title: Isotopic Composition of Inorganic Mercury and Methylmercury Downstream of a Historical Gold Mining Region.
abstract: We measured total mercury (THg) and monomethyl mercury (MMHg) concentrations and mercury (Hg) isotopic compositions in sediment and aquatic organisms from the Yuba River (California, USA) to identify Hg sources and biogeochemical transformations downstream of a historical gold mining region. Sediment THg concentrations and δ(202)Hg decreased from the upper Yuba Fan to the lower Yuba Fan and the Feather River. These results are consistent with the release of Hg during gold mining followed by downstream mixing and dilution. The Hg isotopic composition of Yuba Fan sediment (δ(202)Hg = -0.38 ± 0.17‰ and Δ(199)Hg = 0.04 ± 0.03‰; mean ± 1 SD, n = 7) provides a fingerprint of inorganic Hg (IHg) that could be methylated locally or after transport downstream. The isotopic composition of MMHg in the Yuba River food web was estimated using biota with a range of %MMHg (the percent of THg present as MMHg) and compared to IHg in sediment, algae, and the food web. The estimated δ(202)Hg of MMHg prior to photodegradation (-1.29 to -1.07‰) was lower than that of IHg and we suggest this is due to mass-dependent fractionation (MDF) of up to -0.9‰ between IHg and MMHg. This result is in contrast to net positive MDF (+0.4 to +0.8‰) previously observed in lakes, estuaries, coastal oceans, and forests. We hypothesize that this unique relationship could be due to differences in the extent or pathway of biotic MMHg degradation in stream environments.
authors.affiliation: Department of Earth and Environmental Sciences, University of Michigan , 1100 N. University Avenue, Ann Arbor, Michigan 48109, United States.
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Donovan
authors.affiliation: Department of Earth and Environmental Sciences, University of Michigan , 1100 N. University Avenue, Ann Arbor, Michigan 48109, United States.
authors.forename: Joel D
authors.initials: JD
authors.lastname: Blum
authors.affiliation: Department of Earth and Environmental Sciences, University of St Andrews , North Street, St Andrews, KY16 9AL U.K.|Earth Research Institute, University of California Santa Barbara , Santa Barbara, California 93106 United States.
authors.forename: Michael Bliss
authors.initials: MB
authors.lastname: Singer
authors.affiliation: U.S. Geological Survey , Menlo Park, California 94025, United States.
authors.forename: Mark
authors.initials: M
authors.lastname: Marvin-DiPasquale
authors.affiliation: Department of Biology, University of North Carolina at Greensboro , Greensboro, North Carolina 27402, United States.
authors.forename: Martin T K
authors.initials: MT
authors.lastname: Tsui
mesh_terms: D000818:Animals; D002140:California; D005591:Chemical Fractionation; D004785:Environmental Pollutants / Q000737:chemistry*; D063366:Estuaries; D020387:Food Chain; D006046:Gold; D060106:Lakes / Q000737:chemistry; D008628:Mercury / Q000737:chemistry*; D008767:Methylmercury Compounds / Q000737:chemistry*; D008906:Mining / Q000379:methods*; D045483:Rivers / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis
chemical_list: D004785:Environmental Pollutants; D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D006046:Gold; D008628:Mercury