Potentially hazardous residues of non-ortho chlorine substituted coplanar PCBs in human adipose tissue.

The non-ortho chlorine substituted coplanar polychlorinated biphenyls (PCBs), namely, 3,3',4,4'-tetra-(T4CB), 3,3'4,4',5-penta-(P5CB), and 3,3',4,4',5,5', hexachlorobiphenyl (H6CB) are found to be the most toxic congeners of PCBs eliciting toxic and biological responses typical of 2,3,7,8-tetrachloro dibenzo-p-dioxin (T4CDD). Analyses of human adipose tissues for these congeners revealed 94-860 pg/g of T4CB, 120-730 pg/g of P5CB, and 36-200 pg/g of H6CB on wet weight basis. These were significantly higher than 2,3,7,8-T4CDD detected in the same samples (less than 1-18 pg/g). On the basis of in vitro and in vivo induction of hepatic microsomal benzo(a)pyrene hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD), "T4CDD toxic equivalents" were calculated for coplanar PCBs in humans. "T4CDD toxic equivalent" for 3,3',4,4',5-P5CB was one order of magnitude higher than 2,3,7,8-T4CDD. Considering the extreme toxic potential and persistence of coplanar PCBs, their presence in the human body may pose a greater toxic threat than dioxins and dibenzofurans.