A structure-activity relationship (SAR) approach towards metabolism of PCBs in marine animals from different trophic levels

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A qualitative structure-activity relationship (SAR) to estimate the influence of biotransformation on the degree of bioaccumulation of chlorinated biphenyl (CB) congeners under field conditions, is presented. The CB patterns of different animal species from the western part of the Dutch Wadden Sea are used to illustrate the SAR. The CB pattern in a particular species was compared with that of the bivalve mollusc Macoma balthica. It is assumed that no biotransformation occurs in this species, the CB pattern being determined only by equilibrium partitioning between tissues and the ambient water. When no significant differences in the pattern of a group of persistent congeners existed between a given species and Macoma balthica, significantly lower relative concentrations of congeners with vicinal H-atoms in the meta- and para-positions in that species were attributed to biotransformation. The contribution of metabolizable congeners decreased in the order Macoma balthica > Nereis diversicolor > Pleuronectes platessa, Haematopus ostralegis (male juv.) > H. ostralegis (male (sub-)adult), Phoca vitulina. No significant differences in the patterns of persistent congeners were observed between the latter four species. Phoca vitulina was the only species with a lowered relative concentration of CB-118. Biotransformation of congeners with this configuration, i.e. possessing vicinal H-atoms only in the o, m position and (at maximum) one ortho-chlorine, may be significant from a toxicological point of view, as a number of toxic congeners belong to this group.