Identifying Candidate Persistent, Mobile, and Toxic (PMT) and Very Persistent and Very Mobile (vPvM) Substances in Shale Gas Drilling Fluids by Combining Nontarget Analysis and Machine Learning Model

Shale gas extraction has raised environmental concerns on regional water resources. Horizontal drilling is a process in which drilling fluids containing complex organic and inorganic chemicals are intensively applied. Accidental spill and improper disposal of drilling fluids and related wastes might pose risks to surrounding groundwater environment. Given regional ground water quality, persistent, mobile, and toxic (PMT) and very persistent and very mobile (vPvM) substances should be of particular attention. However, recent research rarely focused on chemical compositions of drilling fluids, and the harmful PMT/vPvM substances in drilling fluids remain unknown. In this study, we utilized a nontarget screening strategy to detect and identify the organic compounds in drilling fluids collected in southwest China. Specifically, a total number of 371 compounds were detected in drilling fluids, and the main fraction of the compounds was alicyclic compounds. Later, an original machine learning model developed by us was applied to identify the candidate PMT/vPvM substances among the detected organic compounds. Our study identified 29 candidate PMT/vPvM substances, thus providing a list of prioritized substances for early warning and risk assessment of regional groundwater contamination

Identifying Candidate Persistent, Mobile, and Toxic (PMT) and Very Persistent and Very Mobile (vPvM) Substances in Shale Gas Drilling Fluids by Combining Nontarget Analysis and Machine Learning Model

Shale gas extraction has raised environmental concerns on regional water resources. Horizontal drilling is a process in which drilling fluids containing complex organic and inorganic chemicals are intensively applied. Accidental spill and improper disposal of drilling fluids and related wastes might pose risks to surrounding groundwater environment. Given regional ground water quality, persistent, mobile, and toxic (PMT) and very persistent and very mobile (vPvM) substances should be of particular attention. However, recent research rarely focused on chemical compositions of drilling fluids, and the harmful PMT/vPvM substances in drilling fluids remain unknown. In this study, we utilized a nontarget screening strategy to detect and identify the organic compounds in drilling fluids collected in southwest China. Specifically, a total number of 371 compounds were detected in drilling fluids, and the main fraction of the compounds was alicyclic compounds. Later, an original machine learning model developed by us was applied to identify the candidate PMT/vPvM substances among the detected organic compounds. Our study identified 29 candidate PMT/vPvM substances, thus providing a list of prioritized substances for early warning and risk assessment of regional groundwater contamination

Table_1_Floral Scents and Fruit Aromas: Functions, Compositions, Biosynthesis, and Regulation.docx

Floral scents and fruit aromas are crucial volatile organic compounds (VOCs) in plants. They are used in defense mechanisms, along with mechanisms to attract pollinators and seed dispersers. In addition, they are economically important for the quality of crops, as well as quality in the perfume, cosmetics, food, drink, and pharmaceutical industries. Floral scents and fruit aromas share many volatile organic compounds in flowers and fruits. Volatile compounds are classified as terpenoids, phenylpropanoids/benzenoids, fatty acid derivatives, and amino acid derivatives. Many genes and transcription factors regulating the synthesis of volatiles have been discovered. In this review, we summarize recent progress in volatile function, composition, biosynthetic pathway, and metabolism regulation. We also discuss unresolved issues and research perspectives, providing insight into improvements and applications of plant VOCs.</p

Integrated Carbon and Chlorine Isotope Modeling: Applications to Chlorinated Aliphatic Hydrocarbons Dechlorination

We propose a self-consistent method to predict the evolution of carbon and chlorine isotope ratios during degradation of chlorinated hydrocarbons. The method treats explicitly the cleavage of isotopically different C–Cl bonds and thus considers, simultaneously, combined carbon–chlorine isotopologues. To illustrate the proposed modeling approach we focus on the reductive dehalogenation of chlorinated ethenes. We compare our method with the currently available approach, in which carbon and chlorine isotopologues are treated separately. The new approach provides an accurate description of dual-isotope effects regardless of the extent of the isotope fractionation and physical characteristics of the experimental system. We successfully applied the new approach to published experimental results on dehalogenation of chlorinated ethenes both in well-mixed systems and in situations where mass-transfer limitations control the overall rate of biodegradation. The advantages of our self-consistent dual isotope modeling approach proved to be most evident when isotope fractionation factors of carbon and chlorine differed significantly and for systems with mass-transfer limitations, where both physical and (bio)­chemical transformation processes affect the observed isotopic values

Table_2_Floral Scents and Fruit Aromas: Functions, Compositions, Biosynthesis, and Regulation.docx

Floral scents and fruit aromas are crucial volatile organic compounds (VOCs) in plants. They are used in defense mechanisms, along with mechanisms to attract pollinators and seed dispersers. In addition, they are economically important for the quality of crops, as well as quality in the perfume, cosmetics, food, drink, and pharmaceutical industries. Floral scents and fruit aromas share many volatile organic compounds in flowers and fruits. Volatile compounds are classified as terpenoids, phenylpropanoids/benzenoids, fatty acid derivatives, and amino acid derivatives. Many genes and transcription factors regulating the synthesis of volatiles have been discovered. In this review, we summarize recent progress in volatile function, composition, biosynthetic pathway, and metabolism regulation. We also discuss unresolved issues and research perspectives, providing insight into improvements and applications of plant VOCs.</p

In Situ Liquid Cell TEM Reveals Bridge-Induced Contact and Fusion of Au Nanocrystals in Aqueous Solution

During nanoparticle coalescence in aqueous solution, dehydration and initial contact of particles are critically important but poorly understood processes. In this work, we used in situ liquid-cell transmission electron microscopy to directly visualize the coalescence process of Au nanocrystals. It is found that the Au atomic nanobridge forms between adjacent nanocrystals that are separated by a ∼0.5 nm hydration layer. The nanobridge structure first induces initial contact of Au nanocrystals over their hydration layers and then surface diffusion and grain boundary migration to rearrange into a single nanocrystal. Classical density functional theory calculations and ab initio molecular dynamics simulations suggest that the formation of the nanobridge can be attributed to the accumulation of auric ions and a higher local supersaturation in the gap, which can promote dehydration, contact, and fusion of Au nanocrystals. The discovery of this multistep process advances our understanding of the nanoparticle coalescence mechanism in aqueous solutions

Chlorine Isotope Analysis of Organic Contaminants Using GC–qMS: Method Optimization and Comparison of Different Evaluation Schemes

Compound-specific online chlorine isotope analysis of chlorinated hydrocarbons was evaluated and validated using gas chromatography coupled to a regular quadrupole mass spectrometer (GC–qMS). This technique avoids tedious off-line sample pretreatments, but requires mathematical data analysis to derive chlorine isotope ratios from mass spectra. We compared existing evaluation schemes to calculate chlorine isotope ratios with those that we modified or newly proposed. We also tested systematically important experimental procedures such as external vs. internal referencing schemes, and instrumental settings including split ratio, ionization energy, and dwell times. To this end, headspace samples of tetrachloroethene (PCE), trichloroethene (TCE), and cis-dichloroethene (cDCE) at aqueous concentrations in the range of 20–500 μg/L (amount on-column range: 3.2–115 pmol) were analyzed using GC–qMS. The results (37Cl/35Cl ratios) showed satisfying to good precisions with relative standard deviations (n = 5) between 0.4‰ and 2.1‰. However, we found that the achievable precision considerably varies depending on the applied data evaluation scheme, the instrumental settings, and the analyte. A systematic evaluation of these factors allowed us to optimize the GC–qMS technique to determine chlorine isotope ratios of chlorinated organic contaminants

In Situ Liquid Cell TEM Reveals Bridge-Induced Contact and Fusion of Au Nanocrystals in Aqueous Solution

During nanoparticle coalescence in aqueous solution, dehydration and initial contact of particles are critically important but poorly understood processes. In this work, we used in situ liquid-cell transmission electron microscopy to directly visualize the coalescence process of Au nanocrystals. It is found that the Au atomic nanobridge forms between adjacent nanocrystals that are separated by a ∼0.5 nm hydration layer. The nanobridge structure first induces initial contact of Au nanocrystals over their hydration layers and then surface diffusion and grain boundary migration to rearrange into a single nanocrystal. Classical density functional theory calculations and ab initio molecular dynamics simulations suggest that the formation of the nanobridge can be attributed to the accumulation of auric ions and a higher local supersaturation in the gap, which can promote dehydration, contact, and fusion of Au nanocrystals. The discovery of this multistep process advances our understanding of the nanoparticle coalescence mechanism in aqueous solutions

In Situ Liquid Cell TEM Reveals Bridge-Induced Contact and Fusion of Au Nanocrystals in Aqueous Solution

During nanoparticle coalescence in aqueous solution, dehydration and initial contact of particles are critically important but poorly understood processes. In this work, we used in situ liquid-cell transmission electron microscopy to directly visualize the coalescence process of Au nanocrystals. It is found that the Au atomic nanobridge forms between adjacent nanocrystals that are separated by a ∼0.5 nm hydration layer. The nanobridge structure first induces initial contact of Au nanocrystals over their hydration layers and then surface diffusion and grain boundary migration to rearrange into a single nanocrystal. Classical density functional theory calculations and ab initio molecular dynamics simulations suggest that the formation of the nanobridge can be attributed to the accumulation of auric ions and a higher local supersaturation in the gap, which can promote dehydration, contact, and fusion of Au nanocrystals. The discovery of this multistep process advances our understanding of the nanoparticle coalescence mechanism in aqueous solutions