Dynamics of PCB transfer from mother to pup during lactation in UK grey seals <i>Halichoerus grypus</i>: Differences in PCB profile between compartments of transfer and changes during the lactation period

The composition of the PCB mixture which is transferred from mother to pup in grey seals Halichoerus grypus throughout lactation was measured in the successive compartments of transfer: maternal blubber, maternal serum, milk and pup serum. Mother-pup pairs were captured regularly between birth and weaning on the Isle of May, Scotland. The PCB profiles of the different compartments of transfer consisted mainly of congeners 153, 138, 180, 187, 170 and 101, which made up 85% of the total PCB burden. Outer blubber contained higher relative concentrations (R153) of hepta-, octa-, and nona-chlorinated congeners (higher chlorinated congeners) than inner blubber, at both early (≤5 d) and late (≥11 d) lactation. The change in the composition of the outer blubber layer between early and late lactation, while in the inner blubber, there was a slight increase in the R153 of higher chlorinated congeners at late lactation. In maternal serum, profiles changed towards having a higher proportion of higher chlorinated congeners as lactation progressed, but in milk, the PCB pattern stayed constant throughout lactation. Surprisingly, in pup serum profiles also changed towards higher R153 of higher chlorinated congeners at late lactation compared to early lactation, which was different to the pattern observed in milk. In all body compartments, higher proportions of higher chlorinated congeners were associated with higher concentrations of total PCBs. Maternal blubber and pup serum contained a higher R153 of higher chlorinated congeners than milk and, to a lesser extent, maternal serum. Thus biomagnification of the higher chlorinated congeners was recorded in pup serum.