Seasonal and spatial contamination statuses and ecological risk of sediment cores highly contaminated by heavy metals and metalloids in the Xiangjiang River.

To reveal seasonal and spatial variations of heavy metals and metalloids (HMMs) in sediment of the Xiangjiang River, a total of 24 water and 649 sediment samples were collected from six sampling stations in the Songbai section of the river which had been polluted by HMMs for 100 years. Their contamination statuses and ecological risk were determined by enrichment factor (EF), geo-accumulation index (Igeo), pollution load index (PLI), and mean probable effect concentration quotients (mPECQs) analyses. The results revealed a unique seasonal distribution of metals in the sampling stations: The highest concentrations were revealed in the dry seasons (autumn and winter) and the lowest during the wet seasons (spring and summer). It exhibited a greater seasonal variation in the estuary sediment cores (sites ME and MW) than in the cores of other sites. Moreover, the highest concentrations of the tested metals were also found in the estuary sediment cores in the dry seasons (autumn and winter). The highest vertical concentrations of Pb, Zn, Cu, Ni, As, Fe, and Mn were observed at the depths of 16-36 cm in all of the sampled sediment cores. The EF, Igeo, PLI, and mPECQs values of all samples in autumn were higher than in summer. Cd posed the highest ecological risk in all seasons, although its concentrations were lower compared to other studied elements. Our results will benefit to develop feasible sediment quality guidelines for government monitor and remediate the local sediments in the Xiangjiang River.

Pollution by Nonylphenol in river, tap water, and aquatic in an acid rain-plagued city in southwest China.

OBJECTIVE: Nonylphenol (NP) has provoked much environmental concern because of their weak estrogenic activities; however, few data are available on the environmental levels of the chemical in China. METHOD: Environmental or river samples were assayed for NP by high-performance liquid chromatography (HPLC) technique. RESULTS: The concentration for NP measured in Xiangjiang River, ranging from 0.174 to 3.411 µg/L with a mean value of 1.73 µg/L, was lower than the Water Quality Criteria for NP of the US (6.6 µg/L); however, the NP concentration was maintained at a higher level compare to the developed countries and other civil cities. NP concentration in downstream water was markedly higher than that both in midstream and upstream water. Tissue accumulation of NP was observed in aquatics. A ratio of mean concentration of NP in aquatic (chlamys farreri and hemiculter leucisculus) to that in river water was 241 and 1087, respectively. The presence of NP in tap water in two urban districts of Zunyi was common with a detectable rate reached 100.0%. Mean NP concentration in terminal tap water in Huichuan district was six times as high as Honghuagang district, which was above Standards for the Drinking Water Quality for Phenols of China (2 µg/L). CONCLUSION: The pollution of NP in Xiangjiang River, tap water, and aquatic in Zunyi belongs to moderate or severe level in the world.

Microbial functional genes enriched in the Xiangjiang River sediments with heavy metal contamination.

BACKGROUND: Xiangjiang River (Hunan, China) has been contaminated with heavy metal for several decades by surrounding factories. However, little is known about the influence of a gradient of heavy metal contamination on the diversity, structure of microbial functional gene in sediment. To deeply understand the impact of heavy metal contamination on microbial community, a comprehensive functional gene array (GeoChip 5.0) has been used to study the functional genes structure, composition, diversity and metabolic potential of microbial community from three heavy metal polluted sites of Xiangjiang River. RESULTS: A total of 25595 functional genes involved in different biogeochemical processes have been detected in three sites, and different diversities and structures of microbial functional genes were observed. The analysis of gene overlapping, unique genes, and various diversity indices indicated a significant correlation between the level of heavy metal contamination and the functional diversity. Plentiful resistant genes related to various metal were detected, such as copper, arsenic, chromium and mercury. The results indicated a significantly higher abundance of genes involved in metal resistance including sulfate reduction genes (dsr) in studied site with most serious heavy metal contamination, such as cueo, mer, metc, merb, tehb and terc gene. With regard to the relationship between the environmental variables and microbial functional structure, S, Cu, Cd, Hg and Cr were the dominating factor shaping the microbial distribution pattern in three sites. CONCLUSIONS: This study suggests that high level of heavy metal contamination resulted in higher functional diversity and the abundance of metal resistant genes. These variation therefore significantly contribute to the resistance, resilience and stability of the microbial community subjected to the gradient of heavy metals contaminant in Xiangjiang River.

[Analysis of Spatiotemporal Variation and Driving Factors of Water Quality in the Xiangjiang River Basin from 1990 to 2016].

In order to explore the spatiotemporal variation characteristics and driving mechanism of water quality in the Xiangjiang River Basin, the data of 16 water quality parameters at 113 stations over 26 years from 1990 to 2016 in the Xiangjiang River Basin were collected for synthetically assessing the water quality and identifying its main pollutants through the water quality index and other methods. The causal mechanism of water quality, especially the driving effect of water level and land use pattern, was analyzed. The results showed that： ① The overall water quality grade of the Xiangjiang River Basin during the study period was "good." However, the water quality deteriorated first （from 1990 to 2003） and then improved （from 2004 to 2016）. The season variation in water quality was not obvious, but the water quality fluctuation of the wet season was larger. The water pollution load of the main stream decreased successively from the middle reaches, downstream reaches, and upstream reaches. The upstream tributaries had the best water quality, whereas areas with poor water quality were mainly distributed at the mouth of the middle and downstream tributaries, especially in areas where multiple tributaries converged. ② Toxic heavy metals had the characteristics of toxicity, persistence, and bioaccumulation. If they exceeded a certain concentration in water, they were difficult to purify, posing great harm to the natural environment and human health. The toxic metal index （CI1） was the leading factor affecting water quality, in which Hg and Cd were the main parameters affecting the overall water quality of the Xiangjiang River Basin. ③ The water level had a positive impact on the water quality of the Xiangjiang River by diluting environmental parameters. Land type had little effect on heavy metal concentration, whereas forest land could improve water quality. Grassland had a negative correlation with permanganate index over a large scale range （≥ 5 km）. The increase in water bodies, arable land, and impermeable surface areas within the watershed increased the probability of high fecal coliform concentration in the water body. ④ With the increase in buffer distance, the water quality explained by the land use pattern increased. On the scale of 10 km buffer zone in the riparian zone, the explanation degree by land use pattern on water quality was the highest, which was an effective scale for water quality control of the Xiangjiang River. This research showed that the driving factors of heavy metal pollution and other pollution were different, but their regional differences were all obvious in the Xiangjiang River Basin. Therefore, pollution control should be classified and taken according to local conditions.

Future land use simulation model-based landscape ecological risk prediction under the localized shared socioeconomic pathways in the Xiangjiang River Basin, China.

Landscape ecological risk (LER) is an effective index to identify regional ecological risk and measure regional ecological security. The localized shared socioeconomic pathways (LSSPs) can provide multi-scenario parameters of social and economic development for LER research. The research of LER under LSSPs is of scientific significance and practical value in curbing the breeding and spread of LER risk areas. In this study, land-cover raster files from 2010 to 2020 were used as the foundational data. Future land use simulation (FLUS), regression, and Markov chain models were used to predict the land cover patterns under the five LSSP scenarios in the Xiangjiang River Basin (XJRB) in 2030. Thus, an evaluation model was established, and the LER of the watershed was evaluated. We found that the rate of land cover change (LCC) in the XJRB between 2010 and 2020 had a higher intensity (increasing at an average of 18.89% per decade) than that projected under the LSSPs for 2020-2030 (averaging an increase of 8.58% per decade). Among the growth rates of all land use types in the XJRB, that of urban land was the highest (33.3%). From 2010 to 2030, the LER in the XJRB was classified as lower risk (33.73%), lowest risk (33.11%), and moderate risk (24.13%) for each decade. Finally, the LER exhibited significant heterogeneity among different scenarios. Specifically, the percentages of regions characterized by the highest (9.77%) and higher LER (9.75%) were notably higher than those in the remaining scenarios. The higher-level risk area under the localized SSP1 demonstrated a clear spatial reduction compared to those of the other four scenarios. In addition, in order to facilitate the differential management and control of LER by relevant departments, risk zoning was carried out at the county level according to the prediction results of LER. And we got three types of risk management regions for the XJRB under the LSSPs.

The aggregation behaviour and mechanism of commercial graphene oxide in surface aquatic environments.

In this study, we comprehensively and critically discuss the aggregation mechanism of commercial graphene oxide (CGO) in surface aquatic environments. The aggregation kinetics and critical coagulation concentration of CGO were obtained through time-resolved dynamic light scattering and batch techniques over a wide range of water types. By employing transmission electron microscopy and elemental mapping, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy, we studied the effects of cations in natural waters on the microstructure transformation, element content and distribution, and oxygen-containing functional group vibrations of CGO. The aggregation of CGO in natural water is induced mainly by Ca2+ by complexing; Na+, with a higher concentration, plays a more important role than Mg2+ in inducing aggregation via electric double layer suppression. Ca2+ mainly interacts with C - COOH, while Mg2+ has a greater effect on C - OH. Na+ has less effect on the oxygen-containing functional group but decreases the C/O ratio in contrast with Mg2+/Ca2+/natural water, indicating the different inducing mechanisms. This study looks forward to providing pivotal knowledge to predict the environmental fate of CGO more accurately in natural surface water.

Application of improved seasonal GM(1,1) model based on HP filter for runoff prediction in Xiangjiang River.

Runoff forecasting is essential for the reasonable use of regional water resources, flood prevention, and mitigation, as well as the development of ecological civilization. Runoff is influenced by the intersection of many factors, and the change process is extremely complex, showing significant stochasticity, nonlinearity, and heterogeneity, making traditional prediction models less adaptable. The Hodrick-Prescott filter (HP filter) is a well-established signal separation method. The traditional GM(1,1) model is capable of portraying the growth trend of the time series but cannot capture the periodic characteristics of the time series. Therefore, a novel coupled prediction model-HPF-GM(1,1) model is proposed in this study and applied to the runoff prediction of the Zhuzhou section of Xiangjiang River in Hunan Province. This model enables to separate seasonal factors from non-seasonal factors in the runoff time series, and introduce seasonal factors based on the traditional GM(1,1) model, which solves the challenge that the traditional GM(1,1) model is unable to predict seasonal time series. The results show that the HPF-GM(1,1) model has a mean relative error of 4.82%, a root mean square error of 7.44, and a Nash efficiency coefficient of 0.93, which is better than the traditional GM(1,1) model, the DGGM(1,1) model and the SGM(1,1) model of prediction accuracy. Obviously, the HP filter provides a new approach to data pre-processing of runoff series and the proposed HPF-GM(1,1)-coupled model extends new ideas for nonlinear runoff prediction.

The prevalence of ampicillin-resistant opportunistic pathogenic bacteria undergoing selective stress of heavy metal pollutants in the Xiangjiang River, China.

The emergence of clinically relevant ß-lactam-resistant bacteria poses a serious threat to human health and presents a major challenge for medical treatment. How opportunistic pathogenic bacteria acquire antibiotic resistance and the prevalence of antibiotic-resistant opportunistic pathogenic bacteria in the environment are still unclear. In this study, we further confirmed that the selective pressure of heavy metals contributes to the increase in ampicillin-resistant opportunistic pathogens in the Xiangjiang River. Four ampicillin-resistant opportunistic pathogenic bacteria (Pseudomonas monteilii, Aeromonas hydrophila, Acinetobacter baumannii, and Staphylococcus epidermidis) were isolated on Luria-Bertani (LB) agar plates and identified by 16S rRNA sequencing. The abundance of these opportunistic pathogenic bacteria significantly increased in the sites downstream of the Xiangjiang River that were heavily influenced by metal mining activities. A microcosm experiment showed that the abundance of ß-lactam resistance genes carried by opportunistic pathogenic bacteria in the heavy metal (Cu2+ and Zn2+) treatment group was 2-10 times higher than that in the control. Moreover, heavy metals (Cu2+ and Zn2+) significantly increased the horizontal transfer of plasmids in pathogenic bacteria. Of particular interest is that heavy metals facilitated the horizontal transfer of conjugative plasmids, which may lead to the prevalence of multidrug-resistant pathogenic bacteria in the Xiangjiang River.

Systematic Assessment of Health Risk from Metals in Surface Sediment of the Xiangjiang River, China.

The common empirical screening method is limited to a preliminary screen target from vast elements for human health risk assessments. Here, an element screening procedure was developed for assessing the human health risk of the elements in the sediment of the Xiangjiang River. Ninety-six surface sediment samples from eight sampling stations were collected and 27 elements of each sample were investigated. Thirteen of the 27 elements were screened for human health risk assessments through the three-run selections by calculating anthropogenic factors, building element maps, and the removal of unnecessary elements. Pb posed the greatest health risk and exhibited a potential noncarcinogenic risk for adults at the stations S4 and S5, although no visible noncarcinogenic and carcinogenic risk for adults and children in the Xiangjiang River. Our study also suggested that the chalcophile elements were associated with greater health risk, compared to the lithophile and siderophile ones.

Distribution, contamination and source identification of heavy metals in bed sediments from the lower reaches of the Xiangjiang River in Hunan province, China.

Concentrations of heavy metals Ba, Sc, V, Cr, Mn, Co, Ni, Th, U, Cu, Pb, Zn, and Cd in sediments from the lower reaches of the Xiangjiang River were analyzed using inductively coupled plasma mass spectrometry. The results suggest that there are two metal distribution patterns in these sediments: (1) Ba, Sc, V, Cr, Mn, Th, and U are relatively homogeneously distributed and (2) Cd, Pb, Zn Cu, Co and Ni are heterogeneously distributed. The heterogeneously distributed metals are significantly enriched in these sediments and, thereby, contribute to contamination. Assessments of heavy metal contamination using the Geoaccumulation index, Pollution load index, and potential ecological risk index suggest that the levels of contamination from Cd and Mn are extremely high and moderately high, respectively, in all the sediments from the lower river. In comparison, the levels of contamination by Cu, Zn, and Pb varied spatially, decreasing progressively downriver. The level of contamination by Pb, Zn, and Cu in sediments from the Zhuzhou reach is extremely high, and is moderate to significant high for the Xiangtan, Changsha, and Xiangyin reaches. The ecological potential risks posed heavy metals are ranked, in descending order, as Cd > Pb > Cu > Zn > Cr > Ni > Co > Mn for sediments from the Zhuzhou reach and Cd > Pb > Cu > Ni > Cr > Co > Zn > Mn for sediments from the Xiangtan, Changsha, and Xiangyin reaches. Principal component analysis and enrichment factor calculations suggest that Ba, Sc, V, Cr, Th, and U mostly originate from natural processes. While, Cd, Pb, Zn, Cu, Co, Ni, and Mn are derived from both natural processes and anthropogenic activities. Therefore, strategies for environmental protection in this watershed should focus on contamination by Cd, Pb, Zn, and Cu, with Cd requiring particular attention.

Multivariate Analyses and Human Health Assessments of Heavy Metals for Surface Water Quality in the Xiangjiang River Basin, China.

Pollution by heavy metals in river water is becoming a major subject of global drinking water concern, and the Xiangjiang River is one of the most heavily polluted rivers in China. Water samples were collected from 17 sites spanning the entire Xiangjiang watershed from 2005 to 2016 to investigate spatial-temporal distributions and potential human health risks related to 8 metal pollutants (As, Cd, Hg, Cr, Cu, Pb, Zn, and Se). The results of spatial-temporal distribution analyses proved that most metals were below the guideline limits the majority of the time. However, the hazard index and carcinogenic risk analyses indicated that As and Cr were associated with a potential risk of cancer, although noncarcinogenic heavy metals in general and carcinogenic risk declined year by year. A nonparametric seasonal Mann-Kendall's test revealed that there were notable decreasing trends in As, Cd, Zn, Cu, Cr, and Pb for most sites, whereas Se and Hg significantly increased in some areas over the targeted 12 yr. The results of principal component analysis agreed with those of dual hierarchical cluster analysis in the identification of pollution sources, the results of which are as follows: 1) As, Cd, Pb, Hg, and Zn were mainly derived from anthropogenic activities and the smelting industry; 2) Cr and Cu mainly originated from agricultural or industrial activities; and 3) Se was predominantly from natural erosion. The present study will be conducive to optimizing the distribution of water monitoring stations and drafting remediation strategies pertaining to the protection of public health in metal-polluted areas. Environ Toxicol Chem 2019;38:1645-1657. © 2019 SETAC.

Sepiolite-Based Adsorbents for the Removal of Potentially Toxic Elements from Water: A Strategic Review for the Case of Environmental Contamination in Hunan, China.

The last few decades have seen rapid industrialization and urban development in many regions globally; with associated pollution by potentially toxic elements; which have become a threat to human health and the food chain. This is particularly prevalent in a number of regions in China that host multiple mineral resources and are important agricultural locations. Solutions to protect contamination of the food chain are more effective and sustainable if locally sourced materials are available; and in this context; we review the potential of local (sepiolite) mineral deposits to treat water contamination in the Hunan Municipality; central south China; widely recognized for significant environmental pollution issues (particularly by Hg; Cd; Pb; and Cr) and the high agricultural productivity of the region. Sepiolite is an abundant fibrous clay mineral with modest to good adsorption properties and extensive industrial process applications. It shows reasonable performance as an adsorbent for element removal. In addition; a number of surface modification strategies are available that improve this capability. We review these studies; focused on sorption reaction mechanisms and regeneration potential; with a view to present options for a localized and effective economic strategy for future application.

Occurrence, distribution, and environmental risk of four categories of personal care products in the Xiangjiang River, China.

The Xiangjiang River is the mother river of the Hunan Province; also, it is a stream receiving effluents from wastewater treatment plants and even sewage, providing raw water for drinking water and habitat for various kinds of aquatic organisms. Thus, the occurrence and distribution of personal care products (PCPs) in the Xiangjiang River, including seven preservatives, four anticorrosion agents, two antimicrobials, and six UV filters, were detected to evaluate their environmental risk. Of 13 detected PCPs, methyl paraben, propyl paraben, 1H-benzotriazole, 5,6-dimethyl-1H-benzotriazole, triclosan, and triclocarban were detected with a high frequency (81.4-100%), and their concentrations were up to 3173.9, 1040.4, 520.5, 15.6, 20.0, and 13.3 ng/L, respectively. Seasonal and spatial differences of the PCP distributions were observed with p < 0.05. Compared with other 37 rivers around the world, the overall pollution level of the Xiangjiang River was moderate, characterized with higher preservatives, lower anticorrosion agents and UV filters in concentration. The risk assessment revealed that methyl paraben, propyl paraben, 2-hydroxy-4-methoxybenzophenone, triclosan, and triclocarban were likely to have ecotoxicological effects on the fish, daphnias, and algae.

Agricultural drought prediction using climate indices based on Support Vector Regression in Xiangjiang River basin.

Drought can have a substantial impact on the ecosystem and agriculture of the affected region and does harm to local economy. This study aims to analyze the relation between soil moisture and drought and predict agricultural drought in Xiangjiang River basin. The agriculture droughts are presented with the Precipitation-Evapotranspiration Index (SPEI). The Support Vector Regression (SVR) model incorporating climate indices is developed to predict the agricultural droughts. Analysis of climate forcing including El Niño Southern Oscillation and western Pacific subtropical high (WPSH) are carried out to select climate indices. The results show that SPEI of six months time scales (SPEI-6) represents the soil moisture better than that of three and one month time scale on drought duration, severity and peaks. The key factor that influences the agriculture drought is the Ridge Point of WPSH, which mainly controls regional temperature. The SVR model incorporating climate indices, especially ridge point of WPSH, could improve the prediction accuracy compared to that solely using drought index by 4.4% in training and 5.1% in testing measured by Nash Sutcliffe efficiency coefficient (NSE) for three month lead time. The improvement is more significant for the prediction with one month lead (15.8% in training and 27.0% in testing) than that with three months lead time. However, it needs to be cautious in selection of the input parameters, since adding redundant information could have a counter effect in attaining a better prediction.

Occurrence and risk assessment of heavy metals in sediments of the Xiangjiang River, China.

Sediment samples were collected from 22 typical metal-polluted sections along the Xiangjiang River (XJR). Spatial distribution and speciation characteristics of heavy metals in sediments of XJR were determined. Furthermore, ecological risk and enrichment degree of metals were assessed by different indices. The results showed that combined metal pollution occurred in sediments of XJR, with content range of Cd, Pb, Zn, Cu, As, Mn, Cr, and Hg reaching 2.95-29.15, 30.93-235.83, 61.50-3771.11, 9.56-81.81, 3.93-46.28, 774.83-8700.72, 10.64-65.16, and 0.13-5.09 mg kg-1, respectively. Pollution levels increased in period of industrialization but decreased after thousands of pollution enterprises were banned. Sections with serious pollution and higher risk were mainly located at Hengyang and Chang-Zhu-Tan regions (Changsha, Zhuzhou, and Xiangtan) for contaminations of Cd, As, Pb, and Hg. Values of both enrichment factor and geo-accumulation index followed the order Cd > Hg > Zn > Mn > Pb > Cu > As > Cr. Bioavailable fractions followed the order Cd (66.93 %), Zn (33.80 %), Pb (30.81 %), Mn (18.38 %), Hg (17.58 %), Cu (10.20 %), As (9.81 %), and Cr (7.65 %). Considering their bioavailability, biotoxicity, or abundance, contamination of Cd was the most dominant, and pollution of other metals should not be ignored.

Heavy metals and metalloids in the surface sediments of the Xiangjiang River, Hunan, China: distribution, contamination, and ecological risk assessment.

Here, we aim to determine the distribution, ecological risk and sources of heavy metals and metalloids in the surface sediments of the Xiangjiang River, Hunan Province, China. Sixty-four surface sediment samples were collected in 16 sites of the Xiangjiang River, and the concentrations of ten heavy metals and metalloids (Mn, Zn, Cr, V, Pb, Cu, As, Ni, Co, and Cd) in the sediment samples were investigated using an inductively coupled plasma mass spectrometer (ICP-MS) and an atomic fluorescence spectrophotometer (AFS), respectively. The results showed that the mean concentrations of the ten heavy metals and metalloids in the sediment samples followed the order Mn > Zn > Cr > V > Pb > Cu > As ≈ Ni >Co > Cd. The geoaccumulation index (I geo), enrichment factor (EF), modified degree of contamination (mCd), and potential ecological risk index (RI) revealed that Cd, followed by Pb, Zn, and Cu, caused severely contaminated and posed very highly potential ecological risk in the Xiangjiang River, especially in Shuikoushan of Hengyang, Xiawan of Zhuzhou, and Yijiawan of Xiangtan. The Pearson's correlation coefficient (PCC) analysis, principal component analysis (PCA), and hierarchical cluster analysis (HCA) indicated that the ten heavy metals and metalloids in the sampling sediments of the Xiangjiang River were classified into three groups: (1) Cd, Pb, Zn, and Cu which possibly originated from Shuikoushan, Xiawan, and Yijiawan clustering Pb-Zn mining and smelting industries; (2) Co, V, Ni, Cr, and Al from natural resources; and (3) Mn and As. Therefore, our results suggest that anthropogenic activities, especially mining and smelting, have caused severe contamination of Cd, Pb, Zn, and Cu and posed very high potential ecological risk in the Xiangjiang River.

Effect of the selective pressure of sub-lethal level of heavy metals on the fate and distribution of ARGs in the catchment scale.

Our previous study demonstrated that high levels of antibiotic resistance genes (ARGs) in the Haihe River were directly attributed to the excessive use of antibiotics in animal agriculture. The antibiotic residues of the Xiangjiang River determined in this study were much lower than those of the Haihe River, but the relative abundance of 16 detected ARGs (sul1, sul2 and sul3, qepA, qnrA, qnrB, qnrD and qnrS, tetA, tetB, tetW, tetM, tetQ and tetO, ermB and ermC), were as high as the Haihe River particularly in the downstream of the Xiangjiang River which is close to the extensive metal mining. The ARGs discharged from the pharmaceutical wastewater treatment plant (PWWTP) are a major source of ARGs in the upstream of the Xiangjiang River. In the downstream, selective stress of heavy metals rather than source release had a significant influence on the distinct distribution pattern of ARGs. Some heavy metals showed a positive correlation with certain ARG subtypes. Additionally, there is a positive correlation between individual ARG subtypes and heavy metal resistance genes, suggesting that heavy metals may co select the ARGs on the same plasmid of antibiotic resistant bacteria. The co-selection mechanism between specific metal and antibiotic resistance was further confirmed by these isolations encoding the resistance genotypes to antibiotics and metals. To our knowledge, this is the first study on the fate and distribution of ARGs under the selective pressure exerted by heavy metals in the catchment scale. These results are beneficial to understand the fate, and to discern the contributors of ARGs from either the source release or the selective pressure by sub-lethal levels of environmental stressors during their transport on a river catchment scale.

Influence of silver nanoparticles on heavy metals of pore water in contaminated river sediments.

Despite the increasing knowledge on the discharge of silver nanoparticles (AgNPs) into the environment and their potential toxicity to microorganisms, the interaction of AgNPs with heavy metals remains poorly understood. This study focused on the effect of AgNPs on heavy metal concentration and form in sediment contaminated with heavy metals from the Xiangjiang River. The results showed that the concentration of Cu, Zn, Pb and Cd decreased and then increased with a change in form. The changes in form and concentrations of heavy metals in pore water suggested that Cu and Zn were more likely to be affected compared to Pb and Cd. The concentrations of Hg in sediment pore water in three AgNPs-dosed containers, increased greatly until they reached their peaks at 4.468 ± 0.133, 4.589 ± 0.235, and 5.083 ± 0.084 µg L(-1) in Bare AgNPs, Citrate AgNPs and Tween 80 AgNPs, respectively. The measurements of Hg concentrations in the sediment pore water, combined with SEM and EDX analysis, demonstrated that added AgNPs stabilized in pore water and formed an amalgam with Hg(0), which can affect Hg transportation over long distance.

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

The pollution of the surface water in the Xiangjiang watershed in China has received much attention, whereas the groundwater conditions in the area have long been ignored. This study investigates the occurrence of Fe and Mn in the groundwater of Chengxi Town located at the terminal of the Xiangjiang River. The study area was monitored for an entire year. Thereafter, the associated health risks were identified. Results showed that approximately 81 and 73 % of the measured samples exceeded the limits for Fe and Mn in Chinese drinking water, respectively. pH level was found to be negatively correlated with the concentrations of Fe and Mn in the groundwater in the study area. The occurrence of Fe in the groundwater showed significant seasonal fluctuations and was possibly affected by the change in environment conditions within the aquifer. By contrast, Mn remained relatively stable in most of the area during the whole year. Overall, no health threats for adults and children in the study area were determined according to the low health index values. Nevertheless, research attention and the implementation of relevant measures are needed for certain villages with exceptionally high Mn concentrations in the groundwater.