The kinetics of individual polychlorinated biphenyl congeners in female harbour seals (Phoca vitulina), with evidence for structure-related metabolism

Female harbour seals were held in captivity. During a period of two years, one group received contaminated fish from the Dutch Wadden Sea, while a second group was given relatively clean fish from the Atlantic Ocean. Concentrations of individual polychlorinated biphenyl (PCB) congeners were measured in fish, seal blood and occasionally in faeces of seals. The PCB patterns within each of these three ‘matrices’ were highly similar, but differed between them. According to their degree of biomagnification in seal blood, PCBs could be divided into persistent congeners and congeners with lowered concentrations. This behaviour was related to molecular structural features; congeners showing lowered concentrations possessed vicinal H atoms at either a meta-para position or at an ortho-meta position. Only in the latter case the number of ortho-chlorines present influenced the toxicokinetical behaviour of the congeners; lowered concentrations were only observed for mono-ortho chlorine containing congeners. Enzyme-mediated metabolism is the most probable cause for the relatively low contribution of such congeners to the PCB pattern in seal blood. On a wet-weight basis, the concentrations of all congeners were lower in seal blood than in their food, but when expressed on a lipid basis, the non-metabolized congeners were biomagnified. At the end of the experiment, the PCB concentrations were significantly lower (P < 0.001) in the seals which had received fish from the Atlantic Ocean.