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The two main sources of PCBs are:
The commercial production of PCBs began in the U.S. in 1929, and were sold as mixtures called Aroclors. In other countries, PCBs were marketed as Clophens, Phenoclors, Askarel, and Therminol. U.S. production peaked in 1970 with a total production volume of 39 million kg of Aroclors. By 1980, the global production of PCBs was more than 1 million tonnes. Aroclor stopped being manufactured in the United States in August 1977 once evidence was established that PCBs accumulate in the environment and could cause harmful effects; however production continued in some other countries. Before 1974, PCBs were used in capacitors, transformers, plasticizers, surface coatings, inks, adhesives, pesticide extenders, and carbonless duplicating paper. After 1974, use of PCBs was restricted to the production of capacitors and transformers, and after 1979 PCBs were no longer used in the production of capacitors and transformers.
PCBs are no longer produced in the United States and are no longer used in the manufacture of new products; the major source of air exposure to PCBs today is the redistribution of PCBs already present in soil and water. Smaller amounts of PCBs may be released to the air from disposal sites, and from a variety of manufactured goods produced before 1977. When these appartus get hot during operation, small amounts of PCBs can leak into the air, increasing PCB levels inside homes, offices, etc. Some household products that may contain PCBs include are:
PCBs have been detected in indoor air at concentrations of an order of magnitude greater than ambient air!
PCB production has led to a few contamination crises in the 20th century. In particular, there are 2 examples where oil used in the machines to manufacture rice oil(a cooking oil) contained PCBs and unknowingly caused mass outbreaks of poisoning in the public:
1) The Yusho Incident in Japan in 1968
2) The Yu-Cheng Incident in Taiwan in 1979
How are PCBs produced?
PCBs are produced by chlorination of biphenyls with anhydrous chlorine in the presence of a catalyst, such as iron filings or ferric chloride:
The degree of chlorination depends on the length of the reaction. The longer the reaction, the more chlorines are added to the biphenyl, with chlorine contents ranging from 21 to 68% in the United States.
The table below shows commercial PCB mixtures as a percentage of total commerial production in the United States between 1955-1977:
Sources:
http://www.inchem.org/documents/ehc/ehc/ehc140.htm#1.1.2
http://www.epa.gov/opptintr/pcb/pcb.pdf
http://www.chem.unep.ch/pops/POPs_Inc/proceedings/cartagena/FIEDLER1.html
www.epa.gov/ttn/atw/hlthef/polychlo.html
ATSDR Toxicological Profile for Polychlorinated Biphenyls (PCBs)
Chapter 1: Public Health Statement http://www.atsdr.cdc.gov/toxprofiles/tp17-c1.pdf
Chapter 4- Physical and Chemical Properties http://www.atsdr.cdc.gov/toxprofiles/tp17-c4.pdf
Chapter 5: Production, Import/Export, Use and Disposal http://www.atsdr.cdc.gov/toxprofiles/tp17-c5.pdf
