Enhanced kinetics and super selectivity toward Cs+ in multicomponent aqueous solutions: A robust Prussian blue analogue/polyvinyl chloride composite membrane.

Developing effective adsorbents for 137Cs removal from complex wastewater systems has been a significant challenge. Although existing spheres adsorbents could improve the post-separation ability and practical operability, the adsorption kinetics are still significantly retarded due to the large intra-particle diffusion resistance. Here, we demonstrate the efficiency of a robust Prussian blue analogue/polyvinyl chloride composite membrane (PPM), which was easily prepared by a simple solvent evaporation method. In virtue of the less dense layer and ion-sieving functionality, it showed enhanced kinetics (5 h) and super selectivity (SF = 248.3-5388.6) towards Cs+. New PPM was robust within a wide pH range (2-10) and exhibited favorable removal capacity (152.8 mg/g), placing it at an outstanding material for Cs+ removal among other adsorbents. Moreover, PPM could be simply eluted and reused using a KCl solution as eluent. A study of the adsorption mechanism confirmed an ion-exchange action during the removal process. Thus, PPM is considered to be a promising candidate for the removal of Cs+ from multicomponent aqueous solutions.

Adsorption behaviors of phenanthrene and bisphenol A in purple paddy soils amended with straw-derived DOM in the West Sichuan Plain of China.

The objectives of this study were to investigate the adsorption and transfer behaviors of phenanthrene (PHE) and bisphenol A (BPA) in purple paddy soils amended with dissolved organic matter (DOM) derived from rice and canola straw in the West Sichuan Plain of China. In the pristine soil, PHE was preferentially adsorbed on both pristine clayey (L) and sandy (T) paddy soils than BPA, indicating that the retention/adsorption by soils is closely dependent on the chemical properties of organic pollutants (OPs). The noticeably higher adsorption of PHE and BPA on smaller size fraction of the soils (L2 and T2) were observed, possibly due to their higher surface areas and higher content in organic matters with higher aromaticity and hydrophobicity in this soil fraction. The DOMs derived from rice (RDOM) and canola (CDOM) straws possessed remarkable differences in E2/E3 and SUV254 measurements, which reflected that their chemical composition might be different. When CDOM was introduced in the studied soil T1, adsorption of BPA was doubled, but the augment in adsorption was much less impressive with RDOM, showing the nature of derived DOM played an important role. The study also demonstrated that in the fine fraction of clayey soil (L2), the retention of a same OP (PHE) was remarkably dropped when CDOM or RDOM was introduced, whereas in a sandy soil of the same size fraction (T2), the phenomenon was the opposite, suggesting a potential risk that, in certain types of soil, the introduction of straw derived DOMs may enhance the mobility of some OPs. The humification time of straw seems not to affect the adsorptions of OPs in most studied systems. Adsorption kinetics of PHE and BPA in the adsorption systems with derived DOMs were well fitted to the two-step first-order model with radj2 values of 0.994-0.998. Results of this study will provide further comprehensive fundamental data for risk assessment and control of organic pollutants (OPs) in farmland ecosystems.

Rates and processes affecting As speciation and mobility in lake sediments during aging.

Sediments from an arsenic (As) contaminated groundwater vent site were used to investigate As(III) binding, transformation and redistribution in native and iron oxide amended lake sediments using aging spiked batch reactions and a sequential extraction procedure that maintains As(V) and As(III) speciation. In the native sediments, fractionation analysis revealed that 10% of the spiked As(III) remained intact after a 32-day aging experiment and was predominantly adsorbed to the strongly sorbed (NH4H2PO4 extractable) and amorphous Fe oxide bound (H3PO4 extractable) fractions. Kinetic modelling of the experimental results allowed identifying the dominant reaction path for depletion of dissolved As(III) to As(III) absorbed on to the solid phase, followed by oxidation in the solid phase. Arsenite was initially adsorbed primarily to the easily exchangeable fraction ((NH4)2SO4 extractable), then rapidly transformed into As(V) and redistributed to the strongly sorbed and amorphous Fe oxide bound fractions. Oxidation of As(III) in recalcitrant fractions was less efficient. The iron oxide amendments illustrated the controls that iron oxides can have on As(III) binding and transformation rates. In goethite amended samples As(III) oxidation was faster and primarily occurred in the strongly sorbed and amorphous Fe oxide bound fractions. In these samples, 19.3µg Mn was redistributed (compared to the native sediment) from the easily exchangeable and crystalline Fe oxide bound fractions to the strongly sorbed and amorphous Fe oxide bound fractions, indicating that goethite may act as a catalyst for Mn(II) oxidation, thereby producing sorbed Mn(III/IV), which then appears to be involved in rapidly oxidizing As(III).

Inorganic Contaminants, Nutrient Reserves and Molt Intensity in Autumn Migrant Red-Necked Grebes (Podiceps grisegena) at Georgian Bay.

Red-necked grebes (Podiceps grisegena) are piscivorous waterbirds that breed on freshwater lakes in northwestern Canada and stop-over at the Great Lakes during autumn migration to molt feathers and replenish lipid and protein reserves. The objectives of this study were to (1) describe concentrations of, and correlations among, inorganic contaminants in a sample of autumn migrant red-necked grebes from the Great Lakes, (2) compare concentrations of inorganic contaminants to those in autumn migrant common loons from Schummer et al. (Arch Environ Contam Toxicol 62:704, 2011a), (3) evaluate if the inorganic elements are negatively associated with lipid and protein reserves, and (4) determine if nutrient reserves and molt intensity were correlated. None of the 14 contaminants analyzed were above threshold levels known to cause acute health problems in piscivorous birds. Body masses of plucked birds were within the normal reported range. Lipid reserves varied positively with hepatic concentrations of arsenic, copper, iron, nickel, lead, and selenium and negatively with mercury and magnesium. Protein reserves variety negatively with hepatic concentrations of arsenic, calcium, nickel, lead, and zinc and positively with aluminum, cadmium, and iron. A negative correlation was observed between chest molt and lipid reserves but not between nutrient reserves and other feather tracts. The relationships between lipid reserves and both mercury and selenium were consistent with current research on other piscivorous waterbirds at the Great Lakes and justify continued work to determine interactions of these contaminants in waterbirds that breed, stage, and winter in the region.

Solvent extraction of tellurium from chloride solutions using tri-n-butyl phosphate: conditions and thermodynamic data.

The extractive separation of tellurium (IV) from hydrochloric acid media with tri-n-butyl phosphate (TBP) in kerosene was investigated. The dependence on the extraction of tellurium species, concentrations of tellurium and TBP, extraction time and stage, organic/aqueous ratio, and interferences from coexist metallic ions were examined and are discussed. Besides, the stripping agent and stripping time were also studied. It was found that the extraction reaction corresponds to the neutral complex formation mechanism and the extracted species is TeCl4 · 3TBP and that the extraction process is exothermic. The thermodynamic parameters of enthalpy (ΔH), entropy (ΔS), and free energy (ΔG) of the extraction process were evaluated at -26.2 kJ · mol(-1), -65.6 J · mol(-1) · K(-1), and -7.0 kJ · mol(-1), respectively at 293 K.

Novel Zr-Doped Thiostannate Spinning Fiber (Fiber-KZrTS) for Highly Efficient and Renewable Recovery of Cesium and Strontium from Geothermal Water.

The efficient and renewable recovery of cesium and strontium by absorption from a new type of geothermal water liquid mineral resource is highly desirable but still challenging. In this work, a new Zr-doped layered potassium thiostannate adsorbent (KZrTS) was first synthesized and used for Cs+ and Sr2+ green and efficient adsorption. It was found that KZrTS had very fast adsorption kinetics toward both Cs+ and Sr2+ with an equilibrium reached within 1 min, and the theoretical maximum adsorption capacities for Cs+ and Sr2+ were 402.84 and 84.88 mg/g, respectively. Moreover, to solve the loss problem of the engineering application of the powdered adsorbent KZrTS, KZrTS was uniformly coated with polysulfone by wet spinning technology to form micrometer-level filament-like absorbents (Fiber-KZrTS), whose adsorption equilibrium rates and capacities toward Cs+ and Sr2+ are almost the same as that of powder. Furthermore, Fiber-KZrTS showed excellent reusability, and the adsorption performance remained virtually unchanged after 20 cycles. Therefore, Fiber-KZrTS has potential application for green and efficient cesium and strontium recovery from geothermal water.

Hepatic concentrations of inorganic contaminants and their relationships with nutrient reserves in autumn-migrant common loons at Lake Erie.

Common loons (Gavia immer) are piscivorous, high-trophic level feeders that bioaccumulate inorganic contaminants at concentrations that can negatively impact their health and reproduction. Concentrations of inorganic contaminants, especially mercury (Hg), in blood, organs, and muscle have been quantified in common loons on breeding grounds, but these data are limited for migrating loons. We investigated sex- and age-related hepatic concentrations of inorganic contaminants in common loons (n = 53) that died from botulism and were salvaged at a Great Lakes staging area (i.e., Long Point, Lake Erie) during November 2005. We also investigated if hepatic concentrations of inorganic contaminants influenced lipid, protein, and mineral in our sample of migrant common loons. Last, we determined if there was correlation between Hg and selenium (Se). Consistent with data from breeding grounds, mean concentrations of Hg in liver were approximately 2.5 times greater in adult ([Formula: see text] = 14.64 ± 16.69 µg g(-1)) compared with juvenile birds ([Formula: see text] = 3.99 ± 2.27 µg g(-1)). Elements detected in liver at potentially harmful levels were Hg and Se, of which lipid reserves varied negatively with Hg concentrations but positively with Se concentrations. In addition, Hg and Se were correlated (r = 0.65) at greater then a demethylation threshold (total Hg ≥ 8.5 µg g(-1) dw) but not lower than that. Concentrations of inorganic contaminants did not influence protein and mineral levels in our sample of common loons. Our results suggest that Hg accumulation negatively affects lipid levels in migrant common loons. Results are also consistent with a nontoxic Hg-Se protein complex protecting loons migrating through areas that are relatively Se rich. Although the acquisition of Se during the nonbreeding season may decrease the toxicity of Hg, future research should consider the synergistic Hg-Se effect on reproduction in common loons that migrate through Se-rich locales, such as the Great Lakes.

Biogeochemical mechanisms of selenium exchange between water and sediments in two contrasting lentic environments.

The biogeochemical mechanisms of Se exchange between water and sediments in two contrasting lentic environments were assessed through examination of Se speciation in the water column, porewater, and sediment. High-resolution (7 mm) vertical profiles of <0.45 µm Se species across the sediment-water interface demonstrate that the behavior of dissolved Se(VI), Se(IV), and organo-Se are closely linked to redox conditions as revealed by porewater profiles of redox-sensitive species (dissolved O2, NO3-, Fe, Mn, SO4(2-), and ΣH2S). At both sites Se(VI) is removed from solution in suboxic near-surface porewaters demonstrating that the sediments are serving as diffusive sinks for Se. X-ray absorption near edge spectroscopy (XANES) of sediments suggests that elemental Se and organo-Se represent the dominant sedimentary sinks for dissolved Se. Dissolved Se(IV) and organo-Se are released to porewaters in the near-surface sediments resulting in the diffusive transport of these species into the water column, where between-site differences in the depths of release can be linked to differences in redox zonation. The presence or absence of emergent vegetation is proposed to present a dominant control on sedimentary redox conditions as well as on the recycling and persistence of reduced Se species in bottom waters.

Elemental contaminants in livers of mute swans on lakes Erie and St. Clair.

Contaminant inputs to the lower Great Lakes (LGL) have decreased since the 1960s and 1970s, but elemental contaminants continue to enter the LGL watershed at levels that are potentially deleterious to migratory waterfowl. Mute swans (Cygnus olor) using the LGL primarily eat plants, are essentially nonmigratory, forage exclusively in aquatic systems, and have increased substantially in number in the last few decades. Therefore, mute swans are an ideal sentinel species for monitoring elemental contaminants available to herbivorous and omnivorous waterfowl that use the LGL. We investigated hepatic concentrations, seasonal dynamics, and correlations of elements in mute swans (n = 50) collected at Long Point, Lake Erie, and Lake St. Clair from 2001 to 2004. Elements detected in liver at levels potentially harmful to waterfowl were copper (Cu) [range 60.3 to 6063.0 µg g(-1) dry weight (dw)] and selenium (SE; range 1.6 to 37.3 µg g(-1) dw). Decreases in aluminum, Se, and mercury (Hg) concentrations were detected from spring (nesting) through winter (nonbreeding). Elemental contaminants may be more available to waterfowl during spring than fall and winter, but study of seasonal availability of elements within LGL aquatic systems is necessary. From April to June, 68% of mute swans had Se levels >10 µg g(-1), whereas only 18% of swans contained these elevated levels of Se from July to March. An increase in the number of mute swans at the LGL despite elevated levels of Cu and Se suggests that these burdens do not substantially limit their reproduction or survival. Se was correlated with Cu (r = 0.85, p < 0.01) and Hg (r = 0.65, p < 0.01), which might indicate interaction between these elements. Some element interactions decrease the toxicity of both elements involved in the interaction. We recommend continued research of elemental contaminant concentrations, including detailed analyses of biological pathways and element forms (e.g., methylmercury) in LGL waterfowl to help determine the role of element interactions on their toxicity in waterfowl.

The geochemical behavior of trace metals and nutrients in submerged sediments of the Three Gorges Reservoir and a critical review on risk assessment methods.

Permanently submerged sediment samples (SS) were collected in the center stream of eleven tributaries of Changjiang (Yangtze River) and at eight confluence zones in the Three Gorges Reservoir (TGR) in May and December of 2017. The work showed that aqua regia digestion is a simpler, more reliable and robust method compared to total digestion with hydrofluoric acid (HF) for the determination of trace metals (TMs) in sediment for risk assessment purpose. Our study revealed a remarkable accumulation of TMs at the confluence zones and a trend of their gradual increase toward this zone. The presence of iron and manganese (oxy)hydroxides combined with hydrodynamic conditions created by the Three Gorges Dam (TGD) and its operation are believed to play a crucial role. This work also found that concentrations of [Formula: see text] in May sediment were significantly higher than those in December, which could have been caused by both the cyclic hydrodynamic conditions and the warmer water. TOC and TP were both very low in the sediment. Although TN was 2 times higher than the Lowest Effect Level suggested by the Ontario Ministry of Environment, it is uncertain if it reflects a natural background level or due to anthropogenic activities. A critical discussion is made by comparing the conclusions obtained when using different TMs risk assessment models. Necessary precautions are highly recommended when performing this exercise. In this study, no significant risk from either TMs or nutrients was identified.

Selenium accumulation in sea ducks wintering at Lake Ontario.

Numbers of wintering sea ducks, including buffleheads (Bucephala albeola; BUFF), common goldeneyes (Bucephala clangula; COGO), and long-tailed ducks (Clangula hyemalis; LTDU), increased substantially at Lake Ontario after Dreissenid mussels (Dreissena bugensis and D. polymorpha) colonized the Great Lakes. Invertebrates, including Dreissenid mussels, are major diving duck prey items that can transfer some trace elements, such as selenium (Se) to higher trophic levels. Se can be problematic for waterfowl and it often has been detected at elevated levels in organisms using the Great Lakes. There are, however, few data on hepatic Se concentrations in sea ducks, particularly during the winter at Lake Ontario. In this study, we evaluated interspecific differences and temporal trends in hepatic Se concentrations among BUFF (n = 77), COGO (n = 77), and LTDU (n = 79) wintering at Lake Ontario. All three species accumulated Se throughout winter, but COGO did so at a higher rate than did BUFF and LTDU. Overall, Se concentrations were higher in LTDU [mean = 22.7; 95% CI = 20.8-24.8 microg/g dry weight (dw)] than in BUFF ([mean = 12.3; 95% CI = 11.6-13.1 microg/g dw) and COGO ([mean = 12.0; 95% CI = 10.7-3.5 microg/g dw) throughout the winter. Se concentrations were deemed elevated (>33 microg/g dw) in 0%, 5%, and 19% of BUFF, COGO, and LTDU, respectively. Presently there are no data on Se toxicity end points for these species, so it is unclear how acquiring concentrations of these magnitudes affect their short- and long-term health or reproduction.

Preparation of a new high-performance calcium-based desulfurizer using a steam jet mill.

Dry flue gas desulfurization is an increasingly attractive technique in SO2 emission control. However, the low efficiency in dry desulphurization is the bottleneck of this technology. To find a high-performance desulfurizer is an urgent task. This research utilized a steam jet mill digestion to prepare a desulfurizer at steam temperature of 220 ℃ and pressure of 0.45 MPa, and compared this product with the conventional digestion desulfurizer. Our results show that the digestion in steam jet mill can transform all the calcium oxide into calcium hydroxide. The calcium hydroxide had good fluidity and with honeycomb morphological characteristics. The experiments of dry flue gas desulfurization demonstrated that under the relative humidity of 15, 30 and 45%, the total dead times were 340, 640 and 720 min, the working time for keeping a 100% desulfurization efficiency were 120, 420 and 580 min, and the total sulfur fixation were 124.05, 274.58 and 332.09 mg. Compared with the desulfurizer by conventional dry digestion, the desulfurizer prepared in this research had a significantly superior performance. This experiment provides a new method for high-performance desulfurizer via quicklime digestion, which is an important step in pushing forward the application of dry flue gas desulfurization.

H2S Protects against Cardiac Cell Hypertrophy through Regulation of Selenoproteins.

Cardiac hypertrophy is defined as the enlargement of the cardiac myocytes, leading to improper nourishment and oxygen supply due to the increased functional demand. This increased stress on the cardiac system commonly leads to myocardial infarction, contributing to 85% of all cardiac-related deaths. Cystathionine gamma-lyase- (CSE-) derived H2S is a novel gasotransmitter and plays a critical role in the preservation of cardiac functions. Selenocysteine lyase (SCLY) has been identified to produce H2Se, the selenium homologue of H2S. Deficiency of selenium is often found in Keshan disease, a congestive cardiomyopathy. The interaction of H2S and H2Se in cardiac cell hypertrophy has not been explored. In this study, cell viability was evaluated with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Oxidative stress and cell size were observed through immunostaining. The expression of genes was determined by real-time PCR and western blot. Here, we demonstrated that incubation of rat cardiac cells (H9C2) with H2O2 lead to increased oxidative stress and cell surface area, which were significantly attenuated by pretreatment of either H2S or H2Se. H2S incubation induced SCLY/H2Se signaling, which next caused higher expressions and activities of selenoproteins, including glutathione peroxidase and thioredoxin reductase. Furthermore, deficiency of CSE inhibited the expressions of SCLY and selenoprotein P in mouse heart tissues. We also found that both H2S and H2Se stimulated Nrf2-targeted downstream genes. These data suggests that H2S protects against cardiac hypertrophy through enhancement of a group of antioxidant proteins.

Selective adsorption of uranyl and potentially toxic metal ions at the core-shell MFe2O4-TiO2 (M=Mn, Fe, Zn, Co, or Ni) nanoparticles.

Potentially toxic metal ions (Xn+: Rb+, Sr2+, Cr3+, Mn2+, Ni2+, Zn2+, Cd2+) usually coexist with uranyl (UO2+), which will have a great influence on the selective adsorption process. Here, the core-shell MFe2O4-TiO2 (M = Mn, Fe, Zn, Co, or Ni) nanoparticles were synthesized and assessed as new selective adsorbents. The results reveal that TiO2(101) preferentially grows along the MFe2O4(311)/(111) orientation. The M2+ ions as the mediators transfer the holes from MFe2O4 to TiO2, at the conduction bands. On the TiO2(101) surfaces and TiO2(101)-TiO2(101) gaps, the paired active electrons mainly complex with water molecules as hydroxyl radicals to capture Xn+ ions, forming an ion layer to block UO22+ from being adsorbed. Simultaneously, it should be noted that an interesting adsorption pathway was UO22+ being horizontally and irreversibly adsorbed in the MFe2O4(311)/(111)-TiO2(101) interface, and therein, the stable adsorption capacity was found to be 66.78 mg g-1 in the MnFe2O4(311)/(111)-TiO2(101) interface. Finally, a mechanism of hybrid orbitals between MnFe2O4-TiO2 and UO2+-Xn+ was proposed.

The competitive role of organic carbon and dissolved sulfide in controlling the distribution of mercury in freshwater lake sediments.

The detailed distribution of mercury was studied in sediments and porewaters of two freshwater lakes, which were selected because of the contrasting conditions they present at their respective sediment-water interface (SWI). One lake is characterized by a SWI that remains oxic all year long whereas the other one shows a clear seasonal variation with the evolution of strongly anoxic conditions through the summer season. The results of the study clearly identify the importance of redox conditions on the geochemical behaviour of Hg at the SWI of both lakes but a very limited influence of an oxidized layer enriched in Fe and Mn oxyhydroxides at the top of the sediment of the oxic lake. In both lakes, a competitive effect on the cycling and mobility of the element was observed between natural organic matter and amorphous or organo-sulfide compounds. The proportion of Hg associated to natural organic matter in sediments showed a general increase with sediment depth. A fraction containing elemental Hg and Hg suspected to be bound to iron sulfides and organo-sulfides constituted the other major fraction of solid Hg in the sediments of both lakes. This second pool of Hg was generally larger at the top of the sediment where the production of dissolved sulfides is usually more detectable and it decreases with depth, suggesting that the metal is partially transferred from one pool being the sulfides including amorphous FeS and organo-sulfides to the organic matter pool. Methyl Hg represented less than 1% of the total Hg in sediments of both lakes. Our results obtained at different times of the summer season from two lakes contrasted by their SWI emphasize the competitive or alternating role played by dissolved and solid natural organic matter and sulfides on the fate of Hg in freshwater systems.

Hydrological and biogeochemical controls governing the speciation and accumulation of selenium in a wetland influenced by mine drainage.

Controls governing the speciation and accumulation of Se in a 3.7-ha marsh influenced by mine drainage were assessed through examination of water balance, water quality, sediment, and plant tissue components. Over the 8-mo study period (April through November, 2009), mean monthly flows ranged from 1600 to 2300 m3 d-1 (hydraulic retention time of 1-3 d). Total Se concentrations in the marsh outflow were lower than the inflow by 0.4 to 6.2 µg L-1 (mean difference = 3.3 µg L-1 ), illustrating Se removal. The Se accumulation pathways are illustrated by elevated concentrations of Se in sediments (3-35 mg kg-1 dry wt) as well as in below-ground (2-41 mg kg-1 dry wt; mean = 10 mg kg-1 dry wt) and above-ground (0.8-6.3 mg kg-1 dry wt; mean = 2 mg kg-1 dry wt) emergent plant tissues. Redox stratification in the shallow water column had a marked effect on Se speciation and behavior, illustrating bottom water removal of dissolved selenate in suboxic horizons and increased mobility of dissolved organo-Se. Mass balance data yielded inflow and outflow loading rates for Se of 27 and 23 g d-1 , respectively (net accumulation rate of 4 g d-1 or 0.11 mg m2 d-1 ). The rate of accumulation as calculated from the mass balance agrees with independently measured rates of Se accumulation in sediments for the site (3.6-8.1 g d-1 or 0.10-0.22 mg m-2 d-1 ). Environ Toxicol Chem 2018;37:1824-1838. © 2018 SETAC.

Adsorption of Cadmium on Degraded Soils Amended with Maize-Stalk-Derived Biochar.

Biochar has been extensively proven to distinctively enhance the sorption capacity of both heavy metal and organic pollutants and reduce the related environmental risks. Soil pollution and degradation widely coexist, and the effect of biochar addition on adsorption behavior by degraded soils is not well understood. Four degraded soils with different degrees of degradation were amended with maize-stalk-derived biochar to investigate the adsorption of cadmium using batch methods. The maximum adsorption capacity (Qm) of degraded soil remarkably decreased in comparison with undegraded soil (5361 mg·kg-1→170 mg·kg-1), and the Qm of biochar increased with increasing pyrolysis temperature (22987 mg·kg-1→49016 mg·kg-1) which was much higher than that of soil. The addition of biochar can effectively improve the cadmium adsorption capacity of degraded soil (36⁻328%). The improving effect is stronger when increasing either the degradation level or the amount of added biochar, or the pyrolysis temperature of biochar. Contrary to the general soil⁻biochar system, adsorption of Cd was not enhanced but slightly suppressed (7.1⁻36.6%) when biochar was incorporated with degraded soils, and the adsorptivity attenuation degree was found to be negatively linear with SOM content in the degraded soil⁻biochar system. The results of the present study suggest that more attention on the adsorption inhibition and acceleration effect difference between the soil⁻biochar system and the degraded soil⁻biochar system is needed.

Detoxification of selenite and mercury by reduction and mutual protection in the assimilation of both elements by Pseudomonas fluorescens.

A study on the assimilation and detoxification of selenium and mercury and on the interaction between these two elements was conducted on Pseudomonas fluorescens. P. fluorescens was able to convert separately both elements to their elemental forms, which are less toxic and biologically less available. To study the converting mechanism of selenite to elemental Se, cells were grown in the presence of various selenite concentrations and several parameters such as extracellular protein concentrations, pH, carbohydrate concentrations, isocitrate dehydrogenase (ICDH) and malic enzyme were monitored. Transmission electron microscopy (TEM) and various analytical methods were applied to confirm the interaction between selenium and cell. The former appeared as a red precipitate localized predominantly in the consumed culture medium. P. fluorescens also resisted to the toxic effect of mercury by converting Hg2+ to the volatile and less toxic form Hg0. Mercury reductase was likely responsible for the conversion of Hg2+ to Hg0. More importantly, the interaction between mercury and selenium was also studied. The presence of selenite significantly reduced the accumulation of mercury in P. fluorescens. It was also interesting to note that mercury appeared to behave as a protecting agent against selenium intoxication as the bioaccumulation of Se was also inhibited by this metal. The formation of Se-Hg complexes could explain this mutual protective effect. No precipitate of elemental Se could be detected when Hg was present in the cultures.

Validation of an updated fractionation and indirect speciation procedure for inorganic arsenic in oxic and suboxic soils and sediments.

A sequential extraction procedure (SEP) for the speciation analysis of As(III) and As(V) in oxic and suboxic soils and sediments was validated using a natural lake sediment and three certified reference materials, as well as spike recoveries of As(III) and As(V). Many of the extraction steps have been previously validated making the procedure useful for comparisons to similar previous SEP studies. The novel aspect of this research is the validation for the SEP to maintain As(III) and As(V) species. The proposed five step extraction procedure includes the extraction agents (NH4)2SO4, NH4H2PO4, H3PO4 + NH2OH·HCl, oxalate + ascorbic acid (heated), and HNO3 + HCl + HF, targeting operationally defined easily exchangeable, strongly sorbed, amorphous Fe oxide bound, crystalline Fe oxide bound, and residual As fractions, respectively. The third extraction step, H3PO4 + NH2OH·HCl, has not been previously validated for fraction selectivity. We present evidence for this extraction step to target As complexed with amorphous Fe oxides when used in the SEP proposed here. All solutions were analyzed on ICP-MS. The greatest concentrations of As were extracted from the amorphous Fe oxide fraction and the dominant species was As(V). Lake sediment materials were found to have higher As(III) concentrations than the soil materials. Because different soils/sediments have different chemical characteristics, maintenance of As species during extractions must be validated for specific soil/sediment types using spiking experiments.

Valence properties of tellurium in different chemical systems and its determination in refractory environmental samples using hydride generation - Atomic fluorescence spectroscopy.

Using HG - AFS as a powerful tool to study valence transformations of Te, we found that, in presence of HCl and at high temperature, Te can form volatile species and be lost during sample digestion and pre-reduction steps. It was also noticed that the chemical valences of Te can be modified under different chemical and digestion conditions and even by samples themselves with certain matrices. KBr can reduce Te(VI) to Te(IV) in 3.0 M HCl at 100 °C, but when HNO3 was >5% (v/v) in solution, Br2 was formed and caused serious interference to Te measurements. HCl alone can also pre-reduce Te(VI) to Te(IV), only when its concentration was ≥6.0 M (100 °C for 15min). Among 10 studied chemical elements, only Cu(2+) caused severe interference. Thiourea is an effective masking agent only when Cu(2+) concentration is equal or lower than 10 mg/L. Chemical reagents, chemical composition of sample, as well as the modes of digestion can greatly affect Te valences, reagent blanks and analytical precisions. A protocol of 2-step-digestion followed by an elimination of HF is proposed to minimize reagent blank and increase the signal/noise ratios. It is important to perform a preliminary test to confirm whether a pre-reduction step is necessary; this is especially true for samples with complex matrices such as those with high sulfide content. The analytical detection limits of this method in a pure solution and a solid sample were 100 ng/L and 0.10 ± 0.02 µg/g, respectively.