Monitoring biochemical oxygen demand (BOD) decay offers critical insights into the aerobic biodegradation of dissolved organic matter (DOM). Focusing on the accumulated metabolites generated during DOM biodegradation, this study introduces novel fluorescence parameters that facilitate the rapid monitoring of BOD decay throughout the entire DOM degradation process until BOD is depleted. BOD decay during degradation of four synthetic DOM samples was first investigated (initial BOD < 10 mg/L) and showed a S-shaped decay pattern with excellent goodness of fit (R² > 0.93; p < 0.001). In contrast, critical spectral signals intensified also in the S-shaped pattern, of which the transition phase converged temporally with BOD decay (time difference < 0.7 d), demonstrating that chromophore-bearing metabolites accumulated synchronously with BOD decay. Pearson analysis further corroborated the highly significant correlations between BOD and spectral signals derived from metabolites throughout the process of DOM degradation. According to Pearson analysis, three metabolite-derived fluorescence parameters were yielded based on three newly specified fluorescence regions related to metabolites (mean r ≈ −0.70; p < 0.05). With a real water sample, we confirmed that these metabolite-derived fluorescence parameters outperformed traditional fluorescence parameters in tracking BOD decay, with a higher R² in multiple linear regression (R² > 0.8; p < 0.001). The findings present a promising approach for rapid tracking and early warning of BOD decay during DOM degradation, potentially contributing to water quality management.

Iron-based nanomaterials (Fe-NPs) have been extensively studied for heavy metal immobilization, yet knowledge of their post-treatment and long-term stability remains limited. Here, we systematically compared the remobilization of cadmium (Cd) from three widely used Fe-NPs, namely, nano–zero-valent iron (nZVI), sulfidated nano–zero-valent iron (S-nZVI), and pyrite nanoparticles (nFeS). Under both oxic and anoxic aging, solution pH strongly controlled Cd(II) speciation and the corrosion behavior of Fe-NPs. Acidic conditions (pH 4) induced substantial Fe-NP dissolution and enhanced Cd release, whereas alkaline conditions (pH 8) greatly suppressed both dissolution and Cd mobilization. During oxic aging, dissolved oxygen significantly accelerated the oxidative corrosion of Fe-NPs, thereby promoting secondary Cd release. The Cd release from nZVI became dramatically higher (up to 50.14%, even at pH 8), which sharply contrasted with the minimal release from S-nZVI (0.37%) and nFeS (0.03%). Elevated concentrations of Na⁺ and Ca²⁺ substantially reduced the stability of spent Fe-NPs, while CO₃^2– buffered the system and helped maintain lower dissolved Cd levels. Furthermore, mechanistic investigation, supported by X-ray diffractometer, X-ray photoelectron spectroscopy, and transmission electron microscopy analyses, revealed that nZVI partially reduced Cd(II) to Cd(0), which subsequently underwent reoxidation under oxic conditions, whereas S-nZVI and nFeS stabilized CdS by forming persistent CdS phases that effectively impeded its release. This study elucidates key factors that govern Cd remobilization and provides a theoretical basis for the long-term application of Fe-NPs in heavy-metal treatment.

The rapid spread of antibiotic resistance genes (ARGs) via plasmid-driven conjugation in pathogenic microbes poses a pressing challenge to global health. Quorum sensing (QS) is pivotal in modulating processes such as biofilm development and the release of virulence determinants, which in turn affect ARG transmission. In this research, an interspecies conjugation model was constructed using Escherichia coli DH5α and Pseudomonas aeruginosa PAO1 as model strains to explore the impact of cinnamaldehyde, a naturally occurring quorum sensing inhibitor (QSI), on the conjugative transfer of antibiotic resistance genes (ARGs) under sub-inhibitory concentrations (sub-MICs). The results revealed that cinnamaldehyde at sub-MICs markedly suppressed transfer frequency without hindering bacterial proliferation. This inhibition of conjugation was largely linked to the suppression of biofilm formation and extracellular polymeric substance (EPS) production, downregulation of QS-related genes rhlI and rhlR, and reduced secretion of virulence factor rhamnolipid, thereby further restricting biofilm-associated ARG dissemination. These mechanisms are all under the governance of the QS system. These findings suggest that cinnamaldehyde, as a QSI, holds promising potential for controlling the spread of bacterial resistance and provides a novel strategy for regulating horizontal gene transfer of ARGs.

Aquatic environmental systems often suffer from low monitoring frequency, limited spatial coverage, and high experimental costs, resulting in small-data characteristics such as limited sample size, high dimensionality, and structural heterogeneity. These issues significantly limit the performance and generalizability of machine learning models. This review examines the challenges associated with applying machine learning to model under small-data conditions in aquatic environments. Building on the structural features of representative datasets, current mainstream approaches are systematically evaluated, and their adaptability and robustness across different application scenarios are compared. Drawing on cross-disciplinary experience, it proposes a modeling framework tailored to aquatic systems and emphasizes the coordinated optimization of data preparation, model construction, and performance evaluation. The analysis highlights that data incompleteness and non-stationarity are the primary obstacles in small-data modeling and that constructing problem-oriented modeling workflows is crucial for enhancing predictive reliability and the robustness of the results. Taken together, these efforts provide theoretical and methodological guidance for intelligent environmental modeling and scientific decision-making under small-data conditions.

Elemental mercury (Hg⁰) in coal-fired and metallurgical flue gases remains a critical concern and technical challenge in air pollution control. In this study, FeCl₃-loaded activated carbon (AC) catalysts were prepared from walnut shells via chemical activation and calcination at 700 °C (Fe-1/AC) and 800 °C (Fe-2/AC) to investigate the removal of Hg⁰. Within a wide temperature range of 50–400 °C, Fe-1/AC achieved a Hg⁰ removal efficiency exceeding 95%. Characterization results indicate that the lower calcination temperature yielded Fe-1/AC with smaller Fe₃O₄ nanoparticles, improved dispersion, a preserved microporous structure, and abundant surface chloride ions and defect oxygen species, all of which contributed to its effective Hg⁰ removal performance resulting from coupled adsorption and oxidation processes. However, the higher calcination temperature led to pore collapse and Fe agglomeration in Fe-2/AC, thereby reducing its efficiency. These findings highlight the crucial role of temperature-controlled synthesis strategies in optimizing the pore structure, metal dispersion, and surface chemistry of AC for efficient mercury capture, laying the foundation for the design of high-performance environmental remediation materials.

The availability of dissolved silicon (DSi) relative to dissolved phosphorus (DP) regulates the dominance of siliceous phytoplankton in eutrophic waters, yet the redox controls on DSi internal loading from natural sediments remain uncertain. We incubated surficial sediments in ten parallel flow-through columns to disentangle Fe-P-Si interactions under alternating oxic and anoxic overlying waters. Columns containing 10 cm of sediment received anoxic influents with different combinations of Fe(II), DSi, and DP delivered through the bottom port using a peristaltic pump, while the effluent were monitored; post-experiment sediments were characterized using buffered ascorbate-citrate (BAC) and 1 mol/L NaOH extractions. Under oxic conditions, more than 90% of inflow Fe(II) was retained in the upper 1 cm of sediment, enriching BAC-extractable Fe and P by up to 40% relative to initial values. Transition to anoxia caused reductive dissolution of these phases, leading to Fe release of up to 193 ± 26 µmol/L and DP peaks of 160 ± 30 µmol/L in the overlying water. In contrast, DSi exhibited neither measurable retention during oxia nor systematic increases under anoxia, with effluent concentrations consistently exceeding influent levels by 20%–50%, indicating steady internal production. Mass-balance calculations show that DSi fluxes (20–40 µmol/d) were dominated by continuous dissolution of amorphous silica, while elevated DP suppressed Fe-Si co-precipitation via competitive sorption on Fe(III) solids. We conclude that the interplay among porewater DP and DSi production rates, along with the pool of reactive iron, governs the extent to which internal Si release responds to redox variations.

Perfluorooctane sulfonate (PFOS) is a dominant per- and polyfluoroalkyl substance (PFAS) at aqueous film-forming foam-impacted sites, yet its specific inhibitory effect on reductive dechlorination of trichloroethene (TCE) remains poorly understood. We investigated TCE dechlorination in a Dehalococcoides (Dhc) and Dehalogenimonas (Dhg)-containing consortium under PFOS stress (20–100 mg/L). While the initial TCE dechlorination rates decreased with increasing PFOS concentrations, the final step of vinyl chloride dechlorination to ethene remained largely unaffected. Microbial community analysis revealed that Dhc and Acetobacterium exhibited greater resilience to 100 mg/L PFOS than Dhg and Clostridium_sensu_stricto_7, with alpha diversity significantly reduced at 100 mg/L PFOS. PFOS, but not perfluorooctanoic acid, was identified as the primary inhibitor of TCE dechlorination. Metagenomic sequencing identified two PFOS-tolerant Dhc strains (THU3 and THU4) that harbored specific reductive dehalogenase genes (vcrA and tceA). Our findings demonstrate the functional resilience of Dhc and its potential as a key agent for bioremediation at PFAS-co-contaminated sites.

Viruses widely existing in the nature play important role in the various ecosystem. However, rare information is available regarding the quantitative effect of viruses on resistance genes in recirculating aquaculture system (RAS) which is an artificially-regulated advanced aquaculture mode. This study investigated the potential effect of viral community on both antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) in a typical RAS based on metagenomic analysis. The results showed that viruses averagely accounted for 24.6%/0.1% of microbial community in water/residues of RAS operational units. Caudovirales were the predominant annotated order covering 32.5% of viral orders while Ligamenvirales and Picornavirales were not detected in residue samples. The total relative abundances of ARGs in the water/residue samples of RAS were in the range of (0.044–0.144)/(0.029–0.162) copies/16S rRNA copy while those of MRGs in the water/residue samples of RAS were in the range of (1058.6–2020.0)/(2263.2–3744.7) copies/16S rRNA copy. Caudovirales and Herpesvirales were frequently negatively related with ARGs in residue samples while Herpesvirales were often negatively related with MRGs in water. Viruses showed inhibition effect on ARGs and MRGs in RAS according to both the network analysis and pathway analysis. This study provided new insight on the relationship between viruses and resistance genes, regarding inhibition effect of viruses on resistance genes.

Acinetobacter represents a genus of bacteria characterized by exceptional ecological adaptability and clinical pathogenicity, with numerous species implicated in multidrug-resistant infections. Their dissemination in aquatic environments poses a significant threat to public health. Rivers traversing densely populated regions serve as dynamic ecological corridors that mediate the exchange of microbial populations between anthropogenic and natural environments, emerging as pivotal reservoirs and dissemination pathways for Acinetobacter species. Despite being a keystone group bridging clinical and environmental microbiology, there remains a lack of systematic methods for assessing its environmental health risks. In this study, a multidimensional risk assessment framework was established, integrating metagenomic sequencing with advanced bioinformatics to characterize Acinetobacter-associated hazards in aquatic ecosystems. This framework incorporates pathogenicity profiling, resistome-mobilome-virulome annotation, and abundance quantification at the metagenome-assembled genome (MAG) level. Using the Yangtze River as a model system, the framework was applied to systematically evaluate the health risks posed by Acinetobacter. Key steps included determination of pathogenic potential, comprehensive screening of antibiotic resistance genes, virulence factors, and mobile genetic elements, followed by integrative risk scoring based on MAG-specific functional attributes and relative abundance. This approach overcomes limitations of traditional culture-dependent or abundance-centric assessments and enables rapid, high-resolution evaluation of microbial threats in complex aquatic environments.

Burnout-derived tire wear particles (B-TWPs) and pharmaceuticals and personal care products (PPCPs), such as tetracycline (TC), commonly coexist in aquatic systems. However, the nature of their interactions is complex and poorly understood. Therefore, this study investigated the synergistic effects of surface functional components and spontaneously released active factors from TWPs on the photodegradation of TC. Notably, B-TWPs significantly enhanced the transformation of TC, increasing the apparent degradation efficiency from 5.67% (blank) to 19.52% (B-TWPs) and 22.98% with aged B-TWPs (AB-TWPs). During photoaging, TWPs exhibited photo-oxidative characteristics, with the hydroxyl index (HI) increasing from 1.032 to 5.453. Aging also enhanced the release of transition metal ions (e.g., Zn: 0.36419 mg/L, Fe: 0.08515 mg/L) and dissolved organic matter (DOM). Electrochemical tests revealed that the increased current density of aged TWPs enhanced their redox capacity, enabling them to function as efficient photosensitizers and electron donors to promote ROS (•OH, O₂^•−) generation. Sankey analysis attributed 33% and 14% of pollutant degradation to TWPs oxygenated groups and self-released DOM, respectively. Antibacterial tests demonstrated that AB-TWPs significantly reduced the antibacterial activity of TC against E. coli and S. aureus, with inhibition zone diameters decreasing to 22.3 and 12.7 mm, respectively. The reduction in toxicity was synchronized with total organic carbon removal, indicating deep degradation and mineralization of TC. This study unveils novel insights into TWPs environmental behavior and their photocatalytic mechanisms for TC attenuation.

The implementation of the nonradical (¹O₂) pathway in conventional Fenton reactions is a promising approach for degrading organic pollutants in water. In this study, a one-step co-pyrolysis method of red mud (RM) and spent coffee grounds (SCG) was employed to prepare an iron-rich catalyst (RMSCG70) for activating H₂O₂ in a photo-Fenton system to degrade tetracycline hydrochloride (TCH). RMSCG70 exhibited excellent TCH degradation performance under visible-light irradiation. At a catalyst dosage of 0.1 g/L, H₂O₂ concentration of 3 mmol/L, and TCH concentration of 20 mg/L, the TCH removal rate reached 99.3% within 60 min. Quenching experiments conducted under the light and dark conditions, together with Electron Paramagnetic Resonance (EPR) analyses, indicated that ¹O₂ is the main reactive oxygen species (ROS). The {\text{O}}_2^{\text{●}-} generated by O₂ reduction reacted with the {}^{\text{●}}{\text{OH}}_{\mathrm{a}\mathrm{d}\mathrm{s}} on the catalyst surface to form ¹O₂, and the FeAl₂O₄ component in RMSCG70 in the photo-Fenton system promoted the generation of {\text{O}}_2^{\text{●}-} and {}^{\text{●}}{\text{OH}}_{\mathrm{a}\mathrm{d}\mathrm{s}}. Cyclic experiments showed that the TCH degradation efficiency remained around 90% after five cycles. Further investigation of its application potential in a continuous-flow reactor revealed that when the hydraulic retention time (t_hr) was 30 min, the TCH removal rate reached approximately 80%. This study revealed the mechanism of organic pollutants under visible-light irradiation using RM and SCG as photocatalysts, while enabling the resource utilization of solid waste.