Browsing by Author "Chin, Yu-Ping"

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    Assessing Iron Complexation by Dissolved Organic Matter Using Mediated Electrochemical Oxidation
    (ACS Earth and Space Chemistry, 2024-08-14) Hudson, Jeffrey M.; Luther, George W., III; Chin, Yu-Ping
    FeII is an abundant reductant in the environment that participates in numerous biogeochemical cycles and pollutant attenuation. FeII in aquatic environments can exist as a complex with dissolved organic matter (DOM), where organic ligands in DOM can modulate iron’s redox potential (EH) and henceforth reactivity as a reductant. Previous studies have assessed the reactivity of FeII-complexes using probe compounds, although these compounds are limited in their ability to profile FeII oxidation across multiple thermodynamic conditions (i.e., both pH and EH) and fail to validate the EH of Fe(II)-complexes via their direct measurement. This study elucidated the redox potentials of FeII-DOM complexes via mediated electrochemical oxidation (MEO) and assessed the extent of FeII oxidation at two different applied EH and pH regimes. Furthermore, we used a Nernstian-based model calibrated with a training set between known iron-ligand thermodynamic stability constants and their respective measured potentials to indirectly determine the stability constants of both FeII and FeIII-DOM complexes as a function of EH and pH. This work highlights the versatility of MEO as an electrochemical technique and is the first to assess stability constants of Fe-complexes with aquatic DOM isolates. We also discuss linkages between speciation modeling and redox reactivity of FeII.
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    Distribution and composition of redox-active species and dissolved organic carbon in Arctic lacustrine porewaters
    (Arctic, Antarctic, and Alpine Research, 2024-07-22) Xin, Danhui; Hudson, Jeffrey M.; Sigman-Lowerya, Anthony; Chin, Yu-Ping
    The interaction between redox-active species and dissolved organic carbon (DOC) is crucial in driving lacustrine benthic microbial processes. In lacustrine porewaters, many redox-active species exist in their reduced form, while DOC acts as a substrate and an electron acceptor. Understanding the types and abundance of redox-active species in porewaters along with their complementary DOC substrate is pivotal for gaining insights into benthic processes, particularly in regions susceptible to climate change. We report the in-situ measurement of redox-active species in sediment porewaters, alongside the ex-situ measurement of DOC extracted from cores collected from two Arctic lakes (Toolik and Fog 1). Fe2+ was abundantly detected below 4 cm of the sediment-water interface in all cores and was inversely related to dissolved O2. Additionally, two distinct Fe(III)-complexes were identified. DOC ranged in the order of 10s of mg/L and either remained stable or increased with depth. A comparison between Toolik and Fog 1 lakes revealed a higher accumulation of Fe2+ and DOC in the latter. This study marks the first of its kind to assess spatial distributions of redox-active species and DOC as a function of depth from multiple sites in Arctic lacustrine porewaters.
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    Photofate of Tetrabromobisphenol-A in the Arctic: Role of photofluence and dissolved organic matter
    (Arctic, Antarctic, and Alpine Research, 2024-08-09) O’Halloran, Robyn C.; Kerrigan, Jill; O’Connor, Lauren E.; Guerard, Jennifer J.; Hageman, Kimberly J.; Chin, Yu-Ping
    Polybrominated diphenyl ethers (PBDEs) used in consumer goods and flame retardants have been replaced by alternatives such as tetrabromobisphenol A (TBBPA). TBBPA does not readily undergo global distal transport, but local sources still threaten aquatic ecosystems. We studied the photofate of TBBPA with a specific focus on how Arctic-derived dissolved organic matter (DOM) affects its reaction kinetics, degradation pathways and formation of photoproducts in artificial and natural sunlight. Our results corroborate earlier studies that reveal a pH-dependent trend in TBBPA’s direct photolysis with longer degradation times for its acidic form. DOM either plays no role or it slightly reduces TBBPA’s rate of photodegradation via inner-filter effects. Photolysis experiments conducted at our Arctic field site, Toolik Lake Field Station, revealed slower than anticipated degradation, which magnified the half-life significantly during in-lake experiments. Importantly, the composition of DOM was found to influence the type and distribution of TBBPA photoproducts formed, which suggests that different degradation pathways occur in the presence of DOM. These findings provide valuable insights into the intricate interplay of environmental variables that govern the fate of TBBPA in sunlit aquatic ecosystems globally. Graphical Abstract available at: https://doi.org/10.1080/15230430.2024.2372867