Guangzhou Institute of Geochemistry
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A Pb-free Sn-Bi alloy mount preparation method for secondary ion mass spectrometry (SIMS) analyses
No full textSample preparation is a critical step to achieve reliable in situ chemical analysis. Sample mounting technique with a tin-based alloy was developed in recent years, which is particularly useful for high-precision volatile analyses by secondary ion mass spectrometry (SIMS). However, the success of this technique is hindered by challenges, such as complex alloy preparation and potential Pb contamination. Herein, we introduce a new Sn-Bi alloy preparation method that may overcome these hurdles and assess its potential as a standard preparation method for in situ volatile and isotope analyses. This new alloy can be manufactured with commercially available pure tin and bismuth metal (atomic Sn : Bi = 42 : 58), and its production requires only a heating plate and clean containers. This ensures its high accessibility to laboratories worldwide. The Pb content of the alloy is dependent on the tin and bismuth used. The material (Sn and Bi) from three different manufacturers were evaluated in this study, resulting in the virtually Pb-free MAC alloy (Pb <0.2 mu g g(-1)). The SIMS U-Pb dating results of the zircon standards (Qinghu, Ple & scaron;ovice, and SA01) are consistent with the recommended values (within error). Furthermore, the mounted samples exhibit satisfactory relief on this alloy, suggesting that this alloy material is appropriate for the analysis of oxygen isotopes. The routine external precision of oxygen isotope ratios is better than 0.30 parts per thousand (2sd), on par with that obtained with epoxy mounts. The water background in the SIMS sample chamber can be recovered rapidly after sample transfer from the storage to the sample chamber. Hence, this tin-based alloy is suitable for sample mounting for SIMS volatile and isotope (incl. U-Pb) analyses
Biogenic silica dynamics in coastal wetland sediments: A key driver of silicon and carbon biogeochemical cycling
No full textBiogenic silica (biogenic Si) is a bioactive component crucial for the biogeochemical cycling of Si in terrestrial and aquatic ecosystems. Its formation and dissolution dynamics are intricately linked to carbon (C) cycling. However, knowledge about the source, composition, and factors controlling the distribution of biogenic Si in coastal wetland sedimentary environments is still limited. To address this lack of knowledge, we introduced a suite of geometric models for biogenic Si biovolume calculation and investigated biogenic Si assemblages, along with biogenic Si and biogenic Si-occluded C contents, in sediments from representative coastal wetlands along the west coast of Bohai Bay. Our analysis showed that sedimentary biogenic Si predominantly derived from phytoliths (78.1% +/- 5.8%), diatoms (18.2% +/- 4.8%), and sponge spicules (3.7% +/- 2.9%). Notably, phytolith assemblages were primarily composed of forms derived from the Poaceae family. The biogenic Si-occluded C content (0.035-1.870 g kg-1) within these wetland sediments was consistent across both sites, accounting for 0.97-5.71% of the total organic C pool. Structural equation modeling indicated that total organic C, pH, and amorphous aluminum oxides either directly or indirectly influenced the biogenic Si content in coastal wetlands sediments. These results demonstrate the critical role that biogenic Si plays in the Si biogeochemical cycle and provide valuable information that advances our understanding of the biogeochemical interactions between Si and C in coastal wetland ecosystems
New natural garnet reference materials for determining the oxidation state of iron in garnet using the electron microprobe flank method
No full textThe oxidation state of iron (e.g., Fe3+/Sigma Fe) in minerals is a direct proxy for the oxygen fugacity of magma and fluid, which plays a key role in the formation of various types of ore deposits. Although many techniques have been developed to determine the Fe3+/Sigma Fe ratio in minerals, the electron microprobe flank method is particularly notable for its easy accessibility and high efficiency. However, the application of this method is limited by a shortage of suitable calibration standards. In this study, we collected a series of natural, euhedral garnet grains and gem-quality garnet fragments, which were carefully crushed and separated under a binocular microscope. Following a detailed examination of their major element compositions and M & ouml;ssbauer spectroscopy measurements for their Fe3+/Sigma Fe ratios, we report ten new garnet samples (three belonging to the andradite-grossular series and seven to the almandine-pyrope-grossular series) that can be used as reference materials to calibrate the Fe3+/Sigma Fe ratio of garnet using the flank method. The andradite-grossular samples are highly enriched in Fe3+, exhibiting Fe3+/Sigma Fe ratios ranging from 0.89 +/- 0.03 to 1.00 +/- 0.03, while the almandine-pyrope-grossular samples contain minimal Fe3+ with Fe3+/Sigma Fe ratios ranging from 0.01 +/- 0.02 to 0.03 +/- 0.01. One andradite sample (And1902) and one almandine sample (Ald1906) were identified as ideal for determining the flank positions for Fe L alpha and Fe L beta. These two end-members, along with the other eight samples, can be employed to quantify the relationship between Fe L beta/L alpha at flank positions and the Fe2+ or Sigma Fe content. The results indicate that the Fe2+ contents and Fe3+/Sigma Fe ratios of the ten garnet samples align with those obtained through M & ouml;ssbauer spectroscopy, with an uncertainty of +/- 1 wt% for Fe2+ and +/- 0.05 for Fe3+/Sigma Fe, respectively. Consequently, these well-characterized natural garnet samples can serve as reliable reference materials when synthetic garnet standards are unavailable
Enhanced optical anisotropy of six-coordinated silica polymorphs <i>via</i> high-pressure hydrothermal treatment
No full textOptical anisotropy determines the performance of birefringent crystals, used in various photonic and optoelectronic instruments. High optical anisotropy often arises from broken crystal symmetry and preferential exciton direction, both of which are readily tuned by applying external stress. In this study, we investigated the birefringence of three silica polymorphs with distinct Si-O polyhedral arrangements via high-pressure hydrothermal treatment combined with polarized optical microscopy and first-principles calculations. Our findings revealed that the birefringence of ambient-stable quartz can be substantially enhanced by approximately 5 times through pressure-controlled polymorphism and doping, reaching up to 0.044 in rutile-type hydrous stishovite and 0.041 in CaCl2-type Al-doped hydrous post-stishovite. The enhanced optical anisotropy stems from the parallel chain-like structures featured in these dense six-coordinated silica. Pressure-induced phase transition may provide a predictive and controllable approach to improve the optical properties of Earth's abundant materials such as silica
Iron fertilization-induced deoxygenation of eastern equatorial Pacific Ocean intermediate waters during the Paleocene-Eocene thermal maximum
No full textThe Paleocene-Eocene thermal maximum (PETM), a transient period of global warming, is considered to be an important analog for future greenhouse conditions. It was accompanied by a significant carbon cycle perturbation. Although ocean deoxygenation across the PETM is reported widely, its mechanism in the open ocean remains uncertain. Here, we present magnetic and geochemical analyses of sediments from the eastern equatorial Pacific Ocean. We found that iron fertilization during the PETM by eolian dust and volcanic eruptions fueled eastern equatorial Pacific Ocean productivity. This process led to increased organic matter degradation and oxygen consumption in intermediate waters, leading to deoxygenation. Our findings suggest that iron fertilization could be an important driver of open-ocean oxygen loss, as a side effect of global warming
Inefficient nitrogen transport to the lower mantle by sediment subduction
No full textThe fate of sedimentary nitrogen during subduction is essential for understanding the origin of nitrogen in the deep Earth. Here we study the behavior of nitrogen in slab sediments during the phengite to K-hollandite transition at 10-12 GPa and 800-1100 degrees C. Phengite stability is extended by 1-3 GPa in the nitrogen (NH4+)-bearing system. The phengite-fluid partition coefficient of nitrogen is 0.031 at 10 GPa, and K-hollandite-fluid partition coefficients of nitrogen range from 0.008 to 0.064, showing a positive dependence on pressure but a negative dependence on temperature. The nitrogen partitioning data suggest that K-hollandite can only preserve similar to 43% and similar to 26% of the nitrogen from phengite during the phengite to K-hollandite transition along the cold and warm slab geotherms, respectively. Combined with the slab sedimentary nitrogen influx, we find that a maximum of similar to 1.5 x 10(8) kg/y of nitrogen, representing similar to 20% of the initial sedimentary nitrogen influx, could be transported by K-hollandite to the lower mantle. We conclude that slab sediments may have contributed less than 15% of the lower mantle nitrogen, most of which is probably of primordial origin
W-Fe isotopes argue against OIB-like basalts in Inner Mongolia originating from primordial peridotite mantle
No full textWhether Inner Mongolia OIB-like basalts originate from the modern upper mantle [e.g. depleted MORB mantle (DMM)] with recycled oceanic crust in the form of pyroxenite or ancient primordial mantle (lower mantle) dominated by peridotite remains unclear. This study presents high-precision W-Fe isotopic data for Late Cenozoic Chifeng basalts (CBs) in Inner Mongolia, NE China, along with their olivine compositions, to better constrain their petrogenesis. The modern mantle-like mu 182W values (mu 182W = - 3.2 +/- 3.8 to + 2.5 +/- 2.4 ppm) of the CBs indicate that they most likely originated from DMM rather than ancient primordial mantle. The CBs exhibit elevated fractional crystallization-corrected delta 56Fe values ranging from 0.09 to 0.16 parts per thousand, compared to those of primitive normal mid-ocean ridge basalts (N-MORBs; delta 56Fe = 0.03-0.07 parts per thousand). This argues against the notion that the CBs could be generated solely by the melting of DMM peridotite. The high delta 56Fe values of the CBs, coupled with their elevated olivine Fe/Mn ratios, suggest the involvement of pyroxenite in their mantle source. The absence of correlation between the Fe isotopes of CBs and Sr-Nd-Hf isotopes, along with their previously reported low delta 98/95Mo values and existing geophysical evidence, supports the idea that pyroxenite in the mantle source of the CBs was most likely generated by the reaction between DMM peridotite and recycled Pacific oceanic crust originating from the mantle transition zone beneath NE China. Therefore, we propose that the mantle source of Inner Mongolia basalts (e.g. CBs) is DMM with some recycled oceanic crust in the form of pyroxenite, without the involvement of ancient primordial mantle. Our study highlights that W-Fe isotopes of basalts can help to identify the nature of mantle source (especially the ancient primordial mantle) and offer valuable insights into mantle lithology and the causes of mantle heterogeneity both locally and globally
Polystyrene microplastics exposure: Disruption of intestinal barrier integrity and hepatic function in infant mice
No full textThe pervasive presence of microplastics (MPs) in infant formula and care products has emerged as a significant and underappreciated risk to public health. Notably, infants are at an elevated risk due to their underdeveloped intestinal defenses and liver detoxification capabilities, factors that could heighten their vulnerability to MPs. This study presents a comprehensive evaluation of the health implications linked to polystyrene microplastics (PSMPs) exposure during early life, examining both environmentally plausible and elevated levels. Based on histological analysis, in vivo imaging analysis, biochemical analysis and 16S rRNA sequencing results, our study found that oral PSMPs exposure in infant mice led to profound toxicological consequences, such as intestinal barrier impairment and hepatic injury, in a dose-dependent manner. Strikingly, even low ambient concentration of PSMPs (20 ppb) was sufficient to inflict considerable harm, disrupting the intestinal barrier, manifested that lessened mucus secretion, elevated iFABP level (276.50+10.73 pg/mL), decreased sIgA levels (0.60+0.03 mg/g), and pathological damage of intestinal tissues, allowing PSMPs accumulation and leakage into blood, inducing hepatotoxicity, such as increased TG levels (0.99+0.05 mmol/gprot) and lipid droplet accumulation. Furthermore, PSMPs exposure gives rise to aberrant bacterial colonization, dropping the abundance of probiotics as well as altering the abundance of pathogenic bacteria, which may contribute to the toxicity outcomes. The study underscores the critical need for vigilance regarding the insidious effects of PSMPs at environmental-relevant concentrations, especially in the context of infant exposure
Characterization and Sources of VOCs during PM<sub>2.5</sub> Pollution Periods in a Typical City of the Yangtze River Delta
No full textTo investigate the characteristics and sources of volatile organic compounds (VOCs) as well as their impacts on secondary organic aerosols (SOAs) formation during high-incidence periods of PM2.5 pollution, a field measurement was conducted in December 2019 in Hefei, a typical city of the Yangtze River Delta (YRD). During the whole process, the mixing ratios of VOCs were averaged as 21.1 +/- 15.9 ppb, with alkanes, alkenes, alkyne, and aromatics accounting for 59.9%, 15.3%, 15.0%, and 9.8% of the total VOCs, respectively. It is worth noting that the contributions of alkenes and alkyne increased significantly during PM2.5 pollution periods. Based on source apportionment via the positive matrix factorization (PMF) model, vehicle emissions, liquefied petroleum gas/natural gas (LPG/NG), and biomass/coal burning were the main sources of VOCs during the research in Hefei. During pollution periods, however, the contribution of biomass/coal burning to VOCs increased significantly, reaching as much as 47.6%. The calculated SOA formation potential (SOAFP) of VOCs was 0.38 +/- 1.04 mu g m(-3) (range: 0.04-7.30 mu g m(-3)), and aromatics were the dominant contributors, with a percentage of 96.8%. The source contributions showed that industrial emissions (49.1%) and vehicle emissions (28.3%) contributed the most to SOAFP during non-pollution periods, whereas the contribution of biomass/coal burning to SOA formation increased significantly (32.8%) during PM2.5 pollution periods. These findings suggest that reducing VOCs emissions from biomass/coal burning, vehicle, and industrial sources is a crucial approach for the effective control of SOA formation in Hefei, which provides a scientific basis for controlling PM2.5 pollution and improving air quality in the YRD region
Comprehensive evaluation of skin exposure to PBDEs and PCBs in diverse South China populations via dermal wipe sampling
No full textThis study analyzed skin wipe samples from the forehead, palm, forearm, and lower leg of 120 volunteers across different age groups-preschoolers, thresholders, middle-aged, and elderly-with each group comprising 30 individuals with a balanced sex ratio from a city in South China. The research aimed to assess the occurrence, concentration, and associated health risks of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) adsorbed onto human skin from environmental sources. We identified 13 PBDE congeners and 10 PCB congeners across all samples, with average detection frequencies of 48% for PBDEs and 16% for PCBs, with concentrations ranging from non-detectable (ND) to 4200 and ND to 2300 ng/m2, respectively. Skin concentrations of both PBDEs and PCBs decreased in the order of face > hand > arm > shank (ANOVA, P < 0.001), suggesting higher exposure to uncovered skin areas than to those covered by clothing, regardless of age or sex. The daily average dose of dermal (DAD(derm)) and oral (DAD(oral)) for PBDEs spanned from 7.0 x 10-4-0.19 ng/kg/d and ND-15 ng/kg/d, respectively, whereas the PCB exposure doses ranged from ND-7.8 ng/kg/d (DAD(derm)) and ND-2.0 ng/kg/d (DAD(oral)), respectively. Preschool children displayed notably higher DAD(oral) levels than the other groups (P < 0.0001), which was attributed to their more frequent hand-to-mouth activity. Preschool boys exhibiting a higher DADderm (P < 0.05) and both preschool boys and university women showing elevated DADoral levels (P < 0.01 and P < 0.05, respectively). Health risk assessments concluded that the carcinogenic risks from BDE209 and PCBs were within acceptable limits (10-4) for all sampled populations