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.

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.

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.

Pulmonary Exposure to Magnéli Phase Titanium Suboxides Results in Significant Macrophage Abnormalities and Decreased Lung Function

Coal is one of the most abundant and economic sources for global energy production. However, the burning of coal is widely recognized as a significant contributor to atmospheric particulate matter linked to deleterious respiratory impacts. Recently, we have discovered that burning coal generates large quantities of otherwise rare Magnéli phase titanium suboxides from TiO2 minerals naturally present in coal. These nanoscale Magnéli phases are biologically active without photostimulation and toxic to airway epithelial cells in vitro and to zebrafish in vivo. Here, we sought to determine the clinical and physiological impact of pulmonary exposure to Magnéli phases using mice as mammalian model organisms. Mice were exposed to the most frequently found Magnéli phases, Ti6O11, at 100 parts per million (ppm) via intratracheal administration. Local and systemic titanium concentrations, lung pathology, and changes in airway mechanics were assessed. Additional mechanistic studies were conducted with primary bone marrow derived macrophages. Our results indicate that macrophages are the cell type most impacted by exposure to these nanoscale particles. Following phagocytosis, macrophages fail to properly eliminate Magnéli phases, resulting in increased oxidative stress, mitochondrial dysfunction, and ultimately apoptosis. In the lungs, these nanoparticles become concentrated in macrophages, resulting in a feedback loop of reactive oxygen species production, cell death, and the initiation of gene expression profiles consistent with lung injury within 6 weeks of exposure. Chronic exposure and accumulation of Magnéli phases ultimately results in significantly reduced lung function impacting airway resistance, compliance, and elastance. Together, these studies demonstrate that Magnéli phases are toxic in the mammalian airway and are likely a significant nanoscale environmental pollutant, especially in geographic regions where coal combustion is a major contributor to atmospheric particulate matter.

Abiotic synthesis of graphite in hydrothermal vents

Deciphering the origin, age, and composition of deep marine organic carbon remains a challenge in understanding the dynamics of the marine carbon cycle. In particular, the composition of aged organic carbon and what allows its persistence in the deep ocean and in sediment is unresolved. Here, we observe that both high and low temperature hydrothermal vents at the 9° 50′ N; 104° 17.5 W East Pacific Rise (EPR) vent field are a source for (sub)micron-sized graphite particles. We demonstrate that commonly applied analytical techniques for quantification of organic carbon detect graphite. These analyses thereby classify graphite as either dissolved or particulate organic carbon, depending on the particle size and filtration method, and overlook its relevance as a carbon source to the deep ocean. Settling velocity calculations indicate the potential for these (sub)micron particles to become entrained in the buoyant plume and distributed far from the vent fields. Thus, our observations provide direct evidence for hydrothermal vents acting as a source of old carbon to the deep ocean.

Deciphering the origin, age, and composition of deep marine organic carbon remains a challenge for understanding the dynamics of the marine carbon cycle. Here, the authors identify (sub)micron-sized graphite emanating from both high and low temperature hydrothermal vents along the East Pacific Rise, and suggest graphite is a source of old carbon in the deep ocean.

Natural, incidental, and engineered nanomaterials and their impacts on the Earth system

Nanomaterials are critical components in the Earth system’s past, present, and future characteristics and behavior. They have been present since Earth’s origin in great abundance. Life, from the earliest cells to modern humans, has evolved in intimate association with naturally occurring nanomaterials. This synergy began to shift considerably with human industrialization. Particularly since the Industrial Revolution some two-and-a-half centuries ago, incidental nanomaterials (produced unintentionally by human activity) have been continuously produced and distributed worldwide. In some areas, they now rival the amount of naturally occurring nanomaterials. In the past half-century, engineered nanomaterials have been produced in very small amounts relative to the other two types of nanomaterials, but still in large enough quantities to make them a consequential component of the planet. All nanomaterials, regardless of their origin, have distinct chemical and physical properties throughout their size range, clearly setting them apart from their macroscopic equivalents and necessitating careful study. Following major advances in experimental, computational, analytical, and field approaches, it is becoming possible to better assess and understand all types and origins of nanomaterials in the Earth system. It is also now possible to frame their immediate and long-term impact on environmental and human health at local, regional, and global scales.

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 (Zn_0.5Fe_2.5O₄) 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.

Ultrafine Mineral Associations in Superhigh-Organic-Sulfur Kentucky Coals

Two high-organic-sulfur Kentucky coals, the eastern Kentucky River Gem coal and the western Kentucky Davis coal, are examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), both including elemental analysis by energy-dispersive spectroscopy (EDS). From the SEM-EDS analysis, it is observed that the western Kentucky coal had areas with Pb and Cd in addition to the expected Fe and S and the eastern Kentucky coal had individual Fe-S-rich areas with La and Ni and with Si, Al, Cr, Ni, and Ti. TEM and selected area electron diffraction (SAED) analyses demonstrate that anglesite with a rim of Pb-bearing amorphous Fe-oxide occurs in the western Kentucky coal. Melanterite, an Fe-sulfate, with minor Al, Si, and K EDS peaks, suggests that clay minerals may be in close association with the sulfate, is also detected in the coal. A polycrystalline metal in the eastern Kentucky sample with a composition similar to stainless steel is adjacent to an Al-rich shard. Euhedral pyrite grains surrounded by kaolinite and gibbsite are detected. Overall, it is noted that element associations should not be assumed to be organic just because minerals cannot be seen with optical microscopy or with standard bulk analytical techniques, such as X-ray diffraction (XRD).

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.

The competing effects of microbially derived polymeric and low molecular-weight substances on the dispersibility of CeO2 nanoparticles

To understand the competing effects of the components in extracellular substances (ES), polymeric substances (PS) and low-molecular-weight small substances (SS) <1 kDa derived from microorganisms, on the colloidal stability of cerium dioxide nanoparticles (CeNPs), we investigated their adsorption to sparingly soluble CeNPs at room temperature at pH 6.0. The ES was extracted from the fungus S. cerevisiae. The polypeptides and phosphates in all components preferentially adsorbed onto the CeNPs. The zeta potentials of ES + CeNPs, PS + CeNPs, and SS + CeNPs overlapped on the plot of PS itself, indicating the surface charge of the polymeric substances controls the zeta potentials. The sizes of the CeNP aggregates, 100-1300 nm, were constrained by the zeta potentials. The steric barrier derived from the polymers, even in SS, enhanced the CeNP dispersibility at pH 1.5-10. Consequently, the PS and SS had similar effects on modifying the CeNP surfaces. The adsorption of ES, which contains PS + SS, can suppress the aggregation of CeNPs over a wider pH range than that for PS only. The present study addresses the non-negligible effects of small-sized molecules derived from microbial activity on the migration of CeNP in aquatic environments, especially where bacterial consortia prevail.

Biofilms as a sink for antibiotic resistance genes (ARGs) in the Yangtze Estuary

Biofilms are ubiquitous throughout aquatic environments and they are thought to promote the acquisition and dissemination of antibiotic resistant genes (ARGs). This study focused on the occurrence and distribution of five types of ARG in naturally-occurring biofilms, in comparison to associated sediment and water samples, from the Yangtze Estuary, which borders the meta-city of Shanghai, China. The detection frequency and abundances of most ARGs showed the following order: biofilm > sediment > water, which can be attributed to a high level of antibiotics and metals that can accelerate the generation and propagation of ARGs in biofilms. Most of ARG abundances were contributed by extracellular DNA (eDNA) in biofilm and sediment samples. ARGs (sul1, sul2, tetA and tetW) in eDNA were significantly correlated with TOC in both biofilm and sediment samples. Furthermore, both intracellular DNA-associated ARGs per gram of microbial biomass carbon (MBC) and eDNA-associated ARGs per gram of non-MBC and were higher in biofilms than sediments, and the partitioning coefficients of ARGs in eDNA between biofilm and water were higher than those between sediment and water. Our results provide new insight for evaluating the occurrence and abundance of ARGs in aquatic environments, confirming that biofilms are a significant sink for ARGs in the estuarine environment.

Sequestration of Pb-Zn-Sb- and As-bearing incidental nanoparticles by mineral surface coatings and mineralized organic matter in soils

Nanoparticles (NPs) often play significant roles in dictating the transport, distribution, bioavailability and toxicity of contaminants in the environment. Incidental NPs (i.e. NPs of anthropogenic origin but not purposely engineered) are often overlooked in contaminant transport and fate studies; yet in many systems they dominate contaminant transport processes. Using surficial contaminated regosols from Trail, British Columbia, Canada, a metal smelting and refining area along the banks of the Columbia River, we show that sequestration of Pb-, Zn-, Sb-, and As-bearing incidental NPs is strongly influenced by their aggregation, crystal growth, and/or particle attachment to mineral surface coatings (MSC) and in mineralized organic matter (MOM). Transmission electron microscopy shows the occurrence of NPs of anglesite (PbSO₄), Fe-As-phosphate, kintoreite (Pb[(Fe,Al)₃(P(As)O₄)(PO₃(OH))(OH)₆]), and franklinite (ZnFe₂O₄) in matrices of amorphous silica which retain different stages of their agglomeration and aggregation. Other identified nano-size phases in the MSC and MOM indicate a complex and previously unrecognized mineralogy of Pb-, Zn-, Sb-, and As-phase in surficial soils. Mineralogical complexity and the various sequestration processes observed in this study indicate a new dimension of nano-scale processes on mineral surfaces and organic matter that have been previously overlooked when studying the fate of contaminants with bulk-analytical tools such as micro-X-ray diffraction or synchrotron-based spectroscopic methods.

Discovery and ramifications of incidental Magnéli phase generation and release from industrial coal-burning

Coal, as one of the most economic and abundant energy sources, remains the leading fuel for producing electricity worldwide. Yet, burning coal produces more global warming CO₂ relative to all other fossil fuels, and it is a major contributor to atmospheric particulate matter known to have a deleterious respiratory and cardiovascular impact in humans, especially in China and India. Here we have discovered that burning coal also produces large quantities of otherwise rare Magnéli phases (Ti _x O_2x-1 with 4 ≤ x ≤ 9) from TiO₂ minerals naturally present in coal. This provides a new tracer for tracking solid-state emissions worldwide from industrial coal-burning. In its first toxicity testing, we have also shown that nanoscale Magnéli phases have potential toxicity pathways that are not photoactive like TiO₂ phases, but instead seem to be biologically active without photostimulation. In the future, these phases should be thoroughly tested for their toxicity in the human lung.Solid-state emissions from coal burning remain an environmental concern. Here, the authors have found that TiO2 minerals present in coal are converted into titanium suboxides during burning, and initial biotoxicity screening suggests that further testing is needed to look into human lung consequences.

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.

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.

Outdoor urban nanomaterials: The emergence of a new, integrated, and critical field of study

Engineered nanomaterials (ENMs) are currently widely incorporated in the outdoor urban environmental fabric and numerous new applications and products containing ENMs are expected in the future. As has been shown repeatedly, products containing ENMs have the potential, at some point in their lifetime, to release ENMs into their surrounding environment. However, the expanding body in environmental nanomaterial research has not yet shifted toward ENMs in the context of the complex outdoor urban environment. This is especially surprising because the world's human populations are on a steady march toward more and more urbanization and technological development, accompanied with increased applications for ENMs in the outdoor urban environment. Our objective for this paper is therefore to review, assess, and provide new information in this emerging field. We provide an overview of nanomaterials (NMs, encompassing both ENMs and incidental nanomaterials, INMs) that are likely to be released in the urban environment from outdoor sources by discussing 1) the applications of ENMs that may lead to release of ENMs in urban areas, 2) the recently published data on the release of ENMs from novel nano-enabled applications in the outdoor urban environment, 3) the available literature on the occurrence of INMs in the atmosphere and within/on dust particles, and 4) the potential pathways and fate of NMs in the outdoor urban environment. This review is then followed by three case studies demonstrating the importance of NMs in the outdoor urban environment. The first and second case studies illustrate the occurrence of NMs in urban dust and stormwater ponds, respectively, whereas the third case study discusses the lessons learned from the release of NMs (e.g. Pt, ph and Rh) from automotive vehicle catalytic convertors. This article ends with a discussion of the research priorities needed to advance this emerging field of "outdoor urban nanomaterials" and to assess the potential risks of NMs in the context of urban environments.

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.

Selected emerging organic contaminants in the Yangtze Estuary, China: a comprehensive treatment of their association with aquatic colloids

Contaminants that are becoming detected in the environment but are not yet generally regulated or monitored are known collectively as emerging contaminants. In the present study, the occurrence and distribution of 42 emerging organic compounds (EOCs) were investigated in the Yangtze River Estuary and adjacent East China Sea coastal areas. Study compounds were mainly pharmaceuticals, including antibiotics, hormones and sterols, and also included two industrial endocrine disruptors. Samples were analyzed using cross-flow ultrafiltration (CFUF) and ultra-performance liquid chromatograph-tandem mass spectrometry (UPLC-MS/MS). Results revealed that chloramphenicols, sulfonamides and non-steroidal anti-inflammatory drugs were the dominant compounds in filtered samples with relatively high concentrations and detection frequencies. EOC levels varied with location, with the highest concentrations being observed around rivers discharging into the estuary, and near sewage outfalls. Colloids that were separated by CFUF tended to be a sink for EOCs with up to 60% being colloid-associated in the water phase. In addition, colloidal properties, including hydrodynamic size, zeta-potential and organic carbon composition, were found to be the main factors controlling the association of EOCs with aquatic colloids. Moreover, these colloidal properties were all significantly related to salinity, indicating the critical role played by increasing salinity in EOCs-colloids interaction in an estuarine system.

Nanotechnology in the real world: Redeveloping the nanomaterial consumer products inventory

To document the marketing and distribution of nano-enabled products into the commercial marketplace, the Woodrow Wilson International Center for Scholars and the Project on Emerging Nanotechnologies created the Nanotechnology Consumer Products Inventory (CPI) in 2005. The objective of this present work is to redevelop the CPI by leading a research effort to increase the usefulness and reliability of this inventory. We created eight new descriptors for consumer products, including information pertaining to the nanomaterials contained in each product. The project was motivated by the recognition that a diverse group of stakeholders from academia, industry, and state/federal government had become highly dependent on the inventory as an important resource and bellweather of the pervasiveness of nanotechnology in society. We interviewed 68 nanotechnology experts to assess key information needs. Their answers guided inventory modifications by providing a clear conceptual framework best suited for user expectations. The revised inventory was released in October 2013. It currently lists 1814 consumer products from 622 companies in 32 countries. The Health and Fitness category contains the most products (762, or 42% of the total). Silver is the most frequently used nanomaterial (435 products, or 24%); however, 49% of the products (889) included in the CPI do not provide the composition of the nanomaterial used in them. About 29% of the CPI (528 products) contain nanomaterials suspended in a variety of liquid media and dermal contact is the most likely exposure scenario from their use. The majority (1288 products, or 71%) of the products do not present enough supporting information to corroborate the claim that nanomaterials are used. The modified CPI has enabled crowdsourcing capabilities, which allow users to suggest edits to any entry and permits researchers to upload new findings ranging from human and environmental exposure data to complete life cycle assessments. There are inherent limitations to this type of database, but these modifications to the inventory addressed the majority of criticisms raised in published literature and in surveys of nanotechnology stakeholders and experts. The development of standardized methods and metrics for nanomaterial characterization and labelling in consumer products can lead to greater understanding between the key stakeholders in nanotechnology, especially consumers, researchers, regulators, and industry.

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.

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.

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.

Low concentrations of silver nanoparticles in biosolids cause adverse ecosystem responses under realistic field scenario

A large fraction of engineered nanomaterials in consumer and commercial products will reach natural ecosystems. To date, research on the biological impacts of environmental nanomaterial exposures has largely focused on high-concentration exposures in mechanistic lab studies with single strains of model organisms. These results are difficult to extrapolate to ecosystems, where exposures will likely be at low-concentrations and which are inhabited by a diversity of organisms. Here we show adverse responses of plants and microorganisms in a replicated long-term terrestrial mesocosm field experiment following a single low dose of silver nanoparticles (0.14 mg Ag kg⁻¹ soil) applied via a likely route of exposure, sewage biosolid application. While total aboveground plant biomass did not differ between treatments receiving biosolids, one plant species, Microstegium vimeneum, had 32 % less biomass in the Slurry+AgNP treatment relative to the Slurry only treatment. Microorganisms were also affected by AgNP treatment, which gave a significantly different community composition of bacteria in the Slurry+AgNPs as opposed to the Slurry treatment one day after addition as analyzed by T-RFLP analysis of 16S-rRNA genes. After eight days, N₂O flux was 4.5 fold higher in the Slurry+AgNPs treatment than the Slurry treatment. After fifty days, community composition and N₂O flux of the Slurry+AgNPs treatment converged with the Slurry. However, the soil microbial extracellular enzymes leucine amino peptidase and phosphatase had 52 and 27% lower activities, respectively, while microbial biomass was 35% lower than the Slurry. We also show that the magnitude of these responses was in all cases as large as or larger than the positive control, AgNO₃, added at 4-fold the Ag concentration of the silver nanoparticles.

Antimicrobial nanotechnology: its potential for the effective management of microbial drug resistance and implications for research needs in microbial nanotoxicology

The development of antibiotics revolutionized human health, providing a simple cure for once dreaded diseases such as tuberculosis. However, widespread production, use, and mis-use of antibiotics have contributed to the next-generation concern for global public health: the emergence of multiple drug-resistant (MDR) infectious organisms (a.k.a. “superbugs”). Recently, nanotechnology, specifically the use of nanomaterials (NMs) with antimicrobial activity, has been presented as a new defense against MDR infectious organisms. We discuss the potential for NMs to either circumvent microbial resistance or induce its development in light of our current state of knowledge, finding that this question points to a need for fundamental research targeting the molecular mechanisms causing antimicrobial activity in NMs. In the context of current microbial nanotoxicology studies, particularly reductionist laboratory studies, we offer suggestions and considerations for future research, using an illustrative example from our work with silver nanoparticles.

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.

Meditations on the ubiquity and mutability of nano-sized materials in the environment

A wide variety of nanomaterials can be found naturally occurring in the environment, although finding and characterizing these materials remains a challenge due to their size. Recent studies in the field have shown that natural nanomaterials are common in many geochemical systems. In this issue of ACS Nano, Hutchison and co-workers make us realize that manmade nanomaterials can often be practically identical to those that spontaneously form in the environment. This Perspective discusses the prevalence of nanomaterials in nature, including anthropogenic and naturally occurring nanomaterials, and the dynamic behavior of these materials in the environment.

An ecological perspective on nanomaterial impacts in the environment

Growing concerns over the potential for unintended, adverse consequences of engineered nanoparticles (ENPs) in the environment have generated new research initiatives focused on understanding the ecological effects of ENPs. Almost nothing is currently known about the fate and transport of ENPs in environmental waters, soils, and sediments or about the biological impacts of ENPs in natural environments, and the bulk of modern nanotoxicogical research is focused on highly controlled laboratory studies with single species in simple media. In this paper, we provide an ecological perspective on the current state of knowledge regarding the likely environmental impacts of nanomaterials and propose a strategy for making rapid progress in new research in ecological nanoscience.

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.

Use of XPS to identify the oxidation state of Mn in solid surfaces of filtration media oxide samples from drinking water treatment plants

X-ray photoelectron spectroscopy (XPS) was used to identify Mn(II), Mn(III), and Mn(IV) in the surfaces of pure oxide standards and filtration media samples from drinking water treatment plants through the determination of the magnitude of the Mn 3s multiplet splitting and the position and shape of the Mn 3p photo-line. The Mn 3p region has been widely studied by applied physicists and surface scientists, but its application to identify the oxidation state of Mn in heterogeneous oxide samples has been limited. This study shows that the use of both the Mn 3s multiplet splitting and the position and shape of the Mn 3p photo-line provides a feasible means of determining the oxidation state of manganese in complex heterogeneous, environmentally important samples. Surface analysis of filtration media samples from several drinking water treatment plants was conducted. While Mn(IV) was predominant in most samples, a mixture of Mn(III) and Mn(IV) was also identified in some of the filtration media samples studied. The predominance of Mn(IV) in the media samples was felt to be related to the maintenance of free chlorine (HOCl) at substantial concentrations (2-5 mg*L(-1) as Cl2) across these filters. XPS could be a useful tool to further understand the specific mechanisms affecting soluble Mn removal using MnOx-coated filtration media.

Influence of size and aggregation on the reactivity of an environmentally and industrially relevant nanomaterial (PbS)

Rarely observed nanoparticle dissolution rate data have been collected and explained for an environmentally and industrially relevant nanomaterial (PbS, the mineral galena) as a function of its particle size and aggregation state using high-resolution transmission electron microscopy (HRTEM) and solution analysis. Under identical anoxic acidic conditions (pH 3 HCl), it has been determined that the dissolution rate of PbS galena varies by at least 1 order of magnitude simply as a function of particle size, and also due to the aggregation state of the particles (dissolution rates measured are 4.4 x 10(-9) mol m(-2) s(-1) for dispersed 14 nm nanocrystals; 7.7 x 10(-10) mol m(-2) s(-1) for dispersed 3.1 microm microcrystals; and 4.7 x 10(-10) mol m(-2) s(-1) for aggregated 14 nm nanocrystals). The dissolution rate difference between galena microparticles and nanoparticles is due to differences in nanotopography and the crystallographic faces present. Aggregate vs. dispersed dissolution rates are related to transport inhibition in the observed highly confined spaces between densely packed, aggregated nanocrystals, where self-diffusion coefficients of water and ions decrease dramatically. This study shows that factors at the nanometer scale significantly influence the release rate of aqueous, highly toxic and bioavailable Pb in natural or industrial environments during galena dissolution.

Decreasing uncertainties in assessing environmental exposure, risk, and ecological implications of nanomaterials

Determining the fate and interactions of nanomaterials in complex environmental contexts is required to assess exposure and possible harm as well as to inform regulation. As the nanotechnology industry moves up into the rarified air of trillion dollar economics over the next several years (1), the number of simple and complex manufactured nanomaterials (NMs), and their uses, will grow tremendously. Large-scale production of engineered NMs presents the possibility that organisms and ecosystems may be exposed to new levels and qualities of substances with unknown consequences. Naturally occurring nanoscale materials are also ubiquitous in the biosphere, comprising the very building blocks of life and likely playing an important role in ecosystem

In vitro evolution of a peptide with a hematite binding motif that may constitute a natural metal-oxide binding archetype

Phage-display technology was used to evolve peptides that selectively bind to the metal-oxide hematite (Fe2O3) from a library of approximately 3 billion different polypeptides. The sequences of these peptides contained the highly conserved amino acid motif, Ser/Thr-hydrophobic/aromatic-Ser/Thr-Pro-Ser/Thr. To better understand the nature of the peptide-metal oxide binding demonstrated by these experiments, molecular dynamics simulations were carried out for Ser-Pro-Ser at a hematite surface. These simulations show that hydrogen bonding occurs between the two serine amino acids and the hydroxylated hematite surface and that the presence of proline between the hydroxide residues restricts the peptide flexibility, thereby inducing a structural-binding motif. A search of published sequence data revealed that the binding motif (Ser/Thr-Pro-Ser/Thr) is adjacent to the terminal heme-binding domain of both OmcA and MtrC, which are outer membrane cytochromes from the metal-reducing bacterium Shewanella oneidensis MR-1. The entire five amino acid consensus sequence (Ser/Thr-hydrophobic/ aromatic-Ser/Thr-Pro-Ser/Thr) was also found as multiple copies in the primary sequences of metal-oxide binding proteins Sil1 and Sil2 from Thalassiosira pseudonana. We suggest that this motif constitutes a natural metal-oxide binding archetype that could be exploited in enzyme-based biofuel cell design and approaches to synthesize tailored metal-oxide nanostructures.

Nanominerals, mineral nanoparticles, and Earth systems

Minerals are more complex than previously thought because of the discovery that their chemical properties vary as a function of particle size when smaller, in at least one dimension, than a few nanometers, to perhaps as much as several tens of nanometers. These variations are most likely due, at least in part, to differences in surface and near-surface atomic structure, as well as crystal shape and surface topography as a function of size in this smallest of size regimes. It has now been established that these variations may make a difference in important geochemical and biogeochemical reactions and kinetics. This recognition is broadening and enriching our view of how minerals influence the hydrosphere, pedosphere, biosphere, and atmosphere.

High-affinity binding and direct electron transfer to solid metals by the Shewanella oneidensis MR-1 outer membrane c-type cytochrome OmcA

The purified outer membrane bacterial protein OmcA binds densely to the surface of hematite (Fe2O3), permitting direct electron transfer to this solid mineral to reduce Fe (III) with an electron flux of about 1013 electrons /cm2/s. In the presence of hematite, there is a substantial increase in the amplitude of internal protein motions that correlate with metal reduction. Binding is highly favorable, with a partition coefficient of approximately 2 x 105 (DeltaGo' = -28 kJ/mol), where approximately 1014 OmcA proteins bind per cm2 to the solid metal surface, indicating the utility of using purified OmcA in the construction of a biofuel cell.

Size-dependent structural transformations of hematite nanoparticles. 1. Phase transition

Using Fourier Transform InfraRed (FTIR) spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), and Transmission Electron Microscopy (TEM), we characterize the structure and/or morphology of hematite (alpha-Fe(2)O(3)) particles with sizes of 7, 18, 39 and 120 nm. It is found that these nanoparticles possess maghemite (gamma-Fe(2)O(3))-like defects in the near surface regions, to which a vibrational mode at 690 cm(-1), active both in FTIR and Raman spectra, is assigned. The fraction of the maghemite-like defects and the net lattice disorder are inversely related to the particle size. However, the effect is opposite for nanoparticles grown by sintering of smaller hematite precursors under conditions when the formation of a uniform hematite-like structure throughout the aggregate is restricted by kinetic issues. This means that not only particle size but also the growth kinetics determines the structure of the nanoparticles. The observed structural changes are interpreted as size-induced alpha-Fe(2)O(3)<-->gamma-Fe(2)O(3) phase transitions. We develop a general model that considers spinel defects and absorbed/adsorbed species (in our case, hydroxyls) as dominant controls on structural changes with particle size in hematite nanoparticles, including solid-state phase transitions. These changes are represented by trajectories in a phase diagram built in three phase coordinates-concentrations of spinel defects, absorbed impurities, and adsorbed species. The critical size for the onset of the alpha-->gamma phase transition depends on the particle environment, and for the dry particles used in this study is about 40 nm. The model supports the existence of intermediate phases (protohematite and hydrohematite) during dehydration of goethite. We also demonstrate that the hematite structure is significantly less defective when the nanoparticles are immersed in water or KBr matrix, which is explained by the effects of the electrochemical double layer and increased rigidity of the particle environment. Finally, we revise the problem of applicability of IR spectroscopy to the lattice vibrations of hematite nanoparticles, demonstrating that structural comparison of different samples is much more reliable if it is based on the E(u) band at about 460 cm(-1) and the spinel band at 690 cm(-1), instead of the A(2u)/E(u) band at about 550 cm(-1) used in previous work. The new methodology is applied to analysis of the reported IR spectra of Martian hematite.

The Case for Nanogeoscience

In the last 200 years, geoscience has been about the convergence of sciences and technologies, particularly from the fields of chemistry and physics, while adding techniques, observations, and reasoning that seem to be wholly "geologic" in origin and nature. However, more recently, geoscience has also become an actively participating domain of at least three of the four major "NBIC" (nano-bio-info-cogno) enterprises, namely nanoscience and technology, modern molecular biology, and information technologies. This article will emphasize perhaps the least obvious of these connections, the "nano" aspects of the geosciences, and also adds a few aspects of the influence of modern molecular biology. There is no question that these new convergences are beginning to change the way geoscientists think about Earth, with critical applications in many areas of modern environmental science.

Experimentally derived sticking efficiencies of microparticles using atomic force microscopy

The sticking efficiencies (alpha) of colloidal particles have been derived from the intersurface potential energy between 2 microm carboxylated polystyrene microspheres and a silica glass plate using the interaction force boundary layer model. The intersurface potential energies were calculated from force-distance data measured using atomic force microscopy (AFM) and from calculations based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. AFM forces were measured in aqueous solutions over a range of pH and ionic strength conditions, and DLVO calculations were performed on identical systems. In most conditions, sticking efficiencies that were calculated from AFM data are considerably largerthan values calculated from DLVO predictions. Sticking efficiencies vary between 0 and 1 and are strongly dependent upon solution chemistry. AFM-derived sticking efficiencies are consistent with measured microsphere and collector zeta-potentials; sticking efficiencies are lower for more negatively charged surfaces. These results provide the first alpha estimates of a microparticle-collector system that are calculated directly from physically measured interfacial nanoforces. This study clearly demonstrates that significant differences exist between DLVO- and AFM-derived sticking efficiencies.

Chrysotile asbestos is progressively converted into a non-fibrous amorphous material by the chelating action of lichen metabolites

A natural deactivation of chrysotile asbestos occurs on serpentinite rocks where lichens selectively grow on the fibres and secrete metabolites, including oxalic acid, which, in the long term, turn the fibres into a non-toxic amorphous material.

Cell adhesion of Shewanella oneidensis to iron oxide minerals: Effect of different single crystal faces

The results of experiments designed to test the hypothesis that near-surface molecular structure of iron oxide minerals influences adhesion of dissimilatory iron reducing bacteria are presented. These experiments involved the measurement, using atomic force microscopy, of interaction forces generated between Shewanella oneidensis MR-1 cells and single crystal growth faces of iron oxide minerals. Significantly different adhesive force was measured between cells and the (001) face of hematite, and the (100) and (111) faces of magnetite. A role for electrostatic interactions is apparent. The trend in relative forces of adhesion generated at the mineral surfaces is in agreement with predicted ferric site densities published previously. These results suggest that near-surface structure does indeed influence initial cell attachment to iron oxide surfaces; whether this is mediated via specific cell surface-mineral surface interactions or by more general interfacial phenomena remains untested.

Bacterial recognition of mineral surfaces: nanoscale interactions between Shewanella and alpha-FeOOH

Force microscopy has been used to quantitatively measure the infinitesimal forces that characterize interactions between Shewanella oneidensis (a dissimilatory metal-reducing bacterium) and goethite (alpha-FeOOH), both commonly found in Earth near-surface environments. Force measurements with subnanonewton resolution were made in real time with living cells under aerobic and anaerobic solutions as a function of the distance, in nanometers, between a cell and the mineral surface. Energy values [in attojoules (10(-18) joules)] derived from these measurements show that the affinity between S. oneidensis and goethite rapidly increases by two to five times under anaerobic conditions in which electron transfer from bacterium to mineral is expected. Specific signatures in the force curves suggest that a 150-kilodalton putative iron reductase is mobilized within the outer membrane of S. oneidensis and specifically interacts with the goethite surface to facilitate the electron transfer process.

Using in vitro iron deposition on asbestos to model asbestos bodies formed in human lung

Recent studies have shown that iron is an important factor in the chemical activity of asbestos and may play a key role in its biological effects. The most carcinogenic forms of asbestos, crocidolite and amosite, contain up to 27% iron by weight as part of their crystal structure. These minerals can acquire more iron after being inhaled, thereby forming asbestos bodies. Reported here is a method for depositing iron on asbestos fibers in vitro which produced iron deposits of the same form as observed on asbestos bodies removed from human lungs. Crocidolite and amosite were incubated in either FeCl(2) or FeCl(3) solutions for 2 h. To assess the effect of longer-term binding, crocidolite was incubated in FeCl(2) or FeCl(3) and amosite in FeCl(3) for 14 days. The amount of iron bound by the fibers was determined by measuring the amount remaining in the incubation solution using an iron assay with the chelator ferrozine. After iron loading had been carried out, the fibers were also examined for the presence of an increased amount of surface iron using X-ray photoelectron spectroscopy (XPS). XPS analysis showed an increased amount of surface iron on both Fe(II)- and Fe(III)-loaded crocidolite and only on Fe(III)-loaded amosite. In addition, atomic force microscopy revealed that the topography of amosite, incubated in 1 mM FeCl(3) solutions for 2 h, was very rough compared with that of the untreated fibers, further evidence of Fe(III) accumulation on the fiber surfaces. Analysis of long-term Fe(III)-loaded crocidolite and amosite using X-ray diffraction (XRD) suggested that ferrihydrite, a poorly crystallized hydrous ferric iron oxide, had formed. XRD also showed that ferrihydrite was present in amosite-core asbestos bodies taken from human lung. Auger electron spectroscopy (AES) confirmed that Fe and O were the only constituent elements present on the surface of the asbestos bodies, although H cannot be detected by AES and is presumably also present. Taken together for all samples, the data reported here suggest that Fe(II) binding may result from ion exchange, possibly with Na, on the fiber surfaces, whereas Fe(III) binding forms ferrihydrite on the fibers under the conditions used in this study. Therefore, fibers carefully loaded with Fe(III) in vitro may be a particularly appropriate and useful model for the study of chemical characteristics associated with asbestos bodies and their potential for interactions in a biosystem.

Quantitative assessment of reactive surface area of phlogopite during acid dissolution

The reactive surface area of a dissolving sheet silicate, phlogopite, was quantitatively assessed in experiments performed in the fluid cell of an atomic force microscope at room temperature and pH values of 2 and 5.7. Additional assessment was provided by surface chemical analysis and electron diffraction. Dissolution rates of phlogopite hk0 edges are in the range of 10(-10) moles per square meters per second, two orders of magnitude faster than bulk rates for this mineral. The basal 001 surfaces also show distinct reactivity, although it is short-lived before they become relatively inert. These basal surfaces are shown to leach, hydrate, and expand to an amorphous silica-enriched film.