South China Institute Of Environmental Sciences

An arsenate reductase (Car1) from the Bacteroidetes species Rufibacter tibetensis 1351T was isolated from the Tibetan Plateau. The strain exhibits resistance to arsenite [As(III)] and arsenate [As(V)] and reduces As(V) to As(III). Here we shed light on the mechanism of enzymatic reduction by Car1. AlphaFold2 structure prediction, active site energy minimization, and steady‐state kinetics of wild‐type and mutant enzymes give insight into the catalytic mechanism. Car1 is structurally related to calcineurin‐like metallophosphoesterases (MPPs). It functions as a binuclear metal hydrolase with limited phosphatase activity, particularly relying on the divalent metal Ni²⁺. As an As(V) reductase, it displays metal promiscuity and is coupled to the thioredoxin redox cycle, requiring the participation of two cysteine residues, Cys74 and Cys76. These findings suggest that Car1 evolved from a common ancestor of extant phosphatases by incorporating a redox function into an existing MPP catalytic site. Its proposed mechanism of arsenate reduction involves Cys74 initiating a nucleophilic attack on arsenate, leading to the formation of a covalent intermediate. Next, a nucleophilic attack of Cys76 leads to the release of As(III) and the formation of a surface‐exposed Cys74‐Cys76 disulfide, ready for reduction by thioredoxin.

The discharge of electroplating wastewater, containing high concentrations of N-nitrosamines, poses significant risks to human health and aquatic ecosystems. Karst aquatic environment is easily impacted by N-nitrosamines due to the fragile surface ecosystem. However, it’s still unclear in understanding N-nitrosamine transformation in karst water systems. To explore the response and transport of nine N-nitrosamines in electroplating effluent within both karst surface water and groundwater, different river and groundwater samples were collected from both the upper and lower reaches of the effluent discharge areas in a typical karst industrial catchment in Southwest China. Results showed that the total average concentrations of N-nitrosamines (∑NAs) in electroplating effluent (1800 ng/L) was significantly higher than that in the receiving river water (130 ng/L) and groundwater (70 ng/L). The dynamic nature of karst aquifers resulted in comparable average concentrations of ∑NAs in groundwater (70 ng/L) and river water (79 ng/L) at this catchment. Based on the principal component analysis and multiple linear regression analysis, the electroplating effluent contributed 89% and 53% of N-nitrosamines to the river water and groundwater, respectively. The results based on the species sensitivity distribution model revealed N-nitrosodibutylamine as a particularly toxic compound to aquatic organisms. Furthermore, the average N-nitrosamine carcinogenic risk was significantly higher in lower groundwater reaches compared to upper reaches. This study represents a pioneering effort in considering specific N-nitrosamine properties in evaluating their toxicity and constructing species sensitivity curves. It underscores the significance of electroplating effluent as a primary N-nitrosamine source in aquatic environments, emphasizing their swift dissemination and significant accumulation in karst groundwater. Graphical abstract

Globally, the circular efficiency of biomass resources has become a priority due to the depletion and negative environmental impacts of fossil fuels. This study aimed to quantify the atmosphere-dependent combustion of Ganoderma lucidum (GL) biomass and its thermodynamic and kinetic parameters toward enhancing its circularity and transformability characteristics. The GL combustion occurred in the three stages of moisture removal, volatile release, and coke combustion. Combustion performance characteristics were more favorable in the N2/O2 atmosphere than in the CO2/O2 atmosphere under the same heating rates. The rising heating rate facilitated the release of volatiles. According to the model-free methods of Ozawa-Flynn-Wall and Kissinger–Akahira–Sunose, the activation energies essential for the primary reaction were 283.09 kJ/mol and 288.28 kJ/mol in the N2/O2 atmosphere and 233.09 kJ/mol and 235.64 kJ/mol in the CO2/O2 atmosphere. The gaseous products of the GL combustion included CH4, H2O, C = O, CO, CO2, NH3, C = C, and C–O(H). Ash prepared in both atmospheres exhibited a tendency for slag formation, with oxy-fuel combustion lowering its risk. This study thus provides a theoretical and practical basis for transforming GL residues into a sustainable energy source. Graphical abstract

The occurrence of microplastics in aquatic environments has attracted increasing interest from both the public and scientists, especially their migration behaviors. Although several environmental behaviors of microplastics have been studied, the issue of microplastic suspension and deposition in lake sediment–water systems remains to be elucidated. In this study, we built an indoor sediment–water system with input and output rivers that simulated the actual situations in lakes, and aimed to explore the suspension and deposition behavior of microplastics using eight group experiments. The abundance of microplastics in overlying water and sediments in different periods was analyzed, and the characteristics of hydrodynamic disturbance on microplastic suspension and deposition were identified. Importantly, the exchange of microplastics in sediments and water under dynamic flow conditions was assessed. The results showed that the middle-scale experiment designed in this study effectively simulated the dynamic transport process of microplastics in lakes, and the hydrodynamic force had a significant impact on the suspension and deposition behaviors of microplastics. The average abundance of polystyrene, polyethylene terephthalate and polyamide microplastics was 1.07, 0.60 and 0.83 particles/L in overlying water during the suspension experiments, respectively. This showed a pattern of first rising and then falling with the extension of suspension time. Even in the environment with the maximum input water volume (8000 ml/min) in this study, only microplastics at a depth of 0 to 2 cm from the sediment were suspended. The average abundance of microplastics was 313.02 particles/kg during the deposition experiments, which gradually increased with the extension of deposition time in sediments. Finally, microplastic sizes in water of the suspension experiments and in sediments of the deposition experiments were concentrated in the range of 500 to 1500 μm and 300 to 1000 μm, respectively.

Opening windows in coach buses is a practical approach to improving natural ventilation and mitigating infection risk (IR). Due to human behavior and weather conditions, the intermittent window opening strategy (IWOS) is a more common practice than keeping windows constantly open. Despite its prevalence, there are no studies exploring IWOS specifically in vehicles. We employed indoor-outdoor coupled CFD simulations to assess the effects of various IWOS on pathogen-laden droplet (PLD) dispersion and IR in a coach bus that occurred a COVID-19 outbreak in Hunan, China. Results reveal that after ventilating through two skylights for 600–1800 s, opening front and rear windows (FW+RW) or FW with a wind catcher (FW+WCH) for just 40 s can reduce PLD concentration (Cave) to 5% of its initial level and the intake fraction of the infector’s neighbor (IFn) drops by 95%. Upon closing FW+RW or FW+WCH, Cave and IFn take over 580 s to return to the pre-opening level. Moreover, intermittent FW opening halves Cave and IFn within 7 min, but leads to rapid increases upon window closure. Therefore, opening FW+RW and FW+WCH intermittently have pronounced impacts on indoor PLD concentration and are applicable approaches to control respiratory disease transmission in vehicles. According to the inhaled viral dose, it is recommended to open windows when driving time is over 12 minutes to reduce infection risk. In scenarios like epidemiological surveys and risk assessments, where assessing passenger infection risk is vital, some behaviors of opening windows cannot be overlooked and necessitate extra attention.

Molecular electrocatalysts have demonstrated potential for the hydrogen evolution reaction (HER) due to their well-defined structures and high intrinsic activities. Achieving rapid production of hydrogen requires molecular electrocatalysts to operate at high current densities, which still presents a challenge. In this work, we demonstrate that molecularly dispersed electrocatalysts of cobalt phthalocyanine anchored on carbon nanotubes (CoPc MDEs) are superior candidates due to the efficient charge transport between the substrate and the active site. The intrinsic activity can be enhanced by introducing functional groups on phthalocyanine. To facilitate mass transport, di(ethylene glycol) substituted CoPc molecules are further anchored on a three-dimensional self-supported electrode (CoPc-DEG MDE@CC), enabling continuous operation for 25 h at −1000 mA/cm2 in 1.0 M KOH. Our study demonstrates the potential of molecular electrocatalysts for HER and emphasizes the importance of adjusting intrinsic activity, and charge and mass transport capacity for practical molecular electrocatalysts.

Scientific assessment of urban ecological security (ES) is an important prerequisite to realize regional sustainable development. Previous studies lack the consideration of quality and poor systematic correlation, which could not reflect the internal dynamic relationship. On the basis of considering the time lag, this study divided the research process into the natural operation stage and the management feedback stage based on the driving forces, pressures, state, impacts, responses, management (DPSIRM) framework model and DEA theory, so as to effectively overcome the above shortcomings. Finally, we analyzed the spatio-temporal characteristics and influencing factors of the ES level of 108 cities in the Yangtze River Economic Belt (YREB) during 2005–2019. The results showed that: (a) both two stages showed a slow and fluctuating upward trend in time series, and the level of urban ES in the management feedback stage was significantly higher than that in the natural operation stage; (b) with the passage of time, the spatial distribution of ES in the natural operation stage gradually developed towards the middle and downstream of the YREB, while the management feedback stage mainly evolved from the midstream to the edge area; (c) the level of urban ES presented a different degree of spatial agglomeration phenomenon, and showed an increasing trend over time; and (d) the key influencing factors gradually changed from pressure to response during 2005–2019. This research aims to provide an innovative perspective for the measurement of urban ES, and provide scientific reference for improving urban ecological sustainable development. Graphical Abstract

It is well-known that water quality has great significance on microbial community composition in aquatic environments. In this study, we detected water column indicates the microbial community composition of nine sampling sites over two seasons using Illumina TruSeq sequencing in Songtao Reservoir, Hainan Province, Southmost China. The study indicated that the dominant phylum was Actinobacteria, Proteobacteria, Bacteroidetes, and Cyanobacteria. The diversity parameters showed that the microbial community composition had significant spatiotemporal variations, including the significantly higher Shannon index and Simpson index upstream than those midstream and downstream. Besides, there were significantly higher Chao1 index, Shannon index, and Simpson index in winter than in summer. Principal coordinates analysis (PCoA) showed the microbial structural composition had significant seasonal differences. The results of microbial community composition further revealed that the eutrophication level upstream was higher than that of midstream and downstream. The redundancy analysis (RDA) diagram indicated that the abundance of microbiology species significantly correlated with temperature, total phosphorus, Se, and Ni. Furthermore, the mantel's test showed that the temperature and total phosphorus significantly affected the community composition of archaea and bacteria. Overall, our finding here partially validated our hypothesis that the spatiotemporal variations of microbial community composition are significantly related to nutrients, physicochemical factors and metals, which has been unknown previously in tropical drinking waterbodies. This study substantially contributed to understanding of the composition of microbial community in tropical drinking water reservoirs and the main environmental driving factors in tropical zones. It also provided a reference for the management of reservoir operation to ensure drinking water safe.

Extensive outbreaks of harmful algal blooms (HABs) occurred in the Fuchunjiang Reservoir in 2022, a crucial urban drinking water source, coinciding with extreme summer heatwaves. We hypothesize that these heatwaves contributed to HABs formation and expansion. Leveraging Landsat 8 and Sentinel-2 data, we employed clustering and machine learning methods to quantify the HABs distribution and area. Concurrent meteorological and water quality data aided in uncovering the effects of heatwave on HABs. When applying different methods to extract HABs from remote sensing images, random forest (RF) analyses indicated accuracies of 99.3% and 99.8% for Landsat 8 and Sentinel-2 data, respectively, while classification and regression tree (CART) analyses indicated 99.1% and 99.7% accuracies, respectively. Support vector machine (SVM) exhibited lower accuracies (83.5% and 97.4%). Thus RF, given its smaller differences between satellites and high accuracy, was selected for further analysis. Both satellites detected extensive HABs in 2022, with Sentinel-2 recording a peak area of 24.13 km2 (44.6% of cloud-free water area) on August 11, 2022. Increasing trends with amplified durations were observed for summer heatwaves in Jiande and Tonglu around the Fuchunjiang Reservoir. Notably, these areas experienced extreme heatwaves for 63 and 58 days in 2022, respectively, more than double the 1980–2022 average. From June 1 to October 8, 2022, water temperature peaks significantly coincided with expansive HABs and elevated chlorophyll a (Chl-a) concentration from 4.8 μg/L to 119.2 μg/L during the summer heatwaves. Our findings indicated that the reservoir became more HAB-prone during heatwave events, escalating the drinking water safety risk. These results emphasize the challenges faced by reservoir managers in dealing with climate-induced extreme heatwaves and underscore the urgency for heightened attention from water source management departments.

Pollutants produced by cremation furnaces have gradually caused concern because of the increasing rate of cremation around the world. In this study, the levels, patterns, and emission factors of unintentional persistent organic pollutants (UPOPs) from cremation were investigated. The toxic equivalent (TEQ) concentrations (11 % O2 normalized) of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in flue gas ranged from 0.036 to 22 ng TEQ/Nm3, while the levels of polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs) in flue gas samples ranged from 0.0023 to 1.2 ng TEQ/Nm3 and 0.17–44 pg TEQ/Nm3, respectively. The average concentrations of UPOPs in flue gas from car-type furnaces were higher than those from flat-panel furnaces. Secondary chambers and air pollution control devices were effective for controlling UPOPs emissions. However, heat exchangers were not as effective for reducing UPOPs emissions. It was observed that the UPOPs profiles exhibited dissimilarities between fly ash and flue gas samples. HxCDF, OCDD, and PeCDF were the dominant homologs of PCDD/Fs in flue gas, while HxCDF, PeCDF, and HpCDF were the dominant homologs in fly ash. The fractions of MoCBs and MoCNs in fly ash were higher than those in flue gas. Finally, we conducted an assessment of the global emissions of UPOPs from cremation in the years of 2019 and 2021. The total emission of UPOPs in 47 countries was estimated at 239 g TEQ in 2021, which was during the peak period of the COVID-19 pandemic worldwide. The emissions in 2021 increased by approximately 24 % compared to 2019, with the impact of COVID-19 being a significant factor that cannot be disregarded.

Increasing nitrogen (N) input to coastal ecosystems poses a serious environmental threat. It is important to understand the responses and feedback of N removal microbial communities, particularly nitrifiers including the newly recognized complete ammonia-oxidizers (comammox), to improve aquaculture sustainability. In this study, we conducted a holistic evaluation of the functional communities responsible for nitrification by quantifying and sequencing the key functional genes of comammox Nitrospira-amoA, AOA-amoA, AOB-amoA and Nitrospira-nxrB in fish ponds with different fish feeding levels and evaluated the contribution of nitrifiers in the nitrification process through experiments of mixing pure cultures. We found that higher fish feeding dramatically increased N-related concentration, affecting the nitrifying communities. Compared to AOA and AOB, comammox Nitrospira and NOB were more sensitive to environmental changes. Unexpectedly, we detected an equivalent abundance of comammox Nitrospira and AOB and observed an increase in the proportion of clade A in comammox Nitrospira with the increase in fish feeding. Furthermore, a simplified network and shift of keystone species from NOB to comammox Nitrospira were observed in higher fish-feeding ponds. Random forest analysis suggested that the comammox Nitrospira community played a critical role in the nitrification of eutrophic aquaculture ponds (40–70 μM). Through the additional experiment of mixing nitrifying pure cultures, we found that comammox Nitrospira is the primary contributor to the nitrification process at 200 μM ammonium. These results advance our understanding of nitrifying communities and highlight the importance of comammox Nitrospira in driving nitrification in eutrophic aquaculture systems.

o-Cresol is a toxic substance with strong irritating and corrosive effects on skin and mucous membranes. To date, information on the effects of o-cresol on microbial communities in the natural environment is very limited. In the present study, 16S rRNA sequencing and metagenomic technique were carried out to elucidate the effects of the o-cresol spill on microbial communities in river sediments and nearby soils. o-Cresol spill induced the increase in the relative abundance of phyla Planctomycetes and Gemmatimonadetes, suggesting their resilience to o-cresol-induced stress. Uncultured Gemmatimonadetes genera and the MND1 genus exhibited enrichment, while the Pseudomonas genus dominated across all samples, indicating their potential pivotal roles in adapting to the o-cresol spill. Moreover, o-cresol spill impaired the metabolic functions of microbes but triggered their defense mechanisms. Under o-cresol pressure, microbial functions related to carbon fixation were upregulated and functions associated with sulfur metabolism were downregulated. In addition, the o-cresol spill led to an increase in functional genes related to the conversion of o-cresol to 3-methylcatechol. Several genes involved in the degradation of aromatic compounds were also identified, potentially contributing to the biodegradation of o-cresol. This study provides fresh insights into the repercussions of an abrupt o-cresol spill on microbial communities in natural environments, shedding light on their adaptability, defense mechanisms, and biodegradation potential.

We investigated spatial heterogeneity and diel variations in bacterioplankton and pico-nanoeukaryote communities, and potential biotic interactions at the extinction stage of the Ulva prolifera bloom in the Jiaozhou Bay, Yellow Sea. It was found that the presence of Ulva canopies significantly promoted the cell abundance of heterotrophic bacteria, raised evenness, and altered the community structure of bacterioplankton. A diel pattern was solely significant for pico-nanoeukaryote community structure. More than 50% of variation in the heterotrophic bacterial abundance was accounted for by the ratio of Bacteroidota to Firmicutes, and dissolved organic nitrogen effectively explained the variations in cell abundances of phytoplankton populations. The factors representing biotic interactions frequently contributed substantially more than environmental factors in explaining the variations in diversity and community structure of both bacterioplankton and pico-nanoeukaryotes. There were higher proportions of eukaryotic pathogens compared to other marine systems, suggesting a higher ecological risk associated with the Ulva blooms.