Guangzhou Institute of Geochemistry
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Fluctuating redox conditions accelerate the electron storage and transfer in magnetite and production of dark hydroxyl radicals
No full textMagnetite (Fe3O4), known as a geo-battery that can store and transfer electrons, often co-occurs with sulfide in subsurface environments with fluctuating redox conditions. However, little is known about how fluctuating redox conditions (e.g., sulfidation-oxidation) affect the electron storage and transfer in Fe3O4 that was associated with the production of dark hydroxyl radicals (center dot OH) and the oxidation of dissolved organic matter (DOM). This study revealed that Fe3O4 sulfidated by sulfide (S-Fe3O4) at neutral pH exhibited higher center dot OH production upon oxygenation than Fe3O4, in which the cumulative center dot OH concentration increased with increasing initial S/Fe ratio (<= 0.50), sulfidation duration and number of sulfidation-oxidation cycle. X-ray photoelectron spectroscopy and wet-chemical analyses of Fe and S species of S-Fe3O4 showed that sulfidation enables electron storage in Fe3O4 by increasing both structural and surface Fe(II). Sulfide was converted into S0, acid volatile sulfur (AVS), and chromium-reducible sulfur (CRS) during Fe3O4 sulfidation. S-Fe3O4 with lower AVS/CRS ratio exhibited higher reactivity to produce center dot OH, indicating the important role of CRS in transferring electrons from Fe(II) to O2. Based on quenching experiments and electron paramagnetic resonance analysis, a one-step two-electron transfer mechanism was proposed for O2 reduction during S-Fe3O4 oxygenation, and surface-bound rather than free center dot OH were identified as the primary reactive oxygen species. The center dot OH from S-Fe3O4 oxygenation was shown to be efficient in degradation of DOM. Overall, these results suggested that sulfidation-oxidation can accelerate the electron storage and transfer in Fe3O4 for dark center dot OH production, having an important impact on the carbon cycling in subsurface environments
Co-occurrence of organophosphate diesters and organophosphate triesters in daily household products: Potential emission and possible human health risk
No full textEight paired organophosphate diesters (Di-OPs) and organophosphate triesters (Tri-OPs) were investigated in wipes from analytical instruments and 47 material samples related to household products, including textiles, electrical/electronic devices, building/ decoration materials and children's products. The total concentrations of Di-OPs ranged in 3577-95551 ng/m(2) in the wipes and limit of detection-23002 ng/g in the materials. The Tri-OPs concentrations varied significantly in the ranges of 107218-1756892 ng/m(2) and 2.13-503149 ng/g, respectively. Four industrial Di-OPs were detected in > 65% of the studied samples suggesting their direct application in the studied materials. Furthermore, we demonstrated for the first time that four non-industrial Di-OPs, e.g., bis(2-chloroethyl) phosphate, bis(1-chloro-2-propyl) phosphate, bis(1,3-dichloro-2-propyl) phosphate, and bis(butoxyethyl) phosphate, identified as degradation products of their respective Tri-OPs were also detected in these studied samples, which might act as important emission sources of Di-OPs in indoor environments. We estimated the burden of Di-OPs and Tri-OPs in a typical residential house and instrumental room, which both exhibited important contributions from furniture, building and decoration materials, and electrical/electronic devices. Limit health risk was posed to local people via air inhalation
Position-specific carbon isotopes of propane in coal systems in China
No full textEvaluating the origin and fate of hydrocarbons holds significance in many fields, such as energy, geology, astrobiology, biosphere, and environment. However, challenges arise in many cases owing to the limitations of conventional methods. Intramolecular isotope analysis of propane is a new technique that offers the potential to provide insights into gas formation mechanisms; however, a comprehensive understanding of the method remains limited. Specifically, there is little knowledge about its ability to distinguish gases generated by source rocks deposited in similar sedimentary environments such as coal and coaly mudstone. Therefore, this study was undertaken to investigate position-specific carbon isotopes of 40 propane samples from 15 coal-type gas accumulations across four basins in China (Sichuan, Ordos, Qaidam, and Songliao); additionally, clumped isotopologues of methane samples were also analyzed. These coal systems cover a wide range of thermal maturity (from marginally mature to over-mature) at various age strata from the Permian, Triassic, and Jurassic periods, to the Cretaceous period. Our results revealed that propane generated from coal and coaly mudstone differed greatly in intramolecular isotope compositions despite having similar bulk delta 13C3 values. Propane generated from coaly mudstone at a wide range of maturity had relatively more stable delta 13C values in both the central (delta 13Ccental) and terminal carbons (delta 13Cterminal), near the theory generation line of chain-alkane cracking in the plot of delta 13Cterminal vs. delta 13Ccental. However, propane generated from coal had higher stable delta 13Cterminal values and lower delta 13Ccentral values that progressively increased with maturity. Under cooling-down conditions, propane from overmature natural gases became extremely 13C-depleted in both the terminal and central positions, with Delta 13Ccentral (delta 13Ccentral minus delta 13Cterminal) values being as low as -10 parts per thousand, suggesting a partial origin of methane polymerization. Two propane samples from Cretaceous brown sandstone in the Songliao Basin exhibited an increase in both central and terminal carbons, suggesting that they may have surpassed chemical oxidation owing to highvalence Fe(Mn) oxides. These results indicate that intramolecular isotopes of propane can effectively differentiate dominant gas sources in a coal system with coal or coaly mudstone, as well as easily identify isotopic fractionation caused by post-generation processes, such as methane polymerization, mixing and chemical oxidation
Molecular-level transformations of biomass burning-derived water-soluble organic carbon during dark aqueous OH oxidation: Insights from absorption, fluorescence, high-performance size exclusion chromatography and high-resolution mass spectrometry analysis
No full textBiomass burning (BB) releases large amounts of water-soluble organic carbon (WSOC), which would undergo heterogenous oxidation processes that induce transformations in both molecular structures and compositions within BB WSOC. This study designed an aqueous oxidation initiated by OH radicals in the absence of light for WSOC extracted from smoke particles generated by burning of corn straw and fir wood. The BB WSOC was comprehensively characterized using a combination of UV-visible spectra, excitation-emission matrix fluorescence in conjunction with parallel factor analysis (EEM-PARAFAC), high-performance size exclusion chroma-tography (HPSEC), and high-resolution mass spectrometry (HRMS) analyses. Over the course of oxidation, both chromophores and fluorophores exhibited gradual decreases. Moreover, EEM-PARAFAC revealed a preferential degradation of larger-sized protein-like/phenol-like organic matters, accompanied by the accumulation and/or formation of humic-like substances in aged BB WSOC. HPSEC analysis showed notable changes in molecular weight (MW) distributions for both types of BB WSOC during oxidation. Specifically, high MW species (>1 kDa) displayed a tendency to form along with oxidation, possibly attributed to the formation of assemblies via intermolecular weak forces. After oxidation, evidence of CHO compound degradation and enrichment/formation of CHON compounds was observed for both types of BB WSOC. Remarkably, the resistant, degraded and produced molecules for BB WSOC were dominated by CHO (38-73 %) and lignin-like molecules (41-47 %), suggesting diverse responses to oxidation within these two groups. Furthermore, polyphenols experienced selective degradation, while CHON, aliphatic and poly-aromatic molecules tended to form during the oxidation process for both types of BB WSOC. In summary, this study provides a comprehensive understanding of the molecular-level transformations undergone by BB WSOC during dark aqueous OH oxidation. The findings significantly contribute to our insights into atmospheric evolution of BB WSOC, thereby playing a crucial role in accurately assessing their effects within climate models and informing policy decisions
Nitrogen isotopic compositions of organic-rich shales (-560 Ma) in the Chengkou region, South China: Implications for a stable and relatively large nitrate reservoir of the late Ediacaran ocean
No full textThe late Ediacaran period is a critical transitional period in Earth's history, marked by the evolution of the Ediacara biota (-574 to 538.8 Ma). The marine redox state and nutrient level, having a close relationship with bioevolution, can be reflected by sedimentary nitrogen isotopes (815N). Doushantuo Formation Member IV, a widespread organic-rich interval during this critical period of South China, may provide important clues for nitrogen (N) cycling. However, high-resolution 815N research on Member IV is still lacking. In this study, a drill core from the Chengkou sub-basin, with the well-developed Doushantuo Member IV, was carefully studied base on its N isotopic composition. The implications for the N cycling characteristics are discussed using a combination of proxies for bottom water redox conditions and basin openness. The total nitrogen (TN) concentrations (up to 0.79 wt%) of these organic-rich samples are substantially higher than those of other counterpart profiles. The TOC content shows a positive linear relationship with TN concentration, and a significant positive TNintercept (-0.21 wt%) represents the addition of inorganic N produced by the remineralization of sinking organic N. The high TN concentrations may also be due to the flourishing and enhanced burial of primary producers. The 815N value in the Doushantuo Member IV progressively decreases from -8.2%o to -3.2%o (from bottom to top), a result of the changes in basin openness and the enhancement of N2-fixation. Compilation shows the 815N and 813Corg values are approximately covariant, and both have significant temporal and spatial variations at this member of South China, indicating a strong heterogeneity in the water column redox environments and changes in the type of primary producers. A mode 815N value of 4%o indicates a stable and relatively large nitrate reservoir in the late Ediacaran ocean
Apatite Textures, Elemental and Isotopic Compositions Unmask the Homogenizing Process in Silicic Magma Chambers
No full textSilicic magmas are the most viscous of all magmas, however some granitic plutons display remarkably homogeneous compositions, which contradicts the hypothesis that mechanical mixing is the main homogenizing process in the magma chamber. Thus much remains controversial about the mechanisms responsible for the homogeneities of silicic plutons. Here, we present textural observations, elemental mapping, and in situ elemental and Nd-O isotopic data of apatites from the compositionally homogeneous Late Permian Yuanyang A-type granitic pluton (SW Yunnan, South China). Apatite grains display oscillatory chemical zonation and resorption-precipitation texture, suggesting incremental growth dominated by co-genetic magma batches injection. The intra-/inter-grain core to rim elemental and Nd-O isotopic variations imply crystal transfer and crystallization from different melt domains within the crystal mush. We propose that rejuvenation events associated with hotter cogenetic intermediate magma batch injection has induced crystal mush reactivation and convective stirring in silicic magma chambers, thereby homogenizing the entire reservoir.
Magma mixing between mafic and viscous felsic magmas is usually incomplete, forming heterogeneous structures and geochemical compositions in felsic magma bodies. However, some silicic magma bodies have homogeneous compositions and structures, such as the Late Permian Yuanyang A-type granites (YAGs) in southwestern South China, and the actual homogenizing process in silicic magma chamber is still unclear. Accessory apatite is ubiquitous in felsic plutons, whose growth zoning could reflect magma chamber evolution. Apatite grains collected from the YAGs show complex resorption-precipitation texture. Their core-rim oscillatory elemental and Nd-O isotopic variations suggest compositional perturbations of ambient magma, probably caused by the injection/mixing of multiple magma pulses. Accordingly, we propose that hot magma recharge could reactivate the crystal-mush, causing magma convection and stirring that gradually homogenized the silicic magma chamber.
The apatites from the compositionally homogeneous Yuanyang A-type granites are texturally and geochemically heterogeneousThe identified four apatite zoning domains documented magma replenishment, mixing and crystal mush reactivationMagma convection and stirring induced by magma batches injection are key to homogenizing the silicic magma chambe
The importance of photochemical loss to source analysis and ozone formation potential: Implications from in-situ observations of volatile organic compounds (VOCs) in Guangzhou, China
No full textThe chemical loss of volatile organic compounds (VOCs) is influenced by atmospheric and is closely related to the photochemical formation of ozone (O3). Therefore, research on the atmospheric chemical transformation of VOCs is essential to understand their contribution to O3 formation. This study collected data on photochemicalrelated atmospheric components and meteorological factors in spring at a typical comprehensive observation platform in Guangzhou, China. The photochemical age method was used to evaluate the loss of VOCs due to atmospheric photochemical transformation and to analyze the contribution of such transformation to the source apportionment of VOCs and to the ozone formation potential (OFP). The results show that the mean photochemical loss of total volatile organic compounds (TVOCs) during the observation period was 4.1 ppbv, accounting for approximately 15% of the initial TVOC content. Alkenes had the highest consumed concentration/ initial concentration (C/I ratio) of 37.3%. A comparison of the source apportionment results obtained using observational positive matrix factorization (Ob-PMF) and in situ positive matrix factorization (In-PMF) revealed that photochemical losses significantly affected VOCs emitted from industrial and biological sources. Furthermore, neglecting the photochemical loss of VOCs in PMF source apportionment could lead to an underestimation of the contribution of VOCs from industrial and biological sources. The calculated values of OFP under VOC loss (OFPC-VOCs) showed that OFPC-VOCs constituted approximately 30% of the OFP of the initial VOCs. 93.2% of the OFP was attributed to the photochemical loss of alkenes and aromatic hydrocarbons, indicating their significant influence on O3 formation. This study emphasizes the importance of fully considering the photochemical loss of VOCs for accurately assessing their sources and contributions to ozone pollution. It also provides theoretical support for formulating VOC emission reduction strategies in the Pearl River Delta region
Oxidation of Biogenic U(IV) in the Presence of Bioreduced Clay Minerals and Organic Ligands
No full textBioreduction of soluble U-(VI) to sparingly soluble U-(IV) is proposed as an effective approach to remediating uranium contamination. However, the stability of biogenic U-(IV) in natural environments remains unclear. We conducted U-(IV) reoxidation experiments following U-(VI) bioreduction in the presence of ubiquitous clay minerals and organic ligands. Bioreduced Fe-rich nontronite (rNAu-2) and Fe-poor montmorillonite (rSWy-2) enhanced U-(IV) oxidation through shuttling electrons between oxygen and U-(IV). Ethylenediaminetetraacetic acid (EDTA), citrate, and siderophore desferrioxamine B (DFOB) promoted U-(IV) oxidation via complexation with U-(IV). In the presence of both rNAu-2 and EDTA, the rate of U-(IV) oxidation was between those in the presence of rNAu-2 and EDTA, due to a clay/ligand-induced change of U-(IV) speciation. However, the rate of U-(IV) oxidation in other combinations of reduced clay and ligands was higher than their individual ones because both promoted U-(IV) oxidation. Unexpectedly, the copresence of rNAu-2/rSWy-2 and DFOB inhibited U-(IV) oxidation, possibly due to (1) blockage of the electron transport pathway by DFOB, (2) inability of DFOB-complexed Fe-(III) to oxidize U-(IV), and (3) stability of the U-(IV)-DFOB complex in the clay interlayers. These findings provide novel insights into the stability of U-(IV) in the environment and have important implications for the remediation of uranium contamination
Complex origins of naphthenic oils in the Junggar Basin, China: Biodegradation vs. non-biodegradation
No full textNaphthenic crude oils are scarce resources of great value. Their origins are generally considered to be related to biodegradation, which consumes paraffins and enriches naphthenes. However, other possible controls on the origins of the naphthenic oils remain insufficiently clear. To fill the knowledge gap, we conducted a case study in the Junggar Basin by using comprehensive two-dimensional gas chromatography-mass spectrometry for semi-quantitative analysis of naphthenes in combination with relevant organic geochemical data, and address its global implications by synthesizing the typical naphthenic oils discovered worldwide. It was found that the occurrence of naphthenic crude oils in the basin was not caused by biodegradation alone, while sedimentary paleoenvironments and source-rock biological inputs (i.e., indicative of organofacies) are important controlling factors. Naphthenic crude oils are mainly derived from dolomitic source rocks of the Permian Fengcheng Formation in the Mahu Sag of the northwestern basin, where the average naphthene content is 43.8 %, with an average naphthene/paraffin (N/P) ratio of 1.24. Source rocks were deposited in a reducing, hypersaline and stratified alkaline lake (0.75 0.23), with source-rock biological inputs being dominated by halophilic algae (steranes/hopanes > 1, C-28/C27-29-steranes > 40 %). In contrast, crude oils in the Jimusaer Sag of the southeastern basin are paraffinic-naphthenic with an average naphthene content of 24.8 % and an average N/P ratio of 0.75. Source rocks here were deposited in an anoxic-oxic lake of low salinity (1.05 < Pr/Ph < 1.59, 0.15 < gammacerane/C-30 alpha beta H < 0.18), and organic matter consists of mixed bacteria, algae, and terrigenous higher plants (steranes/hopanes < 1, C-28/C27-29-steranes < 40 %). Thermal maturity and biodegradation also control the composition of naphthenic oils. High thermal maturity promotes cracking of naphthenic groups, whereas moderate biodegradation (rank PM < 6) promotes naphthenic groups by preferentially catabolizing paraffins. Our results suggest that halophilic algae in strongly-reducing alkaline lakes provide important material for the generation of naphthenic oils in the Mahu Sag and the occurrence of naphthenic crude oils is not controlled solely by biodegradation; influencing factors are complex and vary between regions without universality. This may be the reason for their limited and sparse distribution worldwide
Soil biomass-related enzyme activity indicates minimal functional changes after 16 years of persistent drought treatment in a Mediterranean holm oak forest
No full textLong-term drought impacts soil microbial responses and enzymatic activity, affecting carbon budget and nutrient cycling in terrestrial ecosystems. We examined a Mediterranean holm oak forest subjected to 16 years of drought treatment to understand the effects on soil organic matter decomposition, nutrient cycling, and enzymatic activity. We compared potential and biomass-related (normalized to microbial biomass) soil enzyme activity with measurements taken 10 years earlier. Relationships between potential enzyme activity, soil moisture, temperature, nutrient availability, and plant/microbial activity were explored. The prolonged drought led to decreased potential activities of all enzymes, especially acid phosphatase, protease, and urease. However, biomass-related activities of protease, urease, and phosphatase were unaffected. Interestingly, biomass-related beta-glucosidase activity increased during dry seasons, indicating a functional adaptation for carbon acquisition during extreme dry conditions. The negative impact of drought on potential enzyme activity intensified over time, particularly during summer when drought intensity increased. Soil water availability, microbial biomass, and nutrient availability strongly influenced potential enzyme activity. Long-term drought and summer aridity led to increased substrate accumulation in the soil. However, no significant changes were observed in biomass-related activities of nitrogen and phosphorus-acquiring enzymes. This lack of change is likely attributed to a decrease in the absolute potential enzyme activity capacity, caused by a reduction in microbial biomass in drought-affected plots, thereby favoring substrate accumulation. Specific functional adaptations were observed, including increased carbon acquisition by soil microbes during extreme summer drought. Long-term water scarcity in water-limited ecosystems diminishes the system's capacity to acquire resources through enzyme production, impacting mineralization and nutrient dynamics. Future climate scenarios may entail reduced ecosystem-level mineralization, carbon and nitrogen shifts from plants to soil, compromising plant control over nutrients, and increasing the risk of resource loss through leaching and erosion