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Absence of fractionation of mercury isotopes during trophic transfer of methylmercury to freshwater fish in captivity

Sae Yun Kwon·Joel D. Blum·Michael J. Carvan·Niladri Basu·Jessica A. Head·Charles P. Madenjian·Solomon R. David
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Abstract

We performed two controlled experiments to determine the amount of mass-dependent and mass-independent fractionation (MDF and MIF) of methylmercury (MeHg) during trophic transfer into fish. In experiment 1, juvenile yellow perch ( Perca flavescens ) were raised in captivity on commercial food pellets and then their diet was either maintained on unamended food pellets (0.1 μg/g MeHg) or was switched to food pellets with 1.0 μg/g or 4.0 μg/g of added MeHg, for a period of 2 months. The difference in δ 202 Hg (MDF) and Δ 199 Hg (MIF) between fish tissues and food pellets with added MeHg was within the analytical uncertainty (δ 202 Hg, 0.07 ‰; Δ 199 Hg, 0.06 ‰), indicating no isotope fractionation. In experiment 2, lake trout ( Salvelinus namaycush ) were raised in captivity on food pellets and then shifted to a diet of bloater ( Coregonus hoyi ) for 6 months. The δ 202 Hg and Δ 199 Hg of the lake trout equaled the isotopic composition of the bloater after 6 months, reflecting reequilibration of the Hg isotopic composition of the fish to new food sources and a lack of isotope fractionation during trophic transfer. We suggest that the stable Hg isotope ratios in fish can be used to trace environmental sources of Hg in aquatic ecosystems.

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Sae Yun Kwon, Joel D. Blum, Michael J. Carvan, Niladri Basu, Jessica A. Head, Charles P. Madenjian, Solomon R. David. 2012-06-27. Absence of fractionation of mercury isotopes during trophic transfer of methylmercury to freshwater fish in captivity. https://doi.org/10.1021/es300794q

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