Ecological risk assessment and source apportionment of metals in the surface sediments of river systems in Lake Taihu Basin, China

A retrospective analysis of heavy metals and multi elements in the Yangtze River Basin: Distribution characteristics, migration tendencies and ecological risk assessment

The Yangtze River is the third longest river in the world with more than 6300 km, covering 0.4 billion people. However, the aquatic ecosystem of the Yangtze River has been seriously damaged in the past decades due to a rapid development of economic and industrialization along the coast. In this study, we first established a dataset of fifty elements, including nine common heavy metals (HMs) and forty-one other elements, in the Yangtze River Basin through the collection of historical data from 2000 to 2020, and then analyzed their spatiotemporal distribution characteristics. The results indicated that the Three Gorges Reservoir (TGR), a region formed by the construction of the Three Gorges Dam (TGD), may act as a sink for these elements from upstream regions. The concentrations of seven elements in surface water and 13 elements in sediment obviously increased from the upstream region of the TGR to the TGR. In addition, ten elements in the surface water and 5 elements in the sediments clearly decreased, possibly because of the interception effects of the TGD. On a timescale, Cr obviously tended to migrate from the water phase to the sediment; Pb tended to migrate from the sediment to the water phase. In the ecological risk assessment, all common HMs in surface water were supposed to have negligible risks as protecting 90 % of aquatic organisms; Cd (210.2), Hg (58.0) and As (43.1) in sediment posed high and moderate ecological risks using the methodology of the potential ecological risk index. Furthermore, Hunan Province is at considerable risk according to the sum of the potential risk index (314.8) due to Cd pollution (66.8 %). These fundamental data and results will support follow-up control strategies for elements and policies related to aquatic ecosystem protection in the Yangtze River Basin.

Quantitative risk analysis of sediment heavy metals using the positive matrix factorization-based ecological risk index method: a case of the Kuye River, China

Identifying the sources of heavy metals (HMs) in river sediments is crucial to effectively mitigate sediment HM pollution and control its associated ecological risks in coal-mining areas. In this study, ecological risks resulting from different pollution sources were evaluated using an integrated method combining the positive matrix factorization (PMF) and the potential ecological risk index (RI) model. A total of 59 sediment samples were collected from the Kuye River and analyzed for eight HMs (Zn, Cr, Ni, Cu, Pb, As, Cd, and Hg). The obtained results showed that the sediment HM contents were higher than the corresponding soil background values in Shaanxi Province. The average sediment Hg content was 3.42 times higher than the corresponding background value. The PMF results indicated that HMs in the sediments were mainly derived from industrial, traffic, agricultural, and coal-mining sources. The RI values ranged from 26.15 to 483.70. Hg was the major contributor (75%) to the ecological risk in the vicinity of the Yanjiata Industrial Park. According to the PMF-based RI model, coal-mining activities exhibited the strongest impact on the river ecosystem (48.79%), followed, respectively, by traffic (34.41%), industrial (12.70%), and agricultural (4.10%) activities. These results indicated that the major anthropogenic sources contributing to the HM contents in the sediments are not necessarily those posing the greatest ecological risks. The proposed integrated approach in this study was useful in evaluating the ecological risks associated with different anthropogenic sources in the Kuye River, providing valuable suggestions for reducing sediment HM pollution and effectively protecting river ecosystems.

Ecological risk characteristics of sediment-bound heavy metals in large shallow lakes for aquatic organisms: The case of Taihu Lake, China

Heavy metal contamination in the surface sediments of large shallow lakes in China is becoming increasingly serious. However, more attention has been paid to the human health risk of heavy metals in the past, while little consideration has been given to aquatic organisms. Taking Taihu Lake as an example, we explored the spatial and temporal heterogeneity of the potential ecological risks of seven heavy metals (Cd, As, Cu, Pb, Cr, Ni, and Zn) to species at different taxonomic scales using an improved species sensitivity distribution (SSD) method. The results showed that all six heavy metals, except Cr, were exceeded to some extent compared to background levels, with Cd being the most severe exceedance. Based on the hazardous concentration for 5% of the species (HC₅), Cd had the lowest HC₅ value, implying the highest ecological risk of toxicity. Ni and Pb had the highest HC₅ values and the lowest risk. Cu, Cr, As and Zn were at a relatively moderate levels. For the different groups of aquatic organisms, the ecological risk of most heavy metals was generally lower for vertebrates than for the whole species. The risk for invertebrates and algae was higher than that for all species. Zn and Cu had the highest potentially affected fractions (PAFs) for all classification cases, with mean PAFs of 30.25% and 47.2%, respectively. Spatially, the high ecological risk of sediment heavy metals was significantly related to the spatial characteristics of the type and intensity of human activities in the catchment. Administratively, the environmental quality standards for freshwater sediments proposed by America and Canada are insufficient to protected against the ecological risks of heavy metals in Taihu Lake. In the absence of such standards, China urgently needs to establish an approptiate system of environmental quality standards for heavy metals in lake sediments.

Hydrochemical characteristics of groundwater in a plain river network region: Establishing linkages between source and water quality variables

The chemical characteristics of groundwater can indicate water quality condition and provide useful information for pollution source identification. This study aimed to understand the effects of dissolved organic matter (DOM) on ionic composition of groundwater and identify the main ions and sources of pollution. The Lake Taihu is a typical eutrophic lake in China. In this study, the hydrochemical composition of groundwater in the surrounding aquifer of Lake Taihu Basin was analyzed. The results showed that the values of water quality index (WQI) range from 13.29 to 56.26 (good water quality). The dominant hydrochemical type of groundwater was Ca-Mg-HCO3 type, and the rock dominance was the major mechanism controlling the groundwater chemistry. With an increasing concentration in dissolved organic carbon (DOC), the Na+, Mg2+, and HCO3- concentrations all showed a sharp increase followed by a slow increase, while the NO3- concentration showed an opposite trend, indicating the DOM can affect the ions composition. In addition, K+ was positively correlated with NO3-, As, and Cd. Hence, DOM input may directly or indirectly change the hydrochemistry of groundwater. Besides, the NO3- concentration in groundwater was much higher than that in Lake Taihu, indicating that the NO3- in groundwater mainly came from surface soil leaching. The anthropogenic sources are probably the main sources of different ions, including K+, NO3-, As, and Cd. This study can help to better understand the effects of lake eutrophication on groundwater and its pathways.

Groundwater Quality, Health Risk Assessment, and Source Distribution of Heavy Metals Contamination around Chromite Mines: Application of GIS, Sustainable Groundwater Management, Geostatistics, PCAMLR, and PMF Receptor Model

Groundwater contamination by heavy metals (HMs) released by weathering and mineral dissolution of granite, gneisses, ultramafic, and basaltic rock composition causes human health concerns worldwide. This paper evaluated the heavy metals (HMs) concentrations and physicochemical variables of groundwater around enriched chromite mines of Malakand, Pakistan, with particular emphasis on water quality, hydro-geochemistry, spatial distribution, geochemical speciation, and human health impacts. To better understand the groundwater hydrogeochemical profile and HMs enrichment, groundwater samples were collected from the mining region (n = 35), non-mining region (n = 20), and chromite mines water (n = 5) and then analyzed using ICPMS (Agilent 7500 ICPMS). The ranges of concentrations in the mining, non-mining, and chromite mines water were 0.02-4.5, 0.02-2.3, and 5.8-6.0 mg/L for CR, 0.4-3.8, 0.05-3.6, and 3.2-5.8 mg/L for Ni, and 0.05-0.8, 0.05-0.8, and 0.6-1.2 mg/L for Mn. Geochemical speciation of groundwater variables such as OH^-, H⁺, Cr⁺², Cr⁺³, Cr⁺⁶, Ni⁺², Mn⁺², and Mn⁺³ was assessed by atomic fluorescence spectrometry (AFS). Geochemical speciation determined the mobilization, reactivity, and toxicity of HMs in complex groundwater systems. Groundwater facies showed 45% CaHCO₃, 30% NaHCO₃, 23.4% NaCl, and 1.6% Ca-Mg-Cl water types. The noncarcinogenic and carcinogenic risk of HMs outlined via hazard quotient (HQ) and total hazard indices (THI) showed the following order: Ni > Cr > Mn. Thus, the HHRA model suggested that children are more vulnerable to HMs toxicity than adults. Hierarchical agglomerative cluster analysis (HACA) showed three distinct clusters, namely the least, moderately, and severely polluted clusters, which determined the severity of HMs contamination to be 66.67% overall. The PCAMLR and PMF receptor model suggested geogenic (minerals prospects), anthropogenic (industrial waste and chromite mining practices), and mixed (geogenic and anthropogenic) sources for groundwater contamination. The mineral phases of groundwater suggested saturation and undersaturation. Nemerow's pollution index (NPI) values determined the unsuitability of groundwater for domestic purposes. The EC, turbidity, PO₄^-3, Na⁺, Mg⁺², Ca⁺², Cr, Ni, and Mn exceeded the guidelines suggested by the World Health Organization (WHO). The HMs contamination and carcinogenic and non-carcinogenic health impacts of HMs showed that the groundwater is extremely unfit for drinking, agriculture, and domestic demands. Therefore, groundwater wells around the mining region need remedial measures. Thus, to overcome the enrichment of HMs in groundwater sources, sustainable management plans are needed to reduce health risks and ensure health safety.

Ecological risk assessment based on soil adsorption capacity for heavy metals in Taihu basin, China

Due to the toxicity, bioaccumulation, non-biodegradability and perseverance of heavy metals, their risk assessment is essential for soil quality management. The Hakanson potential ecological risk index (RI), which considers the effects of heavy metal concentration and toxicity, has been widely used in soil ecological risk assessment. However, RI overlooks the influence of soil properties on the mobility and availability of heavy metals in risk assessment. To fill this gap, this study sought to develop an improved ecological risk index (IRI), which incorporates soil adsorption into RI, and applied it to evaluate the ecological risk of heavy metals in the soil of the Taihu basin, China. The soil adsorption models based on the Gradient Boosting Decision Tree (GBDT) was used to predict the soil adsorption capacity of five heavy metals (i.e. cadmium, chromium, copper, lead, zinc). The soil adsorption capacity in 1446 sites in the Taihu basin was predicted by the GBDT models and was assigned as the weight of IRI. The risk assessment results of the five metals in the Taihu basin showed that 40% of the sites were at a moderate risk level and 60% of the sites were at a slight risk level based on the RI. The value of IRI in the basin ranged from 11.1 to 75.5, with a mean value of 28.1. IRI differed from RI in spatial distribution due to the influence of soil adsorption. The comparative analysis between the metal contents in sediments and surrounding soils confirmed the tremendous influence of soil adsorption on ecological risks, indicating that soil adsorption should be taken into consideration in soil risk assessment.

Research on the geochemical background values and evolution rules of lake sediments for heavy metals and nutrients in the Eastern China Plain from 1937 to 2017

For the first time, background quality guidelines have been developed for lake sediments along the Yangtze River. Evolution Rules of watershed environment in Eastern China were analyzed in 1937-2017. These methods of ¹³⁷Cs and ²¹⁰Pb radionuclide, 75% cumulative frequency, and background method were applied to calculate the sediment geochemical backgrounds (GB). The average GB values of Cu, Zn, Cd, Pb, Cr, total carbon (TC), total nitrogen (TN) and total phosphorus (TP) are 45.14 mg/kg, 86.99 mg/kg, 0.29 mg/kg, 33.71 mg/kg, 110.90 mg/kg, 17.20 mg/g, 1.60 mg/g, and 665.78 mg/kg, respectively. The radionuclide methods indicated that the sediment rate of 34 cm corresponding to 1963 is 0.63 cm yr^-1. The risk and accumulation of the sediment metals and nutrients in Yangtze Plain were uncontaminated levels before 1960, raised since 1980, and increased significantly in 2000. The Cd, TC, and TN in lake sediment were at low to moderate pollution, and few lakes are at high pollution. Sediment background values of the plain are different from soil background values in China and Consensus-Based Sediment Quality Guidelines in Europe/America. Results of sediment quality guidelines provide an important guidance for pollution prevention, environmental management, and risk assessment, especially the formulation of environmental laws.

Sediment phosphate release flux under hydraulic disturbances in the shallow lake of Chaohu, China

Quantifying the effect of hydraulic disturbances on sediment phosphate release is a key issue in the water quality assessment of lakes, especially for the shallow lakes which are susceptible to winds and waves. Here, we sampled the original sediment columns from 12 positions in the eastern, central, and western areas of the Chaohu Lake, a representative shallow lake in China, and observed phosphate release under three levels of hydraulic disturbances in the laboratory. When the disturbance was weak and sediment on the surface of bottom mud moved individually (the Individual Motion Mode), sediment phosphate release rate was insignificant (0.24 mg/m²/day). When the disturbance was medium and only a small percentage (< 16%) of surface sediment started to move (the Small Motion Mode), the phosphate release rate sharply increased to 4.81 mg/m²/day. When the disturbance was further strengthened and most (≥ 16%) of the surface sediment moved (the General Motion Mode), the phosphate release rate was more than doubled (10.23 mg/m²/day). With the increase in hydraulic disturbance intensity, the variation range of phosphate release also became wider. Spatial distribution showed that the release rate varies the most in the western area, followed by the eastern and the central areas. By extrapolating the experimental results to the real scale, it was found that the phosphate release fluxes would probably fall within a wide range between 203.43 to 7311.01 kg/day under different levels of hydrodynamic disturbances which considerably affects phosphate release from shallow lakes. This study also has implications for the pollutant management in other shallow lakes.

Analysis of mercury emissions and cycles in typical industrial city clusters: a case study in China

China's Suzhou (SZ), Wuxi (WX), and Changzhou (CZ) (collectively referred to as the SXC area) have developed economies and advanced industrial production, which are typical industrial city clusters. To analyze the Hg flow characteristics, we quantified the Hg emissions and circulation according to six categories (including industrial production, agricultural livestock, vehicle exhaust, solid waste, atmospheric deposition, and runoff). The results showed that the Hg emission from coal accounting for 40.99% of the total circulation. The amount of Hg circulating in SZ is obviously higher than those in WX and CZ, accounting for 47.88% of the total regional emissions. The Hg pollution in SXC area represent an optimistic level. Except that the Hg concentration in the soil in WX is slightly higher than the first-level soil quality standard, the water and atmosphere in the three cities and the soil in SZ and CZ all meet the highest national standards. The study provides in-depth statistics on the Hg cycle characteristics of typical industrial urban agglomerations. It is beneficial to the management of Hg and provides a basis for the implementation of different schemes in different stages of production and emission, so as to effectively prevent the occurrence of serious heavy metal poisoning hazards. This research idea is widely used and can be applied to other regions and other heavy metal elements.

Contamination, risk and quantitative identification of nutrients and potentially toxic elements in the surface sediments of Baiyangdian Lake, North China

Potentially toxic elements (PTEs) in lake sediments are concerning because of their toxic effects on lacustrine ecosystems and human health. Baiyangdian Lake (BYDL), the "pearl of North China", plays a vital role in maintaining the ecological health of North China. Here, risk assessment and source identification of nutrients and PTEs in sediments were performed. The results showed that the sediments were highly contaminated with total organic carbon (TOC) and total nitrogen (TN), but contamination by total phosphorus (TP) was minor, and the ecological risk associated with Cd was considerable, especially in the northern region. The average noncarcinogenic hazard quotient of PTEs increased in the order of Zn < Hg < Cd < Cu < Ni < Pb < Cr < As. Statistical analyses indicated that Al, Ti, Fe, Co, Cr, Hg, Ni, and rare earth elements were primarily from natural origins; Pb was derived from local tourism development and pollution by fishermen; and TOC, TN, TP, As, Cd, Cu, Zn, and Mn were mainly derived from industrial and agricultural activities. Additionally, the mean contribution rates of industrial wastewater and domestic sewage sources, agricultural sources, and natural sources to BYDL sediment pollution were 59.9%, 17.9%, and 22.2%, respectively. Spatially, industrial and domestic sewage sources contributed more in the northwestern region (average 79.8%) than in the southern region (average 35.5%), while agricultural sources contributed the most in the southwestern region (average 41.3%). These findings will advance our knowledge of the spatial differences, contamination risks and sources of nutrients and PTEs in BYDL and provide a scientific basis to help policy-makers establish a healthy ecological community in BYDL of the Xiong'an New Area.

Quantitative source identification and environmental assessment of trace elements in the water and sediment of rivers flowing into Laizhou Bay, Bohai Sea

The concentrations, sources, and ecological risks of nine trace elements in nine rivers flowing into Laizhou Bay were investigated. The dissolved element concentrations were 1.85-74.4, 0.01-0.47, 0.15-3.46, 1.54-19.7, 2.92-45.1, 1.72-11.5, 1.02-8.35, 0.10-1.02, and 21.4-185 μg/L for As, Cd, Co, Cr, Cu, Ni, Sc, Pb, and Zn, respectively. Zinc was the most abundant element in the sediments, with an average concentration of 106 mg/kg, followed by Cr (64.5 mg/kg), Cu (25.5 mg/kg), Pb (24.3 mg/kg), Ni (23.4 mg/kg), Co (10.9 mg/kg), Sc (8.14 mg/kg), As (6.75 mg/kg), and Cd (0.16 mg/kg). Elements including Co, Cr, Ni, and Sc were mainly from natural sources and As, Cd, Cu, Pb, and Zn were largely influenced by anthropogenic activities such as agricultural practice, industrial production, river transportation, and urbanization. Overall, the rivers flowing into Laizhou Bay experienced slight pollution and ecological risk. However, the severe element contamination in Jie River deserves continuous attention.

Effect of river-lake connectivity on heavy metal diffusion and source identification of heavy metals in the middle and lower reaches of the Yangtze River

Metal pollution poses a significant threat to ecological security and human health. Current research on the causes, sources and distribution of metal pollution in the Yangtze River plain is lacking. This study investigated the accumulation, risk, distribution, and sources of heavy metals in 62 lakes along the Yangtze River, and analyzed the relationship between river-lake connectivity, economic structure, population and metal diffusion. The mean concentrations of Cr, Cu, Hg, Zn, Cd, Pb and As in the surface sediments of these lakes were 90.8, 60.1, 0.06, 102, 0.89, 42.7, and 6.01 mg/kg, respectively. Most (99%) of the lake sediments were contaminated with Cd, and the lakes in the middle reach and southern bank of the Yangtze River had a higher ecological risk. Cr originated from the natural environment, whereas Zn, Cu, Pb, Cd and As were affected by human activities. The lakes disconnected from the Yangtze River had higher concentrations of Cu, Zn, Pb and As, while the lakes connected to the river had higher concentrations of Cd and Cr. This comprehensive analysis determined the pollution characteristics of heavy metals, illustrated the causes of non-point pollution in the Yangtze River plain, and showed that soil-water erosion is important in metal diffusion.

Source Identification of Cd and Pb in Typical Farmland Topsoil in the Southwest of China: A Case Study

Cd and Pb in farmland topsoil are controlled by many factors. To identify the source of potential toxic metals in the farmland topsoil around Mianyuan River, the chemical analysis and multivariate statistical analysis are performed in this study. The results indicate the following: (1) The concentration of Cd and Pb in soil exceed the background value of Chinese soil elements. (2) Cd is significantly enriched in the whole region and Pb is locally enriched, both of them are more or less influenced by human activities. (3) The contents of Cd and Pb increase significantly following the flow direction of river. (4) Pb isotope analysis indicates that the main source of Pb in the soil include the air dust, coal and phosphate plant, and the contribution of them decreases successively. (5) Linear correlation analysis and principal component analysis show that the main sources of Cd in the soil are mining phosphate rock, air dust, phosphate plant and coal mining.