Potential Role of the Anammoxosome in the Adaptation of Anammox Bacteria to Salinity Stress.

The underlying adaptative mechanisms of anammox bacteria to salt stress are still unclear. The potential role of the anammoxosome in modulating material and energy metabolism in response to salinity stress was investigated in this study. The results showed that anammox bacteria increased membrane fluidity and decreased mechanical properties by shortening the ladderane fatty acid chain length of anammoxosome in response to salinity shock, which led to the breakdown of the proton motive force driving ATP synthesis and retarded energy metabolism activity. Afterward, the fatty acid chain length and membrane properties were recovered to enhance the energy metabolic activity. The relative transmission electron microscopy (TEM) area proportion of anammoxosome decreased from 55.9 to 38.9% under salinity stress. The 3D imaging of the anammox bacteria based on Synchrotron soft X-ray tomography showed that the reduction in the relative volume proportion of the anammoxosome and the concave surfaces was induced by salinity stress, which led to the lower energy expenditure of the material transportation and provided more binding sites for enzymes. Therefore, anammox bacteria can modulate nitrogen and energy metabolism by changing the membrane properties and morphology of the anammoxosome in response to salinity stress. This study broadens the response mechanism of anammox bacteria to salinity stress.

The recovery potential and utilization pathway of chemical energy from wastewater pollutants during wastewater treatment in China.

Research on the potential for chemical energy recovery and the optimization of recovery pathways in different regions of China is still lacking. This study aimed to address this gap by evaluating the potential and optimize the utilization pathways for chemical energy recovery in various regions of China for achieving sustainable wastewater treatment. The results showed that the eastern and northeastern regions of China exhibited higher chemical energy levels under the existing operating conditions. Key factors affecting chemical energy recovery included chemical oxygen demand removal (ΔCOD), treatment scale, and specific energy consumption (µ) of wastewater treatment plants (WWTPs). Furthermore, the average improvement in the chemical energy recovery rate with an optimized utilization pathway was approximately 40% in the WWTPs. The use of the net-zero energy consumption (NZE) model proved effective in improving the chemical energy recovery potential, with an average reduction of greenhouse gas (GHG) emissions reaching next to 95% in the investigated WWTPs.

MRI as an assessment tool for prognostic risk stratification of endometrial carcinoma patients based on molecular classification.

BACKGROUND: Non-invasive risk stratification for patients with endometrial carcinoma (EC) is important for developing personalised treatment plans. Our study aimed to explore the ability of quantitative MRI parameters to predict the risk stratification of EC patients based on molecular classification. METHODS: Fifty-three patients with histologically proven EC who underwent pelvic MRI and surgical treatment at our hospital between January 2020 and August 2022 were assessed. The tumour volume (TV) and uterine volume (UV) were estimated with the ellipsoid formula and used to calculate the tumour volume ratio (TVR). The mean apparent diffusion coefficient (ADC) of the tumour was measured on a workstation. Quantitative MRI parameters were compared among different risk groups via unpaired Student's t-tests or Mann-Whitney's U-tests. RESULTS: The TV and TVR were significantly different between the low- and high-risk groups (p < 0.001), and cut-off values of 5342 mm3 and 0.055 allowed the differentiation of the high-risk group from the low-risk group, with 77% and 85% sensitivity and 78% and 78% specificity, respectively. There was a significant difference in the ADC between the two groups (p = 0.026), and a cut-off value of 0.65 × 10-3 mm2/s allowed differentiation of the risk groups, with 93% sensitivity and 39% specificity. CONCLUSIONS: Quantitative MRI parameters such as the TV, TVR and ADC may be helpful in preoperatively assessing the risk stratification of patients with EC based on molecular classification.

For patients with endometrial carcinoma (EC), it is important to assess the risk stratification based on molecular classification for developing treatment plans, but risk stratification is obtained most accurately from postoperative samples. We used non-invasive and easily accessible quantitative parameters of magnetic resonance imaging for preoperatively evaluating the risk stratification in these patients. We found that the quantitative parameters may be helpful in preoperatively assessing the risk stratification of patients with EC on the basis of molecular classification.

Nanosecond pulsed cold atmospheric plasma jet suppresses proliferation and migration of human glioblastoma cells via apoptosis promotion and EMT inhibition.

Glioblastoma (GBM) is one of the most aggressive and challenging cancers to treat. Despite extensive research on dozens of cancer cells, including GBM, the effect of cold atmospheric plasma (CAP) on the invasive migration of GBM cells has received limited attention, and the underlying mechanisms remain poorly understood. This study aims to investigate the potential molecular mechanism of ns-CAPJ in inhibiting the invasive migration of human GBM cells. The findings indicate that ns-CAPJ significantly reduces GBM cell invasion and migration, and induces apoptosis in GBM cells. Further mechanistic studies demonstrate a direct correlation between the suppression of the epithelial-mesenchymal transition (EMT) signaling pathway and ns-CAPJ's inhibitory effect on GBM cell invasion and migration. Additionally, combined with the N-acetyl cysteine (NAC, a ROS inhibitor) assay, we found that the ROS stimulated by the ns-CAPJ plays an important role in suppressing the EMT process. This work is expected to provide new insight into understanding the molecular mechanisms of how ns-CAPJ inhibits the proliferation and migration of human GBM cells.

Effects of physiologic activities of plankton on CO2 flux in the Three Gorges Reservoir after rainfall during algal blooms.

The nutrient supply to the freshwater system may be changed by rainfall, which also encourages the cyclic succession of microorganisms. However, in a highly dynamic land-water reservoir, the microbial metabolic changes brought on by the changes of water nutrients following rainfall are not clearly documented. The study selected the Three Gorges Reservoir (TGR) backwater region during algal bloom seasons as the study area and time, and used the Biolog-EcoPlates technique to examine the heterotrophic metabolism conditions of the water before and after rain. The field monitoring assessed how biotic and abiotic variables affected CO2 flux at the water-air interface. The tests conducted in the laboratory investigated the water-integrated metabolic process was affected by post-rainfall environmental changes. The results showed that the average flux of CO2 at the water-air interface before rainfall was -489.17 ± 506.66 mg·(m2·d)-1, while the average CO2 flux reached 393.35 ± 793.49 mg·(m2·d)-1 after rainfall. This is mostly explained by the heterotrophic metabolic variability of plankton in response to changes in the aqueous environment brought on by precipitation. These discoveries help us better understand how biological metabolisms after rain affect the CO2 flux at the water-air interface and reservoir greenhouse gas (GHG) emission equivalents can be evaluated more accurately.

Effect of food-to-microorganisms ratio on aerobic granular sludge settleability: Microbial community, potential roles and sequential responses of extracellular proteins and polysaccharides.

The food-to-microorganism ratio (F/M) is an important parameter in wastewater biotreatment that significantly affects the granulation and settleability of aerobic granular sludge (AGS). Hence, understanding the long-term effects and internal mechanisms of F/M on AGS settling performance is essential. This study investigated the relationship between F/M and the sludge volume index (SVI) within a range of 0.23-2.50 kgCOD/(kgMLVSS·d). Thiothrix and Candidatus_Competibacter were identified as two dominant bacterial genera influencing AGS settling performance. With F/M increased from 0.27 kgCOD/(kgMLVSS·d) to 1.53 kgCOD/(kgMLVSS·d), the abundance of Thiothrix significantly increased from 0.20% to 27.02%, and the hydrophobicity of extracellular proteins (PN) decreased, which collectively reduced AGS settling performance. However, under high-F/M conditions, the gel-like polysaccharides (PS) effectively retained the granular biomass by binding to the highly abundant Thiothrix (53.65%). The progressive increment in biomass led to a concomitant reduction in F/M, resulting in the recovery of AGS settleability. In addition, two-dimensional correlation infrared spectroscopy analysis revealed the preferential responses of PN and PS to the increase and decrease of F/M, and the content and characteristics of PN and PS played important roles in granular settling. The study provides insight into the microbial composition and the potential role of extracellular polymer substances in the AGS sedimentation behavior, offering valuable theoretical support for stable AGS operation.

Screening of Endocrine Disrupting Potential of Surface Waters via an Affinity-Based Biosensor in a Rural Community in the Yellow River Basin, China.

Overcoming the limitations of traditional analytical methods and developing technologies to continuously monitor environments and produce a comprehensive picture of potential endocrine-disrupting chemicals (EDCs) has been an ongoing challenge. Herein, we developed a portable nuclear receptor (NR)-based biosensor within 90 min to perform highly sensitive analyses of a broad range of EDCs in environmental water samples. Based on the specific binding of the fluorescence-labeled NRs with their ligands, the receptors were attached to the EDC-functionalized fiber surface by competing with EDCs in the samples. The biosensor emitted fluorescence due to the evanescent wave excitation, thereby resulting in a turn-off sensing mode. The biosensor showed a detection limit of 5 ng/L E2-binding activity equivalent (E2-BAE) and 93 ng/L T3-BAE. As a case study, the biosensor was used to map the estrogenic binding activities of surface waters obtained from a rural community in the Yellow River basin in China. When the results obtained were compared with those from the traditional yeast two-hybrid bioassay, a high correlation was observed. It is anticipated that the good universality and versatility exhibited by this biosensor for various EDCs, which is achieved by using different NRs, will significantly promote the continuous assessment of global EDCs.

The GHG mitigation opportunity of sludge management in China.

Greenhouse gas (GHG) mitigation in wastewater treatment sector is indispensable in China's carbon neutral target. As an important component of wastewater system, sludge generation is rapidly increased with the acceleration of urbanization in China. It is crucial to investigate the carbon footprint of various sludge management strategies and quantify the potential optimization of GHG reduction effect at national scale. Therefore, this study conducted a comprehensive analysis of sludge distribution and GHG profiles of various sludge systems. The overall dry sludge generation in China is 12.15 Mt, with spatial resolution at city level. Different sludge treatment options were categorized into four types: energy recovery, nutrient recovery (e.g. phosphorus and nitrogen), material valorisation (e.g. brick, biochar) and conventional disposal. With various sludge treatment options, the GHG profile of annual sludge management in China ranges from -35.86 Mt/year to 57.11 Mt/year. The best GHG mitigation can be achieved through energy recovery by co-incineration system and the greatest reduction opportunity is concentrated in highly urbanized regions, such as Yangtze River Delta, Pearl River Delta, and Beijing-Tianjin-Hebei urban agglomerations.

Freeze-thaw alternations accelerate plasticizers release and pose a risk for exposed organisms.

The application of plastic mulch films brings convenience to agricultural production, but also causes plastic waste that can be degraded into microplastics (MPs). However, little is known about the fate of plastic waste in agricultural ecosystem under freeze-thaw alternation in middle and high latitudes, as well as in highlands around the world. Whether the release of plasticizers, i.e. phthalate esters (PAEs), under such conditions would pose a potential risk to exposed organisms due to bioaccumulation is also unknown. To fill these data gaps, the agricultural fields in Liaoning of China with typical freeze-thaw alternation was selected as the study area. The transformation of plastic film was demonstrated by simulation freeze-thaw alternating from -30 to 20 â„ƒ. Soil samples were collected to investigate the patterns of MP composition, abundance, and distribution. Concurrently, the concentrations of two PAEs including bis(2-ethylhexyl) phthalate (DEHP) and diethyl phthalate (DEP) in soils were analyzed to provide information on the correlation between MPs abundance and PAEs concentrations as well as potential risks. The results showed that freeze-thaw alternating can accelerate the formation of MPs and release of PAEs from plastic waste. The abundance of MPs was positively correlated with the concentration of PAEs. Soil PAEs ranged from 3268 ± 213-6351 ± 110 µg/kg, indicating that over 40 % of the PAEs were transferred from plastic films to soils. Such residual amounts could pose risk for exposed organisms. Hence, the current study suggested that special concerns should be given to the release plasticizers in plastic waste of agricultural soils.

Pesticide fate at watershed scale: A new framework integrating multimedia behavior with hydrological processes.

Pesticide pollution has been one serious ecological and environmental issue due to its wide application, high toxicity, and complex environmental behavior. The fugacity model has been widely used to quantify biogeochemical cycles of pesticides due to its clear compartments, simple structure, and easy-accessible data. However, the lack of detailed hydrological processes limits its application for large and heterogeneous watershed. In present study, a new framework was proposed through integration of hydrological processes of SWAT and pesticide fate of fugacity model, and was applied into a typical watershed in the Three Gorges Reservoir Area, China. The results showed that surface runoff, soil erosion, and percolation varied spatiotemporally, which highlighted the importance of considering regional and seasonal heterogeneity of pesticide transport variables in the fugacity model. The amount of dichlorvos (DDV) and chlorpyrifos (CHP) in air, water, soil, and sediment phase were estimated as 0.26 kg, 19.77 kg, 1.06 × 104 kg, and 0.55 kg, respectively. Spatiotemporally, pesticide concentrations in water phase peaked in summer, while the middle and southwest regions of the watershed were identified as the hotspots for pesticide pollution. Compared with the classical model, the new framework provided technical support for the pesticide assessment at watershed scale with heterogeneous hydrological conditions, which can be easily extended to other watersheds, and integrated with other models for comprehensive agricultural management.

Adaptation mechanism of aerobic denitrifier Enterobacter cloacae strain HNR to short-term ZnO nanoparticle stresses.

The adaptation mechanism of a wild type (WT) and resistant type (Re) strain of the aerobic denitrifier Enterobacter cloacae strain HNR to short-term ZnO nanoparticle (NP) stresses was investigated. The results showed that Re maintained higher nitrite reductase (NIR) and nitrate reductase (NR) activities and showed lower increment of reactive oxygen species (ROS) than WT, under ZnO NP stresses. The affinity constant (KA) of WT to Zn2+ was 5.06 times that of Re, indicating that Re was more repulsive to Zn2+ released by ZnO NPs. Transcriptomic analysis revealed that the up-regulation of the nitrogen metabolism of Re helped maintain NIR and NR activities, that the enhancement of purine metabolism lowered the intracellular ROS increment, and that the up-regulation of cationic antimicrobial peptide resistance contributed to the lower KA of Re to Zn2+. These findings provided new insights into the adaptation mechanism of aerobic denitrifying bacteria to ZnO NPs.

The differences in characteristics of extracellular polymeric substances of flocs and anammox granules impacted aggregation.

Extracellular polymeric substances (EPS) are considered crucial components in the formation of microbial aggregates such as biofilms, flocs and granules. However, the role of EPS in sludge aggregation is still unclear. In this study, the differences in EPS characteristics of anammox granular sludge (AG), anammox floc sludge (AF) and activated floc sludge (AS) were investigated to clarify its role in granular aggregation. The results showed that the flocculation ability of EPS extracted from AG (62.8 ± 2.3%) was notably higher than that of EPS extracted from AF (35.7 ± 1.7%) and AS (17.3 ± 1.5%). The zeta potential and hydrophobicity of EPS showed the same tendency. In addition, the PN/PS ratio of AG, AF and AS were 7.66, 4.62 and 3.93, respectively. FTIR, XPS and 3D-EEM fluorescence spectra results revealed that anammox granular sludge has a higher ratio of hydrophobic groups, α-helixs/(ß-sheets and random coils), intermolecular hydrogen bonds, and aromatic amino acids, and a lower ratio of electronegative groups. Anammox granular sludge exhibited high aggregation ability, because its EPS had higher zeta potential, hydrophobicity and intermolecular hydrogen bond ratio. This work provides a better understanding of the high aggregation ability of anammox granules and a theoretical basis for improving granules proportion and retention ability of microbes in reactor system.

Insight into the role of exopolysaccharide in determining the structural stability of aerobic granular sludge.

Extracellular polymeric substances (EPS) have a critical contribution to the stability of aerobic granular sludge (AGS), but the mechanism and details of EPS composition and function are far from clear. This work investigated the contribution of exopolysaccharide (PS) to maintaining the structural stability of AGS. The results revealed that PS hydrolysis induced by α-amylase, dextranase and cellulase significantly decreased the granular stability, whereas a substantial content reduction of extracellular protein (PN) was also observed. It was also found that hydrolysis of PS led to a decrease of sludge hydrophobicity, granular gel mechanical strength by 14.09 %, 38.67 %, respectively, and an increase of surface free energy by 49.59 %, which is not conducive to granular stability. Through fluorescent staining, existence of large amounts of PS and PN conjugates in EPS matrix was verified. It was proposed that these conjugates with PS as skeleton (PS-PN) dominate granular stability by affecting hydrophobicity interactions and hydrogen bonds system, which are two important parameters to gel properties, constituting a crucial finding of this work. This study offers an supplementation of EPS system theory and granular stability mechanism.

Exploring the feasibility of sewage treatment by algal-bacterial consortia.

Current biological wastewater treatment is energy intensive. The application of algal-bacterial consortia to treat wastewater has recently attracted considerable attention because mechanical aeration is unnecessary. Therefore, algal-bacterial bioreactors are emerging as alternatives to activated sludge-based bioprocesses. Most studies have used a plate substratum to support the growth of algal-bacterial biofilms, which results in low reactor efficiencies. Usually, 2-10 days are required for targeted pollutant removal effects. Substratum structures can significantly influence reactor efficiencies. Indeed, substratum-free biofilms (granules) generally achieve high reactor efficiencies that rapidly form. 7-12 h are sufficient for a high-level pollutant removal efficiency. However, granule stability must be validated during long-term experiments (>1 year) involving real wastewater. In addition, the application of algal-bacterial membrane bioreactors represents a novel treatment approach. In membrane bioreactors, good reactor efficiencies and stabilities can be achieved. However, the maximum capacity of algal-bacterial membrane bioreactors requires further investigation. In addition, an accurate model for pollutant removal kinetics in algal-bacterial reactors is not yet available but is necessary for reactor control and up-scaling. The microbial and physical structures of algal-bacterial biofilms require more studies to clarify the system. Finally, the operational costs of algal-bacterial systems must be kept low in order to enhance their potential for sewage treatment at large scales. Good illumination control and recycling biomass for biodiesel or methane production could be applied to reducing the operation cost.

Evaluating the effects of micro-zones of granular sludge on one-stage partial nitritation-anammox nitrogen removal.

The one-stage partial nitritation-anammox (PN-A) process is considered an efficient process for low-cost nitrogen removal. In this study, the nitrogen removal performance of different-sized granules in a one-stage PN-A reactor was studied. The total autotrophic nitrogen removal rate (TANRR) of the granular sludge increased as the granule size increased, and the TANRR of granular sludge with a radius larger than 500 µm reached 0.14 kgN kgVSS-1 d-1. High-throughput sequencing revealed that the abundance of ammonium-oxidizing bacteria and anaerobic ammonium-oxidizing (anammox) bacteria in granular sludge of different sizes differed, indicating that the bacterial community structure was affected by the granule size. The TANRR of different-sized granules was affected by the volumes of aerobic micro-zone and anaerobic micro-zone inside the granule. Appropriate micro-zone volumes inside the granules could be regulated by the dissolved oxygen (DO) concentration of the reactor, which are favourable for achieving a balance between partial nitritation and anammox and then satisfactory nitrogen removal. Small-volume variations in the range of micro-zones have a significant influence on the balance between partial nitritation and anammox. The proper DO concentration required for different-sized granules to achieve better nitrogen removal differed. This study provides a novel perspective for understanding the effect of micro-zones of granular sludge on one-stage PN-A nitrogen removal.

Significant N2O emission from a high rate granular reactor for completely autotrophic nitrogen removal over nitrite.

Expanded granular sludge bed (EGSB) reactors were rarely applied for complete ammonium removal over nitrite. In this study, a high ammonium loading rate of 3677 mg N/L/d was achieved in an EGSB reactor. Approximately 5.5-8.5% of influent ammonium was converted to nitrous oxide (N2O) that is a potent greenhouse gas. Moreover, the percentage increased linearly with the increase in ammonium load. A model well matched the reactor dynamics. The model indicated that hydroxylamine (NH2OH) oxidation contributed to over 40% of produced N2O, and denitrification by ammonium oxidizing bacteria contributed to N2O emission significantly. Furthermore, the model suggests that a low oxygen concentration can result in a low N2O emission at the cost of a slightly low ammonium removal rate while influent organic matter play a minor role in reducing N2O emission. This study shows that EGSB reactors are effective in ammonium removal. In addition, the emission of N2O is significant.

New insights into nitrous oxide emissions in a single-stage CANON process coupled with denitrification: thermodynamics and nitrogen transformation.

The dynamic characteristics of N2O emissions and nitrogen transformation in a sequencing batch biofilm reactor (SBBR) using the completely autotrophic nitrogen removal over nitrite (CANON) process coupled with denitrification were investigated via 15N isotope tracing and thermodynamic analysis. The results indicate that the Gibbs free energy (ΔG) values of N2O production by the nitrifier denitrification and heterotrophic denitrification reactions were greater than that of NH2OH oxidation, indicating that N2O was easier to produce via either nitrifier and heterotrophic denitrification than via NH2OH oxidation. Ammonia-oxidizing bacteria (AOB) denitrification exhibited a higher fs 0 (the fraction of electron-donor electrons utilized for cell synthesis) than NH2OH oxidation. Therefore, AOB preferred the denitrification pathway because of its growth advantage when N2O was produced by the AOB. The N2O emissions by hydroxylamine oxidation, AOB denitrification and heterotrophic denitrification in the SBBRs using different C/N ratios account for 5.4-7.6%, 45.2-60.8% and 33.8-47.2% of the N2O produced, respectively. The total N2O emission with C/N ratios of 0, 0.67 and 1 was 228.04, 205.57 and 190.4 µg N2O-N·g-1VSS, respectively. The certain carbon sources aid in the reduction of N2O emissions in the process.

Underlying mechanisms of ANAMMOX bacteria adaptation to salinity stress.

Dealing with nitrogen-rich saline wastewater produced by industries remains challenging because of the inhibition of functional microorganisms by high salinity. The underlying mechanisms of anaerobic ammonium-oxidizing bacteria (AnAOB) exposed to salinity stress should be studied to investigate the potential of anaerobic ammonium oxidation (ANAMMOX) for applications in such wastewater. In this study, the total DNA from granular sludge was extracted from an expanded granular sludge bed (EGSB) reactor operated at 0, 15 and 30 g/L salinity and subjected to high-throughput sequencing. The nitrogen removal performance in the reactor could be maintained from 86.2 to 88.0% at less than 30 g/L salinity level. The microbial diversity in the reactor under saline conditions was lower than that under the salt-free condition. Three genera of AnAOB were detected in the reactor, and Candidatus Kuenenia was the most abundant. The predictive functional profiling based on the Clusters of Orthologous Groups of proteins (COGs) database showed that the inhibition of AnAOB under saline conditions was mainly characterised by the weakening of energy metabolism and intracellular repair. AnAOB might adapt to salinity stress by increasing their rigidity and intracellular osmotic pressure. The predictive functional profiling based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database revealed that the inhibition of AnAOB was mainly manifested by the weakening of intracellular carbohydrate and lipid metabolism, the blockage of intracellular energy supply and the reduction of membrane transport capacity. AnAOB might adapt to salinity stress by strengthening wall/membrane synthesis, essential cofactors (porphyrins) and energy productivity, enhancing intracellular material transformation and gene repair and changing its structure and group behaviour. The stability of the nitrogen removal performance could be maintained via the adaptation of AnAOB to salinity and their increased abundance.

Adsorption characteristics of nitrite on natural filter medium: Kinetic, equilibrium, and site energy distribution studies.

Nitrite is one of the world's major contaminants in drinking water resources, and granular anthracite is often used as filter medium in water treatment. In this study, the adsorption characteristics of nitrite on granular anthracite under various temperatures were investigated through adsorption kinetic, isotherm models, and site energy distribution theory. The adsorption of nitrite on granular anthracite was an endothermic reaction, while intraparticle diffusion was not the only rate control step. The adsorption could be well described by using pseudo-second-order and Langmuir-Freundlich equations. The adsorption capacity was 402.51 mg NO2--N kg-1 at 298 K, which could be significantly improved to 1380.1 mg NO2--N kg-1 when the temperature reached 308 K. Furthermore, nitrite ions first occupied the high-energy adsorption sites and then diffused to the low-energy adsorption sites on granular anthracite. There were more sites, including high-energy sites and low-energy sites, for nitrite adsorption at 308 K. Besides, the thickness of the boundary layer increased with the adsorption capacity improved at a higher temperature, and nitrite ions were adsorbed mainly through chemical mechanisms. Moreover, the neutral pH was helpful for the adsorption. The presence of co-existing ions could limit the adsorption and the effect followed the order of PO43- > CO32- > SO42- > NO3- > Cl-. The saturated anthracite could be effectively regenerated by 0.2 mol L-1 HCl solution. Therefore, the granular anthracite used as filter medium also has a possible application as a nitrite scavenger at the same time.

Effect of dissolved organic matters on adsorption and desorption behavior of heavy metals in a water-level-fluctuation zone of the Three Gorges Reservoir, China.

Operation of recession and inundation in Three Gorges Reservoir (TGR) revealed a potential contribution to the migration of heavy metals in soil and fluvial systems, thus led to negative ecological impacts. The work herein investigated the concentration and speciation of three typical heavy metals (Cd, Cr and Cu) in a water-level-fluctuation zone of TGR, as well as simulated the adsorption and desorption behavior of heavy metals on soils, which aimed at elucidating the fate of heavy metals in this special area. Field investigation revealed that water level fluctuation greatly enabled the migration of heavy metals to inner or upper soil layers. Laboratory experiments showed that adsorption of Cd(II) was a chemical process and dissolved organic matters (DOM) in soils strengthened the combination of Cd(II) to soil surface which inhibited the desorption process. Cr(VI) was physically adsorbed and readily to be desorbed. DOM enabled deposition of Cr(VI) in soils. Cation exchange was dominate mechanism in Cu(II) adsorption process, whereas DOM presented positive effects on desorption of Cu(II). The results presented in this study would provide basic theory for scientific research in TGR.