Bioaccumulation of legacy organic contaminants in pregnant Indo-Pacific humpback dolphins (Sousa chinensis): Unique features on the transplacental transfer

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The placental transfer and congener composition of organic contaminants (OCs) in Indo-Pacific humpback dolphins have been little studied. In the present study, 16 polycyclic aromatic hydrocarbons (PAHs), 18 organochlorine pesticides (OCPs), and 28 polychlorinated biphenyl (PCB) congeners were analyzed in muscle, lung, liver, kidney, and blubber tissues from three mother–fetus pairs of this species stranded along the Pearl River Estuary, China. For PCBs, tetra-, penta-, hexa-, and hepta-chlorobenzene congeners were dominant in all the analyzed samples. Among them, hexachlorobenzene congeners showed the highest level in most dolphin mother-fetus tissue samples. The concentrations of PCBs and OCPs in adult females were higher in the detoxification organs (liver and kidneys) than in the muscles and lungs, whereas muscle tissues in fetuses generally exhibited higher PCBs and OCPs levels than the livers and kidneys. The most abundant PAHs in the four tissues were those with lower molecular weights, which were also the most water-soluble and bioavailable. Negative correlations between the octanol/water partition coefficients (log KOW) and the fetus/mother ratios for PCB congeners revealed that the transfer of PCBs may be determined by their lipid solubility. OCPs and PCBs with low molecular weights and low log KOW values would be more likely to accumulate in the dolphin liver, lung, kidney and muscle tissues. Furthermore, OCs with low molecular weights and low log KOW values were more concentrated in the fetal blubber, lung, and liver tissues than in their respective mothers. The ubiquitous existence of OCs in the mother–fetus pairs strongly suggested that these contaminants could pass through the placenta and partition in fetal tissue. The high transfer efficiency of PAHs and PCBs indicated that the placenta might not be an efficient barrier for these pollutants. PCBs levels in both mother and fetus dolphins could cause immunosuppression.