlorobenzenes (solvents), polychlorinated biphenyls (PCBs) (hydraulic and insulating fluids), and polybrominated biphenyls and diphenyl ethers (flame retardants). There is widespread concern over both the persistence and the potential toxicity of all these compounds, and sites that have become contaminated during their production represent a threat both to the environment and to human health. Pathways for the aerobic bacterial degradation of chlorobenzenes and chlorobiphe-nyls, and their brominated analogs have been discussed in Chapter 9, Part 1. 

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