Polychlorinated biphenyls chemical transformations

PCB Polychlorinated biphenyls. Aka polychloro-biphenyls. Difficult to remediate chemical used in old-style transformers. Concentrated PCBs used to be referred to as "1268". 

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 water insoluble, highly chemically and thermally stable PCBs used as insulating fluids for transformers and capacitors, in paints, copy paper, etc., are extremely toxic, persistent in the environment and bioaccumulating. PCBs are currently destroyed by incineration of concentrates at high temperatures or chemically with sodium metals or organosodium. Both processes are costly. The cathodic reduction/elimination of the chlorine from polychlorinated biphenyl... 

The POCs include, but are certainly not limited to the polychlorinated biphenyls (PCBs) and the organochlorine pesticides, including those in current use, restricted use and historic use brominated flame retardants including polybrominated diphenyl ethers PAHs and the sometimes more toxic transformation products of these chemicals. Table 1 summarizes information on some of the POCs more commonly detected in alpine environments. 

Polychlorinated biphenyls (PCBs), known by their trade marks of Arochlor (Monsanto U.S.), Phenochlor (in France), and Clophen (in Germany) are chemically similar to the chlorinated insecticides. Although not used for this purpose, their existence and persistence in the environment is well established. They were used to make more flexible and flame retardant plastics and are still used as insulating fluids in electrical transformers since there is no substitute in this application. They have been made by Monsanto since 1930 and were first discovered as a pollutant in 1966. U.S. production peaked at 72 million lb in 1970 but in 1975 it was down to 40 million Ib/yr because in 1971 Monsanto voluntarily adopted the policy of selling PCBs only for electrical systems. At least 105 PCBs are present in the environment. 

PCB organic compounds found as soil and water contaminants continue to grow each year. They include polychlorinated biphenyls (PCBs), phenols, cyanides, plasticizers, solvents, and numerous industrial chemicals. PCBs were historically used as coolants in electrical transformers and are also known by-products of the plastic, lubricant, rubber, and paper industries. They are stable, lipophilic, and break down only slowly in tissues. Because of these properties they accumulate to high concentrations in fish and waterfowl in 1969 PCBs were responsible for the death of thousands of birds in the Irish Sea. 

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. 

Polychlorinated biphenyls (PCBs) are mixtures of biphenyls with 1 to 10 chlorine atoms per molecule. They are oily fluids with high boiling points, great chemical resistance, and low electrical conductivity, and have been used as plasticizers in polyvinyl polymers, insulators and coolants in transformers and heat exchange fluids. Dioxins and furans (see Section 9.1) are not produced intentionally but are derived from combustion processes of chlorinated aromatic hydrocarbons, pesticides and chlorinated solvents. 

Bedard, D.L. Quensen J.F. ni. Microbial Reductive Dechlorination of Polychlorinated Biphenyls In Microbial Transformation and Degradation of Toxic Organic Chemicals, L.Y. Young C.E. Cerniglia, editors, Wiley-Liss New York, 1995, p. 127-216. 

Polychlorinated biphenyls (PCBs) were produced from 1930 to 1983 in the form of complex mixtures for a variety of uses (e.g. dielectric fluids in transformers and capacitors, and plasticizers in paint and rubber sealants). Because of their physical and chemical stability, and also of their lipophilic affinity, they are highly persistent and tend to accumulate in sediments and biota in the aquatic environment [253]. 

Polychlorinated biphenyls (PCBs) have a variety of industrial applications related to their high chemical and thermal stabilities, electrical resistance and low volatilities. Some of their uses are as dielectric fluids in capacitors and transformers, as lubricants and hydraulic fluids, as heat exchangers and fire retardants and as plasticizers. Commercial production began in the USA in 1929, but restrictions were imposed in the 1970s because of growing concerns about adverse biological effects, and the use of PCBs was banned in the USA in 1986. Some 37 kt were produced in 1970 (Goldberg 1976), and total production to 1980 has been estimated at 1.2 Mt, of which c.65% is still in use or has been deposited in landfills, c.4% has been destroyed and c.31% has been released to the environment (Tanabe 1988). 

Polychlorinated biphenyls (PCBs) were manufactured as a liquid transformer oil. Due to leakage, PCBs are now found throughout the environment, and this long-lived chemical represents a health hazard. PCBs have been found to be present in the St. Lawrence River at concentrations of about 0.3 ppb (parts per billion by weight). Estimate the likely concentration ot PCBs in fish in this river. The average octanol-water partition coefficient for PCBs is... 

Polychlorinated biphenyls ( PCBs ) have been manufactured and used commercially for 50 years because of their chemical stability, fire resistance, and electrical resistance properties. PCBs are frequently used in electrical transformers and capacitors. However, concern has been expressed that PCBs may be toxic to humans and to wildlife. Because of these concerns, the major American manufacturer of PCBs limited its sales of PCBs after 1972 to manufacturers of transformers and capacitors and then in 1977 ceased all manufacture of PCBs and shipped the last of its inventory. Today, PCBs are produced in this country only as incidental byproducts of industrial chemical processes. There are known natural sources of PCBs. 

PCB stands for polychlorinated biphenyl. This is found in electrical transformers and components. It is used for insulating and as a heat exchange fluid and hydraulic fluid. It is on the EPA Extremely Hazardous Substances List. It is a confirmed cancer-causing chemical that is toxic and can cause severe liver damage. It has also been linked to behavioral problems in children. 

While any halogen may halogenate a polyphenyl, chlorine and bromine are by far the more usual. They result in a large number of possible polychlorinated biphenyls syn. p.c.b.s, PCBs, PCB s), polyhalogenated biphenyls, and polyhalogenated terphenyls. No longer produced commercially, halogenated polyphenyls were widely used for their exceptional qualities as heat-transfer fluids, solvents, lubricants, dust suppressants, and fire retardants (some equipment that relies on these chemicals, like electrical transformers and capacitors, remains in use). 

Polychlorinated biphenyls (PCB), are a family of toxic, oily, non-flammable chemicals. They are man-made products and were first commercialised in 1929 (by Monsanto). They were mainly used in electrical equipment (e.g., transformers and capacitors), as heat transfer and hydraulic fluids, and as plasticisers from World War I until recently, mainly due to their exceptional thermal and chemical stabilities. Although their production in the USA was stopped in 1977 (they were banned worldwide), some production still continues, and it is believed that large quantities of PCB may still be present in some old transformer and capacitor systems. PCB are certainly still present in the USA in some electrical equipment and are frequently found at toxic waste sites and in contaminated sediments worldwide. The sealants based on polysulfhide polymers that were used in buildings some 20-40 years ago contained PCB, which has been shown still to exist at alarming levels in some houses in Sweden, [24]. 

PCBs Polychlorinated biphenyls, a group of toxic persistent chemicals used in transformers and capacitors for insulating purposes and in gas-pipeline systems as a lubricant. Sale of PCBs for new uses was banned by law in 1979. 

It is evident that to avoid future environmental contamination situations as have occurred with DDT, Mirex, or polychlorinated biphenyls (PCBs), it is essential to develop a better understanding of the processes of transport, transformation, and accumulation of toxic substances in the environment. For compounds which are already present in the environment, it is desirable to assemble mass balances which describe where and at what concentrations the substances are accumulating and the rates at which they are degrading or moving between environmental compartments. For chemical substances which may be introduced in the future, it is desirable to have the capability of generating advance information on their behavior and, of course, their toxic effects. 

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