Major ion and dissolved heavy metal geochemistry, distribution, and relationship in the overlying water of Dongting Lake, China

Vertical Distribution Characteristics and Ecological Risk Assessment of Mercury and Arsenic in Ice, Water, and Sediment at a Cold-Arid Lake

Mercury and arsenic are two highly toxic pollutants, and many researchers have explored the effects of the two substances on the environment. However, the research content of toxic substances in frozen periods is relatively small. To explore the spatial and vertical distribution of mercury and arsenic in the ice, water, and sediments of Wuliangsuhai Lake under ice conditions, and to assess the harm degree of the two toxic substances to human beings. We collected the ice, water, and sediments of the lake in December 2020, and tested the contents of Hg and As. The single-factor pollution index method, the local cumulative index method, and the ecological risk coding method were used to assess the pollution status in these three environmental media, and the Monte Carlo simulation combined with the quantitative model recommended by USEPA was used to assess the population health risk. The results showed that (1) The average single-factor pollution values of Hg and As in water were 0.367 and 0.114, both pollutants were at clean levels during the frozen period. (2) The mean Igeo values of Hg and As were 0.657 and -0.948. The bioavailability of Hg in the sediments of Wuliangsuhai Lake during the frozen period was high, and its average value was 7.8%, which belonged to the low-risk grade. The bioavailability of As ranged from 0.2% to 3.7%, with an average value of 1.3%. (3) Monte Carlo simulation results indicate acceptable levels of health risks in both water and ice. This study preliminarily investigated the distribution characteristics of toxic substances and their potential effects on human health in lakes in cold and arid regions during the frozen period. It not only clarified the pollution characteristics of lakes in cold and arid regions during the frozen period, but also provided beneficial supplements for the ecological protection of lake basins. This study lays a foundation for further environmental science research in the region in the future.

Environmental water in Kolkata is suitable for the survival of Vibrio cholerae O1

Many patients with cholera emerge in Kolkata, India throughout the year. Such emergency indicates that cholera toxin-producing Vibrio cholerae O1 (toxigenic V. cholerae O1) are widespread in Kolkata. This suggests that the suitable conditions for replication of toxigenic V. cholerae O1 is provided in Kolkata. In previous studies, we found that the replication rate of toxigenic V. cholerae O1 is low in the low ionic aqueous solution. Then we measured the ion concentration in the environmental water of Kolkata. As a control, we measured them in Japanese environmental water. The ion concentration in the environmental water of Kolkata was significantly high. Then, we examined the survival of toxigenic V. cholerae O1 in groundwater from Kolkata and found that V. cholerae O1 survive for long time in the solution but not in the solution diluted with Milli Q water. In addition, we found that V. cholerae O1 proliferated in environmental water of Kolkata to which a small amount of nutrient was added, but did not grow in the environmental water diluted with water to which the same amount of nutrient was added. These results indicate that the environmental water from Kolkata is suitable for survival of V. cholerae O1.

A method of assessing the depth of contaminated sediments that should be removed in lakes: a case study of Tangxun Lake, China

The depth of contaminated sediments constrains the water environment of large shallow lakes and can affect shallow lake water quality through sediment resuspension and nutrient release. Although such effects can be avoided by sediment dredging methods, we still cannot precisely quantify the depth of sediment dredging. Therefore, we used organic index method, pollution index method and potential ecological risk evaluation to evaluate the contamination status of split samples of in situ sediments layer by layer, and established a comprehensive contamination index evaluation method for layer-by-layer sediments, then combined with the contamination release characteristics of split samples to assess the contamination degree of the sediments obtained. The results show that the content of nitrogen and phosphorus in the surface layer of Lake Townsend sediments is generally higher than that in the middle and bottom sediments, and the heavy metals also satisfy this pattern, which is consistent in the sediments of both east and west regions. We also simulated the release process of nitrogen and phosphorus nutrients in the in situ sediment of Tangxun Lake in 2019, and the experimental results showed that the risk of nitrogen and phosphorus nutrient release in the sediment was mainly concentrated in the surface and middle layers, and the risk of elemental nitrogen release was significantly greater than that of phosphorus release. Finally, a comprehensive evaluation was carried out to obtain the desilting depth of the sediments in Lake Townsend, and it can be determined that the recommended desilting depth is about 20 cm for West Lake and 30 cm for East Lake. The results show that the recommended dredging depth can be determined based on this method, which provides an important scientific basis for sediment dredging in Tangxun Lake and even provides a new paradigm for sediment dredging depth estimation in similar large shallow lakes.

Multivariate statistical analysis of potentially toxic elements in the sediments of Quanzhou Bay, China: Spatial relationships, ecological toxicity and sources identification

In this paper, the spatial distribution, pollution degree, ecological toxicity and possible sources of seven potentially toxic elements (PTEs) collected from the surface sediments of Quanzhou Bay (QZB) were analyzed by obtaining concentration measurements. The results indicated that the areas with high Cu, Pb, Zn and Hg concentrations were mainly located in the Luoyang River estuary, while the areas with high contents of Cd and As appeared in the Luoyang River estuary area and in the southern part of QZB, respectively. The contamination indices showed that the Cd pollution degree was slight to serious, while other elements were slightly enriched. The calculation results of the potential ecological risk index (RI) and toxic risk index (TRI) indicated that Cd was the main element posing ecological risk among the PTEs of sediments in QZB, followed by Hg. Moreover, in approximately 30% of the surveyed sites, PTEs exhibited low toxicity to aquatic ecosystems. Finally, the self-organizing map (SOM) and positive matrix factorization (PMF) model were used to determine the PTEs sources. Natural sources, industrial emissions, and the combustion of fossil fuels were three main sources for PTEs in the surface sediments of QZB. This study provides a reference for assessing sediment pollution and managing marine pollution in QZB.

Spatial distribution and source identification for heavy metals in surface sediments of East Dongting Lake, China

Dongting Lake is one of the most important inland freshwater lakes in China. To investigate the spatial distribution and seasonal variation characteristics of heavy metals (Cr, Co, Cu, Zn, Cd, and Pb) in the lake, 53 surface sediment samples were collected in the East Dongting Lake (ED Lake) in the wet and dry seasons. Results show Cr, Co, Cu, Zn, Cd, and Pb contents were 1.7 (1.9), 1.8 (2.0), 2.9 (3.0), 1.9 (1.9), 11.7 (13.1), and 2.0 (2.2)-fold of their geochemical soil background values of Hunan province (China) in the wet (dry) season. Spatial and seasonal heterogeneity could be found in the distribution of Cr, Co, Cu, Zn, and Pb in the surface sediments. The enrichment factor (EF) suggested that Cd has reached severe enrichment in the sediment. The result of the geo-accumulation index (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${I}_{geo}$$\end{document}Igeo) indicated that Cr, Co, Cu, Zn, and Pb were at levels corresponding to low contamination, and moderately to highly polluted with Cd. Multivariate statistical analysis including pearson correlation analysis and principal component analysis was used for the identification of potential sources of the heavy metals in the sediments. The results showed that Cu, Zn, and Pb from the sediments of the East Dongting Lake in the wet and dry seasons were possibly anthropogenic sources, such as emissions from mining and smelting while Al, Fe, and Cr are attributed for natural sources. Cd enrichment in the sediments is influenced by both natural factors, and human activities in local areas.

Hydrochemical and stable isotopic spatiotemporal variation characteristics and their environmental significance in the Kashi River Mountain Area of Ili, Xinjiang, China

The supply sources of a water resource in arid area can be determined through analysis of the hydrochemical and stable isotopic characteristics of runoff in an alpine glacier river basin. Using mathematical statistical analyses, Piper diagrams, and Gibbs diagrams, this study analyzed the spatiotemporal variations of the hydrochemistry and the stable hydrogen and oxygen isotopes of the Kashi River in Ili (Xinjiang, China) to investigate their characteristics and environmental importance. Runoff samples were collected in the mountainous area of the Kashi River from December 2017 to November 2018. Results showed that the runoff water type of the Kashi River is Ca²⁺-HCO₃^- and the spring water type is Ca²⁺-HCO₃^--SO₄^2-. The main factors controlling the hydrochemical composition of runoff were rock weathering. Under the influence of supply sources and water conservancy facilities, the hydrochemistry and stable isotopic characteristics of the runoff showed evident spatiotemporal variation. The hydrochemical and stable isotopic values of runoff in winter and spring were lower and more consistent in comparison with those in summer and autumn. The characteristics of the spatial variations of hydrochemical and stable isotopic values in runoff differed with elevation. The supply sources in the Kashi River in different seasons were determined by analyzing the temporal variation characteristics of the hydrochemistry and stable isotopes of runoff.

Geochemical and Statistical Analyses of Trace Elements in Lake Sediments from Qaidam Basin, Qinghai-Tibet Plateau: Distribution Characteristics and Source Apportionment

The safety of lake ecosystems on the Qinghai-Tibet Plateau (QTP) has attracted increasing attention, owing to its unique location and ecological vulnerability. Previous studies have shown that the aquatic systems on the QTP have been polluted to varying degrees by trace elements. However, little is known of the distribution and sources of trace elements in lakes in the northeast QTP. Here, 57 sediment samples were collected from six lakes (Dasugan Lake, Xiaoqaidam Lake, Kreuk Lake, Toson Lake, Gahai Lake and Xiligou Lake) in the Qaidam Basin, northeast QTP, and the trace elements (V, Cr, Ni, Cu, Zn, As, Ba, Tl, Cd, Pb, and U) were analyzed. The results indicated that Ba, Zn, V, and Cr had a higher content and a wider distribution relative to the other tested elements. Correlation coefficient matrix results showed that the trace elements in the study area were strongly correlated, revealing their source of similarity. Self-organizing maps (SOM, an artificial neural network algorithm) results indicated that the degree of pollution in Xiaoqaidam Lake was the highest, and that of Dasugan Lake was the lowest. Furthermore, all sampling points were clustered into four categories through K-means clustering. The positive matrix factorization (PMF) results indicated that atmospheric deposition and anthropogenic inputs were the main trace elements sources in these lakes, followed by traffic emission and geological sources. Collectively, trace elements of six lakes in Qinghai-Tibet Plateau presented high-content and pollution characteristics. This research provides a scientific basis for better water environment management and ecological protection on the QTP.

Restriction of dissolved organic matter on the stabilization of Cu(II) by phosphate

The precipitation of Cu(II) by phosphate and the influence of dissolved organic matter (DOM) on the precipitation are essential for the fate of Cu(II) in aquatic environments. In this study, the influence of DOM on the reaction of phosphate with Cu(II) was investigated. Here, 51.61%, 29.75%, and 24.32% of the added Cu(II) (50 μM) precipitated without DOM and with the addition of fulvic acid (FA) and humic acid (HA), respectively, owing to the reaction with phosphate (50 μM). Excitation-emission matrix spectroscopy-parallel factor (PARAFAC) and two-dimensional ultraviolet-visible correlation spectroscopy analyses were conducted to characterize the influence of DOM on the precipitation of Cu(II) with phosphate. One humic-like and two protein-like fluorescent components were identified by the PARAFAC model for FA, whereas two humic-like fluorescent components and one protein-like fluorescent component were validated for HA. The humic-like components had primary roles, whereas the protein-like components had secondary roles in limiting the precipitation of Cu(II) with phosphate. Cu(II) binding to DOM chromophores initially occurred at shorter wavelengths, and then at longer wavelengths. Phenolic and carboxylic constituents had important roles, and HA exhibited more binding sites than FA. Therefore, humic-like fluorescent components and chromophores containing phenolic and carboxylic groups and functional groups with peaks at short wavelengths (200-220 nm) were primarily responsible for restricting the precipitation of Cu(II) with phosphate.

Estimation of spatial distribution and health risk by arsenic and heavy metals in shallow groundwater around Dongting Lake plain using GIS mapping

Potable groundwater has become the primary water source for the local population because of the serious pollution of As and heavy metals in the surface water around the Dongting Lake Plain. A comprehensive research on the shallow groundwater was performed in this study via geographical information system (GIS) and geochemical method to evaluate groundwater quality and health risks of shallow groundwater in Dongting Lake Plain. Eighty-seven samples were collected and the content of As and twelve other heavy metals (e.g., Al, Fe, Zn, Cu, Mo, Ni, Mn, Co, Ba, Pb, Cd, and Cr) in the samples were detected by inductively coupled plasma-mass spectrum (ICP-MS) technology. The water pollution situation was assessed using heavy metal contents and evaluation indices, and human health risks were evaluated on the basis of both carcinogenic and noncarcinogenic aspects. Results showed that the shallow groundwater quality is moderately to heavily contaminated and should be considered in some areas of the Li and Xiangjiang River coasts. Several regions have the potential of carcinogenic risks induced by As and the groundwater in some regions may have the risk of Cr carcinogenesis in the wet season. These findings suggested that the potential harm caused by Fe, Zn, Mn, Cr, and As pollution of groundwater, especially As and Cr in wet season, must be considered. The spatio-temporal study on the groundwater quality evaluation may be beneficial to the protection and sustainable development of groundwater resources in Dongting Lake Plain.Summary: Although the overall noncarcinogenic health risk by metals in shallow groundwater of Dongting Lake is low, noncarcinogenic health risks caused by Fe, Zn, Mn, and As exist in some areas.

Hydrogeochemical baseline in a human-altered landscape of the central Pacific coast of Costa Rica

Groundwater pollution in tropical and human-altered coastal landscapes is receiving novel attention due to decreasing in annual recharge as a consequence of recurrent droughts and overexploitation, whereby saline intrusion, point and diffuse source contamination, and water conflicts are common denominators. This study presents a detailed groundwater evaluation in a coastal aquifer within the central Pacific coast of Costa Rica. Three sampling campaigns including major ions, heavy metals, and fecal coliform analyses were conducted between July 2013 and March 2014 across 17 wells within the alluvial and fissured units of the Jacó aquifer. The groundwater system is classified as mixed HCO₃^--Ca²⁺-Mg²⁺ type. Coliforms presence was found in two wells, nearby Mona Creek headwaters and near the coastal line. Heavy metal concentrations were below quantification limits in most of the wells; however, chromium concentrations up to 6.56 μg/L were quantified within the coastal line and central portion of the alluvial aquifer in 20 out of the 48 samples. The spatial distribution of major ions (K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^-, SO₄^2-, and HCO₃^-) exhibited an increasing trend towards the central portion of the alluvial aquifer, which may be potentially associated with the large unregulated urban expansion, invoking a need of a continuous water quality monitoring program in this touristic hot spot. This study provides useful information for other similar coastal aquifers in Central America, whereby increasing population growth and unregulated touristic, industrial, and agricultural activities are posing a truly challenge to ensure water security and sustainability parallel to the economic development in a changing climate.

Distribution, sources and health risk assessment of contaminations in water of urban park: A case study in Northeast China

This case study was performed to determine whether the pollutants in water of urban park could bring health risk to human engaging in water-related activities such as swimming and provide evidence demonstrating the critical need for strengthened recreational water resources management of urban park. TN, NH₄⁺-N, TP, Cu, Mn, Zn, Se, Pb, As, Cd and Cr(VI) contents were determined to describe the spatial distribution of contaminations; sources apportionment with the method of correlation analysis, factor analysis and cluster analysis were followed by health risk assessment for swimmers of different age groups. The results reveal that element contents in all sites do not exceed Chinese standard for swimming area and European Commission standard for surface water; all detected elements except Cr(VI) have a tendency to accumulate in the location of lake crossing bridge; Mn and Zn are considered to have the same pollution source including geogenic and anthropogenic sources by multivariable analysis. Carcinogenic risks of different age groups descend in the same order with non-carcinogenic risks. Among all elements, Zn and Mn contribute the lowest non-carcinogenic risk (5.1940E-06) and the highest non-carcinogenic risk (7.9921E-04) through skin contact pathway, respectively. The total average personal risk for swimmers in swimming area is 1.9693E-03, and this site is not suitable for swimming. Overall, it is possible that swimmers are exposed to risk via the dermal route when carrying out water-related activities, it is recommended that necessary precautions and management should be taken in other similar locations around the world.