Oxidative stress in songbirds exposed to dietary methylmercury

Abstract

Long-term, sublethal methylmercury exposure can cause reproductive depression, immune suppression, endocrine disruption and other problems in birds. We used two biomarkers to detect oxidative stress in livers of zebra finches (Taeniopygia guttata) developmentally exposed to sublethal levels of dietary methylmercury (0.0, 0.3, 0.6, 1.2, or 2.4 μg/g wet weight in diet). Our findings indicate that young adult finches exposed to environmentally relevant concentrations of mercury in ovo and through their diets, exhibited oxidative stress in their livers. We measured the ratio of the antioxidant glutathione in its reduced form (GSH) versus its oxidized form (GSSG) and the activity of the superoxide dismutase (SOD) enzyme suite. Blood total mercury served as a proxy for liver mercury concentration, and was on average 8.4 times the dietary dose (e.g., birds consuming 0.6 μg/g had blood mercury levels of ~5 μg/g on a wet weight basis). Consistent with what is known from large, aquatic bird species, there was a significant, negative relationship between GSH/GSSG ratios and tissue mercury concentrations, which is indicative of oxidative stress. This relationship was driven by a significant increase in the oxidized glutathione in the livers of birds with higher blood mercury levels. SOD activity was also found to have a significant, negative relationship with blood mercury.

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Acknowledgments

This study was funded by E. I. DuPont de Nemours and Company and completed with oversight from the South River Science Team, which is a collaboration of state and federal agencies, academic institutions and environmental interests. Additional funding was provided by the Howard Hughes Medical Institute Undergraduate Science Education Program grant and a Llanslo-Sherman award from the Department of Biology at the College of William and Mary to KAH.

Conflict of interest

The authors declare that they have no conflict of interest.

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Correspondence to Eric L. Bradley.

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The experiments conducted in this study were approved by the Institutional Animal Care and Use Committee (IACUC) of the College of William and Mary.

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Henry, K.A., Cristol, D.A., Varian-Ramos, C.W. et al. Oxidative stress in songbirds exposed to dietary methylmercury. Ecotoxicology 24, 520–526 (2015). https://doi.org/10.1007/s10646-014-1400-x

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Keywords

  • Glutathione
  • Liver
  • Mercury
  • Oxidative stress
  • Songbird
  • Superoxide dismutase