Phosphogypsum (PG) can cause severe water pollution and ecological risks. In this study, we developed a sustainable chemistry process that can simultaneously address PG pollution and carbon dioxide (CO2) sequestration by integrating precise reaction control with advanced tail-end wastewater treatment. Through a secondary leaching process, over 99% of the active calcium ions in PG were efficiently recovered. Subsequent carbonation yielded high-purity nano-calcium carbonate (nano-CaCO3), achieving a calcium utilization efficiency exceeding 99%. The synthesized nano-CaCO3 exhibited a high purity of 97.18% with an average particle size of 72.05 +/- 12.31 nm. This sustainable chemical strategy establishes a sustainable and scalable approach for reducing PG stock and capturing low-CO2-content industrial flue gas, followed by mineralization, demonstrating significant potential for practical PG disposal and high-value nano-CaCO3 production. The commercialization of this process could serve as a viable reference for large-scale PG consumption, offering a promising solution for global PG management and carbon emission mitigation.

Most ecotoxicity research with microplastics (MPs) in laboratories uses primary MPs, such as plastic microbeads. The present study aimed to determine the effects of three environmentally representative MPs: nylon and Kevlar microfibers and polystyrene cup fragments on Daphnia magna. The organisms were exposed to each MP type at five test concentrations (0.0064, 0.064, 0.25, 2.5, and 25 mg/L) for 21 days to investigate MP uptake and effects on survivorship, growth, and reproduction. Daphnia magna ingested all MP types and the uptake concentration increased logarithmically with exposure concentration. Microplastics did not significantly affect survival. However, reproduction was significantly reduced at high nylon microfibers concentrations (2.5 and 25 mg/L). Dry weights of D. magna were also significantly lower than the control when exposed to nylon microfibers at 0.064, 2.5, and 25 mg/L. Ingested MPs exhibited a strong and positive correlation with MPs concentration in water. Significant negative correlations were found between body size and ingested MPs and MPs in water of cup MP experiments. Particle size distribution analysis indicated a size-selective ingestion by D. magna. The effects of MPs on D. magna appeared to be influenced by particle size and surface morphology. Results of the present study are useful for ecological risk assessment for MPs. More studies across species are needed to further understand how MP type and uptake relate to biological effects, which is necessary for ecological risk assessment and management of MP pollution.

The roles of suspended particulate matter in regulating phosphorus (P) and organic matter (OM) cycling remain unclear. We investigated 21 catfish aquaculture ponds across four seasons in 2024-2025 to quantify how seasonality and particle size regulate P-OM interactions. Water samples were collected and then separated into five suspended particle-size fractions (>1000, 1000-450, 450-100, 100-50, and 50-1 nm) and the truly dissolved phase (<1 nm). We integrated Hedley's sequential extraction approach, 31P nuclear magnetic resonance spectroscopy, and fluorescence excitation-emission matrix-parallel factor modeling (EEM-PARAFAC) to characterize size-dependent P pools, molecular P signatures, and dissolved- vs. particle-associated OM interactions. Particle mass showed strong seasonal variability, with summer exhibiting substantially higher particle loads, whereas fall showed one-order of magnitude lower particle abundance. Hedley's extraction results showed NaOH-extractable P dominated particulate P pool, while nanoparticles were enriched in exchangeable P fractions (water- and NaHCO3-extractable P). These results indicate decoupling between particle mass and P reactivity, with nanoparticles serving as highly reactive intermediates for rapid dissolved-particulate P exchange. 31P NMR detected orthophosphate across all size fractions, whereas organic monoester P was consistently enriched in larger submicron particles and became weak or undetectable in < 100 nm size fraction. EEM-PARAFAC further linked elevated dissolved P availability with protein-like and labile OM signatures, suggesting enhanced microbial processing and OM-associated nutrient recycling under high-P conditions. Our findings suggest that nanoparticles act as reactive intermediates for dissolved-particulate P exchange; meanwhile, OM composition and microbial transformation processes further regulate the bioavailability of particle-bound P.

The oxic-anoxic transition zone (OATZ) in the vadose zone, driven by wetting-drying cycles (WDCs), facilitates rapid redox turnover and microbial activity, thereby playing a crucial role in contaminant transformation and fate. However, existing WDC experimental systems are often limited by large experimental volumes, restricted in situ monitoring and repeated sampling, inadequate characterization of oxic-anoxic transitions, and open-flow configurations that result in contaminant loss, thereby complicating contaminant fate and transformation analyses. To address these issues, this study employed a compact 500 mL jar system that enables controlled OATZ simulation under WDCs. The jar system was initiated by a 7–20-d anaerobic incubation period, followed by a 14-d wetting phase and 14-d drying phase (one WDC). The spike-recovery experiment using per- and polyfluoroalkyl substances (PFAS) demonstrated that the syringe-based mini-core sampling yielded spatially homogeneous samples throughout wetting and drying phases with high mass recovery of PFAS. The in situ redox potential (Eh) monitoring also effectively captured the redox transition. Under lactate-enriched biotic conditions, anoxic conditions (Eh < 100 mV) were achieved during the wetting phase, with Eh reaching −20.2 mV in loam soil and +83 mV in clay soil, respectively. Comparisons of biotic, abiotic, and control treatments further suggested microbial contributions to the observed Eh variations. A three-WDC experiment using a sandy loam soil further showed clear coupling among water content, Eh, and multi-day delayed responses characteristic of natural OATZ behavior. Microbial community analysis indicated lactate-driven enrichment of facultative anaerobes, consistent with biologically mediated redox transitions. By ensuring a well-controlled redox fluctuation, this system provides a practical and cost-effective approach for investigating contaminant transformation within OATZ, offering new insights into vadose zone biogeochemistry and environmental remediation.

Per- and polyfluoroalkyl substances (PFAS) have reached global occurrence in the environment, including groundwater and vadose zone. Therefore, developing technologies to remediate PFAS in groundwater and vadose zone is urgent, especially for in situ remediation. Colloidal activated carbon (CAC) has emerged as a cost-effective adsorbent that shows potential to in situ immobilize PFAS in groundwater and vadose zone. This review provides state-of-the-art assessment of CAC-enabled technologies to in situ remediate PFAS-impacted groundwater and vadose zone, focusing on the technology feasibility, effectiveness, efficiency, longevity, and environmental factors affecting technology performance. The adsorption mechanisms of CAC for various types of long-chain and short-chain PFAS are discussed to evaluate technology effectiveness and efficiency. Significant efforts are devoted to assessing and predicting the longevity of CAC-based barriers for treating PFAS plumes in groundwater by mathematical modeling and field observations. Key factors on how nonuniform distribution, plume migration, and potential loss of CAC affect the barrier continuity and PFAS breakthrough are elucidated. The unique processes in the vadose zone, such as dynamic wetting-drying cycles, air-water interfacial partitioning, and oxic-anoxic transition zones are highlighted, since they may significantly affect CAC adsorption and migration capacities, underscoring the urgent needs for systematic studies and long-term monitoring efforts. Future research frontiers and challenges on CAC-enabled technologies for in situ remediation of PFAS-impacted groundwater and vadose zone are identified, contributing to the global efforts in addressing PFAS pollution.

In recent decades, China has exerted significant efforts to diminish the influx of exogenous nitrogen (N) and phosphorus (P) into lakes and reservoirs (L&Rs) in an attempt to control algal blooms (ABs). However, climate change has undermined the effectiveness of these measures. Therefore, distinguishing the contributions of climate change and nutrients is crucial for developing effective ABs management strategies, but remains challenging. Here, we combine the onset and end times of ABs with neural network models to study the trends and controlling factors of algal bloom risk periods (ABRPs) of L&Rs in China from 2003 to 2020. Our results showed that over the past 20 years, the ABRPs of lakes and reservoirs increased by 42 days (11.5%) and 54 days (14.8%), respectively. The contribution of air temperature (Tair) (11%) to prolonging ABRPs was much greater than that of P (5.3%) and N (3.5%). Tair's contribution surpasses that of N and P accounted for up to 63% of one year and will continue to extend with global warming. Moreover, the ABRPs for reservoirs showed a faster growth rate compared to lakes. This may be due to the lower Tair threshold in the reservoir (12.6 °C vs. 16.7 °C in the lake) and the higher contribution of temperature (17% vs. 5% in the lake). Overall, our study highlights the potential importance of climate warming on the onset and end times of ABs, and also distinguishes the differences in driving mechanisms between L&Rs ABs, thus providing a scientific basis for the development of ABs prevention and control strategies for L&Rs in China.

Humic Acid (HA), a principal constituent of natural organic matter (NOM), manifests ubiquitously across diverse ecosystems and can significantly influence the environmental behaviors of Cd(II) in aquatic systems. Previous studies on NOM-Cd(II) interactions have primarily focused on the immobilization of Cd(II) solids, but little is known about the colloidal stability of organically complexed Cd(II) particles in the environment. In this study, we investigated the formation of HA-Cd(II) colloids and quantified their aggregation, stability, and transport behaviors in a saturated porous media representative of typical subsurface conditions. Results from batch experiments indicated that the relative quantity of HA-Cd(II) colloids increased with increasing C/Cd molar ratio and that the carboxyl functional groups of HA dominated the stability of HA-Cd(II) colloids. The results of correlation analysis between particle size, critical aggregation concentration (CCC), and zeta potential indicated that both Derjaguin-Landau-Verwey-Overbeek (DLVO) and non-DLVO interactions contributed to the enhanced colloidal stability of HA-Cd(II) colloids. Column results further confirmed that the stable HA-Cd(II) colloid can transport fast in a saturated media composed of clean sand. Together, this study provides new knowledge of the colloidal behaviors of NOM-Cd(II) nanoparticles, which is important for better understanding the ultimate cycling of Cd(II) in aquatic systems.

Cascade damming has significantly altered the hydrological rhythms and hydrodynamic conditions of rivers. Such anthropogenic disturbances have become a key driver of global carbon cycle reorganization. In this research, we conducted a systematic investigation of the spatial and temporal dynamics of organic carbon (OC) in Wujiang River Basin, which is a primary tributary of the Yangtze River in China. Samples were collected twice a year, in August and December 2021, from six reservoirs, the upper, middle, and lower reaches of the mainstream, and three major tributaries of the Wujiang River Basin. We revealed that within the Wujiang River basin, the content of DOC was higher in summer than in winter. In summer, the DOC content decreased by 23.3% from the river to the reservoirs, indicating that cascade damming exerts a pronounced intercepting effect on DOC. This might potentially lead to the conversion of DOC into particulate organic carbon (POC) and subsequent deposition. Cascade damming also caused an increase in the ratio of colloidal organic carbon (COC)/DOC from the river to the reservoirs, with small molecules of truly dissolved organic carbon (UOC) undergoing polymerization to become COC. The autochthonous source characteristic of UOC was more pronounced than that of COC, and the terrestrial source of organic matter predominantly existed in COC. Within the river-reservoir system of the Wujiang River, the spatial and temporal distributions of COC particle Size and Zeta potential do not exhibit a distinct pattern, but both remain in a relatively unstable state. The study illuminated the spatial and temporal dynamics of DOC fractions in the river-reservoir ecosystem on a large scale, have substantial significance for comprehending the river carbon cycle and its ecological effects under the influence of cascade damming.

The Chishui River is the prime production area for Jiang-flavor Baijiu in China, with 85

Applying iron (Fe) amendments to arsenic (As)-contaminated groundwater to form As-laden Fe precipitates represents a promising in situ remediation approach. However, less is known about the secondary risk of As mobilization due to formation of Fe-As colloids released from these precipitates. Here, we systematically explored the nanoscale formation, composition, and stability of Fe-As colloids in high-As contaminated groundwater following the addition of Fe salts under oxic conditions. Batch experiments show that total aqueous As is incorporated into settled particles upon adding Fe(II) and Fe(III). However, we also observe substantial release of Fe-As colloids (168-719 nm), which can remain stably suspended in water for more than 9 days. Higher colloid concentrations and stability occurred at lower molar Fe/As ratios (Fe/As < 5.8), suggesting that colloid-facilitated transport may dominate secondary As mobilization. Colloid characterization confirmed that low Fe/As ratios promote the formation of stable colloids enriched with surface-bound As, with electrostatic interactions stabilizing the colloids. Using advanced analytical and computational techniques, we elucidate the nanoscale structural properties of colloids, showing that As(V) inhibits Fe octahedral polymerization and favors the formation of smaller particles. These mechanistic insights are crucial for evaluating the long-term fate and transport of sequestered As and designing effective groundwater remediation strategies.

The US Environmental Protection Agency recently released strict regulations limiting per- and polyfluoroalkyl substances (PFAS) in drinking water. In response, this study used activated carbons derived from biomass waste components for effective water treatment. By varying the composition of feedstock mixtures, perfluorobutane sulfonic acid adsorption efficiencies ranged from 31 to 98 %, indicating that biomass structure influences PFAS sorption. Activated carbon from a feedstock mixture of 50 % lignin, 35 % cellulose nanocrystals, and 15 % cellulose nanofibers achieved over 98 % removal of three regulated and four unregulated PFAS compounds without requiring additives or surface functionalization.

Little is known about the transport of heavy metals such as cadmium (Cd(II)) with aged biochar colloids in natural soils. Herein, we investigated the cotransport behaviors of Cd(II) with ultraviolet-irradiation aged biochar colloids pyrolyzed at 400 °C (ABC400) and 700 °C (ABC700) in saturated paddy soils. Pristine biochar colloids were included for comparison. Our results showed that Cd(II) transport was significantly facilitated by pristine and aged biochar colloids in saturated paddy soils, compared to the negligible breakthrough of Cd(II) without biochar colloids. This is likely because biochar colloids acted as vehicles carrying adsorbed Cd(II) during cotransport. Compared with pristine biochar colloids, the aged biochar colloids (especially ABC400) exhibited a greater enhancement effect, with 1.4-3.7 times Cd(II) transport in soils, likely due to stronger sorption affinity and higher mobility of aged biochar colloids towards Cd(II). Synergistic transport of aged biochar colloids with Cd(II) was relatively lower in the red soil than that in the huangni soil, probably related to the higher content of iron oxides, larger specific surface area, and lower content of soil organic matter in the red soil. A two-site kinetic retention model was employed to successfully simulate the cotransport of aged biochar colloids with Cd(II) in paddy soils. Our findings illustrate that light irradiation could accelerate the mobility of biochar colloids, as well as their synergistic carrier of Cd(II). This could trigger the potential cotransport risks when biochar is applied for field remediation of Cd-contaminated soils over a long period of time.

Microplastics (MPs) pollution is one of the most pressing environmental problems. Rivers are important conduits for land-sea transport of materials and greatly influence the behaviour of MPs into the ocean. The Pearl River is the second largest river in China in terms of water flow and has a prosperous transport industry. Meanwhile, a large amount of MPs are transported into the South China Sea through the Pearl River. We collected water samples from the origin to the estuary of the Pearl River and studied the abundance, characteristics, ecological risks, and possible impacting factors of MPs. The results showed that the abundance of MPs in the surface water of the Pearl River Basin ranged from 0.7 to 4.5 items/L, and the distribution of abundance showed the order of: origin > estuary > downstream > midstream > upstream. MPs with sizes of 1–1000 µm were the most widely distributed, and fragments and fibers were the most prevalent MPs. The distribution of MPs showed strong spatial heterogeneity, with Polymethyl methacrylate (PMMA) dominating at the origin and upstream, polyethylene terephthalate (PET) dominating in the midstream, while polyethylene (PE) was most abundant in the downstream and estuary of the Pearl River Basin. Compared with the literature data, the concentration of MPs in the Pearl River Basin was overall low, and the pollution load index indicates that the Pearl River is at a low pollution level. However, the highly toxic PMMA could lead to significant ecological risks in the Pearl River, especially at the origin and upstream watersheds. Natural factors such as hydrological conditions, gravity, and topography can affect the migration trajectory of this MPs. Reservoirs and the concave banks of curved rivers may become new"sinks"for MPs.

This study presents a comprehensive methodology of LA-ICP-MS for the simultaneous quantification of selenium (Se) and mercury (Hg) in biological matrices, achieving micrometer-scale spatial resolution and maintaining analytical robustness.

Currently, there is an increasing interest in developing efficient and cost-effective treatment technologies to remediate per- and polyfluoroalkyl substances (PFAS) in water. Biochars (pristine and modified/engineered) can be a good candidate among porous pyrogenic carbonaceous materials for the sorptive removal of PFAS from water/wastewater. There is a need to focus on developing efficient, environmentally friendly, and cost-effective techniques for desorbing PFAS from spent biochars (pristine and modified/engineered) to enable potential reuse or suitable disposal of these adsorbents, facilitating their future full-scale application in the water sector. This review article briefly compiles the state-of-the-art knowledge on the: (i) application of pristine and modified/engineered biochars for the sorptive removal of PFAS from aqueous samples; (ii) regeneration/reuse techniques for the spent biochars; and (iii) economic analysis of their use in PFAS removal from water/wastewater. Further investigations on (i) better modifying/engineering biochars to remove specially short-chain PFAS species in real environmental water samples due to challenging nature of their removal using conventional treatment technologies; (ii) feasible low-energy, environmentally friendly, and cost-effective strategies for regeneration/reuse of the spent biochars (pristine and modified/engineered) and management of their end-of-life; and (iii) large-scale and continuous column sorption operation for the real water/wastewater samples are still desirable to apply biochars for PFAS removal at full-scale in the future.

Organic phosphorus (P-o) is an important component of sediment P in eutrophic lakes and may play a crucial role in maintaining eutrophication, but this is often overlooked. This study analyzed the contents, various chemical forms of P-o in surface sediments collected from the Dianchi Lake in China, with long history of eutrophication and algal blooms. The simultaneous release of P-o and inorganic P (P-i) from the collected sediments under varied pH, temperatures, and oscillation simulation conditions was also investigated. The results showed that: (1) P-o accounts for 42.3 %-49.3 % of the total P (P-t), and contributs almost equally to P-i toward sediment P load. Organic residues such as endophytic algae are likely the main source of P-o in sediments; (2) P-o in sediments was primarily in the forms of NaHCO3-P-o, HCl-P-o, and residual-P-o (Res-P-o) (over 90 % of P-o). The labile P-o (LPo) and moderately labile P-o (MLPo) components accounted for about 60 % of total P-o, indicating its significant potential for participation in the P biogeochemical cycles; (3) The simultaneous release of P-o and P-i from the sediments was significantly affected by pH, temperature, and oscillation simulation conditions. Especially the simultaneous release of P-o relative to P-i becomes consistently higher and shows a significant positive correlation with the release of P-t (P < 0.01), indicating P-o poses high releasing risk from sediments in the Dianchi Lake. Our findings suggest that against the backdrop of increasing eutrophication worldwide, the control of internal P-o pollution in closed water systems (e.g., lake) is urgently needed.

Biochar has received increasing attention in recent years as a potentially cost-competitive adsorbent for removing various contaminants from surface water and groundwater. However, most published studies have been conducted in the laboratory on a bench scale. Laboratory conditions do not necessarily reflect the complex, heterogeneous, and dynamic field conditions of actual contaminated surface water and groundwater environments. There is a lack of comprehensive literature review regarding the performance of biochar for contaminant removal, especially under realistic field conditions and at field scale. Here, we evaluated 31 studies on realistic applications of biochar for water remediation by searching the keywords: pilot scale, field scale, and mesocosm scale combined with biochar and water remediation. Biochar was found to be incorporated into a variety of water remediation technologies for treating both inorganic and organic contaminants, such as nutrients, heavy metals, pesticides, and pharmaceuticals in polluted waters and wastewaters. Also, biochar showed the potential to be effective on a field scale or in realistic remediation technologies, although it is not always as effective as other sorbents, such as activated carbon (AC). This is partially because AC has better physicochemical characteristics such as higher surface area and more micropores. Effectiveness for contaminant removal varies according to the targeted contaminants, the type and dosage of biochar used, and the treatment technology incorporating biochar. Finally, knowledge gaps and future research areas are identified. For example, more field scale studies are needed to test the effectiveness of biochar as an adsorbent under realistic conditions to pinpoint specific characteristics suitable for target contaminants. Physicochemical characteristics of the biochar can also change over time during the treatment process due to weathering, which may negatively affect the treatment performance. The effects of scaling up production on biochar quality should therefore also be further investigated, as physicochemical characteristics can be affected by varying the synthesis conditions. Regeneration and disposal of spent biochar is another active research area to determine the overall treatment costs.

The widespread use of neonicotinoid (NEO) pesticides has raised significant environmental concerns due to their toxicity. We investigated the performance of 16 nanobiochars (NBCs), including NBC produced by Douglas fir at 900 °C (Doug 900 NBC), as sustainable sorbents for removing three common NEOs from aqueous solutions: imidacloprid, clothianidin, and thiamethoxam. The NBCs showed high sorption efficiency (∼ 100 %) and fast sorption kinetics (< 0.5 h) for three NEOs at environmentally relevant concentrations (100 ng/L). The sorption efficiency of NEOs was determined by the physicochemical properties of NBCs, including specific surface area (SSA), pore volume (PV), pore diameter (PD), and elemental composition (carbon, nitrogen, and hydrogen contents). The NBCs with higher SSA and larger PV offered more abundant sorption sites, facilitating fast NEO sorption. Particularly, the Doug 900 NBC achieved ∼ 100 % removal efficiency of NEOs within 0.5 h under simulated groundwater conditions (67.5 mg/L of total dissolved solids and 10 mg/L of humic acid). The Doug 900 NBC also maintained high removal efficiency over four continuous reuse cycles. The structural equation modeling revealed that pyrolysis temperature indirectly affects NEO sorption by modifying NBC's properties of SSA, PV, and PD. Our findings highlight the high potential of NBCs for sustainable removal of NEO pesticides in aquatic environments at environmentally relevant concentrations.

Nanoparticle-bound phosphorus (P) is critical for nutrient cycling in aquatic environments, but its behavior across contrasting aquatic systems remains elusive. A comparative study of P load and speciation on particles in water columns was conducted in eutrophic aquaculture pond and Chesapeake Bay estuarine systems. Particle size separation, Hedley's sequential extraction, and microscopic observations were performed to characterize particle size-dependent distribution and speciation of P in water columns. For both aquatic systems, particles shared similar morphologies and P partitioning patterns. However, aquaculture ponds exhibited significantly higher particle loads and greater presence of colloid- and nanoparticle-associated P. Specifically, over 70 % of both inorganic P (Pi) and organic P (Po) enriched in particles with sizes smaller than 100 nm in ponds. It is the concentration of particulate and dissolved Po that controls the extent of algal blooms in P-rich aquaculture ponds. These Po fractions are mainly derived from suspended colloidal and nanoparticulate matter instead of large algae (>1,000 nm). Seasonal comparisons revealed that both diversity and bulk P (BP) concentrations were greater in summer than winter in both pond and estuarine systems. In the estuarine system, P was mainly present in the form of Si/Al-bound species, whereas in aquaculture ponds, Fe- and Ca-bound P forms were more prevalent. This suggests that P in estuarine systems primarily originates from internal sediment release, while P in ponds is largely derived from external inputs, such as fish feed. Correlation analysis further indicated that soluble reactive phosphorus (SRP) concentrations in ponds were significantly associated with water hardness and dissolved oxygen (DO) levels. Increased DO availability may promote the formation of metal phosphate minerals, thereby reducing free orthophosphate in the water column. The Ca-bound nanoparticulate P-often overlooked in traditional P assessment-was found to be a dominant form in high-P aquaculture ponds. This fraction has the potential to suppress algal bloom development by promoting microbial degradation of Po and limiting the availability of bioactive Po.

With the rapid development of water conservation projects around the world, the potential impacts of damming on river ecosystems have attracted widespread attention. Here, we employed the environmental DNA (eDNA) records of the sediment core profiles to explore the effects of the dam construction on algal and fish community structure and biodiversity in the Three Gorges Reservoir in China for the past few decades. We detected 242 genera of algae and 62 species of fish in the sediment cores of the Xiangxi River estuary, the main tributary of the reservoir. The structure of algal and fish communities was changed significantly before and after damming. The dominant species in the algal community shifted from Cyanophyta to Bacillariophyta, while the dominant species in the fish community remained Cypriniformes, and the species diversity fluctuated greatly after damming. In addition, the Non-metric Multidimensional Scaling (NMDS) analysis showed that the composition of algal communities differed significantly among different sequences, while the differences among fish community groups were relatively small. The total nitrogen (TN) and total phosphorus (TP) in sediments were expected to be the main factors, affecting the abundance of eDNA in algae and fish in sediments. Our research emphasizes the progressiveness of sediment eDNA in retrieving the historical dynamics of biological communities, and especially, obtaining the temporal succession trend of biological communities is crucial to understanding the impact of dam construction on the reservoir ecosystem.