biphenyl

A colourless solid hydrocarbon, C₁₂H₁₀, consisting of two benzene rings linked together by a single bond.

Any substituted or otherwise altered version of biphenyl, such as PCBs.

halogenated biphenyls

Another environmental factor thought to be affecting some coastal birds, although comparatively little is yet known about its extent or origin, is the presence of marine pollutants such as polychlorinated biphenyls (PCBs) and toxic heavy metals.