Polychlorinated biphenyls (PCBs) are aromatic, synthetic chemicals which do not occur naturally in the environment. They consist of the biphenyl structure with two linked benzene rings in which some or all of the hydrogen atoms have been substituted by chlorine atoms. The basic molecular structure, including the conventional numbering of the substituent positions, is shown in Figure 1.
Figure 1. The chemical structure of PCBs compounds
The chemical formula of PCBs is C12H10-nCln, where n ranges from 1 to 10. Theoretically, 209 different congeners are possible, but only about 130 of these have been identified in commercial products.
PCBs are hydrophobic and thus they have very low water solubility. Congeners with a lower degree of chlorination are more volatile than those with a higher degree. As hydrophobic and very stable compounds, PCBs may volatilize from water despite their low vapor pressure. PCBs also easily adsorb onto organic particles in soils, sediments, biological systems, or water. (Panero et al. 2005) These organic particles can be transported long distances and has been shown as one of the reasons PCBs are distributed throughout the planet including remote areas.
By contrast, they are slightly soluble in oil and highly soluble in most organic solvents. PCBs are unaffected by light and they have remarkable heat stability – which increases with their chlorine content – and only break down at very high temperature (> 1,000 °C). PCBs have a high level of chemical inertia and are highly resistant to such chemical agents as acids, bases and oxidizers. While not affecting base metals, they dissolve or soften certain rubbers and plastics.
PCBs are practically fire resistant because of their high flash points (170–380 °C). They form vapours which are heavier than air, but are not explosive. They have low electrical conductivity, high thermal conductivity and high resistance to thermal degradation. On the basis of these properties they have been used in hundreds of industrial and commercial applications including electrical, heat transfer and hydraulic equipment; as plasticizers in paints, plastics, and rubber products; in pigments, dyes, and carbonless copy paper; and many other industrial applications (EPA 2013a). PCBs were attractive in many applications because they resist breakdown at high temperatures or from aging, or oxidation.
PCBs have another feature that contributes greatly to their stability. Carbon and chlorine form a very strong bond and the amount of energy needed to break apart the bond is higher than most other covalent bonds. The strength of this bond greatly increases the ability of PCBs to persist in the environment. Persistence is also related to the number of chlorine atoms with increasing degree of persistence with increasing chlorine mass. Comparatively, the mono- and di-chlorobiphenyls are less persistent than the larger congeners; however, all PCBs meet the definition of persistence.
The aim of this page is to show information on health effects, environmental impact, technical information and general information on polychlorinated biphenyls commonly known as PCBs. The main scope is to inform Serbian audience about National PCB Management Plan, all relevant legal framework and regulations in the Republic of Serbia and worldwide. This web page will help all potential PCBs owners to find all relevant information on technical guidelines, safety procedures, protocols and standard operating procedures for PCBs contaminated oils, equipment and soil, list of services, analytical procedures, laboratories, etc.
The Stockholm Convention on Persistent Organic Pollutants (POPs) was adopted by the Conference of Plenipotentiaries on 22 May 2001 in Stockholm, Sweden. The Convention entered into force on 17 May 2004.READ MORE
Polychlorinated biphenyls (PCBs) are aromatic, synthetic chemicals which do not occur naturally in the environment. They consist of the biphenyl structure with two linked benzene rings in which some or all of the hydrogen atoms have been substituted by chlorine atoms.
PCBs were first identified in the nineteenth century and started being manufactured on an industrial scale in 1929. They were intensively used between 1920 and 1980.READ MORE
PCBs are identified as persistent, bioaccumulative and toxic (PBT). Because of their persistence, PCBs continue to be found in the environment and contamination from legacy sources remains a problem.READ MORE