Polychlorinated biphenyls (PCBs) were widely used in capacitors, machine oils, and as heat transfer fluids in heat exchangers due to their chemical stability and high insulating properties. However, because they pose a risk of causing health problems such as liver dysfunction and dermatitis, their manufacture was banned in 1972 following the Kanemi Oil Poisoning Incident in 1968.

Polychlorinated biphenyls (PCBs) were widely used in capacitors, machine oils, and as heat transfer fluids in heat exchangers due to their chemical stability and high insulating properties. However, because they pose a risk of causing health problems such as liver dysfunction and dermatitis, their manufacture was banned in 1972 following the Kanemi Oil Poisoning Incident in 1968. Since PCBs do not degrade naturally, high-temperature incineration was the primary method of disposal. However, due to problems such as dioxin emissions and difficulties in securing disposal sites, approximately 40,000 tons of PCBs remain in storage, untreated. In addition, the volume of waste requiring treatment increases further when PCB-contaminated materials—such as paper scraps, wood chips, waste plastics, scrap metal, cloths used to wipe off PCBs, and containers from which PCBs have been extracted—are included. In recent years, there has been a demand for methods to replace incineration. Following amendments to the Waste Management and Public Cleansing Act, the “supercritical water oxidation method”—which oxidizes and reduces PCBs using high-pressure, high-temperature water—and the “dechlorination method”—which renders PCBs harmless by reacting chlorine with sodium or calcium—were approved in June 1998. Furthermore, the Industrial Waste Management Promotion Foundation has compiled technical evaluations of five new PCB treatment technologies currently being tested by various manufacturers, and these are expected to be legally approved around the fall of 2000. The following are the main PCB detoxification technologies developed by various companies: 1. Sodium Dispersion Method (Nippon Soda) Developed in 1995, this method causes dechlorination by reacting PCBs with fine sodium particles, decomposing them into biphenyl and sodium chloride. The treatment temperature is low, ranging from 50 to 60°C, and processing can be performed at atmospheric pressure in a short time. 2. Supercritical Fluid Processing Technology (Shine Electronics) PCBs are mixed with water and sodium hydroxide, and the mixture is vaporized under conditions of 600–650°C and 150–190 atmospheres of pressure to render the PCBs harmless in a supercritical state. After processing, the mixture is converted into water, CO₂, and salt. 3. Hydrothermal Decomposition Method (Mitsubishi Heavy Industries) PCBs are fed into a high-temperature, high-pressure reaction tower along with calcium oxide and decomposed using hot water and oxygen. The final products are only salt and water, eliminating the need for further treatment. 4. Sodium Dispersion Method (Japan Nuclear Fuel Limited) Using technology introduced from Canada, PCBs are chemically decomposed using a sodium dispersion solution. The remaining oil is harmless and can be used as fuel. 5. Photodecomposition and Catalytic Decomposition Method (Toshiba) PCBs are dechlorinated by combining ultraviolet irradiation with a precious metal catalyst. This method is suitable for high-concentration PCBs. All of these technologies have completed demonstration tests and, if legally approved, will likely become viable options for businesses storing PCBs. The trust of local residents is crucial for the establishment of treatment facilities, and safety must be the top priority. The Ministry of Health and Welfare is also supporting the widespread adoption of these technologies and plans to construct two facilities by the end of fiscal year 2000. Thus, thanks to advances in PCB detoxification technologies, a ray of hope is beginning to emerge for the long-standing PCB problem.