Soil microbial community responses to acid exposure and neutralization treatment.

Changes in microbial community induced by acid shock were studied in the context of potential release of acids to the environment due to chemical accidents. The responses of microbial communities in three different soils to the exposure to sulfuric or hydrofluoric acid and to the subsequent neutralization treatment were investigated as functions of acid concentration and exposure time by using 16S-rRNA gene based pyrosequencing and DGGE (Denaturing Gradient Gel Electrophoresis). Measurements of soil pH and dissolved ion concentrations revealed that the added acids were neutralized to different degrees, depending on the mineral composition and soil texture. Hydrofluoric acid was more effectively neutralized by the soils, compared with sulfuric acid at the same normality. Gram-negative ß-Proteobacteria were shown to be the most acid-sensitive bacterial strains, while spore-forming Gram-positive Bacilli were the most acid-tolerant. The results of this study suggest that the Gram-positive to Gram-negative bacterial ratio may serve as an effective bio-indicator in assessing the impact of the acid shock on the microbial community. Neutralization treatments helped recover the ratio closer to their original values. The findings of this study show that microbial community changes as well as geochemical changes such as pH and dissolved ion concentrations need to be considered in estimating the impact of an acid spill, in selecting an optimal remediation strategy, and in deciding when to end remedial actions at the acid spill impacted site.

Autophagy and protein kinase RNA-like endoplasmic reticulum kinase (PERK)/eukaryotic initiation factor 2 alpha kinase (eIF2α) pathway protect ovarian cancer cells from metformin-induced apoptosis.

Metformin, an oral biguanide for the treatment of type II diabetes, has been shown to have anticancer effects in ovarian cancer. Energy starvation induced by metformin causes endoplasmic reticulum stress-mediated unfolded protein response (UPR) and autophagy. UPR and autophagy act as a survival or death mechanism in cells. In this study, we observed that metformin-induced apoptosis was relieved by autophagy and the PERK/eIF2α pathway in ovarian cancer cells, but not in peripheral blood mononuclear cells (PBMC) or 'normal' ovarian surface epithelial cells (OSE). Increased PARP cleavage and increased LC3B-II with ATG5-ATG12 complex suggested the induction of apoptosis and autophagy, respectively, in metformin-treated ovarian cancer cells. Accumulation of acidic vacuoles in the cytoplasm and downregulation of p62 further supported late-stage autophagy. Interestingly, metformin induced interdependent activation between autophagy and the UPR, especially the PERK/eIF2α pathway. Inhibition of autophagy-induced PERK inhibition, and vice versa, were demonstrated using small molecular inhibitors (PERK inhibitor I, GSK2606414; autophagy inhibitor, 3-MA, and BafA1). Moreover, autophagy and PERK activation protected ovarian cancer cells against metformin-induced apoptosis. Metformin treatment in the presence of inhibitors of PERK and autophagy, however, had no cytotoxic effects on OSE or PBMC. In conclusion, these results suggest that inhibition of autophagy and PERK can enhance the selective anticancer effects of metformin on ovarian cancer cells. © 2015 Wiley Periodicals, Inc.

Hydrologic Controls on Nitrogen Cycling Processes and Functional Gene Abundance in Sediments of a Groundwater Flow-Through Lake.

The fate and transport of inorganic nitrogen (N) is a critically important issue for human and aquatic ecosystem health because discharging N-contaminated groundwater can foul drinking water and cause algal blooms. Factors controlling N-processing were examined in sediments at three sites with contrasting hydrologic regimes at a lake on Cape Cod, MA. These factors included water chemistry, seepage rates and direction of groundwater flow, and the abundance and potential rates of activity of N-cycling microbial communities. Genes coding for denitrification, anaerobic ammonium oxidation (anammox), and nitrification were identified at all sites regardless of flow direction or groundwater dissolved oxygen concentrations. Flow direction was, however, a controlling factor in the potential for N-attenuation via denitrification in the sediments. Potential rates of denitrification varied from 6 to 4500 pmol N/g/h from the inflow to the outflow side of the lake, owing to fundamental differences in the supply of labile organic matter. The results of laboratory incubations suggested that when anoxia and limiting labile organic matter prevailed, the potential existed for concomitant anammox and denitrification. Where oxic lake water was downwelling, potential rates of nitrification at shallow depths were substantial (1640 pmol N/g/h). Rates of anammox, denitrification, and nitrification may be linked to rates of organic N-mineralization, serving to increase N-mobility and transport downgradient.

A comprehensive review of urban microplastic pollution sources, environment and human health impacts, and regulatory efforts.

Microplastic (MP) pollution in urban environments is a pervasive and complex problem with significant environmental and human health implications. Although studies have been conducted on MP pollution in urban environments, there are still research gaps in understanding the exact sources, regulation, and impact of urban MP on the environment and public health. Therefore, the goal of this study is to provide a comprehensive overview of the complex pathways, harmful effects, and regulatory efforts of urban MP pollution. It discusses the research challenges and suggests future directions for addressing MPs related to environmental issues in urban settings. In this study, original research papers published from 2010 to 2024 across ten database categories, including PubMed, Google Scholar, Scopus, and Web of Science, were selected and reviewed to improve our understanding of urban MP pollution. The analysis revealed multifaceted sources of MPs, including surface runoff, wastewater discharge, atmospheric deposition, and biological interactions, which contribute to the contamination of aquatic and terrestrial ecosystems. MPs pose a threat to marine and terrestrial life, freshwater organisms, soil health, plant communities, and human health through ingestion, inhalation, and dermal exposure. Current regulatory measures for MP pollution include improved waste management, upgraded wastewater treatment, stormwater management, product innovation, public awareness campaigns, and community engagement. Despite these regulatory measures, several challenges such as; the absence of standardized MPs testing methods, MPs enter into the environment through a multitude of sources and pathways, countries struggle in balancing trade interests with environmental concerns have hindered effective policy implementation and enforcement. Addressing MP pollution in urban environments is essential for preserving ecosystems, safeguarding public health, and advancing sustainable development. Interdisciplinary collaboration, innovative research, stringent regulations, and public participation are vital for mitigating this critical issue and ensuring a cleaner and healthier future for urban environments and the planet.

Exploring the vertical transport of microplastics in subsurface environments: Lab-scale experiments and field evidence.

Microplastics (MPs) defined as smaller 5 mm plastic particles have received increasing attention due to their global occurrence and potential toxicity. This study investigated the effects of environmental factors (rainfall intensity, 13 and 29 mm/h) and MP characteristics (morphology (fiber, flake, and film), polymer type (polypropylene (PP), polyethylene terephthalate (PET), and polystyrene (PS)) and size (100-300, 300-500, and 500-1000 µm)) on the vertical transport of MP in unsaturated soil conditions using lab-scale column experiments. Additionally, the occurrence and characteristics of MP detected in soil/sediment (total 13 samples) and groundwater samples (total 6 samples) were explored in the field study. Laboratory-scale column experiments revealed that heavy rainfall intensity (29 mm/h) increased the degree of MP vertical transport in unsaturated soil conditions and MP fibers showed the greatest vertical mobility among the various morphologies of MPs assessed. For the polymer type and size, the lighter PP polymer or the larger size of MP (500-1000 µm) showed higher mobility. In the field study, a statistical difference in MP abundance was observed depending on the population density and degree of urban development in both soil and groundwater samples. Comparing to the two different types of environmental media samples obtained from the same site, there was a significant difference in the composition of polymer types present while statistically no difference in MP abundance was observed between the two media samples (i.e., soil or sediment and groundwater). In addition, MP fibers and polyethylene (PE) were predominantly detected in our two study areas. These results suggest that various types of MP can pass through the unsaturated zone by water infiltration, even if it takes a long time to reach groundwater. Overall, we found that the degree of vertical transport of the MPs was highly sensitive to environmental conditions and MP characteristics.

An Automatic-Vertical Profile Monitoring System for Fresh-Saline Water Zones in Coastal Aquifer.

Coastal aquifers are complex systems governed by fresh-saline water interactions and ocean tidal effects. The vertical electrical conductivity (EC) and temperature (T) are general indicators for detecting the fresh-saline water interface (FSI) and sea water intrusion in groundwater wells located in coastal aquifers. In this method brief, we developed a cost-effective Arduino-based automatic-vertical profile monitoring system (A-VPMS) to continuously record vertical EC and T in groundwater wells, with the aim of testing its effectiveness in spatiotemporal monitoring of the FSI in a coastal aquifer located in eastern Korea. By analyzing the high-density EC and T data obtained by the A-VPMS, we evaluated the characteristics of the FSI, such as depth and spatial distribution. Our established EC and T data collection method using the A-VPMS proved to be efficient and reliable, providing an excellent tool for fine-scale temporal and spatial understanding of sea water intrusion. The results of this study demonstrate the potential of the A-VPMS for continuous monitoring of the FSI in coastal aquifers, which is crucial for sustainable management of groundwater resources.

Uranium reduction and microbial community development in response to stimulation with different electron donors.

Stimulating microbial reduction of soluble U(VI) to less soluble U(IV) shows promise as an in situ bioremediation strategy for uranium contaminated groundwater, but the optimal electron donors for promoting this process have yet to be identified. The purpose of this study was to better understand how the addition of various electron donors to uranium-contaminated subsurface sediments affected U(VI) reduction and the composition of the microbial community. The simple electron donors, acetate or lactate, or the more complex donors, hydrogen-release compound (HRC) or vegetable oil, were added to the sediments incubated in flow-through columns. The composition of the microbial communities was evaluated with quantitative PCR probing specific 16S rRNA genes and functional genes, phospholipid fatty acid analysis, and clone libraries. All the electron donors promoted U(VI) removal, even though the composition of the microbial communities was different with each donor. In general, the overall biomass, rather than the specific bacterial species, was the factor most related to U(VI) removal. Vegetable oil and HRC were more effective in stimulating U(VI) removal than acetate. These results suggest that the addition of more complex organic electron donors could be an excellent option for in situ bioremediation of uranium-contaminated groundwater.

Hydrogeochemistry and isotopic tracing of nitrate contamination of two aquifer systems on Jeju Island, Korea.

The groundwater of Jeju Island (Republic of Korea) is vulnerable to contamination because its aquifers are mainly composed of highly permeable geological units and its agricultural fields are often exposed to excessive use of predominantly synthetic fertilizers. In the Gosan area of Jeju Island, we investigated nitrate contamination in both a perched aquifer above an impermeable clay bed and the regional groundwater beneath this aquitard. The δO and δD values indicate that the perched groundwater is recharged by local precipitation, whereas the regional groundwater is recharged mainly by regional flow from an adjacent mountainous region. The perched groundwater contained very high NO-N concentrations of up to 87 mg/L. The isotopic composition of nitrate in the perched groundwater showed that synthetic fertilizers applied in high excesses of crop N needs were the main cause of aquifer pollution. Elevated nitrate concentrations were also observed in the regional groundwater especially after precipitation events. Concentration and isotopic data revealed that the inflow of shallow perched groundwater along the poorly cemented or uncemented annulus of regional groundwater wells was one of the main reasons for the nitrate contamination observed in the regional groundwater. In both aquifers, δN and δO values showed that the sources of nitrate were derived from synthetic fertilizers that had been recycled in the soil zone by nitrification and in some portions of the perched aquifer (dissolved oxygen concentrations <2 mg/L) indicated that denitrification occurred locally.

Microbial succession in response to 1,4-dioxane exposure in activated sludge reactors: effect of inoculum source and extra carbon addition.

Bacterial community succession related to 1,4-dioxane exposure was investigated in two different activated sludge-inoculated reactors (municipal wastewater and dye industrial wastewater sludge), with or without additional carbon source, for 7 weeks. The denaturing gradient gel electrophoresis (DGGE) analysis revealed that microbial succession varied according to the inoculum sludge sources and the presence or absence of the extra carbon source. In the reactor inoculated with the municipal sludge, bacterial species belonging to alpha- and gamma-Proteobacteria and Nitrospira class were dominant over time. On the other hand, bacterial species showing significant homology to beta-Proteobacteria (e.g., Methylibium petroleiphilum PM1) and Actinobacteria class, who have been reported to have 1,4-dioxane degradation potential, were found in the industrial sludge-inoculated reactors. The appearance of these bacteria demonstrates that the microbial community structure of the inoculum and the presence of an extra carbon source affect the microbial succession in the system exposed to 1,4-dioxane.

Effects of water level and vegetation on nitrate dynamics at varying sediment depths in laboratory-scale wetland mesocosms.

Recent increases in the frequency of extreme floods and droughts associated with climate change can affect fluctuating groundwater or wetland water levels and wetland plant growth, and consequently cause redox condition changes in nitrogen dynamics in wetland sediments. Here, we studied the fate of nitrate (NO3-), dissolved organic carbon (DOC), and the microbial characteristics at different sediment depths in response to water levels (i.e., 5 or 2.5 cm) above the sediment surface and in the presence or absence of plants (Phragmites communis Trin) for four months in three wetland mesocosms. Results showed that mesocosm A (MA) with a high water level (5 cm above the surface) and plants had significantly higher DOC concentrations (17.57 ±â€¯8.22 mg/L) in sediment that were actively consumed by microorganisms than other mesocosms with low water level (MB) and without plant (MC) (8.77 ±â€¯2.38 mg/L and 7.87 ±â€¯2.72 mg/L in MB and MC, respectively). Consequently, the most of influent NO3- (20 mg-N/L) dramatically reduced in the vicinity of plant roots (-20 to -15 cm sediment depth) where active denitrification was expected in MA. Moreover, the functional genes involved in denitrification such as narG (2.4 × 108 -3.5 × 108 copies·g-1) and nirS (5.6 × 106-1.1 × 107 copies·g-1) were more abundant in this mesocosm. The profile of the microbial community structure at the class level revealed that Alphaproteocbacteria (MA: 14.19 ±â€¯1.19%; MB: 14.01 ±â€¯0.51%; MC: 15.21 ±â€¯2.76%) and Actinobacteria (MA: 8.21 ±â€¯1.91%; MB: 13.91 ±â€¯2.13%; MC: 11.75 ±â€¯3.43%) were predominant in all three mesocosms. Interestingly, the clustered heatmap supported the obvious difference in microbial composition of MA from other mesocosms showing relatively more abundant Clostridia (6.71 ±â€¯1.54%) and Deltaproteobacteria (7.05 ±â€¯0.68%). These results can provide an insight to understand the biogeochemical nitrogen cycle associated with climate change in wetland systems.

A multidisciplinary assessment of the impact of spilled acids on geoecosystems: an overview.

We developed and applied a multidisciplinary approach to the impact of an accidentally spilled acid on the underlying geomedia and subsurface environment, based on the concept of geoecosystem. We used mineralogical, geochemical, microbiological, and ecotoxicological techniques to identify and assess the multiple aspects involved. First, we constructed a conceptual model for the acid interactions with the underlying subsurface environment by introducing the concept of a geoecosystem-a multicomponent system composed of inorganic, organic, and biological components to describe the subsurface environment. Second, we designed and manufactured a two dimensional cell to visualize acid transport through geomedia. Third, we hypothesized that the acids are neutralized through dissolution of minerals and protonation of functional groups on the surfaces of minerals and organic matter. We tested this hypothesis by conducting batch-type geomedia-acid reaction and surface titration experiments. Fourth, we observed changes in soil microbial communities before and after the acid exposure and neutralization treatment. Fifth, we performed flow-through experiments using columns packed with soil samples pre-contaminated with arsenic to investigate potential longer term, secondary effects of remnant acids on geoecosystems. Finally, we conducted ecotoxicological investigations using various geomedia and observed that suitability of the geoecosystem as a habitat deteriorated to different degrees depending on the respective systems' acid neutralizing power. We conclude that a holistic understanding of the interactions among the multiple components of geoecosystems and subsequent estimation of the influenced area requires a multidisciplinary approach such as those used in this study. Based on the findings of this study, we propose geoecosystems' vulnerability defined as the reciprocal of their acid-neutralizing capacity against the moving acid fronts and present this concept as central to a quantitative assessment of the impact of acid spills on geoecosystems. We also inventoried the essential components, factors, and parameters necessary in developing geoecosystems' acid vulnerability assessment system.

Glucose-dependent control of leucine metabolism by leucyl-tRNA synthetase 1.

Despite the importance of glucose and amino acids for energy metabolism, interactions between the two nutrients are not well understood. We provide evidence for a role of leucyl-tRNA synthetase 1 (LARS1) in glucose-dependent control of leucine usage. Upon glucose starvation, LARS1 was phosphorylated by Unc-51 like autophagy activating kinase 1 (ULK1) at the residues crucial for leucine binding. The phosphorylated LARS1 showed decreased leucine binding, which may inhibit protein synthesis and help save energy. Leucine that is not used for anabolic processes may be available for catabolic pathway energy generation. The LARS1-mediated changes in leucine utilization might help support cell survival under glucose deprivation. Thus, depending on glucose availability, LARS1 may help regulate whether leucine is used for protein synthesis or energy production.

A long-term performance test on an autotrophic denitrification column for application as a permeable reactive barrier.

The long-term performance of a sulfur-based reactive barrier system was evaluated using autotrophic denitrification in a large-scale column. A bacterial consortium, containing autotrophic denitrifiers attached on sulfur particles, serving as an electron donor, was able to transform 60 mg N L(-1) of nitrate into dinitrogen. In the absence of phosphate, the consortium was unable to remove nitrate, but after the addition of phosphate, nitrate removal was readily evident. Once the column operation had stabilized, seepage velocities of 1.0 x 10(-3) and 0.5 x 10(-3)cms(-1), corresponding to hydraulic residence times of 24 and 48 h, respectively, did not affect the nitrate removal efficiency, as determined by the nitrate concentration in the effluent. However, data on the nitrate, nitrite and sulfate distribution along the column indicated differential transformation patterns with column depths. Based on the dinitrogen concentration in the total gas collected, the denitrification efficiency of the tested column was estimated to be more than 95%. After 500 d operation, the hydrodynamic characteristics of the column slightly changed, but these changes did not inhibit the nitrate removal efficiency. Data from a bacterial community analysis obtained from four parts of the column demonstrated the selective a spatial distribution of predominant species depending on available electron acceptors or donors.

Effect of sulfate on the simultaneous bioreduction of iron and uranium.

The biogeochemistry related to iron- and sulfate-reducing conditions influences the fate of contaminants such as petroleum hydrocarbons, trace metals, and radionuclides (i.e., uranium) released into the subsurface. An understanding of these processes is imperative to successfully predict the fate of contaminants during bioremediation scenarios. A series of flow-through sediment column experiments were performed to determine if the commencement of sulfate-reducing conditions would occur while bioavailable Fe(III) was present and to determine how the bioreduction of a contaminant (uranium) was affected by the switch from iron-dominated to sulfate-dominated reducing conditions. The results presented herein demonstrated that, under biostimulation, sulfate reduction can commence even though a significant pool of bioavailable Fe(III) is present. In addition, the rate of U(VI) reduction was not negatively affected by the commencement of sulfate-reducing conditions.

Fate and toxicity of spilled chemicals in groundwater and soil environment I: strong acids.

We reviewed the chemical/physical properties, toxicity, environmental fate, and ecotoxicity of strong acids in soil and groundwater environments. We recommend that sulfuric acid and hydrofluoric acid be classified as chemicals of priority control based on volumes used, toxicity, carcinogenicity, and past significant spill events. Understanding the behavior and transport of spilled strong acids in soil and groundwater environments requires a multi-disciplinary approach, as they can undergo a variety of geochemical and biochemical reactions with complex geomedia. The toxicity of spilled acid is dependent on the characteristics of the geomedia exposed to the acid and the amount of residual protons following acid-substrate interaction. Soil texture, cation exchange capacity, mineral composition, bedrock type, and aluminum content may be important factors affecting the toxicity of spilled acid in soil-groundwater environments. We expect that the results of this study will contribute preliminary data for future research on chemical spills.

Inhibition of MUC1 biosynthesis via threonyl-tRNA synthetase suppresses pancreatic cancer cell migration.

Mucin1 (MUC1), a heterodimeric oncoprotein, containing tandem repeat structures with a high proportion of threonine, is aberrantly overexpressed in many human cancers including pancreatic cancer. Since the overall survival rate of pancreatic cancer patients has remained low for several decades, novel therapeutic approaches are highly needed. Intestinal mucin has been known to be affected by dietary threonine supply since de novo synthesis of mucin proteins is sensitive to luminal threonine concentration. However, it is unknown whether biosynthesis of MUC1 is regulated by threonine in human cancers. In this study, data provided suggests that threonine starvation reduces the level of MUC1 and inhibits the migration of MUC1-expressing pancreatic cancer cells. Interestingly, knockdown of threonyl-tRNA synthetase (TRS), an enzyme that catalyzes the ligation of threonine to its cognate tRNA, also suppresses MUC1 levels but not mRNA levels. The inhibitors of TRS decrease the level of MUC1 protein and prohibit the migration of MUC1-expressing pancreatic cancer cells. In addition, a positive correlation between TRS and MUC1 levels is observed in human pancreatic cancer cells. Concurrent with these results, the bioinformatics data indicate that co-expression of both TRS and MUC1 is correlated with the poor survival of pancreatic cancer patients. Taken together, these findings suggest a role for TRS in controlling MUC1-mediated cancer cell migration and provide insight into targeting TRS as a novel therapeutic approach to pancreatic cancer treatment.

Effect of dissimilatory iron and sulfate reduction on arsenic dynamics in the wetland rhizosphere and its bioaccumulation in wetland plants (Scirpus actus).

Microbial redox transformations of arsenic (As) are coupled to dissimilatory iron and sulfate reduction in the wetlands, however, the processes involved are complex and poorly defined. In this study, we investigated the effect of dissimilatory iron and sulfate reduction on As dynamics in the wetland rhizosphere and its bioaccumulation in plants using greenhouse mesocosms. Results show that high Fe (50µM ferrihydrite/g solid medium) and SO42- (5mM) treatments are most favorable for As sequestration in the presence of wetland plants (Scirpus actus), probably because root exudates facilitate the microbial reduction of Fe(III), SO42-, and As(V) to sequester As(III) by incorporation into iron sulfides and/or plant uptake. As retention in the solid medium and accumulation in plants were mainly controlled by SO42- rather than Fe levels. Compared to the low SO42- (0.1mM) treatment, high SO42- resulted in 2 times more As sequestered in the solid medium, 30 times more As in roots, and 49% less As in leaves. An As speciation analysis in pore water indicated that 19% more dissolved As was reduced under high SO42- than low SO42- levels, which is consistent with the fact that more dissimilatory arsenate-respiring bacteria were found under high SO42- levels.

Phosphate enhanced abiotic and biotic arsenic mobilization in the wetland rhizosphere.

Although abiotic process of competitive sorption between phosphate (P) and arsenate (As(V)), especially onto iron oxides, are well understood, P-mediated biotic processes of Fe and As redox transformation contributing to As mobilization and speciation in wetlands remain poorly defined. To gain new insights into the effects of P on As mobility, speciation, and bioavailability in wetlands, well-controlled greenhouse experiments were conducted. As expected, increased P levels contributed to more As desorption, but more interestingly the interactions between P and wetland plants played a synergistic role in the microbially-mediated As mobilization and enhanced As uptake by plants. High levels of P promoted plant growth and the exudation of labile organic carbon from roots, enhancing the growth of heterotrophic bacteria, including As and Fe reducers. This in turn resulted in both, more As desorption into solution due to reductive iron dissolution, and a higher fraction of the dissolved As in the form of As(III) due to the higher number of As(V) reducers. Consistent with the dissolved As results, arsenic-XANES spectra from solid medium samples demonstrated that more As was sequestered in the rhizosphere as As(III) in the presence of high P levels than for low P levels. Hence, increased P loading to wetlands stimulates both abiotic and biotic processes in the wetland rhizosphere, resulting in more As mobilization, more As reduction, as well as more As uptake by plants. These interactions are important to be taken into account in As fate and transport models in wetlands and management of wetlands containing As.

Effect of the redox dynamics on microbial-mediated As transformation coupled with Fe and S in flow-through sediment columns.

Arsenic (As) biogeochemistry coupled with iron (Fe) and sulfur (S) was studied using columns packed with As(V)-contaminated sediments under two phases: a reduction phase followed by an oxidation phase. During the reduction phase, four identical columns inoculated with G. sulfurreducens were stimulated with 3mM acetate for 60days. The As(III) in the effluent rapidly increased then gradually decreased. The Fe(II) and sulfate concentration indicated ferrous sulfide precipitation inside the column after day 14 and X-ray absorption near edge structure spectra showed that As(III) was enriched at the column outlet. The genera Desulfosporosinus and Anaeromyxobacter as well as the Geobacter inoculum played a primary role in As reduction. During the oxidation phase, dissolved oxygen was consumed by heterotrophic aerobes belonging to the phylum Cloroflexi in the column with acetate, resulting in more As in the effluent. When only nitrate was injected, sulfur-oxidizing bacteria such as Thiobacillus thioparus instantly oxidized the sulfide formed during the first phase, resulting in less As(V) in the aqueous phase compared to the column with dissolved oxygen alone. This study showed that redox gradients and dynamics linked to Fe and S biogeochemistry have an important role in controlling As mobility in subsurface environments.

Effect of reactive media composition and co-contaminants on sulfur-based autotrophic denitrification.

As a part of a study developing a biological reactive barrier system to treat nitrate-contaminated groundwater, the effects of reactive media composition and co-contaminants on sulfur-oxidizing autotrophic denitrification were investigated. The size of sulfur granules affected the denitrification rates; kinetic constants of 2.883, 2.949, and 0.677 mg-N(1/2)/L(1/2)/day were obtained when the granule sizes were below 2 mm, between 2 and 5 mm, and over 5 mm, respectively. When the volume ratios of sulfur to limestone were 1:1, 2:1, 3:1, and 4:1, kinetic constants of 5.490, 3.903, 4.072, and 2.984 mg-N(1/2)/L(1/2)/day were obtained, respectively. The presence of TCE up to 20 mg/L didn't significantly affect nitrate removal efficiency. At the TCE concentration of 80 mg/L, however, nitrate removal was markedly inhibited. Also, Zn and Cu inhibited the denitrification activity at more than 0.5 mg/L of concentration whereas Cr (VI) did not significantly affect the nitrate removal efficiency at all levels tested.