Release Behavior of Liquid Crystal Monomers from Waste Smartphone Screens: Occurrence, Distribution, and Mechanistic Modeling.

Liquid crystal display (LCD) screens can release many organic pollutants into the indoor environment, including liquid crystal monomers (LCMs), which have been proposed as a novel class of emerging pollutants. Knowing the release pathways and mechanisms of LCMs from various components of LCD screens is important to accurately assess the LCM release and reveal their environmental transport behavior and fate in the ambient environment. A total of 47, 43, and 33 out of 64 target LCMs were detected in three disassembled parts of waste smartphone screens, including the LCM layer (LL), light guide plate (LGP), and screen protector (SP), respectively. Correlation analysis confirmed LL was the source of LCMs detected in LGP and SP. The emission factors of LCMs from waste screen, SP, and LGP parts were estimated as 2.38 × 10-3, 1.36 × 10-3, and 1.02 × 10-3, respectively. A mechanism model was developed to describe the release behaviors of LCMs from waste screens, where three characteristics parameters of released LCMs, including average mass proportion (AP), predicted subcooled vapor pressures (PL), and octanol-air partitioning coefficients (Koa), involving coexistence of absorption and adsorption mechanisms, could control the diffusion-partitioning. The released LCMs in LGP could reach diffusion-partition equilibrium more quickly than those in SP, indicating that LCM release could be mainly governed through SP diffusions.

Identification of Transformation Products of Organic UV Filters by Photooxidation and Their Differential Estrogenicity Assessment.

Organic ultraviolet filters (OUVFs) are extensively released into aquatic environments, where they undergo complex phototransformation. However, there is little knowledge regarding their transformation products (TPs) and associated endocrine disruption potentials. In the present study, we characterized the chemical and toxicological profiles of TPs for two common OUVFs, oxybenzone (BP3) and ethylhexyl methoxycinnamate (EHMC), by photooxidation under environmentally relevant conditions. It is hypothesized that TPs of the tested OUVFs will show varied estrogenicity at different reaction times. High-resolution liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) identified 17 TPs of 7 m/z for BP-3 and 13 TPs of 8 m/z for EHMC at confidence levels ≤2. Five novel TPs of 2 m/z were reported for the first time with structure-diagnostic MS/MS spectra. Estrogenicity assessment using the MCF-7-luc cell line showed discrepant estrogenic activities exhibited by OUVF-TPs over time. Specifically, BP3-TPs exhibited significantly greater estrogenicity than the parent at several reaction times, whereas EHMC-TPs displayed fluctuating estrogenicity with a declining trend. Correlation analysis coupled with molecular docking simulations further suggested several TPs of BP3 as potential endocrine disruptive compounds. These findings underscore the necessity of considering mixtures during chemical testing and risk assessment and highlight the potentially greater risks associated with post-transformation cocktails.

Complex impacts of hydraulic fracturing return fluids on soil microbial community respiration, structure and functional potentials.

The consequences of soils exposed to hydraulic fracturing (HF) return fluid, often collectively termed flowback and produced water (FPW), are poorly understood, even though soils are a common receptor of FPW spills. Here, we investigate the impacts on soil microbiota exposed to FPW collected from the Montney Formation of western Canada. We measured soil respiration, microbial community structure and functional potentials under FPW exposure across a range of concentrations, exposure time and soil types (luvisol and chernozem). We find that soil type governs microbial community response upon FPW exposure. Within each soil, FPW exposure led to reduced biotic soil respiration, and shifted microbial community structure and functional potentials. We detect substantially higher species richness and more unique functional genes in FPW-exposed soils than in FPW-unexposed soils, with metagenome-assembled genomes (e.g. Marinobacter persicus) from luvisol soil exposed to concentrated FPW being most similar to genomes from HF/FPW sites. Our data demonstrate the complex impacts of microbial communities following FPW exposure and highlight the site-specific effects in evaluation of spills and agricultural reuse of FPW on the normal soil functions.

Target, Nontarget, and Suspect Screening and Temporal Trends of Per- and Polyfluoroalkyl Substances in Marine Mammals from the South China Sea.

Per- and polyfluoroalkyl substances (PFASs) have been manufactured and widely used for over 60 years. Currently, there are thousands of marketed PFASs, but only dozens of them are routinely monitored. This work involved target, nontarget, and suspect screening of PFASs in the liver of Indo-Pacific humpback dolphin (Sousa chinensis) and finless porpoise (Neophocaena phocaenoides), two resident marine mammals in the South China Sea, stranded between 2012 and 2018. Among the 21 target PFASs, perfluorooctane sulfonate and 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2 Cl-PFESA) predominated in the samples, accounting for 46 and 30% of the total PFASs, respectively. Significantly higher total target PFAS concentrations (p < 0.05) were found in dolphin liver samples [3.23 × 103 ± 2.63 × 103 ng/g dry weight (dw)] than in porpoise liver samples (2.63 × 103 ± 1.10 × 103 ng/g dw). Significant increasing temporal trends (p < 0.05) were found in the concentrations of two emerging PFASs, perfluoroethylcyclohexane sulfonate and 2,3,3,3-tetrafluoro-2-propanoate in porpoises, indicating increasing pollution by these emerging PFASs. Forty-four PFASs from 9 classes were additionally identified by nontarget and suspect screening, among which 15 compounds were reported for the first time in marine mammals. A primary risk assessment showed that the emerging PFAS 6:2 Cl-PFESA could have possible adverse effects in terms of reproductive injury potential on most of the investigated cetaceans.

Comparison of the Hydraulic Fracturing Water Cycle in China and North America: A Critical Review.

There is considerable debate about the sustainability of the hydraulic fracturing (HF) water cycle in North America. Recently, this debate has expanded to China, where HF activities continue to grow. Here, we provide a critical review of the HF water cycle in China, including water withdrawal practices and flowback and produced water (FPW) management and their environmental impacts, with a comprehensive comparison to the U.S. and Canada (North America). Water stress in arid regions, as well as water management challenges, FPW contamination of aquatic and soil systems, and induced seismicity are all impacts of the HF water cycle in China, the U.S., and Canada. In light of experience gained in North America, standardized practices for analyzing and reporting FPW chemistry and microbiology in China are needed to inform its efficient and safe treatment, discharge and reuse, and identification of potential contaminants. Additionally, conducting ecotoxicological studies is an essential next step to fully reveal the impacts of accidental FPW releases into aquatic and soil ecosystems in China. From a policy perspective, the development of China's unconventional resources lags behind North America's in terms of overall regulation, especially with regard to water withdrawal, FPW management, and routine monitoring. Our study suggests that common environmental risks exist within the world's two largest HF regions, and practices used in North America may help prevent or mitigate adverse effects in China.

Removal of biological effects of organic pollutants in municipal wastewater by a novel advanced oxidation system.

The Advanced Oxidation System (AOS) is a novel electrochemical advanced oxidation process that effectively removes bacterial and organic contaminants from wastewater. However, potential formation of secondary oxidative species may pose additional hazards to aquatic organisms living in the receiving water affected by the post-treatment effluent. The effect of exposure to AOS treated water, especially the potential long-term effects on aquatic organisms, requires further investigation to demonstrate both efficacy and safety of this process. To examine the potential adverse effects of AOS treated water, three aquatic species, including daphnia, zebrafish, and rainbow trout, were exposed to treated and untreated municipal wastewater effluent (MWE) spiked with one of two model organic contaminants, benzo[a]pyrene (BaP) and 17ß-estradiol (E2). The results indicated AOS treatment significantly reduced the adverse effects caused by exposure to MWE and model organic contaminants to baseline levels in daphnia (reduced fecundity), zebrafish embryo (elevated EROD activity), and rainbow trout (elevated plasma vitellogenin). The Ames test was also conducted to confirm the removal efficacy of carcinogenicity of BaP spiked in MWE. Overall, this study demonstrated that AOS treatment is a promising and environmentally friendly technology for wastewater treatment, remediation, and management.

Developmental Toxicity of the Organic Fraction from Hydraulic Fracturing Flowback and Produced Waters to Early Life Stages of Zebrafish ( Danio rerio).

Hydraulic fracturing (HF) has emerged as a major recovery method of unconventional oil and gas reservoirs and concerns have been raised regarding the environmental impact of releases of Flowback and Produced Water (FPW) to aquatic ecosystems. To investigate potential effects of HF-FPW on fish embryo development, HF-FPW samples were collected from two different wells and the organic fractions were isolated from both aqueous and particle phases to eliminate the confounding effects of high salinity. Each organic extract was characterized by non-target analysis with HPLC-Orbitrap-MS, with targeted analysis for polycyclic aromatic hydrocarbons provided as markers of petroleum-affected water. The organic profiles differed between samples, including PAHs and alkyl PAHs, and major substances identified by non-target analysis included polyethylene glycols, alkyl ethoxylates, octylphenol ethoxylates, and other high molecular weight (C49-79) ethylene oxide polymeric material. Zebrafish embryos were exposed to various concentrations of FPW organic extracts to investigate acute (7-day) and developmental toxicity in early life stages. The acute toxicity (LD50) of the extracted FPW fractions ranged from 2.8× to 26× the original organic content. Each extracted FPW fraction significantly increased spinal malformation, pericardial edema, and delayed hatch in exposed embryos and altered the expression of a suite of target genes related to biotransformation, oxidative stress, and endocrine-mediation in developing zebrafish embryos. These results provide novel information on the variation of organic profiles and developmental toxicity among different sources and fractions of HF-FPWs.

Ammonia-independent sodium uptake mediated by Na+ channels and NHEs in the freshwater ribbon leech Nephelopsis obscura.

Freshwater organisms actively take up ions from their environment to counter diffusive ion losses due to inhabiting hypo-osmotic environments. The mechanisms behind active Na+ uptake are quite well understood in freshwater teleosts; however, the mechanisms employed by invertebrates are not. Pharmacological and molecular approaches were used to investigate Na+ uptake mechanisms and their link to ammonia excretion in the ribbon leech Nephelopsis obscura At the molecular level, we identified a Na+ channel and a Na+/H+ exchanger (NHE) in the skin of N. obscura, where the NHE was up-regulated when acclimated to extremely low [Na+] (0.05 mmol l-1, pH 5) conditions. Additionally, we found that leeches in dilute freshwater environments use both a vacuolar-type H+-ATPase (VHA)-assisted uptake via a Na+ channel and a NHE-based mechanisms for Na+ uptake. Immunolocalization of VHA and Na+/K+-ATPase (NKA) indicated at least two cell types present within leech skin, VHA+ and VHA- cells, where the VHA+ cells are probably involved in Na+ uptake. NKA was present throughout the epithelium. We also found that increasing ammonia excretion by decreasing water pH, ammonia loading leeches or exposing leeches to high environmental ammonia does not affect Na+ uptake, providing indications that an NHE-Rh metabolon is not present and that ammonia excretion and Na+ uptake are not coupled in N. obscura To our knowledge, this is the first study showing the mechanisms of Na+ uptake and their links to ammonia excretion in a freshwater invertebrate, where results suggest an ammonia-independent Na+ uptake mechanism relying on both Na+ channels and NHEs.

Effects on Biotransformation, Oxidative Stress, and Endocrine Disruption in Rainbow Trout (Oncorhynchus mykiss) Exposed to Hydraulic Fracturing Flowback and Produced Water.

The effects of hydraulic fracturing (HF) flowback and produced water (HF-FPW), a complex saline mixture of injected HF fluids and deep formation water that return to the surface, was examined in rainbow trout (Oncorhynchus mykiss). Exposure to HF-FPWs resulted in significant induction of ethoxyresorufin-O-deethylase (EROD) activity in both liver and gill tissues. Increased lipid peroxidation via oxidative stress was also detected by thiobarbituric acid reactive substances (TBARS) assay. The mRNA expressions of a battery of genes related to biotransformation, oxidative stress, and endocrine disruption were also measured using quantitative real-time polymerase chain reaction (Q-RT-PCR). The increased expression of cyp1a (2.49 ± 0.28-fold), udpgt (2.01 ± 0.31-fold), sod (1.67 ± 0.09-fold), and gpx (1.58 ± 0.10-fold) in raw sample exposure group (7.5%) indicated elevated metabolic enzyme activity, likely through the aryl hydrocarbon receptor pathway, and generation of reactive oxygen species. In addition, the elevated vtg and era2 expression demonstrated endocrine disrupting potential exerted by HF-FPW in rainbow trout. The overall results suggested HF-FPW could cause significant adverse effects on fish, and the organic contents might play the major role in its toxicity. Future studies are needed to help fully determine the toxic mechanism(s) of HF-FPW on freshwater fish, and aid in establishing monitoring, treatment, and remediation protocols for HF-FPW.

Sublethal and Reproductive Effects of Acute and Chronic Exposure to Flowback and Produced Water from Hydraulic Fracturing on the Water Flea Daphnia magna.

Hydraulic fracturing is an industrial process allowing for the extraction of gas or oil. To fracture the rocks, a proprietary mix of chemicals is injected under high pressure, which later returns to the surface as flowback and produced water (FPW). FPW is a complex chemical mixture consisting of trace metals, organic compounds, and often, high levels of salts. FPW toxicity to the model freshwater crustacean Daphnia magna was characterized utilizing acute (48 h median lethal concentrations; LC50) and chronic (21 day) exposures. A decrease in reproduction was observed, with a mean value of 18.5 neonates produced per replicate over a 21 day chronic exposure to 0.04% FPW, which was a significant decrease from the average of 64 neonates produced in the controls. The time to first brood was delayed in the highest FPW (0.04%) treatment. Neonates exhibited an LC50 of 0.19% of full-strength FPW, making them more sensitive than adults, which displayed an LC50 value of 0.75%. Quantitative PCR highlighted significant changes in expression of genes encoding xenobiotic metabolism (cyp4) and moulting (cut). This study is the first to characterize chronic FPW toxicity and will help with the development of environmental monitoring and risk assessment of FPW spills.

In vitro assessment of endocrine disrupting potential of naphthenic Acid fractions derived from oil sands-influenced water.

Oil sands-influenced process waters have been observed to cause reproductive effects and to induced CYP1A activity in fishes; however, little progress has been made in determining causative agents. Naphthenic acids (NAs) are the predominant organic compounds in process-affected waters, but due to the complexity of the mixture, it has been difficult to examine causal linkages in fishes. The aim of this study was to use in vitro assays specific to reproductive and CYP1A mechanisms to determine if specific acid extractable fractions of NAs obtained from oil sands-influenced water are active toward reproductive processes or interact with the Ah receptor responsible for CYP1A activity. NAs were extracted from aged oil sands-influenced waters by use of acid precipitation, and the mixture was fractionated into three acidic and one neutral fraction. The four fractions were examined for Ah receptor-mediated potency by use of the H4IIE-luc bioassay, effects on production of steroid hormones by use of the H295R steroidogenesis assay, and sex steroid receptor binding activity using the yeast estrogen screen and yeast androgen screen. The mixtures were characterized by high resolution mass spectrometry, (1)H nuclear magnetic resonance, and attenuated total reflectance infrared spectroscopy. The neutral fraction elicited Ah-receptor mediated activity after 24 h but not after 48 or 72 h. None of the fractions contained measurable levels of estrogen or androgen receptor agonists nor did they cause reductions in steroidogenesis. A number of fractions showed antiestrogenic or antiandrogenicity potency, with the neutral and main acidic fractions being the most potent. Neutral aromatic compounds are likely responsible for the CYP1A activity observed. Direct estrogenic, androgenic, or steroidogenic mechanisms are unlikely for NAs based on these results, but NAs act as potent antiandrogen or antiestrogens.

Interactions between microbial communities and polymers in hydraulic fracturing water cycle: A review.

Hydraulic fracturing (HF) has substantially boosted global unconventional hydrocarbon production but has also introduced various environmental and operational challenges. Understanding the interactions between abundant and diverse microbial communities and chemicals, particularly polymers used for proppant delivery, thickening, and friction reduction, in HF water cycles is crucial for addressing these challenges. This review primarily examined the recent studies conducted in China, an emerging area for HF activities, and comparatively examined studies from other regions. In China, polyacrylamide (PAM) and its derivatives products became key components in hydraulic fracturing fluid (HFF) for unconventional hydrocarbon development. The microbial diversity of unconventional HF water cycles in China was higher compared to North America, with frequent detection of taxa such as Shewanella, Marinobacter, and Desulfobacter. While biodegradation, biocorrosion, and biofouling were common issues across regions, the mechanisms underlying these microbe-polymer interactions differed substantially. Notably, in HF sites in the Sichuan Basin, the use of biocides gradually decreased its efficiency to mitigate adverse microbial activities. High-throughput sequencing proved to be a robust tool that could identify key bioindicators and biodegradation pathways, and help select optimal polymers and biocides, leading to more efficient HFF systems. The primary aim of this study is to raise awareness about the interactions between microorganisms and polymers, providing fresh insights that can inform decisions related to enhanced chemical use and biological control measures at HF sites.

Self-motivated photoaging of microplastics by biochar-dissolved organic matter under different pyrolysis temperatures.

Dissolved organic matter (DOM) released from biochar (BDOM) can interact with microplastics (MPs) in the environment, inevitably affecting their environmental behaviour. Information regarding the influence of BDOM on MPs during photoaging and associated variations in the MP aging mechanism remains unclear. This study evaluated the effect of BDOM on the aging of polystyrene (PS) MPs. The results showed that among three pyrolysis temperatures, low-temperature BDOM significantly enhanced the photoaging process of PS MPs, with the smallest average particle size and highest carbonyl index value after 15 days of aging under light conditions. The DOM level decreased after 5 days, increased after 5-10 days, and stabilised after 15 d. BDOM accelerates PS MPs aging, leading to more DOM released from PS, which can be transformed into 1O2 via triplet-excited state (3DOM⁎ and 3PS⁎) to further enhance PS MPs aging, resulting in the realisation of the self-accelerated aging process of PS MPs. 1O2 plays a crucial role in the self-motivated accelerated aging process of PS MPs. These findings provide new insights into the effects of the DOM structure and composition on reactive oxygen species generation during MPs aging.

Plastic takeaway food containers may cause human intestinal damage in routine life usage: Microplastics formation and cytotoxic effect.

The microplastics and organic additives formed in routine use of plastic takeaway food containers may pose significant health risks. Thus, we collected plastic containers made of polystyrene, polypropylene, polyethylene terephthalate, polylactic acid and simulated two thermal usages, including hot water (I) and microwave treatments (M). Nile Red fluorescence staining was developed to improve accurate counting of microplastics with the aid of TEM and DLS analysis. The quantity of MPs released from thermal treatments was determined ranging from 285.7 thousand items/cm2 to 681.5 thousand items/cm2 in containers loaded with hot water with the following order: IPS>IPP>IPET>IPLA, while microwave treatment showed lower values ranging from 171.9 thousand items/cm2 to 301.6 thousand items/cm2. In vitro toxicity test using human intestinal epithelial Caco-2 cells indicated decrease of cell viability in raw leachate, resuspended MPs and supernatants, which might further lead to cell membrane rupture, ROS production, and decreased mitochondrial membrane potential. Moreover, the leachate inhibited the expression of key genes in the electron transport chain (ETC) process, disrupted energy metabolism. For the first time, we isolate the actually released microplastics and organic substances for in vitro toxicity testing, and demonstrate their potential impacts to human intestine. SYNOPSIS: Plastic take-out containers may release microplastics and organic substances during daily usage, both of which can cause individual and combined cytotoxic effects on human colon adenocarcinoma cells Caco-2.

Nanoplastics enhanced the developmental toxicity of aromatic disinfection byproducts to a marine polychaete at non-feeding early life stage.

Micro/nanoplastics can act as vectors for organic pollutants and enhance their toxicity, which has been attributed to the ingestion by organisms and the "Trojan horse effect". In this study, we disclosed a non-ingestion pathway for the toxicity enhancement effect of nanoplastics. Initially, the combined toxicity of polystyrene microplastics (40 µm) or nanoplastics (50 nm) with three disinfection byproducts (DBPs) to a marine polychaete, Platynereis dumerilii, was investigated. No toxic effect was observed for the micro/nanoplastics alone. The microplastics showed no effect on the toxicity of the three DBPs, whereas the nanoplastics significantly enhanced the toxicity of two aromatic DBPs when the polychaete was in its non-feeding early life stage throughout the exposure period. The microplastics showed no interaction with the P. dumerilii embryos, whereas the nanoplastics agglomerated strongly on the embryonic chorion and fully encapsulated the embryos. This could contribute to higher actual exposure concentrations in the microenvironment around the embryos, as the concentrations of the two aromatic DBPs on the nanoplastics were 1200 and 120 times higher than those in bulk solution. Our findings highlight an important and previously overlooked mechanism by which nanoplastics and organic pollutants, such as DBPs, pose a higher risk to marine species at their vulnerable early life stages. This study may contribute to a broader understanding of the environmental impacts of plastic pollution and underscore the necessity to mitigate their risks associated with DBPs.

Evolution of dissolved organic nitrogen chemistry during transportation to the marginal sea: Insights from nitrogen isotope and molecular composition analyses.

Estuaries are hotspots where terrestrially originated dissolved organic matter (DOM) is modified in molecular composition before entering marine environments. However, very few research has considered nitrogen (N) modifications of DOM molecules in estuaries, limiting our understanding of dissolved organic nitrogen (DON) cycling and the associated carbon cycling in estuaries. This study integrated optical, stable isotopes (δ15N and δ13C) and molecular composition (FT-ICR MS) to characterize the transformation of DOM in the Yangtze River Estuary. Both concentration of dissolved organic carbon (DOC) and DON decreased with increasing salinity, while their δ13C and δ15N increased with the increasing salinity. A significant positive correlation was found between δ15N and δ13C during the transportation of DOM to marginal seas, indicating that the behavior of both DOC and DON are primarily controlled by the mixing of freshwater and the seawater in the YRE. During the mixing process, the DON addition was observed using the conservative mixing curves. In the view of molecular composition, DOM molecules became more aromatic as the number of N atoms increased. Spearman correlations reveal that DOM molecules with fewer N atoms exhibited a higher enrichment in protein-like components, while those with more N atoms were more enriched in humic-like components. In addition, the δ15N and δ13C tended to increase as the N content of DOM decreased. Therefore, DON molecules with fewer N atoms were likely to be transformed into those with more N atoms based on the isotopic fractionation theory. This study establishes a linkage between the molecular composition and the δ15N of DOM, and discovers the N transformation pattern within DOM molecules during the transportation to marginal seas.

Risk assessment of e-waste - Liquid Crystal Monomers re-suspension caused by coastal dredging operations.

The Pearl River Estuary (PRE), one of the primary e-waste recycling centers in the world, has been suffering from the pollution of Liquid Crystal Monomers (LCMs), critical materials with persistent, bio-accumulative, and toxic substances used in electronic devices. It has been detected in seabed sediment with both high frequency and concentration near PRE - Hong Kong (HK) waters. In the same area, dredging operations with in-situ sediment have been frequently used in the last decades for coastal land reclamation projects. Dredging is known to cause a huge amount of sediment re-suspension into water columns, with potential damage to marine ecosystems and biodiversity. In this study, we proposed a new risk assessment strategy to estimate the secondary pollution due to the re-suspension sediment highly contaminated by LCMs. We formulate a robust and reliable probabilistic approach based on unsupervised machine learning and hydrodynamic and sediment transport numerical simulation. New risk indexes were also proposed to better quantify the impact of contaminated sediments. We applied the methodology to assess the potential impact of dredging operations in the PRE and Hong Kong waters on the local marine ecosystem. The results of the analysis showed how the potentially contaminated areas depended on the dredging locations.

Degradation of organic UV filters in the water environment: A concise review on the mechanism, toxicity, and technologies.

Organic ultraviolet filters (OUVFs) have been used globally for the past 20 years. Given that OUVFs can be quickly released from sunscreens applied on human skins, they have been frequently detected in aquatic environments and organisms. Some byproducts of OUVFs might be more recalcitrant and toxic than their parent compounds. To further assess the toxicity and potential risk of OUVFs' byproducts, it is necessary to determine the fate of OUVFs and identify their transformation products. This review summarizes and analyzes pertinent literature and reports in the field of OUVFs research. These published research works majorly focus on the degradation mechanisms of OUVFs in aquatic environments, their intermediates/byproducts, and chlorination reaction. Photodegradation (direct photolysis, self-sensitive photolysis and indirect photolysis) and biodegradation are the main transformation pathways of OUVFs through natural degradation. To remove residual OUVFs' pollutants from aqueous environments, novel physicochemical and biological approaches have been developed in recent years. Advanced oxidation, ultrasound, and bio-based technologies have been proven to eliminate OUVFs from wastewaters. In addition, the disinfection mechanism and the byproducts (DBPs) of various OUVFs in swimming pools are discussed in this review. Besides, knowledge gaps and future research directions in this field of study are also mentioned.

Dissolved organic matter composition and characteristics during extreme flood events in the Yangtze River Estuary.

Understanding the molecular composition and fate of dissolved organic matter (DOM) during transport in estuaries is essential for gaining a comprehensive understanding of its role within the global biogeochemical cycle. In 2020, a catastrophic flood occurred in the Yangtze River basin. It is currently unknown whether differences in hydrologic conditions due to extreme flooding will significantly impact the estuarine to oceanic DOM cycle. We determined the DOM composition in the Yangtze River estuary (YRE) to the East China Sea by using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) during the high discharge and the flood period (monthly average discharge was 1.2 times higher) on the same trajectory. Our study found that the composition of DOM is more diverse, and more DOM molecules were introduced to the YRE during the flood, especially in the freshwater end member. The result revealed that the DOM was significantly labile and unstable during the flood period. A total of 1840 unique molecular formulas were identified during the flood period, most of which were CHON, CHONS, and CHOS compounds, most likely resulting from anthropogenic inputs from upstream. Only 194 of these molecules were detected in the seawater end member after transporting to the sea, suggesting that the YRE served as a 'filter' of DOM. However, the flood enhances the transport of a group of terrigenous DOM, that is resistant to photodegradation and biodegradation. As a result, YRE experienced ~1.6 times higher terrigenous DOC flux than high discharge period. Considering the increased frequency of future floods, our study provides a preliminary basis for further research on how floods affect the composition and characteristics of estuarine DOM. With the help of the FT-ICR MS technique, we can now better understand the dynamic of DOM composition and characteristics in large river estuaries.

Coupling iron-carbon micro-electrolysis with persulfate advanced oxidation for hydraulic fracturing return fluid treatment.

Improving the sustainability of the hydraulic fracturing water cycle of unconventional oil and gas development needs an advanced water treatment that can efferently treat flowback and produced water (FPW). In this study, we developed a robust two-stage process that combines flocculation, and iron-carbon micro-electrolysis plus sodium persulfate (ICEPS) advanced oxidation to treat field-based FPW from the Sulige tight gas field, China. Influencing factors and optimal conditions of the flocculation-ICEPS process were investigated. The flocculation-ICEPS system at optimal conditions sufficiently removed the total organic contents (95.71%), suspended solids (92.4%), and chroma (97.5%), but the reaction stoichiometric efficiency (RSE) value was generally less than 5%. The particles and chroma were effectively removed by flocculation, and the organic contents was mainly removed by the ICEPS system. Fourier-transform infrared spectroscopy (FTIR) analysis was performed to track the changes in FPW chemical compositions through the oxidation of the ICEPS process. Multiple analyses demonstrated that PS was involved in the activation of Fe oxides and hydroxides accreted on the surface of the ICE system for FPW treatment, which led to increasing organics removal rate of the ICEPS system compared to the conventional ICE system. Our study suggests that the flocculation-ICEPS system is a promising FPW treatment process, which provides technical and mechanistic foundations for further field application.