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

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 ?g/g MeHg) or was switched to food pellets with 1.0 ?g/g or 4.0 ?g/g of added MeHg, for a period of 2 months. The difference in ?(202)Hg (MDF) and ?(199)Hg (MIF) between fish tissues and food pellets with added MeHg was within the analytical uncertainty (?(202)Hg, 0.07 ‰; ?(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 ?(202)Hg and ?(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.

SUBMITTER: Kwon SY

PROVIDER: S-EPMC4347840 | biostudies-literature | 2012 Jul

REPOSITORIES: biostudies-literature

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

Kwon Sae Yun SY Blum Joel D JD Carvan Michael J MJ Basu Niladri N Head Jessica A JA Madenjian Charles P CP David Solomon R SR

Environmental science & technology 20120627 14

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 ...[more]

PMID: 22681311

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Project description:Hydrogen isotope (?2H) measurements of consumer tissues in aquatic food webs are useful tracers of diet and provenance and may be combined with ?13C and ?15N analyses to evaluate complex trophic relationships in aquatic systems. However, ?2H measurements of organic tissues are complicated by analytical issues (e.g., H exchangeability, lack of matrix-equivalent calibration standards, and lipid effects) and physiological mechanisms, such as H isotopic exchange with ambient water during protein synthesis and the influence of metabolic water. In this study, ?2H (and ?15N) values were obtained from fish muscle samples from Lake Winnipeg, Canada, 2007-2010, and were assessed for the effects of species, feeding habits, and ambient water ?2H values. After lipid removal, we used comparative equilibration to calibrate muscle ?2H values to nonexchangeable ?2H equivalents and controlled for H isotopic exchange between sample and laboratory ambient water vapor. We then examined the data for evidence of trophic ?2H enrichment by comparing ?2H values with ?15N values. Our results showed a significant logarithmic correlation between fork length and ?2H values, and no strong relationships between ?15N and ?2H. This suggests the so-called apparent trophic compounding effect and the influence of metabolic water into tissue H were the potential mechanisms for ?2H enrichment. We evaluated the importance of water in controlling ?2H values of fish tissues and, consequently, the potential of H isotopes as a tracer of provenance by taking account of confounding variables such as body size and trophic effects. The ?2H values of fish appear to be a good tracer for tracking provenance, and we present a protocol for the use of H isotopes in aquatic ecosystems, which should be applicable to a broad range of marine and freshwater fish species. We advise assessing size effects or working with fish of relatively similar mass when inferring fish movements using ?2H measurements.

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

Publications

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

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