Guangzhou Institute of Geochemistry
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New measurements reveal a large contribution of nitrogenous molecules to ambient organic aerosol
No full textNitrogen is a significant element that constitutes ambient organic aerosol. Individual N-containing organic molecules are known to have both natural and anthropogenic sources and implicated in a wide-ranging health and environmental effects. Yet, unlike carbon (C), the total quantity of aerosol organic nitrogen (ON) remains largely unquantified, hindering a quantitative understanding of their major sources and impacts. Here, aerosol ON is quantitatively surveyed in hundreds of aerosol filter samples collected from sites of varying urban influence in China using our recently developed method that permits simple, and yet sensitive, simultaneous detection of inorganic and organic nitrogen. Annual average ON concentration was in the range of 0.4-1.4 mu g N m(-3), representing 17-31% of aerosol total nitrogen. Monte Carlo simulations constrained by paired ON and OC measurements suggest N-containing organic molecules contributed typically 37-50%, with a 95% confidence interval of [12%, 94%], to ambient organic aerosols. Source apportionment analysis reveals that biomass burning and secondary formation are dominant ON sources, accounting for 21-24% and similar to 30% of ON, respectively. Primary biological aerosol is also a significant source of ON (7-18%), with its contribution more prominent in non-urban atmospheres. The results provide the quantitative data for the extent of presence of organic nitrogenous aerosol and the origin of their major sources. Such data, we anticipate, would bring forth a breakthrough in our ability to describe and model organic aerosols and to assess their environmental impacts, such as atmospheric nitrogen nutrient inputs to ecosystems
Molybdenum Isotope Fingerprinting of Microbial Sulfate Reduction in Seep Carbonate Rocks
No full textUnderstanding the interaction between molybdenum (Mo) and organic matter during microbial sulfate reduction is critical for the use of Mo to reconstruct marine redox conditions throughout Earth's history. However, little is known about Mo isotope fractionation and how it relates to organic matter remineralization during microbial sulfate reduction. Here, we report Mo abundances and isotopic (delta 98Mo) compositions for bulk-rock, non-lithogenic and sequentially extracted fractions, including carbonate (carb), pyrite, and organic matter (OM), of seep carbonate rocks. Our data indicate that the difference between delta 98Mocarb and delta 98MoOM (Delta 98Mocarb-OM) displays significant variability in the studied samples, ranging between 0.72 and 1.01 parts per thousand. Remarkably, the obtained Delta 98Mocarb-OM values indicate correlative trends with stable carbon isotope ratios and bulk abundances of (a) total organic carbon, (b) Mo, and (c) pyrite in seep carbonates, which we interpret as reflecting sustained adsorption of isotopically light Mo onto organic matter during enhanced sulfate reduction. On this basis, we put forward the concept that Delta 98Mocarb-OM of authigenic carbonate rocks can be used as a measure of the intensity of sulfate reduction and for reconstructing past interactions between Mo and organic matter in marine sediments.
Molybdenum (Mo) is a useful element for reconstructing marine redox conditions throughout the Earth's history. The sequestration of Mo through sulfate-reducing bacterial activity acts as a significant pathway for Mo burial in the ocean. However, the impact of microbial sulfate reduction in Mo isotope fractionation remains unclear, preventing the understanding of the interaction between Mo and organic matter. We report Mo abundances and isotopic (delta 98Mo) compositions for different phases extracted from seep carbonate rock fractions, including carbonate (carb), pyrite, and organic matter (OM). Our findings indicate that organic matter tends to preferentially adsorb isotopically light Mo. The observed delta 98Mo difference between carbonate and organic matter fractions (Delta 98Mocarb-OM from 0.72 to 1.01 parts per thousand) represents the first report of the extent of Mo isotope fractionation during Mo adsorption to organic matter in marine environments. We attribute greater Delta 98Mocarb-OM offsets to the preferential adsorption of isotopically light Mo onto organic matter during enhanced sulfate reduction, and in turn put forward the idea that such offsets can be possibly used in the sedimentary record to trace the intensity of sulfate reduction and to reconstruct the past interaction between Mo and organic matter in marine sediments.
Organic matter tends to adsorb isotopically light Mo, resulting in low delta 98Mo values of organic matter in marine environments Isotopically light Mo is inferred to be preferentially adsorbed onto organic matter during enhanced sulfate reduction delta 98Mo offset between carbonate and organic phases in authigenic carbonates is promising to trace the past intensity of sulfate reductio
Geochemical signature of a deeply subducted slab in the source of post-collisional magmatism: A case study from the Western Tianshan NW China
No full textThe contributions of deeply subducted slabs to post-collisional magmatism are poorly constrained. Here, we present a study of the post-collisional, Early Permian (ca. 279 Ma), Hamisite basalts from the Western Tianshan NW China to trace the geochemical fingerprints of deeply subducted slab. The Hamisite basalts have arc -like trace element patterns but high Nb/Ta ratios (18.4-23.0). They have slightly enriched Sr-Nd isotopic compositions (87Sr/86Sr = 0.7048-0.7052; epsilon Nd[t] = 2.02-3.85), which indicates that the basalts were derived from an enriched mantle source. Extremely low 67Li values (-5.76%0 to 0.20%0) imply the involvement of a deeply subducted slab (i.e., eclogites) in the source. Correlations among Nb/Ta and (Dy/Yb)N ratios, and rare earth element contents, indicate that the deeply subducted slab contained residual rutile and garnet but no epidote. Given that melting of eclogites requires an anomalously hot mantle source, we propose that mantle upwelling during post-collisional extension triggered melting of the deeply subducted slab. Our results indicate that melting of a deeply subducted slab can generate a metasomatized mantle source with high Nb/Ta ratios, which could be a hidden, high-Nb/Ta reservoir on Earth. Low 67Li values and high Nb/Ta ratios could be a fingerprint of recycling of a deeply subducted slab
Large scale exploration reveals rare taxa crucially shape microbial assembly in alkaline lake sediments
No full textAlkaline lakes are extreme environments inhabited by diverse microbial extremophiles. However, large-scale distribution patterns, environmental adaptations, community assembly, and evolutionary dynamics of microbial communities remain largely underexplored. This study investigated the characteristics of microbial communities on rare and abundant taxa in alkaline lake sediments in west and northwest China. We observed that abundant taxa varied significantly with geographical distance, while rare taxa remained unaffected by regional differences. The assembly process of abundant taxa was influenced by dispersal limitation, whilst rare taxa were predominantly driven by heterogeneous selection. Network analysis indicated that rare taxa as core species for community interactions and community stability. Rare taxa exhibited higher speciation and transition rate than abundant taxa, serving as a genetic reservoir and potential candidates to become abundance taxa, highlighting their crucial role in maintaining microbial diversity. These insights underscore the significant influence of rare taxa on ecosystem biodiversity and stability in alkaline lakes
Experimental constraints on Mg isotope fractionation during the aragonite-calcite transition and implications for seawater δ26Mg reconstruction
No full textThe linkage between the variation of the seawater Mg budget and the long-term carbon cycle can be elucidated by seawater Mg isotope composition (S26Mg). S 26 Mg). However, obtaining primary seawater S 26 Mg signatures from marine archives is challenging due to the widespread alteration of diagenesis. Aragonite, a common primary marine carbonate, can effectively record seawater S 26 Mg but is prone to alteration and transformation into calcite during early diagenesis. Therefore, a comprehensive understanding of Mg isotope behavior during the aragonite-calcite transition is essential to enhance the applicability of aragonite S 26 Mg. In this study, we investigate the variation of aragonite S 26 Mg during diagenesis with a limited supply of Mg by conducting a series of well-controlled aragonite-calcite transition experiments in a closed system. The experimental conditions encompass temperatures of 60 and 90 degrees C, the presence of Ca and Na in the solution, varying Na concentrations, as well as the presence of calcite seed. Results demonstrate that the significant decrease of bulk carbonate S 26 Mg is accompanied by a substantial amount of Mg released into the solution during the aragonite-calcite transition, and the amount of released Mg is controlled by fluid chemistry via altering Mg partitioning in calcite. Furthermore, Mg isotope fractionation during calcite precipitation is influenced by temperature, ionic strength, and the presence of calcite seed, while kinetics played a negligible role in our experiments. Combined with previous experiments, the temperature-dependent Mg isotope fractionation during calcite precipitation in unseeded experiments is Delta 26 Mg cal-sol = (-0.13 f 0.06) x 106/T2 6 /T 2 - (0.47 f 0.68). This fractionation is systematically higher than that of seeded experiments by 0.3-0.6 %o from 15 to 90 degrees C and can mainly be attributed to differences in surface free energy between homogeneous and heterogeneous calcite nucleation. These findings offer fundamental understandings of the Mg isotope behavior during the aragonite-calcite transformation, providing useful insights for interpreting the variation of S 26 Mg in experimental and natural carbonates and facilitating ancient seawater S 26 Mg reconstruction
Spatial distribution, trophic magnification, and risk assessment of per- and polyfluoroalkyl substances in Yangtze finless porpoise (<i>Neophocaena</i><i> asiaeorientalis</i><i> asiaeorientalis</i>): Risks of emerging alternatives
No full textThe Yangtze finless porpoise (YFP, Neophocaena asiaeorientalis asiaeorientalis) is the only freshwater cetacean found in China. However, per- and polyfluoroalkyl substances (PFASs) risks in YFPs remain unclear. In this study, legacy PFASs, their precursors and alternatives, were determined in YFP muscles (n = 32), liver (n = 29), kidney (n = 24), skin (n = 5), and blubbers (n = 25) collected from Poyang Lake (PL) and Yangtze River (YR) between 2017 and 2023. Perfluorooctane sulfonic acid (PFOS) was the predominant PFAS in all YFP tissues, with a median hepatic concentration of 1700 ng/g wet weight, which is higher than that in other finless porpoises worldwide. PFOS, chlorinated polyfluorinated ether sulfonates (Cl-PFESAs), and perfluoroalkane sulfonamides concentrations in YFP livers from PL were significantly higher than those from YR (p 1. Perfluoroheptane sulfonic acid had the highest BMF value (99), followed by 6:2 Cl-PFESA (94) and PFOS (81). The TMFmuscle and TMFliver values of the total PFASs were 3.4 and 6.6, respectively, and were significantly positively correlated with the fluorinated carbon chain length (p 1, which was higher than that of PFOS (48 %), suggesting a high hepatotoxicity of 6:2 Cl-PFESA to YFPs. Bioaccumulation and biotoxicity of legacy and emerging alternatives in aquatic organisms continue to be a concern, especially for underscoring the vulnerability of the long-lived and endangered species
Tracing semi-quantitatively the absorption and removal of organic pollutants in human hair based on secondary ion mass spectrometry
No full textHuman hair has become a promising non-invasive matrix in assessing exposure to environmental organic pollutants (OPs). However, exogenous contaminants, which were absorbed into the hair via sweat, sebum, and air particles/dust, could contribute to OP levels in hair and interfere with the precise exposure assessment. So far, the microscopic mechanisms underlying the absorption of exogenous OPs into hair remain inadequately understood. This study focused on the in-situ investigation of the diffusion processes of exogenous OPs into the hair structure using secondary ion mass spectrometry (SIMS) and isotopic tracer techniques. Results showed that the relative signal intensities of deuterium-labeled tris(1,3-dichloro-2-propyl) phosphate (TDCPP), 1-hydroxypyrene (1-OH-Pry), and bisphenol A (BPA) in the hair cortex were notably elevated after a 6-hour exposure. Diffusion coefficients of contaminants were related to their molecular weight, and absorption volumes to their water solubility and molecular structures. Exposure duration and solvent influenced the rate of diffusion and absorption volumes. The distribution of deuterium-labeled molecules in exposed hair samples after washing with two different solvents (acetone or water) was similar to that before washing. Our findings revealed the diffusion of OPs in hair cross-sections, indicating exogenous contributions to contaminants that are biologically incorporated into the hair
Variations of the atmospheric polycyclic aromatic hydrocarbon concentrations, sources, and health risk and the direct medical costs of lung cancer around the Bohai Sea against a background of pollution prevention and control in China
No full textThe Bohai Sea (BS) region, an area of China that is severely polluted with atmospheric polycyclic aromatic hydrocarbons (PAHs), has received wide attention in recent decades. To characterize the variations of the concentrations and sources of PAHs from June 2014 to May 2019, 15 PAH congeners (Sigma(15)PAHs) were measured in atmospheric samples (N=228) collected at 12 sites around the BS, and the health risk and direct medical costs associated with lung cancer caused by exposure to PAHs were also estimated. The annual daily average concentration of Sigma(15)PAHs was 56.78 +/- 4.75ng m(-3), which was dominated by low molecular weight PAHs (LMW-PAHs) containing three rings (58.7 +/- 7.8%). During the 5-year sampling period, the atmospheric Sigma(15)PAHs concentration reduced by 17.5% for the whole BS region, with an especially large drop of 51.7% observed in the tightly controlled area of Tianjin (TJ), which was mainly due to a decrease in the concentration of high molecular weight PAHs (HMW-PAHs) containing five or six rings. Generally, the concentration of Sigma(15)PAHs was highest in winter and lowest in summer, which can mainly be attributed to the change in LMW-PAH concentration. Based on the positive matrix factorization (PMF) model, PAHs in the BS region were mainly ascribed to coal combustion and biomass burning. The PAH contributions of coal combustion and motor vehicles showed different trends for the BS region (PAHs from coal combustion rose by 7.2% and PAHs from motor vehicles fell by 22.4%) and for TJ (PAHs from coal combustion fell by 12.6% and PAHs from motor vehicles rose by 6.9%). The incidence of lung cancer (ILCR) caused by exposure to atmospheric PAHs decreased by 74.1% and 91.6% from 2014 to 2018 in the BS region and in TJ, respectively. This was mainly due to the decrease in the concentration of highly toxic HMW-PAHs and was reflected in USD10.7 million of savings in direct medical costs of lung cancer caused by exposure to PAHs, which represent a decrease of 46.1% compared to the corresponding costs before air pollution prevention and control was implemented around the BS. There was an even higher reduction in medical costs of 54.5% in TJ. Hence, this study proves that implementing pollution prevention and control not only effectively reduced the concentration of pollutants and the risks caused by them, but it also significantly reduced the medical costs of diseases caused by the corresponding exposure
SIP-metagenomics reveals key drivers of rhizospheric Benzo[a]pyrene bioremediation via bioaugmentation with indigenous soil microbes☆
No full textRhizoremediation and bioaugmentation have proven effective in promoting benzo[a]pyrene (BaP) degradation in contaminated soils. However, the mechanism underlying bioaugmented rhizospheric BaP degradation with native microbes is poorly understood. In this study, an indigenous BaP degrader (Stenotrophomonas BaP-1) isolated from petroleum-contaminated soil was introduced into ryegrass rhizosphere to investigate the relationship between indigenous degraders and rhizospheric BaP degradation. Stable isotope probing and 16S rRNA gene amplicon sequencing subsequently revealed 15 BaP degraders, 8 of which were directly associated with BaP degradation including Bradyrhizobium and Streptomyces. Bioaugmentation with strain BaP-1 significantly enhanced rhizospheric BaP degradation and shaped the microbial community structure. A correlation of BaP degraders, BaP degradation efficiency, and functional genes identified active degraders and genes encoding polycyclic aromatic hydrocarbon-ring hydroxylating dioxygenase (PAH-RHD) genes as the primary drivers of rhizospheric BaP degradation. Furthermore, strain BaP-1 was shown to not only engage in BaP metabolism but also to increase the abundance of other BaP degraders and PAH-RHD genes, resulting in enhanced rhizospheric BaP degradation. Metagenomic and correlation analyses indicated a significant positive relationship between glyoxylate and dicarboxylate metabolism and BaP degradation, suggesting a role for these pathways in rhizospheric BaP biodegradation. By identifying BaP degraders and characterizing their metabolic characteristics within intricate microbial communities, our study offers valuable insights into the mechanisms of bioaugmented rhizoremediation with indigenous bacteria for high-molecular-weight PAHs in petroleum-contaminated soils
Metagenomics and Stable Isotopes Uncover the Augmented Sulfide-Driven Autotrophic Denitrification in a Seasonally Hypoxic, Sulfate-Abundant Reservoir
No full textThe mechanism governing sulfur cycling in nitrate reduction within sulfate-rich reservoirs during seasonal hypoxic conditions remains poorly understood. This study employs nitrogen and oxygen isotope fractionation in nitrate, along with metagenomic sequencing to elucidate the intricacies of the coupled sulfur oxidation and nitrate reduction process in the water column. In the Aha reservoir, a typical seasonally stratified water body, we observed the coexistence of denitrification, bacterial sulfide oxidation, and bacterial sulfate reduction in hypoxic conditions. This is substantiated by the presence of abundant N/S-related genes (nosZ and aprAB/dsrAB) and fluctuations in N/S species. The lower (15)epsilon(NO3)/(18)epsilon(NO3) ratio (0.60) observed in this study, compared to heterotrophic denitrification, strongly supports the occurrence of sulfur-driven denitrification. Furthermore, we found a robust positive correlation between the metabolic potential of bacterial sulfide oxidation and denitrification (p < 0.05), emphasizing the role of sulfide produced via sulfate reduction in enhancing denitrification. Sulfide-driven denitrification relied on & sum;S2- as the primary electron donor preferentially oxidized by denitrification. The pivotal genus, Sulfuritalea, emerged as a central player in both denitrification and sulfide oxidation processes in hypoxic water bodies. Our study provides compelling evidence that sulfides assume a critical role in regulating denitrification in hypoxic water within an ecosystem where their contribution to the overall nitrogen cycle was previously underestimated