Riverbank filtration is a nature-based water treatment strategy known for its effective removal of organic micropollutants. Yet, the mechanisms governing their biodegradation, especially the role of redox transitions in mediating biotransformation, remain insufficiently understood. Here, we integrate metagenomic profiling with chemical analytics in a 10 m simulated riverbank filtration system to demonstrate how sequential oxidizing–reducing degradation enhances organic micropollutant transformation. Oxygen stratification structured distinct microbial and enzymatic pathways: oxidizing zones (>+200 mV redox potential) facilitated cytochrome P450-mediated oxidation (oxidizing condition, OXD), while subsequent redox shifts to reducing conditions (←400 mV, sequential oxidizing–reducing (SOR) conditions) activated reductive transformations (e.g., via nitronate monooxygenase and aldehyde dehydrogenase) and conjugation pathways. These SOR conditions significantly enhanced the removal of recalcitrant compounds, including irbesartan (+25.3%), benzotriazole (13.4%), and gabapentin (+9.7%). Metagenomic analysis revealed redox-driven microbial specialization, with Pseudomonadota and Nitrospirota dominating in oxidizing zones and reducing microzones enriched in pathways associated with nitrotoluene and ethylbenzene degradation, providing genomic evidence for sequential organic micropollutant breakdown. These findings establish a mechanistic framework for harnessing oxidizing–reducing microbial partnerships to amplify organic micropollutant removal in nature-based water treatment systems, which can be used for riverbank filtration site selection and well field construction and optimization.

Microplastics (MPs) serve as carriers for microbial community colonization, forming unique ecosystems known as plastispheres in urban aquatic ecosystems. However, interactions among microbes, extracellular polymeric substances (EPS), and MPs remain poorly understood. This study investigates microbial consortia and their EPS secretion behaviors across various plastispheres at two representative coastal urban water sites. Permutational multivariate analysis of variance revealed that MP type significantly influenced microbial community structures in reservoir environments (R² = 0.60, p < 0.001), highlighting the pronounced impact of MP types in high-quality urban waters. Specific microbial phyla and genera were identified as key contributors to EPS compositional variations across different plastispheres. Hierarchical partitioning results identified Acidobacteria, Nitrospirae, and Planctomycetes as influential phyla positively affecting EPS composition. Spearman correlation analysis pinpointed Robiginitialea (positive correlation) and Fimbriiglobus (negative correlation) as critical genera influencing EPS dynamics. Moreover, EPS-related gene abundance corresponded closely with observed EPS compositional differences. Dominant genes associated with protein biosynthesis included xapD in reservoirs and glnA in bays, while glmS and eno were predominant for polysaccharide biosynthesis in bays. This research advances our understanding of microbial-EPS-MP interactions in urban water systems, offering critical insights into ecological remediation and risk assessment of MP pollution.

Slow sand filters (SSFs) are widely applied to treat potable water; the removal of contaminants (e.g., particles, organic matter, and microorganism) occurs primarily in the top layer. However, the development of the microbial community and its metabolic function is still poorly understood. In the present study, we analyzed the microbial quantity and community of the influents sampled from the effluent of the last step (rapid sand filtration) and of the top layers of SSFs (Schmutzdecke, 0–2 cm, 4–6 cm, 8–10 cm) sampled near terminal head loss when the Schmutzdecke (SCM) was most developed in two full-scale drinking water treatment plants (DWTPs). The two DWTPs use the same artificially recharged groundwater source. The biomass in the filter, quantified by flow cytometric intact cell counts (ICC) and adenosine triphosphate (ATP), decreased rapidly along the depth till 8–10 cm (>1 log TCC; >75% ATP); the decrease was most pronounced from the SCM to the surface sand layer (0–2 cm), after which the biomass stabilized quickly at lower depths (2–10 cm). Remarkably, beta diversity showed that SSFs layers of the same depth in two DWTPs with distinctive filter age and plant location clustered together, which indicated their insignificant effects in shaping microbial communities in SSFs. The alpha diversity indices followed the trend of the biomass, suggesting more active and diverse communities in SCM layer. PICRUSt-based function prediction revealed significant over-representation of metabolism and degradation of complex organic matters (e.g., butanoate, propanoate, xenobiotic, D-Alanine, chloroalkene, and bisphenol) in SCM layer, the functional importance of which was confirmed by the co-occurrence patterns of the dominant taxa and metabolic functions. Using an island biogeography model, we found that microbial communities in SSFs were strongly assembled by selection (68 OTUs, 50.0% sequences), rather than by simple accumulation of the microbial communities in the influents (120 OTUs, 44.8% sequences). Our findings enhance the understanding of microbial community assembly and of metabolic function in the top layers of SSFs, and constitute a valuable contribution to optimizing the design and operation of biofilters in full-scale DWTPs.

Assessment of chronic impact of metallic nanoparticles (NPs) in soil ecosystems is a necessity for ensuring safe and sustainable application. NPs affect plants and their associated microbial life, while the plants and their associated microbiota affect the NPs' fate. Here, we measured the available Ag pool (determined as diethylenetriaminepentaacetic acid-extractable Ag) in AgNP-amended sandy loam soil (1, 10, and 50 mg Ag per kg of soil) over a period of 63 d with and without lettuce. The associated impacts on soil pH, Ag accumulation in lettuce, and the responses of the rhizosphere bacterial community were determined. We found that the addition of AgNPs significantly increased the soil pH from 7.70 to 7.87 after a short-term (7 d) incubation. Noteworthily, the extractability of Ag in AgNP-amended soil was concentration-dependent and changed over time because of their continuous dissolution and uptake by plants. Ag uptake and upward translocation in lettuce positively correlated with the extractable Ag content in soil. Furthermore, a long-term (63 d) exposure to 50 mg/kg of AgNPs altered the structure and composition of the rhizosphere bacterial community potentially by regulation of bacterial groups associated with element (e.g., N and S) cycling and stress tolerance. In conclusion, our results demonstrated that the dynamic dissolution of AgNPs in sandy loam soil plays an important role in influencing the overall Ag bioavailability of the NPs in plants. The enhanced effects of AgNPs on the alterations in the rhizosphere bacterial community highlight that the long time-resolved dynamics of NP exposure should be taken into consideration for accurate ecological risk assessment of NPs in the soil ecosystem.