Browsing by Subject "Radionuclides"
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Item Examining The Binding of Radionuclides with Marine Biopolymers, A Comparative Study On Th, Pa, Be, Po And Pb Isotopes(2013-12-09) Chuang, Chia-YingNatural radioisotopes, Th, Pa, Pb, Po and Be, have been used as important proxies in oceanographic investigations for decades. Biopolymers, produced by both phytoplankton and bacteria, play an important role in the scavenging of these radionuclides, thus regulating the particulate organic carbon (POC)/isotope ratios in different oceanographic regions, which have been used to calculate POC flux. To study the binding mechanisms of colloidal organic material to these radionuclides, marine colloids isolated by cross-flow ultrafiltration from seawater, together with dissolved exopolymeric substances (EPS) produced by laboratory cultured diatoms were collected. By separating, identifying and characterizing radiolabeled organic carriers, the most efficient binding of many of these nuclides likely occurs to acid polysaccharide- and Fe-related protein-containing biomolecules. To differentiate between uptake to amorphous silica or associated biopolymers, radionuclides were incubated with diatom cultures of Phaeodactylum tricornutum. Partition coefficients (K_(d)) of radionuclides to different fractions of diatom cells, and the role of diatom related biopolymers were examined. More than 50% of selected radionuclides were bound to all-inclusive biopolymer fractions, and logK_(d) values of radioisotopes to whole diatom cells with or without silica frustules were similar, but logK_(d) values for cleaned silica frustules were orders of magnitude lower. Results from isoelectric focusing showed the most efficient binding sites occurring in acid-polysaccharides and iron-binding proteins. As revealed by 2D HSQC NMR spectra, the biopolymers in the HF insoluble fraction were mainly composed of carboxyl-rich, aliphatic-phosphoproteins. The concentrations of potential carrier phases for radionuclides and their K_(d) values were determined for particles collected by sediment traps deployed at the Oceanic Flux Program site off Bermuda. Chemical considerations, as well as factor analysis and correlations of logK_(d) values with chemical parameters, indicate that hydroxamate-siderophores (HS) are major classes of biopolymers that have a role in binding Po and Pa. MnO_(2) and FeO_(2), whose presence is closely related to that of HS, are also involved in binding of Pa and Po. The carbonate and biogenic silica phases are identified to be important in predicting removal and fractionation of Th and Be in the ocean.Item Molecular Level Characterization and Mobility of Radionuclide-Carrying Natural Organic Matter in Aquatic Environments(2012-10-19) Xu, ChenRadionuclides, 129I and 239,240Pu, are major products or by-products of nuclear fission and among the top risk drivers for waste disposal at the Savannah River Sites (SRS) and Rocky Flats Environmental Technology Sites (RFETS), respectively, due to their perceived mobility in the environment, excessive inventory, toxicity, and long half-life. The objective of this study is to investigate the role of natural organic matter in retarding or facilitating the migration of 129I and 239,240Pu in the Department of Energy (DOE) sites. Measurements of 127I and 129I in humic acids (HAs) and fulvic acids (FAs) obtained by five successive alkaline, two glycerol and one citric acid-alkaline extractions, demonstrated that these extractable humic substances (HS) together account for 54-56 percent and 46 percent of the total 127I and 129I in the soil, respectively. The variations among 127I and 129I concentrations, isotopic ratios (129I/127I), chemical properties of all these humic substances indicated iodine was bound to a small-size aromatic subunit (~10 kDa), while the large-size subunit (~90 kDa), which likely linked the small-size unit through some weak chemical forces, determined the relative mobility of iodine bound to organic matter. Soil resuspension experiments simulating surface runoff or stormflow and erosion events were conducted with soils collected from SRS. Results showed that 72-77 percent of the newly-introduced I- or IO3- were irreversibly sequestered into the organic-rich soil, while the rest was transformed into colloidal and dissolved organo-iodine by the soil. The resulting iodine remobilization contradicts the conventional view that considers only I- or IO3- as the mobile forms. Quantitative structure analysis by 13C DPMAS NMR and solution state 1H NMR on these humic substances indicate that iodine is closely related to the aromatic regions containing esterified products of phenolic and fomic acid or other aliphatic carboxylic acids, amide functionalities, quinone-like structure activated by electron-donating groups (e.g., NH2) or hemicelluloses-lignin-like complex with phenyl-glycosidic linkage. The micro-molecular environment, such as the hydrophobic aliphatic periphery hindering the active aromatic cores and the hydrophilic polysaccharides favoring its accessibility towards hydrophilic iodine species, play another key role in the interactions between iodine and SOM. NMR spectra of the colloidal organic Pu carrier which can potentially be released from the soil during the surface runoff or stormflow showed Pu was transported, at sub-pM concentrations, by a cutin-derived soil degradation products containing siderophore-like moieties and virtually all mobile Pu.Item Novel approaches in determining baseline information on annual disposal rates and trace element content of U.S. coal combustion residues : a response to EPA’s June 2010 proposed disposal rule(2010-12) Chwialkowski, Natalia Ewa; Groat, Charles G.; Grimshaw, Thomas W.; Kyle, RichardAlthough products of coal combustion (PCCs) such as coal ash are currently exempted from classification as a hazardous waste in the United States under the 1976 Resource Conservation and Recovery Act (RCRA), the U.S. Environmental Protection Agency (EPA) is now revising a proposed rule to modify disposal practices for these materials in order to prevent contamination of ground- and surface water sources by leached trace elements. This paper analyzes several aspects of EPA’s scientific reasoning for instating the rule, with the intent of answering the following questions: 1) Are EPA’s cited values for PCC production and disposal accurate estimates of annual totals?; 2) In what ways can EPA’s leaching risk modeling assessment be improved?; 3) What is the total quantity of trace elements contained within all PCCs disposed annually?; and 4) What would be the potential costs and feasibility of reclassifying PCCs not under RCRA, but under existing NRC regulations as low-level radioactive waste (LLRW)? Among the results of my calculations, I found that although EPA estimates for annual PCC disposal are 20% larger than industry statistics, these latter values appear to be closer to reality. Second, EPA appears to have significantly underestimated historical PCC disposal: my projections indicate that EPA’s maximum estimate for the quantity of fly ash landfilled within the past 90 years was likely met by production in the last 30 years alone, if not less. Finally, my analysis indicates that while PCCs may potentially meet the criteria for reclassification as low-level radioactive waste by NRC, the cost of such regulation would be many times that of the EPA June proposed disposal rule ($220-302 billion for PCCs disposed in 2008 alone, versus $1.47 billion per year for the Subtitle C option and $236-587 million for Subtitle D regulatory options).