Biomedical subjects

Stephen R Sutton

Publications and source records attributed to Stephen R Sutton.

12 recordsLinked to original sources

PubMed2006

Elemental compositions of comet 81P/Wild 2 samples collected by Stardust.

We measured the elemental compositions of material from 23 particles in aerogel and from residue in seven craters in aluminum foil that was collected during passage of the Stardust spacecraft through the coma of comet 81P/Wild 2. These particles are chemically heterogeneous at the largest size scale analyzed ( approximately 180 ng). The mean elemental composition of this Wild 2 material is consistent with the CI meteorite composition, which is thought to represent the bulk composition of the solar system, for the elements Mg, Si, Mn, Fe, and Ni to 35%, and for Ca and Ti to 60%. The elements Cu, Zn, and Ga appear enriched in this Wild 2 material, which suggests that the CI meteorites may not represent the solar system composition for these moderately volatile minor elements.

Journal Article↗

PubMed2006

Plutonium oxidation and subsequent reduction by Mn(IV) minerals in Yucca Mountain tuff.

Plutonium oxidation state distribution on Yucca Mountain tuff and synthetic pyrolusite (beta-MnO2) suspensions was measured using synchrotron X-ray micro-spectroscopy and microimaging techniques as well as ultrafiltration/solventextraction techniques. Plutonium sorbed to the tuff was preferentially associated with manganese oxides. For both Yucca Mountain tuff and synthetic pyrolusite, Pu(IV) or Pu(V) was initially oxidized to more mobile Pu(V/VI), but over time, the less mobile Pu(IV) became the predominant oxidation state of the sorbed Pu. The observed stability of Pu(IV) on oxidizing surfaces (e.g., pyrolusite), is proposed to be due to the formation of a stable hydrolyzed Pu(IV) surface species. These findings have important implications in estimating the risk associated with the geological burial of radiological waste in areas containing Mn-bearing minerals, such as at the Yucca Mountain or the Hanford Sites, because plutonium will be predominantly in a much less mobile oxidation state (i.e., Pu(IV)) than previously suggested (i.e., Pu(V/VI).

Hydrogen-Ion Concentration↗

PubMed2005

Grain-size control in situ at high pressures and high temperatures in a diamond-anvil cell.

The grain-size distribution and the character of individual grain boundaries in microcrystalline networks play a significant role in material properties, such as melting temperature, diffusion coefficients, resistivity, optical absorption, elastic constants, phase transformation pressure, and so on. In this study, the grain size of NaCl, SiO2 and FeC3 is controlled in situ at high pressures over the entire range of the length scale of crystallinity: single-crystal, micro-/nanocrystalline and amorphous materials within a volume commensurate with the size of the probing X-ray beam. The structure refinement of high-pressure samples from X-ray diffraction data can be significantly improved by controlling grain size by selecting the structure of starting materials and following certain high pressure-temperature-time paths.

Journal Article↗

PubMed2005

Facilities for high-pressure research with the diamond anvil cell at GSECARS.

An overview of facilities for high-pressure research with the diamond anvil cell (DAC) at the GeoSoilEnviroCARS (GSECARS) sector at the Advanced Photon Source (Argonne, Illinois) is presented. There are three operational experimental stations (13-ID-C, 13-ID-D and 13-BM-D) where DAC instrumentation is installed for various types of experiments at high pressure and extreme temperature conditions. A fourth station (13-BM-C) is under construction and will be operational in 2006. While most X-ray diffraction experiments have been undertaken with powder samples so far, there is a growing demand for single-crystal diffraction (SCD) at high pressure. As one of the principal components at GSECARS, SCD is currently under rapid development. Other relevant techniques have also been developed for obtaining complementary information from powder or single-crystal samples at high pressure. For example, an on-line Brillouin system is installed and operational at 13-BM-D for acoustic velocity and single-crystal elasticity determinations. In addition, various X-ray spectroscopy techniques (e.g. X-ray emission and X-ray Raman) are employed for measuring electronic and magnetic properties. Future developments are discussed with the DAC program at GSECARS.

Journal Article↗

PubMed2005

Reoxidation of bioreduced uranium under reducing conditions.

Nuclear weapons and fuel production have left many soils and sediments contaminated with toxic levels of uranium (U). Although previous short-term experiments on microbially mediated U(VI) reduction have supported the prospect of immobilizing the toxic metal through formation of insoluble U(IV) minerals, our longer-term (17 months) laboratory study showed that microbial reduction of U can be transient, even under sustained reducing conditions. Uranium was reduced during the first 80 days, but later (100-500 days) reoxidized and solubilized, even though a microbial community capable of reducing U(VI) was sustained. Microbial respiration caused increases in (bi)-carbonate concentrations and formation of very stable uranyl carbonate complexes, thereby increasing the thermodynamic favorability of U(IV) oxidation. We propose that kinetic limitations including restricted mass transfer allowed Fe-(III) and possibly Mn(IV) to persist as terminal electron acceptors (TEAs) for U reoxidation. These results show that in-situ U remediation by organic carbon-based reductive precipitation can be problematic in sediments and groundwaters with neutral to alkaline pH, where uranyl carbonates are most stable.

Biodegradation, Environmental↗

PubMed2004

Arsenic sequestration by ferric iron plaque on cattail roots.

Typha latifolia (cattail) sequesters arsenic within predominantlyferric iron root coatings, thus decreasing mobility of this toxic element in wetland sediments. Element-specific XRF microtomographic imaging illustrated a high spatial correlation between iron and arsenic in root plaques, with little arsenic in the interior of the roots. XANES analyses demonstrated that the plaque was predominantly ferric iron and contained approximately 20% As(III) and 80% As(V), which is significant because the two oxidation states form species that differ in toxicity and mobility. For the first time, spatial distribution maps of As oxidation states were developed, indicating that As(III) and As(V) are both fairly heterogeneous throughoutthe plaque. Chemical extractions showed that As was strongly adsorbed in the plaque rather than coprecipitated. Iron and arsenic concentrations ranged from 0.03 to 0.8 g Fe g(-1) wet plaque and 30 to 1200 microg As g(-1) wet plaque, consistent with a mechanism of As adsorption onto Fe(III) oxyhydroxide plaque. Because this mechanism decreases the concentrations of both As(III) and As(V) in groundwater, we propose that disruption of vegetation could increase the concentrations of mobile arsenic.

Adsorption↗

PubMed2004

Hexavalent uranium diffusion into soils from concentrated acidic and alkaline solutions.

Uranium contamination of soils and sediments often originates from acidic or alkaline waste sources, with diffusion being a major transport mechanism. Measurements of U(VI) diffusion from initially pH 2 and pH 11 solutions into a slightly alkaline Altamont soil and a neutral Oak Ridge soil were obtained through monitoring uptake from boundary reservoirs and from U concentration profiles within soil columns. The soils provided pH buffering, resulting in diffusion at nearly constant pH. Micro X-ray absorption near edge structure spectra confirmed that U remained in U(VI) forms in all soils. Time trends of U(VI) depletion from reservoirs and U(VI) concentration profiles within soil columns yielded Kdvalues consistent with those determined in batch tests at similar concentrations (approximately 1 mM) and much lower than values for sorption at much lower concentrations (nM to microM). These results show that U(VI) transport at high concentrations can be relatively fast at non-neutral pH, with negligible surface diffusion, because of weak sorption.

Adsorption↗

PubMed2004

Structure of liquid iron at pressures up to 58 GPa.

We report structural data on liquid iron at pressures up to 58 GPa measured by x-ray scattering in a laser heated diamond anvil cell. The determined structure factor preserves essentially the same shape along the melting curve. Our data demonstrate that liquid iron at high pressures is a close-packed hard-sphere liquid. The results place important constraints on the thermodynamic and transport properties of liquid iron and the melting curve of iron.

Journal Article↗

PubMed2004

The impact of personal and social comparison information about health risk.

OBJECTIVES: To examine the emotional and cognitive impact of personal and social comparison information about health risk. METHODS: A total of 970 adults responded to vignettes describing risk presentation scenarios that varied in terms of having (a) a 'real world' analogue (cardiac event) versus no such analogue (a fictitious pancreatic disease) condition, (b) high versus low levels of personal risk, and (c) no comparison group information given, comparison group risk higher or lower than own risk. RESULTS: For both the cardiac and pancreatic disease vignettes, respondents' emotional responses and estimates of their own risk were influenced by both personal and social comparison risk information. The cardiac event vignettes produced larger effects than the pancreatic disease vignettes. Unfavourable social comparison information had no discernible impact, relative to not providing any social comparison information. Favourable social comparison information resulted in greater reassurance, less worry, and perceptions of lower susceptibility. Lower personal risk generally produced similar effects, relative to higher personal risk. CONCLUSIONS: In contrast to previous theory and research in this area, we found that both personal and (favourable) social comparison risk information have emotional and cognitive consequences. We hypothesize that the perceived clarity of the information may account for the different patterns of findings in the literature.

Adult↗

PubMed2003

Experience with breast cancer, pre-screening perceived susceptibility and the psychological impact of screening.

This prospective study examined whether the psychological impact of organized mammography screening is influenced by women's pre-existing experience with breast cancer and perceived susceptibility (PS) to the disease. From a target population of 16,886, a random sample of women with a normal screening finding and all women with a false positive or a benign biopsy finding were included (N=1942). Data were collected with postal questionnaires 1-month before screening invitation and 2 and 12 months after screening. Response rate was 63% at baseline; 86, and 80% of the baseline participants responded to the follow-ups. Psychological impact was measured as anxiety (STAI-S), depression (BDI), health-related concerns (IAS), and breast cancer-specific beliefs and concerns. Data was analyzed with repeated measures analyses of variance, with estimates of effect size based on Eta-squared. Women with breast cancer experience had higher risk perception already before screening invitation; after screening they were also more distressed. Women with high PS were more distressed than women with low PS also at pre-invitation. The distress was not alleviated by screening, but instead remained even after normal mammograms. Experience and PS did not influence responses to different screening findings. Of the finding groups, false positives experienced most adverse effects: their risk perception increased and they reported most post-screening breast cancer-specific concerns. Furthermore, they became more frequent in breast self-examination (BSE) despite a simultaneous decrease in BSE self-efficacy. Our findings suggest that women with high PS and women with false positive screening finding may need individualized counseling and follow-up as much as women with a family history of breast cancer. Besides medical risk factors, women's own perceptions of susceptibility should be discussed during the screening process.

Anxiety↗

PubMedDate not supplied

In situ reduction of chromium(VI) in heavily contaminated soils through organic carbon amendment.

Chromium has become an important soil contaminant at many sites, and facilitating in situ reduction of toxic Cr(VI) to nontoxic Cr(III) is becoming an attractive remediation strategy. Acceleration of Cr(VI) reduction in soils by addition of organic carbon was tested in columns pretreated with solutions containing 1000 and 10 000 mg L(-1) Cr(VI) to evaluate potential in situ remediation of highly contaminated soils. Solutions containing 0,800, or 4000 mg L(-1) organic carbon in the form of tryptic soy broth or lactate were diffused into the Cr(VI)-contaminated soils. Changes in Cr oxidation state were monitored through periodic micro-XANES analyses of soil columns. Effective first-order reduction rate constants ranged from 1.4 x 10(-8) to 1.5 x 10(-7) s(-1), with higher values obtained for lower levels of initial Cr(VI) and higher levels of organic carbon. Comparisons with sterile soils showed that microbially dependent processes were largely responsible for Cr(VI) reduction, except in the soils initially exposed to 10 000 mg L(-1) Cr(VI) solutions that receive little (800 mg L(-1)) or no organic carbon. However, the microbial populations (< or = 2.1 x 10(5) g(-1)) in the viable soils are probably too low for direct enzymatic Cr(VI) reduction to be important. Thus, synergistic effects sustained in whole soil systems may have accounted for most of the observed reduction. These results show that acceleration of in situ Cr(VI) reduction with addition of organic carbon is possible in even heavily contaminated soils and suggest that microbially dependent reduction pathways can be dominant.

Bacteria↗

PubMedDate not supplied

Distribution of chromium contamination and microbial activity in soil aggregates.

Biogeochemical transformations of redox-sensitive chemicals in soils can be strongly transport-controlled and localized. This was tested through experiments on chromium diffusion and reduction in soil aggregates that were exposed to chromate solutions. Reduction of soluble Cr(VI) to insoluble Cr(II) occurred only within the surface layer of aggregates with higher available organic carbon and higher microbial respiration. Sharply terminated Cr diffusion fronts develop when the reduction rate increases rapidly with depth. The final state of such aggregates consists of a Cr-contaminated exterior, and an uncontaminated core, each having different microbial community compositions and activity. Microbial activity was significantly higher in the more reducing soils, while total microbial biomass was similar in all of the soils. The small fraction of Cr(VI) remaining unreduced resides along external surfaces of aggregates, leaving it potentially available to future transport down the soil profile. Using the Thiele modulus, Cr(VI) reduction in soil aggregates is shown to be diffusion rate- and reaction rate-limited in anaerobic and aerobic aggregates, respectively. Thus, spatially resolved chemical and microbiological measurements are necessary within anaerobic soil aggregates to characterize and predict the fate of Cr contamination. Typical methods of soil sampling and analyses that average over redox gradients within aggregates can erase important biogeochemical spatial relations necessary for understanding these environments.

Bacteria, Aerobic↗