title: Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the Northeastern U.S.
abstract: We measured mercury (Hg) isotope ratios in sediments and various estuarine organisms (green crab, blue mussel, killifish, eider) to investigate methylmercury (MMHg) sources and exposure pathways in five Northeast coast (U.S.) estuaries. The mass independent Hg isotopic compositions (MIF; Δ(199)Hg) of the sediments were linearly correlated with the sediment 1/Hg concentrations (Δ(199)Hg: r(2) = 0.77, p < 0.05), but the mass dependent isotope compositions (MDF; δ(202)Hg) were not (r(2) = 0.26, p = 0.16), reflecting inputs of anthropogenic Hg sources with varying δ(202)Hg. The estuarine organisms all display positive Δ(199)Hg values (0.21 to 0.98 ‰) indicating that MMHg is photodegraded to varying degrees (5-12%) prior to entry into the food web. The δ(202)Hg and Δ(199)Hg values of most organisms can be explained by a mixture of MMHg and inorganic Hg from sediments. At one contaminated site mussels have anomalously high δ(202)Hg, indicating exposure to a second pool of MMHg, compared to sediment, crabs and fish. Eiders have similar Δ(199)Hg as killifish but much higher δ(202)Hg, suggesting that there is an internal fractionation of δ(202)Hg in birds. Our study shows that Hg isotopes can be used to identify multiple anthropogenic inorganic Hg and MMHg sources and determine the degree of photodegradation of MMHg in estuarine food webs.
authors.affiliation: Department of Earth and Environmental Sciences, University of Michigan , 1100 N. University Avenue, Ann Arbor, Michigan 48109, United States.
authors.forename: Sae Yun
authors.initials: SY
authors.lastname: Kwon
authors.forename: Joel D
authors.initials: JD
authors.lastname: Blum
authors.forename: Celia Y
authors.initials: CY
authors.lastname: Chen
authors.forename: Dustin E
authors.initials: DE
authors.lastname: Meattey
authors.forename: Robert P
authors.initials: RP
authors.lastname: Mason
mesh_terms: D000818:Animals; D058448:Biota; D005591:Chemical Fractionation; D004784:Environmental Monitoring; D063366:Estuaries; D020387:Food Chain; D019015:Geologic Sediments / Q000737:chemistry; D008628:Mercury / Q000032:analysis*; D008629:Mercury Isotopes / Q000032:analysis; D008767:Methylmercury Compounds / Q000032:analysis*; D009511:New England; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D008629:Mercury Isotopes; D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D008628:Mercury