Yamin Deng

Seasonal variation of antibiotics concentration in the aquatic environment: a case study at Jianghan Plain, central China

25 antibiotics (macrolides, tetracyclines, fluoroquinolones and sulfonamides) were detected in swine wastewater, river water, rivulet water and in groundwater samples from multi-level monitoring boreholes (with sampling ports, respectively, at 10, 25 and 50 m below the land surface) at Jianghan Plain, central China. Except swine wastewater, the antibiotic concentrations in groundwater, river and rivulet water were higher in spring than those in winter. Nineteen antibiotics were detected at 100% frequencies in all kinds of water samples. In groundwater, fluoroquinolones and tetracyclines were the predominant antibiotics and the total concentrations of 25 antibiotics commonly decreased with the aquifer depth. Most groundwater samples collected in spring had high concentrations of norfloxacin, with average values of 65.27 ng · L(-1), 37.28 ng · L(-1) and 46.83 ng · L(-1), respectively, at 10, 25 and 50 m deep boreholes. By contrast, the concentrations of sulfamethazine and erythromycin were rather low in groundwater, but high in surface water. Groundwater samples collected from sites close to rivers or rivulets had much higher contents of antibiotics than those from other sites, indicating that the dominant source of antibiotics in groundwater should be the contaminated rivers or rivulets, rather than the scattered pig and poultry farms in the study area.

Microbial communities involved in arsenic mobilization and release from the deep sediments into groundwater in Jianghan plain, Central China.

It was shown that groundwater in Jianghan Plain was severely contaminated by arsenic; however, little is known about the mechanism by which the mineral arsenic was mobilized and released into groundwater from the high-arsenic sediments in this area. Here, we collected sediment samples from the depths of 5-230m in Jianghan Plain. Although all of the samples contain high contents of total arsenic, the soluble arsenic was only detectable in few of the shallow sediments, but was readily detectable in all of the deep sediments at the depths of 190-230m. Analysis of the genes of arsenate-respiring reductases indicated that they were not present in all of the shallow sediments from the depths of 5-185m, but were detectable in all of the deep sediments from the depths of 190-230m; all of the identified reductase genes are new or new-type, and they display unique diversity. Microcosm assay indicated that the microbial communities from the deep sediments were able to reduce As(V) into As(III) using lactate, formate, pyruvate or acetate as an electron donor under anaerobic condition. Arsenic release assay demonstrated that these microbial communalities efficiently catalyzed the mobilization and release of the mineral arsenic into aqueous phase. We also isolated a novel cultivable dissimilatory As(V)-respiring bacterium Aeromonas sp. JH155 from the sediments. It is able to completely reduce 2.0mM As(V) into As(III) in 72h, and efficiently promote the reduction and release of the mineral arsenic into aqueous phase. Analysis of the 16S rRNA genes indicated that the deep sediments contain diversities of microbial communities, which were shaped by the environmental factors, such as As, SO42-, NO3-, Fe and pH value. These data suggest that the microorganisms in the deep sediments in Jianghan Plain played key roles in the mobilization and release of insoluble arsenic into the groundwater.

A cost-effective system for in-situ geological arsenic adsorption from groundwater

An effective and low-cost in-situ geological filtration system was developed to treat arsenic-contaminated groundwater in remote rural areas. Hangjinhouqi in western Hetao Plain of Inner Mongolia, China, where groundwater contains a high arsenic concentration, was selected as the study area. Fe-mineral and limestone widely distributed in the study area were used as filter materials. Batch and column experiments as well as field tests were performed to determine optimal filtration parameters and to evaluate the effectiveness of the technology for arsenic removal under different hydrogeochemical conditions. A mixture containing natural Fe-mineral (hematite and goethite) and limestone at a mass ratio of 2:1 was found to be the most effective for arsenic removal. The results indicated that Fe-mineral in the mixture played a major role for arsenic removal. Meanwhile, limestone buffered groundwater pH to be conducive for the optimal arsenic removal. As(III) adsorption and oxidation by iron mineral, and the formation of Ca-As(V) precipitation with Ca contributed from limestone dissolution were likely mechanisms leading to the As removal. Field demonstrations revealed that a geological filter bed filled with the proposed mineral mixture reduced groundwater arsenic concentration from 400 μg/L to below 10 μg/L. The filtration system was continuously operated for a total volume of 365,000L, which is sufficient for drinking water supplying a rural household of 5 persons for 5 years at a rate of 40 L per person per day.

Bacterial Diversity and Community Structure in High Arsenic Aquifers in Hetao Plain of Inner Mongolia, China

The bacterial diversity and community structure of high arsenic (As) aquifers was investigated using an integrated approach adopting both geochemistry and molecular biology (polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene clone library analyses). Nine borehole sediments and one groundwater sample from the living place of a villager (affected by arseniasis) and 12 sediments from a control borehole in Hetao Plain were investigated. The As concentrations ranged from 33.6 to 77.6 mg/kg in high As borehole sediments and 1.5 to 5.8 mg/kg in those samples from the control. The As concentration in the groundwater was 744.8 μg/L. Ratios between As(III) and total As in high As sediments increased gradually with depth and ranged from 0.02 to 0.34. Similarly, the Fe(II)/total Fe presented the same increasing trend with depth. The correlation between TOC contents and total As was positive. High concentrations of total As, S, Fe and TOC were found in clay and low in sand samples. Phylogenetic analysis showed significantly different bacterial communities among high As sediments, control sediments and the high As groundwater. Both DGGE and 16S rRNA gene clone library results showed that the high As sediments were dominated by Thiobacillus, Pseudomonas, Brevundimonas, and Hydrogenophaga, with Thiobacillus being distinctly dominant (63.5%). Whereas the low As sediments were dominated by some other genera including Psychrobacter, Massilia and Desulfotalea. The bacterial populations in the high As groundwater mainly included Pseudomonas, Acinetobacter and Aquabacterium. These results improve our understanding of the bacterial diversity in high As aquifers in Hetao Plain and suggest how specific bacterial populations help mediate the mobilization of As into high As groundwaters.

Arsenic speciation in aquifer sediment under varying groundwater regime and redox conditions at Jianghan Plain of Central China

At Jianghan Plain of central Yangtze basins where the health of >73, 000 people has been affected by long term intake of high arsenic groundwater, over 100 sediment samples from four boreholes at the field monitoring sites were collected and analyzed to delineate the distribution and speciation of As in the shallow aquifer sediment. Results showed that sediment As concentration is generally dependent on the lithological conditions, with the higher As concentration present in fine particle sediment, especially in the silty sand layers underlying clay or silty clay layers. High As concentration in the sediment mainly occurred in three different depth ranges: <5m, 15-35m, and >35m. Both the groundwater regime and redox conditions played important roles in controlling sediment As speciation. Arsenate (86%) was the dominated As species in the near surface sediment. As the redox turned to be reducing, arsenite (64%) became the dominant species in the underlying clay and silty clay layers. But in the silty sand aquifer near the boundary of unconfined aquifer and confined aquifer, arsenate (85%) became the dominant species again as results of redox potential elevation. In the deep medium to coarse sand aquifers (>35m deep), As-sulfides (49%-63%) were the main species of As. The speciation and reactivity of sediment As strongly controlled the spatial distribution of groundwater As concentration, while seasonal variation in groundwater As concentration and speciation affected the content and speciation of sediment As.

Major geogenic factors controlling geographical clustering of urolithiasis in China

The prevalence of urolithiasis is increasing across the world and exhibits a distinctive characteristic of geographical distribution. Geographical clustering and major geogenic factors for urolithiasis prevalence in China were investigated. High risks of urolithiasis are found in southern China clustered in coastal provinces such as Fujian and Zhejiang and karst regions such as Sichuan, Chongqing, Guizhou, Guangxi, Guangdong, Hunan, and Hubei. The predominant urinary stone composition is a mixture of calcium oxalate and phosphate. We found that the spatial distribution of phosphate-type stones is closely related to that of phosphate ore deposits and carbonate rocks. Hot or warm climate and seasons increase the risk of lithogenesis through high average air temperature. Water and soil environment influence the quality and composition of drinking water and food, thus affecting stone formation in the urinary system. In particular, the increase of Ca(2+)/Mg(2+) ratio (in meq) in drinking water might be the main factor. Besides, the high content of calcium in local plants grown on karst soils and the intake of high oxalate food might contribute to the high prevalence in South China. This study indicates that urolithiasis could be endemic, with geogenic factors playing critical roles in urolithiasis etiology.

Effect of microbially mediated iron mineral transformation on temporal variation of arsenic in the Pleistocene aquifers of the central Yangtze River basin

Significant seasonal variation of groundwater arsenic (As) concentrations in shallow aquifers of the Jianghan Plain, central Yangtze River Basin has been reported recently, but the underlying mechanisms remain not well understood. To elaborate biogeochemical processes responsible for the observed As concentration variation, 42-day incubation experiments were done using sediment samples collected respectively from the depth of 26, 36 and 60m of the As-affected aquifer which were labeled respectively as JH26, JH36, JH60. Where JH denotes Jianghan Plain, and the number indicates the depth of the sediment sample. The results indicated that As could be mobilized from the sediments of 26m and 36m depth under the stimulation of exogenous organic carbon, with the maximum As release amount of 1.60 and 1.03mgkg-1, respectively, while the sediments at 60m depth did not show As mobilization. The microbially mediated reductive dissolution of amorphous iron oxides and reduction of As(V) to As(III) could account for the observed As mobilization. The 16S rRNA high-throughput sequencing results indicated that the variation of microbial community correlated with the released As concentration (R=0.7, P<0.05) and the iron-reducing bacteria, including Pseudomonas, Clostridium and Geobacter, were the main drivers for the As mobilization from the sediments at 26m and 36m depth. The increase of arsC gene abundance (up to 1.4×105 copies g-1) during As release suggested that As reduction was mediated by the resistant reduction mechanism. By contrast, in the 60m sediments where the Fe and As release was absent, the iron-reducing bacteria accounted for a very minor proportion and sulfate-reducing bacteria were predominant in the microbial community. In addition, after 30days of incubation, the released As in the 26m sediments was immobilized via co-precipitation with or adsorption onto the Fe-sulfide mineral newly-formed by the bacterial sulfate reduction. These results are consistent with the results of our previous field monitoring, indicating that the bacterial sulfate reduction could lead to the temporal decrease in groundwater As concentrations. This study provides insights into the mechanism for As mobilization and seasonal As concentration variation in the Pleistocene aquifers from alluvial plains.

Groundwater flow and hydrogeochemical evolution in the Jianghan Plain, central China

Hydrogeochemical analysis and multivariate statistics were applied to identify flow patterns and major processes controlling the hydrogeochemistry of groundwater in the Jianghan Plain, which is located in central Yangtze River Basin (central China) and characterized by intensive surface-water/groundwater interaction. Although HCO3-Ca-(Mg) type water predominated in the study area, the 457 (21 surface water and 436 groundwater) samples were effectively classified into five clusters by hierarchical cluster analysis. The hydrochemical variations among these clusters were governed by three factors from factor analysis. Major components (e.g., Ca, Mg and HCO3) in surface water and groundwater originated from carbonate and silicate weathering (factor 1). Redox conditions (factor 2) influenced the geogenic Fe and As contamination in shallow confined groundwater. Anthropogenic activities (factor 3) primarily caused high levels of Cl and SO4 in surface water and phreatic groundwater. Furthermore, the factor score 1 of samples in the shallow confined aquifer gradually increased along the flow paths. This study demonstrates that enhanced information on hydrochemistry in complex groundwater flow systems, by multivariate statistical methods, improves the understanding of groundwater flow and hydrogeochemical evolution due to natural and anthropogenic impacts.RésuméDes analyses hydrogéologiques et statistiques multivariées ont été utilisées pour identifier les schémas de flux et les processus principaux contrôlant l’hydrogéochimie des eaux souterraines de la plaine de Jianghan, qui est. localisée dans la partie centrale du bassin de la rivière Yangtze (Centre de la Chine) et caractérisée par des interactions importantes entre les eaux de surface et les eaux souterraines. Bien que les eaux de type HCO3-Ca-(Mg) prédominent dans le secteur d’étude, 457 échantillons (21 d’eaux de surface et 436 d’eaux souterraines) ont été classés selon 5 grappes à l’aide de l’analyze hiérarchique par grappe. Selon l’analyze factorielle, les variations hydrochimiques de ces grappes sont gouvernées par trois facteurs. Les composants principaux (ex. Ca, Mg et HCO3) des eaux de surface et eaux souterraines proviennent du lessivage des carbonates et silicates (facteur 1). Les conditions Redox (facteur 2) influencent la contamination par les éléments géogéniques Fe et As dans les parties captives peu profondes des aquifères. Les activités anthropiques (facteur 3) sont responsables principalement des fortes concentrations en Cl et SO4 dans les eaux de surface et des nappes souterraines. De plus, le score du facteur 1 des échantillons de l’aquifère captif peu profond croit le long voies d’écoulement. Cette étude démontre que l’information renforcée sur l’hydrochimie d’un système aquifère complexe, par des méthodes statistiques multivariées, permet d’améliorer la compréhension des flux souterrains et l’évolution hydrogéochimique du fait des impacts naturels et anthropiques.ResumenSe aplicaron análisis hidrogeoquímico y estadísticas multivariantes para identificar patrones de flujo y los procesos principales que controlan la hidrogeoquímica del agua subterránea en la llanura de Jianghan, ubicada en la cuenca central del río Yangtze (China central) y caracterizada por una intensa interacción agua superficial/agua subterránea. Aunque el agua de tipo HCO3-Ca-(Mg) predominó en el área de estudio, las 457 muestras (21 de aguas superficiales y 436 de aguas subterráneas) se clasificaron efectivamente en cinco grupos por análisis de agrupamiento jerárquico. Las variaciones hidroquímicas entre estos grupos se rigen por tres factores del análisis factorial. Los principales componentes (por ejemplo, Ca, Mg y HCO3) en las aguas superficiales y subterráneas se originaron a partir de la meteorización del silicato y del carbonato (factor 1). Las condiciones redox (factor 2) influyeron en la contaminación geológica de Fe y As en agua subterránea confinada poco profundas. Las actividades antropogénicas (factor 3) causaron principalmente altos niveles de Cl y SO4 en aguas superficiales y subterráneas freáticas. Además, la puntuación del factor 1 de las muestras en el acuífero confinado poco profundo aumentó gradualmente a lo largo de las vías de flujo. Este estudio demuestra que la información mejorada sobre hidroquímica en sistemas complejos de flujo de aguas subterráneas, mediante métodos estadísticos multivariantes, mejora la comprensión del flujo de aguas subterráneas y la evolución hidrogeoquímica debido a los impactos naturales y antropogénicos.摘要江汉平原位于中国中部的长江中游地区,区内地表水-地下水相互作用强烈。本文结合水文地球化学分析和多元统计方法识别江汉平原的地下水流模式,并分析影响地下水水文地球化学特征的主控因素。结果显示457个水样(包括21个地表水和436个地下水样)的水化学类型差异不明显,主要为HCO3-Ca-(Mg)型,聚类分析根据水化学特征有效地将这些样品划分为五类。通过因子分析,共提取了三个造成水化学特征差异的公因子:第一公因子为水-岩相互作用,包括碳酸盐溶解和硅酸盐风化过程,控制地表水和地下水中的主要组分(如Ca、Mg和HCO3);第二公因子为氧化还原条件,影响浅层承压水中原生Fe和As的富集;第三公因子为人为活动,常导致地表水和浅层潜水中的Cl和SO4污染。此外,在浅层承压含水层中,水样的第一公因子得分沿地下水流向逐渐增大。本文的研究表明多元统计方法可有效地识别复杂地下水流系统的水化学信息,从而有助于更好地掌握受自然和人为因素双重影响下的地下水径流和水文地球化学演化规律。ResumoAnálises hidrogeoquímicas e estatística multivariada foram aplicadas para identificar os padrões de fluxo e principais processos que controlam a hidrogeoquímica das águas subterrâneas na planície de Jianghan, que está localizado na bacia central do rio Yangtze (centro da China) e é caracterizada pela ocorrência de intensa interação entre águas superficiais e subterrâneas. Apesar do predomínio do tipo de água HCO3-Ca-(Mg) na área de estudo, as 457 amostras (21 de águas superficiais e 436 subterrâneas) foram efetivamente classificados em cinco grupos por análise de agrupamento hierárquico. As variações hidroquímicas entre esses grupos foram governadas por três fatores da análise fatorial. Os componentes principais (p.ex. Ca, Mg e HCO3) da água superficial e subterrânea originaram-se do intemperismo de carbonato e silicato (fator 1). Condições redox (fator 2) influenciaram o Fe gênico e a contaminação por As em águas subterrâneas confinadas rasas. Atividades antropogênicas (fator 3) foram as principais causas dos altos níveis de Cl e SO4 em águas superficiais e subterrâneas freáticas. Além disso, o valor do fator 1 de amostras no aquífero confinado raso aumentou gradualmente ao longo dos caminhos de fluxo. Este estudo demonstra que informações aprimoradas sobre a hidroquímica em sistemas complexos de fluxo de águas subterrâneas, por métodos estatísticos multivariados, melhoram a compreensão do fluxo de águas subterrâneas e a evolução hidrogeoquímica devido a impactos naturais e antropogênicos.

Experimental constraints on redox-induced arsenic release and retention from aquifer sediments in the central Yangtze River Basin

The consumption of arsenic (As) contaminated groundwater affects the health of almost 20 million people in China. Unlike the preponderance of observations within the deltas of South and Southeast Asia, groundwater As concentrations in the central Yangtze River Basin, China, vary by up to an order of magnitude seasonally. In order to decipher the cause of seasonal release and retention of As between sediments and groundwater, we conducted batch sediment incubations under varying (imposed) redox conditions. Incubations were conducted under both N2 and O2 gas purges to simulate conditions observed within the field. In all cases, anoxic conditions resulted in As release to solution while As was removed from solution under oxic conditions. These experiments confirm that anoxia is a prerequisite for As mobilization into groundwater from Yangtze River Basin sediments. Alternating redox conditions resulted in Fe minerals dissolution, transformation, crystallization, and precipitation, and subsequent As release and retention in the system. More importantly, aquifer sediments at depths >15 m release As through multiple redox cycles without an exogenous electron donor (carbon source), organic matter in the sediments is sufficiently reactive to support microbial reduction of As(V) and Fe(III). These results provide direct evidence for previously described mechanisms explaining the observed seasonal variation of groundwater As concentrations in the central Yangtze River Basin, where seasonal changes in surface and groundwater levels drive changes in redox conditions and thus As concentrations.

Molecular Characterization of the Total Bacteria and Dissimilatory Arsenate-Reducing Bacteria in Core Sediments of the Jianghan Plain, Central China

ABSTRACT Arsenic contamination in groundwater has been reported in the Jianghan Plain of China since 2005, yet little is known about the microbial communities involved in As mobilization in this area, especially the dissimilatory arsenate-reducing bacteria (DARB) communities. Here, we conducted a cultivation-independent investigation on core sediments collected from a region with arsenic-contaminated groundwater in the Jianghan Plain to reveal the total bacteria and DARB community structures. Highly diverse As-resistant bacteria communities were found from sediment samples via high-throughput sequencing of 16S rRNA genes. Notably, we identified 27 unique arrA gene (encoding the alpha subunit of dissimilatory arsenate reductase) phylotypes, none of which was related to any previously described arrA gene sequence. This suggests a novel and unique DARB community in the sediments of the Jianghan Plain and expands our knowledge about the distribution and diversity of this group of bacteria in natural environments. Moreover, RDA and CCA demonstrated that total bacterial communities and specific functional groups are controlled by different environmental factors. Specifically, sediment pH, NH4+, total nitrogen, total Fe, total organic carbon and total phosphorus were the key factors driving total bacterial community compositions, while As significantly shaped DARB community structures. This report is the first to describe DARB communities and their correlation with environmental factors in Jianghan Plain sediments, which could give us clues about the origin of the arsenic contamination of groundwater in this region.