PCB exposure of the smallest amount poses serious health risks. Apparently the industry used compressor oils containing PCBs which bypassed the valve seals and contaminated major pipoelines. With over 25 years of PCB fogging - millions of miles of gas pipes now hold tons of PCBs. Here is the mysterry source of PCBs investigators have not been able to locate. It's standard industry practice to inject a fine mist of oil fog into underground metal gas pipes to retard rust and corrosion.
Many large utilities are both gas and electric distributors.
These combined utilities found they were accumulating large volumes of used PCB transformer oil from their electric divisions. Since the oil was already paid for by the electrical division, it made economic sense to dispose of the used PCB oil into the gas division's pipes. Back in the 1950's there was no concern about the pollution effects of PCB exposure. Over time, such fogging procedures pumped more and more PCB oil into utility pipes. Because the gas industry is a closed fraternity, word spread about this free fogging-oil, resulting in gas pipes being contaminated with PCBs throughout the nation and across the globe.