[ { "id": "authors:7wtk7-nsg47", "collection": "authors", "collection_id": "7wtk7-nsg47", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120228-111952036", "type": "article", "title": "Manganese Oxidation Induced by Water Table Fluctuations in a Sand Column", "author": [ { "family_name": "Farnsworth", "given_name": "Claire E.", "clpid": "Farnsworth-C-E" }, { "family_name": "Voegelin", "given_name": "Andreas", "clpid": "Voegelin-A" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "On\u2013off cycles of production wells, especially in bank filtration settings, cause oscillations in the local water table, which can deliver significant amounts of dissolved oxygen (DO) to the shallow groundwater. The potential for DO introduced in this manner to oxidize manganese(II) (Mn(II)), mediated by the obligate aerobe Pseudomonas putida GB-1, was tested in a column of quartz sand fed with anoxic influent solution and subject to 1.3 m water table changes every 30\u201350 h. After a period of filter ripening, 100 \u03bcM Mn was rapidly removed during periods of low water table and high dissolved oxygen concentrations. The accumulation of Mn in the column was confirmed by XRF analysis of the sand at the conclusion of the study, and both measured net oxidation rates and XAS analysis suggest microbial oxidation as the dominant process. The addition of Zn, which inhibited GB-1 Mn oxidation but not its growth, interrupted the Mn removal process, but Mn oxidation recovered within one water table fluctuation. Thus transient DO conditions could support microbially mediated Mn oxidation, and this process could be more relevant in shallow groundwater than previously thought.", "doi": "10.1021/es2027828", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2012-01-03", "series_number": "1", "volume": "46", "issue": "1", "pages": "277-284" }, { "id": "authors:fx5yb-bsp57", "collection": "authors", "collection_id": "fx5yb-bsp57", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110627-112326370", "type": "article", "title": "Inorganic Geochemistry and Redox Dynamics in Bank Filtration Settings", "author": [ { "family_name": "Farnsworth", "given_name": "Claire E.", "clpid": "Farnsworth-C-E" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Bank filtration induces flow of surface water through a hydraulically connected aquifer by excess pumping from a production well in the aquifer. This review presents the four main geochemical processes relevant for inorganic geochemistry, with a focus on iron (Fe) and manganese (Mn), during bank filtration: reduction near the bank, oxidation near the production well, carbonate dissolution, and sorption to aquifer materials. Physical and transport processes affect these geochemical processes and influence the redox state of the infiltrate. The presence of Fe and Mn in bank infiltrate is directly related to its redox status and can necessitate drinking water treatment after extraction. Long-term, in situ sequestration of Fe and Mn requires precipitation of oxide or carbonate solids, since a sorption front can breakthrough at the production well.", "doi": "10.1021/es2001612", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2011-06-15", "series_number": "12", "volume": "45", "issue": "12", "pages": "5079-5087" }, { "id": "authors:73t1r-fy715", "collection": "authors", "collection_id": "73t1r-fy715", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110420-161346767", "type": "article", "title": "Physical, Chemical, and Mineralogical Characteristics of a Reservoir Sediment Delta (Lake Powell, USA) and Implications for Water Quality during Low Water Level", "author": [ { "family_name": "Wildman", "given_name": "Richard A., Jr.", "clpid": "Wildman-R-A-Jr" }, { "family_name": "Pratson", "given_name": "Lincoln F.", "clpid": "Pratson-L-F" }, { "family_name": "DeLeon", "given_name": "Michael", "clpid": "DeLeon-M" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Lake Powell is a large reservoir in Utah and Arizona that has experienced large changes in water level during a recent drought. As a first step in assessing the connection between hydrologic and chemical changes at Lake Powell, we characterized the particle size and solid-phase bulk concentrations for 31 elements and 25 minerals in sediment from the inflow region and some shoreline locations by using laser diffractometry, X-ray fluorescence, elemental analysis, and X-ray diffraction. Our results are consistent with previous results that show a negative correlation between particle size and concentrations of most elements and most minerals other than quartz and some feldspars. In our samples, however, solid-phase iron, rather than particle size or organic carbon, is the best predictor variable for the solid-phase concentrations of elements and minerals. Sediment characteristics vary on a scale of tens of kilometers, with fine sediment that is enriched in trace elements nearer to the dam. These trends allow formulation of an algorithm for determining a water-level threshold below which sediment resuspension may alter water chemistry in a generic reservoir with a long and narrow sediment delta.", "doi": "10.2134/jeq2010.0323", "issn": "0047-2425", "publisher": "American Society of Agronomy", "publication": "Journal of Environment Quality", "publication_date": "2011-03", "series_number": "2", "volume": "40", "issue": "2", "pages": "575-586" }, { "id": "authors:550kj-ewg50", "collection": "authors", "collection_id": "550kj-ewg50", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120227-140012592", "type": "article", "title": "Potential for release of sediment phosphorus to Lake Powell (Utah and Arizona) due to sediment resuspension during low water level", "author": [ { "family_name": "Wildman", "given_name": "Richard A., Jr.", "clpid": "Wildman-R-A-Jr" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "The water level in Lake Powell, an important water-supply reservoir on the Colorado River, United States, decreased in most years from 1999 to 2010, exposing the sediment delta in the inflow region of this reservoir. This study assesses the potential for sediment-associated phosphorus (P) to enter the water column during sediment resuspension. We collected sediment samples from the reservoir inflow region and performed a sequential extraction and a sorption experiment that focused on P. We also collected water samples at locations upstream and downstream of the exposed sediment delta and measured soluble reactive P during base flow and during the yearly flood associated with spring runoff. Results indicate that extractable P is associated with various operationally defined fractions as follows: 50% with calcite and biogenic apatite, 29% with detrital apatite, 10% with Fe(III)-oxide minerals, 6% with organic matter and 4% with easily exchangeable solid-phase association sites. Sorption experiments indicate that the equilibrium P concentration is 0.19 \u00b1 0.07 \u03bcM. Particle size is correlated with sediment P; coarse sediment contains and sorbs much less extractable P than fine sediment does. Measurements of water samples indicate that sediment resuspension probably releases P from sediment to overlying water during base flow, but the effect during floods is less clear. These results indicate that lowering reservoir levels introduces sediment-associated P to the reservoir when sediment resuspension occurs.", "doi": "10.1080/07438141.2011.632705", "issn": "0743-8141", "publisher": "Taylor & Francis", "publication": "Lake and Reservoir Management", "publication_date": "2011", "series_number": "4", "volume": "27", "issue": "4", "pages": "365-375" }, { "id": "authors:qstc0-b3g84", "collection": "authors", "collection_id": "qstc0-b3g84", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110303-113510401", "type": "article", "title": "Effect of changes in water level on sediment pore water redox geochemistry at a reservoir shoreline", "author": [ { "family_name": "Wildman", "given_name": "Richard A., Jr.", "clpid": "Wildman-R-A-Jr" }, { "family_name": "Chan", "given_name": "Nathan W.", "clpid": "Chan-Nathan-W" }, { "family_name": "Dalleska", "given_name": "Nathan F.", "orcid": "0000-0002-2059-1587", "clpid": "Dalleska-N-F" }, { "family_name": "Anderson", "given_name": "Mark", "clpid": "Anderson-M" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Pore water samplers with high vertical resolution were used to evaluate the response of sediment redox geochemistry during transient hydrologic conditions at Lake Powell, a large reservoir in Utah and Arizona, USA. Samplers were deployed at two different yet proximal shoreline locations, White and Farley Canyons, before and after exposure of sediment to air and subsequent resubmersion, which resulted from fluctuations in the water level of the reservoir. Before exposure to air, an observed increase in dissolved Mn concentrations and, at Farley Canyon, an observed decrease in dissolved U concentrations across and immediately below the sediment\u2013water interface indicated reducing conditions in the sub-surface. After exposure and resubmersion of the sediment, pore water profiles at each site differed distinctly from those observed before the fluctuation in water level. At White Canyon, an increase in U concentrations and a decrease in Mn concentrations in pore water after exposure and subsequent resubmersion are suggestive of oxidative processes occurring during the period of sediment exposure. Data from Farley Canyon suggest that the same processes may be occurring, but to a lesser extent. Depth profiles of As and Pb were also examined, but were relatively featureless compared to those of Mn and U. At both sites, sediment evaluated for pore water chemistry in the second sampling was only fully resubmerged for 2\u20135 days prior to the second sampling event, yet reducing conditions were clearly evident in the Mn pore water profiles. This suggests that the dynamics of the biogeochemical processes occurring in surface sediment at Lake Powell are responsive on the timescale defined by the fluctuating water levels in the reservoir.", "doi": "10.1016/j.apgeochem.2010.10.005", "issn": "0883-2927", "publisher": "Elsevier", "publication": "Applied Geochemistry", "publication_date": "2010-12", "series_number": "12", "volume": "25", "issue": "12", "pages": "1902-1911" }, { "id": "authors:47tzk-c5744", "collection": "authors", "collection_id": "47tzk-c5744", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100129-094247179", "type": "article", "title": "Hydrous Manganese Oxide Doped Gel Probe Sampler for Measuring In Situ Reductive Dissolution Rates. 1. Laboratory Development", "author": [ { "family_name": "Farnsworth", "given_name": "Claire E.", "clpid": "Farnsworth-C-E" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Reductive dissolution of redox-sensitive minerals such as manganese (Mn) oxides in natural sediments is an important mechanism for trace element mobilization into groundwater. A gel probe sampler has been constructed to study in situ reductive dissolution of Mn oxides. The gel consists of a polyacrylamide polymer matrix doped with hydrous Mn oxide (HMO). Gel slabs are mounted into a probe, which is designed to be inserted into the sediments. The amount of Mn released from the gel by reductive dissolution is determined by comparing the amount of Mn initially embedded into the gel with the amount remaining in the gel after exposure to conditions in the sediments or, in laboratory studies, to reducing agents. In this laboratory study, the performance of the gel probes was examined using the model reductant ascorbate and the Mn-reducing bacteria Shewanella oneidensis strain MR-1. In addition, a 1-D model was used to relate the reaction rates observed for HMO embedded in gels to those for HMO in suspension. One limitation of the HMO-doped gels for assessing microbial reduction rates is that the gels prevent direct contact between the microbes and the HMO and hence preclude enzymatic reduction at the cell surface. Nonetheless, the HMO-doped gel probes offer the possibility to establish a lower bound for Mn-reduction capacity in sediments.", "doi": "10.1021/es901577q", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2010-01-01", "series_number": "1", "volume": "44", "issue": "1", "pages": "34-40" }, { "id": "authors:gxgp2-kvc05", "collection": "authors", "collection_id": "gxgp2-kvc05", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100128-143510481", "type": "article", "title": "Hydrous Manganese Oxide Doped Gel Probe Sampler for Measuring In Situ Reductive Dissolution Rates. 2. Field Deployment", "author": [ { "family_name": "Farnsworth", "given_name": "Claire E.", "clpid": "Farnsworth-C-E" }, { "family_name": "Griffis", "given_name": "Sarah D.", "clpid": "Griffis-S-D" }, { "family_name": "Wildman", "given_name": "Richard A., Jr.", "clpid": "Wildman-R-A-Jr" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "In situ rates of reductive dissolution in submerged shoreline sediments at Lake Tegel (Berlin, Germany) were measured with a novel hydrous manganese (Mn) oxide-doped gel probe sampler in concert with equilibrium gel probe and sequential extraction measurements. Rates were low in the top 8 cm, then showed a peak from 8 to 14 cm, with a maximum at 12 cm depth. This rate corresponded with a peak in dissolved porewater iron (Fe) at 11 cm depth. Below 14 cm, the reductive dissolution rate reached an intermediate steady value. Lower rates at depth corresponded with increases in operationally defined fractions of carbonate-bound and organic- and sulfide-bound Mn and Fe as detected by sequential extraction. Observed rates of reductive dissolution, which reflect a capacity for Mn reduction rather than actual rates under ambient conditions, appear to correlate with porewater chemistry and sequential extraction fractions as expected in early sediment diagenesis, and are consistent with previous measurements of in situ reductive dissolution rates. Significant downward advection in this bank filtration setting depletes the Mn and Fe oxides in the sediments and enhances the transport of dissolved Fe and Mn into the infiltrating water.", "doi": "10.1021/es901572h", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2010-01-01", "series_number": "1", "volume": "44", "issue": "1", "pages": "41-46" }, { "id": "authors:kbnev-0nj62", "collection": "authors", "collection_id": "kbnev-0nj62", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100216-154255633", "type": "article", "title": "Geochemical processes controlling arsenic mobility in groundwater: A case study of arsenic mobilization and natural attenuation", "author": [ { "family_name": "He", "given_name": "Y. Thomas", "clpid": "He-Y-T" }, { "family_name": "Fitzmaurice", "given_name": "Arthur G.", "clpid": "Fitzmaurice-A-G" }, { "family_name": "Bilgin", "given_name": "Azra", "clpid": "Bilgin-A" }, { "family_name": "Choi", "given_name": "Sunkyung", "clpid": "Choi-S" }, { "family_name": "O'Day", "given_name": "Peggy", "clpid": "O'Day-P" }, { "family_name": "Horst", "given_name": "John", "clpid": "Horst-J" }, { "family_name": "Harrington", "given_name": "James", "clpid": "Harrington-J" }, { "family_name": "Reisinger", "given_name": "James", "clpid": "Reisinger-J" }, { "family_name": "Burris", "given_name": "David R.", "clpid": "Burris-D-R" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "The behavior of As in the subsurface environment was examined along a transect of groundwater monitoring wells at a Superfund site, where enhanced reductive dechlorination (ERD) is being used for the remediation of groundwater contaminated with chlorinated solvents. The transect was installed parallel to the groundwater flow direction through the treatment area. The ERD technology involves the injection of organic C (OC) to stimulate in situ microbial dechlorination processes. A secondary effect of the ERD treatment at this site, however, is the mobilization of As, as well as Fe and Mn. The concentrations of these elements are low in groundwater collected upgradient of the ERD treatment area, indicating that, in the absence of the injected OC, the As that occurs naturally in the sediment is relatively immobile. Batch experiments conducted using sediments from the site inoculated with an Fe(III)- and As(V)-reducing bacterium and amended with lactate resulted in mobilization of As, Fe and Mn, suggesting that As mobilization in the field is due to microbial processes.\n\nIn the areas of the transect downgradient of the ERD treatment area, however, the concentrations of OC, As, Fe and Mn in the groundwater are not elevated relative to background levels. The decrease in the dissolved concentration of OC can be attributed to mineralization by microorganisms. The losses of As, Fe and Mn from the dissolved phase must presumably be accompanied by their uptake onto aquifer solids, but chemical extractions provided evidence only for the enrichment of Fe(II). Nor could sorption of As(III) onto sediments be detected by X-ray absorption spectroscopy (XAS) against the background of native As in the sediments, which was present as As(V).", "doi": "10.1016/j.apgeochem.2009.10.002", "issn": "0883-2927", "publisher": "Elsevier", "publication": "Applied Geochemistry", "publication_date": "2010-01", "series_number": "1", "volume": "25", "issue": "1", "pages": "69-80" }, { "id": "authors:93ehs-26229", "collection": "authors", "collection_id": "93ehs-26229", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091110-144017413", "type": "article", "title": "Neurotoxicity of manganese oxide nanomaterials", "author": [ { "family_name": "Stefanescu", "given_name": "Diana M.", "clpid": "Stefanescu-D-M" }, { "family_name": "Khoshnan", "given_name": "Ali", "clpid": "Khoshnan-A" }, { "family_name": "Patterson", "given_name": "Paul H.", "clpid": "Patterson-P-H" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Manganese (Mn) toxicity in humans has been observed as manganism, a disease that resembles Parkinson's disease. The mechanism of Mn toxicity and the chemical forms that may be responsible for its neurotoxicity are not well understood. We examined the toxicity of Mn oxide nanomaterials in a neuronal precursor cell model, using the MTS assay to evaluate mitochondrial function in living cells and the LDH assay to quantify the release of the enzyme lactate dehydrogenase as a result of damage to the cell membrane. Both assays show that the toxicity of Mn is dependent on the type of Mn oxide nanomaterial and its concentration as well as on the state of cell differentiation. Following exposure to Mn oxide nanomaterials, reactive oxygen species (ROS) are generated, and flow cytometry experiments suggest that cell death occurred through apoptosis. During exposure to Mn oxide nanomaterials, increased levels of the transcription factor NF-\u03baB (which mediates the cellular inflammatory response) were observed.", "doi": "10.1007/s11051-008-9554-1", "issn": "1388-0764", "publisher": "Springer", "publication": "Journal of Nanoparticle Research", "publication_date": "2009-11", "series_number": "8", "volume": "11", "issue": "8", "pages": "1957-1969" }, { "id": "authors:eak0y-mm509", "collection": "authors", "collection_id": "eak0y-mm509", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091210-080110299", "type": "article", "title": "Geochemical and hydrologic controls on the mobilization of arsenic derived from herbicide application", "author": [ { "family_name": "Fitzmaurice", "given_name": "Arthur G.", "clpid": "Fitzmaurice-A-G" }, { "family_name": "Bilgin", "given_name": "A. Azra", "clpid": "Bilgin-A-A" }, { "family_name": "O'Day", "given_name": "Peggy A.", "clpid": "O'Day-P-A" }, { "family_name": "Illera", "given_name": "Virginia", "clpid": "Illera-V" }, { "family_name": "Burris", "given_name": "David R.", "clpid": "Burris-D-R" }, { "family_name": "Reisinger", "given_name": "H. James", "clpid": "Reisinger-H-J" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "The fate and transport of As was examined at an industrial site where soil- and groundwater contamination are derived from the application of As_2O_3 as a herbicide. Application of arsenical herbicides was discontinued in the 1970s and soils in the source area were partially excavated in 2003. Arsenic contamination (up to 280 mg/kg) remains in the source area soils and a plume of As-contaminated groundwater persists in the surficial aquifer downgradient of the source area with maximum observed As concentrations of 1200 \u03bcg/L near the source area. The spatial extent of As contamination as defined by the 10 \u03bcg/L contour appears to have remained relatively stable over the period 1996\u20132006; the boundary of the 1000 \u03bcg/L contour has retreated over the same time period indicating a decrease in total As mass in the surficial groundwater.\n\nIn column experiments conducted with source area soil, the As concentrations in the column effluent were comparable to those observed in groundwater near the source area. A substantial fraction of the As could be leached from the source area soil with ammonium sulfate and ammonium phosphate. Exhaustive extraction with background groundwater removed most of the total As. These results indicate that As in the source area soils is geochemically labile. Source area soils are low in extractable Fe, Mn and Al, and characterization by X-ray absorption spectroscopy and electron microscopy indicated that As is present primarily as arsenate sorbed to (alumino)silicate minerals. Batch sorption experiments showed much less sorption on surficial aquifer sediments than on sediments from the Jackson Bluff Formation (JBF), a presumed confining layer. This limited capacity of the surficial aquifer sediments for As sorption is consistent with the similar As contents observed for these sediments within and upgradient of the As plume. The apparent stability of the As plume cannot be explained by sequestration of As within the surficial aquifer. Sorption to JBF sediments may contribute to As sequestration, but As enrichment in JBF sediments within the plume (i.e., as compared with JBF sediments upgradient) was not observed. These results indicate that neither the persistence of As in the source area soils or the apparent stability of the plume of As-contaminated groundwater at this site can be explained by geochemical controls on As mobility. The absence of demonstrable geochemical bases for such observations suggests that possible hydrologic controls should be further investigated at this site.", "doi": "10.1016/j.apgeochem.2009.09.019", "issn": "0883-2927", "publisher": "Elsevier", "publication": "Applied Geochemistry", "publication_date": "2009-11", "series_number": "11", "volume": "24", "issue": "11", "pages": "2152-2162" }, { "id": "authors:ehzhc-46412", "collection": "authors", "collection_id": "ehzhc-46412", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091013-093446479", "type": "article", "title": "Enhancement of Arsenic(III) Sequestration by Manganese Oxides in the Presence of Iron(II)", "author": [ { "family_name": "He", "given_name": "Y. Thomas", "clpid": "He-Y-T" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Mobilization of arsenic (As) in the subsurface environment can result in elevated concentrations of As in groundwater and potential human exposure and adverse health effects. Natural attenuation (i.e., sequestration) of As may, under appropriate geochemical conditions, serve to limit human exposure to As. The effectiveness of As sequestration by sorption, co-precipitation, and/or precipitation can be strongly influenced by redox conditions, which can control the solubility of sorbent phases and the stability of As-containing solids. The redox transformation of As between the +III and +V oxidation states can also affect the extent of As sorption. The effect of amendment with synthetic manganese (Mn) oxide birnessite (nominally MnO2) on As sequestration in a sediment suspension was examined in the absence and presence of iron (Fe) added as Fe(II). In the absence of Fe(II), the extent of As(III) oxidation to As(V) increased with increasing birnessite amendment, but As sequestration was not increased. In the presence of Fe(II), however, As sequestration did increase with increasing birnessite amendment. Concurrently, Fe(II) was also sequestered, and the Fe(III) content of the solid phase was observed to increase, suggesting that the oxidative precipitation of an Fe(III) oxyhydroxide phase plays an important role in As sequestration. These results suggest that amendment with Mn(III, IV) oxides could be an effective way to augment natural attenuation of As in cases where As-contaminated groundwater also contains elevated concentrations of Fe(II).", "doi": "10.1007/s11270-009-0018-8", "issn": "0049-6979", "publisher": "Springer", "publication": "Water, Air, and Soil pollution", "publication_date": "2009-10", "series_number": "1-4", "volume": "203", "issue": "1-4", "pages": "359-368" }, { "id": "authors:9sg9w-5vc02", "collection": "authors", "collection_id": "9sg9w-5vc02", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090918-114943004", "type": "article", "title": "Hydrologic and Biogeochemical Controls of River Subsurface Solutes under Agriculturally Enhanced Ground Water Flow", "author": [ { "family_name": "Wildman", "given_name": "Richard A., Jr.", "clpid": "Wildman-R-A-Jr" }, { "family_name": "Domagalski", "given_name": "Joseph L.", "clpid": "Domagalski-J-L" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "The relative influences of hydrologic processes and biogeochemistry on the transport and retention of minor solutes were compared in the riverbed of the lower Merced River (California, USA). The subsurface of this reach receives ground water discharge and surface water infiltration due to an altered hydraulic setting resulting from agricultural irrigation. Filtered ground water samples were collected from 30 drive point locations in March, June, and October 2004. Hydrologic processes, described previously, were verified by observations of bromine concentrations; manganese was used to indicate redox conditions. The separate responses of the minor solutes strontium, barium, uranium, and phosphorus to these influences were examined. Correlation and principal component analyses indicate that hydrologic processes dominate the distribution of trace elements in the ground water. Redox conditions appear to be independent of hydrologic processes and account for most of the remaining data variability. With some variability, major processes are consistent in two sampling transects separated by 100 m.", "doi": "10.2134/jeq2008.0448", "issn": "0047-2425", "publisher": "American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America", "publication": "Journal of Environment Quality", "publication_date": "2009-07-23", "series_number": "5", "volume": "38", "issue": "5", "pages": "1830-1840" }, { "id": "authors:btx2g-thp60", "collection": "authors", "collection_id": "btx2g-thp60", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090806-113206412", "type": "article", "title": "Natural attenuation of arsenic by sediment sorption and oxidation", "author": [ { "family_name": "Choi", "given_name": "Sunkyung", "clpid": "Choi-S" }, { "family_name": "O'Day", "given_name": "Peggy A.", "clpid": "O'Day-P-A" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Arsenic sorption onto aquifer sediments was investigated in anaerobic laboratory batch and column uptake experiments and characterized by As, Fe, and Mn X-ray absorption spectroscopy (XAS) to estimate the extent and mechanism of abiotic sorption and oxidation of As(III). Batch experiments at pH 6 showed that the amount of As(III) or As(V) sorption from synthetic background porewater to sediments was similar as a function of total As concentration, but slightly more As(V) was sorbed than As(III) with increasing As concentrations. Column experiments with As(III) solutions in the absence and presence of dissolved Fe^2+ showed more As uptake in the presence of Fe but also more Fe desorption during flushout with As-free solutions such that net As uptake was similar to, or less than that of, the Fe-free experiment. Fits to bulk Fe X-ray absorption near-edge spectroscopy (XANES) spectra showed no change between unreacted and reacted sediments. Manganese XANES revealed small increases in absorption in the spectral region associated with Mn(II) after reaction, indicating sediment Mn reduction. However, XANES spectra showed that Mn is not present as Mn^(IV)O_2(s) but is probably substituted into other sediment minerals as a mixture of Mn(II,III). Quantitative analyses of As XANES spectra, which indicated mixtures of As(III) and As(V) after reaction with As(III) solutions, were used to estimate a fraction of As(V) in excess of native As(V) in the sediment (0.2 mmol kg^\u22121) that corresponds to sorbed As(III) oxidized to As(V). The spectroscopic and solution data indicate that the aquifer sediments have a limited abiotic capacity to oxidize As(III), which did not exceed 30% of the total amount of As sorbed and was estimated in the range of 0.025\u22120.4 mmol kg^\u22121 sediment. In the presence of dissolved Fe^2+, the precipitation of Fe(III) hydrous oxide phases will be an effective mechanism for As scavenging only if there exists sufficient dissolved oxygen in groundwater to oxidize Fe. Once the aqueous oxidative capacity is exhausted, dissolved Fe^2+ may compete with As(III) for the limited abiotic oxidation supplied by sediment Mn-bearing phases.", "doi": "10.1021/es802841x", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2009-06-15", "series_number": "12", "volume": "43", "issue": "12", "pages": "4253-4259" }, { "id": "authors:ecs2j-ndg28", "collection": "authors", "collection_id": "ecs2j-ndg28", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090624-152635632", "type": "article", "title": "Dissolution kinetics of biogenic silica collected from the water column and sediments of three Southern California borderland basins", "author": [ { "family_name": "Cheng", "given_name": "Tao", "orcid": "0000-0003-4830-177X", "clpid": "Cheng-Tao" }, { "family_name": "Hammond", "given_name": "Douglas E.", "clpid": "Hammond-D-E" }, { "family_name": "Berelson", "given_name": "William M.", "clpid": "Berelson-W-M" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" }, { "family_name": "Dixit", "given_name": "Suvasis", "clpid": "Dixit-S" } ], "abstract": "Understanding biogenic silica (bSi) dissolution kinetics in margin environments is important in assessing the global silicon cycle, a cycle closely linked to the global carbon cycle. This understanding is also essential to answer the question of whether bSi content in marine sediment is a valid indicator of productivity in the overlying surface ocean. In this study, plankton tow, sediment trap, and sediment samples were collected at sites in three Southern California borderland basins. Batch dissolution experiments with plankton tow and sediment trap materials (conducted in the laboratory at 22 \u00b0C) showed linear dissolution kinetics, from which mean dissolution rate constants of 0.05 d^(\u22121) for plankton tow samples and 0.07 d^(\u22121) for sediment trap samples could be calculated. The dissolution rate constants for both types of samples showed seasonal variability but not the same seasonal patterns. Faster dissolution was observed with sediment trap samples collected at 800 m than at 550 m. With sediment multi-core samples, non-linear dissolution kinetics was observed, which complicates the direct comparison of dissolution rates. Nonetheless, dissolution appeared to be slower for the sediments samples than for samples collected from the water column and to decrease with depth in the sediments. Rate constants for surface sediment (0\u20130.5 cm) were at least 3\u20135 times less, and sediments at depths > 2 cm had rate constants at least 6\u201313 times less than those for material sinking to the sediment surface at these sites. Dissolution experiments conducted with Santa Barbara Basin surface sediment samples amended with dissolved aluminum (Al) and San Pedro Basin trap samples amended with enriched detrital materials (obtained by leaching bSi from sediment samples) suggested that dissolution was inhibited by Al and that the sediments from the different basins varied in the extent of Al release.", "doi": "10.1016/j.marchem.2008.12.001", "issn": "0304-4203", "publisher": "Elsevier", "publication": "Marine Chemistry", "publication_date": "2009-01-30", "series_number": "1-2", "volume": "113", "issue": "1-2", "pages": "41-49" }, { "id": "authors:0dnzs-7zd42", "collection": "authors", "collection_id": "0dnzs-7zd42", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170409-081329509", "type": "article", "title": "MNA as a Remedy for Arsenic Mobilized by Anthropogenic Inputs of Organic Carbon", "author": [ { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" }, { "family_name": "O'Day", "given_name": "Peggy A.", "clpid": "O'Day-P-A" }, { "family_name": "Ford", "given_name": "Robert G.", "clpid": "Ford-R-G" }, { "family_name": "He", "given_name": "Y. Thomas", "clpid": "He-Y-Thomas" }, { "family_name": "Bilgin", "given_name": "Azra", "clpid": "Bilgin-A" }, { "family_name": "Reisinger", "given_name": "H. James", "clpid": "Reisinger-H-J" }, { "family_name": "Burris", "given_name": "David R.", "clpid": "Burris-D-R" } ], "abstract": "The potential application of monitored natural attenuation (MNA) as a remedy for ground water contaminated with arsenic (As) is examined for a subset of contaminated sites, specifically those where naturally occurring As has been mobilized due to localized anthropogenic organic carbon (OC) releases. This includes sites subject to petroleum releases, exposure to landfill leachates, and OC additions for biostimulation of reductive dechlorination of chlorinated solvents. The key characteristic of these sites is that, under conditions prevailing before the anthropogenic OC introduction, the naturally occurring As in the subsurface was not mobile and did not adversely affect ground water quality. This suggests that, in the far\u2010field (where background conditions are (re) established), As may be sequestered upon contact of the contaminated ground water with either or both the (uncontaminated) ambient ground water and the background aquifer minerals. The observed extents of elevated concentrations (or \"footprints\") of As and other chemical species, such as dissolved OC and iron (Fe), and related parameters, such as redox potential (Eh) and dissolved oxygen, and their evolution over time can be used to assess the mobilization and sequestration of As and the potential feasibility of MNA as a remedial option. Ultimately, the capacity for As sequestration must be assessed in the context of the OC loading to the site, which may require \"active\" measures for source control. Monitoring is needed to confirm the continuing effectiveness of the MNA remedy or to indicate if contingency measures must be implemented.", "doi": "10.1111/j.1745-6592.2009.01242.x", "issn": "1745-6592", "publisher": "Wiley", "publication": "Ground Water Monitoring & Remediation", "publication_date": "2009", "series_number": "3", "volume": "29", "issue": "3", "pages": "84-92" }, { "id": "authors:hc57j-zhb62", "collection": "authors", "collection_id": "hc57j-zhb62", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170320-065640338", "type": "article", "title": "A Gel Probe Equilibrium Sampler for Measuring Arsenic Porewater Profiles and Sorption Gradients in Sediments: II. Field Application to Haiwee Reservoir Sediment", "author": [ { "family_name": "Campbell", "given_name": "Kate M.", "clpid": "Campbell-K-M" }, { "family_name": "Root", "given_name": "Robert", "clpid": "Root-R" }, { "family_name": "O'Day", "given_name": "Peggy A.", "clpid": "O'Day-P-A" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Arsenic (As) geochemistry and sorption behavior were measured in As- and iron (Fe)-rich sediments of Haiwee Reservoir by deploying undoped (clear) polyacrylamide gels and hydrous ferric oxide (HFO)-doped gels in a gel probe equilibrium sampler, which is a novel technique for directly measuring the effects of porewater composition on As adsorption to Fe oxides phases in situ. Arsenic is deposited at the sediment surface as As(V) and is reduced to As(III) in the upper layers of the sediment (0\u20138 cm), but the reduction of As(V) does not cause mobilization into the porewater. Dissolved As and Fe concentrations increased at depth in the sediment column driven by the reductive dissolution of amorphous Fe(III) oxyhydroxides and conversion to a mixed Fe(II, III) green rust-type phase. Adsorption of As and phosphorous (P) onto HFO-doped gels was inhibited at intermediate depths (10\u201320 cm), possibly due to dissolved organic or inorganic carbon, indicating that dissolved As concentrations were at least partially controlled by porewater composition rather than surface site availability. In sediments that had been recently exposed to air, the region of sorption inhibition was not observed, suggesting that prior exposure to air affected the extent of reductive dissolution, porewater chemistry, and As adsorption behavior. Arsenic adsorption onto the HFO-doped gels increased at depths >20 cm, and the extent of adsorption was most likely controlled by the competitive effects of dissolved phosphate. Sediment As adsorption capacity appeared to be controlled by changes in porewater composition and competitive effects at shallower depths, and by reductive dissolution and availability of sorption sites at greater burial depths.", "doi": "10.1021/es071120a", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2008-01-15", "series_number": "2", "volume": "42", "issue": "2", "pages": "504-510" }, { "id": "authors:ykavz-znw26", "collection": "authors", "collection_id": "ykavz-znw26", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:CAMest08b", "type": "article", "title": "A Gel Probe Equilibrium Sampler for Measuring Arsenic Porewater Profiles and Sorption Gradients in Sediments: II. Field Application to Haiwee Reservoir Sediment", "author": [ { "family_name": "Campbell", "given_name": "Kate M.", "clpid": "Campbell-K-M" }, { "family_name": "Root", "given_name": "Robert", "clpid": "Root-R" }, { "family_name": "O'Day", "given_name": "Peggy A.", "clpid": "O'Day-P-A" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Arsenic (As) geochemistry and sorption behavior were measured in As- and iron (Fe)-rich sediments of Haiwee Reservoir by deploying undoped (clear) polyacrylamide gels and hydrous ferric oxide (HFO)-doped gels in a gel probe equilibrium sampler, which is a novel technique for directly measuring the effects of porewater composition on As adsorption to Fe oxides phases in situ. Arsenic is deposited at the sediment surface as As(V) and is reduced to As(III) in the upper layers of the sediment (0\u20138 cm), but the reduction of As(V) does not cause mobilization into the porewater. Dissolved As and Fe concentrations increased at depth in the sediment column driven by the reductive dissolution of amorphous Fe(III) oxyhydroxides and conversion to a mixed Fe(II, III) green rust-type phase. Adsorption of As and phosphorous (P) onto HFO-doped gels was inhibited at intermediate depths (10\u201320 cm), possibly due to dissolved organic or inorganic carbon, indicating that dissolved As concentrations were at least partially controlled by porewater composition rather than surface site availability. In sediments that had been recently exposed to air, the region of sorption inhibition was not observed, suggesting that prior exposure to air affected the extent of reductive dissolution, porewater chemistry, and As adsorption behavior. Arsenic adsorption onto the HFO-doped gels increased at depths >20 cm, and the extent of adsorption was most likely controlled by the competitive effects of dissolved phosphate. Sediment As adsorption capacity appeared to be controlled by changes in porewater composition and competitive effects at shallower depths, and by reductive dissolution and availability of sorption sites at greater burial depths.", "doi": "10.1021/es071120a", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2008-01-15", "series_number": "2", "volume": "42", "issue": "2", "pages": "504-510" }, { "id": "authors:982da-tmh43", "collection": "authors", "collection_id": "982da-tmh43", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:CAMest08a", "type": "article", "title": "A Gel Probe Equilibrium Sampler for Measuring Arsenic Porewater Profiles and Sorption Gradients in Sediments: I. Laboratory Development", "author": [ { "family_name": "Campbell", "given_name": "Kate M.", "clpid": "Campbell-K-M" }, { "family_name": "Root", "given_name": "Robert", "clpid": "Root-R" }, { "family_name": "O'Day", "given_name": "Peggy A.", "clpid": "O'Day-P-A" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "A gel probe equilibrium sampler has been developed to study arsenic (As) geochemistry and sorption behavior in sediment porewater. The gels consist of a hydrated polyacrylamide polymer, which has a 92% water content. Two types of gels were used in this study. Undoped (clear) gels were used to measure concentrations of As and other elements in sediment porewater. The polyacrylamide gel was also doped with hydrous ferric oxide (HFO), an amorphous iron (Fe) oxyhydroxide. When deployed in the field, HFO-doped gels introduce a fresh sorbent into the subsurface thus allowing assessment of in situ sorption. In this study, clear and HFO-doped gels were tested under laboratory conditions to constrain the gel behavior prior to field deployment. Both types of gels were allowed to equilibrate with solutions of varying composition and re-equilibrated in acid for analysis. Clear gels accurately measured solution concentrations (\u00b11%), and As was completely recovered from HFO-doped gels (\u00b14%). Arsenic speciation was determined in clear gels through chromatographic separation of the re-equilibrated solution. For comparison to speciation in solution, mixtures of As(III) and As(V) adsorbed on HFO embedded in gel were measured in situ using X-ray absorption spectroscopy (XAS). Sorption densities for As(III) and As(V) on HFO embedded in gel were obtained from sorption isotherms at pH 7.1. When As and phosphate were simultaneously equilibrated (in up to 50-fold excess of As) with HFO-doped gels, phosphate inhibited As sorption by up to 85% and had a stronger inhibitory effect on As(V) than As(III). Natural organic matter (>200 ppm) decreased As adsorption by up to 50%, and had similar effects on As(V) and As(III). The laboratory results provide a basis for interpreting results obtained by deploying the gel probe in the field and elucidating the mechanisms controlling As partitioning between solid and dissolved phases in the environment.", "doi": "10.1021/es071119b", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2008-01-15", "series_number": "2", "volume": "42", "issue": "2", "pages": "497-503" }, { "id": "authors:k11c0-gyv04", "collection": "authors", "collection_id": "k11c0-gyv04", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20101008-113000430", "type": "article", "title": "Arsenic sequestration by sorption processes in high-iron sediments", "author": [ { "family_name": "Root", "given_name": "Robert A.", "clpid": "Root-R-A" }, { "family_name": "Dixit", "given_name": "Suvasis", "clpid": "Dixit-S" }, { "family_name": "Campbell", "given_name": "Kate M.", "clpid": "Campbell-K-M" }, { "family_name": "Jew", "given_name": "Adam D.", "clpid": "Jew-A-D" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" }, { "family_name": "O'Day", "given_name": "Peggy A.", "clpid": "O'Day-P-A" } ], "abstract": "High-iron sediments in North Haiwee Reservoir (Olancha, CA), resulting from water treatment for removal of elevated dissolved arsenic in the Los Angeles Aqueduct system, were studied to examine arsenic partitioning between solid phases and porewaters undergoing shallow burial. To reduce arsenic in drinking water supplies, ferric chloride and a cationic polymer coagulant are added to the aqueduct upstream of Haiwee Reservoir, forming an iron-rich floc that scavenges arsenic from the water. Analysis by synchrotron X-ray absorption spectroscopy (XAS) showed that the aqueduct precipitate is an amorphous hydrous ferric oxide (HFO) similar to ferrihydrite, and that arsenic is associated with the floc as adsorbed and/or coprecipitated As(V). Arsenic-rich floc and sediments are deposited along the inlet channel as aqueduct waters enter the reservoir. Sediment core samples were collected in two consecutive years from the edge of the reservoir along the inlet channel using 30- or 90-cm push cores. Cores were analyzed for total and extractable arsenic and iron concentrations. Arsenic and iron speciation and mineralogy in sediments were examined at selected depths by synchrotron XAS and X-ray diffraction (XRD). Sediment\u2013porewater measurements were made adjacent to the core sample sites using polyacrylamide gel probe samplers. Results showed that sediment As(V) is reduced to As(III) in all cores at or near the sediment\u2013water interface (0\u20134 cm), and only As(III) was observed in deeper sediments. Analyses of EXAFS spectra indicated that arsenic is present in the sediments mostly as a bidentate\u2013binuclear, inner-sphere sorption complex with local atomic geometries similar to those found in laboratory studies. Below about 10 cm depth, XAS indicated that the HFO floc had been reduced to a mixed Fe(II, III) solid with a local structure similar to that of synthetic green rust (GR) but with a slightly contracted average interatomic Fe\u2013Fe distance in the hydroxide layer. There was no evidence from XRD for the formation of a crystalline GR phase. The release of dissolved iron (presumably Fe^(2+)) and arsenic to solution, as monitored by in situ gel probes, was variable but, in general, occurred at greater depths than arsenic reduction in the sediments by spectroscopic observations and appears to be near or below the depth at which sediment GR was identified. These data point to reductive dissolution of the sorbent iron phase as the primary mechanism of release of sorbed arsenic to solution.", "doi": "10.1016/j.gca.2007.04.038", "issn": "0016-7037", "publisher": "Elsevier", "publication": "Geochimica et Cosmochimica Acta", "publication_date": "2007-12-01", "series_number": "23", "volume": "71", "issue": "23", "pages": "5782-5803" }, { "id": "authors:mymrx-9cw34", "collection": "authors", "collection_id": "mymrx-9cw34", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130611-153514379", "type": "article", "title": "Simultaneous Microbial Reduction of Iron(III) and Arsenic(V) in Suspensions of Hydrous Ferric Oxide", "author": [ { "family_name": "Campbell", "given_name": "Kate M.", "clpid": "Campbell-K-M" }, { "family_name": "Malasarn", "given_name": "Davin", "clpid": "Malasarn-D" }, { "family_name": "Saltikov", "given_name": "Chad W.", "clpid": "Saltikov-C-W" }, { "family_name": "Newman", "given_name": "Dianne K.", "orcid": "0000-0003-1647-1918", "clpid": "Newman-D-K" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Bacterial reduction of arsenic(V) and iron(III) oxides influences the redox cycling and partitioning of arsenic (As) between solid and aqueous phases in sediment-porewater systems. Two types of anaerobic bacterial incubations were designed to probe the relative order of As(V) and Fe(III) oxide reduction and to measure the effect of adsorbed As species on the rate of iron reduction, using hydrous ferric oxide (HFO) as the iron substrate. In one set of experiments, HFO was pre-equilibrated with As(V) and inoculated with fresh sediment from Haiwee Reservoir (Olancha, CA), an As-impacted field site. The second set of incubations consisted of HFO (without As) and As(III)- and As(V)- equilibrated HFO incubated with Shewanella sp. ANA-3 wild-type (WT) and ANA-3\u0394arrA, a mutant unable to produce the respiratory As(V) reductase. Of the two pathways for microbial As(V) reduction (respiration and detoxification), the respiratory pathway was dominant under these experimental conditions. In addition, As(III) adsorbed onto the surface of HFO enhanced the rate of microbial Fe(III) reduction. In the sediment and ANA-3 incubations, As(V) was reduced simultaneously or prior to Fe(III), consistent with thermodynamic calculations based on the chemical conditions of the ANA-3 WT incubations.", "doi": "10.1021/es0600476", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2006-10-01", "series_number": "19", "volume": "40", "issue": "19", "pages": "5950-5955" }, { "id": "authors:njbmn-n8s66", "collection": "authors", "collection_id": "njbmn-n8s66", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170315-124701582", "type": "article", "title": "TiO_2-Photocatalyzed As(III) Oxidation in a Fixed-Bed, Flow-Through Reactor", "author": [ { "family_name": "Ferguson", "given_name": "Megan A.", "clpid": "Ferguson-M-A" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Compliance with the U.S. drinking water standard for arsenic (As) of 10 \u03bcg L^(-1) is required in January 2006. This will necessitate implementation of treatment technologies for As removal by thousands of water suppliers. Although a variety of such technologies is available, most require preoxidation of As(III) to As(V) for efficient performance. Previous batch studies with illuminated TiO_2 slurries have demonstrated that TiO_2-photocatalyzed As(III) oxidation occurs rapidly. This study examined reaction efficiency in a flow-through, fixed-bed reactor that provides a better model for treatment in practice. Glass beads were coated with mixed P25/sol gel TiO_2 and employed in an upflow reactor irradiated from above. The reactor residence time, influent As(III) concentration, number of TiO_2 coatings on the beads, solution matrix, and light source were varied to characterize this reaction and determine its feasibility for water treatment. Repeated usage of the same beads in multiple experiments or extended use was found to affect effluent As(V) concentrations but not the steady-state effluent As(III) concentration, which suggests that As(III) oxidation at the TiO_2 surface undergoes dynamic sorption equilibration. Catalyst poisoning was not observed either from As(V) or from competitively adsorbing anions, although the higher steady-state effluent As(III) concentrations in synthetic groundwater compared to 5 mM NaNO_3 indicated that competitive sorbates in the matrix partially hinder the reaction. A reactive transport model with rate constants proportional to incident light at each bead layer fit the experimental data well despite simplifying assumptions. TiO_2-photocatalyzed oxidation of As(III) was also effective under natural sunlight. Limitations to the efficiency of As(III) oxidation in the fixed-bed reactor were attributable to constraints of the reactor geometry, which could be overcome by improved design. The fixed-bed TiO_2 reactor offers an environmentally benign method for As(III) oxidation.", "doi": "10.1021/es0524853", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2006-07-01", "series_number": "13", "volume": "40", "issue": "13", "pages": "4261-4267" }, { "id": "authors:y61bd-vfq68", "collection": "authors", "collection_id": "y61bd-vfq68", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110304-110400779", "type": "article", "title": "Sorption of Fe(II) and As(III) on goethite in single- and dual-sorbate systems", "author": [ { "family_name": "Dixit", "given_name": "Suvasis", "clpid": "Dixit-S" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Experiments were conducted to quantify Fe(II) sorption onto goethite in the absence and presence of As(III). The experimental data obtained in single-sorbate experiments were modeled using a diffuse double layer surface complexation model and used to predict and compare sorption in dual-sorbate systems. The sorption process was shown to be reversible by the complete recovery of sorbed Fe(II) upon extraction with 0.5 N HCl. Sorption of Fe(II) increases with increasing pH, as observed previously for various iron oxides. Sorption isotherms obtained between pH 6.0 and 7.5 showed continuous increase in sorption density with increase in dissolved Fe(II) concentration; under these conditions, surface saturation was approached but not reached. Experiments conducted in the absence and presence of 500 and 1000 \u03bcM total As(III) did not show any significant difference in the Fe(II) sorption density.\nAs(III) sorption density did not change with increasing sorbed Fe(II) concentration when the total arsenic concentration was 500 \u03bcM. However, when the total As(III) concentration was 1000 \u03bcM, As(III) sorption densities increased almost linearly with increasing sorbed Fe(II) concentrations. The model provided a good-to-adequate description of Fe(II) and As(III) sorption in\nsingle-sorbate systems over a range of experimental conditions but failed to predict the experimental observations in dual-sorbate systems. The predicted sorption densities for both As(III) and Fe(II) were lower than those observed. These discrepancies illustrate\nproblems that may arise when model parameters obtained in single-sorbate systems are used to predict sorption in multi-sorbate systems where all sorbates are presumed to compete for the same sites. The lack of competition observed between As(III) and Fe (II) for sorption sites indicate that the concurrent release of Fe(II) and As(III) during reductive dissolution of iron oxides, inferred as\nthe mechanism of arsenic mobilization in many reducing ground waters, may have relatively minor effects on the subsequent resorption of As(III) to residual iron oxides remaining in the sediment.", "doi": "10.1016/j.chemgeo.2005.11.015", "issn": "0009-2541", "publisher": "Elsevier", "publication": "Chemical Geology", "publication_date": "2006-04-16", "series_number": "1-3", "volume": "228", "issue": "1-3", "pages": "6-15" }, { "id": "authors:1zhbn-2hh70", "collection": "authors", "collection_id": "1zhbn-2hh70", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130415-132151408", "type": "article", "title": "Community and cultivation analysis of arsenite oxidizing biofilms at Hot Creek", "author": [ { "family_name": "Salmassi", "given_name": "Tina M.", "clpid": "Salmassi-T-M" }, { "family_name": "Walker", "given_name": "Jeffrey J.", "clpid": "Walker-J-J" }, { "family_name": "Newman", "given_name": "Dianne K.", "orcid": "0000-0003-1647-1918", "clpid": "Newman-D-K" }, { "family_name": "Leadbetter", "given_name": "Jared R.", "orcid": "0000-0002-7033-0844", "clpid": "Leadbetter-J-R" }, { "family_name": "Pace", "given_name": "Norman R.", "clpid": "Pace-N-R" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "At Hot Creek in California, geothermally derived arsenite is rapidly oxidized to arsenate. This process is mediated by microorganisms colonizing the surfaces of submerged aquatic macrophytes in the creek. Here we describe a multifaceted approach to characterizing this biofilm community and its activity. Molecular techniques were used to describe the community as a function of 16S-rRNA gene diversity. Cultivation-based strategies were used to enumerate and isolate three novel arsenite oxidizers, strains YED1-18, YED6-4 and YED6-21. All three strains are \u03b2-Proteobacteria, of the genus Hydrogenophaga. Because these strains were isolated from the highest (i.e. million-fold) dilutions of disrupted biofilm suspensions, they represent the most numerically significant arsenite oxidizers recovered from this community. One clone (Hot Creek Clone 44) obtained from an inventory of the 16S rDNA sequence diversity present in the biofilm was found to be 99.6% identical to the 16S rDNA sequence of the isolate YED6-21. On the basis of most probable number (MPN) analyses, arsenite-oxidizing bacteria were found to account for 6\u201356% of the cultivated members of the community. Using MPN values, we could estimate an upper bound on the value of V_(max) for the community of 1 \u00d7 10^(\u22129)\u00b5mole arsenite min^(\u22121) cell^(\u22121). This estimate represents the first normalization of arsenite oxidation rates to MPN cell densities for a microbial community in a field incubation experiment.", "doi": "10.1111/j.1462-2920.2005.00862.x", "issn": "1462-2912", "publisher": "Blackwell Publishing", "publication": "Environmental Microbiology", "publication_date": "2006-01", "series_number": "1", "volume": "8", "issue": "1", "pages": "50-59" }, { "id": "authors:rf8se-0b255", "collection": "authors", "collection_id": "rf8se-0b255", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170314-140732740", "type": "article", "title": "Oxidative Dissolution of Chromium(III) Hydroxide at pH 9, 3, and 2 with Product Inhibition at pH 2", "author": [ { "family_name": "Lee", "given_name": "Giehyeon", "clpid": "Lee-Giehyeon" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Hexavalent chromium, Cr(VI), can be immobilized under neutral to alkaline conditions by reduction to Cr(III); similarly, the mobility of naturally occurring Cr in soils and sediments can be limited by its occurrence in the +III oxidation state. Conversely, the oxidation of Cr(III) to Cr(VI) increases both its toxicity and often its mobility. Dissolution of Cr(OH)_(3(s)) in 0.01 M NaNO_3 suspensions was examined in batch experiments in the presence and absence of the strong oxidant sodium hypochlorite (NaOCl). Dissolution of Cr(OH)_(3(s)) (1.0 g/L) was accelerated in the presence of excess strong oxidant (20 mM) at pH 9 by a factor of ca. 200 and to a lesser extent at pH 2 and 3. Linear kinetics of oxidative dissolution was observed at pH 9 and 3. In contrast, the rate of Cr release at pH 2 decreased rapidly with time, and within 2.5 h, the dissolution reaction was completely inhibited. Under oxidizing conditions, Cr released into solution is expected to be present as Cr(VI), which sorbs strongly to Cr(OH)_(3(s)) at low pH. Cr(VI) sorption followed a Langmuir isotherm and reached maximum sorption densities of 308 \u00b1 8 and 271 \u00b1 10 \u03bcmol/g at pH 3 and 2, respectively. However, sorption of Cr(VI) (putatively formed during oxidative dissolution) cannot explain the observed inhibition of the reaction because (1) sorption occurs at both pH 2 and 3 but inhibition only at pH 2 and (2) preequilibration of Cr(OH)_(3(s)) with Cr(VI) did not affect the rate of dissolution observed upon the addition of the oxidant. Thus, we hypothesize that the inhibition of (net) oxidative dissolution at pH 2 may be the result of secondary precipitation of a chromic hydroxy chromate phase.", "doi": "10.1021/es048073w", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2005-07-01", "series_number": "13", "volume": "39", "issue": "13", "pages": "4921-4928" }, { "id": "authors:w8yvm-v1414", "collection": "authors", "collection_id": "w8yvm-v1414", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150806-062700415", "type": "article", "title": "TiO_2-Photocatalyzed As(III) Oxidation in Aqueous Suspensions: Reaction Kinetics and Effects of Adsorption", "author": [ { "family_name": "Ferguson", "given_name": "Megan A.", "clpid": "Ferguson-M-A" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Oxidation of arsenite, As(III), to arsenate, As(V), is required for the efficient removal of arsenic by many water treatment technologies. The photocatalyzed oxidation of As(III) on titanium dioxide, TiO_2, offers an environmentally benign method for this unit operation. In this study, we explore the efficacy and mechanism of TiO_2-photocatalyzed As(III) oxidation at circumneutral pH and over a range of As(III) concentrations approaching those typically encountered in water treatment systems. We focus on the effect of As adsorption on observed rates of photooxidation. Adsorption (in the dark) of both As(III) and As(V) on Degussa P25 TiO_2 was examined at pH 6.3 over a range in dissolved arsenic concentrations, [As]_(diss), of 0.10\u221289 \u03bcM and 0.2 or 0.05 g L^(-1) TiO_2 for As(III) and As(V), respectively. Adsorption isotherms generally followed the Langmuir\u2212Hinshelwood model with As(III) exhibiting an adsorption maxima of 32 \u03bcmol g^(-1). As(V) adsorption did not reach a plateau under the experimental conditions examined; the maximum adsorbed concentration observed was 130 \u03bcmol g^(-1). The extent of As(III) and As(V) adsorption observed at the beginning and end of the kinetic studies was consistent with that observed in the adsorption isotherms. Kinetic studies were performed in batch systems at pH 6.3 with 0.8\u221242 \u03bcM As(III) and 0.05 g L^(-1) TiO_2; complete oxidation of As(III) was observed within 10\u221260 min of irradiation at 365 nm. The observed effect of As(III) concentration on reaction kinetics was consistent with surface saturation at higher concentrations. Addition of phosphate at 0.5\u221210 \u03bcM had little effect on either As(III) sorption or its photooxidation rate but did inhibit adsorption of the product As(V). The selective use of hydroxyl radical quenchers and superoxide dismutase demonstrated that superoxide, O_2^(\u2022-), plays a major role in the oxidation of As(III) to As(V).", "doi": "10.1021/es048795n", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2005-03-15", "series_number": "6", "volume": "39", "issue": "6", "pages": "1880-1886" }, { "id": "authors:kqn3b-93b51", "collection": "authors", "collection_id": "kqn3b-93b51", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130313-141728101", "type": "article", "title": "arrA Is a Reliable Marker for As(V) Respiration", "author": [ { "family_name": "Malasarn", "given_name": "D.", "clpid": "Malasarn-D" }, { "family_name": "Saltikov", "given_name": "C. W.", "clpid": "Saltikov-C-W" }, { "family_name": "Campbell", "given_name": "K. M.", "clpid": "Campbell-K-M" }, { "family_name": "Santini", "given_name": "J. M.", "clpid": "Santini-J-M" }, { "family_name": "Hering", "given_name": "J. G.", "clpid": "Hering-J-G" }, { "family_name": "Newman", "given_name": "D. K.", "orcid": "0000-0003-1647-1918", "clpid": "Newman-D-K" } ], "abstract": "Arsenate [As(V)]-respiring bacteria affect the speciation and mobilization of arsenic in the environment. This can lead to arsenic contamination of drinking water supplies and deleterious consequences for human health. Using molecular genetics, we show that the functional gene for As(V) respiration, arrA, is highly conserved; that it is required for As(V) reduction to arsenite when arsenic is sorbed onto iron minerals; and that it can be used to identify the presence and activity of As(V)-respiring bacteria in arsenic-contaminated iron-rich sediments. The expression of arrA thus can be used to monitor sites in which As(V)-respiring bacteria may be controlling arsenic geochemistry.", "doi": "10.1126/science.1102374", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "2004-10-15", "series_number": "5695", "volume": "306", "issue": "5695", "pages": "455-455" }, { "id": "authors:3gevf-26n95", "collection": "authors", "collection_id": "3gevf-26n95", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170408-172200739", "type": "article", "title": "Factors affecting the dissolution kinetics of volcanic ash soils: dependencies on pH, CO_2, and oxalate", "author": [ { "family_name": "Stephens", "given_name": "Jennie C.", "clpid": "Stephens-J-G" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Laboratory experiments were conducted with volcanic ash soils from Mammoth Mountain, California to examine the dependence of soil dissolution rates on pH and CO_2 (in batch experiments) and on oxalate (in flow-through experiments). In all experiments, an initial period of rapid dissolution was observed followed by steady-state dissolution. A decrease in the specific surface area of the soil samples, ranging from 50% to 80%, was observed; this decrease occurred during the period of rapid, initial dissolution. Steady-state dissolution rates, normalized to specific surface areas determined at the conclusion of the batch experiments, ranged from 0.03 \u03bcmol Si m^(\u22122) h^(\u22121) at pH 2.78 in the batch experiments to 0.009 \u03bcmol Si m^(\u22122) h^(\u22121) at pH 4 in the flow-through experiments. Over the pH range of 2.78\u20134.0, the dissolution rates exhibited a fractional order dependence on pH of 0.47 for rates determined from H^+ consumption data and 0.27 for rates determined from Si release data. Experiments at ambient and 1 atm CO_2 demonstrated that dissolution rates were independent of CO_2 within experimental error at both pH 2.78 and 4.0. Dissolution at pH 4.0 was enhanced by addition of 1 mM oxalate. These observations provide insight into how the rates of soil weathering may be changing in areas on the flanks of Mammoth Mountain where concentrations of soil CO_2 have been elevated over the last decade. This release of magmatic CO_2 has depressed the soil pH and killed all vegetation (thus possibly changing the organic acid composition). These indirect effects of CO_2 may be enhancing the weathering of these volcanic ash soils but a strong direct effect of CO_2 can be excluded.", "doi": "10.1016/S0883-2927(04)00028-9", "issn": "0883-2927", "publisher": "Elsevier", "publication": "Applied Geochemistry", "publication_date": "2004-08", "series_number": "8", "volume": "19", "issue": "8", "pages": "1217-1232" }, { "id": "authors:grhra-0jc91", "collection": "authors", "collection_id": "grhra-0jc91", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20191112-133237602", "type": "article", "title": "Biogeochemical controls on the mobility and bioavailability of metals in soils and groundwater", "author": [ { "family_name": "Kraemer", "given_name": "Stephan M.", "clpid": "Kraemer-S-M" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Numerous trace metals have been identified as essential micronutrients for plants and/or microorganisms (including iron, zinc, copper, selenium, and nickel) and as electron acceptors or donors in metabolic processes. At elevated concentrations, however, many of these same metals exhibit significant toxicity and trace metal pollution in soils and groundwater remains one of the most pressing issues in modern environmental science. Arsenic contamination of drinking water, cadmium, copper, lead, and zinc pollution in soils, the transport of radio nuclides over long time scales, and the cycling of mercury are a few examples of important research areas in this context. As a result of their multifaceted biological functions, the significance of metals in the environment will depend on the concentration at which they occur and on environmental factors that control their mobility and bioavailability. The biogeochemical processes that control metal mobility and bioavailability include sorption on mineral and plant surfaces, dissolution, (bio-)mineralization, redox processes, complexation by biogenic or non-biogenic ligands, and biological uptake and derivatization. A wide range of experimental approaches has been used in trace metal related environmental research. It is therefore imperative to foster the discussion of these fundamental processes and approaches among researchers from various fields including plant nutrition, environmental chemistry and microbiology, environmental engineering, agricultural sciences, geochemistry, mineral surface chemistry, and soil chemistry and biology.", "doi": "10.1007/s00027-004-0004-6", "issn": "1015-1621", "publisher": "Springer", "publication": "Aquatic Sciences - Research Across Boundaries", "publication_date": "2004-03", "series_number": "1", "volume": "66", "issue": "1", "pages": "1-2" }, { "id": "authors:9sect-4de67", "collection": "authors", "collection_id": "9sect-4de67", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170426-071707946", "type": "article", "title": "Influence of Dissolved Sodium and Cesium on Uranyl Oxide Hydrate Solubility", "author": [ { "family_name": "Giammar", "given_name": "Daniel E.", "clpid": "Giammar-D-E" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "The solubility of uranium-containing minerals can control the mobility of uranium in contaminated soil and groundwater. The identity and solubility of these minerals are strongly influenced by solution composition. The influence of dissolved sodium and cesium on the solubility of uranyl oxide hydrates has been investigated in a series of batch experiments conducted with synthetic metaschoepite ((UO_2)8O_2(OH)_(12)\u00b710H_2O). During reaction of metaschoepite in NaNO_3, CsNO_3, and NaF solutions, an initial increase in the dissolved uranium concentration was followed by a decrease as uranium was incorporated into a secondary solid phase. Given sufficient reaction time, metaschoepite was completely transformed to a clarkeite-like sodium uranyl oxide hydrate or a cesium uranyl oxide hydrate that has not previously been described. These secondary solid phases exhibited X-ray diffraction patterns and Raman spectra that were distinct from those of the original metaschoepite. Dissolved uranium concentrations in equilibrium with the sodium and cesium uranyl oxide hydrates can be more than 2 orders of magnitude lower than those in equilibrium with metaschoepite. Initial changes in metaschoepite solubility may also result from particle growth induced by sodium and cesium incorporation into the solid phase.", "doi": "10.1021/es0345672", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2004-01-01", "series_number": "1", "volume": "38", "issue": "1", "pages": "171-179" }, { "id": "authors:q9gyr-m8p42", "collection": "authors", "collection_id": "q9gyr-m8p42", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170315-092108562", "type": "article", "title": "Comparison of Arsenic(V) and Arsenic(III) Sorption onto Iron Oxide Minerals: Implications for Arsenic Mobility", "author": [ { "family_name": "Dixit", "given_name": "Suvasis", "clpid": "Dixit-S" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Arsenic derived from natural sources occurs in groundwater in many countries, affecting the health of millions of people. The combined effects of As(V) reduction and diagenesis of iron oxide minerals on arsenic mobility are investigated in this study by comparing As(V) and As(III) sorption onto amorphous iron oxide (HFO), goethite, and magnetite at varying solution compositions. Experimental data are modeled with a diffuse double layer surface complexation model, and the extracted model parameters are used to examine the consistency of our results with those previously reported. Sorption of As(V) onto HFO and goethite is more favorable than that of As(III) below pH 5\u22126, whereas, above pH 7\u22128, As(III) has a higher affinity for the solids. The pH at which As(V) and As(III) are equally sorbed depends on the solid-to-solution ratio and type and specific surface area of the minerals and is shifted to lower pH values in the presence of phosphate, which competes for sorption sites. The sorption data indicate that, under most of the chemical conditions investigated in this study, reduction of As(V) in the presence of HFO or goethite would have only minor effects on or even decrease its mobility in the environment at near-neutral pH conditions. As(V) and As(III) sorption isotherms indicate similar surface site densities on the three oxides. Intrinsic surface complexation constants for As(V) are higher for goethite than HFO, whereas As(III) binding is similar for both of these oxides and also for magnetite. However, decrease in specific surface area and hence sorption site density that accompanies transformation of amorphous iron oxides to more crystalline phases could increase arsenic mobility.", "doi": "10.1021/es030309t", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2003-09-15", "series_number": "18", "volume": "37", "issue": "18", "pages": "4182-4189" }, { "id": "authors:nw8j1-t1k28", "collection": "authors", "collection_id": "nw8j1-t1k28", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170412-073833190", "type": "article", "title": "Comparative characterization of volcanic ash soils exposed to decade-long elevated carbon dioxide concentrations at Mammoth Mountain, California", "author": [ { "family_name": "Stephens", "given_name": "Jennie C.", "clpid": "Stephens-J-G" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Elevated concentrations of soil CO_2, ranging from 20% to 90%, from a magmatic source have been killing coniferous trees in the last decade in several distinct areas on the flanks of Mammoth Mountain, California. These areas of elevated soil CO_2 provide a natural laboratory to examine how chemical weathering in soils responds to extremely high-CO_2 concentrations in conjunction with possible changes in organic acids resulting from vegetation mortality. These volcanic ash soils have a particularly low resistance to chemical weathering due to the predominance of volcanic glass and other noncrystalline phases. Thus, decade-long exposure to anomalous conditions may result in differences in soil characteristics. Soil samples from within the high-CO_2 region have been analyzed and compared to samples from outside the anomalous area in the adjacent healthy forest areas where background CO_2 concentrations are less than 1%. Compared to the control soil, the high-CO_2 soil has lower pH values (5.0 compared to 5.6), higher soil moisture content, and higher surface area. Dithionite-citrate and acid-oxalate extractants were less effective in leaching Al and Si from the high CO_2 than from the control soil, indicating a distinct difference in the mineralogy of these soils. The observed differences between the high-CO_2 and control soils are consistent with an enhancement of weathering intensity in the soil exposed to elevated CO_2 concentrations.", "doi": "10.1016/S0009-2541(02)00007-4", "issn": "0009-2541", "publisher": "Elsevier", "publication": "Chemical Geology", "publication_date": "2002-06-15", "series_number": "3-4", "volume": "186", "issue": "3-4", "pages": "301-313" }, { "id": "authors:atq93-rtz51", "collection": "authors", "collection_id": "atq93-rtz51", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170315-140511084", "type": "article", "title": "Deposition and Fate of Arsenic in Iron- and Arsenic-Enriched Reservoir Sediments", "author": [ { "family_name": "Kneebone", "given_name": "P. E.", "clpid": "Kneebone-P-E" }, { "family_name": "O'Day", "given_name": "P. A.", "clpid": "O'Day-P-A" }, { "family_name": "Jones", "given_name": "N.", "clpid": "Jones-N" }, { "family_name": "Hering", "given_name": "J. G.", "clpid": "Hering-J-G" } ], "abstract": "Deposition of arsenic to the sediments of Haiwee Reservoir (Olancha, CA) has dramatically increased since March 1996 as a result of an interim strategy for arsenic management in the Los Angeles Aqueduct (LAA) water supply. Ferric chloride and cationic polymer are introduced into the Aqueduct at the Cottonwood treatment plant, 27 km north of the Haiwee Reservoir. This treatment decreases the average arsenic concentration from 25 \u03bcg/L above Cottonwood to 8.3 \u03bcg/L below Haiwee. Iron- and arsenic-rich flocculated solids are removed by deposition to the reservoir sediments. Analysis of sediments shows a pronounced signature of this deposition with elevated sediment concentrations of iron, arsenic, and manganese relative to a control site. Sediment concentrations of these elements remain elevated throughout the core length sampled (ca. 4% iron and 600 and 200 \u03bcg/g of manganese and arsenic, respectively, on a dry weight basis). A pore water profile revealed a strong redox gradient in the sediment. Manganese in the pore waters increased below 5 cm; iron and arsenic increased below 10 cm and were strongly correlated, consistent with reductive dissolution of iron oxyhydroxides and concurrent release of associated arsenic to solution. X-ray absorption near-edge spectroscopy revealed inorganic As(V) present only in the uppermost sediment (0\u22122.5 cm) in addition to inorganic As(III). In the deeper sediments (to 44 cm), only oxygen-coordinated As(III) was detected. Analysis of the extended X-ray absorption fine structure spectrum indicates that the As(III) at depth remains associated with iron oxyhydroxide. We hypothesize that this phase persists in the recently deposited sediment despite reducing conditions due to slow dissolution kinetics.", "doi": "10.1021/es010922h", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2002-02-01", "series_number": "3", "volume": "36", "issue": "3", "pages": "381-386" }, { "id": "authors:zxwwx-tg619", "collection": "authors", "collection_id": "zxwwx-tg619", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131127-130752075", "type": "article", "title": "Oxidation of Arsenite by Agrobacterium albertimagni, AOL15, sp. nov., Isolated from Hot Creek, California", "author": [ { "family_name": "Salmassi", "given_name": "Tina M.", "clpid": "Salmassi-T-M" }, { "family_name": "Venkateswaren", "given_name": "Kasthuri", "clpid": "Venkateswaren-K" }, { "family_name": "Satomi", "given_name": "Masataka", "clpid": "Satomi-Masataka" }, { "family_name": "Nealson", "given_name": "Kenneth H.", "orcid": "0000-0001-5189-3732", "clpid": "Nealson-K-H" }, { "family_name": "Newman", "given_name": "Dianne K.", "orcid": "0000-0003-1647-1918", "clpid": "Newman-D-K" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "An arsenite-oxidizing bacterium, Agrobacterium albertimagni strain AOL15 (ATCC BAA-24), was isolated from the surface of aquatic macrophytes collected in Hot Creek, California. Under laboratory conditions, whole cell suspensions of AOL15 oxidized arsenite with a K_s of 3.4 \u00b1 2.2\u00b5M and a V_(Max) of 1.81 \u00b1 0.58 x 10^(-12) \u00b5mole \u00b7 cell^(-1)\u00b7 min^(-1) (or 0.043 \u00b1 0.017 \u00b5mole \u00b7 mg protein^(-1)\u00b7 min^(-1)). The K_s value for AOL15 is the lowest value to date reported for whole cell suspensions and is comparable to ambient concentrations of arsenic of 2.7 \u00b5M reported for Hot Creek, indicating that AOL15 can oxidize arsenite under ambient conditions. Previous studies at this site revealed a rapid in situ oxidation of geothermally-derived arsenite while field incubation studies demonstrated that this oxidation was bacterially mediated. The isolation of the arsenite oxidizer AOL15 from this environment supports these previous observations. Arsenite does not support chemolithoautotrophic growth of AOL15 and toxicity studies with AOL15 showed that arsenite (at 5 mM) is toxic to AOL15, yet arsenate concentrations as high as 50 mM do not show any toxic effects. These results suggest that the oxidation of arsenite by AOL15 is a detoxification mechanism.", "doi": "10.1080/014904502317246165", "issn": "0149-0451", "publisher": "Taylor & Francis", "publication": "Geomicrobiology Journal", "publication_date": "2002-01", "series_number": "1", "volume": "19", "issue": "1", "pages": "53-66" }, { "id": "authors:3c855-vv613", "collection": "authors", "collection_id": "3c855-vv613", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170315-130320168", "type": "article", "title": "Time Scales for Sorption\u2212Desorption and Surface Precipitation of Uranyl on Goethite", "author": [ { "family_name": "Giammar", "given_name": "Daniel E.", "clpid": "Giammar-D-E" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "The sorption of uranium on mineral surfaces can significantly influence the fate and transport of uranium contamination in soils and groundwater. The rates of uranium adsorption and desorption on a synthetic goethite have been evaluated in batch experiments conducted at constant pH of 6 and ionic strength of 0.1 M. Adsorption and desorption reactions following the perturbation of initial states were complete within minutes to hours. Surface\u2212solution exchange rates as measured by an isotope exchange method occur on an even shorter time scale. Although the uranium desorption rate was unaffected by the aging of uranium\u2212goethite suspensions, the aging process appears to remove a portion of adsorbed uranium from a readily exchangeable pool. The distinction between sorption control and precipitation control of the dissolved uranium concentration was also investigated. In heterogeneous nucleation experiments, the dissolved uranium concentration was ultimately controlled by the solubility of a precipitated uranyl oxide hydrate. The X-ray diffraction pattern of the precipitate is characteristic of the mineral schoepite. Precipitation is kinetically hindered at low degrees of supersaturation. In one experiment, metastable sorption controlled dissolved uranium concentrations in excess of the solubility limit for more than 30 d.", "doi": "10.1021/es0019981", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2001-08-15", "series_number": "16", "volume": "35", "issue": "16", "pages": "3332-3337" }, { "id": "authors:bbsy1-z7q63", "collection": "authors", "collection_id": "bbsy1-z7q63", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170316-082328287", "type": "article", "title": "Behavior of Arsenic and Other Redox-Sensitive Elements in Crowley Lake, CA: A Reservoir in the Los Angeles Aqueduct System", "author": [ { "family_name": "Kneebone", "given_name": "Penelope E.", "clpid": "Kneebone-P-E" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Elevated arsenic concentrations in Crowley Lake derive from upstream geothermal inputs. We examined the water column of Crowley Lake under stratified and unstratified conditions, seeking evidence for algal uptake and transformation of arsenic and its deposition to and release from the sediments. Vertical profiles of other elements, which might either influence or track the cycling of arsenic, were also examined. Manganese and phosphorus concentrations increased with depth below the oxycline under stratified conditions, consistent with a sediment source of these elements. However, these elements did not accumulate in the hypolimnion during the period of stratification. This can be explained by accounting for the dynamics of reservoir operation in which water withdrawn from the hypolimnion is replaced from the epilimnion or surface inflows. Depletion of phosphorus in the surface water was incomplete during stratification, suggesting that phosphorus is not a limiting nutrient. Vertical profiles of total arsenic during stratification did not provide evidence for release of arsenic from the sediment; concentrations were either uniform with depth or showed a mid-depth minimum at the oxycline attributable to internal recycling within the water column. There was neither depletion of arsenic nor evidence for methylated arsenic species in the productive surface water. Arsenic was present as arsenate in the epilimnion and as a mixture of arsenate and arsenite in the hypolimnion. In the absence of an efficient mechanism to transport arsenic from the water column to the sediments, the substantial mass flux of arsenic through Crowley Lake results in only a moderate accumulation of arsenic in the sediments. Arsenic in the sediments appears to be sequestered by sulfide phases, thus release of arsenic from Crowley Lake sediments should not constitute a threat to the water quality of the Los Angeles Aqueduct.", "doi": "10.1021/es000923u", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2000-10-15", "series_number": "20", "volume": "34", "issue": "20", "pages": "4307-4312" }, { "id": "authors:bs9xa-qsa50", "collection": "authors", "collection_id": "bs9xa-qsa50", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170314-154330918", "type": "article", "title": "Arsenic Adsorption and Oxidation at Manganite Surfaces. 1. Method for Simultaneous Determination of Adsorbed and Dissolved Arsenic Species", "author": [ { "family_name": "Chiu", "given_name": "Van Q.", "clpid": "Chiu-Van-Q" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Arsenic occurs in the +III oxidation state as a metastable species in oxic waters. Under oxic conditions, As(III) is both more mobile in natural waters and less efficiently removed by water treatment processes than As(V). Other oxidants, however, can react with As(III) more rapidly than oxygen. The oxidation of As(III) by manganite occurs on the time scale of hours. Here, a method is introduced for the rapid determination of the total and dissolved concentrations of arsenic species in this heterogeneous system; adsorbed arsenic concentrations are calculated by difference. The oxidation reaction is quenched by the addition of ascorbic acid to effect the reductive dissolution of manganite and concomitant release of adsorbed As(III) and As(V) into solution. Once in solution, As(III) and As(V) are separated using anion-exchange chromatography. Comparison of dissolved and total concentrations of As(III) and As(V) clearly illustrates that the overall conversion rate of As(III) to As(V) in this system would be overpredicted based solely on dissolved As(III) concentrations and underpredicted based solely on dissolved As(V) concentrations. The overall conversion of As(III) to As(V) was more rapid at pH 4 than at pH 6.3 and was unaffected by the presence of boric acid at 95 \u03bcM or 3 mM. However, the presence of 200 \u03bcM phosphate (at pH 4) decreased the overall rate of conversion of As(III) to As(V). Comparison of total and dissolved As(III) concentrations during the reaction time course demonstrates that the effects of pH and phosphate on adsorbed As(III) concentrations are generally consistent with these kinetic observations.", "doi": "10.1021/es990788p", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2000-05-15", "series_number": "10", "volume": "34", "issue": "10", "pages": "2029-2034" }, { "id": "authors:9a2ht-ff913", "collection": "authors", "collection_id": "9a2ht-ff913", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180320-144131381", "type": "article", "title": "Influence of pH and Competitive Adsorption on the Kinetics of Ligand-Promoted Dissolution of Aluminum Oxide", "author": [ { "family_name": "Kraemer", "given_name": "Stephan M.", "clpid": "Kraemer-S-M" }, { "family_name": "Chiu", "given_name": "Van Q.", "clpid": "Chiu-Van-Q" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "The kinetics of \u03b4-Al_2O_3 dissolution were examined in the presence of 8-hydroxyquinoline-5-sulfonate (HQS) and salicylate over the pH range 3\u22129. The greatest effects of both of these ligands on \u03b4-Al_2O_3 dissolution were observed at pH values higher than those corresponding to maximal adsorbed ligand concentrations. Thus, calculated rate constants were pH dependent. For HQS, correlation between the fluorescence of the surface complex and the adsorbed HQS concentration indicates that the pH dependence of the rate constant cannot be explained by a change in the structure of the metal\u2212organic surface complex. Rather, it is proposed that the rate-determining step in the dissolution reaction involves a mixed surface complex in which aluminum is coordinated by both the organic ligand and hydroxide. Similarly, dissolution rates in the presence of the competing adsorbates HQS and fluoride suggest a synergistic action of these two ligands. Dissolution rates predicted from measured adsorbed concentrations of both ligands assuming independent, parallel pathways for HQS- and fluoride-promoted dissolution underpredict observed dissolution rates at some adsorbed ligand concentrations. In contrast, dissolution rates in the presence of the competing adsorbates HQS and arsenate could be predicted simply by accounting for the displacement of HQS from the oxide surface by arsenate.", "doi": "10.1021/es980253g", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "1998-10-01", "series_number": "19", "volume": "32", "issue": "19", "pages": "2876-2882" }, { "id": "authors:d0snv-94788", "collection": "authors", "collection_id": "d0snv-94788", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180510-152203058", "type": "article", "title": "Rapid Oxidation of Geothermal Arsenic(III) in Streamwaters of the Eastern Sierra Nevada", "author": [ { "family_name": "Wilkie", "given_name": "Jennifer A.", "clpid": "Wilkie-J-A" }, { "family_name": "Hering", "given_name": "Janet G.", "clpid": "Hering-J-G" } ], "abstract": "Arsenic redox cycling was examined in source waters of the Los Angeles Aqueduct, specifically at Hot Creek, a tributary of the Owens River. Elevated arsenic concentrations in Hot Creek result from geothermal inputs. Total arsenic and As(III) concentrations were determined in the creek and in hot spring pools along its banks. Samples were processed in the field using anion-exchange columns to separate inorganic As(III) and As(V) species. Downstream of the geothermal inputs, decreasing contribu tions of As(III) to total arsenic concentrations indicated rapid in-stream oxidation of As(III) to As(V) with almost complete oxidation occurring within 1200 m. Based on assumed plug flow transport and a flow velocity of about 0.4 m/s, the pseudo-first-order half-life calculated for this reaction was approximately 0.3 h. Conservative transport of total dissolved arsenic was observed over the reach. Pseudo-first-order reaction rates determined for As(III) oxidation in batch studies conducted in the field with aquatic macrophytes and/or macrophyte surface matter were comparable to the in-stream oxidation rate observed along Hot Creek. In batch kinetic studies, oxidation was not observed after sterile filtration or after the addition of antibiotics, which indicates that bacteria attached to submerged macrophytes are mediating the rapid As(III) oxidation reaction.", "doi": "10.1021/es970637r", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "1998-03-01", "series_number": "5", "volume": "32", "issue": "5", "pages": "657-662" } ]