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Polychlorinated biphenyls are a group of related compounds or congeners made by reacting biphenyl with chlorine and replacing anywhere from one to ten of the original hydrogens of the biphenyl. In so doing there are a total of 209 congeners that are collectively referred to as polychlorinated bihenyls (PCB's). The prime manufacturer of PCB's in the United States was the Monsanto Chemical Company, which first marketed them in the late 1920's. They designated them with the trade name Aroclor followed by a numerical designation of four digits. The first two digits designated the ring system, e.g. 12 was for derivatives of biphenyl. The last two digits designated the average weight percent chlorine in the mixture. Thus Aroclor 1221, 1242, 1254, and 1260 all represent chlorinated biphenyls that contain 21, 42, 54, and 60 % chlorine respectively. The higher chlorine containing Aroclors are solids and to make them useful for an insulating fluid in a transformer they are blended with various chlorinated benzenes to give mixtures known as Askarels, which are then marketed under a variety of trade names, such as Inerteen (Westinghouse) and Pyranol (General Electric).
The details of the entire procedure for determining the PCB content of an insulating fluid are given in the ASTM D 4059 method and are only briefly mentioned here. A sample of the fluid to be analyzed is diluted with a suitable solvent and the resulting solution is treated to remove any substances that could interfere with the determination. A sample of the treated solution is then analyzed by gas chromatography utilizing an electron capture detector, which is very sensitive for chlorine containing species. The resulting chromatogram is compared against standard chromatograms for the various known Aroclors. This data then allows one to identify which Aroclor or mixture of Aroclors is present and to quantitate them. The results are usually reported in terms of parts per million (ppm) of each Aroclor present.
The PCB content of a unit is usually required for regulatory purposes in order to establish whether a unit is free of PCB's, contaminated with PCB,s, or does it have to be treated as a PCB filled unit. The values of the PCB,s that must be present to classify the unit as described above will depend on the location of the unit and the regulatory agency that has jurisdiction.
PCB's have been shown to have a low order of toxicity in humans. There is no adverse effect on the reproductive process, there is no teratogenicity risk to offspring, no mutagenicity, and no carcinogenic effect in humans. There is an occasional chloracne that disappears after exposure ceases. These materials are very stable and do not biodegrade easily. They do tend to bioconcentrate and have a more serious effect on the lower life forms, thus they are of concern in the environment.