Arsenic In Sediments Research Articles

Ecological factors affecting the accumulation and speciation of arsenic in twelve Australian coastal bivalve molluscs

Environmental contextKnowledge of the pathways by which arsenic is accumulated and transferred in marine ecosystems is scarce. Molluscs are important keystone organisms providing a link between primary producers (micro and macroalgae) and higher trophic levels such as fish. The present study examines the accumulation and species of arsenic in common bivalve molluscs from south-east Australia to understand the cycling of arsenic in marine food webs. AbstractThe present paper reports the whole-tissue total arsenic concentrations and water-soluble arsenic species in 12 common coastal Australian bivalve mollusc species. Mean arsenic concentrations ranged from 18 to 57 µg g−1 dry mass. Planktivores had significantly less arsenic (20–40 µg g−1; 22 ± 3 µg g−1) than did suspension and deposit feeders (36–57 µg g−1; 43 ± 7 µg g−1), with those associated with fine clay–silt sediments (49 ± 7 µg g−1) having significantly more arsenic than those associated with sand substrates (31 ± 11 µg g−1 ). Most planktivores and suspension feeders had similar arsenic species, with high proportions of arsenobetaine (AB) (64–92 %) and relatively low proportions of other arsenic species (0.55–15.8 %). Lower proportions of AB (13–57 %) and larger proportions of inorganic arsenic (6–7 %) were found in deposit feeders, reflecting increased exposure to inorganic arsenic in sediments. The study indicated that at lower trophic levels, organisms feed on algae and suspended matter containing a range of arsenic species including arsenosugars and AB. The implications for arsenic cycling are that as all bivalve molluscs accumulate AB and are a source of AB in benthic food webs. Because all bivalve molluscs also contained appreciable concentrations of arsenoriboses, precursors are present for the de novo synthesis of AB. As well, deposit feeders have higher proportions of inorganic arsenic that can be metabolised to different end products when ingested by higher trophic organisms

Arsenic mobility and characterization in lakes impacted by gold ore roasting, Yellowknife, NWT, Canada.

The controls on the mobility and fate of arsenic in lakes impacted by historical gold ore roasting in northern Canada have been examined. A detailed characterization of arsenic solid and aqueous phases in lake waters, lake sediments and sediment porewaters as well as surrounding soils was conducted in three small lakes (<200ha) downwind and within 5km of the historic mining and roasting operations of Giant Mine (Northwest Territories). These lakes are marked by differing limnological characteristics such as area, depth and organic content. Radiometric age-dating shows that the occurrence of arsenic trioxide in lake sediments coincides with the regional onset of roasting activities. Quantification by advanced electron microscopy shows that arsenic trioxide accounts for up to 6wt% of the total arsenic in sediments. The bulk (>80wt%) of arsenic is contained in the form of secondary sulphide precipitates, with iron oxy-hydroxides hosting a minimal amount of arsenic (<1wt%). Soluble arsenic trioxide particles act as the primary source of arsenic into sediment porewaters. Dissolved arsenic in reducing porewaters both precipitates in-situ as secondary sulphides, and diffuses upwards into the overlying lake waters. Geogenic arsenic phases are present in sediments in low concentrations and are not considered a significant source of arsenic to porewaters or lake waters. Sediment-water interface diffusive flux calculations suggest that the diffusion of dissolved arsenic from porewaters, combined with lake water residence time, are the predominant mechanisms controlling arsenic concentrations in lake waters.

Risk Assessment for Children Exposed to Beach Sands Impacted by Oil Spill Chemicals.

Due to changes in the drilling industry, oil spills are impacting large expanses of coastlines, thereby increasing the potential for people to come in contact with oil spill chemicals. The objective of this manuscript was to evaluate the health risk to children who potentially contact beach sands impacted by oil spill chemicals from the Deepwater Horizon disaster. To identify chemicals of concern, the U.S. Environmental Protection Agency’s (EPA’s) monitoring data collected during and immediately after the spill were evaluated. This dataset was supplemented with measurements from beach sands and tar balls collected five years after the spill. Of interest is that metals in the sediments were observed at similar levels between the two sampling periods; some differences were observed for metals levels in tar balls. Although PAHs were not observed five years later, there is evidence of weathered-oil oxidative by-products. Comparing chemical concentration data to baseline soil risk levels, three metals (As, Ba, and V) and four PAHs (benzo[a]pyrene, benz[a]anthracene, benzo[b]fluoranthene, and dibenz[a,h]anthracene) were found to exceed guideline levels prompting a risk assessment. For acute or sub-chronic exposures, hazard quotients, computed by estimating average expected contact behavior, showed no adverse potential health effects. For cancer, computations using 95% upper confidence limits for contaminant concentrations showed extremely low increased risk in the 10−6 range for oral and dermal exposure from arsenic in sediments and from dermal exposure from benzo[a]pyrene and benz[a]anthracene in weathered oil. Overall, results suggest that health risks are extremely low, given the limitations of available data. Limitations of this study are associated with the lack of toxicological data for dispersants and oil-spill degradation products. We also recommend studies to collect quantitative information about children’s beach play habits, which are necessary to more accurately assess exposure scenarios and health risks.

Evidence of arsenic mobilization mediated by an indigenous iron reducing bacterium from high arsenic groundwater aquifer in Hetao Basin of Inner Mongolia, China

A facultative anaerobic iron reducing bacterium IMCUGIR-ZA was isolated from high arsenic (As) groundwater in Hetao Basin of Inner Mongolia and was identified as Klebsiella oxytoca. Strain IMCUGIR-ZA could reduce more than 96.8% of 2.78 mmol L−1 soluble Fe(III)-citrate in 7 days and 0.42 mmol solid iron from ferrihydrite into aqueous phase in 10 days using glucose as an electron donor under strictly anaerobic conditions. Appropriate concentrations of As could improve microbially-mediated iron reduction and release from ferrihydrite. Nearly threefold iron was reduced and released by strain IMCUGIR-ZA from As(V)-doped ferrihydrite (As 100 μmol L−1). When the strain was incubated with high arsenic sediments from Hetao Basin of Inner Mongolia under anaerobic conditions, 0.894 mmol L−1 Fe(III) and 12.44 μmol L−1 As were released to aqueous phase in 7 days. The results provided evidence of microbially-mediated mobilization of As in high arsenic groundwater aquifer in Hetao Basin of Inner Mongolia, China.

In situ, high resolution ZrO-Chelex DGT for the investigation of iron-coupled inactivation of arsenic in sediments by macrozoobenthos bioturbation and hydrodynamic interactions

The influence of chironomid larvae and hydrodynamics on the bioavailable arsenic (As) in sediments under different conditions was comprehensively investigated through water tank experiments spanning 132days. The high-resolution technique of revealing diffusive gradients in thin films (DGT) with ZrO-Chelex resin was employed in this study; this was done to simultaneously obtain concentrations of labile As and Fe in the profile at millimeter resolution. Bioturbation by larvae may significantly decrease the bioavailable As and Fe concentrations under different hydrodynamic intensities during the first two months of larval burrowing; the greatest difference between the bioavailable As concentration with and without the addition of larvae was seen on the 56th day, with around 49%, 47%, 73% and 67% reduction of As in the profile under static water, 0.3ms−1, 0.5ms−1 and 1.0ms−1, respectively. However, these effects were diminished after the 56th day due to the eclosion of the chironomid larvae. The hydrodynamic conditions appeared to not have any significant effect on the labile concentration of As or Fe until after eclosion. The changing distributions of labile As and Fe were consistent with the dissolved oxygen concentrations in the profile under different conditions. Labile As showed the significantly correlation coefficients with labile Fe by a stepwise multiple linear regression under different experimental conditions in this study. We conclude that the decreases in bioavailable As are directly related to conversions between Fe2+ and Fe3.

Enhanced bioreduction of iron and arsenic in sediment by biochar amendment influencing microbial community composition and dissolved organic matter content and composition

Biochar derived from the pyrolysis at 500°C with fresh biogas slurry and residue, was conducted to investigate its potential role in mediating the speciation and mobilization of As(V) and Fe(III) from arsenic-contaminated tailing mine sediment, with consideration of the changes in microbial populations and dissolved organic matter (DOM). The reduction of As(V) (10–13%) and Fe(III) (12–17%) were partly in response to biochar abiotically causing desorption and reduction effect, but were predominantly (87–90% and 83–88% for As(V) and Fe(III)) attributed to biochar stimulating biological reduction. The level of As(III) released from sediment upon biochar amendment (656.35±89.25μgL−1) was significantly higher than the level released without biochar amendment (98.06±19.38μgL−1) after 49 days incubation. Although a low level of Fe(II) (0.81±0.07mgL−1) was determined in the solution when amending with biochar, most of released Fe(II) (166.25±40.25mgL−1) was formed as biochar-Fe(II)minerals composite. More importantly, biochar stimulated the DOM bioavailability in association with bacterial activities mediating As(V) and Fe(III) reduction. High-throughput sequencing results indicated biochar application shifted the soil microbial community and increased the relative abundance of As(V)-/Fe(III)-reducing bacteria, mostly Geobacter, Anaeromyxobacter, Desulfosporosinus and Pedobacter. The discovery of biochar-bacteria-DOM consortium may broaden new understanding into speciation and mobilization of metals, which arouses attention to exploit feasible bioremediation for metal-contaminated sediment.

Microbial Community Structure and Arsenic Biogeochemistry in an Acid Vapor-Formed Spring in Tengchong Geothermal Area, China.

Arsenic biogeochemistry has been studied extensively in acid sulfate-chloride hot springs, but not in acid sulfate hot springs with low chloride. In this study, Zhenzhuquan in Tengchong geothermal area, a representative acid sulfate hot spring with low chloride, was chosen to study arsenic geochemistry and microbial community structure using Illumina MiSeq sequencing. Over 0.3 million 16S rRNA sequence reads were obtained from 6-paired parallel water and sediment samples along its outflow channel. Arsenic oxidation occurred in the Zhenxhuquan pool, with distinctly high ratios of arsenate to total dissolved arsenic (0.73–0.86). Coupled with iron and sulfur oxidation along the outflow channel, arsenic accumulated in downstream sediments with concentrations up to 16.44 g/kg and appeared to significantly constrain their microbial community diversity. These oxidations might be correlated with the appearance of some putative functional microbial populations, such as Aquificae and Pseudomonas (arsenic oxidation), Sulfolobus (sulfur and iron oxidation), Metallosphaera and Acidicaldus (iron oxidation). Temperature, total organic carbon and dissolved oxygen significantly shaped the microbial community structure of upstream and downstream samples. In the upstream outflow channel region, most microbial populations were microaerophilic/anaerobic thermophiles and hyperthermophiles, such as Sulfolobus, Nocardia, Fervidicoccus, Delftia, and Ralstonia. In the downstream region, aerobic heterotrophic mesophiles and thermophiles were identified, including Ktedonobacteria, Acidicaldus, Chthonomonas and Sphingobacteria. A total of 72.41–95.91% unassigned-genus sequences were derived from the downstream high arsenic sediments 16S rRNA clone libraries. This study could enable us to achieve an integrated understanding on arsenic biogeochemistry in acid hot springs.

Arsenic in freshwater ecosystems of the Bengal delta: status, sources and seasonal variability

The study aimed to examine the contamination status of arsenic (As) in excavated small water bodies, commonly known as ponds – the integral part of daily life in the arsenic-affected rural areas of West Bengal, India in comparison to the unaffected areas. The ponds of the contaminated area had higher levels of As: water 2–174 µg L−1 (mean 31 ± 2 µg L−1) and sediment 1.3–37.3 mg kg−1 (mean 10.3 ± 0.4 mg kg−1), than those from the unaffected area: water 1–8 µg L−1 (mean 4 ± 0 µg L−1) and sediment 1.4–5.3 mg kg−1 (mean 3.0 ± 0.1 mg kg−1). A moderate positive correlation was observed between the water and sediment arsenic content of the ponds of the arsenic-affected region (r = 0.688, n = 277, p < 0.0001). Contaminated ground water, either as direct input or through agricultural washings, was found to be the major contributor of arsenic pollution to these ecosystems. Seasonal variations were not prominent. This study emphasized the beneficial role of using the studied ecosystems over the highly contaminated ground water for various livelihood activities in the Gangetic delta region.

Microbial community in high arsenic shallow groundwater aquifers in Hetao Basin of Inner Mongolia, China.

A survey was carried out on the microbial community of 20 groundwater samples (4 low and 16 high arsenic groundwater) and 19 sediments from three boreholes (two high arsenic and one low arsenic boreholes) in a high arsenic groundwater system located in Hetao Basin, Inner Mongolia, using the 454 pyrosequencing approach. A total of 233,704 sequence reads were obtained and classified into 12–267 operational taxonomic units (OTUs). Groundwater and sediment samples were divided into low and high arsenic groups based on measured geochemical parameters and microbial communities, by hierarchical clustering and principal coordinates analysis. Richness and diversity of the microbial communities in high arsenic sediments are higher than those in high arsenic groundwater. Microbial community structure was significantly different either between low and high arsenic samples or between groundwater and sediments. Acinetobacter, Pseudomonas, Psychrobacter and Alishewanella were the top four genera in high arsenic groundwater, while Thiobacillus, Pseudomonas, Hydrogenophaga, Enterobacteriaceae, Sulfuricurvum and Arthrobacter dominated high arsenic sediments. Archaeal sequences in high arsenic groundwater were mostly related to methanogens. Biota-environment matching and co-inertia analyses showed that arsenic, total organic carbon, SO4 2-, SO4 2-/total sulfur ratio, and Fe2+ were important environmental factors shaping the observed microbial communities. The results of this study expand our current understanding of microbial ecology in high arsenic groundwater aquifers and emphasize the potential importance of microbes in arsenic transformation in the Hetao Basin, Inner Mongolia.

Origin of arsenic in Late Pleistocene to Holocene sediments in the Nawalparasi district (Terai, Nepal)

A sedimentological and geochemical study was carried out to explore the origin of arsenic contamination in sediments in Nawalparasi district, in the western Terai of Nepal. The investigation tools include major, trace and rare earth element analyses of core sediments, as well as 14C datings, and O, C isotopic analyses on mollusk shells. The results show that black schists from the Lesser Himalaya highly contributed to the detrital input in Parasi during the Pleistocene–Holocene transition because of focused erosion related to rapid uplift and high rainfall along the Main Central Thrust zone. In addition, aquifer silts, sands, and most of the brown clays underwent a certain degree of chemical weathering and physical reworking, and show possible inputs from the Siwaliks during the Late Holocene. A possible correlation between late Quaternary climate regimes and the concentration of arsenic in sediments is suspected, with arsenic preferentially concentrated during the drier periods of the last 25 kyr BP. The process of arsenic eluviations in sandy and silty sediments can explain the lower arsenic concentrations in sediments during humid periods. During the drier periods, seasonal precipitation was smaller and temperature was lower, leading to wet (less evaporative) soils in swampy environments. This environment favoured the development of aquatic plants and bacteria growing within in the moist land areas, enhancing the strong weathering of initially suspended load particles (micas and clays), which were preferentially deposited in quiet hydraulic environments. These sorting and weathering processes presumably allowed the arsenic to be concentrated in the finest sediment fraction.

Occurrence and possible sources of arsenic in seafloor sediments surrounding sea-disposed munitions and chemical agents near Oʻahu, Hawaiʻi

The Department of Defense disposed of conventional and chemical munitions as well as bulk containers of chemical agents in US coastal waters including those surrounding the State of Hawaiʻi. The Hawaiʻi Undersea Military Munitions Assessment has been collecting biota, water, and sediment samples from two disposal areas south of the island of Oʻahu in waters 500 to 600m deep known to have received both conventional munitions and chemical agents (specifically sulfur mustard). Unlike a number of other sea-disposed munitions investigations which used grabs or corers lowered from surface vessels, we used manned submersibles to collect the samples. Using this approach, we were able to visually identify the munitions and precisely locate our samples in relation to the munitions on the seafloor. This paper focuses on the occurrence and possible sources of arsenic found in the sediments surrounding the disposed military munitions and chemical agents. Using nonparametric multivariate statistical techniques, we looked for patterns in the chemical data obtained from these sediment samples in order to determine the possible sources of the arsenic found in these sediments. The results of the ordination technique nonmetric multidimensional scaling indicate that the arsenic is associated with terrestrial sources and not munitions. This was not altogether surprising given that: (1) the chemical agents disposed of in this area supposedly did not contain arsenic, and (2) the disposal areas studied were under terrestrial influence or served as dredge spoil disposal sites. The sediment arsenic concentrations during this investigation ranged from <1.3 to 40mg/kg-dry weight with the lower concentrations typically found around control sites and munitions (not located in dredge disposal areas) and the higher values found at dredge disposal sites (with or without munitions). During the course of our investigation we did, however, discover that mercury appears to be loosely associated with munitions. Given that mercury contamination has been seen in about 20% of the munitions and ton containers of sulfur mustard, the association of mercury with chemical agents is not totally unexpected.

Distribution of arsenic in sediment of Hangjinhou Banner-Linhe transect in Hetao Basin, North China

Distribution of arsenic in sediment of Hangjinhou Banner-Linhe transect in Hetao Basin, North China

Effects of salinity and (an)ions on arsenic behavior in sediment of Bosten Lake, Northwest China

Bosten Lake, the largest inland lake in China, has been contaminated with arsenic (As) due to anthropogenic activities. Salinity of the lake water has been increasing due to the extremely dry climate and salt drainage from the farmland. Effects of the increasing salinity on the geochemical behavior of arsenic in sediment are still unclear. In this study, vertical variation of geochemical fractions of As in sediment and arsenic concentration in porewater along the salinity gradient of Bosten Lake was studied. Effects of salinity and ions and anions in porewater on arsenic concentration were also examined. Arsenic content in the five Tessier fractions followed the decreasing order of residual ≫ exchangeable > Fe and Mn oxides > organic > carbonate. The ecological risk of arsenic in the sediment was at low or medium levels, indicated by the low percentage of exchangeable and carbonate bound fractions. Contrary to the decreasing electrical conductivity of porewater with depth, arsenic concentration in porewater showed an increasing trend with depth. Arsenic concentration in porewater increased from around zero at the surface layer of sediment to over 600 μg L−1 in deeper layers of some sites. Arsenic concentration inversely correlated with electrical conductivity in porewater. Arsenic concentration generally decreased with increasing concentrations of SO4 2−, Ca2+, Mg2+ and Na+ but showed no clear relation with concentrations of K+ and Cl−. This study implies that increase of salinity may decrease the release of arsenic from sediment and its ecological risk.

Vertical distribution of bacterial communities in high arsenic sediments of Hetao Plain, Inner Mongolia.

Vertical distribution of bacterial communities was detected in high arsenic (As) sediments in a representative high As area in Inner Mongolia. Nineteen sediment samples were collected from a 30 m borehole and detected by geochemistry and molecular ecological approaches including polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), 16S rRNA gene clone library and 454 pyrosequencing. As contents ranged from 42.1 to 111.3 mg kg(-1) which fluctuated with different depth and significantly high in clay and mild clay sediment samples at depth of 8, 20, 25 and 28 m respectively. The ratios of As(III) to total As generally increased with depth but As(V) dominated in all sediment samples. High concentrations of total As, sulfur, iron and total organic carbon were generally found in clay and low in sand samples. Both DGGE patterns and 454 pyrosequencing results indicated that bacterial communities dynamically diversified with increasing depth and were dominated by Firmicutes, Bacteroidetes, Proteobacteria and Chloroflexi. Most of the sediment samples were dominated by populations including Sporosarcina, Acinetobacter, Pseudomonas, Halomonas, Polaromonas, Paenibacillus and Flavobacterium. These populations were found with high similarities with those microbes capable of denitrification, sulfur oxidation, organic matter degradation and As resistance and reduction. These results implied that microbes might play an important role in As mobilization in the shallow aquifers of Hetao Plain, Inner Mongolia.

Evaluation of internal standardization for the determination of semivolatile analytes in difficult matrices by simultaneous multielement atomic absorption spectrometry

The aim of the present work is to investigate the use of the internal standardization technique combined with permanent chemical modification for the determination of two semivolatile analytes, such as As and Se, in difficult matrices by electrothermal atomic absorption spectrometry. Bismuth and tellurium have been evaluated as internal standards to minimize matrix effects on the direct determination of selenium and arsenic in sediments, by simultaneous electrothermal atomic absorption spectrometry using graphite tubes with integrated platform, pre-treated with different masses of Zr and Ir as permanent modifier. A Perkin-Elmer SIMAA 6000 simultaneous multielement spectrometer was used to study the correlation between two integrated absorbance signals. Matrix effects were evaluated by calculating the slope ratio between the analytical curve obtained from reference solutions prepared in 1.0% (v/v) HNO3 and analytical curve obtained from IS additions in matrix solutions. The results showed that Te was the optimal internal standard and 200μg Zr and 20μg Ir was the optimal permanent chemical modifier for both analytes. The instrumental limits of detection for As and Se were 1.48 and 1.96μgL−1 without the use of an internal standard and 0.59 and 0.35μgL−1 when Te was used as an internal standard, respectively. Relative standard deviations for a sample with matrix effect containing 100μgL−1 As and 200μgL−1 Se were 1.3% and 2.3% (n=20) using 100μgL−1 Te, respectively, and for a standard solution sample containing 100μgL−1 As and 200μgL−1 Se were 3.0% and 1.2% (n=20) using 100μgL−1 Te, respectively. The accuracy of the proposed method was evaluated by an addition-recovery experiment and by the analysis of different certified reference materials. The recovered values were in the 95–100% range for both analytes.

Distribution of Arsenic in Presque Isle State Park Pond Sediments

ABSTRACT A study of arsenic in pond sediments on the Presque Isle peninsula, Erie, PA, was conducted in 2000 and 2001 by Murnoch (2002) due to concerns expressed by citizens and various local officials. Samples of pond and lagoon sediments were collected at thirteen primary sites and additional reference sites for analysis of arsenic content during the fall, 2000, and again in spring, 2001. The probable effect concentration (PEC) for arsenic of 33.0 mg/kg-DW, an indication of the concentration above which adverse impacts on benthic organisms are expected to occur, was exceeded in the surface sediments at all 13 primary sites during fall sampling and in all but one site during spring sampling, with concentrations as high as 393 mg/kg-DW measured. For deeper sediments, the PEC was exceeded in the fall at nine sites and in the spring at six sites. Surface sediments contained more arsenic than did deeper sediments. These differences were more pronounced in the spring samples than in the fall samples. There was a general trend, with numerous exceptions, for sites closer to Gull Point (the geologically ‘new’ end of the peninsula) to have lower arsenic levels. While the source of the arsenic in the sediments of Presque Isle is unknown, these high levels are likely due to natural processes that, over time, have resulted in an enrichment of arsenic in surface sediments. A possible mechanism for this enrichment is proposed. This study has not attempted to document the risk to the ecosystem associated with elevated arsenic concentrations, but it is reasonable to speculate that there could be an adverse impact on some organisms.

Distribution and Abundance of Arsenic in the Soils and Sediments of O‘ahu, Hawai‘i

Lack of high-spatial-resolution soil and sediment arsenic data for Hawai‘i has generated substantial disagreement between researchers and regulators regarding the magnitude of natural levels of arsenic in Hawai‘i and rendered difficult the defining of areas of anthropogenically elevated arsenic. Our earlier research into the occurrence of arsenic in terrestrial and marine environments revealed widely disparate concentrations of arsenic with no apparent spatial pattern. To better understand the distribution and abundance of arsenic in soils and sediments of O‘ahu, we collected an additional 64 samples at locations chosen to represent different environments with varying degrees of human impact. We found surface arsenic values that ranged from 0.28 to 740 ppm with a median concentration of 8.1 ppm, which is above the global median of 5 ppm and US soil median of 5.2 ppm. Higher concentrations of arsenic (up to 913 ppm) were encountered at depth in soil cores. The median arsenic in streambed sediments from one of our earlier studies of 6.1 ppm was comparable to the conterminous US median of 6.3 ppm; however, we encountered arsenic concentrations as high as 43.9 ppm (median = 8.60 ppm, n = 75) in marine sediments in recent work off the leeward coast of O‘ahu. Overall, arsenic in the soils and sediments of O‘ahu is elevated relative to world and national values, but there still is no readily discernible pattern in the distribution of arsenic to explain these elevated values.

Relative Abundance of Ammonia Oxidizers, Denitrifiers, and Anammox Bacteria in Sediments of Hyper‐Nutrified Estuarine Tidal Flats and in Relation to Environmental Conditions

The relative abundances of nitrifying, denitrifying and anammox prokaryotes in sediments of three hyper‐nutrified estuarine tidal flats of Laizhou Bay, Bohai Sea, China were investigated. Quantitative PCR estimates indicated that in most cases archaeal (AOA) amoA genes were more abundant than bacterial (AOB) amoA genes, and ratio of AOA/AOB was correlated with pH, Cd, and Cu. Of the denitrifiers, nirK‐type outnumbered nirS‐type, with nosZ‐type being the lowest. Variation of the ratio between nirK and nirS abundance depends on pH, nitrite, nitrate, and Cd. The combination of (nirS + nirK‐nosZ), an indicator of genetic potentials for N2O emission, was only related to the temperature. Anammox bacterial 16S rRNA gene abundances were correlated with salinity, pH, nitrite, and Cu. In contrast, the contribution of anammox to N2 production, by using anammox bacterial 16S rRNA/nosZ ratio as a proxy, was correlated to temperature, ammonium and dissolved oxygen in the overlying water, ratio of organic carbon to nitrogen, and arsenic in sediments. Our study stresses that abundances of N‐cycling functional groups respond differently to variations of environmental conditions, and multiple factors including heavy metals with relatively low concentrations may play a role in shaping nitrogen cycling processes in these estuarine tidal flats.

Influence of Arsenate on Lipid Peroxidation Levels and Antioxidant Enzyme Activities in Bacillus cereus Strain XZM002 Isolated from High Arsenic Aquifer Sediments

Bacillus cereus strain XZM002 isolated from high arsenic aquifer sediments of Datong Basin was applied to examine the effects of arsenate stress on antioxidant enzyme activities, lipid peroxidation levels and cell growth inhibition rate. After 2 d exposure, the cell growth inhibition rate enhanced with an increase of As(V) concentrations (0, 800, 1600 μg/l). Reactive oxygen species and glutathione contents, lipid peroxidation levels, and antioxidant enzymes (glutathione peroxidase, and other three) activities of the treated cells were significantly higher than those of the controls during 3 d exposure (p < 0.05). Besides, the levels of nine parameters reached maximum after 2 d exposure and increased significantly with increasing arsenate stress (p < 0.05). However, they returned to levels similar to those of the control on the fourth day of exposure. The results suggested that the antioxidant defense system in B. cereus strain XZM002 could protect the cells from oxidative damage induced by arsenate.

Bacterial Diversity in the High Arsenic Groundwater Systems of Jianghan Plain and Datong Basin by 16S rDNA Clone Library

To compare the difference bacterial diversity between Jianghan plain and Datong basin. The high arsenic sediment samples in this study were collected from different depths of borehole. The bacterial diversity in high arsenic aquifer sediments was studied by 16S rDNA clone library. The dominant bacterial community included Burkholderiales, Pseudomonadales, and Enterobacteriales in Jianghan plain, and Burkholderiales,Enterobacteriales and Actinomycetales in Datong basin.