PCBs or in other words, polychlorinated biphenyls are widely used as organic compounds and as dielectric fluids in transformers and capacitors. PCBs are organic compounds that contain 1-10 chlorine atoms attaché to biphenyl group (C12H10-xClx) and they are formed by electrophilic chlorination of biphenyl with chlorine gas. PCBs or Polychlorinated biphenyls were first commercially used in 1929 as a “safer” cooling and as an insulating fluid in electrical industry.
These PCBs are not only used as coolants and insulating fluid but they are also used as components in early light fittings and in electrical transformers. Besides all these usages, PCBs are also used as plasticizers in paint and cement, as stabilizing additives in flexible PVC coating, in electrical wiring and in electronic components. Since PCBs have high viscosity, high flashing point and high thermal conductivity they can be used for cutting oils, as reactive flame retardants, lubricant oils, hydraulic fluids and sealants. And PCBs are organic compounds that contain Chlorine in it and therefore can also be used as pesticide.
These harmful PCBs got entered to the environment through illegal waste disposal and the use of PCB products. They also reached through spills of PCBs containing oils like hydraulic oils and through Industrial effluents containing PCBs. When these PCBs entered the environment they produce harmful effects in several ways. Hence, PCB pollution has already created crucial problems to several developed countries since they use more electronic equipments containing PCBs in order to accelerate their economic development. With the development and wide usage of electronic products, not only developed countries but also the developing countries face the same environmental problem thus making PCB pollution a threat to the whole world. PCBs being less soluble in water and highly soluble in organic solvents and in fats, when they are released to the environment they get accumulated in animals through the biomagnifications. Further, PCBs are fairly chemically inert and they are resistant to oxidation, reduction, addition, elimination and electrophilic substitution. Therefore once they are emitted to the nature, it certainly takes a very long time to get decomposed.
As a result, these PCBs create many environmental issues causing many health care problems to humans and other animals. One of the major environmental issues that arise due to PCB is toxicity which is associated with it. This was first reported in 1970’s in seabirds. Depending on the number of chlorine atoms, some PCBs tend to have dioxin- like properties that cause health problems to humans.PCB can also cause genetic mutations. Sometimes, these PCBs can affect the estragon and thus cause serious development problems in both males and females. It can also lead to cancers. In addition to all these, when a person is exposed to the PCB by breathing contaminated air, by consuming contaminated food or by breast feeding, it can cause sexual, skeletal, and mental development problems. Some people might show certain symptoms when they are exposed to PCBs, like skin rashes, changes in blood and urine due to liver damage and irregular menstrual cycles. And sometimes the PCBs affect the immune system as well. When the exposure to PCBs takes place in pregnancy period, it may cause low weight child births, babies with problems in motor skills and problems in immune system. When considering animals, mostly sea animals are affected by PCB contamination. Even though, PCB is less soluble in water, a large amount of PCB is present in sea water thus causing biomagnifications in sea mammals like whales which ultimately lead to mass death due to low immune defense.
Because of these critical social issues created by PCBs, PCB is considered an environmental pollutant and several attempts were taken to ban the use of PCBs. Even if we are to stop the use of PCBs, due to the chemically inert nature of PCBs, they remain in the environment for a long period of time without getting decomposed and thus causing environmental issues. Therefore we, as the affected lot have to decompose PCBs in every possible way, either chemically, physically or biologically.
For chemical decomposing we can use Neucleophylic aromatic substitution or cleave C-Cl bond by Hydrogen gas which is more expensive. Other than that, reactions with strong reducing agents or reactions with highly electro positive metals can be used, and there are many more chemical decomposing methods as well. For physical methods, incineration, ultrasound, irradiation, pyrolysis can be used. As biological methods we use microbial activities for the biodegrade of PCBs hence, microbes use PCBs as their carbon source. And their enzymes and vitamins are also helpful to stop the PCB activities in the environment.
Since, the use of PCB is a burning environmental issue some countries have prohibited the production while some countries have stopped using equipments that contain PCBs, like capacitors that are used with florescent lights. And also PCB storage and disposal are done according to the EPA (Environment Protection Agency) and under the TSCA (Toxic Substances Control Act) rules and regulations. Hopefully, these measures will help us to live in a healthier environment with minimal threats from Poly Chlorinated Biphenyls (PCBs).