Current understanding on the fate and behavior of microplastics (MPs) in complex soil media remains inadequate. We characterized the aging and hetero-aggregation of a MP sampled in farmland soil, and ...explored its vertical downward transport in natural loamy sand. The MP was identified with FTIR spectrum as polypropylene, a plastic lighter than water. FTIR spectrum combined with SEM imaging confirmed the MP was highly aged, generating colloidal plastic fibers and carbonyl groups. SEM imaging coupled with EDX analysis suggested hetero-aggregation of the MP with soil minerals. Soil leaching tests performed with the clean MP (without soil minerals) (CMP), the raw MP (RMP) (with soil minerals), and the RMP with humic acid (HA) (RMP + HA) demonstrated that the mobility was insignificant for the CMP, moderate for the RMP and highest for the RMP + HA, resulting in a maximal downward traveling distance of 0 cm, 3–4 cm, and 9–10 cm, respectively. Correlation between the maximal traveling distance and zeta potential of the CMP, RMP, and RMP + HA confirmed surface charge as a dominant control on the MP mobility; while the increasing density of the MP, due to hetero-aggregation with soil minerals, was identified as a driving mechanism for its downward transport, despite its intrinsic density lower than water. Occurrence of only the lower-sized rod-shaped plastic fibers at the maximal traveling distance suggested the natural aging, a process leading to plastic vibration and fragmentation, was conducive to plastic translocation. The three explored classes of antibiotic resistance genes (ARGs) (tetracycline, beta-lactam and sulfonamide) were all detected in the plastic surface, suggesting the MP may function as a potential pathway for the dissemination of ARGs to the deeper soil layer. These findings are important to understand the concentration distribution of both the MPs and ARGs in agriculture impacted soils, a natural reservoir of both emerging contaminants.
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•MPs even with a virgin density lower than water could transport downward in soil.•Both hetero-aggregation and aging promote the downward transport.•Hetero-aggregation with soil mineral and NOM increased MP density and zeta potential.•Aging reduced plastic particle size and produced rod-shaped plastic fibers.•MPs are potential vehicles for downward transport of ARGs in agricultural land.
Microplastics even lighter than water could transport downward in soil, due to hetero-aggregation and natural aging, and convey the ARGs to deep soil layers.
•Primary accumulations of transition metals and metalloids in Archean stromatolites.•Element distributions and concentrations correlate with microbial growth fabrics.•Accumulation owing to binding to ...organic matter of microbial communities.•Accumulation driven by microbial utilization.
Stromatolites of the ~3.48 billion–year–old Dresser Formation (Pilbara Craton, Western Australia) provide some of the oldest convincing evidence of life on Earth. Here, we augment previous evidence with a detailed investigation of the concentrations and distributions of various transition metals (Cr, Mn, Co, Ni, Cu, Zn, Mo, Se, Ag, Sn, Au, Hg, and Pb) and metalloids (As, Sb, and Te) in unweathered samples of strongly sulfidized stromatolites from drill cores. High–resolution elemental mapping and in situ compositional analysis of sulfides (pyrite and sphalerite) show that these sedimentary and hydrothermally sourced elements are strongly concentrated in texturally distinctive, nano-porous pyrite enriched in autochthonous organic matter, which forms the major, petrogenetically earliest component of wrinkly laminated and digitate growth fabrics within the stromatolites. Repeated cyclic alternations of various transition metals and metalloids (most importantly Ni and Zn), plus the presence of disconformities and overgrowth relationships between wrinkly stromatolite laminae, suggest that these element accumulations were primarily established by depositional processes during continuous stromatolite formation. Because transition metals and metalloids generally have strong affinities for organic matter, and can play active roles in biochemical processes, we interpret these element accumulations in the Dresser Formation stromatolites to be the result of binding to organic matter of living microbial communities and/or dead biomass, and perhaps also microbial utilization. Collectively, our results show that the precise characterization of transition metal–metalloid concentrations and distributions can unveil element enrichment patterns suggestive of biological activity, even in some of Earth’s oldest stromatolites.
The Iron Mountain Mine Superfund site in California is a prime example of an acid mine drainage (AMD) system with well developed assemblages of sulfate minerals typical for such settings. Here we ...present and discuss the vibrational (infrared), X-ray absorption, and Mössbauer spectra of a number of these phases, augmented by spectra of a few synthetic sulfates related to the AMD phases. The minerals and related phases studied in this work are (in order of increasing Fe
2O
3/FeO): szomolnokite, rozenite, siderotil, halotrichite, römerite, voltaite, copiapite, monoclinic Fe
2(SO
4)
3, Fe
2(SO
4)
3·5H
2O, kornelite, coquimbite, Fe(SO
4)(OH), jarosite and rhomboclase. Fourier transform infrared spectra in the region 750–4000
cm
−1 are presented for all studied phases. Position of the FTIR bands is discussed in terms of the vibrations of sulfate ions, hydroxyl groups, and water molecules. Sulfur K-edge X-ray absorption near-edge structure (XANES) spectra were collected for selected samples. The feature of greatest interest is a series of weak pre-edge peaks whose position is determined by the number of bridging oxygen atoms between Fe
3+ octahedra and sulfate tetrahedra. Mössbauer spectra of selected samples were obtained at room temperature and 80
K for ferric minerals jarosite and rhomboclase and mixed ferric–ferrous minerals römerite, voltaite, and copiapite. Values of Fe
2+/Fe
2+
+
Fe
3+ determined by Mössbauer spectroscopy agree well with those determined by wet chemical analysis. The data presented here can be used as standards in spectroscopic work where spectra of well-characterized compounds are required to identify complex mixtures of minerals and related phases.
► Detailed mineralogy of one of the world's most extreme acid mine drainage sites. ► Global and local structure of iron sulfate minerals. ► Mineral spectra which can be used in laboratory studies of sulfate speciation in crystalline or amorphous solids, biological materials, and liquids. ► Mineral spectra which can be used for remote studies of terrestrial or extraterrestrial targets.
The development of hydrothermal activities on mid-ocean ridges is primarily influenced by magmatic and tectonic activities close to the ridge axis. On slow and ultraslow spreading ridges featured by ...limited magma supply, prolonged hydrothermal activity can also occur in non-transform offsets (NTO), where sustained ultramafic-related hydrothermal circulation happens due to prolonged hydrothermal processes associated with the expose of ultramafic rocks. In contrast, basalt-hosted hydrothermal fields are barely developed in NTOs, especially in off-axis area, due to insufficient magma supply. In this study, we reported the occurrence of a distal axis (∼9.5 km) basalt-hosted hydrothermal field (50.63°E) on the NTO of segment 27 of the ultraslow spreading Southwest Indian ridge. The hydrothermal products are characterized by layered crusts mainly composed of oxides, such as limonite and goethite, rich in Fe and depleted in Si. These crusts contain high contents of trace elements derived from seawater, such as P, As, Mo, U, and Sb and show REE pattens with negative Eu and mostly positive Ce anomalies. However, the high Cu content (1.82 ± 0.89 wt%, N = 27), low absorption ratio of Cu (18.39 ± 12.71%, N = 9), and residual chalcopyrite altered by goethite suggest prior high-temperature hydrothermal activity. Lead isotopic composition with basaltic rocks signatures that distinct from those of low-temperature crusts of seawater origin also support this conclusion. The Fe-rich crusts appears to be the result of high-temperature sulfides altered by late-stage low-temperature diffuse flow. This field is currently the furthest known distal axis basalt-hosted hydrothermal field located in NTOs of ultraslow spreading ridges. The hydrothermal circulation is likely due to a combination of off-axis normal fault and gabbro diking. Our results emphasize the occurrence of distal axis basalt-hosted high-temperature hydrothermal activities on NTOs of ultraslow spreading ridges, and may lead to an increased estimation of hydrothermal heat and chemical influx to the ocean.
•A distal axis inactive hydrothermal field (50.63°E) was newly identified on the Southwest Indian ridge.•The Fe-rich crusts appears to be altered result of high-temperature sulfides by late-stage low-temperature diffuse flow.•Hydrothermal circulation in 50.63°E is likely due to a combination of off-axis normal fault and gabbro diking.
The origins of mafic mineral clots and microgranular enclaves in Mesoproterozoic granites were investigated in a case study of felsic A-type Hiltaba Suite granites from the Gawler Craton, South ...Australia. Mafic mineral clots display interlocked textures comprising plagioclase, amphibole, biotite, apatite and magnetite and occur interstitial to coarse rapakivi feldspar, compositionally zoned plagioclase, and quartz phenocrysts. The microgranular enclaves, which may be partly disaggregated, are rounded, contain partially resorbed K-feldspar xenocrysts and have a similar mineralogy to the clots. Whole-rock geochemistry, mineral chemistry and textural features (e.g., rapakivi and granophyric textures, quartz-amphibole ocelli, multiple generations of biotite, xenocrysts, evidence of undercooling) indicate that mineral clots and enclaves may have similar origins and were sourced via multistage magma mixing. Magma rejuvenation caused mingling with a partially crystalline and ductile mush resulting in the formation of microgranular mafic enclaves which contain numerous xenocrysts. Prolonged input of mafic magma and elevated F within the residual melt promoted partial disaggregation of enclaves and recrystallization of mineral clots. Geochemically distinct biotite generations show this evolution from initially F-poor annite to F-rich phlogopite dispersed throughout mineral clots and as ‘free’ grains within the Hiltaba Suite granites. Annite-bearing mineral clots formed at higher pressures than phlogopite clots, corresponding to crystallization at greater depths. The abundance of Cu and S in mineral clots and enclaves within Hiltaba Suite granite studied here indicates that repeated magma mixing processes may have provided a source of metals for the formation of the nearby Olympic Dam Fe-oxide Cu-U-Au-Ag deposit.
•Multistage magma mixing processes recorded in A-type Hiltaba Suite granites.•Ubiquitous mafic mineral clots and microgranular enclaves reflect timing and source.•Late-stage partial disaggregation and re-equilibration of microgranular enclaves.•Clots and enclaves host Cu and S, provide source for nearby Olympic Dam deposit.
The detection of exoplanets orbiting other stars has revolutionized our view of the cosmos. First results suggest that it is teeming with a fascinating diversity of rocky planets, including those in ...the habitable zone. Even our closest star, Proxima Centauri, harbors a small planet in its habitable zone, Proxima b. With the next generation of telescopes, we will be able to peer into the atmospheres of rocky planets and get a glimpse into other worlds. Using our own planet and its wide range of biota as a Rosetta stone, we explore how we could detect habitability and signs of life on exoplanets over interstellar distances. Current telescopes are not yet powerful enough to characterize habitable exoplanets, but the next generation of telescopes that is already being built will have the capabilities to characterize close-by habitable worlds. The discussion on what makes a planet a habitat and how to detect signs of life is lively. This review will show the latest results, the challenges of how to identify and characterize such habitable worlds, and how near-future telescopes will revolutionize the field. For the first time in human history, we have developed the technology to detect potential habitable worlds. Finding thousands of exoplanets has taken the field of comparative planetology beyond the Solar System.
Production of hydroxyl radicals (OH) has been recently revealed upon oxygenation of sediments in redox-dynamic subsurface environments. In particular, Fe(II)-bearing clay minerals are the major ...sediment components contributing to OH production upon oxygenation, and the produced OH can oxidize contaminants and inactivate bacteria. Whereas, the mechanisms of OH production from oxygenation of Fe(II)-bearing clay minerals remain elusive. The objectives of this study were to identify the structural variation of Fe(II) entities during the oxidation of Fe(II)-bearing clay minerals by O2, and to unravel the mechanisms of electron transfer within the mineral structure and from mineral to O2 for OH production. Nontronite (NAu-2, 23% Fe) which was chemically reduced to 54.5% Fe(II) in total Fe was used as a model Fe(II)-bearing clay mineral. Production of OH and oxidation of Fe(II) were measured during the oxidation of reduced NAu-2 by O2. A wide spectrum of spectroscopic techniques, including Fourier transform infrared spectroscopy (FTIR), Fe K-edge X-ray absorption spectroscopy (XAS), Mössbauer spectra, and X-ray photoelectron spectroscopy (XPS), were employed to explore the structural variation of Fe(II) entities in NAu-2 and the electron transfer within NAu-2 and from NAu-2 to O2. For 180 min oxidation of 1 g/L reduced NAu-2, a biphasic OH production was observed, being quick within the initial 15 min and slow afterwards. Production of OH correlates well with oxidation of Fe(II) in the reduced NAu-2. Within the initial 15 min, trioctahedral Fe(II)-Fe(II)-Fe(II) entities and edge Fe(II) in the reduced NAu-2 were preferentially and quickly oxidized, and electrons from the interior Fe(II)-Fe(II)-Fe(II) entities were most likely ejected from the basal siloxane plane to O2. Meanwhile, trioctahedral Fe(II)-Fe(II)-Fe(II) entities were mainly transformed to dioctahedral Fe(II)-Fe(II) entities. When the time of oxygenation was longer than 15 min, dioctahedral Al-Fe(II), Fe(II)-Fe(II) and Fe(II)-Fe(III) entities were slowly oxidized, and the interior electrons were transported through Fe(II)-O-Fe(III) linkages to edges and then ejected to O2. In the slow stage of oxidation, electrons from interior Fe(II) accumulated towards the near surface layers and fueled the regeneration of edge Fe(II) for OH production. In both stages, one-electron transfer mechanism with the involvement of O2− and H2O2 applies for OH production from the oxidation of structural Fe(II) by O2. The mechanisms unraveled in this study advance the understanding of reactive oxygen species (ROS) production and structural Fe variation when Fe(II)-bearing clay minerals are oxygenated in redox-dynamic systems.
The development of complex alteration layers on silicate mineral surfaces undergoing dissolution is a widely observed phenomenon. Given the complexity of these layers, most kinetic models used to ...predict rates of mineral–fluid interactions do not explicitly consider their formation. As a result, the relationship between the development of the altered layers and the final dissolution rate is poorly understood. To improve our understanding of the relationship between the alteration layer and the dissolution rate, we developed a spatially resolved surface kinetic model for olivine dissolution and applied it to a series of closed-system experiments consisting of three-phases (water (±NaCl), olivine, and supercritical CO2) at conditions relevant to in situ mineral carbonation (i.e. 60°C, 100bar CO2). We also measured the corresponding δ26/24Mg of the dissolved Mg during early stages of dissolution. Analysis of the solid reaction products indicates the formation of Mg-depleted layers on the olivine surface as quickly as 2days after the experiment was started and before the bulk solution reached saturation with respect to amorphous silica. The δ26/24Mg of the dissolved Mg decreased by approximately 0.4‰ in the first stages of the experiment and then approached the value of the initial olivine (−0.35‰) as the steady-state dissolution rate was approached. We attribute the preferential release of 24Mg to a kinetic effect associated with the formation of a Mg-depleted layer that develops as protons exchange for Mg2+.
We used experimental data to calibrate a surface kinetic model for olivine dissolution that includes crystalline olivine, a distinct “active layer” from which Mg can be preferentially removed, and secondary amorphous silica precipitation. By coupling the spatial arrangement of ions with the kinetics, this model is able to reproduce both the early and steady-state long-term dissolution rates, and the kinetic isotope fractionation. In the early stages of olivine dissolution the overall dissolution rate is controlled by exchange of protons for Mg, while the steady-state dissolution rate is controlled by the net removal of both Mg and Si from the active layer. Modeling results further indicate the importance of the spatial coupling of individual reactions that occur during olivine dissolution. The inclusion of Mg isotopes in this study demonstrates the utility of using isotopic variations to constrain interfacial mass transfer processes. Alternative kinetic frameworks, such as the one presented here, may provide new approaches for modeling fluid–rock interactions.
Synchrotron-based microscale X-ray absorption near edge structure spectroscopy (μ-XANES) has been combined with X-ray fluorescence (μ-XRF) mapping to investigate Ge, Cu and Fe oxidation states in ...compositionally zoned Ge-rich sphalerite from the Saint-Salvy deposit (France). The present study aims at improving our understanding of substitution mechanisms and trace element uptake relative to Ge isotope fractionation in sphalerite. K-Edge XANES records of various Ge-, Cu- and Fe-bearing sulphides are presented for comparison with sphalerite, and ab initio calculations at the Ge K-edge complete our experimental data. The Ge K-edge spectra of the Ge-bearing sphalerite are identical to those of germanite, renierite and briartite, indicating the presence of tetrahedrally-coordinated Ge4+. In addition, Cu and Fe K-edge spectra suggest the presence of Cu+ and Fe2+, respectively, in the tetrahedral site. No significant differences in the oxidation states of Ge, Cu and Fe were observed within or between the zoning types or between the samples. The intake of Ge4+ in sphalerite may therefore occur in the tetrahedral divalent metal site via coupled substitutions charge-balanced by monovalent elements such as 3Zn2+↔Ge4++2Cu+, resulting in a strong Ge–Cu elemental correlation, or, when Ge does not correlate with monovalent elements, through the creation of lattice vacancies such as 2Zn2+↔Ge4++□(vacancy). The tetravalent state of Ge is compatible with temperature-related Ge isotopic fractionation and can explain the large range of δ74Ge measured in the Saint-Salvy sphalerite. Moreover, the exceptional enrichment in Ge and the large variations in the ‘bulk’ Ge contents in these sphalerites do not appear to be related to charge effects but would instead result from the effect of temperature-related partitioning.
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•Element geochemistry in coals varies notably in a laterally correlated coal seam.•Various geological factors are responsible for the difference in the elemental geochemistry of the ...coals.•Some critical metals including REY are redeposited within the coal section as a result of acidic leaching.•The Datanhao coal seam has potential in industrial utilization of certain critical metals.
This paper discusses the modes of occurrence of critical elements and their origins in the studied coal and associated rock samples (partings and roof strata) from the Datanhao coal mine, Daqingshan Coalfield, Inner Mongolia, northern China. The studied coals are enriched in trace elements including Zr, Hf, Th, Be, F, Zn, Ga, Nb, Mo, Cd, In, Sn, Ta, Hg, W, Pb, and rare earth elements and Y (REY). Zirconium, Nb, Ta, and Hf are largely associated with anatase in the studied coal and non-coal samples. The main carriers of REY, Th, and U in both coal and non-coal samples are Ca-bearing REE-phosphate minerals, most likely monazite, although U is partly associated with organic matter. Fluorine in the Datanhao coals is mainly associated with kaolinite.
Most partings identified as volcanic ash-derived tonsteins from the Datanhao Mine exhibit negative Eu anomalies that, along with the common presence of equant-shaped euhedral volcanic quartz (beta-quartz), indicate a felsic volcanic source located in the Xing'an-Mongolia Orogenic Belt. Other probable sources of clastic material into the basin include the pre-Cambrian granites from the adjacent uplands, which may be responsible for the light rare earth element enrichment of the studied deposits, and associated metamorphic rocks from the adjacent uplands.
Owing to acidic hydrothermal fluids, which are most likely related to the Yanshanian (Jurassic to Early Cretaceous) intrusive activity and/or low-temperature basinal waters circulating within the coal-bearing unit during the epigenetic stage, most of the coal benches from the Datanhao mine are also relatively enriched in middle rare earth elements. On the other hand, some coal and non-coal bench samples from the middle Datanhao section are enriched in heavy REE. This, along with the presence of abundant syngenetic or early diagenetic carbonate minerals, indicates deposition in an episodic alkaline environment, the origin of which is mostly probably attributed to evaporation and/or saline water inputs resembling a playa lake environment.
As the concentrations of Zr, Hf, Nb, and Ta are all close to or higher than the respective industry cut-off grades or standards for these critical elements, the Datanhao coal seam has potential economic significance for these as an important by-product of the coal mining.
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