Methylmercury degradation and exposure pathways in streams and wetlands impacted by historical mining

Patrick M. Donovan; Joel D. Blum; Michael B. Singer; Mark C. Marvin-DiPasquale; Martin T.K. Tsui

doi:10.1016/j.scitotenv.2016.04.139

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Methylmercury degradation and exposure pathways in streams and wetlands impacted by historical mining

Patrick M. Donovan·Joel D. Blum·Michael B. Singer·Mark C. Marvin-DiPasquale·Martin T.K. Tsui

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Abstract

Monomethyl mercury (MMHg) and total mercury (THg) concentrations and Hg stable isotope ratios (δ 202 Hg and Δ 199 Hg) were measured in sediment and aquatic organisms from Cache Creek (California Coast Range) and Yolo Bypass (Sacramento Valley). Cache Creek sediment had a large range in THg (87 to 3870 ng/g) and δ 202 Hg (−1.69 to −0.20&permil;) reflecting the heterogeneity of Hg mining sources in sediment. The δ 202 Hg of Yolo Bypass wetland sediment suggests a mixture of high and low THg sediment sources. Relationships between %MMHg (the percent ratio of MMHg to THg) and Hg isotope values (δ 202 Hg and Δ 199 Hg) in fish and macroinvertebrates were used to identify and estimate the isotopic composition of MMHg. Deviation from linear relationships was found between %MMHg and Hg isotope values, which is indicative of the bioaccumulation of isotopically distinct pools of MMHg. The isotopic composition of pre-photodegraded MMHg (i.e., subtracting fractionation from photochemical reactions) was estimated and contrasting relationships were observed between the estimated δ 202 Hg of pre-photodegraded MMHg and sediment IHg. Cache Creek had mass dependent fractionation (MDF; δ 202 Hg) of at least −0.4&permil; whereas Yolo Bypass had MDF of +0.2 to +0.5&permil;. This result supports the hypothesis that Hg isotope fractionation between IHg and MMHg observed in rivers (−MDF) is unique compared to +MDF observed in non-flowing water environments such as wetlands, lakes, and the coastal ocean.

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Science of the Total Environment Article

Source-reported bounding extent: 38.464611135935776° to 39.00771295997199° latitude; -122.53292083740234° to -121.57779693603517° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Patrick M. Donovan, Joel D. Blum, Michael B. Singer, Mark C. Marvin-DiPasquale, Martin T.K. Tsui. 2016. Methylmercury degradation and exposure pathways in streams and wetlands impacted by historical mining. https://doi.org/10.1016/j.scitotenv.2016.04.139

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