163
Occurrence
PCBs are extensively used as plasticizers in cement and paints industry, wax extenders, coolants and insulating fluids, and flame retardants. According to the occurrence PCBs are divided into dioxin and non-dioxin-like compounds. Depending on
the similarity with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Examples include
3,3′,4,4′-tetrachlorobiphenyl (PCB 77) and 3,3′,4,4′,5-pentachlorobiphenyl (PCB
126). PCBs are also produced in large scale industries, which are known as famous
Aroclors. Because of having a potential of environmental toxicity and considered as
persistent organic pollutants (POPs), their manufacturing was banned by the
Stockholm Convention on POPs in 2001. The International Agency for Research on
Cancer (IARC) classified PCBs as Group 1 carcinogens in humans. Although the
levels of PCBs are diminishing in the atmosphere due to their limited use but their
acquaintance still considered harmful [10]. PCBs are known to cause and contribute
to glucose and lipid metabolic disorders including hypertension, diabetes, obesity,
and NAFLD in exposed humans [11, 12]. In animal studies, it is confirmed that it
can induce steatosis and steatohepatitis [10, 12].
Chemical Structure
Chemical structures of certain PCBs are shown in Fig. 11.1. Meanwhile, chlorine
atom is the foremost part of the group, though other halogens can also form a bond
with biphenyls. PCBs are composed of up to 50 or 60 congeners (or individual chlorobiphenyls). Mixtures are formed by the reaction of unique compositions at specified reaction conditions. Their composition results in the formation of specific
congeners, thus different proportions of these congeners used in industrial mixtures.
These mixtures are found in liquid to viscous turbid solids [13]. The industrial manufacture of these mixtures was forbidden in the USA (between 1930 and 1977) as
only Monsanto companies were solely producing these chemicals under the commercial name of Aroclors (Aro: Aromatic clor: Chlorine). Each Aroclor is coded by
number (e.g., Aroclor 1242, 1248, and 1254), the last two numbers usually denote
the percentage of chlorine by weight in the composition. For example, Aroclor 1248
contains 48% chlorine by weight. Furthermore, PCBs are marketed in different
commercial names in several countries like Clophens (Germany), Soval (Soviet
Union), Santotherm (Japan), Phenolclor (France), Pyralene (France), Fenclor
(Italy), and Kanechlor (Japan). It is noteworthy that Aroclor is also the trade name
of the other halogenated biphenyls [14].
11 Role of Polychlorinated Biphenyls as EDCs in Metabolic Disorders
Occurrence
PCBs are extensively used as plasticizers in cement and paints industry, wax extenders, coolants and insulating fluids, and flame retardants. According to the occurrence PCBs are divided into dioxin and non-dioxin-like compounds. Depending on
the similarity with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Examples include
3,3′,4,4′-tetrachlorobiphenyl (PCB 77) and 3,3′,4,4′,5-pentachlorobiphenyl (PCB
126). PCBs are also produced in large scale industries, which are known as famous
Aroclors. Because of having a potential of environmental toxicity and considered as
persistent organic pollutants (POPs), their manufacturing was banned by the
Stockholm Convention on POPs in 2001. The International Agency for Research on
Cancer (IARC) classified PCBs as Group 1 carcinogens in humans. Although the
levels of PCBs are diminishing in the atmosphere due to their limited use but their
acquaintance still considered harmful [10]. PCBs are known to cause and contribute
to glucose and lipid metabolic disorders including hypertension, diabetes, obesity,
and NAFLD in exposed humans [11, 12]. In animal studies, it is confirmed that it
can induce steatosis and steatohepatitis [10, 12].
Chemical Structure
Chemical structures of certain PCBs are shown in Fig. 11.1. Meanwhile, chlorine
atom is the foremost part of the group, though other halogens can also form a bond
with biphenyls. PCBs are composed of up to 50 or 60 congeners (or individual chlorobiphenyls). Mixtures are formed by the reaction of unique compositions at specified reaction conditions. Their composition results in the formation of specific
congeners, thus different proportions of these congeners used in industrial mixtures.
These mixtures are found in liquid to viscous turbid solids [13]. The industrial manufacture of these mixtures was forbidden in the USA (between 1930 and 1977) as
only Monsanto companies were solely producing these chemicals under the commercial name of Aroclors (Aro: Aromatic clor: Chlorine). Each Aroclor is coded by
number (e.g., Aroclor 1242, 1248, and 1254), the last two numbers usually denote
the percentage of chlorine by weight in the composition. For example, Aroclor 1248
contains 48% chlorine by weight. Furthermore, PCBs are marketed in different
commercial names in several countries like Clophens (Germany), Soval (Soviet
Union), Santotherm (Japan), Phenolclor (France), Pyralene (France), Fenclor
(Italy), and Kanechlor (Japan). It is noteworthy that Aroclor is also the trade name
of the other halogenated biphenyls [14].
11 Role of Polychlorinated Biphenyls as EDCs in Metabolic Disorders