Joel D. Blum Michael B. Singer Mark C. Marvin-DiPasquale Martin T.K. Tsui Patrick M. Donovan 2016 <p>Monomethyl mercury (MMHg) and total mercury (THg) concentrations and Hg stable isotope ratios (&delta;²⁰²Hg and &Delta;¹⁹⁹Hg) 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 &delta;²⁰²Hg (&minus;1.69 to &minus;0.20&permil;) reflecting the heterogeneity of Hg mining sources in sediment. The &delta;²⁰²Hg 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 (&delta;²⁰²Hg and &Delta;¹⁹⁹Hg) 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 &delta;²⁰²Hg of pre-photodegraded MMHg and sediment IHg. Cache Creek had mass dependent fractionation (MDF; &delta;²⁰²Hg) of at least &minus;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 (&minus;MDF) is unique compared to +MDF observed in non-flowing water environments such as wetlands, lakes, and the coastal ocean.</p> application/pdf 10.1016/j.scitotenv.2016.04.139 en Elsevier Methylmercury degradation and exposure pathways in streams and wetlands impacted by historical mining article