Study and health risk assessment of the occurrence of iron and manganese in groundwater at the terminal of the Xiangjiang River

Human exposures to multiple water sources in the southwestern coastal region of Bangladesh: water quality, pollution sources, and preliminary health risks appraisals

The coastal areas of Bangladesh have poor accessibility to fresh drinking water and the groundwater is not suitable for drinking, cooking, and other domestic uses due to high levels of salinity and potentially toxic elements. The current study focuses on understanding of the distribution of some physicochemical parameters (temperature, pH, EC, TDS, and salinity) and chemical elements (Fe, Mn, Zn, Ca, Mg, Na, K, Cu, Co, Pb, As, Cr, Cd, and Ni) with health perspective in drinking water from the southwestern coastal area of Bangladesh. The physicochemical properties of the water samples were examined with a multiparameter meter, while the elemental concentrations were analyzed using atomic absorption spectrometer. Water quality index (WQI) and irrigation indices were utilized to determine the drinking water quality and irrigation feasibility, respectively, whereas hazard quotients (HQs) and hazard index (HI) were used to assess the probable pathways and the associated potential risks to human health. The concentrations of some toxic elements in measured samples were relatively higher compared to drinking water guidelines, indicating that ground and surface water are not apt for drinking and/or domestic uses. The multivariate statistical approaches linked the source of the pollutants in the studied water body mostly to the geogenic origin including saline water intrusion. WQI values ranged from 18 to 430, reflecting excellent to unsuitable categories of water quality. The assessment of human health risks due to exposure to contaminated water demonstrated both carcinogenic and non-carcinogenic health risks in the exposed residents of the study area. Therefore, appropriate long-term coastal area management strategies should be adopted in the study region for environmental sustainability. The findings of this research will be supportive in understanding the actual situation of fresh drinking water in the area for policymakers, planners, and environmentalists to take effective necessary measures to ensure safe drinking water in the study area.

Efficient Mn(II) removal by biological granular activated carbon filtration

Sufficient and sustainable manganese(II) removal is a challenging task to prevent Mn-related drinking water discoloration problems. This study investigated Mn(II) removal by granular activated carbon (GAC) filtration under various conditions. The results showed that biological GAC filter columns could reduce Mn(II) from 400 μg/L to 10 μg/L after a short ripening period, while sand filter columns did not show evident Mn(II) removal function. Water quality changes, pretreatment with NaClO and chemogenic MnO_x coating on GAC media surface did not influence the Mn(II) removal capacity of GAC filter columns. 16S rRNA gene sequencing showed that the abundance of potential Mn(II)-oxidizing bacteria in the GAC media was similar to that in the sand media. However, qPCR results indicated that GAC media colonized dramatically more biomass than sand media, resulting in highly effective Mn(II) removal by GAC filter columns. Under chlorinated conditions, GAC filtration underperformed sand filtration in Mn(II) removal, although activated carbon has been reported to be capable of catalyzing Mn(II) oxidation by chlorine. Fast chlorine decay in GAC filter columns made it hard to sustain chemical Mn(II) oxidation and thus led to less Mn(II) removal. This study highlighted the advantage of biological GAC filtration over sand filtration in Mn(II) removal.

Removal of ammonium and manganese from surface water using a MeOx filter system as a pretreatment process

Residual aluminium from the coagulation-sedimentation process in the treatment of surface water can decrease the catalytic activity of a manganese co-oxide filter film (MeO_x) used for ammonium and manganese removal. To solve this problem, a MeO_x filter was used as a pretreatment process to filtrate source water directly before the coagulation and sedimentation treatment. The removal performance and the mechanism of change in the activity of MeO_x were investigated. The experimental results indicated that the MeO_x filter removed ammonium and manganese from surface water sources effectively, and its manganese removal activity was enhanced. The characteristics of MeO_x were investigated via SEM, EDS, XPS, and the BET surface area. Analysis of the experimental results showed that the increase in the content of Al under this condition was much lower than that under treatment with the coagulation-sedimentation process. After long-term operation, the amount and surface area of MeO_x coated on the filter sand increased significantly, leading to an increase in the catalytic activity. However, in cold water, the catalytic activity of MeO_x decreased, and more Mn(II) was obtained on the surface of MeO_x. Thus, the morphology of MeO_x changed. Fortunately, when water temperature increases, the removal activity can recover immediately. By inactivating microorganisms and comparing the removal performance with that under other conditions, the MeO_x activity of the pretreatment process is preserved effectively and no strengthening measures are required. This study will provide a new strategy for the use of the MeO_x catalytic technology.

New Insights in factors affecting ground water quality with focus on health risk assessment and remediation techniques

Groundwater is considered as the primary source of water for the majority of the world's population. The preponderance of the nation's drinking water, as well as agricultural and industrial water, comes from groundwater. Groundwater level is becoming increasingly challenging to replenish due to climate change. Fertilizer application and improper processing of industrial waste are the two major anthropogenic drivers of groundwater pollution. Arsenic and cadmium are two of the principal heavy metal pollutants that have affected groundwater quality by human activity. When people are exposed to both non-carcinogenic and carcinogenic contaminants for an extended period, toxic effects might occur. It can have detrimental health effects from long-term exposure to contaminants, even in low amounts. As a result, metal contamination concentrations and fractions can be used to determine potential health concerns. At the same time, contaminants also need to be removed or converted to harmless products by groundwater remediation. Remediation of groundwater quality can be accomplished in several ways, including natural and artificial means. The purpose of this review is to explore a wide range of factors that affect groundwater quality, including their possible health effects. This communication provides state-of-the-art information about remediation approaches for groundwater contamination including hindrances and perspectives in this area of research. The in-depth information provided in different sections of this communication would expand the scope of interdisciplinary research.

The origin of Uranium in groundwater of the eastern Halkidiki region, northern Greece

Uranium (U) pollution in groundwater has become a serious problem worldwide. Even in low concentrations, U has both radiological and toxicological impacts on human health. In this study an integrated hydrogeological approach was applied to conceptualize an aquifer system, and determine the origin of U detected in the aquifer of the eastern Halkidiki region in northern Greece. Data from measurements of groundwater level and hydrochemical and stable isotope analyses of groundwater samples were applied to perform geochemical modeling and multivariate statistical analysis. The modeling and statistical analysis identified three hydrogeochemical groups within the studied hydro-system, and U(VI) as the dominant U species. The first group is linked to the deeper aquifer which is characterized by water-rock interactions with weathering products of granodiorite. In this group the dominant U species is uranyl phosphate and U concentration is 3.7 μg/L. The upper aquifer corresponds to the second hydrogeochemical group where U concentrations are mainly influenced by high concentrations of nitrogen species (NO₃^- and NO₂^-). Factor analysis further discriminated the upper aquifer into a saline coastal zone and an inland zone impacted by agricultural activities. The third hydrogeochemical group presents the highest concentration of U (up to 15 μg/L) in groundwater and corresponds to the internal aquifer system. The U within this system is triggered by the presence of Mn²⁺, while the long residence time of the groundwater contributes synergistically to the hydrogeochemical process. Manganese triggers U oxidation in parallel with Fe²⁺ precipitation that acts as a regulator of U concentration. Groundwater depletion of the upper aquifers promotes the up-coning of geothermal fluids from fault zones leading to increased concentrations of U in the mid-depth aquifers.

Effectiveness of Aerator Ventures, Deposition with Magnets, Filtering, and Ion Exchange in One Unit against Reduction of Iron, Total Dissolved Solid, and Marine Well Water

BACKGROUND: It is known the effectiveness of a venturi aerator, deposition with a sand filter magnet and ion exchange in one unit to reduce Fe content, total dissolved solid (TDS) and saltiness (CL content) in clean water, and the ability of ion exchange to reduce CL content is known. AIM: This study aims to analyze the effectiveness of venturi aerator, magnetic sedimentation, filtration, and ion exchange in one unit against Fe, TDS, and CL well water. METHODS: The method used is a quasi-experimental method using aeration with a venturi system, deposition with magnets, filtration, and ion exchange. The population in this study was all water containing Fe and CL in the Darul Kamal sub-district, Aceh Besar. The sample in this study is part of the population following research needs. RESULTS: The results showed an effect of a venturi aerator, deposition with magnets, filtering sea sand, anion, and cation resins in one unit to decrease Fe content and did not affect decreasing TDS content and Salinity. Moreover, a venturi aerator has an effect, deposition with magnets, filtering sea sand, anion, and cation resins in one unit on the decrease in Fe content, TDS, and salinity at deposition time of 24 h. Venturi aerator’s effect on Fe reduction does not affect TDS and CL of well water. There is an effect of venturi aerator and precipitation with magnets, in one unit on Fe reduction, and does not affect TDS and CL of well water. There is an effect of venturi aerator, precipitation with magnets, filtration in one unit on Fe reduction, no effect on TDS, and CL of well water. CONCLUSION: This tool effectively reduces Fe content and effectively reduces Fe, TDS, and salinity at a 24 h deposition time.

Survey of six metal contaminants and impurities and eleven metals and alloy components released from stainless-steel sheets on the Chinese market

The release of metal elements from stainless-steel products in contact with food may endanger human health. To protect human health, different countries or international organisations have formulated corresponding regulations or technical guidelines. Limits for only five metal elements are stipulated in the China National Food Safety Standard (GB 4806.9) and food simulants and test conditions are fixed regardless of the actual use condition. In this study, inductively coupled plasma mass spectroscopy and inductively coupled plasma optical emission spectroscopy were used to measure the concentrations of six metal contaminants and impurities and 11 metals and alloy component released from stainless-steel sheets on Chinese market. The effects were also investigated on metal release of six grades (201, 202, 304, 430, 443, and 30Cr13) and 6 exposure conditions (food simulant 5 g L^-1 citric acid or 4 vol% acetic acid, contact temperature 70 °C or 100 °C, and contact time 2 h, 0.5 h, or 0.5 h followed by ambient temperature for 24 h). For reusable stainless-steel sheets, especially for grade 30Cr13, it was essential to perform three consecutive release tests to check compliance. However, there was no need to conduct three consecutive release tests for the other five grades if the results of the first test met the regulations. It was recommended that 5 g L^-1 citric acid should be used as food simulant and contact temperature and time should be based on the actual using conditions. No relationships were found between metal release amounts and contact test temperature or time. The specific release limits for Pb, Cr, As, Cd, and Ni should be lowered and Al, Mn, and Fe be added in GB 4806.9. The results of this study can be a reference for further analysis of the release behaviour of metal elements in actual stainless-steel products.

Spatial distribution of manganese in groundwater and associated human health risk in the southern part of the Bengal Basin

The scarcity of arsenic and iron-free safe drinking water is an alarming issue in the southern part of the Bengal Basin. The objectives of the present study were to investigate the spatial distribution of manganese (Mn) concentration in the shallow and deep groundwater and its associated health risks for the children and adults of entire southern Bengal Basin. The Mn concentration in the groundwater varied from 0 to 5.4 mg/L with an average value of 0.47 mg/L that exceeded the WHO's and Bangladesh drinking water guideline values of 0.4 and 0.1 mg/L, respectively. Mn concentration in the shallow wells overrode the deep ones. About 23% of the shallow wells and 11% of deep wells exceeded the WHO's safety limit of Mn concentration for human health. The human health risk related to Mn contamination was estimated by computing the average daily dosage (ADD) and hazard quotient (HQ) values for children and adults. The average computed HQ values found 0.108 and 0.099 for children and adults, respectively. The HQ values delimitated that children are posing a higher risk compared to the adults for the shallow wells. Deep wells were found risk-free for both children and adults. The areal coverage of shallow wells with HQ values > 1 was minimal compared to the total study area and covered only a small portion of Patuakhali and Barguna districts. The rest of the site does not pose any health risk due to Mn contamination for children and adults.

Effects of the natural environment and human activities on iron and manganese content in groundwater: a case study of Changchun city, Northeast China

Excessive Fe and Mn in groundwater of the Songnen Plain, northeast China, pose a threat to water security. Human activities over recent decades have had significant effects on the water quantity and quality of the Songnen Plain. By adopting the large city of Changchun in the Songnen Plain as a research area, this study analyzed the effects of the natural environment (including characteristics of soil and aquifer, climate, and groundwater level) and human activities (including groundwater salinization, groundwater exploitation, and nitrate effects) on groundwater Fe and Mn using statistical and spatial analysis methods. The results showed that the characteristics of soil and aquifer determine the source of groundwater Fe and Mn. The correlations between Fe and Mn with TDS (total dissolved solids) increased with increasing TDS from southeast to northwest in different microclimate regions. The salinization of groundwater caused by human activities will also lead to the increase of Fe content. The decrease in groundwater Fe and Mn was attributed to an increase in groundwater [Formula: see text], through the use of chemical fertilizers. The variation of Fe concentration in groundwater corresponded well with that of groundwater depth, but the excessive exploitation will lead to the continuous decrease in groundwater level and a corresponding decrease in the concentration of groundwater Fe. This study provides a reference for understanding the influence of human activities and the natural environment on groundwater hydrochemistry in the Songnen Plain.

Occurrence, distribution, and prediction of iron and manganese in groundwater of opencast mines: an example from Inner Mongolia, China

Based on the geological and hydrologic data, the generation, enrichment, and transportation of iron (Fe) and manganese (Mn) ions in Yimin open-pit mining area were investigated using water quality analysis of groundwater samples, Statistical Product and Service Solutions (SPSS) principal component analysis, and geostatistics analysis by Geographic Information System (GIS). The water quality test results showed that the groundwater of this area was mainly the Na-Ca-HCO₃ type, and the content of Fe and Mn ions significantly exceeded the national standard. The groundwater in the mining area was strongly affected by human activity, deep groundwater mixing effect, and water-rock interaction associated with mining activities. It was also found that Fe and Mn in the research area had a large variation in spatial distribution. On the whole, Fe and Mn ion concentrations found in the groundwater to the north of the research area were higher than those in the south area, with the mining area as the dividing line. The removing of non-mineral layer and the draining of gushing water in the mining area resulted in the formation of a water funnel and the strengthening of an effect between each aquifer. The change of hydrogeological and redox conditions in the mining area promoted the dissolution of Fe and Mn in soil and stratum and migration in groundwater.

State, source and triggering mechanism of iron and manganese pollution in groundwater of Changchun, Northeastern China

The present state of iron (Fe) and manganese (Mn) concentration in groundwater of Changchun city located within the Songnen Plain of northeastern China was evaluated in this study. Heavy metal sources, as well as triggering mechanism, were analyzed using a physicochemical, statistical and spatial approach. Results revealed that out of the 2600 samples analyzed, 214 (representing 8.24%) for Fe and 606 wells (representing 23.34%) for Mn exceeded the water standard. Organic matter-rich sediments and Fe-Mn nodules in aquifer and soil serve as sources of Fe and Mn. Organic and inorganic complex formations, as well as long residence time, were found to foster the release of Fe and Mn into groundwater. Additionally, pH and well depth was important in triggering Mn dissolution while groundwater mineralization, depth to the water table and well proximity to the river were found to have minimal/negligible effect on heavy metal mobilization. The removal of Fe and Mn from the water before use was proposed along with the sinking of deeper wells for groundwater exploitation to limit the use of polluted water.

Source and Mobilization Mechanism of Iron, Manganese and Arsenic in Groundwater of Shuangliao City, Northeast China

Excessive levels of Fe, Mn and As are the main factors affecting groundwater quality in Songliao plain, northeast China. However, there are few studies on the source and mobilization mechanisms of Fe, Mn and As in the groundwater of Northeastern China. This study takes Shuangliao city in the middle of Songliao plain as an example, where the source and mobilization mechanisms of iron, manganese and arsenic in groundwater in the study area were analyzed by statistical methods and spatial analysis. The results show that the source of Fe and Mn in the groundwater of the platform is the iron and manganese nodules in the clay layer, while, in the river valley plain, it originates from the soil and the whole aquifer. The TDS, fluctuation in groundwater levels and the residence time are the important factors affecting the content of Fe and Mn in groundwater. The dissolution of iron and manganese minerals causes arsenic adsorbed on them to be released into groundwater. This study provides a basis for the rational utilization of groundwater and protection of people’s health in areas with high iron, manganese and arsenic contents.

Understanding of the high hydrothermal stability of a catalyst prepared from Mn slag for low-temperature selective catalytic reduction of NO

Manganese slag is a hazardous waste, which lacks proper treatment. For the first time, an effective catalyst for selective catalytic reduction of nitric oxide was synthesized from manganese slag by a sol-gel method. The obtained catalyst had an excellent low-temperature activity and high hydrothermal stability. It removed 46.3% of nitric oxide (990 ppm) at a temperature as low as 100 °C; its removal increased to 100% at 220 °C, which lasted for more than 2000 min. Moreover, hydrothermal treatment at 400 °C showed little influence on its activity. Even after hydrothermal treatment at 900 °C, the catalyst still removed 39.7% of NO at 220 °C, 22.7% higher than another catalyst synthesized from pure reagents. The hydrothermal stability was attributed to an amorphous layer of MnSi_xO_y. This layer covered the catalyst surface, protected active metal species, pore size and pore volume from steam attacking. Manganese slag thus realized the high-value-added utilization by synthesizing a catalyst with the high hydrothermal stability.

Evaluation of the raw water quality: physicochemical and toxicological approaches

Environmental degradation has increased, mainly as a result of anthropogenic effects arising from population, industrial and agricultural growth. Water pollution is a problem that affects health, safety and welfare of the whole biota which shares the same environment. In Goiânia and metropolitan region, the main water body is the Meia Ponte River that is used for the abstraction of water, disposal of treated wastewater and effluents. In addition, this river receives wastewater from urban and rural areas. The aim in this present study was to evaluate the quality of raw water by some physical, chemical and toxicological tests. The physicochemical results found high levels of turbidity, conductivity, aluminum, phosphorus and metal iron, manganese, copper and lithium when compared to the standards of the Brazilian legislation. The values found of toxicity demonstrated a high degree of cytotoxicity and genotoxicity. Therefore, it was concluded that the Meia Ponte River has been undergoing constant environmental degradation, causing the poor quality of its waters. Thus, measures for the prevention and recovery should be adopted for the maintenance of the Meia Ponte River.

Binding characteristics of cadmium and zinc onto soil organic matter in different water managements and rhizosphere environments

Soil organic matter (SOM) could immobilize most of metals, but it could promote the migration of a small part of metals in special environments. Heavy rainfall and drought makes wetlands affected by the alternation of drought and flood, altering the mobility of metals. Few studies have been conducted on the changes of binding characteristics of metals onto SOM which derived from different water conditions and rhizospheric environments. The objective of this paper was to explore the sequential differences of spectral variations of fluorescent groups and UV-Vis groups of metals onto SOM which derived from different water managements and rhizospheric environments. The method adopted was mainly two-dimensional correlation analysis (2DCOS). The results showed that flooding samples contained more aromatic substances compared to draining samples, which could promote metal binding. The binding characteristics were shown in the following: (1) Cd²⁺ and Zn²⁺ could react with aromatic substances, react with functional groups in SOM, and promote the formation of new groups such as carboxyl; (2) both Zn²⁺ and Cd²⁺ could bind with functional groups on proteins but relatively reductive environment can weaken the binding ability of Cd²⁺; (3) the protein-like or fulvic-like groups gave the fastest responses and then came the amide and carboxyl groups in nearly all flooding samples; (4) in flooding samples, Cd²⁺ was most easily to bind with fulvic-like groups, while Zn²⁺ was most easily to bind with protein-like groups. This work is conducive to the long-term management of heavy metal pollutants in wetlands.

Research on the Migration of the Total Manganese during the Process of Water Icing

Our research focused on the migration law of the total manganese (TMn) during the process of water icing. We utilized two experimental methods: (1) natural icing and (2) simulated icing. While using laboratory simulation, we explored the effects of ice thickness, freezing temperature, and initial concentrations on the migration of TMn in the ice-water system. The distribution coefficient “K” (the ratio of the average concentration of TMn in the ice body to the average concentration of TMn in the under-ice water body) was used to characterize it. The results indicated that TMn continuously migrated from ice to under-ice water during the process of water icing. The concentration of TMn in the ice was the upper layer < middle layer < lower layer, and K decreases as the ice thickness, freezing temperature, and initial concentration increased. We explained the migration of TMn during the process of water icing from the perspective of crystallography. Our research can arouse other researcher’s attention towards the change of TMn concentration in lakes in high latitudes during the icebound period.

The Use of Chalcedonite as a Biosorption Bed in the Treatment of Groundwater

The conducted laboratory tests allowed determination of the efficiency of removing ammonium nitrogen, iron, and manganese in the biofiltration process on chalcedonite beds. The process of water purification was carried out by a single- and two-stage biofiltration method with gravitational and anti-gravitational flow. The study examined the extent to which chemical activation of the bed with potassium manganese (VII) affects the course of the nitrification process and the rate of biofilm formation. The obtained test results indicate that two-stage biofiltration, with initial chemical activation at the first stage of biofiltration, is an effective method for purifying waters with an abnormal content of ammonium nitrogen with simultaneous removal of iron and manganese. Activation of the bed had an effect on, among other things: biofilm formation time, efficiency of removing manganese (II) ions, and oxygen consumption in the biofiltration process. Due to the longer maturation time of the activated bed, the normative value of ammonium nitrogen (< 0.39 N-NH4+) was obtained on the 23rd day of the operation of the filters, and in the non-activated bed on the 14th day. The method of bed preparation did not affect the efficiency of removal of iron compounds.

Impact of Mn and ammonia on nitrogen conversion in biofilter coupling nitrification and ANAMMOX that simultaneously removes Fe, Mn and ammonia

One lab-scale biofilter coupling nitrification and anaerobic ammonium oxidation (ANAMMOX) that simultaneously removes Fe, Mn and ammonia from simulated groundwater was adopted to investigate the influence of Mn and ammonia on nitrogen conversion and Mn removal kinetics in this study. The results showed that autotrophic nitrogen removal proportion (ANRP) rose slightly with the raise of Mn concentration and declined along with the raise of ammonia; the average ratios were 49.6%, 51.5%, 51.8%, 52.3%, 52.6%, 48.9%, 47.4% and 38.8%, respectively. Relative constant or slight down trend of accumulated ANRP was detected in filter bed which indicated the superiority of nitrification in relevant areas. After reaching a certain value, Mn could promote ANAMMOX in the upper part of the filter bed and shorten the main ammonia conversion area. As ammonia content rising, the maximum accumulated ANRP reduced and the maximum value acquired height went up. Moreover, the ammonia inhibition threshold for ANAMMOX in the biofilter might be different from waste water treatment. Mn removal could be assessed by first order reaction in all the eight periods and the k values were more comparable than those in abiotic Mn oxidation.

Fe(ii) and Mn(ii) removal by Ca(ii)–manganite (γ-MnOOH)-modified red mud granules in water

In this study, a material (DLRMG) was synthesized by modifying Ca²⁺ and manganite (γ-MnOOH) on red mud granules (RMG), which were the main raw materials derived from industrial alumina. Moreover, a series of experiments were conducted on the adsorption of Fe²⁺ and Mn²⁺ in underground water. The prepared samples were analyzed by X-ray diffraction (XRD), thermogravimetric analysis-differential thermal analysis (TG-DTA), zeta potential analysis, BET and scanning electron microscopy (SEM); the concentration of the effluent was found to be of acceptable standard after the treatment. DLRMG continued to treat fluoride wastewater even after the saturated adsorption of Fe²⁺ and Mn²⁺, and the results clearly showed that the treatment was effective. Overall, the problems of red mud stockpile and pollution in China would be effectively controlled by DLRMG.

The use of the waste of aluminum industry to prepare effective polluted materials for the treatment of underground water.

Passivating effect of dehydrated sludge and sepiolite on arsenic contaminated soil

Exploring an efficient and economical method to remove arsenic from soil is of great practical significance but there were few studies on the combined use of sepiolite and dehydrated sludge as a repair agent to passivate heavy metals. Through soil passivation experiments, arsenic sequential extractions, and analysis of basic physicochemical properties of contaminated soils and repair agents, this study was to explore the applicability of dehydrated sludge-sepiolite compound repair agents and dehydrated sludge individual repair agents to passivate soil arsenic and its passivating effect. After passivation experiment, the best remediation period was 1-10 days. The best cultivated time was 10 day using DS2 repair agent. With a comparison of passivation effect of different repair agents, it was found that the best treatment group in individual repair agents was DS2 (10 days), and the best treatment group in compound repair agents was S1 (1 day). The passivation effect of individual repair agents was better than compound repair agents in 10-days cultivation. In the short term, the repair effect was increasing and then decreasing, thus this experiment was only suitable for use as a short-term repair method. The application of dehydrated sludge combined with sepiolite as repair agents provided a new way for both making full use of dehydrated sludge and controlling metal mobility.

Investigating organic matter properties affecting the binding behavior of heavy metals in the rhizosphere of wetlands

Soil organic matter (SOM) is a crucial factor affecting the immobilization of heavy metal in wetlands. Recent studies have shown that the rhizosphere SOM has great ability to immobilize heavy metals. However, there existed few works on studying molecular characteristics of SOM to explore the mechanisms. Electrospray ionization-Fourier transform ion cyclotron resonance-mass spectrometry (ESI-FTICR-MS) combined with FTIR spectroscopy were applied to investigate the characteristics of SOM in rhizosphere and nonrhizosphere samples and to find out what characteristics the rhizosphere SOM embodies conducive to metal binding in this paper. The rhizosphere contained higher C, P, Mn, and other metal concentrations. The adsorption of Cr on rhizosphere SOM was greater than that on nonrhizosphere SOM. Compared to nonrhizosphere SOM, rhizosphere SOM contained less saturated and more oxidized compounds, greater overall molecular weights (MW), more condensed aromatic structures (56.59% VS 51.56% by peak intensity), less carboxylate and N-containing COO functional groups (25.98% VS 56.63% by peak intensity), more hydrophilicity, and the latter four are conducive to metal binding. This study showed that the rhizosphere SOM had unique compositional and structural characteristics. These results provided evidence for the phytoremediation technologies of heavy metal contaminated wetlands.

The complexation of rhizosphere and nonrhizosphere soil organic matter with chromium: Using elemental analysis combined with FTIR spectroscopy

Complexation is a main mechanism controlling the reactions between soil organic matter (SOM) and heavy metals, which still have not been fully understood up to date. The objective of this study was to compare the SOM composition of nonrhizosphere and rhizosphere in low Cr treatment with that in high Cr treatment and to find out how metal concentrations affect the complexation with SOM. The results revealed that both the hydroxyl and the carboxyl were significantly different under different Cr treatment groups. For nonrhizosphere samples, the high Cr treatment tended to have less hydroxyl contents and more structural changes on hydroxyl (3389-3381 cm^-1) than the low Cr treatment (3389-3388 cm^-1), while in the rhizosphere samples the reverse happened. The gap of the different Cr treated band area in the rhizosphere samples (44 a.u of the gap) was greatly smaller than that in the nonrhizosphere samples (576 a.u of the gap). In both the rhizosphere and nonrhizosphere samples, the high Cr treatment showed greater structural changes on carboxylic acids (11, 12 a.u changes based on the control) than the low Cr treatment (4, 6 a.u). The unsaturated carboxylic acids could account for downward frequency shift and the contents in the nonrhizosphere samples were slightly greater than that in the rhizosphere samples. This study used elemental analysis combined with FTIR spectroscopy to explore the effects of metal concentrations on the complexation of Cr with SOM and the composition of SOM. These findings give a way to understanding part of the complexation mechanisms between the metal and SOM.

Assessment of trace elements in terminal tap water of Hunan Province, South China, and the potential health risks

A total of 116 terminal tap water (TTW) samples from Xiangjiang, Zijiang, Yuanjiang, and Lishui river basins of Hunan province were collected and concentrations of As, Cd, Cr, Pb, Mn, Zn, Fe, Al, and Cu were determined using inductively coupled plasma mass spectrometry. The results showed that 10% of the water samples exceeded the limit level of Cd established by World Health Organization (WHO) of 0.003 mg L^-1. Three percent of the samples had Fe level and 1% had As level above the WHO limits of 0.3 and 0.01 mg L^-1, respectively. Multivariate statistic approach (cluster analysis and principal component analysis) results revealed that anthropogenic activities and pipeline corrosion were major sources of TTW contamination in Hunan province. The individual and total hazard quotient values estimated by deterministic and probabilistic approaches were both less than 1. However, the mean cancer risk values of Cd were 2.2 × 10^-4 and 1.4 × 10^-4 for Xiangjiang and Yuanjiang river basin, respectively, both greater than 10^-4. The 95th percentile value of cancer risk for Cr was slightly greater than 10^-4 in Xiangjiang river basins. Long-term exposure to Cd and Cr through tap water consumption poses moderate carcinogenic health risks to the local residents.

Key blackening and stinking pollutants in Dongsha River of Beijing: Spatial distribution and source identification

Elimination of black-stinking water contamination has been listed as an urgent task in the Water pollution prevention action plan promulgated by State Council of China. However, the key blackening and stinking pollutants and their sources are still unclear. In this study, water quality of a black-stinking urban river in Beijing, Dongsha River, was evaluated firstly; then the distribution of the blackening and stinking pollutants was investigated, and the key pollutants and their potential sources were identified; and finally, the health risk of those pollutants was assessed. The results showed that NH₃N, total phosphorus, dissolved oxygen and chemical oxygen demand ranged from 1.3 to 5.3 mg/L, 0.7-3.0 mg/L, 1.0-3.2 mg/L and 29-104 mg/L, respectively. The value of TP-based trophic level index indicated that Dongsha River reached severe eutrophication level; the maximum value of chroma and odor level reached 32 and 4, respectively. The main dissolved organic compounds included aromatic protein II, soluble microbiological metabolites, fulvic acids and humic acids. The blackening pollutants Fe, Mn, Cu and S^2- were extensively detected, with significantly spatial differences along the river. Dimethyl sulfide, β-ionone, 2-methylisoborneol and geosmin were identified to be the stinking pollutants. Their concentrations covered wide ranges, and even the lowest concentration value was thousands of times higher than its olfactory threshold. Correlation analysis indicated that in the overlaying water S^2- was the key blackening pollutant, while β-ionone and geosmin were the key stinking pollutants. Principal components analysis combining with the site survey revealed their potential sources. S^2- was mainly associated with the decomposition of endogenous sulfur-containing organics; β-ionone might be generated by the endogenous β-carotene bio-conversion and the exogenous discharges, while geosmin might originate from the endogenous humus bio-conversion and anthropic wastes. Furthermore, multi-metals in the sediment posed health risks to children, while dimethyl sulfide had non-cancer health risk for adults and children.

Groundwater nitrate pollution and human health risk assessment by using HHRA model in an agricultural area, NE China

In order to learn the pollution circumstance of groundwater nitrate detailedly in Songnen Plain of Northeast China and estimate its potential risk to human health of local residents, a total of 389 groundwater samples were collected in 2014 and studied from residential areas and public water supply wells in 11 cities and counties in southeastern of Songnen Plain. The analysis results showed that the spatial distributions of main chemical components in groundwater had great variations with statistical concentrations in the order of TDS> HCO₃> Ca> NO₃> Cl> Na> SO₄> Mg> K> NH₄> NO₂. As for NO₃, it ranged from less than 0.02mg/L to 497mg/L with an average value of 39.46mg/L indicating an obviously anthropogenic pollution. Even more than 32% of the samples exceeded the Grade III threshold (20mg/L of N) according to China's standard. The results obtained from principal component analysis showed that high NO₃ concentration could be attributed to human activities, especially the excessive use of chemical fertilizers in agriculture. Further, a human health risk assessment (HHRA) model derived from the US Environmental Protection Agency (USEPA) was applied to estimate the potential health risk of groundwater nitrate considering both drinking water and dermal contact pathways. The results indicated that potential health risks of adult males and females within about 60% of the area were at the acceptable level, while those within about 40% were beyond the acceptable level. The area at the acceptable level for children covered 49% of the total area while the same value for infants was 37%. The NO₃ concentration in southeast and northeast of the study area was the highest so that residents in these regions were at the highest health risk. In conclusion, risk levels for different crowds in the study area varied obviously, generally in the order of infants> children> adult females> adult males, and the potential health risks of residents, especially minors and rural residents, should cause enough attention both from the society and the academic community.

Does the groundwater nitrate pollution in China pose a risk to human health? A critical review of published data

Nitrate pollution has pervaded many parts of the world, especially in developing countries such as China. Based on the available groundwater nitrate data sets in China (2000-2015), the groundwater pollution levels at the provincial scale are evaluated which contains 33 provinces (units) except for Macau because of lacking data. Then, the potential risks posed to human health in national scale are quantified. In order to make the results more precise and systematical, both drinking and dermal contact exposure pathways are considered, and the influenced crowd are more finely divided into four groups to study the impacts of age and gender on the outcome, which include infants (0-6 months), children (7 months-17 years old), adult males (18 years old-), and adult females (18 years old-). Results indicate that there are seven units whose groundwater nitrate concentrations exceed the standard value with Shaanxi being a seriously poor condition. Facing the same level of nitrate, the health risk level changes in the order of infants > children > adult males > adult females. That is to say, minors and males are more vulnerable compared with adults and females, respectively. There is no adverse effect on adult females of the whole country, while gender really impacts on the health risk assessment result. Adult males, children, and infants face various degrees of health risk respectively in Shaanxi and Shandong, which are needed to pay more attention to.

Dynamics of natural contamination by aluminium and iron rich colloids in the volcanic aquifers of Central Italy

The dynamics of natural contamination by Al and Fe colloids in volcanic aquifers of central-southern Italy were investigated. Localized perched aquifers, and their relative discharges, are strongly affected by the presence of massive suspended solids, which confer a white-lacteous coloration to the water. This phenomenon occasionally caused the interruption of water distribution due to the exceeding of Al and Fe concentrations in aquifers exploited for human supply. The cause was ascribed to water seepage from perched aquifers. Water discharges affected by such contamination was investigated for the Rocca Ripesena area (north-eastern sector of Vulsini Volcanic District) and for the Rianale Stream Valley (Roccamonfina Volcanic Complex). Hydrogeological survey of both areas confirmed the presence of perched aquifers not previously considered due to their low productivity. Pluviometric data and chemical parameters were periodically monitored. Water mineralization decreased with increasing rainfall, conversely Al and Fe concentrations increased. Statistical analysis confirmed the dependence of all the chemical variables on rock leaching, with the sole exception of Al and Fe which were imputed to colloids mobilization from local, strongly pedogenized pyroclastic material. The similarities in hydrogeological settings and mobilization dynamics in both areas suggest that the Al and Fe colloidal contamination should be more abundant than currently known in quaternary volcanic areas.

Mobilisation processes responsible for iron and manganese contamination of groundwater in Central Adriatic Italy

Iron and manganese are two of the most common contaminants that exceed the threshold imposed by international and national legislation. When these contamination occurs in groundwater, the use of the water resource is forbidden for any purposes. Several studies investigated these two metals in groundwater, but research focused in the Central Adriatic area are still lacking. Thus, the objective of this study is to identify the origin of Fe and Mn contamination in groundwater and the hydrogeochemical processes that can enrich aquifers with these metals. This work is based on hydrogeochemical and multivariate statistical analysis of analytical results undertaken on soils and groundwater. Fe and Mn contamination are widespread in the alluvial aquifers, and their distribution is regulated by local conditions (i.e. long residence time, presence of peat or organic-rich fine sediments or anthropic pollution) that control redox processes in the aquifers and favour the mobilisation of these two metals in groundwater. The concentration of iron and manganese identified within soil indicates that the latter are a concrete source of the two metals. Anthropic impact on Fe and Mn contamination of groundwater is not related to agricultural activities, but on the contrary, the contribution of hydrocarbons (e.g. spills) is evident.