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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2021)

Exposure to vanadium (V) results in adverse health outcomes in humans and a plethora of species in the environment across trophic levels. V is released from rock, slag and mine tailings, where it is able to oxidize to vanadate (VV) (HnVO4 −3+n), which poses the greatest risk to human health. Vanadate is highly soluble unlike its VIII or VIV, and is readily taken up by well systems, resulting in human exposure in areas where water treatment is minimal. However, the geochemical controls that determine the mobility of V in the environment are poorly understood, making the behavior of V in the subsurface difficult to predict. This dissertation addresses this knowledge gap by investigating the abiotic reactions of V with common iron and manganese mineral phases. These mineral phases are already known to play an important role in the fate and transport of similar contaminants, but many aspects of their specific reactivity towards V are unknown. To address this knowledge gap, their surface capacity, adsorption affinity and their ability to retain vanadate via surface complexation is investigated. The vanadate adsorption capacity and surface affinity are both found to be inversely proportional to the crystallinity of the oxide examined. One manganese oxide, birnessite is also known to promote the oxidation of many trace metal contaminants. The oxidative capacity of birnessite towards VIV is much greater than its surface capacity for VV. At the aggregate scale, birnessite, V and Fe oxides coexist in close spatial proximity where rates of diffusion limit the transport of solutes. In such an environment, birnessite effectively oxidizes VIV and retains more VV than adjacent Fe oxide phases. Further, FeII-bearing oxides can reduce VV back to VIV. However, this pathway is slow compared to the oxidation rate of VIV by birnessite. This suggests that surface complexation of vanadate, even by birnessite is a greater attenuation pathway than abiotic FeII-mediated reduction. The result of this research emphasizes the role of abiotic surface processes in constraining the mobility of V within the soil matrix which will improve the reliability of models implemented in the management and reclamation of V contaminated sites.

    Cover page: Vanadium Environmental Chemistry: Adsorption and Oxidation Processes
    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2021)
    This study investigated the reaction kinetics on the oxidative transformation of lead(ii) minerals by free chlorine (HOCl) and free bromine (HOBr) in drinking water distribution systems. According to chemical equilibrium predictions, lead(ii) carbonate minerals, cerussite PbCO3(s) and hydrocerussite Pb3(CO3)2(OH)2(s), and lead(ii) phosphate mineral, chloropyromorphite Pb5(PO4)3Cl(s) are formed in drinking water distribution systems in the absence and presence of phosphate, respectively. X-ray absorption near edge spectroscopy (XANES) data showed that at pH 7 and a 10 mM alkalinity, the majority of cerussite and hydrocerussite was oxidized to lead(iv) mineral PbO2(s) within 120 minutes of reaction with chlorine (3 : 1 Cl2 : Pb(ii) molar ratio). In contrast, very little oxidation of chloropyromorphite occurred. Under similar conditions, oxidation of lead(ii) carbonate and phosphate minerals by HOBr exhibited a reaction kinetics that was orders of magnitude faster than by HOCl. Their end oxidation products were identified as mainly plattnerite β-PbO2(s) and trace amounts of scrutinyite α-PbO2(s) based on X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopic analysis. A kinetic model was established based on the solid-phase experimental data. The model predicted that in real drinking water distribution systems, it takes 0.6-1.2 years to completely oxidize Pb(ii) minerals in the surface layer of corrosion scales to PbO2(s) by HOCl without phosphate, but only 0.1-0.2 years in the presence of bromide (Br-) due the catalytic effects of HOBr generation. The model also predicts that the addition of phosphate will significantly inhibit Pb(ii) mineral oxidation by HOCl, but only be modestly effective in the presence of Br-. This study provides insightful understanding on the effect of residual disinfectant on the oxidation of lead corrosion scales and strategies to prevent lead release from drinking water distribution systems.
      Cover page: Effects of residual disinfectants on the redox speciation of lead( ii )/( iv ) minerals in drinking water distribution systems
      • Article
      • Peer Reviewed
      UC Riverside Previously Published Works (2022)
      Anthropogenic emissions of vanadium (V) into terrestrial and aquatic surface systems now match those of geogenic processes, and yet, the geochemistry of vanadium is poorly described in comparison to other comparable contaminants like arsenic. In oxic systems, V is present as an oxyanion with a +5 formal charge on the V center, typically described as H x VO4 (3-x)-, but also here as V(V). Iron (Fe) and manganese (Mn) (oxy)hydroxides represent key mineral phases in the cycling of V(V) at the solid-solution interface, and yet, fundamental descriptions of these surface-processes are not available. Here, we utilize extended X-ray absorption fine structure (EXAFS) and thermodynamic calculations to compare the surface complexation of V(V) by the common Fe and Mn mineral phases ferrihydrite, hematite, goethite, birnessite, and pyrolusite at pH 7. Inner-sphere V(V) complexes were detected on all phases, with mononuclear V(V) species dominating the adsorbed species distribution. Our results demonstrate that V(V) adsorption is exergonic for a variety of surfaces with differing amounts of terminal -OH groups and metal-O bond saturations, implicating the conjunctive role of varied mineral surfaces in controlling the mobility and fate of V(V) in terrestrial and aquatic systems.
        Cover page: Vanadate Retention by Iron and Manganese Oxides
        • Article
        • Peer Reviewed
        LBL Publications (2024)
        Heme has a critical role in the chemical framework of the cell as an essential protein cofactor and signaling molecule that controls diverse processes and molecular interactions. Using a phylogenomics-based approach and complementary structural techniques, we identify a family of dimeric hemoproteins comprising a domain of unknown function DUF2470. The heme iron is axially coordinated by two zinc-bound histidine residues, forming a distinct two-fold symmetric zinc-histidine-iron-histidine-zinc site. Together with structure-guided in vitro and in vivo experiments, we further demonstrate the existence of a functional link between heme binding by Dri1 (Domain related to iron 1, formerly ssr1698) and post-translational regulation of succinate dehydrogenase in the cyanobacterium Synechocystis, suggesting an iron-dependent regulatory link between photosynthesis and respiration. Given the ubiquity of proteins containing homologous domains and connections to heme metabolism across eukaryotes and prokaryotes, we propose that DRI (Domain Related to Iron; formerly DUF2470) functions at the molecular level as a heme-dependent regulatory domain.
          Cover page: A hemoprotein with a zinc-mirror heme site ties heme availability to carbon metabolism in cyanobacteriaCreative Commons 'BY' version 4.0 license
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