Browsing by Author "Sparks, Donald L."
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Item Hydrologic Control on Arsenic Cycling at the Groundwater–Surface Water Interface of a Tidal Channel(Environmental Science and Technology, 2023-01-10) Yu, Xuan; LeMonte, Joshua J.; Li, Junxia; Stuckey, Jason W.; Sparks, Donald L.; Cargill, John G.; Russoniello, Christopher J.; Michael, Holly A.Historical industrial activities have resulted in soil contamination at sites globally. Many of these sites are located along coastlines, making them vulnerable to hydrologic and biogeochemical alterations due to climate change and sea-level rise. However, the impact of hydrologic dynamics on contaminant mobility in tidal environments has not been well studied. Here, we collected data from pressure transducers in wells, multi-level redox sensors, and porewater samplers at an As-contaminated site adjacent to a freshwater tidal channel. Results indicate that sharp redox gradients exist and that redox conditions vary on tidal to seasonal timescales due to sub-daily water level fluctuations in the channel and seasonal groundwater–surface water interactions. The As and Fe2+ concentrations decreased during seasonal periods of net discharge to the channel. The seasonal changes were greater than tidal variations in both Eh and As concentrations, indicating that impacts of the seasonal mechanism are stronger than those of sub-daily water table fluctuations. A conceptual model describing tidal and seasonal hydro-biogeochemical coupling is presented. These findings have broad implications for understanding the impacts of sea-level rise on the mobility of natural and anthropogenic coastal solutes.Item The influence of environmental conditions on kinetics of arsenite oxidation by manganese‑oxides(BIOMED CENTRAL LTD, 2015-09-16) Fischel, Matthew H. H.; Fischel, Jason S.; Lafferty, Brandon J.; Sparks, Donald L.; Matthew H. H. Fischel, Jason S. Fischel, Brandon J. Lafferty and Donald L. Sparks; Fischel, Matthew H. H.; Fischel, Jason S.; Sparks, Donald L.BACGROUND: Manganese-oxides are one of the most important minerals in soil due to their widespread distribution and high reactivity. Despite their invaluable role in cycling many redox sensitive elements, numerous unknowns remain about the reactivity of different manganese-oxide minerals under varying conditions in natural systems. By altering temperature, pH, and concentration of arsenite we were able to determine how manganese-oxide reactivity changes with simulated environmental conditions. The interaction between manganese-oxides and arsenic is particularly important because manganese can oxidize mobile and toxic arsenite into more easily sorbed and less toxic arsenate. This redox reaction is essential in understanding how to address the global issue of arsenic contamination in drinking water. RESULTS: The reactivity of manganese-oxides in ascending order is random stacked birnessite, hexagonal birnessite, biogenic manganese-oxide, acid birnessite, and δ-MnO2. Increasing temperature raised the rate of oxidation. pH had a variable effect on the production of arsenate and mainly impacted the sorption of arsenate on δ-MnO2, which decreased with increasing pH. Acid birnessite oxidized the most arsenic at alkaline and acidic pHs, with decreased reactivity towards neutral pH. The δ-MnO2 showed a decline in reactivity with increasing arsenite concentration, while the acid birnessite had greater oxidation capacity under higher concentrations of arsenite. The batch reactions used in this study quantify the impact of environmental variances on different manganese-oxides’ reactivity and provide insight to their roles in governing chemical cycles in the Critical Zone. CONCLUSIONS: The reactivity of manganese-oxides investigated was closely linked to each mineral’s crystallinity, surface area, and presence of vacancy sites. δ-MnO2 and acid birnessite are thought to be synthetic representatives of naturally occurring biogenic manganese-oxides; however, the biogenic manganese-oxide exhibited a lag time in oxidation compared to these two minerals. Reactivity was clearly linked to temperature, which provides important information on how these minerals react in the subsurface environment. The pH affected oxidation rate, which is essential in understanding how manganese-oxides react differently in the environment and their potential role in remediating contaminated areas. Moreover, the contrasting oxidative capacity of seemingly similar manganese-oxides under varying arsenite concentrations reinforces the importance of each manganese-oxide mineral’s unique properties.Item Isolation of dissolved organic matter from aqueous solution by precipitation with FeCl3: mechanisms and significance in environmental perspectives(Scientific Reports, 2023-03-20) Zhang, Jie; Mostofa, Khan M. G.; Yang, Xuemei; Mohinuzzaman, Mohammad; Liu, Cong-Qiang; Senesi, Nicola; Senesi, Giorgio S.; Sparks, Donald L.; Teng, H. Henry; Li, Longlong; Yuan, Jie; Li, Si-LiangFerric ions can bind strongly with dissolved organic matter (DOM), including humic acids (HA), fulvic acids (FA), and protein-like substances, whereas isolation of Fe-DOM precipitates (Fe-DOMP) and their biochemical characteristics remain unclear. In this work FeCl3 was used to isolate DOM components from various sources, including river, lake, soil, cow dung, and standard tryptophan and tyrosine, through precipitation at pH 7.5–8.5. The Fe-DOMP contribute to total DOM by approximately 38.6–93.8% of FA, 76.2% of HA and 25.0–30.4% of tryptophan and tyrosine, whilst fluorescence spectra allowed to monitor/discriminate the various DOM fractions in the samples. The relative intensity of the main infrared peaks such as 3406‒3383 cm−1 (aromatic OH), 1689‒1635 cm−1 (‒COOH), 1523–1504 cm−1 (amide) and 1176–1033 cm−1 (‒S=O) show either to decline or disappear in Fe‒DOMP. These results suggest the occurrence of Fe bonds with various functional groups of DOM, indicating the formation of π–d electron bonding systems of different strengths in Fe‒DOMP. The novel method used for isolation of Fe-DOMP shows promising in opening a new frontier both at laboratory and industrial purposes. Furthermore, results obtained may provide a better understanding of metal–organic complexes involved in the regulation of the long-term stabilization/sequestration of DOM in soils and waters.Item The Joint Risks of Anticipated Sea Level Rise and Coastal Contaminated Sites: Economic and Scientific Evidence(Department of Applied Economics and Statistics, University of Delaware, Newark, DE., 2014-10) Duke, Joshua M.; Messer, Kent D.; Michael, Holly A.; Sparks, Donald L.Item Scanning X-ray fluorescence spectroscopy and micro-X-ray absorption near-edge structure analysis as a guiding tool for the conservation treatment of two eighteenth-century Philadelphian portraits(X-Ray Spectrometry, 2023-04-02) Porell, Mina; Cushman, Matthew; Fischel, Jason S. T.; Fischel, Matthew H. H.; Sparks, Donald L.; Grayburn, RosieAn in-depth technical examination and conservation treatment of paintings by William Williams (Bristol 1727–1791 Bristol) has shed light on the artist's materials and technique. This investigation centered primarily on Williams's two 1766 portraits of William and David Hall. The paintings are considered the earliest life-sized, full-length portraits executed in the Philadelphia area. The analysis of the artist's palette indicated deliberate choices in the use of orpiment (As2S3). The mineral's tendency to oxidize to colorless and water-soluble arsenic oxides likely caused color changes and degraded organic binder in the orpiment-rich areas. μ-XANES revealed orpiment photodegradation to arsenate species at the paint surface, with migration to the ground layers. Just below the paint surface, arsenic remains bound primarily as arsenite, with some associated with sulfur as orpiment. This As distribution suggests that the paint is liable to further degradation by photooxidation and use of moisture would be detrimental. Given this treatment-critical degradation phenomenon, it was important to identify all arsenic-containing areas of both portraits. Scanning XRF allowed rapid and accurate collection of maps from both portraits. Elemental maps of arsenic identified the orpiment-rich areas of the painting, which would be susceptible to further degradation upon exposure to water during treatment. An aqueous adhesive was necessary to consolidate the cupped paint of the glue-paste lined paintings. The arsenic maps guided the use of two different consolidants–BEVA 371 for the water-sensitive orpiment-rich paint and sturgeon glue for all other areas, striking a compromise between esthetic improvement and long term preservation.