Understanding sources of methylmercury in songbirds with stable mercury isotopes: Challenges and future directions

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Martin Tsz-Ki Tsui, Assistant Professor (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site: http://library.uncg.edu/

Abstract: Mercury (Hg) stable isotope analysis is an emerging technique that has contributed to a better understanding of many aspects of the biogeochemical cycling of Hg in the environment. However, no study has yet evaluated its usefulness in elucidating the sources of methylmercury (MeHg) in songbird species, a common organism for biomonitoring of Hg in forested ecosystems. In the present pilot study, we examined stable mercury isotope ratios in blood of 4 species of songbirds and the invertebrates they are likely foraging on in multiple habitats in a small watershed of mixed forest and wetlands in Acadia National Park in Maine (USA). We found distinct isotopic signatures of MeHg in invertebrates (both mass-dependent fractionation [as d202Hg] and mass-independent fractionation [as ?199Hg]) among 3 interconnected aquatic habitats. It appears that the Hg isotopic compositions in bird blood cannot be fully accounted for by the isotopic compositions of MeHg in lower trophic levels in each of the habitats examined. Furthermore, the bird blood isotope results cannot be simply explained by an isotopic offset as a result of metabolic fractionation of d202Hg (e.g., internal demethylation). Our results suggest that many of the birds sampled obtain MeHg from sources outside the habitat they were captured in. Our findings also indicate that mass-independent fractionation is a more reliable and conservative tracer than mass-dependent fractionation for identifying sources of MeHg in bird blood. The results demonstrate the feasibility of Hg isotope studies of songbirds but suggest that larger numbers of samples and an expanded geographic area of study may be required for conclusive interpretation.

Additional Information

Environmental Toxicology and Chemistry. v37 n1 (Jan 2018) 166-174. https://doi.org/10.1002/etc.3941
Language: English
Date: 2018
Songbird, Wetland, Methylation, Isotopic fractionation, Trophic transfer

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