Biotransformation and thyroidogenic effects of organochlorine and organobromine pollutants in avian and mammalian top predator sentinel species

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Man-made chemicals that persist and bioaccumulate in the environment are increasingly being linked to adverse effects in wildlife and humans. Many bioaccumulative "legacy" and "emerging' contaminants found wildlife contain chlorine and bromine, including polychlorinated biphenyls (PCBs) and the brominated flame retardant (BFR) class known as polybrominated diphenyl ethers (PBDEs). An organism's ability to eliminate organohalogens and other foreign chemicals from the body is dependent on enzymes that can mediate metabolism and biotransformation. Much remains unknown as to role and significance of biotransformation (e.g., oxidative and debromination processes) in the fate and bioaccumulation of chlorinated and brominated organohalogens, which includes the formation of hydroxyl- (OH-) containing or "phenolic" metabolites, in different species and food webs, and especially in top predator wildlife. As has been shown for PCBs and PBDEs in some wildlife, biotransformation can lead to persistent OH-PCB and OH-PBDE metabolites, although there remains minimal understanding of the formation, bioaccumulation and toxicokinetics of these "second level" pollutants. OH-PCBs, OH-PBDEs, related phenolic compounds/metabolites, and debrominated products of PBDEs and current-use BFRs are "bioactive" via hormone mimicry, and can interfere with thyroid hormone-dependent functions and processes (e.g., hormone transport and enzyme-mediated inter-conversion). Endocrine (thyroid) activity and effects in relation to organohalogen biotransformation has received minimal attention in top predator, marine wildlife, which accumulate high organohalogen levels. The proposed research will expand the understanding and commence with new research on the species-specific role, mechanisms and environmental ecological importance and significance of biotransformation in the fate, bioaccumulation and thyroid hormone transport/inter-conversion, on legacy and emerging, chlorinated and brominated organics in top-predator wildlife sentinels of contaminant and other (e.g., climate change) stresses from the Great Lakes (herring gulls) and the Arctic (polar bears and glaucous gulls).