Home > Polychlorinated biphenyl
Polychlorinated biphenyls (PCBs) are a class of organic compounds with 1 to 10 chlorine atoms are attached to bi phenyl and a general structure of C12H10-xClx. Most PCB congeners are colorless, odorless crystals. The commercial mixtures are clear viscous liquids (the more highly chlorinated mixtures are more viscous, for example, Aroclor 1260 is a "sticky resin"). Although the physical and chemical properties vary widely across the class, PCBs have low water solubilities and low vapor pressures. They are soluble in most organic solvents, oils, and fats. PCBs are very stable compounds and do not degrade easily. However, under certain conditions they may be destroyed by chemical, thermal, and biochemical processes. These processes may occur intentionally (e.g., incineration), unintentionally, or metabolicallyMetabolism in the most general sense, is the ingestion and breakdown of complex compounds, coupled with the liberation of energy, and the consequent generation of waste products. It is major process of living organisms, and because this process can happen. Because of their high thermodynamic stability, all degradation mechanisms are difficult. Intentional degradation as a treatment of unwanted PCBs generally requires high heat or a catalysisEnthalpy profile for catalysed and uncatalysed reactions. A is the activation energy for an uncatalysed reaction, A is the reduced activation energy for the same reaction when catalysed. I represents the point at which a chemical intermediate has been for. Environmental and metabolic degradation generally proceeds quite slowly relative to most other compounds.PCBs were commercially produced as complex mixtures containing multiple isomers at different degrees of chlorination for a variety of applications, including dielectric fluids for capacitorA capacitor (historically known as a "condenser") is a device that stores energy in the electric field established between a pair of conductors on which equal but opposite electric charges have been impressed. Historically, capacitors have taken the forms and transformerThe word Transformer can also mean: The Transformers toys, and the related comics and animated television series which have run from the 1980s onwards. A glam rock album by Lou Reed, named Transformer . Transformers ''Typical electrical configurations Sees, heat transfer fluids, hydraulic fluids, lubricatingA lubricant (colloquially, lube is a substance introduced between two moving surfaces to reduce the friction and wear between them. Worldwide, more than 50 million tonnes of lubricants are consumed annually. Automotive engine lubricants comprise approxima and cutting oils, and as additives in pesticideA pesticide is a chemical used to control, to repel, to attract or to kill pests, for example, insects, weeds, birds, mammals, fish, or microbes, that are considered a nuisance. Pesticides are usually, but not always, poisons. Examples of pesticides herbis, paintFor information on the U. borough, see Paint, Pennsylvania. Paint is the general term for a family of products used to protect and add color to an object or surface by covering it with a pigmented coating. As a verb, painting is the application of paint.s, carbonless copy ("NCR") paper, adhesives, sealant s, and plastics. The major producer, Monsanto, marketed PCBs under the trade name Aroclor from 1930 to 1977. Their commercial utility was based largely on their chemical stability, including low flammability, and desirable physical properties, including electrical insulating properties. Their chemical and physical stability has also been responsible for their continuing low-level persistence in the environment, and the lingering interest decades after regulations were imposed to control environmental contamination.
In the 1970s, their use declined and essentially terminated because of environmental concerns. PCBs have entered the environment through both use and disposal. The environmental transport of PCBs is complex and global. The public, legal, and scientific concerns about PCBs arose from research indicating they were environmental contaminants that had a potential to adversely impact the environment, and, therefore, were undesirable as commercial products. The extent to which PCBs are toxic remains controversial. Despite active research spanning five decades, extensive regulatory actions, and an effective ban on their production since the 1970s, PCBs remain a focus of environmental attention.
