Effect of natural organic matter on toxicity and reactivity of nano-scale zero-valent iron

Nano-scale zero-valent iron (NZVI) particles are increasingly used to remediate aquifers contaminated with hazardous oxidized pollutants such as trichloroethylene (TCE). However, the high reduction potential of NZVI can result in toxicity to indigenous bacteria and hinder their participation in the cleanup process. Here, we report on the mitigation of the bactericidal activity of NZVI towards gram-negative Escherichia coli and gram-positive Bacillus subtilis in the presence of Suwannee River humic acids (SRHA), which were used as a model for natural organic matter (NOM). B. subtilis was more tolerant to NZVI (1 g/L) than E. coli in aerobic bicarbonate-buffered medium. SRHA (10 mg/L) significantly mitigated toxicity, and survival rates after 4 h exposure increased to similar levels observed for controls not exposed to NZVI. TEM images showed that the surface of NZVI and E. coli was surrounded by a visible floccus. This decreased the zeta potential of NZVI from −30 to −45 mV and apparently exerted electrosteric hindrance to minimize direct contact with bacteria, which mitigated toxicity. H₂ production during anaerobic NZVI corrosion was not significantly hindered by SRHA (p > 0.05), However, NZVI reactivity towards TCE (20 mg/L), assessed by the first-order dechlorination rate coefficient, decreased by 23%. Overall, these results suggest that the presence of NOM offers a tradeoff for NZVI-based remediation, with higher potential for concurrent or sequential bioremediation at the expense of partially inhibited abiotic reactivity with the target contaminant (TCE).     

Impact of nano zero valent iron (NZVI) on methanogenic activity and population dynamics in anaerobic digestion

Nano zero valent iron (NZVI), although being increasingly used for environmental remediation, has potential negative impact on methanogenesis in anaerobic digestion. In this study, NZVI (average size = 55 ± 11 nm) showed inhibition of methanogenesis due to its disruption of cell integrity. The inhibition was coincident with the fast hydrogen production and accumulation due to NZVI dissolution under anaerobic conditions. At the concentrations of 1 mM and above, NZVI reduced methane production by more than 20%. At the concentration of 30 mM, NZVI led to a significant increase in soluble COD (an indication of cell disruption) and volatile fatty acids in the mixed liquor along with an accumulation of H₂, resulting in a reduction of methane production by 69% (±4% [standard deviation]). By adding a specific methanogenesis inhibitor-sodium 2-bromoethanesulfonate (BES) to the anaerobic sludge containing 30 mM NZVI, the amount of H₂ produced was only 79% (±1%) of that with heat-killed sludge, indicating the occurrence of bacterially controlled hydrogen utilization processes. Quantitative PCR data was in accordance with the result of methanogenesis inhibition, as the level of methanogenic population (dominated by Methanosaeta) in the presence of 30 mM NZVI decreased significantly compared to that of the control. On the contrary, ZVI powder (average size <212 μm) at the same concentration (30 mM) increased methane production presumably due to hydrogenotrophic methanogenesis of hydrogen gas that was slowly released from the NZVI powder. While it is a known fact that NZVI disrupts cell membranes, which inhibited methanogenesis described herein, the results suggest that the rapid hydrogen production due to NZVI dissolution also contribute to methanogenesis inhibition and lead to bacterially controlled hydrogenotrophic processes.     

The contribution of phytoplankton degradation to chromophoric dissolved organic matter (CDOM) in eutrophic shallow lakes: Field and experimental evidence

Eight field campaigns in the eutrophic, shallow, Lake Taihu in the summers from 2005 to 2007, and a phytoplankton degradation experiment of 33 days, were carried out to determine the contribution of phytoplankton degradation to CDOM. Significant and positive correlations were found between the CDOM absorption coefficient at 355 nm [a_CDOM(355)], normalized fluorescence emission (QSU) at 450 nm from excitation at 355 nm [F_n(355)], and the chlorophyll a (Chla) concentration for all eight field campaigns, which indicates that the decomposition and degradation of phytoplankton is an important source of CDOM. In the degradation experiment, the CDOM absorption coefficient increased as phytoplankton broke down during the first 12 days, showing the production of CDOM from phytoplankton. After 12 days, a_CDOM(355) had increased from the initial value 0.41 ± 0.03 m⁻¹ to 1.37 ± 0.03 m⁻¹ (a 234% increase), and the Chla concentration decreased from the initial value of 349.1 ± 11.2 μg/L to 30.4 ± 13.2 μg/L (a 91.3% decrease). The mean daily production rate of CDOM from phytoplankton was 0.08 m⁻¹ for a_CDOM(355). Parallel Factor Analysis (PARAFAC) was used to assess CDOM composition from EEM spectra, and four components were identified: a terrestrial-like humic component, two marine-like humic components, and a protein-like component. The rapid increase in marine-like humic fluorophores (C3 and C4) during the degradation experiment suggests that in situ production of CDOM plays an important role in the dynamics of CDOM. The field campaigns and experimental data in the present study show that phytoplankton can be one of the important CDOM producers in eutrophic shallow lakes.     

硫酸铝强化纳米铁还原硝酸盐氮的研究

在水体溶解氧较高的条件下,采用投加硫酸铝的方式强化纳米铁对硝酸盐氮的去除效果。结果表明,投加硫酸铝可明显提高纳米铁对硝酸盐氮的去除效果,当硝酸盐氮初始浓度为10mg/L、纳米铁投量为5g/L、硫酸铝投量为100mg/L时,反应6h后对硝酸盐氮的去除率可达到83%,而不投加硫酸铝的情况下仅为51%。纳米铁对硝酸盐氮的还原过程符合拟一级反应动力学规律,其反应速率常数k随纳米铁投量和硫酸铝投量的增加而增大;纳米铁对硝酸盐氮的去除率随pH的降低而升高,随初始硝酸盐氮浓度的增加而下降;纳米铁还原硝酸盐氮的表观活化能较低,还原反应在常温下即很容易进行;硝酸盐氮的最终还原产物为氨氮。     

Magnetic binary oxide particles (MBOP): a promising adsorbent for removal of As (III) in water

Magnetic binary oxide particles (MBOP) synthesized using chitosan template has been investigated for uptake capacity of arsenic (III). Batch experiments were performed to determine the rate of adsorption and equilibrium isotherm and also effect of various rate limiting factors including adsorbent dose, pH, optimum contact time, initial adsorbate concentration and influence of presence cations and anions. It was observed that uptake of arsenic (III) was independent of pH of the solution. Maximum adsorption of arsenic (III) was ∼99% at pH 7.0 with dose of adsorbent 1 g/L and initial As (III) concentration of 1.0 mg/L at optimal contact time of 14 h. The adsorption equilibrium data fitted well to Langmuir and Freundlich isotherm. The maximum adsorption capacity of adsorbent was 16.94 mg/g. With increase in concentration of Ca²⁺, Mg²⁺ from 50 mg/L to 600 mg/L, adsorption of As (III) was significantly reduced while for Fe³⁺ the adsorption of arsenic (III) was increased with increase in concentration. Temperature study was carried out at 293 K, 303 K and 313 K reveals that the adsorption process is exothermic nature. A distinct advantage of this adsorbent is that adsorbent can readily be isolated from sample solutions by application of an external magnetic field. Saturation magnetization is a key factor for successful magnetic separation was observed to be 18.78 emu/g which is sufficient for separation by conventional magnate.     

Biological oxidation of arsenite in synthetic groundwater using immobilised bacteria

Biological oxidation of arsenite (As(III)) in synthetic groundwater was examined by using arsenite oxidising bacteria (AOB) isolated from an activated sludge. The phylogenetic analysis indicated that the isolated AOB was closely related to Ensifer adhaerens. Batch experiments showed that for an As(III) oxidation with the isolated AOB the optimum ratio of nitrogen source (NH₄-N) concentration to As(III) concentration was 0.5 (52 mg/L-110 mg/L) and the isolated AOB preferred pH values ranging from 6 to 8, and water temperatures greater than 20 °C. Further continuous experiments were conducted using a bioreactor with immobilised AOB. With an initial As(III) concentration of 1 mg/L at a hydraulic retention time (HRT) of 1 h, an As(III) oxidation rate was around 1 × 10⁻⁹ μg/cell/min and an As(III) oxidation efficiency of 92% was achieved. Although the maximum oxidation rate measured at an HRT of 0.5 h was 2.1 × 10⁻⁹ μg/cell/min, the oxidation efficiency decreased to 87%.These results advocate that a biological process involving immobilised AOB may be useful as an economical and environmentally friendly pre-treatment step for As removal from groundwater.     

Removal of atrazine by nanoscale zero valent iron supported on organobentonite

The organobentonite (CTMA-Bent) was prepared from Na⁺-saturated bentonite (Na-Bent) by intercalation with cetyltrimethylammonium bromide (CTMA), and used as a carrier of nanoscale zero valent iron (NZVI) for the removal of atrazine. The NZVI/CTMA-Bent composite was characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM), and good dispersion of nanoscale iron particles on the carrier was observed. The removal efficiency of atrazine by this composite was compared with that by commercial iron powder and NZVI itself. For both treatments by NZVI and NZVI/CTMA-Bent, the removal efficiency increased as the pH of the solution decreased, and the removal percentage of atrazine by NZVI/CTMA-Bent reached 63.5% at initial pH = 5.0 after 120 min. It is not only much higher than that (26.6%) by NZVI containing the same amount of iron, but also superior to the sum (32.1%) of reduction by NZVI plus adsorption by CTMA-Bent (5.5%). Besides, the NZVI/CTMA-Bent has a good long-term stability, and the carrier CTMA-Bent could prevent the iron ions (the byproduct of dechlorination) from leaching into the solution.     

Adsorption of rotavirus and bacteriophage MS2 using glass fiber coated with hematite nanoparticles

Batch and flow-through experiments were conducted to investigate the removal and inactivation of rotavirus (RV) and bacteriophage MS2 using glass fiber coated with hematite nanoparticles. Batch tests showed a high removal of MS2 (2.49 × 10¹¹ plaque forming unit/g) and RV (8.9 × 10⁶ focal forming unit/g) at a low concentration of hematite nanoparticles in solution (0.043 g/L and 0.26 g/L, respectively). Virus adsorption was, however, decreased in the presence of bicarbonate ions and natural organic matter (NOM) in solution, suggesting a great affinity of iron oxide nanoparticles for these competitors. Adsorption on hematite nanoparticles by MS2 and RV was also tested with aquifer groundwater under saturated flow conditions to mimic environmental conditions with promising results (8 × 10⁸ plaque forming unit/g and 3 × 10⁴ focal forming unit/g, respectively). Desorption of up to 63% of infectious MS2 and only 2% of infectious RV from hematite nanoparticles were achieved when an eluant solution containing beef extract and glycine was used. Transmission electron microscopy (TEM) images showed evidence of electrostatic adsorption of apparently intact MS2 and structurally damaged RV particles to hematite nanoparticles. Results from this research suggest that a cartridge made of glass fiber coated with hematite nanoparticles could be used as a point-of-use device for virus removal for drinking water treatment.     

Biological and environmental exposure monitoring of volatile organic compounds among nail technicians in the Greater Boston area

Nail technicians are exposed to volatile organic compounds (VOCs) from nail products, but no studies have previously measured VOC biomarkers for these workers. This study of 10 nail technicians aimed to identify VOCs in nail salons and explore relationships between air concentrations and biomarkers. Personal and area air samples were collected using thermal desorption tubes during a work shift and analyzed using gas chromatography/mass spectrometry (GC/MS) for 71 VOCs. Whole blood samples were collected pre‐shift and post‐shift, and analyzed using GC/MS for 43 VOCs. Ventilation rates were determined using continuous CO₂ measurements. Predominant air VOC levels were ethyl methacrylate (median 240 µg/m³), methyl methacrylate (median 205 µg/m³), toluene (median 100 µg/m³), and ethyl acetate (median 639 µg/m³). Blood levels were significantly higher post‐shift than pre‐shift for toluene (median pre‐shift 0.158 µg/L and post‐shift 0.360 µg/L) and ethyl acetate (median pre‐shift <0.158 µg/L and post‐shift 0.510 µg/L); methacrylates were not measured in blood because of their instability. Based on VOCs measured in these seven nail salons, we estimated that emissions from Greater Boston area nail salons may contribute to ambient VOCs. Ventilation rates did not always meet the ASHRAE guideline for nail salons. There is a need for changes in nail product formulation and better ventilation to reduce VOC occupational exposures.     

Implications of organic matter on arsenic mobilization into groundwater: Evidence from northwestern (Chapai-Nawabganj), central (Manikganj) and southeastern (Chandpur) Bangladesh

Boreholes (50 m depth) and piezometers (50 m depth) were drilled and installed for collecting As-rich sediments and groundwater in the Ganges, Brahmaputra, and Meghna flood plains for geochemical analyses. Forty-one groundwater samples were collected from the three areas for the analyses of cations (Ca²⁺, Mg²⁺, K⁺, Na⁺), anions (Cl⁻, NO₃⁻, SO₄²⁻), total organic carbon (TOC), and trace elements (As, Mn, Fe, Sr, Se, Ni, Co, Cu, Mo, Sb, Pb). X-ray powder diffraction (XRD) and X-ray fluorescence (XRF) were performed to characterize the major mineral and chemical contents of aquifer sediments. In all three study areas, results of XRF analysis clearly show that fine-grained sediments contain higher amounts of trace element because of their high surface area for adsorption. Relative fluorescent intensity of humic substances in groundwater samples ranges from 30 to 102 (mean 58 ± 20, n = 20), 54-195 (mean 105 ± 48, n = 10), and 27-243 (mean 79 ± 71, n = 11) in the Ganges, Brahmaputra and Meghna flood plains, respectively. Arsenic concentration in groundwater (20-50 m of depth) ranges from 3 to 315 μg/L (mean 62.4 ± 93.1 μg/L, n = 20), 16.4-73.7 μg/L (mean 28.5 ± 22.4 μg/L, n = 10) and 4.6-215.4 μg/L (mean 30.7 ± 62.1 μg/L, n = 11) in the Ganges, Brahmaputra and Meghna flood plains, respectively. Specific ultra violet adsorption (SUVA) values (less than 3 m⁻¹ mg⁻¹ L) indicate that the groundwater in the Ganges flood plain has relatively low percentage of aromatic organic carbon compared to those in the Brahmaputra and Meghna flood plains. Arsenic content in sediments ranges from 1 to 11 mg/kg (mean 3.5 ± 2.7 mg/kg, n = 17) in the three flood plains. Total organic carbon content is 0.5-3.7 g/kg (mean 1.9 ± 1.1 g/kg) in the Ganges flood plain, 0.5-2.1 g/kg (mean: 1.1 ± 0.7 g/kg) in the Brahmaputra flood plain and 0.3-4.4 g/kg (mean 1.9 ± 1.9 g/kg) in the Meghna flood plain. Arsenic is positively correlated with TOC (R² = 0.50, 0.87, and 0.85) in sediments from the three areas. Fourier transform infrared (FT-IR) analysis of the sediments revealed that the functional groups of humic substances in three areas include amines, phenol, alkanes, and aromatic carbon. Arsenic and Fe speciation in sediments were determined using XANES and the results imply that As(V) and Fe(III) are the dominant species in most sediments. The results also imply that As (V) and Fe (III) in most of the sediment samples of the three areas are the dominant species. X-ray absorption fine structure (EXAFS) analysis shows that FeOOH is the main carrier of As in the sediments of three areas. In sediments, As is well correlated with Fe and Mn. However, there is no such correlation observed between As and Fe as well as As and Mn in groundwater, implying that mobilizations of Fe, Mn, and As are decoupled or their concentrations in groundwater have been affected by other geochemical processes following reductive dissolution of Fe or Mn-hydroxides. For example, dissolved Fe and Mn levels may be affected by precipitation of Fe- and Mn-carbonate minerals such as siderite, while liberated As remains in groundwater. The groundwaters of the Brahmaputra and Meghna flood plains contain higher humic substances in relative fluorescence intensity (or fluorescence index) and lower redox potential compared to the groundwater of Ganges flood plain. This leads to the release of arsenic and iron to groundwater of these three plains in considerable amounts, but their concentrations are distributed in spatial variations.     

Influence of nanoscale zero-valent iron on geochemical properties of groundwater and vinyl chloride degradation: A field case study

A 200 m² pilot-scale field test successfully demonstrated the use of nanoscale zero-valent iron (NZVI) for effective remediation of groundwater contaminated with chlorinated organic compounds in Taiwan within six months. Both commercially available and on-site synthesized NZVI were used. A well-defined monitoring program allowing to collect three-dimensional spatial data from 13 nested multi-level monitoring wells was conducted to monitor geochemical parameters in groundwater. The degradation efficiency of vinyl chloride (VC) determined at most of monitoring wells was 50-99%. It was found that the injection of NZVI caused a significant change in total iron, total solid (TS) and suspended solid (SS) concentrations in groundwater. Total iron concentration showed a moderate and weak correlation with SS and TS, respectively, suggesting that SS may be used to indicate the NZVI distribution in groundwater. A decrease in oxidation-reduction potential (ORP) values from about −100 to −400 mV after NZVI injection was observed. This revealed that NZVI is an effective means of achieving highly reducing conditions in the subsurface environment. Both VC degradation efficiency and ORP showed a correlative tendency as an increase in VC degradation efficiency corresponded to a decrease of ORP. This is in agreement with the previous studies suggesting that ORP can serve as an indicator for the NZVI reactivity.     

Adverse health effects of lead exposure on children and exploration to internal lead indicator

Our research on adverse effects of lead exposures on physical and neurobehavioral health of children aged 6–12 years in 4 villages, labeled as K, M, L, and X, in rural China, was reported in this article. Lead in blood (PbB), urine (PbU), hairs (PbH), and nails (PbN) were measured by graphite furnace atomic absorption spectrometry. Abbreviated Symptom Questionnaire of Conner's instruments and Revised Raven's Standard Progressive Matrices were applied to evaluate childhood attention deficit/hyperactivity disorders (ADHD) and intelligences. Geometric means (SD) of PbB, PbU, PbH and PbN concentrations were 71.2 μg/L (1.56), 11.7 μg/g (1.75), 12.5 μg/g (2.82), and 25.3 μg/g (2.79), respectively. 54 (17.0%) children had PbB levels of ≥ 100 μg/L. Boys, the 6–10 years old, and living in village K were 2.11, 2.48, and 9.16 times, respectively, more likely to be poisoned by lead than girls, aged 11–12 years, and residing in X. 18 (5.7%) and 37 (11.7%) subjects had ADHD and mental retardations, respectively. Inverse relationships between intelligences and natural log transformed PbU and PbH levels were observed with respective odds ratios (95%CI) of 1.79 (1.00–3.22) and 1.46 (1.06–2.03) or 1.28 (1.04–1.58) and 1.73 (1.18–2.52) by binary or ordinal logistic regression modeling. ADHD prevalence was different by gender and age of subjects. PbU, PbH, and PbN related to PbB positively with respective correlation coefficients of 0.530, 0.477, and 0.181. Receiver operating characteristic (ROC) curves of the three measurements reveled areas under curves (AUCs) being 0.829, 0.758, and 0.687, respectively. In conclusion, children had moderate levels of lead exposures in this rural area. Intelligence declines were associated with internal lead levels among children. ROC analysis suggests PbU an internal lead indicator close to PbB.     

Enrichment of bacteria possessing catechol dioxygenase genes in the rhizosphere of Spirodela polyrrhiza: A mechanism of accelerated biodegradation of phenol

The bacterial community structure in bulk water and in rhizosphere fractions of giant duckweed, Spirodela polyrrhiza, was quantitatively and qualitatively investigated by PCR-based methods using 6 environmental water samples to elucidate the mechanisms underlying selective accumulation of aromatic compound-degrading bacteria in the rhizosphere of S. polyrrhiza. S. polyrrhiza selectively accumulated a diverse range of aromatic compound-degrading bacteria in its rhizosphere, regardless of the origin of water samples, despite no exposure to phenol. The relative abundances of the catechol 1,2-dioxygenase (C12O) gene (C12O DNA) and catechol 2,3-dioxygenase (C23O) gene (C23O DNA) were calculated as the ratios of the copy numbers of these genes to the copy number of 16S rDNA and are referred to as the rhizosphere effect (RE) value. The RE values for C12O DNA and C23O DNA were 1.0 × 10¹–9.3 × 10³ and 1.7 × 10²–1.5 × 10⁴ times as high, respectively, in rhizosphere fractions as in bulk water fractions, and these higher values were associated with a notably higher sequence diversity of C12O DNA and C23O DNA. The RE values during phenol degradation were 3.6 × 10⁰–4.3 × 10² and 2.2 × 10⁰–1.7 × 10², respectively, indicating the ability of S. polyrrhiza to selectively accumulate aromatic compound-degrading bacteria in its rhizosphere during phenol degradation. The bacterial communities in the rhizosphere fractions differed from those in the bulk water fractions, and those in the bulk water fractions were notably affected by the rhizosphere bacterial communities. S. polyrrhiza released more than 100 types of phenolic compound into its rhizosphere as root exudates at the considerably high specific release rate of 1520 mg TOC and 214 mg phenolic compounds/d/g root (wet weight). This ability of S. polyrrhiza might result in the selective recruitment and accumulation of a diverse range of bacteria harboring genes encoding C12O and C23O, and the subsequent accelerated degradation of phenol in the rhizosphere.     

Health benefits of improving air quality in the rapidly aging Korean society

Korea is experiencing an extraordinarily rapid demographic transition. We investigated the short-term association between air pollution and mortality and assessed the impact of improved air quality on mortality in a rapidly aging city, Seoul, Korea.The generalized additive model (GAM) was used to estimate the relative risks (RR) of mortality associated with changes in air pollution. The time trends, seasonal variations, day of the week effects, and weather effects were controlled in the models. To estimate the health benefits, we used the US Environmental Protection Agency's BenMAP.For people 0–64 years of age, elderly people (65+ years), and all age groups, an increase of 10 μg/m³ in PM₁₀ was associated with increases in daily death counts of 0.27% (95% CI: 0.04–0.50), 0.45% (95% CI: 0.27–0.64), and 0.37% (95% CI: 0.23–0.52), respectively. For ages 0–64 years, elderly people, and all age groups, a 10 ppb increase in 1-hour maximum ozone concentration resulted in an increased risk of daily death counts of 0.28% (95% CI: − 0.19–0.74), 0.96% (95% CI: 0.46–1.47), and 0.81% (95% CI: 0.35–1.26), respectively.For elderly people, it was estimated that the health benefits of attaining the World Health Organization's (WHO) air quality guidelines (AQGs) for PM₁₀ (24-hour average 50 μg/m³) would suggest an annual reduction of 964 (95% CI: 564–1366) premature deaths, and 329 (95% CI: 159–500) premature deaths could be prevented annually in 2015 from attaining the WHO's guidelines for ozone (8-hour average 100 μg/m³).The rapid increase of the elderly population has major consequences and implications for society and public health. This study showed that elderly people are at higher risk for the acute mortality effects of air pollution. Therefore, cleaner air will substantially contribute to improved public health in Seoul, given the growing concern about the adverse effects of air pollution for elderly people.     

Characteristics of trihalomethane (THM) production and associated health risk assessment in swimming pool waters treated with different disinfection methods

Swimming pool water must be treated to prevent infections caused by microbial pathogens. In Korea, the most commonly used disinfection methods include the application of chlorine, ozone/chlorine, and a technique that uses electrochemically generated mixed oxidants (EGMOs). The purpose of this study was to estimate the concentrations of total trihalomethanes (TTHMs) in indoor swimming pools adopting these disinfection methods, and to examine the correlations between the concentrations of THMs and TTHMs and other factors affecting the production of THMs. We also estimated the lifetime cancer risks associated with various exposure pathways by THMs in swimming pools. Water samples were collected from 183 indoor swimming pools in Seoul, Korea, and were analyzed for concentrations of each THM, TOC, and the amount of KMnO₄ consumption. The free chlorine residual and the pH of the pool water samples were also measured. The geometric mean concentrations of TTHMs in the swimming pool waters were 32.9 ± 2.4 µg/L for chlorine, 23.3 ± 2.2 µg/L for ozone/chlorine, and 58.2 ± 1.7 µg/L for EGMO. The concentrations of THMs differed significantly among the three treatment methods, and the correlation between THMs and TTHMs and the other factors influencing THMs varied. The lifetime cancer risk estimation showed that, while risks from oral ingestion and dermal exposure to THMs are mostly less than 10^− 6, which is the negligible risk level defined by the US EPA, however swimmers can be at the greater risk from inhalation exposure (7.77 × 10^− 4-1.36 × 10^− 3).     

Kaolinite-supported nanoscale zero-valent iron for removal of Pb2+ from aqueous solution: reactivity, characterization and mechanism

The use of nanoscale zero-valent iron (nZVI) to remediate contaminated groundwater is limited due to its lack of durability and mechanical strength. To address this issue, 20% (w/w) nZVI was loaded onto kaolinite as a support material (K-nZVI). More than 96% of Pb²⁺ was removed from aqueous solution using K-nZVI at an initial condition of 500 mg/L Pb²⁺ within 30 min under the conditions of 10 g/L of K-nZVI, pH 5.10 and a temperature of 30 °C. To understand the mechanism of removal of Pb²⁺, various techniques were implemented to characterize K-nZVI. Scanning electron microscopy (SEM) indicated that K-nZVI had a suitable dispersive state with a lower aggregation, where the mean specific surface area and average particle size as determined by the BET-N₂ method and X-ray diffraction (XRD), were 26.11 m²/g and 44.3 nm, respectively. The results obtained from XRD, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) indicated that a small number of iron oxides formed on the surface of K-nZVI, suggesting that free Pb²⁺ was adsorbed onto K-nZVI and subsequently reduced to Pb⁰.     

Mercury speciation in the Valdeazogues River-La Serena Reservoir system: Influence of Almadén (Spain) historic mining activities

Mercury (Hg) speciation and partitioning have been investigated in a river-reservoir system impacted by the Almadén mining activities, the world's largest Hg district. This study is the first to simultaneously investigate Hg dynamics from above the mining district and into the La Serena Reservoir (3219 Hm³), being the third largest reservoir in Europe and the largest in Spain.Water, sediment and biota were sampled at different seasons during a 2-year study from the Valdeazogues River, which flows east-west from the mining District, to La Serena Reservoir. Simultaneously, a comprehensive study was undertaken to determine the influence of some major physico-chemical parameters that potentially influence the fate of Hg within the watershed.Concentrations of dissolved Hg in water were below 0.14 µg/L, whereas particulate Hg ranged from 0.1 to 87 µg/g, with significant seasonal variation. Total Hg concentrations varied from 7 to 74 µg/g in sediment from the Valdeazogues River, while in sediments from La Serena Reservoir were below 2 µg/g. On the other hand, methyl-Hg reached concentrations up to 0.3 ng/L in water and 6 ng/g in sediment from La Serena Reservoir, whereas maximum concentrations in Valdeazogues River were 5 ng/L and 880 ng/g in water and sediment, respectively. The distribution of Hg species in the Valdeazogues River-La Serena Reservoir system indicated a source of Hg from the mine waste distributed along the river. Total Hg in water was strongly correlated with total dissolved solids and chlorophyll a concentrations, whereas organic carbon and Fe concentrations seem to play a role in methylation of inorganic Hg in sediment. Total Hg concentrations were low in fish from Valdeazogues River (0.8-8.6 ng/g, wet weight) and bivalves from La Serena Reservoir (10-110 ng/g, wet weight), but most was present as methyl-Hg.     

Optimization of PMA‐qPCR for Staphylococcus aureus and determination of viable bacteria in indoor air

Staphylococcus aureus may cause infections in humans from mild skin disorders to lethal pneumonia. Rapid and accurate monitoring of viable S. aureus is essential to characterize human exposure. This study evaluated quantitative PCR (qPCR) with propidium monoazide (PMA) to quantify S. aureus. The results showed comparable S. aureus counts between exclusively live cells and mixtures of live/dead cells by qPCR with 1.5 or 2.3 μg/mL PMA (P>.05), illustrating the ability of PMA‐qPCR to detect DNA exclusively from viable cells. Moreover, qPCR with 1.5 or 2.3 μg/mL PMA performed optimally with linearity over 10³‐10⁸ CFU/mL (R²≥0.9), whereas qPCR with 10, 23 or 46 μg/mL PMA significantly underestimated viable counts. Staphylococcus aureus and total viable bacteria were further determined with PMA‐qPCR (1.5 μg/mL) from 48 samples from a public library and two university dormitories and four from outside. Viable bacteria averaged 1.9×10⁴ cells/m³, and S. aureus were detected in 22 (42%) samples with a mean of 4.4×10³ cells/m³. The number of S. aureus and viable bacteria were positively correlated (r=.61, P<.005), and percentages of S. aureus relative to viable bacteria averaged 12‐44%. The results of field samples suggest that PMA‐qPCR can be used to quantify viable S. aureus cells.     

The effect of inorganic precursors on disinfection byproduct formation during UV-chlorine/chloramine drinking water treatment

Ultraviolet (UV) disinfection is being increasingly used in drinking water treatment. It is important to understand how its application to different types of water may influence finished water quality, particularly as anthropogenic activity continues to impact the quality of source waters. The objective of this study was to evaluate the effect of inorganic precursors on the formation of regulated and unregulated disinfection byproducts (DBPs) during UV irradiation of surface waters when combined with chlorination or chloramination. Samples were collected from three drinking water utilities supplied by source waters with varying organic and inorganic precursor content. The filtered samples were treated in the laboratory with a range of UV doses delivered from low pressure (LP, UV output at 253.7 nm) and medium pressure (MP, polychromatic UV output 200-400 nm) mercury lamps followed by chlorination or chloramination, in the presence and absence of additional bromide and nitrate. The regulated trihalomethanes and haloacetic acids were not affected by UV pretreatment at disinfection doses (40-186 mJ/cm²). With higher doses (1000 mJ/cm²), trihalomethane formation was increased 30-40%. While most effects on DBPs were only observed with doses much higher than typically used for UV disinfection, there were some effects on unregulated DBPs at lower doses. In nitrate-spiked samples (1-10 mg N/L), chloropicrin formation doubled and increased three- to six-fold with 40 mJ/cm² MP UV followed by chloramination and chlorination, respectively. Bromopicrin formation was increased in samples containing bromide (0.5-1 mg/L) and nitrate (1-10 mg N/L) when pretreated with LP or MP UV (30-60% with 40 mJ/cm² LP UV and four- to ten-fold increase with 40 mJ/cm² MP UV, after subsequent chlorination). The formation of cyanogen chloride doubled and increased three-fold with MP UV doses of 186 and 1000 mJ/cm², respectively, when followed by chloramination in nitrate-spiked samples but remained below the World Health Organization guideline value of 70 μg/L in all cases. MP UV and high LP UV doses (1000 mJ/cm²) increased chloral hydrate formation after subsequent chlorination (20-40% increase for 40 mJ/cm² MP UV). These results indicate the importance of bench-testing DBP implications of UV applications in combination with post-disinfectants as part of the engineering assessment of a UV-chlorine/chloramine multi-barrier disinfection design for drinking water treatment.     

Comparison of chlorine and chloramine in the release of mercury from dental amalgam

The purpose of this project was to compare the ability of chlorine (HOCl/OCl⁻) and monochloramine (NH₂Cl) to mobilize mercury from dental amalgam. Two types of amalgam were used in this investigation: laboratory-prepared amalgam and samples obtained from dental-unit wastewater. For disinfectant exposure simulations, 0.5 g of either the laboratory-generated or clinically obtained amalgam waste was added to 250 mL amber bottles. The amalgam samples were agitated by end-over-end rotation at 30 rpm in the presence of 1 mg/L chlorine, 10 mg/L chlorine, 1 mg/L monochloramine, 10 mg/L monochloramine, or deionized water for intervals of 0 h, 2 h, 4 h, 8 h, and 24 h for the clinically obtained amalgam waste samples and 4 h and 24 h for the laboratory-prepared samples. Chlorine and monochloramine concentrations were measured with a spectrophotometer. Samples were filtered through a 0.45 µm membrane filter and analyzed for mercury with USEPA standard method 245.7. When the two sample types were combined, the mean mercury level in the 1 mg/L chlorine group was 0.020 mg/L (n = 25, SD = 0.008). The 10 mg/L chlorine group had a mean mercury concentration of 0.59 mg/L (n = 25, SD = 1.06). The 1 mg/L chloramine group had a mean mercury level of 0.023 mg/L (n = 25, SD = 0.010). The 10 mg/L chloramine group had a mean mercury level of 0.024 mg/L (n = 25, SD = 0.011). Independent samples t-tests showed that there was a significant difference between the natural log mercury measurements of 10 mg/L chlorine compared to those of 1 mg/L and 10 mg/L chloramine. Changing from chlorine to chloramine disinfection at water treatment plants would not be expected to produce substantial increases in dissolved mercury levels in dental-unit wastewater.