POLYCHLORINATED BIPHENYLS (PCB's) - Environmental Implications

Production & Major Commercial uses of PCB's

The commercial production of PCB’s began in 1930 and they have been used widely in electrical equipments. Between 1930 and 1977, the sole manufacturer of PCB’s in United States – M/s Monsanto Company produced approx. 700,000 tonnes of PCB’s, of which 75,000 tonnes were exported from the United States. By the end of 1980, the total world production of PCB’s was in excess of 1 million tonnes and since then the production of PCB’s has continued in several countries. Despite increasing withdrawal of the use and restrictions on the production of PCB’s, very large amounts of these compounds continue to be used and existing in the environment, due to their unabated contribution in the past from their use or from the waste.

The major use of PCB's can be grouped in three major categories:
  1. Open Uses e.g. use in paints, inks, plastics, paper coating, de-dusting agent, fire retardants, adhesives etc.
  2. Use in partially closed system - heat exchangers, hydraulic system, vacuum pump, gas transmission, turbine, electrical capacitors and electrical transformers.
  3. Closed system use - In closed system use the chances of PCB release to environment are comparatively less.
PCB's are valuable for industrial applications due to their chemical inertness, resistance to heat, low vapor pressure (particularly with the high chlorinated compounds), non-flammability and high dielectric constant. Throughout the 20th century, PCB's were used for many diverse purposes ranging from dielectric fluids to pesticide carriers. Their uses had been curtailed sharply in recent times. In a span of less than 20 years PCB's have moved from one of the most widely used chemicals to one of the most tightly controlled chemicals, because of their environmental implications in various other countries. The uses of PCB's for various applications is depicted in Fig. 2. PCB's are used for various applications viz. capacitors, transformers etc. The technical PCB's mixtures used in transformers are mostly highly chlorinated e.g. Aroclor 1254 and Aroclor 1260. Smaller volumes of PCB's have been often used as fire resistant liquid because of their high flash point. The valuable properties of PCB's as plasticizers has led to their use in furnishings, interior decoration, surface treatment for textiles, adhesive for water proof wall coatings, paints, putties and sealant. PCB's have also been used as plasticizers for plastic materials and in the formulation of printing inks. Although, most PCB's related activities have been banned or tightly restricted in western countries. PCB's still remain in industrial and commercial use in allowable concentration. In India, the uses of PCB for various purposes are not much clear and no definite information about these are readily available. However, it may be predicted that these compounds are extensively been used for various purposes in India.