Since industrial production of PCBs began in 1929 it is estimated that approximately 1.2-1.5 million metric tonnes have been produced. Production peaked in the late 1960s, and ended in most countries in the 1970s and 1980s. However, it is not certain whether production has completely ceased in all countries, even in 2006. It is estimated that approximately one-third of all PCBs produced have been released into the environment. This, combined with their properties (notably their stability, vapor pressures and Kow), has led to them becoming ubiquitous in the environment, having been found in biota and other environmental media from all regions of the globe and in all habitats.
Their dielectric properties and fire resistance led to PCBs being used widely in electrical equipment, such as transformers and capacitors, predominantly in enclosed systems. However, PCBs have also had a very broad range of other, often unenclosed, uses, including in heat transfer liquids, sealants, lubricants, paints, adhesives, and as plasticizers.
PCBs were produced by a number of companies, at production plants in a number of industrialized countries. A range of mixtures, with different average chlorine contents, were produced by each company - in each mixture the range of individual PCB congeners present was different, and there are likely to have been differences in congener composition between different batches of the same mixture. Each company used their own names for the mixtures they marketed, so there are a great number of trade names for PCB-containing commercial products, the most well known being Aroclor, Clophen, Kanechlor, and Phenoclor. The use of PCBs was overwhelmingly concentrated in industrial countries, meaning that use was concentrated in the temperate regions of the Northern Hemisphere where most industrial regions are situated.
In the 1960s and 1970s, following the discovery of the widespread environmental occurrence of PCBs, and industrial accidents which led to acute human and environmental exposure to PCBs, many countries introduced legislation to control the manufacture, use, and disposal of PCBs. This was most notable after 1973, after recommendations from the OECD. PCB production and use was banned in Japan in 1972, and the leading manufacturer in the USA ceased production in 1977. Most other countries banned PCBs and introduced special disposal requirements (typically highly controlled incineration) in the late 1970s and 1980s, although previously established enclosed use continues in many countries, and production and new uses may still occur in others.
In addition to national controls, international efforts have been made to control PCBs, and the United Nations Environment Programme's Stockholm Convention on 'persistent organic pollutants' (POPs) is a global agreement to strictly control, with the aim of eliminating, PCBs and other persistent organic chemicals (including some organo-chlorine pesticides and 'dioxins' - polychlorinated dibenzo-/>-dioxins and dibenzofurans), to which only a handful of countries are not either party or signatory.
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