The natural occurrence of arsenic (As) in groundwater & soils and its bioaccumulation in rice grains is a major health concern worldwide. To combat the problem, best combination of irrigation management and suitable rice variety altering As content in grains must be ensured. With this aim, a field trial was conducted with two rice varieties and water management including alternate wetting and drying (AWD) and continuous flooding (CF) irrigation regimes with As contaminated groundwater (AsW) and temporarily stored groundwater (TSG) and river water for only CF (as control). Results revealed that As content in different portions of paddy plant was significantly different (P < 0.001) with irrigation practices and rice varieties. AWD irrigation with TSG accumulated lower As in rice grains compared with CF-AsW for both varieties. Data showed that AWD-TSG practice led to 61.37% and 60.34% grain As reduction for BRRI dhan28 and BRRI dhan29, respectively, compared with CF-AsW. For Principle Component Analysis (PCA), first principle component (PC1) explained 91.7% of the variability and irrigation water As, soil total and available As, straw As, root As and husk As were the dominating parameters. With significant (P < 0.05) variation in yields between the genotypes, AWD increased grain yield by 29.25% in BRRI dhan29 Compared with CF. However, translocation factor (TF) and bioconcentration factor (BCF) for both varieties were less than one for all the treatments. The addition of this study to our knowledge base is that, AWD-TSG with BRRI dhan29 can be an As–safe practice without compromising yields.

Nitrate pollution in oxygenated karst aquifers is common due to nitrification and anthropogenic inputs. However, the shift of nitrogen sources influenced by enhanced rural tourism activities and land use changes are not well understood. In this study, hydrochemistry and dual nitrate isotopes of water samples from a rural karst basin in Chongqing, southwestern China were employed to investigate the nitrate fate and its decadal change during the periods from 2007–2008 and 2017–2019. The results showed that δ¹⁵N–NO₃ and δ¹⁸O–NO₃ values at the groundwater basin resurgence averaged 9 ± 3.4‰ and 2.5 ± 3.4‰, respectively, with a mean NO₃⁻ concentration of 19.7 ± 5.4 mg/L in 2017–2019, clearly exceeding natural background levels. The dual isotope results suggested that nitrification occurred at the sampled sites. From 2007–2008 to 2017–2019, the mean δ¹⁵N–NO₃ values from the primary sink point and the resurgence of the underground river water samples increased from −0.2 ± 2.1 to 11.2 ± 4.8‰, 4.2 ± 0.9 to 9.0 ± 3.4‰, respectively. A Bayesian mixing model in R (MixSIAR) based on the isotopes revealed that soil organic nitrogen, and manure and sewage proportions for the groundwater increased by 34% and 23%, respectively, while chemical fertilizer and atmospheric precipitation proportions decreased by 32% and 25%, respectively. These decadal changes resulted from reforestation practices and enhanced rural tourism activities in the basin, which were evidenced by the change of land use patterns. The elevated nitrogen load from the rapid development of rural tourism is likely to increase this contamination in the near future if the infrastructure cannot meet the demands. The results from this study could contribute to minimizing environmental health risks in drinking water when rural tourism activities are increasing.

Research on per- and polyfluoroalkyl substances (PFAS) in freshwater ecosystems has focused primarily on legacy compounds and little is still known on the presence of emerging PFAS. Here, we investigated the occurrence of 60 anionic, zwitterionic, and cationic PFAS in a food web of the St. Lawrence River (Quebec, Canada) near a major metropolitan area. Water, sediments, aquatic vegetation, invertebrates, and 14 fish species were targeted for analysis. Levels of perfluorobutanoic acid (PFBA) in river water exceeded those of perfluorooctanoic acid (PFOA) or perfluorooctane sulfonate (PFOS), and a zwitterionic betaine was observed for the first time in the St. Lawrence River. The highest mean PFAS concentrations were observed for the benthopelagic top predator Smallmouth bass (Micropterus dolomieu, Σ₆₀PFAS ∼ 92 ± 34 ng/g wet weight whole-body) and the lowest for aquatic plants (0.52–2.3 ng/g). Up to 33 PFAS were detected in biotic samples, with frequent occurrences of emerging PFAS such as perfluorobutane sulfonamide (FBSA) and perfluoroethyl cyclohexane sulfonate (PFECHS), while targeted ether-PFAS all remained undetected. PFOS and long-chain perfluorocarboxylates (C10–C13 PFCAs) dominated the contamination profiles in biota except for insects where PFBA was predominant. Gammarids, molluscs, and insects also had frequent detections of PFOA and fluorotelomer sulfonates, an important distinction with fish and presumably due to different metabolism. Based on bioaccumulation factors >5000 and trophic magnification factors >1, long-chain (C10–C13) PFCAs, PFOS, perfluorodecane sulfonate, and perfluorooctane sulfonamide qualified as very bioaccumulative and biomagnifying. Newly monitored PFAS such as FBSA and PFECHS were biomagnified but moderately bioaccumulative, while PFOA was biodiluted.

Optimizing landscape pattern to reduce the risk of non-point source (NPS) pollution is an effective measure to improve river water quality. The “source-sink” landscape theory is a recent research tool for landscape pattern analysis that can effectively integrate landscape type, area, spatial location, and topographic features to depict the spatial heterogeneity of NPS pollution. Based on this theory, we quantitatively analyzed the influence of “source-sink” landscape pattern on the river water quality in one of the most intensive agricultural watersheds in Southeastern China. The results indicated that the proportion of “sink” landscape (68.59%) was greater than that of “source” landscape (31.41%) in the study area. In addition, when elevation and slope increased, the “source” landscape proportion decreased, and the “sink” landscape proportion increased. Nitrogen (N) and phosphorus (P) pollutants in rivers showed significant seasonal and spatial variations. Farmland was the primary source of nitrate nitrogen (NO₃⁻-N) and total nitrogen (TN) pollution, whereas residential land was the primary source of ammonium nitrogen (NH₄⁺-N) and total phosphorus (TP) pollution. Intensively cultivated areas and densely inhabited areas degraded water quality despite high proportions of forest land. The four “source-sink” landscape indices (LWLI, LWLI'e, LWLI's, LWLI'd) had significant positive correlations with NO₃⁻-N and TN and weak correlations with NH₄⁺-N and TP. The capacity of LWLI to quantify the NPS pollution was greater in agricultural areas than in residential areas. The “source-sink” landscape thresholds resulted in abrupt changes in water quality. When LWLI was ∼0.35, the probability of river water quality degradation increased sharply. The results suggest the importance of optimizing the “source-sink” landscape pattern for mitigating agricultural NPS pollution and provide policy makers with adequate new information on the agroecosystem-environmental interface in highly developed agricultural watersheds.

Estuarine rivers are the primary medium for transporting pollutants from human activities to the ocean. Polycyclic aromatic hydrocarbons (PAHs) have substantial toxicity and pose a significant risk to ecosystem and human health. However, the influences of urbanization on their distribution, particularly in China where urbanization is occurring rapidly, remain unclear. This study took three coastal economic circles of China as research areas, and investigated PAHs (16 species) in the estuarine river water. 95.9% of the sampling sites demonstrated moderate PAHs pollution and moderate ecological risk. Coal and petroleum combustion was the primary source of PAHs, but the source composition varied among the regions. Air pollution caused by energy emissions, particularly carbon emissions, has a critical and differential effect on PAHs distribution and deposition. With the increasing use of clean energy, PAHs emissions have been gradually reduced, which provides an effective option for PAHs reduction in a rapidly urbanizing coastal region.

Nitrogen (N) is an essential nutrient but may become a pollution source in the environment when the N concentration exceeds a certain threshold for humans and nature. Nitrate is a major N species in river water with notable spatial and temporal variations under the influences of natural factors and anthropogenic N inputs. We analyzed the relationship between riverine N (focusing on nitrate) concentration and various factors (land use, climate, basin topography, atmospheric N deposition, agricultural N sources and human-derived N) in 104 rivers located throughout the Japanese Archipelago except small remote islands. We aimed to better understand processes and mechanisms to explain the spatial and temporal changes in riverine nitrate concentration. A publicly available river water quality database observed in the 1980s (1980–1989) and 2000s (2000–2009) was used. This study is the first to evaluate the long-term scale of 20 years in the latter half of Japan's economic growth period at the national level. A geographic information system (GIS) was employed to determine average values of each variable collected from multiple sources of statistical data. We then performed regression analysis and structural equation modeling (SEM) for each period. The forestland area influenced by the basin topography, climate (i.e., air temperature) and other land uses (i.e., farmland and urban area) played a major role in decreasing nitrate concentrations in both the 1980s and 2000s. Atmospheric N deposition (especially N oxides) and agricultural N sources (fertilizer and manure) were also significant variables regarding the spatial variations in riverine nitrate concentrations. The SEM results suggested that human-derived N (via food consumption) intensified by demographic shifts during the 2000s increased riverine nitrate concentrations over other variables within the context of spatial variation. These findings facilitate better decision making regarding land use, agricultural practices, pollution control and individual behaviors toward a sustainable society.

Microplastic pollution in the Yangtze River Basin has become a major concern; however, the variations in different environmental compartments are unknown. Here, we compiled published information including detection methods, occurrence, and characterization of microplastics from 624 sampling sites in river water, river sediment, lake and reservoir water, and lake and reservoir sediment in the Yangtze River Basin. The spatial distribution of sampling sites shows fractal pattern and was uniformly concentrated around the main stream of the Yangtze River and the lake geographical zone. Collection, pretreatment, identification, and quantification processes varied among different studies. Non-parametric tests were performed to compare the different microplastic indices. A Pearson correlation analysis was used to study the relationship between microplastic pollution and local socioeconomic conditions. We found that the microplastic size and abundance distribution in river water and lake and reservoir water showed different patterns for different sampling methods, indicating that different methods influenced the results. Population density and urbanization rate are suggested to be important factors influencing the spatial heterogeneity of microplastic abundances in water, rather than in sediment. The microplastic abundances in lake and reservoir water were higher than that in river water in bulk samples. However, microplastic abundances among different sediment environments shows no significant difference. For bulk water samples and sediment samples overall, the proportion of small microplastics (<1 mm, i.e. SMP), fibers, transparent debris, and polypropylene (PP) were 65.1%, 67.8%, 31.8%, and 29.7%, respectively. The microplastic characteristics of lake and reservoir water and sediment were similar, differing from those of river water and sediment. This study provides the first basin scale insight into microplastic occurrence and characteristics in different environments in the Yangtze River Basin.

The sulfate pollution in water environment gains more and more concerns in recent years. The discharge of domestic, municipal, and industrial wastewaters increases the riverine sulfate concentrations, which may cause local health and ecological problems. To better understand the sources of sulfate, this study collected water samples in a typical agricultural watershed in East Thailand. The source apportionment of sulfide was conducted by using stable isotopes and receptor models. The δ³⁴SSO₄ value of river water varied from 1.2‰ to 16.4‰, with a median value of 8.9‰. The hydrochemical data indicated that the chemical compositions of Mun river water were affected by the anthropogenic inputs and natural processes such as halite dissolution, carbonate, and silicate weathering. The positive matrix factorization (PMF) model was not suitable to trace source of riverine sulfate, because the meaning of the extracted factors seems to be vague. Based on the elemental ratio and isotopic composition, the inverse model yielded the relative contribution of sulfide oxidation (approximately 46.5%), anthropogenic input (approximately 41.5%), and gypsum dissolution (approximately 12%) to sulfate in Mun river water. This study indicates that the selection of models for source apportionment should be careful. The large contribution of anthropogenic inputs calls an urgent concern of the Thai government to establish effective management strategies in the Mun River basin.

The extensive use of melamine and its three derivatives (i.e., ammeline, ammelide, and cyanuric acid) resulted in their widespread occurrence in the environment. Nevertheless, limited information is available on their distribution in the aquatic environment. In this study, concentrations and profiles of melamine and its derivatives were determined in 223 water samples, comprising river water, lake water, seawater, tap water, bottled water, rain water, wastewater, and swimming pool water, collected from New York State, USA. The sum concentrations of melamine and its derivatives (∑₄MELs) decreased in the following order: swimming pool water (median: 1.5 × 10⁷ ng/L) ≫ wastewater (1240) > precipitation (739) > tap water (512) > river water (370) > lake water (347) > seawater (186) > bottled water (98). Cyanuric acid was the major compound, accounting for 60–100% of ∑₄MELs concentrations in swimming pool water, wastewater, precipitation, tap water, seawater, and bottled water, whereas melamine dominated in river and lake water (54–64% of ∑₄MELs). Significant positive correlations (0.499 < R < 0.703, p < 0.002) were found between the concentrations of melamine and atrazine (a triazine herbicide) in surface waters. The geographic distribution in the concentrations of ∑₄MELs in river, lake, and tap water corresponded with the degree of urbanization, suggesting that human activities contribute to the sources melamine and cyanuric acid in the aquatic environments. A preliminary hazard assessment of melamine and cyanuric acid in waters suggested that their ecological or human health risks were minimal. This is the first study to document the occurrence and spatial distribution of melamine and its derivatives in waters from the United States.