Polychlorinated biphenyls (PCBs)

PCBs belong to the most resistant chemicals known. A low dielectric constant and high boiling point make them ideal for use as dielectric fluid in electric capacitors and transformers. It may be noted that in addition to power transformers and capacitors PCBs had many other applications: in lacquers, waxes, synthetic resins, epoxy paints and paints for vessel underwater parts, coatings, lubricating fluids, liquid coolants, hydraulic fluids, etc.

The same physical and chemical properties that made PCBs useful in industries account for their inclusion in the group of the most hazardous environmental pollutants. Being thermally and chemically stable, PCBs are extremely resistant to biotic and abiotic factors.

PCBs are released into environment in different ways. This occurs due to PCB use by modern industries or due to their possible production as byproducts. PCB can be released into the environment from industrial products, transformers, capacitors, coatings, paints, chemicals, building materials, etc. After release into the environment, PCBs are distributed to all components (air, water, soil, etc.). They are able to infiltrate the global circulation system and can be transported by air and water for large distances. Currently, PCBs are found everywhere, including areas far removed from the places of their production and use.

Like other POPs, PCBs are carried to the Arctic region by air currents from the mid-latitudes and intensively accumulate in the environment. According to some estimates, approximately 1 ton of PCBs falls out per year in the Murmansk region due to long-range atmospheric transport.

It has been established that PCBs can be carried by some rivers.  Low air and surface temperatures in the Arctic, snow cover and absence of light during long winters drastically slow down intensity of POPs biological (microbial) degradation and assimilation.  

Thus, the Arctic climatic conditions contribute to the accumulation of PCBs in water, soil and bottom sediments.

PCBs passing along food chains (bioconcentration) and their accumulation in fat-containing tissues are dangerous. It has been established that the PCBs rate of accumulation in some biological objects reaches millions of times. Therefore, even if PCBs concentrations in the environment are low, there is risk of their accumulation in human bodies, as the top link in the food chain. PCBs, like the vast majority of POPs, are lipotropic and accumulated in fat-containing tissues of animals. High fat proportion in the traditional diet of indigenous peoples of the North, contributes to excessive penetration of PCBs and other POPs into their bodies.

Special risk of exposure occurs during pregnancy, because PCBs, like other POPs, are easily transferred through the placenta, penetrating the fetus during growth. To date, it has been proved that PCBs have pronounced embryotoxic and potential carcinogenic effects. However, the mutagenic impact is the most dangerous.

Decades of widespread use of PCBs in power and other industries have caused significant deterioration of environmental conditions which poses health and reproduction risks in future generations, increases child mortality and reduces life expectancy in humans.

Therefore, it is necessary to obtain objective data on quantities of electric equipment and volumes of PCB-containing materials in use.  

From 1939 to 1993 approximately 180 thousand tons of PCBs were produced in the Soviet Union. Commercial products containing POPs:

• sovol - a mixture of tetra-and pentachlorinated biphenyls;
• sovtol – a mixture of sovol with 1,2,4-trichlorobenzene, ratio 9:1;
• trichlorobiphenyl (TCB) - a mixture of trichlorobiphenyl isomers.

Sovol is used as a plasticizer to manufacture paint materials, lubricants. Up to 1969 it was used as insulating fluids in capacitors and in the defense industry. By now all products with addition of sovol have been used up.

Electric engineering was the main consumer of sovtol and TCB. Sovtol was used as dielectric fluid in transformers of TNZP and TNZ types. TCB was used as insulating fluid in KS power capacitors.  

Other consumers (the automobile, petrochemical and forest chemical industries, metallurgy and machinery, defense, construction companies and organizations) used 0.25% to 0.35% of sovtol produced.

More than half of the manufactured TCB was delivered to the electric power industry enterprises in the Former Soviet Republics.

Transformers and capacitors have a long service life (25-40 years), so part of PCB-containing equipment is still in operation (PCB transformers, PCB-filled capacitors).

• 380 power transformers filled with sovtol-10 or foreign analogs; 
• over 46,000 power PCB-containing capacitors;
• 29 containers with PCB-based dielectric fluids;
• around 40 thousand small-sized capacitors
• have been reported in Belarus.                                                               

The total number of detected PCBs is estimated at more than 1,500 tons (net), including:

• in power transformers - 860 tons;
• in power capacitors - 690 tons

It has been established that PCB-containing equipment is installed at enterprises working in different fields: the mechanical engineering, metal working, electric power, chemical, petrochemical, light and food industries, housing and communal services and in many others. The largest quantities of PCBs are concentrated at engineering plants (40%) and petrochemical enterprises (25%).

In Belarus 762 companies have been found to have PCB-containing equipment on balance. These companies are spread throughout the country.

PCBs are released into the environment due to leaks from damaged electrical equipment. Damage of metal casings, physical wear of equipment, casings corrosion are among the main causes of damage.

PCBs environmental impact and mitigation measures

Many European countries have developed measures regulating production, use, recycling and disposal of PCBs. These measures include:

• total ban of PCBs production;
• gradual replacement of PCBs by alternative materials with less toxic properties;
• management of PCB-containing materials during their operation, storage, transportation and disposal;
• development of effective environmentally friendly recycling technologies and disposal of PCB-containing materials; waste disposal management;
• new Regulations for PCB-containing equipment, taking into account more rigorous requirements to ecological safety during production.

The most promising way to reduce the amount of PCBs in the environment is to process them into environmentally friendly products. The following PCBs processing techniques can be distinguished:

• alkaline dechlorination (for regeneration of contaminated transformer oils);
• high temperature incineration (1200 ° C);
• plasma-chemical processing;
• photochemical oxidation by intense UV irradiation combined with ozone and hydrogen peroxide.

These techniques may include PCBs concentration prior to their processing. Concentration techniques are extraction, adsorption, dialysis, evaporation, distillation, and filtration. These techniques gain particular importance when it becomes necessary to remove PCBs residues from transformers and capacitors.

Over the past few years, thanks to liquid extraction at the critical temperature and pressure, the efficiency of PCBs extraction from units to be cleaned has significantly improved.

In general, the choice of PCBs, PCB-containing equipment or waste disposal techniques depends on the aggregate state of waste and PCBs concentration.