Photoelectric conversion on Earth's surface via widespread Fe- and Mn-mineral coatings.

Sunlight drives photosynthesis and associated biological processes, and also influences inorganic processes that shape Earth's climate and geochemistry. Bacterial solar-to-chemical energy conversion on this planet evolved to use an intricate intracellular process of phototrophy. However, a natural nonbiological counterpart to phototrophy has yet to be recognized. In this work, we reveal the inherent "phototrophic-like" behavior of vast expanses of natural rock/soil surfaces from deserts, red soils, and karst environments, all of which can drive photon-to-electron conversions. Using scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy, and X-ray absorption spectroscopy, Fe and Mn (oxyhydr)oxide-rich coatings were found in rock varnishes, as were Fe (oxyhydr)oxides on red soil surfaces and minute amounts of Mn oxides on karst rock surfaces. By directly fabricating a photoelectric detection device on the thin section of a rock varnish sample, we have recorded an in situ photocurrent micromapping of the coatings, which behave as highly sensitive and stable photoelectric systems. Additional measurements of red soil and powder separated from the outermost surface of karst rocks yielded photocurrents that are also sensitive to irradiation. The prominent solar-responsive capability of the phototrophic-like rocks/soils is ascribed to the semiconducting Fe- and Mn (oxyhydr)oxide-mineral coatings. The native semiconducting Fe/Mn-rich coatings may play a role similar, in part, to photosynthetic systems and thus provide a distinctive driving force for redox (bio)geochemistry on Earth's surfaces.

Metal-Containing Nanoparticles in Low-Rank Coal-Derived Fly Ash from China: Characterization and Implications toward Human Lung Toxicity.

Characterization of nanoparticles (NPs) in coal fly ashes (CFAs) is critical for better understanding the potential health-related risks resulting from coal combustion. Based on single-particle (SP)-inductively coupled plasma mass spectrometry (ICP-MS) coupled with transmission electron microscopy techniques, this study is the first to determine the concentrations and sizes of metal-containing NPs in low-rank coal-derived fly ashes. Despite only comprising a minor component of the studied CFAs by mass, NPs were the dominant fraction by particle number. Fe- and Ti-containing NPs were identified as the dominant NPs with their particle number concentration ranging from 2.5 × 107 to 2.5 × 108 particles/mg. In addition, the differences of Fe-/Ti-containing NPs in various CFAs were regulated by the coalification degree of feed coals and combustion conditions of all of the low-rank CFAs tested. In the cases where these NPs in CFAs become airborne and are inhaled, they can be taken up in pulmonary interstitial fluids. This study shows that in Gamble's solution (a lung fluid simulant), 51-87% of Fe and 63-89% of Ti (ratio of the mass of Fe-/Ti-containing NPs to the total mass of Fe/Ti) exist in the NP form and remain suspended in pulmonary fluid simulants. These NPs are bioavailable and may induce lung tissue damage.

Insights into the Biogeochemical Cycling of Cobalt: Precipitation and Transformation of Cobalt Sulfide Nanoparticles under Low-Temperature Aqueous Conditions.

Cobalt sulfide precipitates, key phases in the natural biogeochemistry of cobalt and in relevant remediation and resource recovery processes, are poorly defined under low-temperature aqueous conditions. Here, we systematically studied Co (Fe) sulfides precipitated and aged in environmentally relevant solutions, defined by different combinations of pH, initial cobalt to iron ratios ([Co]aq/[Fe]aq), with/without S0, and the presence/absence of sulfate-reducing bacteria. The initial abiogenic precipitates were composed exclusively of amorphous Co sulfide nanoparticles (CoS·xH2O) that were stable in anoxic solution for 2 months, with estimated log K* values 1-5 orders of magnitude higher than that previously reported for Co sulfides. The addition of S0, in combination with acidic pH and elevated temperature (60 °C), resulted in recrystallization of the amorphous precipitates into nanocrystalline jaipurite (hexagonal CoS) within 1 month. In the presence of Fe(II)aq, the abiogenic precipitates were composed of more crystalline Co sulfides and/or Co-rich mackinawite, the exact phase being dependent on the [Co]aq/[Fe]aq value. The biogenic precipitates displayed higher crystallinity for Co sulfides (up to the formation of nanocrystalline cobalt pentlandite, Co9S8) and lower crystallinity for Co-rich mackinawite, suggestive of mineral-specific bacterial interaction. The revealed precipitation and transformation pathways of Co (Fe) sulfides in this study allows for a better constraint of Co biogeochemistry in various natural and engineered environments.

Differential Reactivity of Copper- and Gold-Based Nanomaterials Controls Their Seasonal Biogeochemical Cycling and Fate in a Freshwater Wetland Mesocosm.

Reliable predictions of the environmental fate and risk of engineered nanomaterials (ENMs) require a better understanding of ENM reactivity in complex, biologically active systems for chronic low-concentration exposure scenarios. Here, simulated freshwater wetland mesocosms were dosed with ENMs to assess how their reactivity and seasonal changes in environmental parameters influence ENM fate in aquatic systems. Copper-based ENMs (Kocide), known to dissolve in water, and gold nanoparticles (AuNPs), stable against dissolution in the absence of specific ligands, were added weekly to mesocosm waters for 9 months. Metal accumulation and speciation changes in the different environmental compartments were assessed over time. Copper from Kocide rapidly dissolved likely associating with organic matter in the water column, transported to terrestrial soils and deeper sediment where it became associated with organic or sulfide phases. In contrast, Au accumulated on/in the macrophytes where it oxidized and transferred over time to surficial sediment. A dynamic seasonal accumulation and metal redox cycling were found between the macrophyte and the surficial sediment for AuNPs. These results demonstrate the need for experimental quantification of how the biological and chemical complexity of the environment, combined with their seasonal variations, drive the fate of metastable ENMs.

The formation of spinel-group minerals in contaminated soils: the sequestration of metal(loid)s by unexpected incidental nanoparticles.

Mineralogical studies of contaminated soils affected by smelter emission and dust from mining activities indicate that minerals of the spinel group are one of the common hosts of metal-bearing contaminants. Spinel group minerals typically originate from high temperature processes, but an increasing number of studies indicate that metal-bearing spinel group minerals can also form under ambient Earth surface conditions in surficial soils. In this contribution to honor Donald Sparks, we show that the spinels Zn-bearing magnetite (Zn0.5Fe2.5O4) and minium (Pb3O4) form during low temperature alteration of Pb-bearing silica glass in surficial organic rich soils in proximity to a former Cu-smelter in Timmins, Ontario, Canada. The glass most likely formed during high-temperature processes and has been either emitted by the smelter or wind-blown from waste rock piles to near-by soils. The alteration of the glass by percolating pore solutions has resulted in the formation of large micrometer-size dendritic etch features and in nanometer-size dendritic alteration halos composed of nano-size prismatic crystals of Zn-rich magnetite and spherical nanoparticles of minium. Both spinel-type phases are embedded in an amorphous silica matrix which formed during the alteration of the glass at low temperature. A review on the occurrence of spinel-group minerals in smelter-affected soils or mine tailings indicates that the formation of these minerals under ambient Earth surface conditions is quite common and often results in the sequestration of contaminants such as Cu, Ni, Zn and Sb. The pedogenic spinels often occur as euhedral crystals in nano-size mineral assemblages within alteration features such as dendritic etch patterns, mineral surface coatings and mineralized organic matter. Their well-developed crystal forms indicate that (a) they have not formed during a rapid cooling process in a smelter or refinery which typically creates spherical particulate matter, and (b) they have not been part of particulate matter added via fluvial or Aeolian processes which most commonly yield anhedral morphologies. The formation of nano-size spinel-group minerals in low temperature environmental settings may lead to the long-term storage of metal(loid)s in mineral phases and their transport over vast distances via fluvial, alluvial and Aeolian processes.

Size-Based Differential Transport, Uptake, and Mass Distribution of Ceria (CeO2) Nanoparticles in Wetland Mesocosms.

Trace metals associated with nanoparticles are known to possess reactivities that are different from their larger-size counterparts. However, the relative importance of small relative to large particles for the overall distribution and biouptake of these metals is not as well studied in complex environmental systems. Here, we have examined differences in the long term fate and transport of ceria (CeO2) nanoparticles of two different sizes (3.8 vs 185 nm), dosed weekly to freshwater wetland mesocosms over 9 months. While the majority of CeO2 particles were detected in soils and sediments at the end of nine months, there were significant differences observed in fate, distribution, and transport mechanisms between the two materials. Small nanoparticles were removed from the water column primarily through heteroaggregation with suspended solids and plants, while large nanoparticles were removed primarily by sedimentation. A greater fraction of small particles remained in the upper floc layers of sediment relative to the large particles (31% vs 7%). Cerium from the small particles were also significantly more bioavailable to aquatic plants (2% vs 0.5%), snails (44 vs 2.6 ng), and insects (8 vs 0.07 µg). Small CeO2 particles were also significantly reduced from Ce(IV) to Ce(III), while aquatic sediments were a sink for untransformed large nanoparticles. These results demonstrate that trace metals originating from nanoscale materials have much greater potential than their larger counterparts to distribute throughout multiple compartments of a complex aquatic ecosystem and contribute to the overall bioavailable pool of the metal for biouptake and trophic transfer.

Transformation of Cerium Oxide Nanoparticles from a Diesel Fuel Additive during Combustion in a Diesel Engine.

Nanoscale cerium oxide is used as a diesel fuel additive to reduce particulate matter emissions and increase fuel economy, but its fate in the environment has not been established. Cerium oxide released as a result of the combustion of diesel fuel containing the additive Envirox, which utilizes suspended nanoscale cerium oxide to reduce particulate matter emissions and increase fuel economy, was captured from the exhaust stream of a diesel engine and was characterized using a combination of bulk analytical techniques and high resolution transmission electron microscopy. The combustion process induced significant changes in the size and morphology of the particles; ∼15 nm aggregates consisting of 5-7 nm faceted crystals in the fuel additive became 50-300 nm, near-spherical, single crystals in the exhaust. Electron diffraction identified the original cerium oxide particles as cerium(IV) oxide (CeO2, standard FCC structure) with no detectable quantities of Ce(III), whereas in the exhaust the ceria particles had additional electron diffraction reflections indicative of a CeO2 superstructure containing ordered oxygen vacancies. The surfactant coating present on the cerium oxide particles in the additive was lost during combustion, but in roughly 30% of the observed particles in the exhaust, a new surface coating formed, approximately 2-5 nm thick. The results of this study suggest that pristine, laboratory-produced, nanoscale cerium oxide is not a good substitute for the cerium oxide released from fuel-borne catalyst applications and that future toxicity experiments and modeling will require the use/consideration of more realistic materials.

Environmental Risk Implications of Metals in Sludges from Waste Water Treatment Plants: The Discovery of Vast Stores of Metal-Containing Nanoparticles.

Nanoparticle (NP) assessment in sludge materials, although of growing importance in eco- and biotoxicity studies, is commonly overlooked and, at best, understudied. In the present study, sewage sludge samples from across the mega-city of Shanghai, China were investigated for the first time using a sequential extraction method coupled with single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) to quantify the abundance of metal-containing NPs in the extraction fractions and transmission electron microscopy to specifically identify the nanophases present. In general, most sludges observed showed high concentrations of Cr, Cu, Cd, Ni, Zn, and Pb, exceeding the maximum permitted values in the national application standard of acid soil in China. NPs in these sludges contribute little to the volume and mass but account for about half of the total particle number. Based on electron microscopy techniques, various NPs were further identified, including Ti-, Fe-, Zn-, Sn-, and Pb-containing NPs. All NPs, ignored by traditional metal risk evaluation methods, were observed at a concentration of 107 -1011 particles/g within the bioavailable fraction of metals. These results indicate the underestimate or misestimation in evaluating the environmental risks of metals based on traditional sequential extraction methods. A new approach for the environmental risk assessment of metals, including NPs, is urgently needed.

Importance of a nanoscience approach in the understanding of major aqueous contamination scenarios: case study from a recent coal ash spill.

A coal ash spill that occurred from an ash impoundment pond into the Dan River, North Carolina, provided a unique opportunity to study the significance and role of naturally occurring and incidental nanomaterials associated with contaminant distribution from a large-scale, acute aquatic contamination event. Besides traditional measurements of bulk watercolumn and sediment metal concentrations, the nanoparticle (NP) analyses are based on cross-flow ultrafiltration (CFUF) and advanced transmission electron microscopy (TEM) techniques. A drain pipe fed by coal ash impoundment seepage showed a high level of arsenic, with concentrations many times over the EPA limit. The majority of the arsenic was found sorbed to large aggregates dominated by incidental iron oxyhydroxide (ferrihydrite) NPs, while the remainder of the arsenic was truly dissolved. These ferrihydrites were probably formed in situ where Fe(II) was leached through subsurface flowpaths into an aerobic environment, and further act as a significant contributor to the elevated As concentrations in downstream sediments after the spill. In addition, we discovered and describe a photocatalytic nano-TiO2 phase (anatase) present in the coal ash impacted river water that was also carrying/transporting transition metals (Cu, Fe), which may also have environmental consequences.

Oxidation of c60 aerosols by atmospherically relevant levels of o3.

Atmospheric processing of carbonaceous nanoparticles (CNPs) may play an important role in determining their fate and environmental impacts. This work investigates the reaction between aerosolized C60 and atmospherically relevant mixing ratios of O3 at differing levels of humidity. Results indicate that C60 is oxidized by O3 and forms a variety of oxygen-containing functional groups on the aerosol surface, including C60O, C60O2, and C60O3. The pseudo-first-order reaction rate between C60 and O3 ranges from 9 × 10(-6) to 2 × 10(-5) s(-1). The reaction is likely to be limited to the aerosol surface. Exposure to O3 increases the oxidative stress exerted by the C60 aerosols as measured by the dichlorofluorescein acellular assay but not by the uric acid, ascorbic acid, glutathione, or dithiothreitol assays. The initial prevalence of C60O and C60O2 as intermediate products is enhanced at higher humidity, as is the surface oxygen content of the aerosols. These results show that C60 can be oxidized when exposed to O3 under ambient conditions, such as those found in environmental, laboratory, and industrial settings.

Integrated approaches of x-ray absorption spectroscopic and electron microscopic techniques on zinc speciation and characterization in a final sewage sludge product.

Integration of complementary techniques can be powerful for the investigation of metal speciation and characterization in complex and heterogeneous environmental samples, such as sewage sludge products. In the present study, we combined analytical transmission electron microscopy (TEM)-based techniques with X-ray absorption spectroscopy (XAS) to identify and characterize nanocrystalline zinc sulfide (ZnS), considered to be the dominant Zn-containing phase in the final stage of sewage sludge material of a full-scale municipal wastewater treatment plant. We also developed sample preparation procedures to preserve the organic and sulfur-rich nature of sewage sludge matrices for microscopic and spectroscopic analyses. Analytical TEM results indicate individual ZnS nanocrystals to be in the size range of 2.5 to 7.5 nm in diameter, forming aggregates of a few hundred nanometers. Observed lattice spacings match sphalerite. The ratio of S to Zn for the ZnS nanocrystals is estimated to be 1.4, suggesting that S is present in excess. The XAS results on the Zn speciation in the bulk sludge material also support the TEM observation that approximately 80% of the total Zn has the local structure of a 3-nm ZnS nanoparticle reference material. Because sewage sludge is frequently used as a soil amendment on agricultural lands, future studies that investigate the oxidative dissolution rate of ZnS nanoparticles as a function of size and aggregation state and the change of Zn speciation during post sludge-processing and soil residency are warranted to help determine the bioavailability of sludge-born Zn in the soil environment.

Abiotic reductive immobilization of U(VI) by biogenic mackinawite.

During subsurface bioremediation of uranium-contaminated sites, indigenous metal and sulfate-reducing bacteria may utilize a variety of electron acceptors, including ferric iron and sulfate that could lead to the formation of various biogenic minerals in situ. Sulfides, as well as structural and adsorbed Fe(II) associated with biogenic Fe(II)-sulfide phases, can potentially catalyze abiotic U(VI) reduction via direct electron transfer processes. In the present work, the propensity of biogenic mackinawite (Fe 1+x S, x = 0 to 0.11) to reduce U(VI) abiotically was investigated. The biogenic mackinawite produced by Shewanella putrefaciens strain CN32 was characterized by employing a suite of analytical techniques including TEM, SEM, XAS, and Mössbauer analyses. Nanoscale and bulk analyses (microscopic and spectroscopic techniques, respectively) of biogenic mackinawite after exposure to U(VI) indicate the formation of nanoparticulate UO2. This study suggests the relevance of sulfide-bearing biogenic minerals in mediating abiotic U(VI) reduction, an alternative pathway in addition to direct enzymatic U(VI) reduction.

Combustion conditions and feed coals regulating the Fe- and Ti-containing nanoparticles in various coal fly ash.

Quantitative characteristics and sizes of nanoparticles (NPs) in coal fly ash (CFA) produced in coal-fired power plants as a function of coal type and plant design will help reveal the NP emission likelihood and their environmental implications. However, little is known about how combustion conditions and types of coal regulate the NP abundance in CFAs. In this study, based on single particle (SP)-ICP-MS technology, particle number concentrations (PNCs) and sizes of Fe- and Ti-containing NPs in CFAs were determined for samples collected from power plants of different designs and burning different types of coal. The PNCs of Fe- and Ti-containing NPs in all CFAs measured were in the range of 1.3 × 107 - 3.4 × 108 and 6.8 × 106 - 2.2 × 108 particles/mg, with the average particle sizes of 111 nm and 87 nm, respectively. The highest Fe-NP PNCs likely relate to the highest contents of Fe and pyrite in the feed coal. In addition, high TOC in CFAs are associated with metal-containing NPs, resulting in elevated abundances of these NPs with relatively large sizes. Moreover, elevated PNCs of NPs were found in CFAs produced by coal-fired power plants burning low-rank coals and with small installed capacity (especially those under 100-MW units). Compared to cyclone filters, ESPs and FFs with higher removal efficiency typically retain more Fe-/Ti- containing NPs with smaller sizes. Based on a structural equation (SE) model, raw coal properties (coal rank and Fe/Ti content), boiler types, and efficiency of particulate emission control devices likely indirectly affect PNCs of Fe- and Ti-containing NPs by influencing TOC contents and their corresponding metal concentrations of CFAs. This study provides the first analytic and comprehensive information concerning the direct and indirect regulating factors on NPs in various CFAs.

Direct observation of Mn distribution/speciation within and surrounding a basidiomycete fungus in the production of Mn-oxides important in toxic element containment.

Biogenic manganese (Mn) oxides occur ubiquitously in the environment including the uranium (U) mill tailings at the Ningyo-toge U mine in Okayama, Japan, being important in the sequestration of radioactive radium. To understand the nanoscale processes in Mn oxides formation at the U mill tailings site, Mn2+ absorption by a basidiomycete fungus, Coprinopsis urticicola, isolated from Ningyo-toge mine water samples, was investigated in the laboratory under controlled conditions utilizing electron microscopy, synchrotron-based X-ray analysis, and fluorescence microscopy with a molecular pH probe. The fungus' growth was first investigated in an agar-solidified medium supplemented with 1.0 mmol/L Mn2+, and Cu2+ (0-200 µM), Zn2+ (0-200 µM), or diphenyleneiodonium (DPI) chloride (0-100 µM) at 25 °C. The results revealed that Zn2+ has no significant effects on Mn oxide formation, whereas Cu2+ and DPI significantly inhibit both fungal growth and Mn oxidation, indicating superoxide-mediated Mn oxidation. Indeed, nitroblue tetrazolium and diaminobenzidine assays on the growing fungus revealed the production of superoxide and peroxide. During the interaction of Mn2+ with the fungus in solution medium at the initial pH of 5.67, a small fraction of Mn2+ infiltrated the fungal hyphae within 8 h, forming a few tens of nm-sized concentrates of soluble Mn2+ in the intracellular pH of ∼6.5. After 1 day of incubation, Mn oxides began to precipitate on the hyphae, which were characterized as fibrous nanocrystals with a hexagonal birnessite-structure, these forming spherical aggregates with a diameter of ∼1.5 µm. These nanoscale processes associated with the fungal species derived from the Ningyo-toge mine area provide additional insights into the existing mechanisms of Mn oxidation by filamentous fungi at other U mill tailings sites under circumneutral pH conditions. Such processes add to the class of reactions important to the sequestration of toxic elements.

Characterization and environmental implications of nano- and larger TiO(2) particles in sewage sludge, and soils amended with sewage sludge.

Titanium dioxide (TiO(2)) is the most extensively used engineered nanoparticle to date, yet its fate in the soil environment has been investigated only rarely and is poorly understood. In the present study, we conducted two field-scale investigations to better describe TiO(2) nano- and larger particles in their most likely route of entry into the environment, i.e., the application of biosolids to soils. We particularly concentrated on the particles in the nano-size regime due to their novel and commercially useful properties. First, we analyzed three sewage sludge products from the US EPA TNSSS sampling inventory for the occurrence, qualitative abundance, and nature of TiO(2) nano- and larger particles by using analytical scanning electron microscopy and analytical (scanning) transmission electron microscopy. Nano- and larger particles of TiO(2) were repeatedly identified across the sewage sludge types tested, providing strong evidence of their likely concentration in sewage sludge products. The TiO(2) particles identified were as small as 40 nm, and as large as 300 nm, having faceted shapes with the rutile crystal structure, and they typically formed small, loosely packed aggregates. Second, we examined surface soils in mesocosms that had been amended with Ag nanoparticle-spiked biosolids for the occurrence of TiO(2) particles. An aggregate of TiO(2) nanoparticles with the rutile structure was again identified, but this time TiO(2) nanoparticles were found to contain Ag on their surfaces. This suggests that TiO(2) nanoparticles from biosolids can interact with toxic trace metals that would then enter the environment as a soil amendment. Therefore, the long-term behavior of TiO(2) nano- and larger particles in sewage sludge materials as well as their impacts in the soil environment need to be carefully considered.

Potential use of engineered nanoparticles in ocean fertilization for large-scale atmospheric carbon dioxide removal.

Artificial ocean fertilization (AOF) aims to safely stimulate phytoplankton growth in the ocean and enhance carbon sequestration. AOF carbon sequestration efficiency appears lower than natural ocean fertilization processes due mainly to the low bioavailability of added nutrients, along with low export rates of AOF-produced biomass to the deep ocean. Here we explore the potential application of engineered nanoparticles (ENPs) to overcome these issues. Data from 123 studies show that some ENPs may enhance phytoplankton growth at concentrations below those likely to be toxic in marine ecosystems. ENPs may also increase bloom lifetime, boost phytoplankton aggregation and carbon export, and address secondary limiting factors in AOF. Life-cycle assessment and cost analyses suggest that net CO2 capture is possible for iron, SiO2 and Al2O3 ENPs with costs of 2-5 times that of conventional AOF, whereas boosting AOF efficiency by ENPs should substantially enhance net CO2 capture and reduce these costs. Therefore, ENP-based AOF can be an important component of the mitigation strategy to limit global warming.

Using Macro- and Microscale Preservation in Vertebrate Fossils as Predictors for Molecular Preservation in Fluvial Environments.

Exceptionally preserved fossils retain soft tissues and often the biomolecules that were present in an animal during its life. The majority of terrestrial vertebrate fossils are not traditionally considered exceptionally preserved, with fossils falling on a spectrum ranging from very well-preserved to poorly preserved when considering completeness, morphology and the presence of microstructures. Within this variability of anatomical preservation, high-quality macro-scale preservation (e.g., articulated skeletons) may not be reflected in molecular-scale preservation (i.e., biomolecules). Excavation of the Hayden Quarry (HQ; Chinle Formation, Ghost Ranch, NM, USA) has resulted in the recovery of thousands of fossilized vertebrate specimens. This has contributed greatly to our knowledge of early dinosaur evolution and paleoenvironmental conditions during the Late Triassic Period (~212 Ma). The number of specimens, completeness of skeletons and fidelity of osteohistological microstructures preserved in the bone all demonstrate the remarkable quality of the fossils preserved at this locality. Because the Hayden Quarry is an excellent example of good preservation in a fluvial environment, we have tested different fossil types (i.e., bone, tooth, coprolite) to examine the molecular preservation and overall taphonomy of the HQ to determine how different scales of preservation vary within a single locality. We used multiple high-resolution mass spectrometry techniques (TOF-SIMS, GC-MS, FT-ICR MS) to compare the fossils to unaltered bone from extant vertebrates, experimentally matured bone, and younger dinosaurian skeletal material from other fluvial environments. FT-ICR MS provides detailed molecular information about complex mixtures, and TOF-SIMS has high elemental spatial sensitivity. Using these techniques, we did not find convincing evidence of a molecular signal that can be confidently interpreted as endogenous, indicating that very good macro- and microscale preservation are not necessarily good predictors of molecular preservation.

Fungal hyphae develop where titanomagnetite inclusions reach the surface of basalt grains.

Nutrient foraging by fungi weathers rocks by mechanical and biochemical processes. Distinguishing fungal-driven transformation from abiotic mechanisms in soil remains a challenge due to complexities within natural field environments. We examined the role of fungal hyphae in the incipient weathering of granulated basalt from a three-year field experiment in a mixed hardwood-pine forest (S. Carolina) to identify alteration at the nanometer to micron scales based on microscopy-tomography analyses. Investigations of fungal-grain contacts revealed (i) a hypha-biofilm-basaltic glass interface coinciding with titanomagnetite inclusions exposed on the grain surface and embedded in the glass matrix and (ii) native dendritic and subhedral titanomagnetite inclusions in the upper 1-2 µm of the grain surface that spanned the length of the fungal-grain interface. We provide evidence of submicron basaltic glass dissolution occurring at a fungal-grain contact in a soil field setting. An example of how fungal-mediated weathering can be distinguished from abiotic mechanisms in the field was demonstrated by observing hyphal selective occupation and hydrolysis of glass-titanomagnetite surfaces. We hypothesize that the fungi were drawn to basaltic glass-titanomagnetite boundaries given that titanomagnetite exposed on or very near grain surfaces represents a source of iron to microbes. Furthermore, glass is energetically favorable to weathering in the presence of titanomagnetite. Our observations demonstrate that fungi interact with and transform basaltic substrates over a three-year time scale in field environments, which is central to understanding the rates and pathways of biogeochemical reactions related to nuclear waste disposal, geologic carbon storage, nutrient cycling, cultural artifact preservation, and soil-formation processes.

Application of XPS and solution chemistry analyses to investigate soluble manganese removal by MnO(x)(s)-coated media.

X-ray photoelectron spectroscopy (XPS) was applied to investigate Mn(II) removal by MnO(x)(s)-coated media under experimental conditions similar to the engineered environment of drinking water treatment plants in the absence and presence of chlorine. Macroscopic and spectroscopic results suggest that Mn(II) removal at pH 6.3 and pH 7.2 in the absence of chlorine was mainly due to adsorption onto the MnO(x)(s) surface coating, while removal in the presence of chlorine was due to a combination of initial surface adsorption followed by subsequent surface-catalyzed oxidation. However, Mn(III) was identified by XPS analyses of the Mn 3p photoline for experiments performed in the absence of chlorine at pH 6.3 and pH 7.2, suggesting that surface-catalyzed Mn oxidation also occurred at these conditions. Results obtained at pH 8.2 at 8 and 0.5 mg·L(-1) dissolved oxygen in the absence of chlorine suggest that Mn(II) removal was mainly due to initial adsorption followed by surface-catalyzed oxidation. XPS analyses suggest that Mn(IV) was the predominant species in experiments operated in the presence of chlorine. This study confirms that the use of chlorine combined with the catalytic action of MnO(x)(s) oxides is effective for Mn(II) removal from drinking water filtration systems.

Discovery and characterization of silver sulfide nanoparticles in final sewage sludge products.

Nanosized silver sulfide (α-Ag(2)S) particles were identified in the final stage sewage sludge materials of a full-scale municipal wastewater treatment plant using analytical high-resolution transmission electron microscopy. The Ag(2)S nanocrystals are in the size range of 5-20 nm with ellipsoidal shape, and they form very small, loosely packed aggregates. Some of the Ag(2)S nanoparticles (NPs) have excess S on the surface of the sulfide minerals under S-rich environments, resulting in a ratio of Ag to S close to 1. Considering the current extensive production of Ag NPs and their widespread use in consumer products, it is likely that they are entering wastewater streams and the treatment facilities that process this water. This study suggests that in a reduced, S-rich environment, such as the sedimentation processes during wastewater treatment, nanosized silver sulfides are being formed. This field-scale study provides for the first time nanoparticle-level information of the Ag(2)S present in sewage sludge products, and further suggests the role of wastewater treatment processes on transformation of Ag nanoparticles and ionic Ag potentially released from them.