Dynamics of persistent organic pollutants (POPs) in finless porpoises (Neophocaena asiaeorientalis): Accumulation, tissue-specific distribution, and maternal transfer

Abstract

Marine mammals accumulate a high level of organic contaminants, such as persistent organic pollutants (POPs), due to their high trophic level, large lipid contents, and low metabolic capacity. However, POPs are known to be toxic, which can ultimately adversely affect the population of marine mammals. In this study, the accumulation, tissue distribution, and maternal (placental) transfer of various POPs, including PCBs, OCPs (DDTs, CHLs, HCHs, and HCB), PBDEs, and PFASs, were analyzed in numerous organs and tissues of finless porpoises (Neophocaena asiaeorientalis) from Korean coastal waters. This is the first study to examine the time trends, tissue-specific distribution, and placental transfer of emerging PFASs (FOSA and F-53B) in marine mammals. DDTs followed by PCBs were still found at the highest concentration compared to other chemicals in the blubber of finless porpoises from 2015, suggesting the strong persistence of those chemicals after their long-term regulation. Among the PFASs, the concentration of PFOS was the highest in the liver, and long chain carboxylates (PFUnDA and PFTrDA) were dominantly present. In particular, the concentration of F-53B was the third highest followed by PFOS and PFUnDA, which indicates its historical and/or current use in Korea and its bioaccumulative properties. Depending on the age and sex of the specimens, lipophilic POPs increased with age and decreased after gestation and lactation, while PFASs showed the highest concentration in younger specimens. This result might be derived from matrix differences where blubber functions as a final storage site, while the liver reflects more current contamination. Approximately 15%, 23%, and 15% of the finless porpoises exceeded the toxicological criteria for PCBs, DDTs, and PFOS, respectively. The POPs in finless porpoises during 2002/03–2015 showed a decreasing trend of PCBs, OCPs, and PBDEs from 2003 to 2010, and the concentrations of PCBs, DDTs, HCHs, CHLs, and PBDEs subsequently plateaued. The concentration of PFASs, including F-53B, during 2002/03–2010, showed an increasing trend, whereas FOSA did not show any trend. After 2010, the concentration of FOSA and sulfonates decreased, while carboxylates and F-53B increased, which is consistent with the local and global regulation history. In the organs and tissues of the finless porpoises, PCBs, OCPs, and PBDEs mostly accumulated in the lipid-rich tissues of the blubber and melon. In the immature specimens and mature males, the blubber and melon showed similar concentrations of PCBs and PBDEs, whereas their concentrations were higher in melon than blubber tissue in mature females. This is because the lipids in blubber are excreted before those in the melon during gestation and lactation. PFASs mostly accumulated in the liver, kidneys, and gonads due to their protein binding properties. The partitioning ratios of kidney to liver and gonad to liver showed that PFOS, PFUnDA, and F-53B tended to remain in the liver. The body burden of POPs showed that over 90% of the PCBs, OCPs, and PBDEs were in the blubber, whereas PFASs were primarily found in the liver and muscles. Among four mother–fetus pairs, the concentration of PFASs was higher in the fetuses than in the mothers, which indicates that PFASs can be transferred to the fetus. The maternal concentration of PFASs was highly associated with parity, and fetus exposure was affected by gestational age. The umbilical cord to placenta ratio showed a high transport efficiency of long-chain carboxylates. Among the carboxylates, the velocity of placental transport was different depending on the carbon chain length. The total placental transfer ratios for PFASs, FOSA, and F-53B were 58%, 2.7%, and 74%, respectively, which implies that fetuses are exposed to PFASs to a greater extent than lipophilic POPs during pregnancy. Considering the higher accumulation and placental transfer of POPs, continuous regulation and management is needed to conserve populations of marine mammals.