1,127 research outputs found
Modelling Cu(II) adsorption to ferrihydrite and ferrihydrite–bacteria composites: Deviation from additive adsorption in the composite sorption system
No full textBacterially associated iron (hydr)oxides are widespread in natural environments and are potent scavengers of dissolved metal ions. However, it is unclear whether metal sorption on these composites adheres to the additivity principle, and thus whether metal concentrations in environments where these composites comprise a significant proportion of the reactive iron phases can be modelled assuming component additivity. Here we address this issue for Cu adsorption on ferrihydrite–Bacillus subtilis composites. We precipitated pure ferrihydrite and ferrihydrite composites with different ferrihydrite:bacteria mass ratios, and measured Cu adsorption as a function of pH, Cu adsorbed concentration and composite mass ratio. We develop a molecular-level surface complexation model for Cu adsorption on pure ferrihydrite. We then combine our end-member models for Cu adsorption on B. subtilis (Moon and Peacock, 2011) and ferrihydrite to model the observed Cu adsorption on the composites, adopting a component linear additivity approach. By comparing observed Cu adsorption to that predicted by our composite model, constrained to the exact best fitting end-member stability constants, we find that Cu adsorption behaviour on ferrihydrite–B. subtilis composites deviates from additivity. Specifically, Cu adsorption on composites composed mainly of ferrihydrite is enhanced across the adsorption pH edge (pH ?3–6), while on our composite composed mainly of bacteria adsorption is enhanced at mid-high pH (pH ?5–6) but diminished at mid-low pH (pH ?5–3), compared to additivity. In current surface complexation modelling constructs, Cu adsorption on composites composed mainly of ferrihydrite can be modelled in a component additivity approach, by optimising the stability constants for Cu adsorption on the ferrihydrite and bacteria fractions to values that are within the uncertainty on the end-member stability constant values. The deviation from additivity of these composites, apparent when using the exact best fitting end-member stability constants, is therefore either a modelling artefact due to uncertainties in the surface adsorption properties of the end-member phases, or is relatively minor and cannot be separated from these uncertainties that are inherently present in the parameterisation of the surface adsorption properties in the modelling. In contrast, composites composed mainly of bacteria express significant deviation from Cu adsorption additivity that cannot be modelled in a component additivity approach. We propose that the deviations in Cu adsorption from additivity are the result of physiochemical interactions between the composite fractions that change the surface charge of the ferrihydrite and B. subtilis fractions compared to the isolated end-member phases. The magnitude and direction of the additivity deviations due to these electrostatic effects are then a function of the affinity of Cu for the bacterial fraction and the mass fraction of bacteria in the composite
Adsorption of Cu(II) to ferrihydrite and ferrihydrite–bacteria composites: Importance of the carboxyl group for Cu mobility in natural environments
No full textBacterially associated iron (hydr)oxide composites are widespread in natural environments, and by analogy with isolated iron (hydr)oxides and bacteria, are important scavengers of dissolved trace-metals. We precipitated ferrihydrite via rapid Fe(III) hydrolysis in the absence and presence of the non-Fe metabolising, Gram-positive bacterium Bacillus subtilis, commonly found in natural waters, soils and sediments. We combined XRD, SEM, BET and Fe K-edge EXAFS to examine the mineralogy, morphology and crystallinity of the ferrihydrite composites. We find that the mineral fraction of the composites is unaltered in primary mineralogy, morphology and crystallinity compared to pure ferrihydrite. We then measured the adsorption of Cu to ferrihydrite and the ferrihydrite–B. subtilis composites as a function of pH and the ferrihydrite:bacteria mass ratio of the composites, and used EXAFS to determine the molecular mechanisms of Cu adsorption. We determine directly for the first time that Cu uptake by ferrihydrite–B. subtilis composites is the result of adsorption to both the ferrihydrite and B. subtilis fractions. Adsorption of Cu by the B. subtilis fraction results in significant Cu uptake in the low pH regime (pH ?4, ?20% of [Cu]total) and significantly enhanced Cu uptake in the mid pH regime. This composite sorption behaviour is in stark contrast to pure ferrihydrite, where Cu adsorption is negligible at low pH. Overall, for composites dominated by either ferrihydrite or B. subtilis, the bacterial fraction is exclusively responsible for Cu adsorption at low pH while the ferrihydrite fraction is predominantly responsible for adsorption at high pH. Furthermore, with an increased mass ratio of bacteria, the dominance of Cu adsorption to the bacterial fraction persists into the mid pH regime and extends significantly into the upper pH region. As such, the distribution of the total adsorbed Cu between the composite fractions is a function of both pH and the ferrihydrite:bacteria mass ratio of the composite. EXAFS shows that Cu adsorbs to ferrihydrite as an inner-sphere, (CuO4Hn)n ? 6 bidentate edge-sharing complex; and to ferrihydrite composites as an inner-sphere, (CuO5Hn)n ? 8 monodentate complex with carboxyl surface functional groups present on the bacterial fraction plus the bidentate edge-sharing complex on the ferrihydrite fraction. Our new results combined with previous work on Cu sorption to bacteria, humic substances and iron (hydr)oxides coated with humics, demonstrate the universal importance of the carboxyl moiety for Cu sorption and mobility in natural environments. Taken together these results show that Cu-carboxyl binding is the predominant mechanism by which Cu interacts with abiotic and biotic organic matter, and provides a ubiquitous control on Cu fate and mobility in natural waters, soils and sediments. Our results indicate that in environments where a significant proportion of iron (hydr)oxides are intimately intermixed with an organic fraction, we must consider Cu sequestration by these composites in addition to pure mineral phases
Oxidative scavenging of thallium by birnessite: Explanation for thallium enrichment and stable isotope fractionation in marine ferromanganese precipitates
No full textTl stable isotopes recorded in marine ferromanganese crusts show great promise as a tracer of past marine and climatic conditions. Key to interpreting recent Tl stable isotope time-series data is a detailed, molecular-level understanding of Tl scavenging by ferromanganese crust minerals and Tl stable isotope fractionation occurring during uptake. To this end, we determine the mechanism of Tl sorption to the primary ferromanganese minerals in crusts, namely hexagonal birnessite, todorokite and ferrihydrite, using XAS. We compliment our data with micro-focus XAS of a Tl-enriched hydrogenetic ferromanganese crust. We show that Tl(I) is oxidised to Tl(III) during sorption to hexagonal birnessite, but not during sorption to todorokite, triclinic birnessite and ferrihydrite. Tl(III) forms an inner-sphere complex at the hexagonal birnessite surface, located at vacant octahedral sites in the phyllomanganate sheets. We show that oxidation of Tl(I) to Tl(III) during reductive dissolution of birnessite is thermodynamically unfavourable; and propose that oxidation of Tl(I) is driven by the formation of the Tl(III) surface complex. Recent theoretical calculations predict a large equilibrium stable isotope fractionation between Tl(I) and Tl(III), leading to Tl(III) species that are enriched in the heavy 205Tl isotope. In light of this work, we propose a molecular sorption–oxidation–fractionation mechanism that provides a unifying explanation for the recently observed geochemical behaviour of Tl in marine ferromanganese-rich sediments. In this mechanism, the proportion of hexagonal birnessite dictates the extent of Tl oxidation, which controls the extent of Tl enrichment and isotope fractionation. This work is among the first to provide a molecular explanation for reported trends in trace element enrichments and stable isotope compositions in geologic deposits. Our molecular sorption–oxidation–fractionation mechanism will ultimately help interpret Tl signals in marine sedimentary archives to provide new constraints on past oceanic and climatic change. In addition, our mechanism should also help explain compositional relationships of other redox-sensitive elements in ferromanganese-rich marine sediments that might also be used as paleoceanographic and paleoclimate proxies
Towards an understanding of thallium isotope fractionation during adsorption to manganese oxides
No full textWe have conducted the first study of Tl isotope fractionation during sorption of aqueous Tl(I) onto the manganese oxide hexagonal birnessite. The experiments had different initial Tl concentrations, amounts of birnessite, experimental durations, and temperatures, but all of them exhibit heavy Tl isotope compositions for the sorbed Tl compared with the solution, which is consistent with the direction of isotope fractionation observed between seawater and natural ferromanganese sediments. However, the magnitude of fractionation in all experiments (? ? 1.0002–1.0015, where ?=205Tl/203Tlsolid/205Tl/203Tlliq is smaller than observed between seawater and natural sediments (? ? 1.0019–1.0021; Rehkämper et al., 2002, Earth. Planet. Sci. Lett. 197, 65–81). The experimental results display a strong correlation between the concentration of Tl in the resulting Tl-sorbed birnessite and the magnitude of fractionation. This correlation is best explained by sorption of Tl to two sites on birnessite, one with large isotope fractionation and one with little or no isotope fractionation. Previous work (Peacock and Moon, 2012, Geochim. Cosmochim. Acta 84, 297–313) indicates that Tl in natural ferromanganese sediments is oxidized to Tl(III) and adsorbed over Mn vacancy sites in the phyllomanganate sheets of birnessite, and we hypothesize that this site is strongly fractionated from Tl in solution due to the change in oxidation state from aqueous Tl(I). In most experiments, which have orders of magnitude more Tl associated with the solid than in nature, these vacancy sites are probably fully saturated, so various amounts of additional Tl are likely sorbed to either edge sites on the birnessite or triclinic birnessite formed through oxidative ripening of the hexagonal starting material, with unknown oxidation state and little or no isotopic fractionation. Thus each experiment displays isotopic fractionation governed by the proportions of Tl in the fractionated and slightly fractionated sites, and those proportions are controlled by how much total Tl is sorbed per unit of birnessite. In the experiments with the lowest initial Tl concentrations in solution (?0.15–0.4 ?g/g) and the lowest concentrations of Tl in the resulting Tl-sorbed birnessite (?17 ?g Tl/mg birnessite), we observed the largest isotopic fractionations, and fractionation is inversely proportional to the initial aqueous Tl concentration. Again, this correlation can be explained by the simultaneous occupation of two different sorption sites; vacancy sites that carry isotopically fractionated Tl and a second site carrying slightly fractionated Tl. The fractionation factors observed in nature exceed those in the experiments likely because the Tl concentrations in seawater and in ferromanganese sediments are three to four orders of magnitude lower than in our experiments, and therefore the second slightly fractionated sorption site is not significantly utilized. Temperature (6–40 °C) and experimental duration (3 min–72 h) appear to have little or no effects on isotope behaviour in this system
Catalog of lunar mare basalts greater than 40 grams. Part 1, major and trace chemistry, with megascopic descriptions and rock and thin section photographs
No full textMegascopic descriptions of 133 basaltic rocks returned from the Moon are presented along with photographs of each rock and its thin section, if available. The major and trace element chemistry of each is included wherever possible.by Gary E. Lofgren, Ellen M. Lofgre
Immigrating in nursing: a grounded theory of how nurses process their professional practice specialization within the pharmaceutical/biotech industry
No full textRationale for the study: Despite the fact that nursing shortages have been reported for a prolonged period of time across all traditional practice settings within the US (Buerhaus & Staiger, 1999; Buerhaus, Staiger & Auerbach, 2000; 2003; 2009), there has been a growth in the number of nurses employed within the non-traditional practice setting of the pharmaceutical/biotech industry. The literature is void of both qualitative and quantitative studies that address the perspective of nurses who pursue professional practice within the non-traditional practice setting of the pharmaceutical/biotech industry. Understanding how nurses within the pharmaceutical/biotech industry perceive their professional practice may help illuminate the importance of characteristics of non-traditional practice settings. Methodology: Classic Grounded Theory was used to examine the process that nurses undertake to restore, support, and foster their professional practice within the non-traditional practice setting of the pharmaceutical/biotech industry. Rutgers University IRB approval was obtained prior to study initiation. Fifteen participants were interviewed regarding their perspectives of the decision-making process surrounding their migration and establishment of professional practice from traditional practice settings into the non-traditional practice setting of the pharmaceutical/biotech industry. All participants met eligibility criteria. All interviews were recorded and transcribed verbatim. This data was analyzed using constant comparative analysis as described by Glaser (1978). Results: The theory which emerged from the data is a four phase process which includes: Becoming Disillusioned, Acclimating into the Corporate Role, Achieving Belonging, and Nursing Specialty Actualization. Immigrating in Nursing is the Core Category which explains how participants resolved their main concern: to restore, support, and foster their professional practice in the non-traditional practice setting of the pharmaceutical/biotech industry. Conclusion: The study findings illuminate the challenges, milestones, and achievements that nurses within the pharmaceutical/biotech industry consider integral to their professional practice development and specialty actualization. The inside views of the choices and actions made by each participant in this study demonstrated many of the reasons why nurses within the pharmaceutical/biotech industry value their professional practice and the public health advancement and advocacy that they undertake.Ph. D.Includes bibliographical referencesIncludes vitaby Ellen M. Shanno
182 - Ellen Claire Martin
No full textIncludes bibliographical references.Shorebird populations are declining globally and little is known about the use and distribution of breeding species in interior Alaska. The Program for Regional and International Shorebird Monitoring (PRISM) has developed shorebird survey methodology, with most effort in the Arctic and less effort in the boreal forest region. We fill this information void by using PRISM methods to estimate shorebird use of military lands in interior Alaska on Tanana Flats Training Area and Donnelly Training Areas (Fairbanks and Delta Junction, Alaska). We conducted surveys to (1) identify shorebird species using military lands, and (2) create occupancy/use models for these species and determine associated habitat covariates. We predicted species-specific covariate relationships (e.g., elevation, shrub height, distance to water). In general, we predict that shorebirds would more likely use open shrub and wet grassland Viereck habitat classifications. Using a stratified random sampling design, we surveyed 140 plots (400x400 m) twice. We found 6 shorebird species of moderate to high conservation concern as listed by the Alaska Shorebird Conservation Plan and 4 species of conservation concern as listed by the USFWS. For Lesser Yellowlegs, Wilson’s Snipe, and Spotted Sandpiper we will present correlations of use with variables of interest derived from occupancy/use models
After Constantine\u27s Sword: The Past, Present, and Future of Jewish-Christian Relations
No full textAn Interfaith Conversation with award-winning author: James Carroll. With responses by: Dr. Ellen M. Umansky, Carl and Dorothy Bennett Professor of Judaic Studies and Dr. Elizabeth A. Dreyer, Professor of Religious Studies. Also participating: Bill Huselman \u2798; M.T.S. Harvard Divinity School, \u2701.https://digitalcommons.fairfield.edu/bennettcenter-posters/1216/thumbnail.jp
Adsorption of Cu(II) to Bacillus subtilis: A pH-dependent EXAFS and thermodynamic modelling study
No full textBacteria are very efficient sorbents of trace metals, and their abundance in a wide variety of natural aqueous systems means biosorption plays an important role in the biogeochemical cycling of many elements. We measured the adsorption of Cu(II) to Bacillus subtilis as a function of pH and surface loading. Adsorption edge and XAS experiments were performed at high bacteria-to-metal ratio, analogous to Cu uptake in natural geologic and aqueous environments. We report significant Cu adsorption to B. subtilis across the entire pH range studied (pH ?2–7), with adsorption increasing with pH to a maximum at pH ?6. We determine directly for the first time that Cu adsorbs to B. subtilis as a (CuO5Hn)n?8 monodentate, inner-sphere surface complex involving carboxyl surface functional groups. This Cu–carboxyl complex is able to account for the observed Cu adsorption across the entire pH range studied. Having determined the molecular adsorption mechanism of Cu to B. subtilis, we have developed a new thermodynamic surface complexation model for Cu adsorption that is informed by and consistent with EXAFS results. We model the surface electrostatics using the 1pK basic Stern approximation. We fit our adsorption data to the formation of a monodentate, inner-sphere triple bond; length of mdashRCOOCu+ surface complex. In agreement with previous studies, this work indicates that in order to accurately predict the fate and mobility of Cu in complex biogeochemical systems, we must incorporate the formation of Cu-bacteria surface complexes in reactive transport models. To this end, this work recommends log K triple bond; length of mdashRCOOCu+ = 7.13 for geologic and aqueous systems with generally high B. subtilis-to-metal ratio
I Am Joseph Your Brother: Relations Between the Catholic Church and the Jewish People Over the Past Half Century
No full textViewing of this award-winning documentary film, followed by an inter-religious discussion led by Rabbi Ron Kronish and Sister Mary C. Boys, moderated by Dr. Ellen M. Umansky. [Speaker descriptions] Rabbi Ron Kronish, Director of the Inter-religious Coordinating Council in Israel and noted rabbi, educator, author, and lecturer. Sister Mary C. Boys, Union Theological Seminary, N.Y. Jewish Theological Seminary of America; Teachers College, Columbia University.https://digitalcommons.fairfield.edu/bennettcenter-posters/1235/thumbnail.jp
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