Photomicrobial Visible Light-Induced Magnetic Mass Independent Fractionation of Mercury in a Marine Microalga

Kritee, K.; Motta, Laura C.; Blum, Joel D.; Tsui, Martin Tsz‐Ki; Reinfelder, John R.

doi:10.1021/acsearthspacechem.7b00056

Cited by 66 publications

(87 citation statements)

References 61 publications

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“…S1). This reduced-sulfur-induced negative MIF has also been observed in photoreduction of Hg(II) within marine phytoplankton cells [where Hg(II) is mostly complexed by thiols] in simulated seawater (23). The range of the negative MIF observed in euxinic sediments only requires less than ∼20% photoreduction of S-bound Hg(II) based on the experimental fractionation factor (15), suggesting that this photoreduction process is able to account for part or all of the negative MIF in our samples.…”

Section: Resultssupporting

confidence: 57%

Mercury isotope signatures record photic zone euxinia in the Mesoproterozoic ocean

Zheng

Gilleaudeau

Kah

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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Photic zone euxinia (PZE) is a condition where anoxic, H2S-rich waters occur in the photic zone (PZ). PZE has been invoked as an impediment to the evolution of complex life on early Earth and as a kill mechanism for Phanerozoic mass extinctions. Here, we investigate the potential application of mercury (Hg) stable isotopes in marine sedimentary rocks as a proxy for PZE by measuring Hg isotope compositions in late Mesoproterozoic (∼1.1 Ga) shales that have independent evidence of PZE during discrete intervals. Strikingly, a significantly negative shift of Hg mass-independent isotope fractionation (MIF) was observed during euxinic intervals, suggesting changes in Hg sources or transformations in oceans coincident with the development of PZE. We propose that the negative shift of Hg MIF was most likely caused by (i) photoreduction of Hg(II) complexed by reduced sulfur ligands in a sulfide-rich PZ, and (ii) enhanced sequestration of atmospheric Hg(0) to the sediments by thiols and sulfide that were enriched in the surface ocean as a result of PZE. This study thus demonstrates that Hg isotope compositions in ancient marine sedimentary rocks can be a promising proxy for PZE and therefore may provide valuable insights into changes in ocean chemistry and its impact on the evolution of life.

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Section: Resultssupporting

confidence: 57%

Mercury isotope signatures record photic zone euxinia in the Mesoproterozoic ocean

Zheng

Gilleaudeau

Kah

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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“…The Δ 199 Hg values of surface (25 m) zooplankton display a clear diurnal pattern, where Δ 199 Hg values are greater during the day than at night, and their isotopic composition is significantly higher than deeper samples (125–1,250 m, Wilcoxon test, W = 15, p < 0.01). A diurnal cycle of Δ 199 Hg values in zooplankton is expected given the recent reports that marine phytoplankton and bacterioplankton can photochemically degrade Hg (Grégoire & Poulain, ; Kritee et al, ; Lee & Fisher, ). We suggest the Δ 199 Hg value in surface zooplankton represents the isotopic composition of photodegraded MMHg in phytoplankton or particle‐associated MMHg that has been photodemethylated before entering the food web.…”

Section: Discussionmentioning

confidence: 96%

Mercury Cycling in the North Pacific Subtropical Gyre as Revealed by Mercury Stable Isotope Ratios

Motta

Blum

Johnson

et al. 2019

Global Biogeochemical Cycles

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The oceans are an important global reservoir for mercury (Hg), and marine fish consumption is the dominant human exposure pathway for its toxic methylated form. A more thorough understanding of the global biogeochemical cycle of Hg requires additional information on the mechanisms that control Hg cycling in pelagic marine waters. In this study, Hg isotope ratios and total Hg concentrations are used to explore Hg biogeochemistry in oligotrophic marine environments north of Hawaii. We present the first measurements of the vertical water column distribution of Hg concentrations and the Hg isotopic composition in precipitation, marine particles, and zooplankton near Station ALOHA (22°45′N, 158°W). Our results reveal production and demethylation of methylmercury in both the euphotic (0–175 m) and mesopelagic zones (200–1,000 m). We document a strong relationship between Hg isotopic composition and depth in particles, zooplankton, and fish in the water column and diurnal variations in Δ199Hg values in zooplankton sampled near the surface (25 m). Based on these observations and stable Hg isotope relationships in the marine food web, we suggest that the Hg found in large pelagic fish at Station ALOHA was originally deposited largely by precipitation, transformed into methyl‐Hg, and bioaccumulated in situ in the water column. Our results highlight how Hg isotopic compositions reflect abiotic and biotic production and degradation of methyl‐Hg throughout the water column and the importance of particles and zooplankton in the vertical transport of Hg.

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“…Previously, there was little to no mechanistic data available for direct phototroph-mediated MeHg demethylation (Grégoire and Poulain 2014). Recently, Kritee et al 2017 used Hg stable isotope fractionation in Isochrysis galbana to demonstrate MeHg demethylation in algal cells. In this study, cells preferentially demethylated lighter MeHg isotopes resulting in a pool of isotopically light Hg II (Kritee et al 2017).…”

Section: Phototrophic Methylmercury Demethylationmentioning

confidence: 99%

Shining light on recent advances in microbial mercury cycling

Grégoire

Poulain

2018

FACETS

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Mercury (Hg) is a global pollutant emitted primarily as gaseous Hg0 that is deposited in aquatic and terrestrial ecosystems following its oxidation to HgII. From that point, microbes play a key role in determining Hg’s fate in the environment by participating in sequestration, oxidation, reduction, and methylation reactions. A wide diversity of chemotrophic and phototrophic microbes occupying oxic and anoxic habitats are known to participate directly in Hg cycling. Over the last few years, new findings have come to light that have greatly improved our mechanistic understanding of microbe-mediated Hg cycling pathways in the environment. In this review, we summarize recent advances in microbially mediated Hg cycling and take the opportunity to compare the relatively well-studied chemotrophic pathways to poorly understood phototrophic pathways. We present how the use of genomic and analytical tools can be used to understand Hg transformations and the physiological context of recently discovered cometabolic Hg transformations supported in anaerobes and phototrophs. Finally, we propose a conceptual framework that emphasizes the role that phototrophs play in environmental Hg redox cycling and the importance of better characterizing such pathways in the face of the environmental changes currently underway.

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Photomicrobial Visible Light-Induced Magnetic Mass Independent Fractionation of Mercury in a Marine Microalga

Cited by 66 publications

References 61 publications

Mercury isotope signatures record photic zone euxinia in the Mesoproterozoic ocean

Mercury isotope signatures record photic zone euxinia in the Mesoproterozoic ocean

Mercury Cycling in the North Pacific Subtropical Gyre as Revealed by Mercury Stable Isotope Ratios

Shining light on recent advances in microbial mercury cycling

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