Stereochemical effects of PCBs in the marine environment: Seasonal variation of coplanar and atropisomeric PCBs in blue mussels (Mytilus edulis L.) of the german bight

The toxic potential of coplanar polychlorinated biphenyls (PCBs), expressed by their toxic equivalent (TEQ) values according to Safe and to the recent WHO/ICPS recommendations, was determined in blue mussel (Mytilus edulis L.) samples collected at six sites in the Weser, Jade, and Elbe river estuaries during the spring and the autumn period. The maximum ∑TEQ value of about 1.5 ng g−1 EOM was found in the Elbe estuary, however, at all sampling sites the ∑TEQ values were alarming during both seasons. The non-ortho coplanar congener PCB 126 turned out to give a highest toxic potential in blue mussels. Based upon the present data set the possibilities and limitations of the TEQ concept are critically discussed. Furthermore, the stereochemical aspect of atropisomeric PCBs is investigated for the first time for marine biota. Five of the nine atropisomeric congeners present in commercial PCB formulations were found in blue mussels at all six sampling sites, i.e. PCB 88, PCB 149, PCB 183, PCB 174, and PCB 171, where their concentrations were significantly lower during the autumn than during the spring period. Furthermore, the enantiomers of PCB 149 in all mussel samples collected during the spring and autumn period were separated, which revealed that only weak enzymatic degradation of atropisomeric PCBs occurs in blue mussels. Although sufficient evidence is available that chirality of atropisomeric PCBs plays an important role in many recognition events associated with enzymatic processes, a risk assessment concept is lacking that might compete with the ‘toxic equivalence factor’ concept applied to coplanar PCBs.