Environmental Science and Engineering Seminar

The bioavailability of sulfur compounds in any aqueous setting is potentially affected by abiotic reactions between sulfur and other dissolved inorganic species, (nano)particles, and organic materials. The coupling of element cycles can have a significant effect on the sulfur intermediates present at any point in time, and pools of potential electron donor and acceptors is often controlled by fluxes of material that can display chaotic periodicity. The available energy available for any microbial metabolism is thus a function of many possible reactions that may vary significantly over time. How do we then unravel the processes controlling bioavailable sulfur?

Au-amalgam microelectrode voltammetry allows in situ, real time determination of a host of redox species, including a number of sulfur and iron dissolved species and nanoparticles, with appropriate temporal and spatial resolution, that are key to this problem. Coupling voltammetry with Raman spectroscopy, chromatography, light scattering, light and electron microscopy, and x-ray diffraction has facilitated a detailed look at the speciation of dissolved forms together with nanoparticle characteristics to improve insight on how elemental sulfur nanoparticles are a key player in the development of intermediate sulfur speciation. Isotopic evidence also helps shed light on key processes involving these species in different settings. Ongoing experiments are showing that the size of sulfur nanoparticles and the presence of surfactant molecules affect the rates of reaction with sulfide to generate polysulfides, a key intermediate as well in the formation of thiosulfate and in reactions driving pyritization.

We have additionally applied fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS, in collaboration with colleagues at the Helmholtz Institute in Munich, Germany) to gain a broad spectrum view of how these different intermediate sulfur species interact with organic matter. We utilize Suwannee River natural organic matter and fresh extracts from pine needles (thought to be one significant source of organic material to Yellowstone thermal features) for experiments with sulfide, polysulfide, elemental sulfur, thiosulfate, and sulfite. These experiments and analysis of thermal waters at Yellowstone are allowing us to probe further the interactions between intermediate sulfur species and organic matter in both sulfurization and redox reactions.