Environmental Origins of Methylmercury Accumulated in Subarctic Estuarine Fish Indicated by Mercury Stable Isotopes.
Methylmercury (MeHg) exposure can cause adverse reproductive and neurodevelopmental health effects. Estuarine fish may be exposed to MeHg produced in rivers and their watersheds, benthic sediment, and the marine water column, but the relative importance of each source is poorly understood. We measured stable isotopes of mercury (δ202Hg, Δ199Hg, and Δ201Hg), carbon (δ13C), and nitrogen (δ15N) in fish with contrasting habitats from a large subarctic coastal ecosystem to better understand MeHg exposure sources. We identify two distinct food chains exposed to predominantly freshwater and marine MeHg sources but do not find evidence for a benthic marine MeHg signature. This is consistent with our previous research showing benthic sediment is a net sink for MeHg in the estuary. Marine fish display lower and less variable Δ199Hg values (0.78‰ to 1.77‰) than freshwater fish (0.72‰ to 3.14‰) and higher δ202Hg values (marine: 0.1‰ to 0.57‰; freshwater: -0.76‰ to 0.15‰). We observe a shift in the Hg isotopic composition of juvenile and adult rainbow smelt (Osmerus mordax) when they transition between the freshwater and marine environment as their dominant foraging territory. The Hg isotopic composition of Atlantic salmon (Salmo salar) indicates they receive most of their MeHg from the marine environment despite a similar or longer duration spent in freshwater regions. We conclude that stable Hg isotopes effectively track fish MeHg exposure sources across different ontogenic stages.
Department of Environmental Health, Harvard T. H. Chan School of Public Health , Boston, Massachusetts 02115, United States.|Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University , Cambridge, Massachusetts 02138, United States.
Miling
M
Li
Department of Environmental Health, Harvard T. H. Chan School of Public Health , Boston, Massachusetts 02115, United States.|Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University , Cambridge, Massachusetts 02138, United States.
Amina T
AT
Schartup
Department of Environmental Health, Harvard T. H. Chan School of Public Health , Boston, Massachusetts 02115, United States.|Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University , Cambridge, Massachusetts 02138, United States.
Amelia P
AP
Valberg
Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University , Cambridge, Massachusetts 02138, United States.
Jessica D
JD
Ewald
U. S. Geological Survey , Middleton, Wisconsin 53562, United States.
David P
DP
Krabbenhoft
Department of Civil and Environmental Engineering, University of Wisconsin , Madison, Wisconsin 53706, United States.|State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences , Guiyang 550002, China.
Runsheng
R
Yin
Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University , Cambridge, Massachusetts 02138, United States.
Prentiss H
PH
Balcom
Department of Environmental Health, Harvard T. H. Chan School of Public Health , Boston, Massachusetts 02115, United States.|Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University , Cambridge, Massachusetts 02138, United States.
Elsie M
EM
Sunderland
D000293:Adolescent; D000818:Animals; D004784:Environmental Monitoring; D006801:Humans; D008628:Mercury; D008629:Mercury Isotopes; D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical
D008629:Mercury Isotopes; D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D008628:Mercury