Biological Activity, Determination and Occurrence of Planar, Mono- and Di-Ortho PCBs

Of the 209 PCB congeners, the planar congeners have the greatest harmful effect on the environment. The introduction of chlorine atoms (called mono-ortho substitution for one atom, di-ortho for two) into the central phenyl-phenyl bond of the PCB does not seem to reduce the toxicity of these congeners very much. Because of the extremely low concentrations of planar PCBs found in the environment, the determination of such concentrations and analysis of the effect of these congeners on wildlife require unusual gas chromatography procedures such as the use of large sample sizes. Although there are important data available concerning planar, mono-ortho, and di-ortho PCB concentrations in marine mammals, these data are not a sufficient basis for an ecotoxicological evaluation. Even less information is available on concentrations in other aquatic life and in terrestrial ecosystems. However, these PCBs may be responsible for the local extinctions of certain aquatic mammals in polluted European waters.