Dissolved organic matter (DOM), usually measured as concentrations of dissolved organic carbon (DOC) and nitrogen (DON) and chromophoric dissolved organic matter (CDOM), plays a crucial role in the global carbon and nitrogen cycles in inland waters. The aim of this study is to characterize spatial variations of DOC, DON, and C:N molar ratios and CDOM using absorption spectroscopy and further determine their relationships using pearson correlations (r) for urban waters along trophic gradients in the lower reaches of the Yellow River (YR) of China. A dataset of 122 urban water samples were collected from four typical cities during 2021-2022. Principal component analysis (PCA) was performed to assess the relative distribution of these urban water samples. These urban waters can be grouped into two categories: mesotrophic waters (n = 57) and eutrophic waters (n = 65) based on trophic state index (TSI) threshold value of 50. Results revealed that there were significantly higher DOC, CDOM absorption and SUVA254 along with lower S275-295 and M (t-test, p < 0.01) in eutrophic waters compared with mesotrophic waters. DOC was significantly higher than DON (p < 0.01). DOC was highly related to DON (R2 = 0.649) and COD (R2 = 0.840) suggesting they were derived from a common source. CDOM absorption a(254) was strongly correlated with DOC (R2 = 0.770) and COD (R2 = 0.800). DON can be calculated based on the strong correlations between DOC and DON and then C:N molar ratios can be further obtained for these urban waters. These results implied that CDOM optical absorption a(254) can be viewed as the best indicators of DOC and associated with water quality parameters. These findings can help us to better understand DOC, DON and CDOM of DOM coupled cycling processes for urban waters with similar climatic and hydrologic conditions on basin scale in China.

Microplastics (MPs), measuring less than 5 mm, pose threats to ecological security and human health in urban waters. Additionally, they act as carriers, transporting pollutants from terrestrial systems into oceanic circulation, contributing to global pollution. Recognizing the significance of identifying MPs in urban waters, one potential solution to the time-consuming and labor-intensive manual identification process is the application of a convolutional neural network (CNN). Therefore, having a reliable CNN model that efficiently and accurately identifies MPs is essential for extensive research on MPs pollution in urban waters. In this work, an MPs dataset with complex background was acquired from urban waters in southern China. The dataset was used to train and validate CNN models, including UNet, UNet2plus, and UNet3plus. Subsequently, the computational and inference performance of the three models was evaluated using a newly collected MPs dataset. The results showed that UNet, UNet2plus, UNet3plus, after being trained for 120 epochs, provided efficient inferences within less than 1 s, 2 s, and 3 s for 100 MPs images, respectively. Accurate segmentation with mIoU of 91.45 ± 5.93 % and 91.08 ± 6.18 % was achieved using UNet and UNet2plus, respectively, while UNet3plus exhibited a lower performance with only 82.21 ± 10.33 % mIoU. This work demonstrated that UNet and UNet2plus deliver efficient and accurate identification of MPs in urban waters. Developing CNN models that efficiently and accurately identify MPs is crucial for reducing manual time, especially in large-scale investigations of MPs pollution in urban waters.

In urban waters, microplastics (MPs) usually form hetero-aggregates through adsorption of organics and microbes. However, the effects of hetero-aggregates on water quality are rarely reported. In this study we found that the hetero-aggregates, which accumulated contaminants, were like a \"time bomb\". Chlorination was able to trigger the \"time bomb\" through destruction of hetero-aggregates, lysis of microbial cells and elevation of the concentration of low-molecular-mass organics. Thereupon previously adhered organics desorbed from MPs, intracellular metabolites were released from lysed cells, and re-formation of hetero-aggregates was limited. This process rapidly increased the concentration of organics but prevented the re-adsorption of organics, which leads to secondary pollution. Thus, to alleviate the risks of secondary pollution caused by hetero-aggregates, the choice of oxidant species and dose should be optimized based on the characteristics of existent hetero-aggregates when purifying urban waters containing MPs.

Urban stream monitoring programs rarely consider the daily cycle of water quality. Furthermore, water quality indexes (WQIs) often rely on an excessive number of correlated parameters. To the best of our knowledge, no previous study used both the principal component analysis (PCA) and the daily cycle of the water quality of urban streams to create better WQIs. In this context, the present study aimed to develop a novel urban WQI (WQIurban) considering these two factors. Moreover, the main WQI in Brazil for water quality assessment for public supply (WQIcetesb) was used as a starting point (parameters: total solids (TS), temperature, turbidity, biochemical oxygen demand, pH, dissolved oxygen (DO), total nitrogen, total phosphorus, and thermotolerant coliforms (Escherichia coli)). The selected parameters to integrate the WQIurban received weights according to their importance for the conformation of water quality and a quality value was assigned to each parameter as a function of its concentration or measure. The developed WQIurban (parameters: pH, TS, E. coli, and DO) was able to maintain the seasonal and daily patterns of the urban stream water quality compared to the WQIcetesb. Nevertheless, the spatial relationship among the sampling sites was somewhat lacking. Our findings can help environmental managers, policy planners, and local researchers to improve their urban stream monitoring programs, saving money, time, and resources. Moreover, the WQIurban can be helpful during exceptional circumstances in which the water quality of urban streams must be quickly assessed.

The ubiquitous micro/nanoplastics (MPs/NPs) in urban waters are priority pollutants due to their toxic effects on living organisms. Currently, great efforts have been made to realize a plastic-free urban water system, and the identification and removal of MPs/NPs are two primary issues. Among diverse methods, emerging electrochemical techniques have gained growing interests owing to their facile implementation, high efficiency, eco-compatibility, onsite operation, etc. Herein, recent progress in the electrochemical identification and removal of MPs/NPs in urban waters are comprehensively reviewed. The electrochemical sensing of MPs/NPs and their released pollutants (e.g., bisphenol A (BPA)) has been analyzed, and the sensing principles and the featured electrochemical devices/electrodes are examined. Afterwards, recent applications of electrochemical methods (i.e., electrocoagulation, electroadsorption, electrokinetic separation and electrochemical degradation) in MPs/NPs removal are discussed in detail. The influences of critical parameters (e.g., plastics\' property, current density and electrolyte) in the electrochemical identification and removal of MPs/NPs are also analyzed. Finally, the current challenges and prospects in electrochemical sensing and removal of MPs/NPs in urban waters are elaborated. This review would advance efficient electrochemical technologies for future MPs/NPs pollutions management in urban waters.

The omnipresent micro/nanoplastics (MPs/NPs) in urban waters arouse great public concern. To build a MP/NP-free urban water system, enormous efforts have been made to meet this goal via separating and degrading MPs/NPs in urban waters. Herein, we comprehensively review the recent developments in the separation and degradation of MPs/NPs in urban waters. Efficient MP/NP separation techniques, such as adsorption, coagulation/flocculation, flotation, filtration, and magnetic separation are first summarized. The influence of functional materials/reagents, properties of MPs/NPs, and aquatic chemistry on the separation efficiency is analyzed. Then, MP/NP degradation methods, including electrochemical degradation, advanced oxidation processes (AOPs), photodegradation, photocatalytic degradation, and biological degradation are detailed. Also, the effects of critical functional materials/organisms and operational parameters on degradation performance are discussed. At last, the current challenges and prospects in the separation, degradation, and further upcycling of MPs/NPs in urban waters are outlined. This review will potentially guide the development of next-generation technologies for MP/NP pollution control in urban waters.

Freshwater ecosystems are characterized by complex and highly dynamic microbial communities that are strongly structured by their local environment and biota. Accelerating urbanization and growing city populations detrimentally alter freshwater environments. To determine differences in freshwater microbial communities associated with urbanization, full-length 16S rRNA gene PacBio sequencing was performed in a case study from surface waters and sediments from a wastewater treatment plant, urban and rural lakes in the Berlin-Brandenburg region, Northeast Germany. Water samples exhibited highly habitat specific bacterial communities with multiple genera showing clear urban signatures. We identified potentially harmful bacterial groups associated with environmental parameters specific to urban habitats such as Alistipes, Escherichia/Shigella, Rickettsia and Streptococcus. We demonstrate that urbanization alters natural microbial communities in lakes and, via simultaneous warming and eutrophication and creates favourable conditions that promote specific bacterial genera including potential pathogens. Our findings are evidence to suggest an increased potential for long-term health risk in urbanized waterbodies, at a time of rapidly expanding global urbanization. The results highlight the urgency for undertaking mitigation measures such as targeted lake restoration projects and sustainable water management efforts.

Non-target screening (NTS) has gained interest in recent years for environmental monitoring purposes because it enables the analysis of a large number of pollutants without predefined lists of molecules. However, sample preparation methods are diverse, and few have been systematically compared in terms of the amount and relevance of the information obtained by subsequent NTS analysis. The goal of this work was to compare a large number of sample extraction methods for the unknown screening of urban waters. Various phases were tested for the solid-phase extraction of micropollutants from these waters. The evaluation of the different phases was assessed by statistical analysis based on the number of detected molecules, their range, and physicochemical properties (molecular weight, standard recoveries, polarity, and optical properties). Though each cartridge provided its own advantages, a multilayer cartridge combining several phases gathered more information in one single extraction by benefiting from the specificity of each one of its layers.

One way to monitor watercourses regarding water quality is by using Water Quality Indexes (WQIs). Currently, there is a lack of information about their behavior in the diurnal cycle as sampling is often carried out in the morning. Also, few papers focus on assessing the urban impact on the spatial variability of WQIs in tropical first-order streams. Such streams receive many pollutants varying in intensity according to population habits, justifying the possible diurnal variation in water quality, in addition to climatic attributes. This paper aimed to evaluate the fluctuations in the Brazilian WQI and its parameters [temperature, turbidity, total solids (TS), hydrogen potential, dissolved oxygen (DO), biochemical oxygen demand (BOD), total phosphorus (TP), total nitrogen (TN), and E. coli] between the morning (8 am), afternoon (2 pm), and night (7 pm) periods for an urban first-order tropical stream. Overall, the lowest DO concentrations and highest values of TS, turbidity, BOD, TP, TN, and E. coli were obtained in the morning, possibly representing population habits: the greatest generation of pollutants occurs overnight and early morning since there are clandestine domestic wastewater inputs into the stream, whose hourly periodicity generates a similar periodicity in the WQI of the evaluated stream. Although there was a significant variation in WQI average values between morning (15.50 ± 1.97) and afternoon (20.83 ± 5.42) only during the dry season (p < 0.05), different results ​​were common throughout the day in all months and the water quality was often classified in distinct categories: \'very bad\', \'bad\', and \'regular\'. Our findings present another dimension to be considered when assessing urban water quality, leading to direct benefits to the management and use of urban waters. This article is protected by copyright. All rights reserved.

Pharmaceutical micropollutants\' contamination of urban waters has been studied globally for decades, but the concentration of innovations in management initiatives is still in developed economies. The gap between the locus of innovations in pharmaceuticals and the relative stagnation in less developed economies to manage waste originating in this activity seems fruitful for investigations on innovation in integrated micropollutant management strategies. These tensions allow for advances in current knowledge for environmental management and, particularly, finding solutions for the contamination by pharmaceutical micropollutants of urban water bodies in developing countries. We aim to list the main strategies for managing pharmaceutical micropollutants discussed to point out opportunities for developing countries to advance in this direction. Methodologically, we conducted a systematic literature review from 1990 to 2020, covering 3027 documents on \"pharmaceutical micropollutants management.\" The framework formed by the macro-approach to integrated management operationalized by the dimensional micro-approaches: technical, organizational, community, and governmental allowed us to understand that (1) the management of pharmaceutical micropollutants tends to occur through a technical approach centered on the removal of aquatic matrices, green chemistry, and urine diversion; (2) management with an organizational approach has enabled removing drugs from water bodies by drug take-back program, collaborative projects, drug use reduction, and better organizational practices; (3) the community approach have helped minimize this type of pollution by reducing the consumption of medicines and the proper destination for medicines that are no longer in use. Finally, the government management approach emerges as a source of legal, economic, and informational instruments to reduce pollution by pharmaceutical micropollutants. Furthermore, these management approaches allowed us to identify 15 opportunities for possible adjustments for developing societies. These opportunities can be promising for practices and research and, in the medium term, contribute to minimizing pollution by pharmaceutical micropollutants in urban waters.