diphenyl

polybrominated biphenyl (PBB) any of various brominated derivatives of biphenyl; uses and toxic hazards are similar to those of polychlorinated biphenyls. They typically are deposited in body fat stores and are rarely mobilized except through lactation.

polychlorinated biphenyl (PCB) any of various chlorinated derivatives of biphenyl, toxic and carcinogenic nonbiodegradable compounds used as heat-transfer agents and electrical insulators; they are readily absorbed from the gastrointestinal tract, and those with a lower percentage of chlorine are associated with a higher toxicity but are more readily excreted.