Danjiangkou Reservoir is the core water source area for the Middle Route Project of the South-to-North Water Diversion.The heavy metal pollution in the soil of the water-level-fluctuation zone of this reservoir directly affects the ecological environment and water quality safety of the reservoir.This study set up 11 sampling points in the water-level-fluctuation zone of the Danjiangkou Reservoir,systematically analyzed the total and available contents of seven heavy metals,including Cu,Pb,Zn,Cr,Cd,Ni,and As.The pollution degree and ecological risk of heavy metals were evaluated using single-factor pollution index method,comprehensive pollution index method,and potential ecological risk index method.Correlation analysis and principal component analysis methods were used to analyze the sources of heavy metals in the study area.The results show that:①Although the total contents of the seven heavy metals in the study area are all higher than the soil background values in Henan Province,they are all lower than the national soil risk control values.The overall pollution level of heavy metals in the soil in the study area is relatively low.②The overall potential ecological risk of each sampling point is generally at a low level.However,it is worth noting that the potential ecological risk of sampling points 1 and 3 has reached a medium level.Further analysis reveals that the contribution rates of Cd to the comprehensive potential ecological risk index of the above two sampling points are 78.1%and 86.1%respectively,indicating that Cd is the core contributing factor to the regional ecological risk.③Correlation analysis shows that Cd content is significantly positively correlated with total phosphorus,and the biological availability of Cd accounts for up to 24.3%,and its spatial distribution shows a moderate degree of variation.These results collectively indicate that Cd mainly originates from agricultural activities-phosphorus fertilizer input.The results of principal component analysis show that Cr,Ni,Pb,and As mainly come from natural geological background such as rock weathering,while Cu and Zn are mainly related to human activities.The study shows that although the total content of heavy metals in the soil of the study area does not exceed the standard,the current control standard based on the total content of heavy metals in the soil may underestimate the actual ecological risk of Cd.The high reactivity of Cd in the water-level-fluctuation zone and its agricultural source characteristics pose a potential threat to water sources.Therefore,future management should focus on the control of agricultural non-point source pollution of high-reactivity Cd and implement precise prevention and control to ensure the long-term safety of the water source area for the South-to-North Water Diversion.
With the widespread detection of antibiotics in the environment,rapid online monitoring of trace tetracycline in water is of great significance for pollution early warning and risk assessment.To address the drawbacks of conventional analytical methods such as high-performance liquid chromatography,which involve expensive instruments,complex operation,and difficulty in achieving real-time on-site monitoring,this study develops an online detection technique and device based on membrane continuous solid-phase extraction coupled with fluorescence spectroscopy(CSPES).A mixed cellulose membrane is used to selectively enrich tetracycline,and the fluorescence signal on the membrane surface is collected in situ via a light source and an optical fiber probe.System parameters including the distance between the fiber probe and the membrane surface,vacuum pump pressure,and membrane material are optimized to achieve efficient spectral acquisition of tetracycline.By introducing a two-dimensional(2D)smoothing pretreatment method,a CSPES theoretical model is constructed and a quantitative relationship among fluorescence intensity,time,and concentration is established.The calibration curve exhibits a linear correlation coefficient of R²=0.996 6,confirming the applicability of the CSPES model for trace analysis.The method provides a limit of detection of 0.1 μg/L and a linear range of 0.5-5 μg/L.For the prediction of unknown samples,the relative error is less than 2%,and the relative standard deviation(RSD)ranges from 1.27%to 2.08%,demonstrating good quantitative accuracy and repeatability.The method is further applied to spiked drinking water,tap water,and river water samples,yielding recoveries of 95.27%-105.8%with RSDs(n=5)of 1.65%-5.06%,which are consistent with the results obtained by HPLC.This indicates that the device has good adaptability and anti-interference capability in complex water matrices.Compared with traditional detection approaches,the CSPES online detection system features a compact structure,a high degree of automation,fast analysis,and low cost.It provides an efficient,sensitive and scalable technical solution for on-site online monitoring of tetracycline and other antibiotic pollutants and lays a methodological foundation for future extension to simultaneous multi-component detection and intelligent environmental monitoring systems.
With the growing demand for clean energy,electrochemical energy storage devices with high energy density and low cost have become increasingly important for modern electronics,electric vehicles,and large scale energy storage systems.Owing to the high theoretical specific capacity and low cost of sodium metal,sodium metal batteries are regarded as promising candidates for large scale energy storage applications.However,during repeated sodium plating and stripping processes,sodium metal anodes are prone to dendrite growth and side reactions,which may lead to increased polarization and even internal short circuit,thereby severely limiting their cycling life and practical application.Improving the interfacial stability and plating and stripping reversibility of sodium metal anodes is therefore crucial for the practical deployment of high energy density sodium metal batteries.This paper reviews the major challenges associated with sodium metal anodes,including dendrite growth,unstable solid electrolyte interphase(SEI),and volume change.The modification strategies and corresponding mechanisms for stabilizing sodium metal anodes are then systematically summarized,mainly involving the design of composite three dimensional conductive hosts,electrolyte regulation,and artificial interfacial engineering.Finally,the remaining challenges and future research directions are discussed.Future studies should focus on the synergistic integration of multiple strategies and mechanism innovation,while simultaneously optimizing interfacial stability and energy density under practical conditions such as high areal capacity,low sodium excess,and pouch cell evaluation,so as to accelerate the practical application of sodium metal batteries.
