Heterocyclic fluorescent Schiff base chemosensors for the detection of Fe(III) and Cu(II) ions

Two new Schiff bases were synthesized from 1-(2,4-dihydroxyphenyl)ethanone and pyridine derivatives. Both compounds were characterized using infrared, UV-Vis., 1H NMR, 13C NMR and mass spectral studies. Density functional theory (DFT) calculations were performed for both the Schiff bases with 6-31G(d, p) as the basis set. Vibrational frequencies calculated using the theoretical method were in good agreement with the experimental values. Both the Schiff bases were highly fluorescent in nature. The cation-recognizing profile of the compounds was investigated in aqueous methanol medium. The Schiff base 4-(1-(pyridin-4-ylimino)ethyl)benzene-1,3-diol (PYEB) was found to interact with Fe(III) and Cu(II) ions, whereas the Schiff base 4,4'-((pyridine-2,3-diylbis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(benzene-1,3-diol) (PDEB) was found to detect Cu(II) ions. The mechanism of recognition was established as combined excited state intramolecular proton transfer (ESIPT)-chelation-enhanced fluorescence (CHEF) effect and chelation-enhanced quenching (CHEQ) process for the detection of Fe(III) and Cu(II) ions, respectively. The stability constant of the metal complexes formed during the sensing process was determined. The limit of detection for Fe(III) and Cu(II) ions with respect to Schiff base PYEB was found to be 1.64 × 10-6 and 2.16 × 10-7 M, respectively. With respect to Schiff base PDEB, the limit of detection for Cu(II) ion was found to be 4.54 × 10-4 M. The Cu(II) ion sensing property of the Schiff base PDEB was applied in bioimaging studies for the detection of HeLa cells.

The role of plants in ironstone evolution: iron and aluminium cycling in the rhizosphere

The Carajás plateaus in Brazil host endemic epilithic vegetation ("campo rupestre") on top of ironstone duricrusts, known as canga. This capping rock is primarily composed of iron(III) oxide minerals and forms a physically resistant horizon. Field observations reveal an intimate interaction between canga's surface and two native sedges (Rhynchospora barbata and Bulbostylis cangae). These observations suggest that certain plants contribute to the biogeochemical cycling of iron. Iron dissolution features at the root-rock interface were characterised using synchrotron-based techniques, Raman spectroscopy and scanning electron microscopy. These microscale characterisations indicate that iron is preferentially leached in the rhizosphere, enriching the comparatively insoluble aluminium around root channels. Oxalic acid and other exudates were detected in active root channels, signifying ligand-controlled iron oxide dissolution, likely driven by the plants' requirements for goethite-associated nutrients such as phosphorus. The excess iron not uptaken by the plant can reprecipitate in and around roots, line root channels and cement detrital fragments in the soil crust at the base of the plants. The reprecipitation of iron is significant as it provides a continuously forming cement, which makes canga horizons a 'self-healing' cover and contributes to them being the world's most stable continuously exposed land surfaces. Aluminium hydroxide precipitates ("gibbsite cutans") were also detected, coating some of the root cavities, often in alternating layers with goethite. This alternating pattern may correspond with oscillating oxygen concentrations in the rhizosphere. Microbial lineages known to contain iron-reducing bacteria were identified in the sedge rhizospheric microbiome and likely contribute to the reductive dissolution of iron(III) oxides within canga. Drying or percolation of oxygenated water to these anaerobic niches have led to iron mineralisation of biofilms, detected in many root channels. This study sheds light on plants' direct and indirect involvement in canga evolution, with possible implications for revegetation and surface restoration of iron mine sites.

Histamine Recognition by Carbon Dots from Plastic Waste and Development of Cellular Imaging: Experimental and Theoretical Studies

The present work highlights the sustainable approach for the transformation of plastic waste into fluorescent carbon dots (CDs) through carbonization and then they were functionalized with L-cysteine and o-phenylenediamine. CDs which were characterized by different analytical techniques such as X-ray diffraction (XRD), thermogravimetric analysis (TGA), Scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are employed to recognize Cu2+, Fe2+, and Hg2+ ions. The results show that the fluorescence emission was considerably quenched, and it is consistent with the interference and Jobs plots. The detection limit was found to be 0.35µM for Cu(II), 1.38 µM for Hg(II), and 0.51µM Fe(III). The interaction of CDs with metal ions enhances the fluorescence intensity detecting histamine successfully. It shows that plastic waste-based CDs can be applied clinically to detect toxic metals and biomolecules. Moreover, the system was employed to develop the cellular images using Saccharomyces cerevisiae cells with the support of a confocal microscope. Furthermore, theoretical studies were performed for the naphthalene layer (AR) as a model for C-dots, then optimized its structure and analyzed by using the molecular orbital. The obtained TD-DFT spectra coincided with experimental spectra for CDs/M2+/histamine systems.

Spectral Detection of Nanophase Iron Minerals Produced by Fe(III)-Reducing Hyperthermophilic Crenarchaea

Mineral transformations by two hyperthermophilic Fe(III)-reducing crenarchaea, Pyrodictium delaneyi and Pyrobaculum islandicum, were examined using synthetic nanophase ferrihydrite, lepidocrocite, and akaganeite separately as terminal electron acceptors and compared with abiotic mineral transformations under similar conditions. Spectral analyses using visible-near-infrared, Fourier-transform infrared attenuated total reflectance (FTIR-ATR), Raman, and Mössbauer spectroscopies were complementary and revealed formation of various biomineral assemblages distinguishable from abiotic phases. The most extensive biogenic mineral transformation occurred with ferrihydrite, which formed primarily magnetite with spectral features similar to biomagnetite relative to a synthetic magnetite standard. The FTIR-ATR spectra of ferrihydrite bioreduced by P. delaneyi also showed possible cell-associated organics such as exopolysaccharides. Such combined detections of biomineral assemblages and organics might serve as biomarkers for hyperthermophilic Fe(III) reduction. With lepidocrocite, P. delaneyi produced primarily a ferrous carbonate phase reminiscent of siderite, and with akaganeite, magnetite and a ferrous phosphate phase similar to vivianite were formed. P. islandicum showed minor biogenic production of a ferrous phosphate similar to vivianite when grown on lepidocrocite, and a mixed valent phosphate or sulfate mineral when grown on akaganeite. These results expand the range of biogenic mineral transformations at high temperatures and identify spacecraft-relevant spectroscopies suitable for discriminating mineral biogenicity.

Contrasting behaviors of groundwater arsenic and fluoride in the lower reaches of the Yellow River basin, China: Geochemical and modeling evidences

Genesis of the contrasting distributions of high arsenic (>10 μg/L) and fluoride (>1 mg/L) groundwater and their negative correlations remain poorly understood. We investigated spatial distributions of groundwater arsenic and fluoride concentrations in the lower reaches of the Yellow River basin, Henan Province, China, using bivariate statistical analyses and geochemical simulations. Results suggest that high arsenic and fluoride groundwater showed contrasting distributions with few overlapped area. Groundwater arsenic concentrations were significantly negatively correlated with oxidation-reduction potential (ORP) values and positively with NH₄⁺ and Fe(II) concentrations, while the opposites were true for groundwater fluoride concentrations. These may suggest that high arsenic groundwater is related to stronger organic matter degradation and Fe(III) oxide reduction, while groundwater fluoride enrichment occurs with less extent of organic matter degradation. Geochemical calculations supported that groundwater fluoride enrichment was governed by extent of fluorite dissolution, which was constrained by varied saturation indices of fluorite in groundwater. However, groundwater arsenic mobility may be explained by different solubility of Fe(III) oxides. Higher Fe(III) oxide solubility corresponding to goethite and lepidocrocite was related to higher arsenic concentrations, while hematite was too low in solubility to produce high arsenic groundwater. The study presented both geochemical and modeling evidences for the contrasting behaviors of groundwater arsenic and fluoride concentrations in anoxic aquifers.

Increases in groundwater arsenic concentrations and risk under decadal groundwater withdrawal in the lower reaches of the Yellow River basin, Henan Province, China

The spatiotemporal variability in groundwater arsenic concentrations following extensive groundwater extractions over decades was rarely studied on a large scale. To fill this gap, variations in groundwater arsenic concentrations in the North Henan Plain in China from 2010 to 2020 were investigated. The possibility of high-arsenic groundwater (>10 μg/L) was higher than 40% in aquifers within a distance of 100 m from paleochannels. This may be due to the fact that deposits in paleochannels were rich in organic matter and suitable for arsenic enrichment. Following groundwater withdrawal over ten years from 2010 to 2020, nearly half of groundwater samples (44%) were elevated in groundwater arsenic concentrations, and the proportion of high arsenic groundwater increased from 24% in 2010 to 26% in 2020. These may be related to enhanced Fe(III) oxide reduction under decadal groundwater withdrawal. However, around 56% groundwater samples were decreases in arsenic concentrations because of increased NO₃^- levels in these samples in 2020. Furthermore, extensive groundwater withdrawal decreased groundwater tables averagely by 4.6 m from 2010 to 2020, which induced the intrusion of high-arsenic groundwater from shallow aquifers into deeper ones. More importantly, the long-term groundwater pumping has perturbed groundwater flow dynamics and redistributed high-arsenic groundwater in the plain, leading to 18% more areas and 33.8% more residents being potentially at risk. This study suggests that the threat of groundwater overexploitation may be much more severe than previously expected.

Arsenic polluted waters: Application of geochemical modelling as a tool to understand the release and fate of the pollutant in crystalline aquifers

Arsenic (As) is one of the most investigated elements worldwide due to its negative impact on the natural system. Its geochemical behavior depends on several geogenic processes, which can cause hazardous enrichment into natural waters, even in remote areas, far from anthropogenic sources. In this work the arsenic pollution issue has been addressed by studying water-rock interaction processes and applying reaction path modelling as a tool to understand the rock-to-water release of As and the fate of this natural pollutant in crystalline aquifers. In-depth geochemical characterization of several water samples discharging from crystalline aquifers was performed. The obtained data were used to fix the boundary conditions and validate the modelling outcomes. The performed modelling allowed to reconstruct the water-rock interaction processes which occur (i) in shallow and relatively shallow crystalline aquifers in which no As anomalies were observed and (ii) in As-rich areas, coupling reaction path modelling of granite dissolution with adsorption of dissolved As onto precipitating crystalline and amorphous Fe(III)-oxyhydroxides given the widespread presence of these phases in the studied environment. The results of the geochemical modelling are in agreement with the analytical data and reproduce them satisfactorily. The performed geochemical modelling is of high environmental significance because it is a flexible and powerful tool that correctly defines the water-rock interaction processes occurring in crystalline aquifers, providing valuable data to improve the knowledge on As behavior, not only in the study area, but also in similar geological settings worldwide. Therefore, the present research has broad future perspectives in the environmental field.

Effects of magnetite nanoparticles on physiological processes to alleviate salinity induced oxidative damage in wheat

BACKGROUND

One of the major abiotic stressors that have a serious effect on plant growth and productivity worldwide is the salinity of soil or irrigation water. The effect of foliar application of magnetite nanoparticles (size = 22.05 nm) at different concentrations (0, 0.25, 0.5, and 1.0 ppm) was investigated to improve salinity tolerance in two wheat cultivars, namely, Misr1 (Tolerant) and Gimmeza11 (Sensitive). Moreover, toxicological investigations of magnetite oxide nanoparticle in Wistar albino rats were estimated.

RESULTS

The magnetite nanoparticles positively affected growth, chlorophyll, and enzymatic antioxidants such as superoxide dismutase (SOD), stimulating reduced glutathione and improving the aggregation of several polypeptide chains that may be linked to the tolerance of saline stress. In contrast, magnetite nanoparticles reduced malondialdehyde (MDA). Inverse sequence-tagged repeat (ISTR) assay of DNA molecular marker showed the change in band numbers with the highest polymorphic bands with 90% polymorphism at primer F3, B5 and 20 positive bands in Gimmeza11 with 0.5 ppm magnetite nanoparticles. In the median lethal dose (LD₅₀ ) study, no rats died after the oral administration of magnetite nanoparticle at different doses. Therefore, the iron oxide nanoparticle was nontoxic when administered orally by gavage.

CONCLUSION

Magnetite nanoparticles partially helped to alleviate the effects of salt stress by activating growth, chlorophyll content, SOD, glutathione, and soluble proteins in two wheat cultivars (Misr1 and Gimmeza11) and decreasing MDA content. © 2021 Society of Chemical Industry.

Iron isotope evidence for arsenic mobilization in shallow multi-level alluvial aquifers of Jianghan Plain, central China

Intake of groundwater with arsenic (As) concentrations exceeding the World Health Organization standard of 10 μg L^-1 adversely impacts over 100 million people worldwide. Geogenic As contaminated groundwater within central Yangtze River Basin has recently been reported, but the variations within different depths of aquifers are not commonly observed and the processes controlling As variations have yet to be resolved. Here we report the significant As variations within two different depths (10 m and 25 m) of shallow multi-level alluvial aquifers at Jianghan Plain, a floodplain in the central Yangtze River Basin, which is also a recently discovered geogenic As affected area with cases of waterborne arsenicosis. The multi-year monitoring of aquifer chemistry results show that the As concentrations increase with the Fe(II) concentrations when As contents are relatively lower (<200 μg L^-1) in upper phreatic aquitard (at 10 m depth), while decrease with Fe(II) concentrations when As contents are much greater in lower confined aquifer (at 25 m depth), and the highest is up to 1070 μg L^-1. Iron isotope analysis were conducive to characterize Fe cycling in the aquifers and thus illustrate geochemical processes controlling As mobilization of shallow groundwaters. Results showed that groundwater is generally enriched in isotopically light Fe with δ⁵⁶Fe values between - 1.60‰ and + 0.06‰ (median - 0.55‰). In the upper phreatic aquitard, microbial reductive dissolution of As-associated Fe(III) oxides, hydroxides and oxyhydroxides is the major process controlling As concentrations lower than 200 μg L^-1. The reduction process could lead to the increasing As concentrations with the gradually increasing δ⁵⁶Fe values, and a positive correlation between Fe and δ⁵⁶Fe, and between dissolved As and δ⁵⁶Fe values is observed, respectively. In strongly reducing conditions as the lower confined aquifer, jointly microbial reduction of sulfate promotes the As mobilization through HS^- abiotic reduction of Fe(III) minerals, resulting in As concentrations greater than 200 μg L^-1. These findings could provide new insights for differentiating the major factors controlling As mobilization at different depths of aquifers, and provide better water managements for similar geogenic As-affected shallow alluvial aquifers.

Combined biochar and metal-immobilizing bacteria reduces edible tissue metal uptake in vegetables by increasing amorphous Fe oxides and abundance of Fe- and Mn-oxidising Leptothrix species

In this study, a highly effective combined biochar and metal-immobilizing bacteria (Bacillus megaterium H3 and Serratia liquefaciens CL-1) (BHC) was characterized for its effects on solution Pb and Cd immobilization and edible tissue biomass and Pb and Cd accumulation in Chinese cabbages and radishes and the mechanisms involved in metal-polluted soils. In the metal-containing solution treated with BHC, the Pb and Cd concentrations decreased, while the pH and cell numbers of strains H3 and CL-1 increased over time. BHC significantly increased the edible tissue dry weight by 17-34% and reduced the edible tissue Pb (0.32-0.46 mg kg^-1) and Cd (0.16 mg kg^-1) contents of the vegetables by 24-45%. In the vegetable rhizosphere soils, BHC significantly decreased the acid-soluble Pb (1.81-2.21 mg kg^-1) and Cd (0.40-0.48 mg kg^-1) contents by 26-47% and increased the reducible Pb (18.2-18.8 mg kg^-1) and Cd (0.38-0.39 mg kg^-1) contents by 10-111%; while BHC also significantly increased the pH, urease activity by 115-169%, amorphous Fe oxides content by 12-19%, and relative abundance of gene copy numbers of Fe- and Mn-oxidising Leptothrix species by 28-73% compared with the controls. These results suggested that BHC decreased edible tissue metal uptake of the vegetables by increasing pH, urease activity, amorphous Fe oxides, and Leptothrix species abundance in polluted soil. These results may provide an effective and eco-friendly way for metal remediation and reducing metal uptake in vegetables by using combined biochar and metal-immobilizing bacteria in polluted soils.

Production and provenance of architectural glass from the Umayyad period

A large assemblage (n = 307) of architectural glasses (tesserae and windows) from the early 8th-century Umayyad residential site at Khirbat al-Minya was analysed by laser ablation inductively coupled plasma mass spectrometry. Trace element patterns are essential to establish the provenance of the base glass, while the comparative evaluation of the colouring and opacifying additives allow us to advance a production model for the manufacture of glass mosaic tesserae during the early Islamic period. The primary glass types are Levantine I and Egypt 1a, as well as a few older, reused tesserae, and Mesopotamian plant ash glass used for amber-coloured window fragments. Chemical data revealed fundamental differences in the colouring and opacification technologies between the Egyptian and Levantine tesserae. Co-variations of lead and bismuth, and copper, tin and zinc in the Egypt 1a tesserae provide first evidence for the production of different mosaic colours in a single workshop, specialising in the manufacture of tesserae of different colours. No such trend is apparent in the Levantine samples. Red, cobalt blue and gold leaf tesserae were found to be exclusively made from a Levantine base glass, indicating that the generation of some colours may have been a specialised process. The same may apply to the amber-coloured window glass fragments of Mesopotamian origin that exhibit very unusual characteristics, combining elevated copper (2% CuO) with an excess in iron oxide (5% Fe2O3). These findings have significant implications for the production model of strongly coloured glass and the exploitation of resources during the early Islamic period.

Simulating Mars Drilling Mission for Searching for Life: Ground-Truthing Lipids and Other Complex Microbial Biomarkers in the Iron-Sulfur Rich Río Tinto Analog

Sulfate and iron oxide deposits in Río Tinto (Southwestern Spain) are a terrestrial analog of early martian hematite-rich regions. Understanding the distribution and drivers of microbial life in iron-rich environments can give critical clues on how to search for biosignatures on Mars. We simulated a robotic drilling mission searching for signs of life in the martian subsurface, by using a 1m-class planetary prototype drill mounted on a full-scale mockup of NASA's Phoenix and InSight lander platforms. We demonstrated fully automated and aseptic drilling on iron and sulfur rich sediments at the Río Tinto riverbanks, and sample transfer and delivery to sterile containers and analytical instruments. As a ground-truth study, samples were analyzed in the field with the life detector chip immunoassay for searching microbial markers, and then in the laboratory with X-ray diffraction to determine mineralogy, gas chromatography/mass spectrometry for lipid composition, isotope-ratio mass spectrometry for isotopic ratios, and 16S/18S rRNA genes sequencing for biodiversity. A ubiquitous presence of microbial biomarkers distributed along the 1m-depth subsurface was influenced by the local mineralogy and geochemistry. The spatial heterogeneity of abiotic variables at local scale highlights the importance of considering drill replicates in future martian drilling missions. The multi-analytical approach provided proof of concept that molecular biomarkers varying in compositional nature, preservation potential, and taxonomic specificity can be recovered from shallow drilling on iron-rich Mars analogues by using an automated life-detection lander prototype, such as the one proposed for NASA's IceBreaker mission proposal.

Characterizing a riverine microbiome impacted by extreme disturbance caused by a mining sludge tsunami

Studies on disturbance events in riverine systems caused by environmental disasters and their effects on microbial diversity are scarce. Here, we evaluated the impact of the collapse of an iron ore dam holding approximately 50 million cubic meters of waste on both water and sediment microbiomes by deeply sequencing the 16S rRNA gene. Samples were taken from two impacted rivers and one reference river 7, 30 and 150 days postdisturbance. The impacted community structure changed greatly over spatiotemporal scales, being less diverse and more uneven, particularly on day 7 for the do Carmo River (the closest to the dam). However, the reference community structure remained similar between sampling events. Moreover, the impacted sediments were positively correlated with metals. The taxa abundance varied greatly over spatiotemporal scales, allowing for the identification of several potential bioindicators, e.g., Comamonadaceae, Novosphingobium, Sediminibacterium and Bacteriovorax. Our results showed that the impacted communities consisted mostly of Fe(II) oxidizers and Fe(III) reducers, aromatic compound degraders and predator bacteria. Network analysis showed a highly interconnected microbiome whose interactions switched from positive to negative or vice versa between the impacted and reference communities. This work revealed potential molecular signatures associated with the rivers heavily impacted by metals that might be useful sentinels for predicting riverine health.

Chemometric Analysis of Antioxidant and Mineral Elements in Colostrum of Native and Non-native Goat Breeds to Hypoxic Conditions at High Altitude

Colostrum of goat is a well-known nutritional source of animal product, which is attributed to innumerable nutritional properties. To enrich nutritional resources for understanding various nutritional values of animal product at high altitude, chemometric analysis of antioxidant and mineral element study was carried out by comparing antioxidants capacity, free radical scavenging activity, and certain mineral elements in colostrums of native and non-native goat breeds. Colostrum samples were collected from native Changthangi (CNG) and non-native Sirohi (SIRO) goat breeds, situated at naturally exposed high altitude of 3505.2 m above mean sea level. The antioxidant of samples was measured by ferric reducing ability of plasma (FRAP) and 2, 2-diphenyl-1-picrylhydrazyl (DPPH) activity assay, and mineral elemental quantification of Fe, Mg, Mn, Zn, Co, Cu, K, Ca, B, Ni, and Cr was performed using ICP-OES. The values of FRAP, DPPH, and Fe, Mg, Mn, Zn, Co, Cu, K, and Ca in colostrums of native goat breed was significantly (p ≤ 0.05) higher than the non-native goat. These data conclude that high altitude native goat has more antioxidant and mineral elements in colostrum than non-native colostrum. This study could provide a basis for establishing the role of colostrum supplements as a natural source to strengthen the endurance to modalities for the survival of newborn kids of goat within the native high altitude environment. This is the first report of a comparative chemometric analysis of colostrums of goat species and can be utilized to characterize the nutritional aspect of animal product with unique antioxidant and mineral nutrients composition in colostrum of goat.

Effect of ferric chloride on phosphorus immobilization and speciation in Dianchi Lake sediments

Immobilization of phosphorus in lake sediments and control of internal-loading phosphorus release have become crucial aspects of eutrophication lake management. In this study, the immobilization efficiency of phosphorus by ferric chloride in Dianchi Lake sediments was investigated. In addition, effects of the dosage of ferric chloride and contact time on the release of phosphorus from sediments were investigated. Laboratory experiments revealed that ferric chloride can effectively inhibit the release of phosphorus from sediments. At a ferric chloride dosage of 10 mg/g, the total phosphorus concentration of the overlying water was reduced by ~87%. With the increase in the contact time, the amount of phosphorus immobilized by ferric chloride increased. To further evaluate the feasibility of ferric chloride for immobilising phosphorus in sediments, an amplification experiment with a water volume of 50 L was carried out. By the addition of 6 mg/g of ferric chloride, the total phosphorus concentration of the overlying water was still less than 0.01 mg/L after 100 days. At the same time, the phosphorus species in the sediment after treatment with ferric chloride were analyzed. Results revealed that ferric chloride mainly converts unstable exchangeable phosphorus (Ex-P), ferric phosphate (Fe-P) and organic phosphorus (Or-P) into more stable occluded phosphate (O-P), reducing the possible release of phosphorus from sediments. Practical applications of ferric chloride to control the release of phosphorus from Dianchi Lake sediments were discussed.

Dual-Emitting N/S-Doped Carbon Dots-Based Ratiometric Fluorescent and Light Scattering Sensor for High Precision Detection of Fe(III) Ions

Precise and rapid sensing of Fe(III) under concerned facile conditions is important in environmental monitoring. Herein, a facile and label-free ratiometric sensor is constructed for selective determination of Fe(III) ions by coupling second-order scattering (SOS) and fluorescence. We were synthesized fluorescent N, S-doped carbon dots (N/S-CDs) via facile one-step hydrothermal treatment with an intensive fluorescence and a weak SOS signal and high quantum yield (32%). The fluorescence of N/S-CDs was quenched whereas the intensity of SOS was relatively increased by Fe(III) ions due to aggregation-induced fluorescence quenching or enhancement. Based on this effect, a novel fluorescent ratiometric probe with the combined fluorescence and SOS is proposed for the sensing of Fe(III) ions, and with the detection limit of 83 nM and linear range of 0.1-10 μM and 10-40 μM, respectively.

Photoreaction characteristics of ferrous oxalate recovered from wastewater

Photoreaction with the Fe(III)-oxalate complex has been reported to play an important role in various photochemical reactions in the natural atmospheric environment, and are applicable to treat various recalcitrant compounds in wastewater. We previously showed that a Fe(II) oxalate (FeOx) crystal can be recovered from the wastewater generated from soil washing, which can then be applied to the photoreaction for degradation of recalcitrant pollutants; however, photoreactions with FeOx compounds have not been fully reported yet. Therefore, this study aims to investigate the photoreaction characteristics of FeOx recovered from wastewater, to demonstrate the feasibility of its application to wastewater treatment. The physical and chemical properties of FeOx were characterized with X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy analyses. The photoreaction of FeOx showed high methylene blue (MB) removal efficiencies similar to the reaction with TiO₂, indicating that FeOx is applicable to the photoreaction for degradation of pollutants. Furthermore, the photodegradation of MB with FeOx was observed under visible light, as opposed to TiO₂. MB could be removed by the photoreaction of FeOx under both basic and acidic pH conditions. Under basic pH conditions, MB could be removed by FeOx via both photoreaction and surface adsorption. The concentration of FeOx affected light penetration and Fe and oxalate levels in the solution, resulting in different MB removal kinetics. The photoreaction efficiency of FeOx could be affected by both photoreaction of Fe and oxalate in the solution and photoreaction and adsorption reaction of the FeOx surface.

The provenance of deep groundwater and its relation to arsenic distribution in the northwestern Hetao Basin, Inner Mongolia

High-arsenic (As) groundwater has been widely found throughout the world. The source of groundwater would determine spatial distribution of groundwater As. In order to trace the source of high-As deep groundwater (DGW, depths > 50 m), groundwater, sediments, and local bedrock samples were taken to investigate chemical and isotopic compositions in the Hetao Basin, China. Results showed that ⁸⁷Sr/⁸⁶Sr in DGW gradually decreased with the increase in As concentrations along the approximate flow path. In recharge-oxic zone (Zone I), DGW was mainly recharged by fissure water, influenced mostly by weathering of phyllite bedrock and meta-basalt. In groundwater flow-moderate reducing zone (Zone II), DGW was mainly related to incongruent dissolution of feldspar. However, in groundwater flow-reducing zone (Zone III), DGW was partly recharged from shallow groundwater (SGW) with depths < 50 m. The mixing contributions of SGW to DGW in Zone III mostly exceeded 80% during groundwater irrigation season. In Zone I, DGW As concentrations were mostly lower than 50 μg/L due to oxic conditions. In Zone II, the weakly alkaline pH and the decreasing Ca/Na resulting from incongruent dissolution of feldspar caused As desorption, which was the major contribution to As mobilization (As mostly > 200 μg/L). In Zone III, the recharge of SGW introduced labile organic matter to support reduction of Fe(III) oxyhydroxides/oxides and predominantly led to As release into groundwater (As > 300 μg/L). This study has provided insights into the source of high-As DGW and the effect of SGW mixing on As mobilization.

Effect of interactions between various humic acid fractions and iron nanoparticles on the toxicity to white rot fungus

Humic acid plays an important role in controlling the toxicity of nanoparticles to organisms. However, little is known about the influence of different fractions of dissolved humic acid (DHA) from soil on the toxicity of nanoparticles to organisms. The concentration of γ-Fe₂O₃ and the exposure time affected the malondialdehyde (MDA) content, reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) activity in P. chrysosporium cells and were inversely proportional to the relative activities of the cells. P. chrysosporium was exposed to γ-Fe₂O₃ and DHA₁ for 3 h, 6 h and 12 h. Catalase (CAT) and peroxidase (POD) activities were generally higher than control. Particularly, under the influence of 50 mg/L DHA₁ and different concentrations of γ-Fe₂O₃ (10 and 50 mg/L), the CAT and POD activities were higher than those of cells exposed to γ-Fe₂O₃ alone. Conversely, both activities of P. chrysosporium exposed to DHA₄ combined with γ-Fe₂O₃ for 12 h were lower than those of cells exposed to γ-Fe₂O₃ alone and gradually decreased with increasing DHA₄ concentration (0, 10 and 50 mg/L). The μ-XAFS normalized spectrum indicated that Fe³⁺ entering the cells tended to transform into Fe²⁺ as the stress time prolonged. TEM analysis confirmed the toxicity of high concentrations of γ-Fe₂O₃ to P. chrysosporium. The comet assay showed that DHA₄ in soil enhanced the toxicity of γ-Fe₂O₃ to P. chrysosporium more than DHA₁ did. Namely, compared to DHA₁, DHA₄ made it easier for nano-Fe₂O₃ to enter P. chrysosporium cells, causing more toxicity of γ-Fe₂O₃ to P. chrysosporium.

ExoMars Raman Laser Spectrometer: A Tool for the Potential Recognition of Wet-Target Craters on Mars

In the present work, near-infrared, laser-induced breakdown spectroscopy, Raman, and X-ray diffractometer techniques have been complementarily used to carry out a comprehensive characterization of a terrestrial analogue selected from the Chesapeake Bay impact structure (CBIS). The obtained data clearly highlight the key role of Raman spectroscopy in the detection of minor and trace compounds, through which inferences about geological processes occurred in the CBIS can be extrapolated. Beside the use of commercial systems, further Raman analyses were performed by the Raman laser spectrometer (RLS) ExoMars Simulator. This instrument represents the most reliable tool to effectively predict the scientific capabilities of the ExoMars/Raman system that will be deployed on Mars in 2021. By emulating the analytical procedures and operational restrictions established by the ExoMars mission rover design, it was proved that the RLS ExoMars Simulator can detect the amorphization of quartz, which constitutes an analytical clue of the impact origin of craters. Beside amorphized minerals, the detection of barite and siderite, compounds crystallizing under hydrothermal conditions, helps indirectly to confirm the presence of water in impact targets. Furthermore, the RLS ExoMars Simulator capability of performing smart molecular mappings was successfully evaluated.

Pesticide-derived bright chlorine-doped carbon dots for selective determination and intracellular imaging of Fe(III)

Inspired by the conversion from organics or biomass to fluorescent carbon dots (C-dots), the use of pesticide 4-chlorophenol (4-CP) as a precursor to prepare C-dots has been reported. The as-prepared chlorine-doped C-dots display a brightly blue emission at ∼445 nm with ∼22.8% quantum yield. Also, the surface of C-dots enriches functional groups, such as phenolic hydroxyl and carboxylic acid, etc., which can capture ferric ion (Fe(III)), resulting in the quenching of blue fluorescence of C-dots through an inner filter effect. The quantitative assay for Fe(III) was therefore realized by this probe with a 0.36 μM detection limit in the 0.6-25 μM concentration range. Most significantly, the cytotoxicity on Hela cells indicates the 4-CP-derived C-dots have a negligible cytotoxicity. The C-dots were applied in detection in environmental samples and imaging in Hela cells of Fe(III), demonstrating their good applicability, low toxicity and good biocompatibility, and providing an alterative approach to totally eliminate the harm of chlorophenols (CPs).

Thallium(I) sequestration by jarosite and birnessite: Structural incorporation vs surface adsorption

Jarosite and birnessite secondary minerals play a pivotal role in the mobility, transport and fate of trace elements in the environment, although geochemical interactions of these compounds with extremely toxic thallium (Tl) remain poorly known. In this study, we investigated the sorption behavior of Tl(I) onto synthetic jarosite and birnessite, two minerals commonly found in soils and sediments as well as in mining-impacted areas where harsh conditions are involved. To achieve this, sorption and desorption experiments were carried out under two different acidic conditions and various Tl(I) concentrations to mimic natural scenarios. In addition, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and inductively coupled plasma (ICP) analyses were conducted to determine the performance of both minerals for Tl(I) sequestration. Our results indicate that both phases can effectively remove aqueous Tl by different sorption mechanisms. Jarosite preferentially incorporates Tl(I) into the structure to form Tl(I)-jarosite and eventually the mineral dorallcharite (TlFe₃(SO₄)₂(OH)₆) as increasing amounts of Tl are employed. Birnessite, however, favorably uptakes Tl(I) through an irreversible surface adsorption mechanism, underlining the affinity of Tl for this mineral in the entire concentration range studied (0.5-5 mmol L^-1). Lastly, the presence of Tl(I) in conditions where aqueous molar ratio Tl/Mn is ∼0.25 inhibits the formation of birnessite since oxidation of Tl(I) to Tl(III) followed by precipitation of avicennite (Tl₂O₃) take place. Thus, the present research may provide useful insights on the role of both jarosite and birnessite minerals in Tl environmental cycles.

Uncommon chemical species in PM2.5 and PM10 and its potential use as industrial and vehicular markers for source apportionment studies

Chemical characterization of PM_2.5 and PM₁₀ is important to identify potential compounds that induce biological responses that translate into cardio-respiratory health problems. This study shows the reliability of the use of crystalline phases, identified in samples from receptor sites, as source markers, helping researchers to infer the main sources of air pollution, even without the use of receptor models. PM_2.5 and PM₁₀ samples were collected at two sites in an urban industrialized region located at southeast of Brazil and analyzed by Synchrotron X-ray Diffraction to identify crystalline compounds. Results show 5 PM₁₀ and PM_2.5 species not previously reported in the literature. We propose reaction mechanisms for these species and identify specific sources for each crystalline phase found: BaTiO₃ was found in PM₁₀ receptor samples and proved to be a vehicular marker formed during brake action; maghemite (γ-Fe₂O₃), pyracmonite [(NH₄)₃Fe(SO₄)₃], ammonium perchlorate (NH₃OHClO₄) and potassium ferrate (K₂Fe₂O₄) were found in PM_2.5 proved to be markers of industrial activities. The crystalline phases found in PM samples from receptor sites and the mechanisms of reactions showed the reliability of the use of crystalline phases as source markers in the identification of potential sources of air pollution without misinterpretation of the likely source.

Lipid Biomarkers in Ephemeral Acid Salt Lake Mudflat/Sandflat Sediments: Implications for Mars

Sedimentary strata on Mars often contain a mix of sulfates, iron oxides, chlorides, and phyllosilicates, a mineral assemblage that is unique on Earth to acid brine environments. To help characterize the astrobiological potential of depositional environments with similar minerals present, samples from four naturally occurring acidic salt lakes and adjacent mudflats/sandflats in the vicinity of Norseman, Western Australia, were collected and analyzed. Lipid biomarkers were extracted and quantified, revealing biomarkers from vascular plants alongside trace microbial lipids. The resilience of lipids from dead organic material in these acid saline sediments through the pervasive stages of early diagenesis lends support to the idea that sulfates, in tandem with phyllosilicates and iron oxides, could be a viable target for biomarkers on Mars. To fully understand the astrobiological potential of these depositional environments, additional investigations of organic preservation in ancient acidic saline sedimentary environments are needed.

Evolution of As speciation with depth in a soil profile with a geothermal As origin

High contents of arsenic were detected in soils in Guandu plain, northwest Taiwan. To determine the sources and speciation of As in the soils, the depth profiles of soil properties, elemental composition and As speciation were investigated. The As concentrations in the soil profile ranged from 152 to 1222 mg kg^-1, with the highest concentration at the depth of 70-80 cm. The As distribution was found to be positively correlated to Fe, Pb, and Ba. The As(V)-adsorbed ferrihydrite and scorodite were the predominant phases in the top layers (<50 cm), while beudantite was the predominant phase below 50 cm along with As(III)- and As(V)-adsorbed ferrihydrite as the minor components. The results of sequential extraction showed that As-associated with noncrystalline and crystalline Fe/Al hydrous oxides and residual phases were predominant at the depths of 0-60, 60-100 and 100-140 cm, respectively, indicating an increasing As recalcitrance with soil depth. Based on the soil properties, and elemental and mineral compositions at different soil depths, the origin of beudantite in the soils was likely allogenic rather than authigenic or anthropogenic. The formation of scorodite in the surface soils was suggested to be transformed from beudantite. As-associated Fe hydrous oxides may be contributed by the progressive dissolution of beudantite and scorodite, and the continuous influxes of As and Fe. While Fe hydrous oxides were able to immobilize As during the dissolution of As-bearing minerals, the increase of As mobility in soils may imply an increase in the environmental risk of As over time.

Fluorometric assay of iron(II) lactate hydrate and ammonium ferric citrate in food and medicine based on poly(sodium-p-styrenesulfonate)-enhanced Ag nanoclusters

Poly(sodium-p-styrenesulfonate)-enhanced and D-penicillamine stabilized Ag nanoclusters (PSS-DPA-AgNCs) were prepared using one-step ultraviolet irradiation combined with microwave heating method, and the effects of the AgNCs photo-luminescence performance based on different types of polyelectrolytes and energy suppliers were studied detailedly. The as-prepared AgNCs can be used as a viable fluorescent probe for monitoring indirectly iron(II) lactate hydrate (ILH) and ammonium ferric citrate (AFC), respectively. The fluorescence (FL) quenching of PSS-DPA-AgNCs by Fe³⁺ (it is obtained from oxidized ILH/ionized AFC) mainly derives from a dynamic quenching process. Excellent linear relationships exist between the FL quenching degree of the AgNCs and the concentrations of ILH/AFC in the range of 0.17-6.00/0.067-3.33 μmol·L^-1, and corresponding limit of detection (at 3σ/slope) is 12.4/6.04 nmol·L^-1. Moreover, the AgNCs probe was extended to the assays of ILH in tablets, solid beverage or ILH additive and AFC in two kinds of edible salts or syrup with satisfactory results compared with the standard 1, 10-phenanthroline method. In addition, the AgNCs probe reveals a good temperature sensing capability.

Reduced Cd, Pb, and As accumulation in rice (Oryza sativa L.) by a combined amendment of calcium sulfate and ferric oxide

A combined amendment (CF) consisting of 90% calcium sulfate (CaSO₄) and 10% ferric oxide (Fe₂O₃) was used to investigate the feasibility, active principles, and possible mechanisms of the immobilization of heavy metals in paddy soil. A soil incubation experiment, two consecutive pot trials, and a field experiment were conducted to evaluate the effectiveness and persistence of CF on metal(loid) immobilization. Soil incubation experiment results indicated that the application of CF significantly decreased the concentrations of cadmium (Cd), lead (Pb), and arsenic (As) in soil solution. CF treatments simultaneously reduced the accumulation of Cd, Pb, and As in two consecutive pot trials. The total Cd, Pb, and As concentrations in the rice grains were respectively 0.02, 2.08, and 0.62 mg kg^-1 in the control treatment in the second year, which exceeded the safety limits of contaminants in food products in China. However, a high amount of CF amendment (CF-H, 0.3%) effectively decreased Cd, Pb, and As by 75.0%, 75.5%, and 46.8%, respectively. Further, with the CF amendment, the bioavailable Cd and Pb in the soil and the accumulation of Cd, Pb, and As in rice grain in the field experiment were also significantly decreased. The concentrations of Cd, Pb, and As in grains were respectively 0.02, 0.03, and 0.39 mg kg^-1 in the control treatment in the field experiment, which decreased to 0.01, 0.01, and 0.22 mg kg^-1 with CF addition, suggesting that grains produced in the field could pose less health risk. In conclusion, these results implied that CF was an effective and persistent combined amendment to immobilize heavy metals in soil and thereby can reduce the exposure risk of metal(loid)s associated with rice consumption.

Common and rare iron, sulfur, and zinc minerals in technogenically contaminated hydromorphic soil from Southern Russia

Soils formed after the desiccation of Lake Atamanskoe, which has served as a reservoir for liquid industrial waste from the city of Kamensk-Shakhtinsky during a long time, were studied. These soils differ from zonal soils by a strong contamination with zinc and sulfur. Preliminary studies showed that Fe compounds fix a significant part of zinc. This requires to study S, Zn, and Fe minerals. In this work, Mössbauer spectroscopy was used for the identification of iron compounds and scanning electron microscopy was used for the microanalysis of these and other minerals. To facilitate the identification of Fe minerals, brown iron ocher was removed from a contaminated soil sample and analyzed. From electron microscopy and Mössbauer spectroscopy data, ocher contained hydrogoethite with a high content of sorption water and schwertmannite (a rare mineral, probably found in Russia for the first time). The chemical composition of this schwertmannite better corresponds to the Cashion-Murad model than to the Bigham model. Particles of partially oxidized magnetite and wustite enriched with zinc were revealed under electron microscope. Siderite with partial substitution of Fe²⁺ by Zn²⁺ was detected. Thus, contaminated hydromorphic soil contains both common minerals (illite, goethite, hematite, gypsum) and rare minerals (schwertmannite, Zn siderite, partially oxidized magnetite and wustite enriched with zinc).

Boron and nitrogen codoped carbon dots as fluorescence sensor for Fe3+ with improved selectivity

Carbon dots (CDs) are popular as fluorescence sensors, and metal ions are typical analytes. However, CDs used as fluorescent sensors for Fe³⁺ have some interferences coming from co-existed ions. In this study, we suspect that sp³ boron atom in phenylboronic acid group will be more compatible with Fe³⁺ to form coordination bonds, thereby increasing the selectivity to Fe³⁺. Hence, we designed and synthesized boron and nitrogen codoped carbon dots (BN-CDs) for detection of Fe³⁺ via a hydrothermal method using o-phenylenediamine (OPA) and 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzylchloroformate as precursors. From the results, we found that BN-CDs had superior selectivity to Fe³⁺ in the presence of the other common interfering metal ions like Cu²⁺, Fe²⁺ and Pb²⁺. Besides, the obtained BN-CDs exhibited good water solubility, favorable photostability, excellent pH stability between pH 2-11, and strong fluorescence intensity with quantum yield up to 31.5 %. These excellent properties of carbon dots validate that our idea is feasible, and can be used for design CDs for Fe³⁺ detection. Quenching mechanism study showed the fluorescence intensity of BN-CDs could be dramatically quenched by Fe³⁺ through dynamic and static synergy process. Finally, the as prepared BN-CDs were successfully applied to the determination of Fe³⁺ in fetal bovine serum and lake water.

Continuous synthesis of carbon dots with full spectrum fluorescence and the mechanism of their multiple color emission

Carbon dots with different emission fluorescence have a great number of potential applications for various areas from in vitro imaging and biotherapy, due to the good biosafety of red fluorescent CDs, to efficient ion detection and photocatalysis, due to the excellent photoluminescence properties of blue fluorescent carbon dots. Traditional methods for the synthesis of full-spectrum carbon dots require 24 h of synthesis and complex column chromatography. In this paper, a facile and efficient microfluidic method to continuously synthesize small and uniform carbon dots with full-spectrum emission fluorescence is developed for the first time. The synthesis process could be reduced to 20 minutes. Through XPS analysis and DFT calculations, it is quantitatively revealed that the number of primary amino groups determines the energy gap of the carbon dots and thus determines the fluorescence emission wavelength of the carbon dots. Applications for precise Fe³⁺ detection and in vitro bio-imaging were successfully implemented, showing great potential application value of the carbon dots.

Metal/metalloid and phosphorus characteristics in porewater associated with manganese geochemistry: A case study in the Jiulong River Estuary, China

Sediment porewater can be an important source of contaminants in the overlying water, but the mechanisms of metal(loid) and phosphorus (P) remobilization remain to be investigated. In this study, high-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) samplers were used to determine the porewater dissolved iron (Fe), manganese (Mn), cobalt (Co), chromium (Cr), vanadium (V), selenium (Se), arsenic (As), P and DGT-Labile S in coastal sediments in the Jiulong River Estuary (JRE), China. The results showed that high concentrations of dissolved Mn, Se and P were present in the overlying water, indicating potential water pollution with excessive amounts of Mn, Se and P. The dissolved Mn concentrations in the porewater were higher than the dissolved Fe concentrations, especially at submerged sites, demonstrating that Mn(III/IV) reduction is the dominant diagenetic pathway for organic carbon (OC) degradation, which directly affects Fe cycling by the competitive inhibition of Fe(III) reduction and Fe(II) reoxidation. Dissolved Co, Cr, V, Se, As and P show significant positive correlations with Mn but nearly no correlations with Fe, suggesting that the mobility of these metal(loid)s and P is associated with Mn but not Fe cycling in this region. In addition, the coelevated concentrations of the metal(loid)s, P and Mn at the submerged sites are attributed to the strengthened Mn reduction coupled with OC degradation fueled by hypoxia. The higher positive diffusion fluxes of Mn, Se and P were consistent with the excess Mn, Se and P concentrations in the overlying water, together with the approximately positive fluxes of the other metal(loid)s, indicating that sediment Mn(III/IV) reduction and concomitant metal(loid) and P remobilization might be vital pathways for metal(loid) and P migration to the overlying water.

Introducing Specificity to Iron Oxide Nanoparticle Imaging by Combining 57Fe-Based MRI and Mass Spectrometry

Iron oxide nanoparticles (ION) are highly sensitive probes for magnetic resonance imaging (MRI) that have previously been used for in vivo cell tracking and have enabled implementation of several diagnostic tools to detect and monitor disease. However, the in vivo MRI signal of ION can overlap with the signal from endogenous iron, resulting in a lack of detection specificity. Therefore, the long-term fate of administered ION remains largely unknown, and possible tissue deposition of iron cannot be assessed with established methods. Herein, we combine nonradioactive ⁵⁷Fe-ION MRI with ex vivo laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) imaging, enabling unambiguous differentiation between endogenous iron (⁵⁶Fe) and iron originating from applied ION in mice. We establish ⁵⁷Fe-ION as an in vivo MRI sensor for cell tracking in a mouse model of subcutaneous inflammation and for assessing the long-term fate of ⁵⁷Fe-ION. Our approach resolves the lack of detection specificity in ION imaging by unambiguously recording a ⁵⁷Fe signature.

Mass spectrometry-based analytical developments to link iron speciation to iron bioavailability in maize

A sequential fractionation procedure based on (i) water extraction, (ii) hexane extraction, (iii) saccharification, and (iv) proteolysis was developed to provide the first ever data on the molecular distribution of iron in maize. This was completed by the operational determination of the iron bioavailability using an in-vitro simulated model for gastro-intestinal digestion. The coupling of hydrophilic interaction chromatography (HILIC) and size exclusion chromatography (SEC) with the parallel detection by inductively coupled plasma mass spectrometry (ICP-MS) and high resolution electrospray mass spectrometry (HR-ESI-MS) allowed the identification of water-soluble Fe(III)-mugineate, Fe(III)-(citrate)₂, and Fe(III)₂-(phytate)₂. The procedures were applied to study some well characterized maize varieties having shown previously differences in iron bioavailability during cell culture and animal model feeding studies. The combined analytical methods developed in this work could unambiguously discriminate low from high Fe bioavailable seeds in these closely related maize varieties.

Variation of Feammox following ammonium fertilizer migration in a wheat-rice rotation area, Taihu Lake, China

Feammox is a newly discovered and important anaerobic nitrogen (N) loss pathway, and its variation and role in removing N following the application of N fertilizer and its migration from paddies to other land use types and from surface soils to deep soils have not been thoroughly elucidated to date. In this study, field sampling and slurry incubation experiments were performed to evaluate the Feammox rate between different land use types (paddy, irrigation ditch, riparian zone and lake, 0-10 cm) and different paddy soil depths (0-70 cm) in a wheat-rice rotation area in China. Based on a ¹⁵N-labelled isotope-tracing technique and analysis of microbial communities, it was estimated that the potential Feammox rate ranged from 0.031 to 0.42 mg N kg^-1 d^-1 in this area. In the soil profile of the paddy, the depth of 20-30 cm was the active region of Feammox, with a value of 0.37 ± 0.057 mg N kg^-1 d^-1. Compared with the surface soil (0-10 cm) of the paddy (0.18 ± 0.031 mg N kg^-1 d^-1), the potential Feammox rate of the irrigation ditch soil was not significantly different, but that of the lake riparian soil and lake sediment were decreased by 27.27% and 32.11%, respectively (p < 0.01). Fe(III) content was the best predictor of the Feammox rate and explained the variation of the Feammox rate by 36.00% in the surface soil. At the genus level, the paddy soil at a depth of 20-30 cm had the greatest abundance of the genera in which the Fe reduction bacteria were distributed; and where Bacillus, Geobacter and Anaeromyxobacter had higher proportions. It was estimated that the potential N loss by Feammox was in the range of 7.36 (the lake) ∼43.35 (the paddy) kg N ha^-1 year^-1 in the surface soil of this area. Considering denitrification and the Feammox rate as a whole, we found that denitrification remained to be the main contributor to N loss in the surface soil (94.72-96.89% of N loss), although Feammox dominated N loss in the deep soil (below 0-10 cm).

Deciphering Biosignatures in Planetary Contexts

Microbial life permeates Earth's critical zone and has likely inhabited nearly all our planet's surface and near subsurface since before the beginning of the sedimentary rock record. Given the vast time that Earth has been teeming with life, do astrobiologists truly understand what geological features untouched by biological processes would look like? In the search for extraterrestrial life in the Universe, it is critical to determine what constitutes a biosignature across multiple scales, and how this compares with "abiosignatures" formed by nonliving processes. Developing standards for abiotic and biotic characteristics would provide quantitative metrics for comparison across different data types and observational time frames. The evidence for life detection falls into three categories of biosignatures: (1) substances, such as elemental abundances, isotopes, molecules, allotropes, enantiomers, minerals, and their associated properties; (2) objects that are physical features such as mats, fossils including trace-fossils and microbialites (stromatolites), and concretions; and (3) patterns, such as physical three-dimensional or conceptual n-dimensional relationships of physical or chemical phenomena, including patterns of intermolecular abundances of organic homologues, and patterns of stable isotopic abundances between and within compounds. Five key challenges that warrant future exploration by the astrobiology community include the following: (1) examining phenomena at the "right" spatial scales because biosignatures may elude us if not examined with the appropriate instrumentation or modeling approach at that specific scale; (2) identifying the precise context across multiple spatial and temporal scales to understand how tangible biosignatures may or may not be preserved; (3) increasing capability to mine big data sets to reveal relationships, for example, how Earth's mineral diversity may have evolved in conjunction with life; (4) leveraging cyberinfrastructure for data management of biosignature types, characteristics, and classifications; and (5) using three-dimensional to n-D representations of biotic and abiotic models overlain on multiple overlapping spatial and temporal relationships to provide new insights.

Zinc and lead encapsulated in amorphous ferric cements within hardpans in situ formed from sulfidic Cu-Pb-Zn tailings

Hardpans are massively indurated layers formed at the top layer of sulfidic tailings dams, which develop cementation structures and result in heavy metal immobilization. However, the micro-structural and complex forms of the cementing materials are not fully understood, as well as the mechanisms by which Zn and Pb are stabilized in the hardpans. The present study deployed synchrotron-based X-ray fluorescence microscopy (XFM) to have characterized the cementing structures, examined the distribution of Fe, Zn and Pb, and obtained laterally-resolved speciation of Zn within the hardpans using fluorescence X-ray absorption near-edge structure (XANES) imaging. The XFM analyses revealed that the Fe-rich cement layers consisted of Fe (oxyhydr)oxides coupled with amorphous Si materials, immobilizing Zn and Pb. Through laterally-resolved XANES imaging analyses, Zn-ferrihydrite-like precipitates were predicted to account for >76% of the total Zn within the Fe-rich cement layers. In contrast, outside of the cement layers, 9-63% of the Zn was estimated as labile ZnSO₄^.7H₂O, with the remainder in the form of Zn-sulfide. These findings demonstrated that the Fe-rich cement layers were critical in immobilizing Zn and Pb within hardpans via mineral passivation and encapsulation, as the basis for long-term geochemical stability in the hardpan layer of sulfidic mine tailings.

Sb(V) adsorption and desorption onto ferrihydrite: influence of pH and competing organic and inorganic anions

In this study, we investigated the Sb(V) adsorption on ferrihydrite (Fh) at different pH values, in the presence and absence of common competing anions in soil such as phosphate (P(V)) and arsenate (As(V)). Batch adsorption experiments, carried out at pH 4.5, 6.0, and 7.0, showed a greater affinity of Fh towards P(V) and As(V) with respect to Sb(V), especially at higher pH values, while the opposite was true at acidic pH. The capacity of Fh to accumulate greater amounts of phosphate and arsenate in the 6.0-7.0 pH range was mainly linked to the different acid properties of P(V), As(V), and Sb(V) oxyanions. The Sb(V) adsorption on Fh was highly pH-dependent and followed the following order: pH 4.5 (0.957 mmol·g^-1 Fh) > pH 6.0 (0.701 mmol·g^-1 Fh) > pH 7.0 (0.583 mmol·g^-1 Fh). Desorption of antimonate from Sb(V)-saturated Fh, treated with citric and malic acid solutions, was ~equal to 55, 68, and 76% of that sorbed at pH 4.5, 6.0, and 7.0, respectively, while phosphate, arsenate, and sulfate were able to release significantly lower Sb(V) amounts. The FT-IR spectra revealed substantial absorbance shifts related to the surface hydroxyl groups of Fh, which were attributed to the formation of Fe-O-Sb(V) bonds and supported the formation of inner-sphere bonding between Sb(V) and Fh.

Carbon Dot-functionalized Interferometric Optical Fiber Sensor for Detection of Ferric Ions in Biological Samples

This work reports an interferometric optical microfiber sensor functionalized with nitrogen- and sulfur-codoped carbon dots (CDs) for the detection of ferric ions (Fe³⁺). Compared to other CD-based ferric ion sensors, the sensing mechanism of this presented sensor is dependent on the refractive index modulations due to selective Fe³⁺ adsorption onto the CD binding sites at the tapered region. This is the first study in which CD-based sensing was performed at the solid phase as a chelator, which does not rely on its fluorescence properties. The detection performance of the proposed sensor is not only comparable to a conventional fluorescence-based CD nanoprobe sensor but also capable of delivering quantitative analysis results and ease of translation to a sensor device for on-site detection. The presented sensor exhibits Fe³⁺ detection sensitivity of 0.0061 nm/(μg/L) in the linear detection range between 0 and 300 μg/L and a detection limit of 0.77 μg/L based on the Langmuir isotherm model. Finally, the potential use of the CD-functionalized optical microfiber sensor in the real environmental and biological Fe³⁺ monitoring applications has also been validated in this work.

A ratiometric fluorescence and light scattering sensing platform based on Cu-doped carbon dots for tryptophan and Fe(III)

A new Cu-doped carbon dots (Cu-CDs) were synthesized rapidly and simply via one-step thermolysis of Na₂[Cu(EDTA)] and ascorbic acid (AA) at 250°C for 2h with a high quantum yield of 9.8%. The Cu-CDs exhibits two signals of fluorescence at 396nm and second-order scattering (SOS) at 617nm under a single excitation wavelength of 308nm, and can be obviously enhanced by tryptophan (Trp) or Fe(III) leading to the ratiometric fluorescence and SOS response with a good linear wider range of 0.5-250μM and 0.1-50μM, respectively. This sensing system exhibits good selectivity and sensitivity toward Trp and Fe(III) over other analytes with a low detection limit of 275nM and 46nM, respectively. Furthermore, the proposed sensing system displays a prospective application for quantitative assay of Trp and Fe(III) in practical sample.

A laboratory investigation on the performance of South African acid producing gold mine tailings and its possible use in mine reclamation

This paper presents the results of laboratory investigations conducted on gold mine tailings (GMT) to assess their chemical, mineralogical and geotechnical characteristics in view of assessing its suitability as an alternative backfilling solution in mine reclamation. Chemical characterization revealed that GMT is dominated by Si, Al, and Fe with notable amounts of Cr, Zr, Zn, Pb, Ce, As, Ba, Ni, V, Sr, Nd, Cu, U, and Co. Mineralogical characterization revealed a composition of silicate minerals with secondary minerals such as jarosite, goethite and hematite. GMT composites showed improved strength characteristics. The particle sizes of the tailings are capable of producing a good paste fill that will require lower water-cement ratio. Moreover, the plasticity of the tailings provide for a likelihood for shear resistance to sliding in fluvial conditions. Curing and addition of cement showed positive effects on the compressive strength and shear strength of the tailings. However, the effect of curing and cement addition on the compaction characteristics and permeability of the tailings were negligible. GMT showed favorable characteristics for use in mine backfilling; it would be interesting to evaluate higher cement ratios to improve the characteristics of the tailings.

Differences in main processes to transform phosphorus influenced by ammonium nitrogen in flooded intensive agricultural and steppe soils

Exogenous ammonium nitrogen (AN) fertilization/deposition and the subsequently induced soil acidification, might exacerbate soil phosphorus (P) transformation and mobility, whereas poor understanding in abiotic and biotic processes still existed between intensively cultivated soil with high proportion of legacy inorganic P (P_i) in comparison to natural steppe soil with high proportion of organic P (P_o). Column batch flooded experiment using vegetable (VEG) and steppe (STE) soils was conducted to investigate the P transformation and mobility influenced by 60-day intermittent elution with an (1500 mg N kg^-1) solution or an acid sulfate (107 mmol H⁺ kg^-1) solution. The results showed that AN elution significantly decreased the contents of all P_i fractions and strengthened P_i leaching, whereas acid elution increased the contents of Al-P_i, Fe-P_i, and reductant-soluble P_i and reduced P leaching in VEG soil. In contrast, AN elution increased the contents of soluble-P_o and Al-(P_i + P_o) and decreased Ca-P and Fe-P_i, no effects on P leaching, whereas acid elution increased the contents of soluble-(P_i + P_o), Al-(P_i + P_o), Fe-(P_i + P_o) and reduced P leaching in STE soil. Variances analysis showed that pH and microbial biomass carbon were the most important factors to predict the P composition of the VEG and the STE soil, respectively. This indicated that AN elution released the soil mineral-bound phosphate with ammonia oxidation coupled with Fe(III) reduction, besides the same chemical influences on Fe/Al oxides as acid elution in VEG soil; while predominantly affected biochemical/biological processes of soil P by changing microbial biomass and enzyme activities in STE soil.

Fractions and colloidal distribution of arsenic associated with iron oxide minerals in lead-zinc mine-contaminated soils: Comparison of tailings and smelter pollution

The mining and smelting of lead-zinc (Pb-Zn) ores cause widespread As contamination. The fractions and colloidal distribution of As associated with Fe oxide minerals in Pb-Zn mine-contaminated soils have not been well understood. In this study, As fractions associated with Fe oxide minerals in Pb-Zn tailings- and smelter-contaminated soils were compared using sequential extraction techniques. Kinetic experiments were conducted to characterize the reactivity of Fe oxide minerals. The distribution of As and Fe oxide minerals in soil colloids were analyzed. The results show that in mining-contaminated soils (both tailings and smelter) the relatively active fraction (amorphous hydrous oxide-bound As, As_F3) has a strong relationship with easily reducible Fe (Fe_ox1). In smelter-contaminated soils, relatively stable fractions (crystalline hydrous oxide-bound As, As_F4) were closely associated with reducible Fe (Fe_ox2). Although the average proportions of specifically-bound As (As_F2) and As_F3 in contaminated soils were similar, high As release in tailings-contaminated soils was observed because of the high reactivity of Fe oxide minerals in those soils compared with that in smelter-contaminated soils. Some slightly polluted soils with high pH and TOC concentrations formed As-bearing colloidal suspensions. Especially in smelter-contaminated soils, many small-sized soil colloids could facilitate As migration with surface runoff or vertical transport.

Optimization and Design of Magnetic Ferrite Nanoparticles with Uniform Tumor Distribution for Highly Sensitive MRI/MPI Performance and Improved Magnetic Hyperthermia Therapy

Two major technical challenges of magnetic hyperthermia are quantitative assessment of agent distribution during and following administration and achieving uniform heating of the tumor at the desired temperature without damaging the surrounding tissues. In this study, we developed a multimodal MRI/MPI theranostic agent with active biological targeting for improved magnetic hyperthermia therapy (MHT). First, by systematically elucidating the magnetic nanoparticle magnetic characteristics and the magnetic resonance imaging (MRI) and magnetic particle imaging (MPI) signal enhancement effects, which are based on the magnetic anisotropy, size, and type of nanoparticles, we found that 18 nm iron oxide NPs (IOs) could be used as superior nanocrystallines for high performance of MRI/MPI contrast agents in vitro. To improve the delivery uniformity, we then targeted tumors with the 18 nm IOs using a tumor targeting peptide, CREKA. Both MRI and MPI signals showed that the targeting agent improves the intratumoral delivery uniformity of nanoparticles in a 4T1 orthotopic mouse breast cancer model. Lastly, the in vivo antitumor MHT effect was evaluated, and the data showed that the improved targeting and delivery uniformity enables more effective magnetic hyperthermia cancer ablation than otherwise identical, nontargeting IOs. This preclinical study of image-guided MHT using cancer-targeting IOs and a novel MPI system paves the way for new MHT strategies.

Occupational survey of airborne metal exposures to welders, metalworkers, and bystanders in small fabrication shops

The objective of this study was to characterize worker exposure to airborne metal and particulate matter in shops where multiple types of metalworking tasks were performed. The sampling strategy included full-shift and task-based personal samples on workers who performed flux-cored arc welding, personal samples on workers performing non-welding metalworking tasks, and area samples near welders, representing bystanders to welding. Size-fractionated particulate matter adjacent to welding activities was measured using real-time monitoring devices. Samples were analyzed for 21 individual metals, of which 8 were frequently detected. Exceedance fractions were calculated based on the distribution of results for each frequently detected metal. Exceedance fractions were <5% for all metals, except manganese (6% of the REL, 55% of the inhalable TLV-TWA and 91% of the respirable TLV-TWA) and iron oxide (10% of the REL and TLV-TWA) for Shop 1 bystander samples, manganese (68% for the inhalable TLV-TWA and 98% of the respirable TLV-TWA) for welder samples, and manganese (35% for the inhalable TLV-TWA and 80% of the respirable TLV-TWA) and iron oxide (12% for the PEL and 23% for the REL and TLV-TWA) for metalworker samples. Particulate matter concentrations measured at distances of 0.9-1.5 m and 2.1-2.7 m from the welder were within the same order of magnitude. The results of this study allow for comparison to health-based exposure limits for select individual components of welding fume with a low to medium degree of censorship.

Effects of Fe/S ratio on the kinetics and microbial ecology of an Fe(III)-dosed anaerobic wastewater treatment system

Effects of Fe(III)/sulfate (Fe/S) ratio on organic carbon oxidation kinetics and microbial ecology of a novel Fe(III)-dosed anaerobic wastewater treatment system were investigated in this study. Fixed-film batch bioreactors under three Fe/S molar ratios (1, 2, and 3) yielded COD oxidation rates that increased with the Fe/S ratio, and estimated Michaelis-Menten model parameters V_max ranging in 0.47-1.09 mg/L⋅min and K_m in 2503-3267 mg/L. Both iron and sulfate reducing bacteria contributed to the organics oxidation, and the produced sludge materials contained both biomass (32-45 wt.%) and inorganic precipitates from biogenic ferrous iron and sulfide (68-55 wt.%). Spectroscopic and chemical elemental analyses indicated that the inorganic fraction of the sludge materials contained both FeS and FeS₂, and had Fe/S stoichiometric ratios close to 1. Microbiological analyses of the biofilm samples revealed that the major putative iron- and sulfate reducers were Geobacter sp. and Desulfovibrio sp. along with noticeable N-fixing and fermentative bacteria. The COD oxidation rate had a positive correlation with the relative abundance of iron reducers, and both increased with the Fe/S ratio. A conceptual framework was proposed to illustrate the effects of Fe/S ratio on organics oxidation rate, microbial ecology and their interplays.

Early Achilles Enthesis Involvement in a Murine Model of Spondyloarthropathy: Morphological Imaging with Ultrashort Echo-Time Sequences and Ultrasmall Superparamagnetic Iron Oxide (USPIO) Particle Evaluation in Macrophagic Detection

Purpose

To confirm the interest of 3-dimensional ultrashort echo-time (3D-UTE) sequences to assess morphologic aspects in normal and pathological Achilles entheses in a rat model of spondyloarthropathy (SpA) with histological correlations, in comparison with conventional RARE T2 Fat-Sat sequences, and, furthermore, to evaluate the feasibility of a 3D multiecho UTE sequence performed before and after the intravenous injection of ultrasmall superparamagnetic iron oxide (USPIO) particles to assess macrophagic involvement in the Achilles enthesis in the same rat model of SpA.

Materials and Methods

Fourteen rats underwent in vivo MRI of the ankle at 4.7 T, including a 3D RARE T2 Fat-Sat sequence and a 3D ultrashort echo-time (UTE) sequence for morphologic assessment at baseline and day 3 after induction of an SpA model, leading to Achilles enthesopathy in the left paw (right paw serving as a control). A 3D multiecho UTE sequence was also performed at day 3 before and then 24 (4 rats) and 48 (2 rats) hours after intravenous injection of USPIO. Visual analysis and signal intensity measurements of all images were performed at different locations of the Achilles enthesis and preinsertional area. Visual analysis and T2∗ measurements were performed before and after USPIO injection, on the 3D multiecho UTE sequence in the same locations. Normal and pathological values were compared by Wilcoxon signed-rank tests. MR findings were compared against histological data.

Results

3D-UTE sequences enabled morphologic identification of the anterior fibrocartilage and posterior collagenic areas of the Achilles enthesis. Visual analysis and signal intensity measurements distinguished SpA-affected entheses from healthy ones at day 3 (P=0.02). After administration of USPIO, no differences in signals were detected. Similarly, both visual analysis and signal T2∗ measurements in the enthesis were unable to distinguish the SpA-affected tendons from healthy ones (P=0.914). Neither the normal anatomy of the enthesis nor its pathological pattern could be distinguished using the standard RARE sequence. Histology confirmed the absence of USPIO in Achilles entheses, despite marked signs of inflammation.

Conclusion

Unlike conventional RARE T2 Fat-Sat sequences, 3D-UTE sequences enable morphologic assessment of normal enthesis anatomy and early detection of abnormalities in pathological conditions. However, 3D multiecho UTE sequences combined with USPIO injections with T2∗ measurements were unable to detect macrophagic involvement in these pathological conditions.

Surface characterization and chemical speciation of adsorbed iron(iii) on oxidized carbon nanoparticles

Carbonaceous nanomaterials represent a significant portion of ultra-fine airborne particulate matter, and iron is the most abundant transition metal in air particles. Owing to their high surface area and atmospheric oxidation, carbon nanoparticles (CNP) are enriched with surface carbonyl functional groups and act as a host for metals and small molecules. Using a synthetic model, concentration-dependent changes in the chemical speciation of iron adsorbed on oxidized carbon surfaces were investigated by a combination of X-ray and electron microscopic and spectroscopic methods. Carbon K-edge absorption spectra demonstrated that the CNP surface was enriched with carboxylic acid groups after chemical oxidation but that microporosity was unchanged. Oxidized CNP showed a high affinity for sorption of Fe(iii) from solution (75-95% uptake) and spectroscopic measurements confirmed a 3+ oxidation state of Fe on CNP irrespective of surface loading. The bonding of adsorbed Fe(iii) at variable loadings was determined by iron K-edge X-ray absorption spectroscopy. At low loadings (3 and 10 μmol Fe m-2 CNP), mononuclear Fe was octahedrally coordinated to oxygen atoms of carboxylate groups. As Fe surface coverage increased (21 and 31 μmol Fe m-2 CNP), Fe-Fe backscatters were observed at interatomic distances indicating iron (oxy)hydroxide particle formation on CNP. Electron-donating surface carboxylate groups on CNP coordinated and stabilized mononuclear Fe(iii). Saturation of high-affinity sites may have promoted hydroxide particle nucleation at higher loading, demonstrating that the chemical form of reactive metal ions may change with surface concentration and degree of CNP surface oxidation. Model systems such as those discussed here, with controlled surface properties and known chemical speciation of adsorbed metals, are needed to establish structure-activity models for toxicity assessments of environmentally relevant nanoparticles.

Guest-Induced Ultrasensitive Detection of Multiple Toxic Organics and Fe3+ Ions in a Strategically Designed and Regenerative Smart Fluorescent Metal-Organic Framework

Luminescent metal-organic frameworks (LMOFs) are promising functional materials for sustainable applications, where an analyte-induced multiresponsive system with good recyclability is beneficial for detecting numerous lethal pollutants. We designed and built the dual-functionalized, three-dimensional Zn(II)-framework [Zn₃( bpg)_1.5( azdc)₃]·(DMF)_5.9·(H₂O)_1.05 (CSMCRI-1) using an -OH group-integrated bpg linker and a -N═N- moiety containing H₂ azdc ligand, which functions as a unique tetrasensoric fluorescent probe. The activated CSMCRI-1 (1') represents the hitherto unreported pillar-layer framework for extremely selective fluorescence quenching by nitrofurazone antibiotics as well as explosive nitro-aromatic 2,4,6-trinitrophenol, where ultrasensitive detection is achieved for both the electron-lacking analytes. Impressively, 1' represents the first ever MOF for significant fluorescence "turn-on" detection of toxic and electron-rich 4-aminophenol in the concurrent presence of isomeric analogues. Density functional theory calculations highlight the specific importance of pillar functionalization in the "turn-on" or "turn-off" responses of 1' by electronically divergent toxic organics and provide further proof of supramolecular interactions between the framework and analytes. The fluorescence intensity of 1' dramatically quenches by a trace amount of Fe³⁺ ions over other competing metal ions, alongside visible colorimetric change of the framework in solid and solution phase upon Fe³⁺ encapsulation. The sensing ability of 1' remains unaltered for multiple cycles toward all lethal pollutants. The sensing mechanism is attributed to both dynamic and static quenching as well as resonance energy transfer, which strongly comply with the predictions of theoretical simulations. Considering the long-term and real-time monitoring, AND as well as OR molecular logic gates are constructed based on the discriminative fluorescence response for each analyte that provides a platform to fabricate smart LMOFs with multimode logic operations.

Primary Production in the Water Column as Major Structuring Element of the Biogeographical Distribution and Function of Archaea in Deep-Sea Sediments of the Central Pacific Ocean

Information on environmental conditions shaping archaeal communities thriving at the seafloor of the central Pacific Ocean is limited. The present study was conducted to investigate the diversity, composition, and function of both entire and potentially active archaeal communities within Pacific deep-sea sediments. For this purpose, sediment samples were taken along the 180° meridian of the central Pacific Ocean. Community composition and diversity were assessed by Illumina tag sequencing targeting archaeal 16S rRNA genes and transcripts. Archaeal communities were dominated by Candidatus Nitrosopumilus (Thaumarchaeota) and other members of the Nitrosopumilaceae (Thaumarchaeota), but higher relative abundances of the Marine Group II (Euryarchaeota) were observed in the active compared to the entire archaeal community. The composition of the entire and the active archaeal communities was strongly linked to primary production (chlorophyll content), explaining more than 40% of the variance. Furthermore, we found a strong correlation of the entire archaeal community composition to latitude and silicic acid content, while the active community was significantly correlated with primary production and ferric oxide content. We predicted functional profiles from 16S rRNA data to assess archaeal community functions. Latitude was significantly correlated with functional profiles of the entire community, whereas those of the active community were significantly correlated with nitrate and chlorophyll content. The results of the present study provide first insights into benthic archaeal communities in the Pacific Ocean and environmental conditions shaping their diversity, distribution, and function. Additionally, they might serve as a template for further studies investigating archaea colonizing deep-sea sediments.

Selenium and mercury in Brazilian Cerrado soils and their relationships with physical and chemical soil characteristics

The objective of this study was to determine the natural concentrations of Hg and Se in 45 representative soil profiles from the Cerrado biome in central Brazil, and to correlate their concentrations with soil chemical and physical characteristics. The study area was composed of three sub-regions: Goiás, Northwest of Minas Gerais, and Minas Gerais Triangle. Selenium and Hg concentrations were determined by acid digestion and atomic absorption spectroscopy. Data were subjected to analysis of variance on the means of the Hg and Se variables within each soil class at two depths, followed by multivariate statistical methods. The Hg concentrations ranged from 15 to 182 μg kg^-1 and the Se concentrations ranged from 22 to 72 μg kg^-1. The soil characteristics that most contributed to Hg concentrations in the soils, according to principal component analysis, were Fe₂O₃, FeO, TiO₂, pH, P₂O₅, and effective CEC. In general, the soils of the Cerrado biome have deficient Se concentrations. The Humic Rhodic Acrustoxes have Hg concentrations above the prevention reference value for soils of Minas Gerais.