DOE-SBR, “Collaborative Research: “The Importance of Organo-Iodine and Iodate In Iodine-127,129 Speciation, Mobility and Microbial Activity in Groundwater at DOE Sites”,  Santschi, P.H., PI, Schwehr, K.A., Kaplan, D.I., and Yeager, C.M., co-PIs 2011-2015 ($671,819.- to TAMUG).

129I is among the key risk driver at all DOE nuclear disposal facilities where 129I is buried because of its long half-life (16 million years), high toxicity (90% of the body’s iodine accumulates in the thyroid), high inventory, perceived high mobility in the subsurface environment, and uncertainty regarding its biogeochemical fate and transport in the environment. In our on-going SBR project we developed several highly sensitive iodine speciation techniques and among our key findings was that sediment bacteria are capable of influencing the chemical behavior of iodide, the most common form of iodine found in groundwater, via accumulation and oxidation to iodate. In turn, sediment bacteria, as well as reduced metals in the aquifer, are capable of reducing iodate to organo-iodine via iodide.  Based on this conclusion and others, we propose the following hypotheses (H) and objectives. H1: Despite its thermodynamic stability, iodide is readily transformed to organic iodine and iodate, a transformation that is facilitated by biotic (e.g., microbial activity such as nitrification) and abiotic (e.g., redox reactions by Mn(IV,II), Fe(III,II), or Hydroquinone/Quinone moieties in humic acids) factors. 

Objective 1.1: Determine the chemical speciation of iodine (I) from field groundwater samples from the Savannah River Site (SRS) and Hanford Site (including analyses of redox-active compounds) and experimental samples in the lab using model compounds to determine abiotic vs. biotic factors controlling I speciation. 

Objective 1.2: Determine the identity and activity of iodide oxidizing bacteria in SRS sediments. Determine the role of Mn oxidizing and nitrifying (NH4+ and NO2- oxidizers) bacteria on the chemical speciation of iodine in SRS field samples and in experimental samples in the lab using known Mn oxidizing and nitrifying strains from culture collections, SRS isolates, and SRS enrichment cultures (coupled to Objective 1.1).  H2: Microbially mediated oxidation of iodine species irreversibly transfers I into natural organic matter, of which aromatically bound iodine is the most stable. Objective 2.1: Assess iodide transformation by iodide oxidizing/accumulating bacteria in the presence and absence of soluble organic matter (e.g. humic acids, fulvic acids, amino acids, etc.). When organic I is formed, determine its molecular-level chemical composition.  H3: I mobility is dependent on physico-chemical speciation, which decreases from iodide to iodate to organic iodine, and from low molecular weight to high molecular weight to particulate organic I species.

Objective 3.1: Determine mobility/retardation and irreversible removal of well-characterized I-bearing compounds (extracted and model compounds) in soil column experiments under biotic (ambient, bioaugmented) and abiotic (sterile) conditions.

Our experimental approach will determine how microbial activity, concentrations and chemical speciation (iodide, iodate, and organo-I) of 129I and 127I , as well as redox reactive metals and organic carbon, affect I mobility and isotopic fractionation in selected groundwater samples from contaminated SRS locations. Experiments will assess the extent and mechanisms of I uptake and species conversions by biotic and abiotic mechanisms. Methods will include: 16S rRNA gene sequencing, FISH, microFISH, and species-specific DNA probes for microbiology, LSC, EM, HPLC, CHN, TOC, GC-MS, NMR, AAS, ICP-MS, and AMS for iodine, organic I, and metals characterization, and use of 125I radiotracers.

A critical knowledge gap for BER is a credible conceptual model of radioiodine biogeochemistry, especially in complex systems.  The potential benefits of this project to DOE are as follows: Should our hypotheses prove correct, then direct or indirect microbial-I interactions may have a remarkable immobilizing and/or transformative effect on 129I speciation and mobility in the surface and subsurface environment.  It should be possible to exploit such effects for remediation purposes or to include it in risk calculations. Present transport or risk models do not include any microbial processes in their treatment of iodine transport, even though the effect(s) are likely profound. Thus, this proposed research will support the BER Long Term Measure to provide sufficient scientific understanding such that site stake holders would be able to incorporate coupled physical, chemical and biological processes into decision making with regarding to radioiodine.

Publications:

  • Chang, H.-S., Xu, C., Schwehr, K.A., Zhang, S., Kaplan, D.I., Seaman, J.C., Yeager, C., and Santschi, P.H. 2013. Model of Radioiodine Speciation and Partitioning in Organic-rich and Organic-poor Soils from the Savannah River Site. Journal of Environmental Chemical Engineering, 2, 1321-1330.
  • Emerson, H.P., Xu, C., Ho, Y.-F., Zhang, S., Schwehr, K.A., Lilley, M., Kaplan, D.I., Santschi, P.H., and Powell, B.A. 2014. Geochemical controls of iodine transport in Savannah River Site subsurface environments. Applied Geochem., 45, 105–113.
  • Kaplan, D. I., M. E. Denham, S. Zhang, C. Yeager, C. Xu, K. A. Schwehr, H. P. Li, Y. F. Ho, D. Wellman, and P. H. Santschi. 2014. Radioiodine Biogeochemistry and Prevalence in Groundwater. Critical Reviews of Environmental Science and Technology, 44(20), 2287-2335.
  • Kaplan, D.I., Roberts, K.A.,  Schwehr, K.A., Lilley, M.S., Brinkmeyer, R., Denham, M.E., DiPrete, D., Hsiu-Ping Li, H.-P., Powell, B.A., Yeager, C.M., Zhang, S.J., Santschi, P.H. 2011. Evaluation of a Radioiodine Plume Increasing in Concentration at the Savannah River Site. Env. Sci. Technol., 45, 489-495.
  • Kaplan, D.I., Zhang, S., Roberts, K.A., Schwehr, K.A., Xu, C., Creeley, D., Ho, Y.-F., Li, H.-P., Yeager, C.M., and Peter H. Santschi, P.H. 2014. Radioiodine concentrated in a wetland. J. Environmental Radioactivity, 131, 57-61.
  • Li, H.-P., Brinkmeyer, R., Jones, W.L., Zhang, S., Xu, C., Ho, Y.-F., Schwehr, K.A., Kaplan, D.I.,  Santschi, P.H., and Chris M. Yeager, C.M. 2012. Iodide Oxidizing Activity of Bacteria from Subsurface Sediments of the Savannah River Site, SC, USA, p. 89-97. In M. Kawaguchi, K. Misaki, H. Sato, T. Yokokawa, T. Itai, T. M. Nguyen, J. Ono, and S. Tanabe (ed.), Interdisciplinary Studies on Environmental Chemistry Vol. 6 - Environmental Pollution and Ecotoxicology. Terra Scientific Publishing Company Tokyo.
  • Li, H.-P., Brinkmeyer, R., Jones, W.L., Zhang, S.J., Xu, C., Schwehr, K.A., Santschi, P.H., Kaplan, D., Yeager, C.M. 2011. Iodide accumulation by aerobic bacteria isolated from subsurface sediments of a 129I-contaminated aquifer at the Savannah River Site, S.C. Applied Environmental Microbiology, 77(6), 2153–2160.
  • Li, H.-P., Daniel, B., Creeley, D., Grandbois, R., Zhang, S., Xu, C., Ho, Y.-F., Schwehr, K.A., Kaplan, D.I., Santschi, P.H., Hansel, C., Yeager, C.M. 2014. Superoxide production by a manganese-oxidizing bacterium facilitates iodide oxidation. Applied and Environmental Microbiology, 80(9), 2693-2699.
  • Li, H.-P., Yeager, C.M., Brinkmeyer, R., Zhang, S., Ho, Y.-F., Xu, C., Jones, W.L., Schwehr, K.A., Otosaka, S., Kaplan, D.I., Santschi, P.H. 2012. Organic acids produced by subsurface bacteria enhance iodide oxidation in the presence of hydrogen peroxide. Environmental Science and Technology, 46, 4837-4844.
  • Otosaka, S., Schwehr, K.A., Kaplan, D.I., Roberts, K.A., Zhang, S., Xu, C., Li, S.-P., Ho, Y.-F., Brinkmeyer, R., Yeager, C.M., Santschi, P.H. 2011. Transformation and transport processes of 127I and 129I species in an acidic groundwater plume at the Savannah River Site. Science of the Total Environment, 409, 3857–3865.
  • Schwehr, K.A., Otosaka, S., Merchel, S., Kaplan, D.I., Zhang, S., Xu, C., Li, H.-P., Ho, Y.-F., Yeager, C.M., Santschi, P.H., ASTER Team. 2014. Speciation of iodine isotopes inside and outside of a contaminant plume at the Savannah River Site. Science of the Total Environment, 497–498, 671–678.
  • Xu, C., Chen, H.M., Sugiyama, Y., Zhang, S.J., Li, H.-P., Ho, Y.-F., Chuang, C.-Y., Schwehr, K.A., Kaplan, D.I., Yeager, C., Roberts, K.A., Hatcher, P.G., Santschi, P.H. 2013. Novel Molecular-Level Evidence of Iodine Binding to Natural Organic Matter from Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. Science of the Total Environment, 449, 244–252.
  • Xu, C., Miller, E.J., Zhang, S., Li, H.-S., Ho, Y.-F., Schwehr, K.A., Kaplan, D.I., Roberts, K.A., Otosaka, S., Brinkmeyer, R., Yeager, C.M., Santschi, P.H. 2011. Sequestration and re-mobilization of radioiodine (129I) by soil organic matter and possible consequences of the remedial action at Savannah River Site. Env. Sci. Technol., 45, 9975–9983.
  • Xu, C., Zhang, S., Athon, M., Ho, Y.-F., Li, H.-P., Grandbois, R., Schwehr, K.A., Kaplan, D.I., Yeager, C.M., Wellman, D., Santschi, P.H. 2015. A Re-evaluation of Radioiodine Transformation and Migration in the subsurface of Hanford Site. J. Env. Radioactivity, 139, 43-55.
  • Xu, C., Zhang, S., Ho, Y.-F., Miller, E.J., Roberts, K.A., Li, H.-P., Schwehr, K.A., Otosaka, S., Kaplan, D.I., Brinkmeyer, R., Yeager, C.M., Santschi, P.H. 2011. Is soil natural organic matter a sink or source for radioiodine (129I) at the Savannah River Site? Geochim. Cosmochim. Acta, 75, 5716–5735.
  • Xu, C., Zhong, J.Y., Hatcher, P.G., Zhang, S., Li, H.-P., Ho, Y.-F., Schwehr, K.A., Kaplan, D.I., Roberts, K.A., Brinkmeyer, R., Yeager, C.M., Santschi, P.H. 2012. The molecular environment of stable iodine and radioiodine (129I) in natural organic matter: evidence from NMR. Geochim. Cosmochim. Acta, 97, 166–182.
  • Zhang, S., Du, J., Xu, C., Schwehr, K.A., Ho, Y.-F., Li, H.-P., Roberts, K.A., Kaplan, D.I., Brinkmeyer, R., Yeager, C.M., Chang, H.-S., Santschi, P.H. 2011. Concentration dependent mobility, retardation and speciation of iodine in surface sediment from the Savannah River Site. Environmental Science and Technology, 45, 5543-5549.
  • Zhang, S., Ho, Y.-F., Creeley, D., Roberts, K.A., Xu, C., Li, H.-P., Schwehr, K.A., Kaplan, D.I., Yeager, C.M., and Santschi, P.H. 2014. Temporal Variation of Iodine Concentration and Speciation (127I and 129I) in Wetland Groundwater from the Savannah River Site, USA. Environ. Sci. Technol., 48, 11218-11226.
  • Zhang, S., Schwehr, K.A., Ho, Y., Xu, C., Roberts, K.A., Kaplan, D., Brinkmeyer, R., Yeager, C.M., Santschi, P.H. 2010. A novel approach for the simultaneous determination of iodide, iodate, and organo-iodide for 127I and 129I in Environmental Samples Using Gas Chromatography - Mass Spectrometry. Env. Sci. Technol., 44, 9042-9048.
  • Zhang, S., Xu, C., Creeley, D., Ho, Y.-F., Li, H.-P., Grandbois, R., Schwehr, K.A., Kaplan, D.I., Yeager, C.M., Wellman, D., and Santschi, P.H. 2013. Iodine-129 and Iodine-127 Speciation in Groundwater at the Hanford Site, U.S.: Iodate Incorporation into Calcite. ES&T, 47, 9635-9642.
  • Zhang, Saijin; Xu, Chen; Creeley, Danielle; Ho, Yi-Fang; Li, Hsiu-Ping; Grandbois, Russell; Schwehr, Kathy; Kaplan, Daniel; Yeager, Chris; Wellman, Dawn; Santschi, Peter H. 2013. Response to Comment on “Iodine-129 and Iodine-127 Speciation in Groundwater at Hanford Site, U.S.: Iodate Incorporation into Calcite”. Env. Sci. Technol., 47, 13205-13206.
Dr. Peter H.Santschi

Dr. Peter H.Santschi
Professor
Department of Marine Sciences
1001 Texas Clipper Rd
Bld# 3029, Office 346
Galveston, TX, 77554 USA

E-mail: santschi@tamug.edu
Phone: (409) 740-4476
Fax: (409) 740-4786