Guangzhou Institute of Geochemistry
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Clay minerals inhibit the release of Cd(II) during the phase transformation of Cd(II)-ferrihydrite coprecipitates
No full textClay minerals and iron (hydr)oxides are important geosorbents in controlling the migration of heavy metal cations in the environment. Despite the widespread occurrence of clay minerals/iron (hydr)oxides composites, their complex mutual effects on the fate of heavy metal cations are not well recognized. In this work, we investigated the effect of clay minerals on the redistribution of Cd(II) during the phase transformation of ferrihydrite containing coprecipitated Cd(II) (Cd-Fh). Three systems were considered: i.e., Cd-Fh, Cd-Fh/kaolinite composite, and Cd-Fh/montmorillonite composite. Our results showed that the transformation of Fh into goethite and hematite caused the release of Cd(II), while the presence of kaolinite and montmorillonite inhibited the phase transformation of Fh and the release of Cd(II), with montmorillonite being more effective in these process. Multiple factors contributed to the reduced release of Cd(II), including the retarded transformation of Fh, the buffering of solution pH, and the re-adsorption of the released Cd(II). Our findings show that clay minerals have multiple effects in reducing the release of heavy metal cations from Fh during its transformatio
Composite of gum arabic and halloysite as a bio-based acidic catalyst for efficient synthesis of 5-hydroxymthylfurfural
No full textA novel acidic bio-based composite has been synthesized via covalent conjugation of two acidic natural compounds, i.e. halloysite clay mineral and Gum Arabic. Measurement of the acidity of the composite confirmed that its acidity was higher than that of individual components. Halloysite-Gum Arabic composite was successfully applied as a biocompatible catalyst for the dehydration of fructose to 5-hydroxymthylfurfural. The reaction conditions were also optimized via Response Surface Method (RSM) and it was found that using 30 mg catalyst per 0.1 mmol fructose led to 99.2% product yield at 100 degrees C in 105 min. Gratifyingly, the as-prepared composite was recyclable for seven consecutive runs and only insignificant loss of activity was observed after each run. Notably, the recycled catalyst was structurally and morphologically stable
Composite of gum arabic and halloysite as a bio-based acidic catalyst for efficient synthesis of 5-hydroxymthylfurfural
No full textA novel acidic bio-based composite has been synthesized via covalent conjugation of two acidic natural compounds, i.e. halloysite clay mineral and Gum Arabic. Measurement of the acidity of the composite confirmed that its acidity was higher than that of individual components. Halloysite-Gum Arabic composite was successfully applied as a biocompatible catalyst for the dehydration of fructose to 5-hydroxymthylfurfural. The reaction conditions were also optimized via Response Surface Method (RSM) and it was found that using 30 mg catalyst per 0.1 mmol fructose led to 99.2% product yield at 100 degrees C in 105 min. Gratifyingly, the as-prepared composite was recyclable for seven consecutive runs and only insignificant loss of activity was observed after each run. Notably, the recycled catalyst was structurally and morphologically stable
Nitrogen isotopes and geochemistry of the basal Datangpo Formation: Contrasting redox conditions in the upper and lower water columns during the Cryogenian interglaciation period
No full textThe late Neoproterozoic witnessed series of remarkable geological evolutions, including the Sturtian and Marinoan glaciation events during the Cryogenian. A stratified oceanic redox structure has been proposed for this period, and the dynamics of the deep water redox conditions have been well illustrated by trace metals and their isotopes. However, variations in the redox conditions of the upper water column have received much less attention. Sedimentary nitrogen isotopes (815N) are critical for reconstructing the redox conditions in the upper water columns of ancient oceans. Existing research on the N cycle during the Cryogenian period is scarce, and the majority of studied samples were collected from shallow and medium water depth facies. To address this paucity of studies, we conducted a high -resolution N isotope study in combination with Fe speciation and Mo concentration data from two deep -water sections of black shales in the basal Datangpo Formation in the Nanhua Basin, a typical organic -rich stratum deposited during the Cryogenian interglaciation period. While the trace metal proxies suggest a fluctuating euxinic-ferruginous bottom water column for the lower interval and a stable euxinic bottom water column for the upper interval, the redox conditions of the upper water column were relatively stable, as indicated by minimal changes in the recorded 815N values. Furthermore, the 815N values of black shales in the basal Datangpo Formation of the Nanhua Basin have a limited range (3.1%o - 5.8%o, average of 4.3%o, standard deviation (SD) = 0.5%o, n = 104) and show no water -depth gradient, indicating the presence of a relatively large and stable nitrate reservoir and a deep redox chemocline in the Nanhua Basin. The characteristic of the nitrate reservoir reflected by these 815N signals can be roughly analogized to the global interglacial ocean, although only the counterpart northeast Svalbard can be used for comparison. Therefore, the nitrate availability in the marine water column may have had little effect on animal radiation during the Cryogenian interglacial period. These findings help to clarify the N cycle in the Cryogenian Nanhua Basin and shed light on its significance on bioevolution
The occurrence and geochemical origin of 9-alkyl HDBTs substituted by long isoprenoid alkyl chains in crude oil
No full text1,1,4a,6-tetramethyl-9-alkyl-1,2,3,4,4a,9b-hexahydrodibenzo[b,d]thiophene (9-alkyl HDBT) was initially found in highly desulfurized diesel oils. This and related organic sulfur compounds (OSCs) have a special shielding structure that make them extremely resistant to hydrodesulfurization. The structure of 9-alkyl HDBTs is likely directly inherited from biological precursors related to terpenoids, but their origins have not been determined. In this study, OSCs were isolated from a low sulfur crude oil from the Junggar Basin in China by the methylation/ demethylation method and characterized by gas chromatography-mass spectrometry. A series of 9-alkyl HDBTs substituted with long isoprenoid alkyl chains were identified in the OSCs. Raney nickel desulfurization was conducted to assist the structural identification. The presence of 9-alkyl HDBTs with a beta-carotene carbon skeleton and the predominance in specific carbon numbers of alkyl-substituted 9-alkyl HDBTs support a carotenoid origin of such OSCs. Possible geochemical pathways are proposed for the formation of these OSCs via beta-carotene, involving processes such as sulfur incorporation, cyclization, aromatization, hydrogenation, and cleavage
Multimodal Model to Predict Tissue-to-Blood Partition Coefficients of Chemicals in Mammals and Fish
No full textTissue-to-blood partition coefficients (P-tb) are key parameters for assessing toxicokinetics of xenobiotics in organisms, yet their experimental data were lacking. Experimental methods for measuring P-tb values are inefficient, underscoring the urgent need for prediction models. However, most existing models failed to fully exploit P-tb data from diverse sources, and their applicability domain (AD) was limited. The current study developed a multimodal model capable of processing and integrating textual (categorical features) and numerical information (molecular descriptors/fingerprints) to simultaneously predict P-tb values across various species, tissues, blood matrices, and measurement methods. Artificial neural network algorithms with embedding layers were used for the multimodal modeling. The corresponding unimodal models were developed for comparison. Results showed that the multimodal model outperformed unimodal models. To enhance the reliability of the model, a method considering categorical features, weighted molecular similarity density, and weighted inconsistency in molecular activities of structure-activity landscapes was used to characterize the AD. The model constrained by the AD exhibited better prediction accuracy for the validation set, with the determination coefficient, root mean-square error, and mean absolute error being 0.843, 0.276, and 0.213 log units, respectively. The multimodal model coupled with the AD characterization can serve as an efficient tool for internal exposure assessment of chemicals
Contribution of Ship Emission to Volatile Organic Compounds Based on One-Year Monitoring at a Coastal Site in the Pearl River Delta Region
No full textShip emission impacts ambient air quality, especially in coastal regions, by emitting air pollutants such as fine particles, nitrogen oxides (NOx), and sulfur dioxide (SO2), yet its contributions to volatile organic compounds (VOCs) and the formation of secondary organic aerosol (SOA) and ozone (O3) are much less constrained with the challenge in distinguish ship emission from land diesel emission. In this study, we conducted a 1-year online measurement of VOCs with a 1-hr resolution at a coastal site in south China's Pearl River Delta region, which holds three of the world's top 10 container ports. The results revealed that C10-C12 n-alkanes, as typical diesel-related emission tracers, were significantly enhanced and strongly related to oceanic air masses. Receptor modeling revealed two diesel-related sources of land diesel emission and ship emission, which could be differentiated based on their source profiles, seasonal trends and air mass back trajectories. Ship emissions contributed 6.4%, 5.0%, and 13.6% of total VOC mixing ratios, ozone formation potentials (OFPs), and secondary organic aerosol formation potentials (SOAFPs), while these percentages were 3.4%, 14.7%, and 15.9% for land diesel emission, respectively. In particular, in July, ship emissions could contribute 21.7%, 14.6%, and 31.2% of VOCs, OFPs, and SOAFPs, respectively. Our results highlight the important contribution of diesel-related emission VOCs in forming O3 and SOA in coastal regions, and ship emission is a non-negligible source of VOCs, particularly after the strict control of land emission sources.
Ships emit pollutants like fine particles, nitrogen oxides (NOx), sulfur dioxide (SO2), and volatile organic compounds (VOCs), impacting significantly on air quality in coastal areas. Ship-emitted VOCs are potential precursors of secondary organic aerosol (SOA) and ozone (O3), yet its contribution to ambient VOCs even in coastal areas is highly uncertain based on bottom-up estimates. Meanwhile, observation-based source attribution often fails to successfully differentiate between land-based diesel emissions and ship emissions. Here we carried out a year-long online monitoring of VOCs at a coastal site in south China, to explore the contribution of ship emissions to VOCs by receptor modeling in consideration of air mass trajectories. We used concentration-weighted trajectory (CWT) and air mass cluster analysis for C10-C12 n-alkanes, which are typical diesel emission tracers, to distinguish ship emission from land-based diesel emission. Results revealed that ship emissions on average could accounted for 6.4% of total VOCs, 5.0% of ozone formation potentials, and 13.6% of secondary organic aerosol formation potential, and in particular, these percentages could reach 21.7%, 14.6%, and 31.2% in July. This study highlights the importance of reducing ship emissions to improve air quality in coastal regions.
One-year online monitoring of VOCs at a coastal site reveals relatively higher C10-C12 alkanes due to diesel-related emissionsShip and land-diesel emissions are differentiated based on air mass back trajectories and source profilesShip emissions contributed substantially to VOC mixing ratios, OFPs and SOAFPs especially in July when air masses were mostly from the ocea
Natural and anthropogenic controls on environmental change during the Holocene based on a multi-proxy record obtained from subalpine peatland in southern China
No full textThe interactions between past climate, human activity and environmental change in subtropical mountainous areas are poorly understood due to the lack of reliable records in South China. In this study, the evolution of the East Asian summer monsoon (EASM) during the Holocene, and the interactions between regional human activity and environmental change, were studied using multi-proxy records from a subalpine peat core recovered from South China. The chronology of this peat core has been well-constrained by 10 AMS 14C dates of peat stems. A series of proxy indicators, including carbon isotopes (delta 13C), loss on ignition (LOI), magnetic susceptibility (MS)
Stable Zirconium Isotopic Compositions of the Metasomatized Mantle
No full textMantle metasomatism, which affects the geochemical and lithological properties of the Earth, is crucial to the evolution and modification of the Earth's interior. Variations in chemical proxy of metasomatism, including high-field strength elements (HFSE, e.g., Zr-Ti isotopes and isovalent Zr-Hf), have been commonly utilized as a tool to unravel the processes associated with the evolution of the Earth. However, the impact of mantle metasomatism by diverse agents on the Zr isotopic compositions of metasomatized mantle remains poorly understood. Here we carried out high-precision double-spike delta 94/90Zr measurements for a suite of basalts, which were derived from the mantle sources metasomatized by typical metasomatic agents of fluid, silicate melt and carbonate melt originating from the deep mantle or recycled crustal materials. Mantle metasomatism results in lithological diversities within the mantle, ranging from hybridized peridotites to pyroxenite/eclogite and carbonated eclogite, which can significantly fractionate the isovalent HFSEs. However, our data show that these basalts have primitive mantle-like delta 94ZrNIST values (-0.033-0.043 parts per thousand), regardless of their superchondritic Zr/Hf. The primitive mantle-like delta 94ZrNIST, irrelevant to any proxy of metasomatism (e.g., Sr-Nd isotopes, Zr/Hf and La/Sm), indicate that mantle metasomatism and subsequence melting produce no measurable Zr isotopic variations in metasomatized mantle-derived basalts. The delta 94ZrNIST of basalts thus can be representative of the mean metasomatized mantle compositions. Combined with previously reported komatiites and oceanic basalts, we show that the Earth's mantle displays consistent delta 94ZrNIST (-0.013 +/- 0.053 parts per thousand), even if it has a secular dynamic evolution with the interaction between Earth's exterior and interior.
Mantle metasomatism has a significant impact on the geochemical and lithological properties of the Earth's interior. The chemical variations, including the high-field strength elements (HFSE), caused by this process, could provide key insights into such modification. However, the variation of Zr isotopes during mantle metasomatism remains enigmatic. Here, we analyzed the Zr isotopes of fresh basalts derived from mantle sources metasomatized by diverse metasomatic agents. We find that although mantle metasomatism leads to the substantial fractionation of Zr (Nb) from Hf (Ta), no measurable Zr isotopic variation occurs for metasomatized mantle-derived melts, as reflected by the homogeneous and primitive mantle-like Zr isotopic compositions of different samples. Combining our findings with previous data, we conclude that the Earth's mantle, from large-scale and secular perspectives, maintains a consistent Zr isotopic composition, although the Earth underwent complex and dynamic evolution.
A first comprehensive investigation of Zr isotopes of mantle metasomatized by diverse agents of fluid, silicate melt and carbonate melt Basalts derived from metasomatized mantle show variable radiogenic isotopes and trace element patterns, but limited Zr isotope variation The Earth's mantle exhibits consistent delta 94Zr, despite its secular dynamic evolution with interaction between Earth's exterior and interio
Toxicity and chemical characterization of shale gas wastewater discharged to the receiving water: Evidence from toxicity identification evaluation
No full textFlowback and produced water (FPW) generated from shale gas extraction is a complex mixture consisting of injected drilling fluid, deep formation water, and byproducts of downhole reactions. Limited knowledge is available regarding the impact of discharged FPW on surface water in China. With the development of shale gas exploitation, this emphasizes an urgent need for comprehensive assessments and stringent regulations to ensure the safe disposal of shale gas extraction-related wastewater. Herein, we explored potential impacts of treated shale gas wastewater discharged into a local river in southwest China through toxicity identification evaluation (TIE). Results revealed that organics and particulates significantly contributed to the overall toxicity of the treated FPW wastewater. Through target and suspect chemical analyses, various categories of organic contaminants were detected, including alkanes, aromatic hydrocarbons, biocides, phenols, and phthalates. Furthermore, non-target analysis uncovered the presence of surfactant-related contaminants in tissues of exposed organisms, but their contribution to the observed toxicity was unclear due to the lack of effect data for these compounds. Higher toxicity was found at the discharge point compared with upstream sites; however, the toxicity was rapidly mitigated due to dilution in the receiving river, posing little impact on downstream areas. Our study highlighted the importance of monitoring toxicity and water quality of FPW effluent even though dilution could be a viable approach when the water volume in the discharge was small