Influence of life history parameters on patterns of persistent organic pollutants in cetaceans with an emphasis on the gray whale (Eschrichtius robustus)
Hayes, Kia Rose Renwick
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The presence of persistent organic pollutants (POPs) in the marine environment is of global concern for the health of marine wildlife. These lipophilic contaminants are known to bioaccumulate in lipid-rich tissues such as marine mammal blubber and have been associated with developmental dysfunction, reproductive failure, and immunosuppression in terrestrial and marine mammals. Contaminant concentrations in marine mammals have been shown to vary across life history parameters such as sex, age, and reproductive status. Enhanced understanding of the influence of life history parameters on contaminant loads in species of cetaceans is critical for interpretation of contaminant burden monitoring. Here we provide a review of the influence of sex, age, reproductive status and other life history parameters on cetacean POP burdens and then go on to investigate these trends specifically in the eastern North Pacific gray whale (Eschrichtius robustus). This study on gray whales provides current POP concentration data and POP trends across various biological parameters to aid in the interpretation of contaminant burdens in this protected species and to inform development of future contaminant monitoring efforts. Blubber biopsies (n=121) were collected from free-swimming whales between 2003 and 2017 along the pacific coast of Canada, United States of America and Baja California, Mexico. Individuals sampled include males and females of various age-groups. To investigate maternal offloading, 19 mother and calf pairs plus 13 unpaired calves and 4 mothers were sampled. POPs and lipids were extracted from the blubber samples using dichloromethane with accelerated solvent extraction. Sample cleanup was conducted using silica/alumina column chromatography and size-exclusion high-performance liquid chromatography. POPs including polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethanes (DDTs), chlordanes (CHLDs), hexachlorocyclohexanes (HCHs), and polybrominated diphenyl ethers (PBDEs) were determined in blubber extracts using gas chromatography-mass spectrometry. Blubber lipid content was determined gravimetrically. A subset of 96 samples and 18 analytes were used for statistical modeling and revealed significant life history-related POP trends using linear regression of log-transformed congeners with multiple imputation and robust standard errors. Adult males had significantly higher POP concentrations than adult females while young whales in this study had similar concentrations across sexes. Resting mature females had slightly higher contaminant concentrations than females with calves and calves also had slightly higher contaminant concentrations than mothers. All life history related POP trends were conclusive of maternal contaminant offloading in gray whales.