Contamination characteristics, source identification, and source-specific health risks of heavy metal(loid)s in groundwater of an arid oasis region in Northwest China

Arsenic-contaminated groundwater of the Western Banat (Pannonian basin): Hydrogeochemical appraisal, pollution source apportionment, and Monte Carlo simulation of source-specific health risks

Due to rapid urbanization and industrial growth, groundwater globally is continuously deteriorating, posing significant health risks to humans. This study employed a comprehensive methodology to analyze groundwater in the Western Banat Plain (Serbia). Using Piper and Gibbs plots, hydrogeochemistry was assessed, while the entropy-weighted water quality index (EWQI) was used to evaluate groundwater quality. Pollution sources were identified using positive matrix factorization (PMF) accompanied by Pearson correlation and hierarchical cluster analysis, while Monte Carlo simulation assessed health risks associated with groundwater consumption. Results showed that groundwater, mainly Ca-Mg-HCO3 type, is mostly suitable for drinking. Geogenic pollution, agricultural activities, and sewage were major pollution sources. Consumption of contaminated groundwater poses serious non-carcinogenic and carcinogenic health risks. Additionally, arsenic from geogenic source was found to be the main health risks contributor, considering its worryingly elevated concentration, ranging up to 364 μg/L. These findings will be valuable for decision-makers and researchers in managing groundwater vulnerability. PRACTITIONER POINTS: Groundwater is severely contaminated with As in the northern part of the study area. The predominant hydrochemical type of groundwater in the area is Ca-Mg-HCO3. The PMF method apportioned three groundwater pollution sources. Monte Carlo identified rock dissolution as the primary health risk contributor. Health risks and mortality in the study area are positively correlated.

Source identification and migration fate of heavy metals of soil-groundwater system in a thousand-year cultivation region

Pollution of farmland by heavy metals threatens food security and human health. In addition, heavy metals in soil could infiltrate into groundwater to influence the water quality and safety of drinking water. However, the relationship between heavy metal pollution in soil and groundwater is still not clear. In this study, we investigated the soil and groundwater in the Guanzhong Plain region, which is a significant grain production base in China, and determined the spatial distributions, ecological risk, sources, and migration fates of heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn). The results showed that the mean values (0-20 cm) in the soil were 19.57 mg kg-1 for As, 0.71 mg kg-1 for Cd, 69.65 mg kg-1 for Cr, 21.97 mg kg-1 for Cu, 28.67 mg kg-1 for Ni, 17.54 mg kg-1 for Pb, and 73.77 mg kg-1 for Zn, and the corresponding mean values in groundwater were 1.2, 0.04, 4.69, 0.15, 0.07, 0.3, and 3.6 μg L-1, respectively. The mean values for As, Cd, Cr, Pb, and Zn in soil exceeded the background values, and the mean values for As, Cd and Pb exceeded those in groundwater. Positive matrix factorization models identified five sources (fertilizers and organic fertilizers, natural sources, pesticides and herbicides, industrial activities, and sedimentation caused by transportation) for heavy metal pollution in soil and four sources (industry activity, atmospheric sedimentation caused by transportation, natural sources, and agriculture) for heavy metal pollution in groundwater. The soil particle composition and soil organic carbon content were important factors that affected the vertical distribution of heavy metals in the soil. The migration modes (convection and diffusion) were not found for all heavy metals. These results help to understand the relationships between heavy metals in soil and groundwater in farmland ecosystems regionally.

Source-oriented health risk assessment of groundwater nitrate by using EMMTE coupled with HHRA model

Conventional concentration-oriented approaches for nitrate risk diagnosis only provide overall risk levels without identifying risk values of individual sources or sources accountable for potential health risks. Therefore, a hybrid model combining the end-member mixing model tool on Excel™ (EMMTE) with human health risk assessment (HHRA) was developed to assess the source-oriented health risks for groundwater nitrate, particularly in the Poyang Lake Plain (PLP) region. The results indicated that the EMMTE and the Bayesian stable isotope mixing model (MixSIAR) exhibited remarkable consistency in source apportionment of groundwater nitrate. The source contribution of groundwater nitrate in PLP was related to land use types, hydrogeological conditions, and soil properties. Notably, manure and sewage sources, contributing up to 53.4 %, represented the largest nitrate pollution sources, with a significant contribution of soil nitrogen and nitrogen fertilizers. The non-carcinogenic risk for four potential sources was below the acceptable threshold of 1. Given the factors including rainfall dilution and economic development, attention should be directed towards mitigating the health risks posed by manure and sewage. This study can verify the efficacy of EMMTE in source apportionment and offer valuable insights for decision-makers to regulate the largest sources of nitrate contamination and enhance groundwater management efficiency.

Health Risk Assessment of Heavy Metal(loid)s in the Overlying Water of Small Wetlands Based on Monte Carlo Simulation

Heavy metal(loid) (HM) contamination is a significant threat to wetland ecosystem. However, contamination risks of HMs in overlying water of small wetlands, which are easily ignored because of their minor occupancy in an overall area, are nearly unknown. A total of 36 water samples containing six HMs were collected from the urban and rural small wetlands of Urumqi in China, and the contamination levels and probabilistic health risks caused by HMs were assessed using the Nemerow pollution index (NPI) and the health risk assessment model introduced by the US EPA. The results revealed that the average concentration of Hg in the urban and rural small wetlands surpassed the Class II thresholds of the Environmental Quality Standards for Surface Water (GB 3838-2002) by factors of 3.2 and 5.0 times, respectively. The overall contamination levels of HMs in the small wetlands fall into the high contamination level. Results of a health risk assessment indicated that non-carcinogenic health risk of the investigated HMs are found to be lower than the acceptable range for adults, but higher than the acceptable range for children. Meanwhile, As falls into the low carcinogenic risk level, whereas Cd falls into the very low carcinogenic risk level. Overall, HMs in rural small wetlands showed relatively higher contamination levels and probabilistic health risks than that of urban small wetlands. In addition, As was identified as the dominant health risk factor in the overlying water of small wetlands in the study area. Findings of this study provide scientific support needed for the prevention of HM contamination of small wetlands in arid zones.

Heavy metals in a typical industrial area-groundwater system: Spatial distribution, microbial response and ecological risk

The environmental burden due to industrial activities has been quite observable in the last few years, with heavy metals (HMs) like lead, cadmium, and arsenic inducing serious perturbations to the microbial ecosystem of groundwater. Studies carried out in North China, a region known for interconnection of industrial and groundwater systems, sought to explore the natural mechanisms of adaptation of microbes to groundwater contamination. The results showed that heavy metals permeate from surface increased the diversity and abundance of microbial communities in groundwater, producing an average decrease of 40.84% and 34.62% in the relative abundance of Bacteroidetes and Proteobacteria in groundwater, respectively. Meanwhile, the key environmental factors driving the evolution of microbial communities shift from groundwater nutrients to heavy metals, which explained 50.80% of the change in the microbial community composition. Microbial indicators are more sensitive to HMs pollution and could accurately identify industrial area where HMs permeation occurred and other extraneous pollutants. The phylum Bacteroidetes could act as appropriate indicators for the identification. Significant genera that were identified, being Mesorhizobium, Clostridium, Bacillus and Mucilaginibacter, were found to play important roles in the microbial network in terms of the potential to assist in groundwater clean-up. Notably, pollution from heavy metals has diminished the effectiveness and resilience of microbial communities in groundwater, thereby heightening the susceptibility of these normally stable microbial ecosystems. These findings offer new perspectives on how to monitor and detect groundwater pollution, and provide scientific guidance for developing suitable remediation methods for groundwater contaminated with heavy metals. Future research is essential explore the application of metal-tolerant or resistant bacteria in bioremediation strategies to rehabilitate groundwater systems contaminated by HMs.

Pollution and Health Risk Assessment of Potentially Toxic Elements in Groundwater in the Kǒnqi River Basin (NW China)

Potentially toxic elements (PTEs) pose a significant threat to the groundwater system and human health. Pollution and the potential risks of PTEs in groundwater in the Kǒnqi River Basin (KRB) of the northwest arid zones of China are still unknown. A total of 53 groundwater samples containing eight PTEs (Al, As, Cd, Cu, Mn, Pb, Se, and Zn) were collected from the KRB, and the pollution levels and probabilistic health risks caused by PTEs were assessed based on the Nemerow Index (NI) method and the health risk assessment model. The results revealed that the mean contents of Al, As, and Mn in the groundwater surpassed the Class III threshold of the Standard for Groundwater Quality of China. The overall pollution levels of the investigated PTEs in the groundwater fall into the moderate pollution level. The spatial distributions of contents and pollution levels of different PTEs in the groundwater were different. Health risk assessment indicated that all the investigated PTEs in groundwater in the KRB may pose a probabilistic non-carcinogenic health risk for both adults and children. Moreover, As may pose a non-carcinogenic health risk, whereas the non-carcinogenic health risk posed by the other seven PTEs in groundwater will not have the non-carcinogenic risks. Furthermore, As falls into the low carcinogenic risk level, whereas Cd falls into the very low carcinogenic risk level. Overall, As was confirmed as the dominant pollution factor and health risk factor of groundwater in the KRB. Results of this study provide the scientific basis needed for the prevention and control of PTE pollution in groundwater.

Source-specific probabilistic health risk assessment of heavy metals in surface water of the Yangtze River Basin

The detrimental effects of heavy metal accumulation on both ecosystems and public health have raised widespread concern. Source-specific risk assessment is crucial for developing effective strategies to prevent and control heavy metal contamination in surface water. This study aims to investigate the contamination characteristics of heavy metals in the Yangtze River Basin, identifying the pollution sources, assessing the risk levels, and further evaluating the health risks to humans. The results indicated that the average concentrations of heavy metals were ranked as follows: zinc (Zn) > arsenic (As) > copper (Cu) > chromium (Cr) > cadmium (Cd) > nickel (Ni) > lead (Pb), with average concentrations of 38.02 μg/L, 4.34 μg/L, 2.53 μg/L, 2.10 μg/L, 1.17 μg/L, 0.84 μg/L, and 0.32 μg/L, respectively, all below the WHO 2017 standards for safe drinking water. The distribution trend indicates higher concentrations in the upper and lower reaches and lower concentrations in the mid-reaches of the river. By integrating the Absolute Principal Component Scores-Multiple Linear Regression (APCS-MLR) receptor model and Positive Matrix Factorization (PMF) model, the main sources of heavy metals were identified as industrial activities (APCS-MLR: 41.3 %; PMF: 42.1 %), agricultural activities (APCS-MLR: 30.1 %; PMF: 27.4 %), and unknown mix sources (APCS-MLR: 29.1 %; PMF: 30.4 %). The calculation of the hazard index (HI) for both children and adults was <1, indicating no non-carcinogenic or carcinogenic risks. Based on the source-specific risk assessment, agricultural activities contribute the most to non-carcinogenic risks, while industrial activities pose the greatest contribution to carcinogenic risks. This study offers a reference for monitoring heavy metals and controlling health risks to residents, and provides crucial evidence for the utilization and protection of surface water in the Yangtze River Basin.

Determination of high-risk factors and related spatially influencing variables of heavy metals in groundwater

Identifying high-risk factors (heavy metals (HMs) and pollution sources) by coupling receptor models and health risk assessment model (HRA) is a novel approach within the field of risk assessment. However, this coupled model ignores the contribution of spatial differentiation to high-risk factors, resulting in the assessment being subjective. Taking Dongting Plain (DTP) as an example, a coupling framework by jointly using the positive matrix factorization model (PMF), HRA, Monte Carlo simulation, and geo-detector was developed, aiming to identify high-risk factors in groundwater, and further explore key environmental variables influencing the spatial heterogeneity of high-risk factors. The results showed that at least 82.86 % of non-carcinogenic risks and 97.41 % of carcinogenic risks were unacceptable for people of all ages, especially infants and children. According to the relationships among HMs, pollution sources, and health risks, As and natural sources were defined as high-risk HMs and sources, respectively. The interactions among Holocene thickness, oxidation-reduction potential, and dissolved organic carbon emerged as the primary drivers of spatial variability in high-risk factors, with their combined explanatory power reaching up to 74%. This proposed framework provides a scientific reference for future studies and a practical reference for environmental authorities in developing effective pollution management measures.

In-situ reactivation and reuse of micronsized sulfidated zero-valent iron using SRB-enriched culture: A sustainable PRB technology

Sulfidated zero-valent iron (S-ZVI) is an attractive material of permeable reactive barriers (PRBs) for the remediation of contaminated groundwater. However, S-ZVI is prone to be passivated due to the oxidation of reactive and conductive iron sulfide (FeSx) shell and the formation of inactive and non-conductive ferric (hydr)oxides, which serve as electron transfer barriers to hinder the electron flow from Fe° core to contaminants. This study thus proposed a novel approach for in-situ reactivation and reuse of micronsized S-ZVI (S-mZVI) in PRB using sulfate-reducing bacteria (SRB) enriched culture to realize long-lasting remediation of Cr(VI)-contaminated groundwater. S-mZVI were passivated after reactions with Cr(VI) due to the formation of electron transfer barriers (mainly inactive and non-conductive Fe(III) (hyd)oxides, which increased the polarization resistance from 16.38 to 27.38 kΩ cm2 and hindered the electron transfer from the Fe° core. Interestingly, the passivated S-mZVI was efficiently reactivated by providing the SRB-enriched culture and organic carbon within 12 h, and the Cr(VI) removal capacity of S-mZVI in the three use cycles increased to 37.4 mg Cr/g, which was 2.1 times higher than that of the virgin S-mZVI. After biological reactivation, the Rp of reactivated S-mZVI decreased to 12.30 kΩ cm2. SRB-mediated reactivation removed the electron transfer barriers via biotic and abiotic reduction of Fe(III) (hyd)oxides. Especially, the microbial Fe(III) reduction mediated by FmnA-dmkA-fmnB-pplA-ndh2-eetAB-dmkB protein family enhanced the Fe2+ release from the surface and the subsequent re-formation of reactive and conductive FeSx shell. A long-term PRB column test further demonstrated the feasibility of in-situ biological reactivation and reuse of S-mZVI for enhanced Cr(VI)-contaminated groundwater remediation. Within 64 days, the Cr(VI) removal capacity of S-mZVI in the four use cycles increased by 3.2 times, compared to the virgin one. The bio-reactivation using the SRB-enriched culture and sulfate locally-available in groundwater will reduce the chemical and maintenance costs associated with the frequent replacement of reactive ZVI-based materials. The PRB technology based on the bio-renewable S-mZVI can be a sustainable alternative to the conventional PRBs for the long-lasting and low-cost remediation of groundwater contaminated by oxidative pollutants.

Adsorption properties and mechanism of Cu(II) on virgin and aged microplastics in the aquatic environment

Microplastics (MPs) migrate by adsorbing heavy metals in aquatic environments and act as their carriers. However, the aging mechanisms of MPs in the environment and the interactions between MPs and heavy metals in aquatic environments require further study. In this study, two kinds of materials, polyamide (PA) and polylactic acid (PLA) were used as target MPs, and the effects of UV irradiation on the physical and chemical properties of the MPs and the adsorption behavior of Cu(II) were investigated. The results showed that after UV irradiation, pits, folds and pores appeared on the surface of aged MPs, the specific surface area (SSA) increased, the content of oxygen-containing functional groups increased, and the crystallinity decreased. These changes enhanced the adsorption capacity of aged MPs for Cu(II) pollutants. The adsorption behavior of the PA and PLA MPs for Cu(II) conformed to the pseudo-second-order model and Langmuir isotherm model, indicating that the monolayer chemical adsorption was dominant. The maximum amounts of aged PA and PLA reached 1.415 and 1.398 mg/g, respectively, which were 1.59 and 1.76 times of virgin MPs, respectively. The effects of pH and salinity on the adsorption of Cu(II) by the MPs were significant. Moreover, factors such as pH, salinity and dosage had significant effects on the adsorption of Cu(II) by MPs. Oxidative complexation between the oxygen-containing groups of the MPs and Cu(II) is an important adsorption mechanism. These findings reveal that the UV irradiation aging of MPs can enhance the adsorption of Cu(II) and increase their role as pollutant carriers, which is crucial for assessing the ecological risk of MPs and heavy metals coexisting in aquatic environments.

Entropy-weighted water quality index, hydrogeochemistry, and Monte Carlo simulation of source-specific health risks of groundwater in the Morava River plain (Serbia)

Population growth, urbanization, industry, floods, and agriculture globally degrade groundwater in river plains, necessitating action for its quality assessment and management. Hence, a comprehensive methodology, including hydrogeochemical facies (Piper, Gibbs), irrigation indices (SAR, Wilcox), entropy-weighted water quality index (EWQI), positive matrix factorization (PMF), and Monte Carlo simulation of source-specific health risks was used in this study to analyze groundwater in the Morava river plain (Serbia). The results revealed a prevalent Ca-Mg-HCO3 groundwater type, influenced by water-rock interactions. Although groundwater was found suitable for irrigation, only 66.7 % of the samples were considered drinkable. Agricultural activities, natural processes, and municipal wastewater were identified as primary pollution sources. The incremental lifetime cancer risk (ILCR) and hazard index (HI) threshold exceedance for adults and children ranged from 8.5 % to 39 % of the samples, with arsenic identified as the most risk-contributing contaminant. These findings provide valuable insights for researchers studying groundwater vulnerability in river plains.

Spatial and temporal distribution characteristics and risk assessment of heavy metals in groundwater of Pingshuo mining area

Groundwater pollution in the Pingshuo mining area is strongly associated with mining activities, with heavy metals (HMs) representing predominant pollutants. To obtain accurate information about the pollution status and health risks of groundwater, 189 groups of samples were collected from four types of groundwater, during three periods of the year, and analyzed for HMs. The results showed that the concentration of HMs in groundwater was higher near the open pit, waste slag pile, riverfront area, and human settlements. Except for Ordovician groundwater, excessive HMs were found in all investigated groundwater of the mining area, as compared with the standard thresholds. Fe exceeded the threshold in 13-75% of the groundwater samples. Three sources of HMs were identified and quantified by Pearson's correlation analysis and the PMF model, including coal mining activities (68.22%), industrial, agricultural, and residential chemicals residue and leakage (16.91%), and natural sources (14.87%). The Nemerow pollution index revealed that 7.58% and 100% of Quaternary groundwater and mine water samples were polluted. The health risk index for HMs in groundwater showed that the non-carcinogenic health risk ranged from 0.18 to 0.42 for adults, indicating an acceptable level. Additionally, high carcinogenic risks were identified in Quaternary groundwater (95.45%), coal series groundwater (91.67%), and Ordovician groundwater (26.67%). Both carcinogenic and non-carcinogenic risks were greater for children than adults, highlighting their increased vulnerability to HMs in groundwater. This study provides a scientific foundation for managing groundwater quality and ensuring drinking water safety in mining areas.

Assessing heavy metal pollution in sediments from the northern margin of Chinese mangrove areas: Sources, ecological risks, and health impacts

With the rapid economic development of coastal cities, the discharge of substantial amounts of heavy metal pollutants poses a serious hazard to mangroves; however, the potential sources of heavy metals and the resulting health risks are not fully understood. In this study, we analyzed the contents, sources, and ecological and health risks of heavy metal contamination in mangrove sediments from the northern margin of China. The accumulation of heavy metals in mangroves was primarily driven by five potential sources, namely agricultural (33.5 %), natural sources (21.3 %), industrial (19.1 %), aquaculture (14.3 %), and traffic (11.8 %). The assessment of health risks using a probabilistic approach demonstrated that noncarcinogenic risks were within acceptable limits for all populations. It was worth noting that both noncarcinogenic and carcinogenic risks were greater in children than in adults. Analysis of source-oriented health risks revealed that agricultural sources and As and Cd were priority sources and elements of pollution requiring attention.

Hydrogeochemical characterization, quality assessment, and potential nitrate health risk of shallow groundwater in Dongwen River Basin, North China

Assessing groundwater geochemical formation processes and pollution circumstances is significant for sustainable watershed management. In the present study, 58 shallow groundwater samples were taken from the Dongwen River Basin (DRB) to comprehensively assess the hydrochemical sources, groundwater quality status, and potential risks of NO3- to human health. Based on the Box and Whisker plot, the cation's concentration followed the order of Ca2+  > Mg2+  > Na+  > K+, while anions' mean levels were HCO3-  > SO42-  > NO3-  > Cl-. The NO3- level in groundwater samples fluctuated between 4.2 and 301.3 mg/L, with 67.2% of samples beyond the World Health Organization (WHO) criteria (50 mg/L) for drinking. The Piper diagram indicated the hydrochemical type of groundwater and surface water were characterized as Ca·Mg-HCO3 type. Combining ionic ratio analysis with principal component analysis (PCA) results, agricultural activities contributed a significant effect on groundwater NO3-, with soil nitrogen input and manure/sewage inputs also potential sources. However, geogenic processes (e.g., carbonates and evaporite dissolution/precipitation) controlled other ion compositions in the study area. The groundwater samples with higher NO3- values were mainly found in river valley regions with intense anthropogenic activities. The entropy weight water quality index (EWQI) model identified that the groundwater quality rank ranged from excellent (70.7%) and good (25.9%) to medium (3.4%). However, the hazard quotient (HQ) used in the human health risk assessment (HHRA) model showed that above 91.38% of groundwater samples have a NO3- non-carcinogenic health risk for infants, 84.48% for children, 82.76% for females, and 72.41% for males. The findings of this study could provide a scientific basis for the rational development and usage of groundwater resources as well as for the preservation of the inhabitants' health in DRB.

Understanding spatial heterogeneity of groundwater arsenic concentrations at a field scale: Taking the Datong Basin as an example to explore the significance of hydrogeological factors

The spatial heterogeneity of arsenic (As) concentration exceeding the 10 μg/L WHO limit at the field scale poses significant challenges for groundwater utilization, but it remains poorly understood. To address this knowledge gap, the Daying site was selected as a representative case (As concentration ranged from 1.55 to 2237 μg/L within a 250 × 150 m field), and a total of 28 groundwater samples were collected and analyzed for hydrochemistry, As speciation, and stable hydrogen and oxygen isotope. Principal component analysis was employed to identify the primary factors controlling groundwater hydrochemistry. Results indicate that the spatial heterogeneity of groundwater As concentration is primarily attributed to vertical recharge and competitive adsorption. Low vertical recharge introduces reductive substances, such as dissolved organic matter, which enhances the reductive environment and facilitates microbial-induced reduction and mobilization of As. Conversely, areas with high vertical recharge introduce oxidizing agents like SO42- and DO, which act as preferred electron acceptors over Fe(III), thus inhibiting the reductive dissolution of Fe(III) oxides and the mobilization of As. PCA and hydrochemistry jointly indicate that spatial variability of P and its competitive adsorption with As are important factors leading to spatial heterogeneity of groundwater As concentration. However, the impacts of pH, Si, HCO3-, and F- on As adsorption are insignificant. Specifically, low vertical recharge can increase the proportion of As(III) and promote P release through organic matter mineralization. This process further leads to the desorption of As, indicating a synergistic effect between low vertical recharge and competitive adsorption. This field-scale spatial heterogeneity underscores the critical role of hydrogeological conditions. Sites with close hydraulic connections to surface water often exhibit low As concentrations in groundwater. Therefore, when establishing wells in areas with widespread high-As groundwater, selecting sites with open hydrogeological conditions can prove beneficial.

Spatial distribution characteristics and source analysis of shallow groundwater pollution in typical areas of Yangtze River Delta

With the accelerated industrialisation and urbanisation in the Yangtze River Delta region, shallow groundwater has also suffered some pollution. In order to clarify the current state of pollution and its causes, principal component analysis (PCA) was used to classify the main factors. An absolute principal component-multiple linear regression model (APCS-MLR) was also used to determine the contribution of the main pollution sources to the shallow groundwater quality. The analysis results showed that the exceedance of water quality indicators such as iron, manganese, aluminium and COD in shallow groundwater in the study area was more serious. With the exception of Mg2+, the other indicators are highly variable and are more likely to be influenced by human factors. The main pollution factor affecting the quality of shallow groundwater is the dissolution filtration - migration enrichment factor, followed by agricultural and urban sewage factors, industrial pollution factors, and geological environmental background factors. And the main sources of pollution in shallow groundwater are mainly located in the western, northwestern and northern parts of the study area. The use of fertilizers and pesticides in urban life and urban runoff, industrial production and agricultural production are the main causes of pollution. The effects of leaching and transport enrichment, agricultural and urban runoff, and industrial pollution on groundwater quality are significant. The predicted concentrations calculated by the model are generally consistent with the measured concentrations, indicating the accuracy of the calculation of the contribution of each pollution source. This study is applicable to the analysis of shallow groundwater pollution sources in the study area, and also provides a scientific basis for the evaluation of regional groundwater resources and pollution prevention.

An integrated overview of metals contamination, source-specific risks investigation in coal mining vicinity soils

Heavy metals in soil are harmful to natural biodiversity and human health, and it is difficult to estimate the effects accurately. To reduce pollution and manage risk in coal-mining regions, it is essential to evaluate risks for heavy metals in soil. The present study reviews the levels of 21 metals (Nb, Zr, Ag, Ni, Na, K, Mg, Rb, Zn, Ca, Sr, As, Cr, Fe, Pb, Cd, Co, Hg, Cu, Mn and Ti) in soils around Barapukuria coal-mining vicinity, Bangladesh which were reported in literature. An integrated approach for risk assessments with the positive matrix factorization (PMF) model, source-oriented ecological and health hazards were applied for the study. The contents of Rb, Ca, Zn, Pb, As, Ti, Mn, Co, Ag, Zr, and Nb were 1.63, 1.10, 1.97, 14.12, 1.20, 3.13, 1.22, 3.05, 3.85, 5.48, and 7.21 times greater than shale value. About 37%, 67%, 12%, and 85% of sampling sites posed higher risks according to the modified contamination factor, Nemerow pollution index, Nemerow integrated risk index, and mean effect range median quotient, respectively. Five probable metal sources were computed, including industrial activities to coal mining (17%), agricultural activities (33%), atmospheric deposition (19%), traffic emission (16%), and natural sources (15%). Modified Nemerow integrated risk index reported that agricultural activities, industrial coal mining activities, and atmospheric deposition showed moderate risk. Health hazards revealed that cancer risk values computed by the PMF-HHR model with identified sources were higher than the standard value (1.0E-04) for children, adult male, and female. Agricultural activities showed higher cancer risks to adult male (39%) and children (32%) whereas traffic emission contributed to female (25%). These findings highlight the ecological and health issues connected to potential sources of metal contamination and provide useful information to policymakers on how to reduce such risks.

Spatio-temporal variation of groundwater pollution in urban wetlands and management strategies for zoning

Groundwater is an important resource to maintain the sustainable development of urban wetlands. The Jixi National Wetland Park (JNWP) was studied to realize the refined prevention and control of groundwater. The self-organizing map-K-means algorithm (SOM-KM), improved water quality index (IWQI), health risk assessment model and forward model were used comprehensively to evaluate the groundwater status and solute sources in different periods. The results showed that the groundwater chemical type in most areas was the HCO₃-Ca type. Groundwater chemistry data from different periods were clustered into five groups. Groups 1 and 5 are affected by agricultural and industrial activities, respectively. The IWQI value in the normal period was higher in most areas due to the influence of spring ploughing. The east side of the JNWP was disturbed by human activities, and the quality of drinking water continued to deteriorate from the wet period to the dry period. 64.29% of the monitoring points showed good irrigation suitability. The health risk assessment model showed that the health risk was the largest in the dry period and the smallest in the wet period. The main factors causing health risks in the wet period and other periods were NO₃^- and F^-, respectively. The overall cancer risk was within acceptable limits. The forward model and ion ratio analysis showed that the weathering of carbonate rocks was the main factor affecting the evolution of groundwater chemistry, accounting for 67.16%. The high-risk areas of pollution were mainly concentrated in the east of the JNWP. K⁺ and Cl^- were the key monitoring ions in the risk-free zone and potential risk zone, respectively. The research can be used to help decision-makers carry out fine zoning control of groundwater.

Source-oriented ecological and resistome risks associated with geochemical enrichment of heavy metals in river sediments

Heavy metals (HMs) pose ecological and resistome risks to aquatic systems. To efficiently develop targeted risk mitigation strategies, apportioning HM sources and assessing their source-oriented risks are essential. Although many studies have reported risk assessment and source apportionment of HMs, yet few have explored source-specific ecological and resistome risks associated with geochemical enrichment of HMs in aquatic environments. Therefore, this study proposes an integrated technological framework to characterize source-oriented ecological and resistome risks in the sediments of a plain river in China. Several geochemical tools quantitatively showed Cd and Hg had the highest pollution levels in the environment, with 19.7 and 7.5 times higher than their background values, respectively. Positive matrix factorization (PMF) and Unmix were comparatively used to apportion sources of HMs. Essentially, the two models were complementary and identified similar sources including industrial discharges, agricultural activities, atmospheric deposition and natural background, with contributions of 32.3-37.0%, 8.0-9.0%, 12.1-15.9% and 42.8-43.0%, respectively. To analyze source-specific ecological risks, the apportionment results were integratively incorporated into a modified ecological risk index. The results showed anthropogenic sources were the most significant contributors to the ecological risks. Particularly, industrial discharges majorly contributed high- (44%) and extremely high (52%) ecological risk for Cd, while agricultural activities posed a greater percentage of considerable-(36%) and high- (46%) ecological risk for Hg. Furthermore, the high-throughput sequencing metagenomic analysis identified abundant and diverse antibiotic resistance genes (ARGs), including some carbapenem-resistance genes and emerging genes such as mcr-type in the river sediments. Network and statistical analyses displayed significant correlations between ARGs and geochemical enrichment of HMs (ρ > 0.8; P-value <0.01), indicating their important impacts on resistome risks in the environment. This study provides useful insights into risk prevention and pollution control of HMs, and the framework can be made applicable to other rivers facing environmental challenges worldwide.

Heavy metals in influent and effluent from 146 drinking water treatment plants across China: Occurrence, explanatory factors, probabilistic health risk, and removal efficiency

Heavy metals (HMs) in drinking water have drawn worldwide attention due to their risks to public health; however, a systematic assessment of the occurrence of HMs in drinking water treatment plants (DWTPs) at a large geographical scale across China and the removal efficiency, human health risks, and the correlation with environmental factors have yet to be established. Therefore, this study characterised the occurrence patterns of nine conventional dissolved HMs in the influent and effluent water samples from 146 typical DWTPs in seven major river basins across China (which consist of the Yangtze River, the Yellow River, the Songhua River, the Pearl River, the Huaihe River, the Liaohe River and the Haihe River) for the first time and removal efficiency, probabilistic health risks, and the correlation with water quality. According to the findings, a total of eight HMs (beryllium (Be), antimony (Sb), barium (Ba), molybdenum (Mo), nickel (Ni), vanadium (V), cobalt (Co) and titanium (Ti)) were detected, with detection frequencies in influent and effluent water ranging from 2.90 (Mo) to 99.30% (Ba) and 1.40 (Ti) to 97.90% (Ba), respectively. The average concentration range was 0.41 (Be)- 77.36 (Sb) μg/L. Among them, Sb (exceeding standard rate 8%), Ba (2.89%), Ni (21.43%), and V (1.33%) were exceeded the national standard (GB5749-2022). By combining Spearman's results and redundancy analysis, our results revealed a close correlation among pH, turbidity (TURB), potassium permanganate index (COD_Mn), and total nitrogen (TN) along with the concentration and composition of HMs. In addition, the concentration of HMs in finished water was strongly affected by the concentration of HMs in raw water, as evidenced by the fact that HMs in surface water poses a risk to the quality of finished water. Metal concentration was the primary factor in assessing the health risk of a single metal, and the carcinogenic risk of Ba, Mo, Ni, and Sb should be paid attention to. In DWTPs, the removal efficiencies of various HMs also vary greatly, with an average removal rate ranging from 16.30% to 95.64%. In summary, our findings provide insights into the water quality and health risks caused by HMs in drinking water.

Ecological and health risk assessment and quantitative source apportionment of dissolved metals in ponds used for drinking and irrigation purposes

In this study, dissolved metal levels of 10 different ponds used as irrigation and drinking water sources in the north of Saros Bay (Türkiye) were evaluated using multivariate statistical methods, contamination and ecological risk indices, and absolute principal component score-multiple linear regression (APCS-MLR). The mean levels of metals in the ponds ranged from 0.045 µg/L (Cd) to 127 µg/L (Mn). Pond 7 used for drinking water source had the lowest total metal level. Only Mn levels in two ponds (P1 and P2) slightly exceeded the critical value set by EU Drinking Water Directive. However, the levels of all metals in all ponds were lower than the critical values set for irrigation water and aquatic life. According to the heavy metal pollution index (HPI), five ponds showed low metal pollution in terms of drinking water quality, four ponds showed moderate metal pollution, and one pond (P1) showed moderate to heavy pollution. According to the Nemerow pollution index (NPI) values (0.26-1.82), ponds P1 and P2 showed slight metal pollution, while other ponds showed insignificant metal pollution. Contamination degree (CD) values of ponds varied between 0.95 and 3.33, indicating that all ponds showed low pollution. In terms of irrigation water quality, all ponds showed low or insignificant metal pollution according to the HPI, NPI, and CD values. According to the ecological risk index (ERI) values, metals in all ponds posed low ecological risks for both drinking and irrigation purposes. Factor analysis identified two potential sources: mixed sources and natural sources. The APCS-MLR model results revealed that mixed sources and natural sources contributed 78.99% and 21.01% to dissolved metals in the ponds, respectively. Health risk assessment results indicated that both individual and combined metals in the ponds would not cause non-carcinogenic risks to both adults and children. Similarly, it was found that Cr and As would not cause carcinogenic risks to the residents of the region.

Insights into As accumulation in soil-groundwater-wheat-hair system of suburban farmland: Distribution, transfer and potential health risk

Health risks caused by arsenic (As) contamination in soils and its migration in environmental media have attracted much attention. In this study, suburban farmland of KF city in the ecotone of the Yellow River and Huaihe River Basin was taken as the research area. A series of samples including topsoils (246), profile soils (280), matched wheat grains (22 groups), groundwater (26) and human hair (355) were collected. As distribution and transfer in soil-groundwater-wheat-hair (SGWH) system in typical sites were explored, and comprehensive health risk of As in SGWH system was assessed based on US EPA model and local exposure parameters. The results showed that spatial distribution of total As presented a significant high value area, and higher As contents (in the range of 0.45-29.86 mg kg^-1) and bioavailability was mainly in topsoils, which indicated that anthropogenic sources have led to As enrichment in studied area. Also, it was found that the As contents in 95 % of wheat grain samples were higher than that in the control soils, and 9 % groundwater samples were above national Class I standards. Especially, average As content in hair in typical sites was obviously influenced by that in soil, wheat and groundwater. Moreover, As migration curve along soil → wheat (groundwater) → hair appeared an irregular 'V' shape, and transfer coefficients of T_{f water/soil} (10^-5), T_{f wheat/soil} (10^-3), T_{f hair/soil} (10^-2), T_{f hair/wheat} (10¹) and T_{f hair/water} (10⁴) presented an obvious increasing trend of magnitude, implying that human body has a higher As enrichment risk. Furthermore, comprehensive health risks for children and adults in typical sites were significant, while wheat is the main risk medium. In general, arsenic accumulation in human hair is good consistent with EPA health risk model, and their combination can better evaluate environmental exposure risk of As.

Source apportionment and source-specific risk evaluation of potential toxic elements in oasis agricultural soils of Tarim River Basin

As rapidly developing area of intensive agriculture during the past half century, the oases in the source region of the Tarim River have encountered serious environmental challenges. Therefore, a comparative analysis of soil pollution characteristics and source-specific risks in different oases is an important measure to prevent and control soil pollution and provide guidance for extensive resource management in this area. In this study, the concentration of potential toxic elements (PTEs) was analyzed by collecting soil samples from the four oases in the source region of the Tarim River. The cumulative frequency curve method, pollution index method, positive matrix factorization (PMF) model, geographical detector method and health risk assessment model were used to analyze the pollution status and source-specific risk of potential toxic elements in different oases. The results showed that Cd was the most prominent PTE in the oasis agricultural soil in the source region of the Tarim River. Especially in Hotan Oasis, where 81.25% of the soil samples were moderately contaminated and 18.75% were highly contaminated with Cd. The PTEs in the Hotan Oasis corresponded to a moderate level of risk to the ecological environment, and the noncarcinogenic risk of soil PTEs in the four oases to local children exceeded the threshold (TH > 1), while the carcinogenic risk to local residents was acceptable (1E-06 < TCR < 1E-04). The research results suggested that the Hotan Oasis should be the key area for soil pollution control in the source region of the Tarim River, and agricultural activities and natural sources, industrial sources, and atmospheric dust fall are the priority sources that should be controlled in the Aksu Oasis, Kashgar Oasis and Yarkant River Oasis, respectively. The results of this study provide important decision-making support for the protection and management of regional agricultural soil and the environment.

Multivariate and spatio-temporal groundwater pollution risk assessment: A new long-time serial groundwater environmental impact assessment system

Groundwater pollution risk assessment is an important part of environmental assessment. Although it has been developed for many years, there has not yet been a multi-dimensional method that takes into account long time series and spatial factors. We proposed a new method combines the advantages of remote sensing cloud computing, long-term groundwater modeling simulation and GIS technology to solve it efficiently. A coastal industrial park in Hainan was used as the study area. The depth of groundwater level, rainfall, topography and geomorphology, soil moisture, pollution source, pollution toxicity and other more than 10 parameters were used as the indexes. A comprehensive model with remote sensing cloud computing, DRASTIC model and Modflow + MT3DMS was established to assess the pollution risk from 2014 to 2021. The multi-year results indicated that the risk assessment of groundwater pollution was usually on the vertical coastal direction, and the risk increased from far away to near coast. With the discharge of pollutants in the industrial park, the pollution risk in the area 5 km away from the centre increased year by year until it became stable in 2019, and the risk in the centre of the park reached 1 level, covered an area of up to 145400 square metres, accounted for 0.012% of the whole study area. The assessment results in 2020 and 2021 fluctuate slightly compared with those in 2019. Therefore, in terms of groundwater resource protection and resource management, it is necessary to focus on the detection of pollution in the coastal zone and the pollution within 5 km of the centre to strictly control pollution discharge. In this study, the comprehensive assessment includes surface indicators, subsurface indicators, and pollutant indicators. Finally, we achieve a multivariate, spatial and long time series groundwater pollution risk assessment system, which is a new groundwater environmental impact assessment (GEIA) system.

Health Risk Assessment Based on Source Identification of Heavy Metal(loid)s: A Case Study of Surface Water in the Lijiang River, China

In this study, 24 surface water samples were collected from the main trunk/tributary of the Lijiang River during the wet season (April) and the dry season (December) in 2021. The total concentration of 11 heavy metal(loid)s (Al, Cu, Pb, Zn, Cr, Ni, Co, Cd, Mn, As, and Hg) was determined to investigate their physicochemical properties and spatial-temporal distribution characteristics. The heavy metal evaluation index (HEI) and the positive matrix factorization (PMF) model were employed to evaluate water quality and to reveal quantitatively identified pollution sources for further investigation to obtain a health risk assessment using the hazard index (HI) and carcinogenic risk (CR) of various pollution sources. The mean concentrations of heavy metal(loid)s in surface water in the wet and dry seasons were ranked as: Al > Mn > Zn > Ni > Cd > Cr > Cu > As >Hg = Pb > Co, with the mean concentration of Hg being higher than the national Class II surface water environmental quality standard (GB3838-2002). In terms of time scale, the concentration of most heavy metal(loid)s was higher in the wet season; most heavy metal(loid)s were distributed mainly in the midstream area. HEI index indicated that the main water quality status was “slightly affected” in the study area. Five potential sources of pollution were obtained from the PMF model, including industrial activities, traffic sources, agricultural activities, domestic waste emissions, and natural resources. The source-oriented risk assessment indicated that the largest contributions of HI and CR were agricultural sources in the Lijiang River. This study provides a “target” for the precise control of pollution sources, which has a broad impact on improving the fine management of the water environment in the basin.

Hg Pollution Indices along the Reis Magos River Basin-Brazil: A Precursory Study

Mercury is a metal present in the Earth's crust, but due to human contribution, its concentration can increase, causing environmental impacts to aquatic ecosystems, among others. The Reis Magos River Hydrographic Basin represents economic and socio-environmental importance for the state of Espírito Santo, Brazil. However, there are not many publications regarding the quality of water and sediments, so no data is reported concerning the total concentration of Hg. Thus, the present work aimed to evaluate the distribution of total Hg in water and sediments along this hydrographic basin. For a better inference, physicochemical parameters of the water were determined (temperature, pH, electrical conductivity, oxidation-reduction potential (ORP), turbidity, dissolved oxygen (DO), total dissolved solids (TDS), and salinity), and in the sediments, the contents of matter organic matter, pH, carbonates and granulometry. Mercury determination was performed by Thermodecomposition and Amalgamation Atomic Absorption Spectrometry (TDA AAS) with a DMA-80 spectrometer. The Hg determined in the water was lower than the limit of quantification, 0.14 µg∙L^-1, which is lower than the maximum limits recommended by world reference environmental agencies. In the sediment samples, the Hg found were below 170 µg∙kg^-1, values below which there is less possibility of an adverse effect on the biota. However, when the degree of anthropic contribution was evaluated using the Geoaccumulation index (IGeo), the contamination factor (CF), and the ecological risk potential index (E_F), there was evidence of moderate pollution. Thus, this highlighted the need for monitoring the region since climatic variations and physical-chemical parameters influence the redistribution of Hg between the water/sediment interface.