Selective transfer of persistent organic pollutants and their metabolites in grey seals during lactation

Twenty grey seal (Halichoerus grypus) mother–pup pairs from the colony of the Isle of May (Scotland) were sampled at early and late lactation in order to study the transfer of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and their metabolites (HO-PCBs and HO-PBDEs) as well as organochlorine pesticides (OCPs), such as DDT and metabolites (DDXs) and hexachlorobenzene (HCB). The transfer of the naturally produced MeO-PBDEs was also investigated. Generally, concentrations (on a lipid weight basis) of the sum of PCBs, PBDEs and DDXs tended to be higher in all tissues at late lactation (for maternal outer blubber ΣPCBs=3860±2091ng/g, ΣPBDEs=120±74ng/g and ΣDDXs=559±207ng/g; for maternal inner blubber ΣPCBs=4229±3274ng/g, ΣPBDEs=148±118ng/g and ΣDDXs=704±353ng/g; for maternal serum ΣPCBs=1271±796ng/g, ΣPBDEs=27±16ng/g and ΣDDXs=242±125ng/g; for milk ΣPCBs=1190±747ng/g, ΣPBDEs=55±36ng/g and ΣDDXs=357±160ng/g; for pup serum ΣPCBs=1451±901ng/g, ΣPBDEs=48±31ng/g and ΣDDXs=395±201ng/g). In all tissues, ΣMeO-PBDEs were found at very low levels or even undetected and their concentrations appeared to increase at late lactation only in maternal inner blubber (2.7±1.3 to 5.3±2.9ng/g for early and late lactation, respectively) and milk (0.6±0.3 to 1.1±0.5ng/g for early and late lactation, respectively). The transfer from inner blubber to maternal serum was selective and strongly depended on the log Kow value of the compounds, with less lipophilic compounds being more efficiently released. Only a limited amount of HO-PCBs was transferred during lactation as 4-HO-CB-107 was the only metabolite detected in milk (29 to 40pg/g lw). On the contrary, most of HO-PCB metabolites found in maternal serum were also detected in pup serum. These findings suggest not only a transplacental transfer of HO-PCBs from mothers to pups but also the possibility of endogenous biotransformation in suckling pups or accumulation of undetectable low amounts from milk.