The complex hydrological conditions caused by the backwater effect at the confluence inevitably modify the geochemical processes of elements. However, there is still a lack of comprehensive understanding regarding the precise transformation mechanisms of nutrients in large river systems. This study aimed to investigate the hydrodynamic characteristics and their impact on phosphorus transfer in the lower Han River, which is influenced by backwater from the Yangtze River (the largest river in China). By establishing a hydrodynamic-water quality model, we have determined that the discharge ratio (the ratio of flow between the Han River discharge and the Yangtze River discharge) can be utilized as a representative indicator of the backwater effect from the Yangtze River on the Han River. Three distinct patterns were identified in this study: mixing, backwater, and intrusion. The corresponding discharge ratio values were categorized as >0.08, 0.01∼0.08, and <0.01 respectively. Additionally, the extent of the backwater zone was determined, revealing that the length of the backwater zone increased from 50 km (XG) to 100 km (FS) as the discharge ratio decreased from 0.08 to 0.01. Furthermore, it was observed that the water level at the confluence rose from 2.52 m to 6.83 m in accordance with these changes in discharge ratio values. The migration pattern of phosphorus primarily involved the settling and retention of particulate phosphorus, particularly the labile particulate organic phosphorus (LOP) and dissolved organic phosphorus (DOP). When the confluent patterns became the intrusion pattern, the backwater zone expanded to 150 m (XT), causing a 10.40 m increase in water level at the confluence. An intrusion zone formed, and its phosphorus concentrations were same as Yangtze River\'s. Above the intrusion area, a backwater region formed and its concentrations of LOP and DOP decreased, while the concentration of PO43- increased due to the release from resuspended particles. This release was induced by higher velocity of bottom water brought about by the water exchange of two rivers. The discharge ratio of 0.01-0.08 resulted in the sedimentation of LOP and DOP, causing the lower Han River to act as a \"sink\" for phosphorus, potentially exacerbating phosphorus pollution. Higher discharge ratios in spring led to phosphorus release from sediment, increasing dissolved phosphorus concentrations and raising the risk of algal blooms in the lower Han River. These findings have significant implications for larger rivers worldwide and provide insights into strategies for ecological management and prevention of algal blooms.

Antibiotics can generally be detected in the water-sediment systems of lakes. However, research on the migration and transformation of antibiotics in water-sediment systems based on the influences of light and wind waves is minimal. To address this research gap, we investigated the specific impacts of light and wind waves on the migration and transformation of three antibiotics, norfloxacin (NOR), trimethoprim (TMP), and sulfamethoxazole (SMX), under simulated light and wind waves disturbance conditions in a water-sediment system from Taihu Lake, China. In the overlying water, NOR was removed the fastest, followed by TMP and SMX. Compared to the no wind waves groups, the disturbance of big wind waves reduced the proportion of antibiotics in the overlying water. The contributions of light and wind waves to TMP and SMX degradation were greater than those of microbial degradation. However, the non-biological and biological contributions of NOR to degradation were almost equal. Wind waves had a significant impact on the microbial community changes in the sediment, especially in Methylophylaceae. These results verified the influence of light and wind waves on the migration and transformation of antibiotics, and provide assistance for the risk of antibiotic occurrence in water and sediments.

Cadmium (Cd)-contaminated soil poses a severe threat to crop production and human health, while also resulting in a waste of land resources. In this study, two types of organic fertilizer (ZCK: Low-content available iron; Z2: High-content available iron) were applied to Cd-contaminated soil for rice cultivation, and the effects of the fertilizer on rice growth and Cd passivation were investigated in conjunction with soil microbial analysis. Results showed that Z2 could alter the composition, structure, and diversity of microbial communities, as well as enhance the complexity and stability of the microbial network. Both 2% and 5% Z2 significantly increased the fresh weight and dry weight of rice plants while suppressing Cd absorption. The 2% Z2 exhibited the best Cd passivation effect. Gene predictions suggested that Z2 may promote plant growth by regulating microbial production of organic acids that dissolve phosphorus and potassium. Furthermore, it is suggested that Z2 may facilitate the absorption and immobilization of soil cadmium through the regulation of microbial cadmium efflux and uptake systems, as well as via the secretion of extracellular polysaccharides. In summary, Z2 can promote rice growth, suppress Cd absorption by rice, and passivate soil Cd by regulating soil microbial communities.

The hazardous trace elements (HTEs) emitted during the municipal solid waste incineration (MSWI) process have been widely concerned. In this work, the bottom ash (BA), heat recovery boiler ash (HA), and ash after desulfurization (SA) were collected to explore the occurrence forms of HTEs in the three types of ash and their relationship with minerals and leaching characteristics. The results show that the volatility of the seven studied HTEs follows the order of Cd, As > Ni, Zn > Pb > Cr, Cu. In the process of BA → HA → SA, the content of Cd, As, Zn, and Pb shows an increasing trend. The seven HTEs are mainly in the forms of chlorides and oxides. There is an obvious relationship between the occurrence forms and simulated existence form of HTEs. SiO2 and CaCO3 are the major mineral components in the three ashes, while SA also contains chlorine-containing compounds which are easily leached out. The risk assessment code and soluble ratio show that HTEs in SA are more leachable than BA and HA, where Cd, Pb and Ni need to be addressed to reduce their impact on soil or water during subsequent landfill treatment of SA.

Phosphorus (P) conveyed by surface runoff plays an essential role in regulating nutrient balance and primary production in estuarine waters. In this study, basic physiochemical properties, total phosphorus (TP, including speciation), particulate iron (PFe), particulate manganese (PMn), and particulate aluminum (PAl) of the surface water in the Pearl River Estuary (PRE) in different seasons were determined to investigate the spatiotemporal distribution characteristics of P and to identify the crucial factor controlling P migration and transformation in the freshwater-saltwater interaction zone. TP concentrations (28.88-233.68 μg·L-1) decreased with increasing salinity gradient owing to deposition and dilution. The proportions of P speciation followed a decreasing order as dissolved inorganic phosphorus (DIP, 37.3%) > particulate inorganic phosphorus (PIP, 22.7%) > dissolved organic phosphorus (DOP, 21.0%) > particulate organic phosphorus (POP, 19.0%). PIP was positively related to PFe, PMn, and PAl (P < 0.05), confirming their concurrent migration behaviors. In addition, the increase in salinity promoted the desorption of phosphate on the suspended particulate matters, which mainly took place near the freshwater-saltwater interface. A significant positive correlation (P < 0.001) between the solid-liquid phase partitioning coefficient (Kd) of phosphate and salinity indicated that PIP was present mainly in more stable forms in the brackish water. Most importantly, a better relationship between Kd and PMn (P < 0.01) supported our scientific hypothesis of the \"load-unload\" effect of Mn oxides on P:particulate-carrying phosphates transported from the freshwater zone tend to be desorbed and released into the brackish water.

The recycling and utilization of phosphorus resources in sludge is becoming increasingly important. In this study, we compared the conversion of phosphorus and toxic metal passivation effects of different Ca additives under oxygen-rich combustion conditions and elucidated their specific mechanisms of action. The experimental results indicated that four Ca-based additives improved the recovery rate of total phosphorus, and promoted the generation of stable apatite phosphorus (AP). The effect of CaCl2 and CaO was greater than that of Ca(OH)2 and CaSO4. CaCl2 promoted the formation of Ca3(PO4)2 and Ca2P2O7, and CaSO4 improved the conversion of AlPO4 to Ca(H2PO4)2 with increasing temperature. The conversion capacity of CaO on non-apatite inorganic phosphorus to AP was greater than that of Ca(OH)2, and more CaH2P2O7, Ca(PO3)2, and Ca-Al-P minerals were found. Toxic metal percentages decreased after sludge incineration with CaCl2. Compared with CaO and Ca(OH)2, the toxic metal adsorption effect of CaSO4 was more significant. The influence of Ca additives on the conversion of Zn into stable components was as follows: CaCl2 > Ca(OH)2 > CaO > CaSO4. Ca additives reduced the toxic metal contamination level and ecological risk index values, and the order of toxic metal contamination levels was Ni > Zn > Cr > Cu > Mn. The experiment confirmed the conversion of phosphorus and the toxic metal passivation effect of Ca additives during oxy-fuel combustion of sludge, which is beneficial for its resource utilization.

The issue of heavy metal pollution caused by human production and living activities is progressively worsening. This study explored the effect of iron-rich organic fertilizer on the growth, quality, and cadmium (Cd) absorption of Chinese cabbage under Cd stress. The results showed that iron-rich organic fertilizer could increase the soluble protein content and root length of Chinese cabbage. Meanwhile, it could change the form of Cd to inhibit the enrichment of Cd in Chinese cabbage. The alkali hydrolyzed nitrogen (AN), total potassium (TK), organic matter (OM), and moisture content (MC) of the Z3 treatment group (2 % ferrous sulfate heptahydrate) were significantly higher than those of other treatment groups. The microbial network of Z3 was more complex than the other three groups. PICRUSt analysis and correlation analysis showed that the genes related to protein synthesis (e.g., glutathione S-transferase, zinc and Cd transporter, outer membrane protein, ArsR family transcriptional regulator, catalase, etc.) can also promote microbial absorption. This study aims to provide theoretical insights into soil Cd pollution immobilization techniques.

Anions accompanying inorganic fertilizers, such as chloride and sulfate ions, potentially affect the solubility, uptake, and transport of Cd to rice grains. However, the role of anions in controlling Cd transport in the soil-soil solution-Fe plaque-rice plant continuum remains poorly understood. Cd isotope ratios were applied to Cd-contaminated soil pots, hydroponic rice, and adsorption experiments with or without KCl and K2SO4 treatments to decipher transport processes in the complex soil-rice system. The chloride and sulfate ions increased the Cd concentrations in the soil solution, Fe plaque, and rice plants. Accordingly, the magnitude of positive fractionation from soil to the soil solution was less pronounced, but that between soil and Fe plaque or rice plant is barely varied. The similar isotope composition of Fe plaque and soil, and the similar fractionation magnitude between Fe plaque and the solution and between goethite and the solution, suggested that desorption-sorption between iron oxides and the solution could be important at the soil-soil solution-Fe plaque continuum. This study reveals the roles of chloride and sulfate ions: (i) induce the mobility of light Cd isotopes from soil to the soil solution, (ii) chloro-Cd and sulfato-Cd complexes contribute to Cd immobilization in the Fe plaque and uptake into roots, and (iii) facilitate second leaves/node II-to-grain Cd transport within shoots. These results provide insights into the anion-induced Cd isotope effect in the soil-rice system and the roles of anions in facilitating Cd migration and transformation.

Synthetic fluoroquinolones (FQs) are the third most commonly used antibiotics in the world and play an extremely important role in antibacterial drugs. The excessive use and discharge will alter ecological environment, with consequence on human health and global sustainable development. It is therefore of great significance for scientific use and management of FQs to systematically understand their biogeochemical behavior and eco-environmental effects. After drug administration in humans and animals, only a small part of FQs are transformed in vivo. The main transformation processes include formylation, acetylation, oxidation and cleavage of piperazine ring, defluorination and decarboxylation of aromatic core ring, etc. About 70% of the original drug and a small amount of transformed products would be migrated to the environment through excretion. After entering the environment, FQs and their transformation products mainly exist in environmental media such as water, soil and sediment, and undergo migration and transformation processes such as adsorption, photolysis and biodegradation. Adsorption facilitates transfer of FQs from medium to another. The photolysis mainly affects the C7-amine substituents of FQs, whereas the core structure of FQs remains intact. Biodegradation mainly refers to the degradation of FQs by microorganisms and microalgae, including piperazine modification of the piperazine ring such as acetylation and formylation, partial or complete ring cleavage, core structure decarboxylation, defluorination and conjugation formation. The migration and transformation processes of FQs cannot completely eliminate them from the environment. Instead, they would become \"pseudo-persistent\" pollutants, which seriously affect the behavior, growth and reproduction of algae, crustaceans and fish, change biogeochemical cycle, destroy aquatic environment, and stimulate microbial resistance and the generation of resistance genes. In the future, more in-depth studies should be conducted on the environmental behavior of FQs and their impacts on ecological environment, the risk assessment of microbial resistance and resistance genes of FQs, and the mechanism and effect of micro-biodegradation of FQs.
人工合成药物氟喹诺酮类(FQs)是全球使用量第三大的抗生素,在抗菌类药物中发挥着极其重要的作用,然而其过量使用和排放会导致生态环境的变化,严重威胁着人类健康和全球可持续发展。系统研究FQs的生物地球化学行为及其生态环境效应对科学使用和管理此类药物具有重要意义。在人类和动物给药后,仅有小部分FQs在生物体内发生代谢,主要代谢过程包括哌嗪环的甲酰化、乙酰化、氧化和裂解以及芳香核心环的脱氟、脱羧等,约70%的原药和少量的代谢产物通过排泄迁移到环境中。进入环境后,FQs及代谢产物主要存在于水体、土壤和沉积物等环境介质中,发生吸附、光解和生物降解等迁移转化过程。吸附使得FQs从一种介质转移到另一种介质;光解主要影响FQs的C7-胺取代基,而其核心结构仍保持完整;生物降解主要指在微生物和微藻作用下的降解,涉及哌嗪基的乙酰化、甲酰化等修饰和环的部分或完全裂解,核心结构的脱羧、脱氟和共轭物的形成等过程。FQs的迁移转化过程并不能使其从环境中彻底消除,反而成为“伪持久性”污染物,严重影响藻类、甲壳类和鱼类等的行为、生长和繁殖,导致生物地球化学循环改变和水生环境的破坏,加速微生物耐药性的增加和抗性基因的产生。因此,未来应在FQs的海洋环境行为及其生态环境影响、FQs微生物耐药性与抗性基因的风险评估及FQs在微型生物作用下的降解机制与效应等方面进行更深入的研究。.

Irrational use of fipronil for rice pest control often occurred, resulting in high concentrations of fipronil and its transformation products (TPs) (collectively termed fiproles) in aquatic sediment, calling for a better understanding of the migration and transformation of fipronil in surface water as well as efficient methods for source identification. Herein, the fate and transport of fiproles from a paddy field to receiving rivers were assessed in Poyang Lake basin, Jiangxi, China using polar organic chemical integrative samplers with mixed-mode adsorbents (POCIS-MMA). Average concentrations of fiproles in water were 6.16 ± 6.32 ng/L, with median, minimum, and maximum values being 2.99 ± 0.67, 0.40 ± 0.08, and 18.6 ± 3.1 ng/L, respectively. In all samples, over half of fiproles (55.9 %-90.8 %) presented in the form of TPs and fipronil desulfinyl was the dominant TP. Two approaches were applied for source identification, including the change of molar concentration ratios of fipronil to its TPs and the relative attenuation values of fiproles normalized to a reference compound (acetamiprid) that was stable in aquatic environment. While the paddy field upstream was the main source of waterborne fiproles, additional input sources in the downstream region were identified. The present study indicated that the combination of attenuation of molar concentration ratios of micro-pollutants to their respective TPs and relative attenuation values of micro-pollutants\' concentrations normalized to a reference compound measured by POCIS is an effective means to study the migration and transformation of micro-pollutants in field.