polychlorinated biphenyls polychlorinated biphenyl compounds PCB's PCBs PCB's PCB's PCBs produced PCBs PCBs produced PCB's PCBs polychlorinated biphenyls polychlorinated biphenyls polychlorinated biphenyls PCB's PCBs polychlorinated biphenyl compounds PCBs polychlorinated biphenyls used in many different products PCBs PCBs PCB's polychlorinated biphenyl compounds compounds were removed from use in the 1970s http://www.greenfacts.org/en/pcbs/ PCBs produced produced PCBs PCBs PCB's produced PCBs produced PCBs PCBs