Speciation Experiments Research Articles

Waste Bauxite Residue Valorization as Trace Metal Sorbent: Application to Acid Mine Drainage Remediation

With an output of more than two million tons of alumina per year, Venezuela is an important producer. As observed, this mining extraction activity generates a large number of by-products poorly valorized for many reasons (economic, technical, and due to environmental standards and regulations) Venezuela production generates wastes (more than 15 million of m3) called red muds, which are dumped in old lagoons near the Orinoco river or stored. This sludge has a high alkalinity (pH between 10 and 13) and a chemical composition containing some heavy metals (40 ppm Cr, 107 ppm La, 178 ppm Ce) that means it is considered environmentally problematic waste. However, their mineralogical, textural and structural characteristics make them adsorption materials. So, the aim of the study presented here was to investigate the sorption properties of these residues in the case of treatment of water from acid mine drainage. In fact, with an important reactive surface, their capacities to trap by adsorption trace elements such as cadmium, lead or zinc has been studied. Batch sorption tests revealed significant retention of contaminants such as Pb, Zn and As. These retention processes were interpreted using the Langmuir isotherm model. The promising first results indicate that the red mud named Venezuelan bauxite residue (VBR) reveals its great potential as a sorbent of inorganic pollutants. The sorption process is chemically dependent and efficient for certain pH and IS ranges. In addition, the material showed a strong affinity for the adsorption of arsenate (As5+). This was observed during post adsorption chemical speciation experiments, through the very high affinity of this element for the least mobile fractions, including oxyhydroxides mobile fractions, including Fe oxyhydroxides (amorphous). Nevertheless, these mining by-products could be considered as valuable absorbent materials. Despite this promising results, further studies are required to evaluate their potential in different conditions (dynamic tests, pH, IS, inorganic and organic contaminants, concentration and time effect).

In-cell Catalysis by Tethered Organo-Osmium Complexes Generates Selectivity for Breast Cancer Cells.

Anticancer agents that exhibit catalytic mechanisms of action offer a unique multi-targeting strategy to overcome drug resistance. Nonetheless, many in-cell catalysts in development are hindered by deactivation by endogenous nucleophiles. We have synthesised a highly potent, stable Os-based 16-electron half-sandwich ('piano stool') catalyst by introducing a permanent covalent tether between the arene and chelated diamine ligand. This catalyst exhibits antiproliferative activity comparable to the clinical drug cisplatin towards triple-negative breast cancer cells and can overcome tamoxifen resistance. Speciation experiments revealed Os to be almost exclusively albumin-bound in the extracellular medium, while cellular accumulation studies identified an energy-dependent, protein-mediated Os accumulation pathway, consistent with albumin-mediated uptake. Importantly, the tethered Os complex was active for in-cell transfer hydrogenation catalysis, initiated by co-administration of a non-toxic dose of sodium formate as a source of hydride, indicating that the Os catalyst is delivered to the cytosol of cancer cells intact. The mechanism of action involves the generation of reactive oxygen species (ROS), thus exploiting the inherent redox vulnerability of cancer cells, accompanied by selectivity for cancerous cells over non-tumorigenic cells.

Genetic algorithm optimization of a master equation cyclopentane oxidation model against time-resolved speciation experiments

We demonstrate a new approach to constraining rate coefficients in complex chemical reaction mechanisms by master equation (ME) modeling with genetic algorithm optimization, as illustrated for low-temperature cyclopentane oxidation. Our chemical model is based on calculated R• + O2 and •QOOH + O2 potential energy surfaces and is validated against time-resolved speciation experiments, both of which we recently reported (Sheps et al., J. Phys. Chem. A, 125 (2021), 4467). A global sensitivity analysis identifies key parameters of our ME-based sub-mechanism. These parameters are perturbed, and modeled species concentrations are compared with experimental results at 450 – 575 K, to constrain the rate parameters for two major reaction pathways: 1) isomerization of the peroxy radical, ROO•, via H transfer to the carbon-centered •QOOH, radical and 2) HO2 elimination from ROO• to form cyclopentene. The optimization yields temperature-dependent rate coefficients with associated uncertainties for isomerization that are approximately a factor of two lower than our initially calculated values and those from literature. In contrast, the rate coefficients for the HO2 elimination channel are similar to our initial model values and those from the literature at 450 – 800 K but increasingly exceed these values above 800 K. By combining our optimized sub-mechanism with a comprehensive cyclopentane combustion mechanism (Lockachari et al., Combust. Flame, 225 (2021), 255), we find good extrapolation to higher temperatures when tested against our time-resolved speciation data at 600 – 650 K and against literature jet-stirred reactor speciation data at 700 – 1200 K.

Studies on stabilization effect of calcium dihydrogen phosphate (Ca(H2PO4)2) -on Lead(Pb)-contaminated Soil

This study investigated the effect of Ca(H2PO4)2 on pH, leaching toxicity and speciations of soil before and after leaching on it. Different amounts of Ca(H2PO4)2 were added to Pb-contaminated soil and stabilized for 30 days. The changes of pH and leaching toxicity of Pb-contaminated soil were tracked during that period. The content of Pb in soil before and after leaching was also determined after 30 days of stabilization. Results showed that the pH of the Pb-contaminated soil didn’t change much with the addition of-Ca(H2PO4)2. When the amount of Ca(H2PO4)2 reached to 3 wt%, the leaching toxicity met the standard limiting level of groundwater class III of China. The change of leaching toxicity was found to be mainly affected by the water-soluble fraction and mild acid-soluble fraction of lead. The speciation experiments revealed that the changes on reducible, oxidizable, and residual fractions are significant, while there are only minor changes on the water-soluble and mild acid-soluble fractions. X-ray diffractometry (XRD) analysis showed that Pb9(PO4)6 and Pb2P2O7 substances were generated in the stabilized soil. The stabilization mechanism of Ca(H2PO4)2 was mainly attributed to the formation of insoluble Pb phosphate precipitates through interactions between the heavy metal Pb and the Ca(H2PO4)2. In such a way the active species of Pb in the soil can be successfully stabilized. Novelty statement At present, the leaching toxicity is currently used for the evaluation of stabilization effect of heavy metal contaminated soil. The speciation distribution of stabilized contaminated soil before and after leaching has rarely been studied, and the research on stabilizing contaminated soil after leaching is less. Therefore, this paper mainly studies the stabilization effect through the speciation changes of contaminated soil before and after leaching, providing a new idea and method for the evaluation of the stabilization effect of contaminated soil remediation. Ca(H2PO4)2 has no significance in pH of contaminated soil: 5.05＜pH＜5.5. The content of the water-soluble fraction and the mild acid-soluble fraction of Pb were availably reduced by Ca(H2PO4)2. The content of the water-soluble fraction and the mild acid-soluble fraction of Pb has no marked change before and after leaching. The stabilization mechanism of Ca(H2PO4)2 is through interaction between the Pb in the soil and phosphate to form insoluble substances of lead phosphate. Ca(H2PO4)2 has a good effect on the stabilization of lead-contaminated soil.

Ab initio molecular dynamics simulations and experimental speciation study of levofloxacin under different pH conditions.

Levofloxacin is an extensively employed broad-spectrum antibiotic belonging to the fluoroquinolone class. Despite the extremely wide usage of levofloxacin for a plethora of diseases, the molecular characterization of this antibiotic appears quite poor in the literature. Moreover, the acid-base properties of levofloxacin - crucial for the design of efficient removal techniques from wastewaters - have never extensively been investigated so far. Here we report on a study on the behavior of levofloxacin under standard and diverse pH conditions in liquid water by synergistically employing static quantum-mechanical calculations along with experimental speciation studies. Furthermore, with the aim of characterizing the dynamics of the water solvation shells as well as the protonation and deprotonation mechanisms, here we present the unprecedented quantum-based simulation of levofloxacin in aqueous environments by means of state-of-the-art density-functional-theory-based molecular dynamics. This way, we prove the cooperative role played by the aqueous hydration shells in assisting the proton transfer events and, more importantly, the key place held by the nitrogen atom binding the methyl group of levofloxacin in accepting excess protons eventually present in water. Finally, we also quantify the energetic contribution associated with the presence of a H-bond internal to levofloxacin which, on the one hand, stabilizes the ground-state molecular structure of this antibiotic and, on the other, hinders the first deprotonation step of this fluoroquinolone. Among other things, the synergistic employment of quantum-based calculations and speciation experiments reported here paves the way toward the development of targeted removal approaches of drugs from wastewaters.

Effects of stereoisomeric structure and bond location on the ignition and reaction pathways of hexenes

AbstractThe current work presents new experimental autoignition and speciation data on the two cis‐hexene isomers: cis‐2‐hexene and cis‐3‐hexene. The new data provide insights on the effects of carbon‐carbon double bond location and stereoisomeric structures on ignition delay times and reaction pathways for linear hexene isomers. Experiments were performed using the University of Michigan rapid compression facility to determine ignition delay times from pressure‐time histories. Stoichiometric (ϕ = 1.0) mixtures at dilution levels of inert gas to O2 = 7.5:1 (mole basis) were investigated at an average pressure of 11 atm and temperatures from 809 to 1052 K. Speciation experiments were conducted at T = 900 K for the two cis‐hexene isomers, where fast‐gas sampling and gas chromatography were used to identify and quantify the two cis‐hexene isomers and stable intermediate species. The ignition delay time data showed negligible sensitivity to the location of the carbon‐carbon double bond and the stereoisomeric structure (cis‐trans), and the species data showed no correlation with the stereoisomeric structure, but there was a strong correlation of some of the measured species with the location of the double bond in the hexene isomer. In particular, 2‐hexene showed strong selectivity to propene, acetaldehyde, and 1,3‐butadiene, and 3‐hexene showed selectivity to propanal. Model predictions of ignition delay times were in excellent agreement with the experimental data. There was generally good agreement for the model predictions of the species data for 2‐hexene; however, the mechanism overpredicted some of the small aldehyde (C2‐C4) species for 3‐hexene. Reaction pathway analysis indicates the hexenes are almost exclusively consumed by H‐atom abstraction reactions at the conditions studied (P = 11 atm, T > 900 K), and not by C3‐C4 scission as observed in high‐temperature (>1300 K) hexene ignition studies. Improved estimates for 3‐hexene + OH reactions may improve model predictions for the species measured in this work.

Fragmentation mechanisms from electron-impact of complex cyclic ethers formed in combustion

Cyclic ethers are important intermediates involved in degenerate chain-branching reactions during hydrocarbon and biofuel oxidation at temperatures below 1000 K. Depending on the molecular structure of the parent species, e.g. 1-butanol, butanone, or diethyl ether, cyclic ethers can include additional functional groups, such as an alcohol, carbonyl, or a second ether group. Electron-impact mass spectrometry (EI-MS) is a commonly used diagnostic to infer the molecular structure of cyclic ethers, and while mass spectra of simple cyclic ethers using EI are abundant in literature, measurements and related fragmentation patterns of complex cyclic ethers containing multiple functional groups are not, yet are important for determining the presence of species and inferring reaction mechanisms in combustion. The measurements in the present work provide reference EI mass spectra, which enable direct identification of cyclic ether species that are relevant to experimental chemical kinetics measurements of hydrocarbon and biofuel combustion.EI-MS measurements were conducted for 29 cyclic ethers with diverse functional groups such as alcohols, carbonyls, and alkyl substituents of varying length, 10 of which are reported for the first time: 2,3-epoxypentane, 3,4-epoxybutanol, (2-methyloxiranyl)methanol, 2,3-epoxybutanol, 1-(oxiran-2-yl)ethan-1-one, 3,4-epoxycyclohexene, 4,5-epoxycyclohexene, 2-methyloxetane, tetrahydrofuran-3-one, and 2-hydroxytetrahydrofuran. The objective of the present work is two-fold: (i) to provide reference measurements of EI mass spectra for complex combustion intermediates and (ii) to analyze fragmentation patterns of each species to assess the applicability of conventional mechanisms that are commonly employed for discerning molecular structure. The impetus for the latter objective is that, in the majority speciation experiments, EI mass spectra and fragmentation mechanisms are not reported, which raises open questions concerning the reliability of conventional mechanisms to define structural isomers of multi-functional cyclic ethers.In the present work, four conventional mechanisms were employed to analyze fragmentation patterns in the mass spectra: α-cleavage, inductive effect, hydrogen rearrangement, and transannular cleavage. The most common mechanism for the cyclic ethers was inductive cleavage, followed by α-cleavage or hydrogen rearrangement. Multi-functional cyclic ethers were more likely to undergo transannular cleavage occurring across the ring in a single step. For several species, however, abundant ion peaks in the mass spectra are not explained using conventional mechanisms. The present results highlight the importance of reference measurements of EI mass spectra for identifying complex molecules in speciation experiments, which is relevant given that ion fragments of the same mass-to-charge ratio (m/z) are common for species of the same mass.

The [Rh(Xantphos)]+ catalyzed hydroboration of diphenylacetylene using trimethylamine-borane

The rhodium(I) complex [Rh(κ3-P,O,P-Xantphos)(η2-PhC≡CPh)][BArF4] (ArF = 3,5-(CF3)2C6H4) is an effective catalyst for the cis-selective hydroboration of the alkyne diphenylacetylene using the amine-borane H3B·NMe3. Detailed mechanistic studies, that include initial rate measurements, full simulation of temporal profiles for a variety of catalyst and substrate concentrations, and speciation experiments, suggest a mechanism that involves initial coordination of alkyne and a saturation kinetics regime for amine-borane binding. The solid-state molecular structure of a model complex that probes the proposed resting state is also reported, [Rh(κ3-P,O,P-Xantphos)(NCMe)(η2-PhC≡CPh)][BArF4].

Mercury distribution in the upper troposphere and lowermost stratosphere according to measurements by the IAGOS-CARIBIC observatory: 2014–2016

Abstract. Mercury was measured onboard the IAGOS-CARIBIC passenger aircraft from May 2005 until February 2016 during near monthly sequences of mostly four intercontinental flights from Germany to destinations in North and South America, Africa and South and East Asia. Most of these mercury data were obtained using an internal default signal integration procedure of the Tekran instrument but since April 2014 more precise and accurate data were obtained using post-flight manual integration of the instrument raw signal. In this paper we use the latter data.Increased upper tropospheric total mercury (TM) concentrations due to large scale biomass burning were observed in the upper troposphere (UT) at the equator and southern latitudes during the flights to Latin America and South Africa in boreal autumn (SON) and boreal winter (DJF). TM concentrations in the lowermost stratosphere (LMS) decrease with altitude above the thermal tropopause but the gradient is less steep than reported before. Seasonal variation of the vertical TM distribution in the UT and LMS is similar to that of other trace gases with surface sources and stratospheric sinks. Speciation experiments suggest comparable TM and gaseous elementary mercury (GEM) concentrations at and below the tropopause leaving little space for Hg2+ (TM − GEM) being the dominating component of TM here. In the stratosphere significant GEM concentrations were found to exist up to 4 km altitude above the thermal tropopause. Correlations with N2O as a reference tracer suggest stratospheric lifetimes of 72±37 and 74±27 years for TM and GEM, respectively, comparable to the stratospheric lifetime of COS. This coincidence, combined with pieces of evidence from us and other researchers, corroborates the hypothesis that Hg2+ formed by oxidation in the stratosphere attaches to sulfate particles formed mainly by oxidation of COS and is removed with them from the stratosphere by air mass exchange, gravitational sedimentation and cloud scavenging processes.

Investigation of mercury adsorption and cyclic mercury retention over MnOx/γ-Al2O3 sorbent

In this study mercury sorbent based on manganese oxides impregnated γ-alumina was synthesized. Mercury retention characteristics were investigated by mercury speciation and thermal desorption experiments. No gaseous mercuric oxide was observed in mercury speciation experiments with a mercury mass balance ratio of 89.11%. Maximum mercury desorption peak at 480 °C indicated that mercury was adsorbed in the form of mercuric oxide. Three cycles of mercury retention were tested with different thermal treatment in-between to evaluate the cyclic performance. Changes in surface phase and manganese chemistry before and after thermal treatment were characterized by XRD and XPS. Deterioration in mercury retention capacity was observed after thermal desorption at 500 °C, which was interpreted with reduced initial adsorption rate calculated by Pseudo-second order kinetic model. XPS studies suggested that atomic ratios of Mn4+/(Mn4++Mn3+) decreased from 73.2% to 32.3% and 33.9% after thermal desorption in N2 and air, respectively. The reduction of MnO2 to Mn2O3 was irreversible thus the mercury retention capacity could not be restored by thermal desorption at high temperatures. Spent sorbents that were reactivated at 200 °C in air without thermal desorption at 500 °C possessed considerable cycling performance for mercury retention due to the preserved Mn4+.

Combustion chemistry of iso-octane/ethanol blends: Effects on ignition and reaction pathways

This work presents new experimental data on the ignition of iso-octane and ethanol fuel blends, including measurements of pollutant species and precursors, using the University of Michigan Rapid Compression Facility (UM RCF). Ignition delay times were determined from pressure–time histories of ignition experiments for stoichiometric mixtures of iso-octane, ethanol, and 5, 11, 26, 50 and 67% by volume iso-octane and ethanol blends with air. A range of temperatures (900–1080 K) were studied at a pressure of 10 atm. Speciation experiments were performed for pure iso-octane (E0), pure ethanol (E100) and a 50% by volume blend of the two fuels (E50) at 10 atm and ∼930 K. Fast-gas sampling, gas chromatography and mass spectrometry were used to identify and quantify 14 stable intermediate species formed during the ignition delay periods for the three fuels. The measurements of eight stable intermediates: iso-butene (i-C4H8, 2-methyl-1-propene), propene (C3H6), ethanal (CH3CHO), ethene (C2H4), ethane (C2H6), methane (CH4), carbon monoxide (CO), carbon dioxide (CO2) were considered in detail and were used to describe reaction pathways important during iso-octane and ethanol ignition and how they were altered for iso-octane/ethanol blends. Simulations were carried out using a detailed reaction mechanism for gasoline surrogates available in the literature and the agreement with the ignition and speciation experiments was generally excellent (within the experimental uncertainty and expected computational uncertainty) for ignition delay times and for the species time-histories, with a few small discrepancies. The results indicate the reaction pathways of iso-octane and ethanol in the blend develop in parallel with a shared radical pool with no significant fuel-to-fuel interactions.

Combustion Chemistry of Ethanol: Ignition and Speciation Studies in a Rapid Compression Facility.

Ethanol remains the most important alternative fuel for the transportation sector. This work presents new experimental data on ethanol ignition, including stable species measurements, obtained with the University of Michigan rapid compression facility. Ignition delay times were determined from pressure histories of ignition experiments with stoichiometric ethanol-air mixtures at pressures of ∼3-10 atm. Temperatures (880-1150 K) were controlled by varying buffer gas composition (Ar, N2, CO2). High-speed imaging was used to record chemiluminescence during the experiments, which showed homogeneous ignition events. The results for ignition delay time agreed well with trends on the basis of previous experimental measurements. Speciation experiments were performed using fast gas sampling and gas chromatography to identify and quantify ethanol and 11 stable intermediate species formed during the ignition delay period. Simulations were carried out using a chemical kinetic mechanism available in the literature, and the agreement with the experimental results for ignition delay time and the intermediate species measured was excellent for the majority of the conditions studied. From the simulation results, ethanol + HO2 was identified as an important reaction at the experimental conditions for both the ignition delay time and intermediate species measurements. Further studies to improve the accuracy of the rate coefficient for ethanol + HO2 would improve the predictive understanding of intermediate and low-temperature ethanol combustion.

Quantitative evaluation of cellular uptake, DNA incorporation and adduct formation in cisplatin sensitive and resistant cell lines: Comparison of different Pt-containing drugs

The use of Pt-containing compounds as chemotherapeutic agents facilitates drug monitoring by using highly sensitive elemental techniques like inductively coupled plasma mass spectrometry (ICP-MS). However, methodological problems arise when trying to compare different experiments due to the high variability of biological parameters. In this work we have attempted to identify and correct such variations in order to compare the biological behavior of cisplatin, oxaliplatin and pyrodach-2 (a novel platinum-containing agent). A detailed study to address differential cellular uptake has been conducted in three different cell lines: lung adenocarcinoma (A549); cisplatin-sensitive ovarian carcinoma (A2780); and cisplatin-resistant ovarian carcinoma (A2780cis). The normalization of Pt results to cell mass, after freeze-drying, has been used to minimize the errors associated with cell counting. Similarly, Pt accumulation in DNA has been evaluated by referencing the Pt results to the DNA concentration, as measured by 31P monitoring using flow-injection and ICP-MS detection. These strategies have permitted to address significantly lower Pt levels in the resistant cells when treated with cisplatin or oxaliplatin as well as an independent behaviour from the cell type (sensitive or resistant) for pyrodach-2. Similarly, different levels of incorporation in DNA have been found for the three drugs depending on the cell model revealing a different behavior regarding cell cisplatin resistance. Further speciation experiments (by using complementary HPLC–ICP-MS and HPLC–ESI-Q-TOF MS) have shown that the main target in DNA is still the N7 of the guanine but with different kinetics of the ligand exchange mechanism for each of the compounds under evaluation.

Speciation study of the heavy metals in commercially available recharge cards coatings in Nigeria and the health implication

This work assessed levels of heavy metals exposure from silver coatings of mobile phones recharge cards of three major companies (designated as A, B and C) with price denominations ▪ 100, ▪ 200 and ▪ 400 from companies A, B and C respectively, which were carefully scratched using a plastic scraper into a glass tube. The coatings were acid digested for total metal concentration, while speciation experiment for Mn, Cu, Cd and Pb was carried out. Total metals and speciation analysis were done using AAS and XRF techniques. The total metal concentration from XRF analysis was in the range: Ca (70–2140 μg/g), K (20–4930 μg/g), Sc (80–270 μg/g), Ti (1530–12,580 μg/g), Fe (50–6660 μg/g), Ni (20–2040 μg/g), Cu (20–850 μg/g) and Zn (40–460 μg/g). Cr had the lowest concentration (10 μg/g) in A (▪ 400) while Ti had the highest concentration (12,580 μg/g) in C (▪ 500) for all the coatings analyzed. AAS and XRF results agreed closely except for Fe with higher concentration. A (▪ 100) contained high concentration of the metals compared with others. Speciation study identified Mn as the most mobile element when present in the environment.

Speciation Analysis of Heavy Metals in Sludge from a Wastewater Treatment Plant

The Tessiers five-stage sequential extraction procedure for extractable heavy metals determination was applied to sludge samples collected from wastewater treatment plant of Yanan city, Shaanxi province, China. According to the Tessiers guidelines, Copper (Cu), Zinc (Zn), Nickel (Ni), Cadmium (Cd) and Chromium (Cr) were determined by atomic absorption spectrometry (AAS). The heavy metal concentrations from high to low are Cu > Zn > Ni > Cr > Cd, which are lower than maximum permitted levels for agricultural use in relation to current international legislation. As shown in the speciation experiment, Cu mainly exists in organic form and sulfides, which is relatively stable. Zn with potentially hazards mainly exists in iron/manganese form. Ni mainly exists in insoluble form, which is stable and not easy to migrate to the environment. Cd with potential biological effectiveness mainly exists in acid soluble form and is easy to migrate to the environment.

Polyaluminium chloride as an alternative to alum for the direct filtration of drinking water

The efficiency of various polyaluminium chloride coagulants (PACls) was compared to the efficiency of aluminium sulfate (alum) in the coagulation–flocculation process preceding direct filtration in drinking water treatment. The comparative study consisted of two separate yet complementary series of experiments: the first series included short (5–7 h) and long (24 h) filter runs conducted at a pilot filtration plant equipped with large filter columns that simulated full-scale filters. Partially treated surface water from the Sea of Galilee, characterized by very low turbidity (∼1 NTU), was used. In the second series of experiments, speciation of aluminium in situ was investigated using the ferron assay method. Results from the pilot-scale study indicate that most PACls were as or more efficient a coagulant as alum for direct filtration of surface water without requiring acid addition for pH adjustment and subsequent base addition for re-stabilizing the water. Consequently, cost analysis of the chemicals needed for the process showed that treatment with PACl would be significantly less costly than treatment with alum. The aluminium speciation experiments revealed that the performance of the coagulant is more influenced by the species present during the coagulation process than those present in the original reagents.

Determination of free metal ion concentrations with AGNES in low ionic strength media

The determination of free metal ion concentrations of heavy metals, like Zn2+ or Cd2+, with AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) requires an adequate selection of parameters such as deposition potential (linked to the gain, [M0]/[M2+]) and deposition time. In systems with low ionic strength, the peak potential of the Differential Pulse Polarogram (DPP) measured with low supporting electrolyte is not always suitable for the computation of the gain with existing expressions. The application of AGNES with a constant potential (regardless of the ionic strength) provides a direct measurement of the metal ion activity. When working with low ionic strength solutions, the selection of appropriate instrumentation is important to avoid changes in liquid junction potentials or leakages from the employed electrodes. The deposition times (for a given gain) have not been found to be greatly affected by the probed ionic strengths when working with just metal. A new strategy for the practical implementation of AGNES to measure free metal ion concentrations in samples with low KNO3 or Ca(NO3)2 concentrations consists in the computation of the deposition potential (to reach a certain gain) from the DPP peak potential at a sufficiently high ionic strength using a new expression. A speciation experiment with Zn2+ and glycine at pHs between 4 and 7.5, where [KNO3]=0.001M, shows that this methodology works well and also proves that it is possible to perform AGNES in systems with very low ionic strength.

ADAPTATION TO DESICCATION FAILS TO GENERATE PRE- AND POSTMATING ISOLATION IN REPLICATEDROSOPHILA MELANOGASTERLABORATORY POPULATIONS

Many laboratory speciation experiments have raised allopatric populations in different environments to determine whether reproductive isolation evolves as a byproduct of adaptation (a form of ecological speciation). Few, however, have addressed the evolution of both pre- and postmating isolation or investigated the conditions affecting the process. We present results of an evolution experiment in which 12 lines of Drosophila melanogaster were derived from a common population and then independently evolved for more than 57 generations under alternative selection treatments. Six "desiccation" populations had access to food and water removed during a period of their adult lives generating strong desiccation selection, and six "starvation" populations had access to food but not water removed for the same period, generating a mild starvation stress. Substantial divergence of cuticular hydrocarbons occurred between the desiccation and starvation populations, key traits that have been implicated in sexual isolation in Drosophila. Despite this divergence, there was no detectable premating isolation between desiccation and starvation populations and postmating isolation was asymmetrical: the fitness of F1 hybrids was reduced in the desiccation but not the starvation environment. This asymmetry was likely caused by the absence of divergent selection: adaptation to desiccation appears to have come at no cost to performance in the starvation environment. Novel environments are thought to promote the evolution of reproductive isolation. Understanding the conditions that favor or hamper this remains a key challenge for speciation research.

Niobium in boreal stream waters and brackish-water sediments

The focus is on ‘non-detrital’ Nb in boreal stream waters (dissolved fraction and acid-available particulate fraction) and brackish-water/lacustrine sediments (aqua regia extractable fraction). Spatial patterns, temporal trends and speciation experiments all point to dissolved humic substances and colloidal Fe as the main control of Nb concentrations in stream waters. In addition, clay-silt deposits and/or ore deposits may be responsible for producing local streamwater Nb anomalies. In groundwater in overburden (glacial till) overlying Proterozoic granitoids, dissolved Nb concentrations were about an order of magnitude higher than in stream waters and strongly correlated with dissolved Fe. In the brackish-water sediments, the Nb concentrations (1.33–4.20 ppm) were higher than in the lacustrine ones (0.25–0.53 ppm). To explain this, we assessed the potential role of organic material, biological processes, sulphide mineralogy, silicate mineralogy and input factors. However, none of them could satisfactorily explain the observed Nb geochemical features. Although Nb can be considered relatively immobile, the data presented in this paper show that under certain conditions its abundance in the aquatic environment increases.

Adsorption and oxidation of mercury in tail-end SCR-DeNOx plants—Bench scale investigations and speciation experiments

The results of a bench scale investigation on mercury adsorption and oxidation under the conditions of tail-end DeNOx plants are reported. It was shown that HCl has a strong influence on mercury adsorption as well as mercury oxidation.Adsorption of elemental mercury and HgCl2 on a DeNOx catalyst with 2.5wt.% V2O5 is appreciably in flue gases that contain HCl in concentrations below 0.5mg/m3. Mercury adsorption increases linearly with the mercury concentration in the flue gas. The amount of HgCl2 adsorbed on the catalysts is higher than of elemental mercury, under otherwise comparable conditions. Mercury adsorption depends on the V2O5 content of the DeNOx catalyst. The nature of the adsorbed mercury species was investigated by sequential chemical extraction and X-ray absorption fine structure spectroscopy. According to these methods mercury does form a Hg–O bond on the surface of the catalysts. In terms of regeneration of mercury loaded catalysts it is of interest, that more than two-third of the adsorbed mercury can be removed by washing the DeNOx catalyst at room temperature with a dilute solution containing acetic and hydrochloric acid.In the presence of higher concentrations of HCl in the flue gas elemental mercury is no longer adsorbed but oxidized by DeNOx catalysts. The rate of oxidation decreases with increasing temperature. NO has compared to HCl only a slightly accelerating influence, whereas NH3 shows a small detrimental effect. The simultaneous presence of NO and NH3 inhibits the HCl assisted oxidation of elemental mercury strongly.