POLYCHLORINATED-BIPHENYLS (PCBS) IN FISH-EATING SEA BIRDS .3. MOLECULAR-FEATURES AND METABOLIC INTERPRETATIONS OF PCB ISOMERS AND CONGENERS IN ADIPOSE TISSUES

1. Enrichment factors have been calculated for several persistent PCB congeners in the adipose tissue for five species of fish-eating sea birds (female razorbills, puffins, guillemots, shags and cormorants) obtained from the same sites during 1978-1984 (see preceding papers). 2. The enrichment factor of an individual PCB is expressed as its concentration in the tissue compared with its abundance in commercial mixtures of PCBs or compared with the concentration in the tissue of the abundant congener 2,2',4,4',5,5'-hexachlorobiphenyl (congener 153, IUPAC system of numbering). 3. There were no significant differences between the five species in the enrichment factor of individual persistent PCBs compared with congener 153, indicating similar levels of diminished metabolism of this group of congeners. 4. Of the 47 individual PCBs identified, ten congeners had enrichment factors of > 1 in all of the species and these accounted for up to 70% of the concentration of total PCBs present. Some of these persistent congeners had approximately coplanar configurations (i.e. non-ortho-substituted congeners). Five congeners, which accounted for about 35% of the total concentration of PCBs in the tissues, shared the molecular feature of chlorine substituents at adjacent meta-para carbon atoms. 5. A number of congeners were identified with enrichment factors of < 1 compared with their abundance in Aroclor 1260, and very striking differences were observed between the five species in the ratio of non-persistent congeners to the persistent congener 153. These non-persistent congeners share the molecular feature of at least one pair of adjacent unsubstituted meta-para carbon atoms in the rings. This agrees with our molecular "rule" (see preceding papers) that congeners with this structural feature are subjected to metabolism by the cytochrome P-450 component of hepatic microsomal monooxygenases. 6. Evidence is presented that this molecular rule applies to the persistence or non-persistence of classes of PCBs in other biological systems and that the complete absence of H atoms at adjacent carbon atoms is an essential structural requirement for the accumulation of PCBs in tissues. 7. The persistence or non-persistence of individual PCBs is compared with their ability to induce specific isoforms of the cytochrome P-450 components of hepatic microsomal monooxygenases, and the toxic effects of individual PCBs that accumulate is discussed in terms of the potential environmental hazard that they represent.