Production Use

The industrial synthesis of PCBs is a bit crude and does not result in pure congeners but in complex mixtures, referred to in the United States as Aroclors, the trade name patented by U.S. Swann Chemical Company in 1929. U.S. Swann Chemical

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Figure 12.3. Structure of 2,2',4,4',6,6'-hexachlorobiphenyl, a PCB.

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Figure 12.3. Structure of 2,2',4,4',6,6'-hexachlorobiphenyl, a PCB.

Company was later bought in 1935 by Monsanto Chemical Company, which became the main manufacture of PCBs in the United States. Trade names for industrial-grade PCBs include Clophen (Bayer, Germany), Phenoclor (Caffaro, Italy), Pyralene (Kanegafuchi Chemical Company, Japan), Kanechlor (Prodelec, France), Fenchlor (Chemko, former Czechoslovokia), and Delor (from the former USSR), but there are many others.

The common Aroclor mixtures include Arochlors 1221, 1232, 1242, 1248, 1254, 1260, 1262, 1268, and 1270. The basic rules of Aroclor nomenclature are that the first two numbers in the name refer to the 12-carbon basic structure of the biphenyl structure. The last two numbers refer to the average degree of chlorination of the biphenyl rings. Note that any given Aroclor mixture will contain tens of different PCB molecular structures. The degree of chlorination is a result of the reaction time with chlorine, which is determined by the desired chemical and physical properties. As a side note, it is interesting to note the shift in nomenclature when PCBs started receiving a "bad name." At this time, a "new" Aroclor was released that was supposed to have less detrimental environmental properties. The new Aroclor was numbered 1016. The selection of "10" was unclear, but in keeping with the established numbering system, the "16" was clearly meant to imply a lower degree of chlorination. In fact, Aroclor 1016 was essentially the same as Aroclor 1242.

During the early years of their production, PCBs were thought of as the perfect chemical—they were highly unreactive and did not degrade. However, this means that PCBs are also very persistent in the environment, as we will discuss in the next section. The unreactive nature of PCBs lends them to many functions, including use as dielectric fluids in capacitors and transformers, as heat transfer fluids, as hydraulic fluids, and in lubricating and cutting oils. PCBs were also employed as additives in pesticides, paints, copying paper, carbonless copy paper, adhesives, and sealants, as well as in plastic formulations.

Little was known about the dangers of PCBs prior to the 1980s. For example, at the height of the environmental movement in the mid-1970s, PCBs were presented in undergraduate microbiology classes as an ideal fluid for preparing microscope slides, due to the fact that they do not cause refraction of light. Students were neither told the name of the fluid nor advised to take precautions in handling it, and there fore they came into extensive contact with the fluid. Of course, in the 1970s, there was no such things as material safety data sheet (MSDS) or the Citizen's Right-to-Know Act. Still, this example demonstrates the importance of always having and reading the label of chemicals that you work with.

One of the most common and unfortunate uses of PCBs was as dielectric fluid, used as a fluid insulator in electrical systems. In order for a chemical to be a good dielectric fluid, it should be an excellent electrical insulator (a nonconductor) and be heat resistant and not thermally degrade, since most electrical equipment becomes very hot. Aroclor mixtures were ideal for this, and for a time they were legally placed in all transformers and capacitors. But transformers wear out, on occasion explode, and sometimes leak, spreading PCBs wherever transformers were used or disposed of.

The Toxic Substances Control Act of 1976 gave EPA the authority to regulate all aspects of the manufacture, distribution, use, and disposal of chemicals, including PCBs. The U.S. Congress banned the manufacture, processing, distribution in commerce, or use of PCBs after January 1, 1978. Congress further specified that after January 1, 1979, no person could process or distribute in commerce any PCBs unless granted permission by the EPA. But the United States Congress only regulates the United States, and some chemical companies simply shifted their operations to countries where PCBs were, and in some cases still are, legal.

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