Speciation In Waters Research Articles

Mechanisms of ammonium transformation and loss in intermittently aerated leachfield soil.

Optimization of N removal in soil-based wastewater treatment systems requires an understanding of the microbial processes involved in N transformations. We examined the fate of NH in intermittently aerated leachfield mesocosms over a 24-h period. Septic tank effluent (STE) was amended with NHCl to help determine N speciation and distribution in drainage water, soil, and headspace gases. Our results show that 5.7% of the N was found in soil, 10.0% in drainage water, and 84.3% in the gas pool. Ammonium accounted for 41.7% of the soil N pool, followed by NO (29.2%), organic N (21.7%), and microbial biomass N (7.5%). In drainage water, NO constituted ∼80% of the N pool, whereas NH was absent from this pool. Nitrous oxide was the dominant form of N in the gas phase 6 h after addition of NH-amended STE to the mesocosms, after which its mass declined exponentially; by contrast, the mass of N was initially low but increased linearly with time to become the dominant form of N after 24 h. Analysis based on the isotopic enrichment of NO and N indicates that nitrification contributed 98.8 and 23.1% of the NO flux after 6 and 24 h, respectively. Our results show that gaseous losses are the main mechanism for NH removal from wastewater in intermittently aerated soil. In addition, nitrification, which is generally not considered a significant pathway for N loss in soil-based wastewater treatment, is an important source process for NO.

Tungsten speciation in sulfidic waters: Determination of thiotungstate formation constants and modeling their distribution in natural waters

Using UV/VIS spectrophotometry the equilibrium constants for the formation of monothiotungstate, WO3S2− (WO42-+H2S↔WO3S2-+H2O; log K01=3.08±0.11), dithiotungstate, WO2S22− (WO3S2-+H2S↔WO2S22-+H2O; log K12=3.22±0.22), trithiotungstate, WOS32− (WO2S22-+H2S↔WO3S2-+H2O; log K23=2.76±0.10), and tetrathiotungstate, WS42− (WO3S2-+H2S↔WS42-+H2O; log K34 ∼2.36) were determined. The equilibrium constants describing the formation of thiotungstates are approximately two orders of magnitude less than the equilibrium constants for the formation of the analogous thiomolybdates. These equilibrium constants for thiotungstates were used to model tungstate speciation in sulfidic waters. The model predicts that thiotungstate species are negligible in most natural waters, but are likely to be important in circum-neutral, anoxic waters with ⩾0.1mM S(-II) concentrations. Natural waters that are conducive to thiotungstate formation include the Black Sea, Tyro and Bannock Basins, and porewaters with high rates of sulfate reduction such as those common in salt marshes. Preliminary field investigations indicate that thiotungstate formation may lead to increased W solubility.

Spatial and seasonal variations of iron speciation in surface waters of the Subantarctic front and the Otago Continental Shelf

Here we present the longest time series of iron speciation along a coastal shelf area. A time series of a surface transect across the Otago Continental Shelf and into the high-nutrient low-chlorophyll (HNLC) Subantarctic surface water (SAW) was undertaken between 2000 and 2008 to measure the dissolved iron (DFe) concentration, organic iron-complexation parameters, as well as macronutrient concentrations and general hydrographic data. The study area contains three distinct water types: 1) neritic water; 2) modified subtropical water (STW); and 3) Subantarctic surface water (SAW). Variations in nutrient concentrations in the study area indicated that SAW is the predominant source of nitrate and phosphate to the shelf. Dissolved iron (DFe) concentrations dropped seawards from several nanomolar to sub-nanomolar levels. The dissolved iron was fully complexed with strong organic ligands (L1) in all three water types, and the ligand concentrations decreased seawards. However the ratio between [L1]/[DFe], a measure of the ligand saturation, increased from <2 in the neritic water to 10 in SAW. Seasonal trends in DFe and the L1 concentrations were only significant in SAW, where DFe was lowest in early spring and late autumn and highest in summer. The seasonal DFe maximum coincided with [L1] minimum, as well as minimum concentrations of macronutrients, indicating a shift from iron limitation in spring with potential siderophore production to probably silica limitation in summer. This study provides new insight on the driving forces of iron speciation in a coastal shelf area and HNLC waters.

Chromium geochemistry and speciation in natural waters, Iceland

Natural waters in Iceland were collected and analyzed for chromium concentration and speciation (CrIII, CrVI and CrTOT). The water sampled included non-thermal surface and spring water, surface geothermal water, and single and two-phase geothermal well discharges with sampling temperatures of 0–178°C, pH of 2.0–9.5, and total dissolved solids (TDS) of 35–4030ppm. The total Cr concentration was between <0.01 and 660ppb with highest concentrations in waters with the lowest pH. At pH>4 the measured CrIII concentration was low, generally <1ppb but with decreasing pH higher CrIII concentrations were observed reaching values of hundreds of ppb. At pH<6 no measurable CrVI was detected whereas in neutral to alkaline waters measured CrVI concentrations were as high as 3ppb, frequently dominating over CrIII. The Cr chemistry in natural waters associated with mafic rocks in Iceland is largely influenced by the water pH. At low pH Cr-containing minerals are unstable and Cr leaches into the waters as CrIII. Possible oxidation of CrIII to CrVI is minimized thermodynamically and the mobility of CrVI is further reduced by surface complexation reactions. At neutral to alkaline pH the primary Cr-containing mineral phases like titanomagnetite and chromite may be stable, limiting Cr-rock leaching. Solubility of secondary CrIII–FeIII-mineral phases may further reduce and/or limit the CrIII availability. In contrast, CrVI mobility is enhanced at a pH>8 associated with decreasing importance of mineral surface complexation. Hence, CrVI becomes an increasingly dominant form of dissolved Cr at pH above 7–8. Many groundwater drinking supplies associated with mafic rocks are characterized by moderately alkaline pH resulting in CrVI concentrations of a few ppb.

Arsenic speciation in natural sulfidic geothermal waters

The speciation of arsenic in natural sulfidic geothermal waters was studied using chemical analyses and thermodynamic aqueous speciation calculations. Samples were collected in three geothermal systems in Iceland, having contrasting H2S concentrations in the reservoir (high vs. low). The sampled waters contained 7–116ppb As and <0.01–77.6ppm H2S with pH of 8.56–9.60. The analytical setup used for the determination of arsenic species (Ion Chromatography-Hydride Generation Atomic Fluorescence Spectrometry, IC-HG-AFS) was field-deployed and the samples analyzed within ∼5min of sampling in order to prevent changes upon storage, which were shown to be considerable regardless of the sample storage method used. Nine aqueous arsenic species were detected, among others arsenite (HnAsIIIO3n-3), thioarsenite (HnAsIIIS3n-3), arsenate (HnAsVO4n-3), monothioarsenate (HnAsVSO3n-3), dithioarsenate (HnAsVS2O2n-3), trithioarsenate (HnAsVS3On-3) and tetrathioarsenate (HnAsVS4n-3). The results of the measured aqueous arsenic speciation in the natural geothermal waters and comparison with thermodynamic calculations reveal that the predominant factors determining the species distribution are sulfide concentration and pH. In alkaline waters with low sulfide concentrations the predominant species are AsIII oxyanions. This can be seen in samples from a liquid-only well, tapping water that is H2S-poor and free of oxygen. At intermediate sulfide concentration AsIII and AsV thio species become important and predominate at high sulfide concentration, as seen in two-phase well waters, which have high H2S concentrations in the reservoir. Upon oxidation, for instance due to mixing of the reservoir fluid with oxygenated water upon ascent to the surface, AsV oxyanions form, as well as AsV thio complexes if the sulfide concentration is intermediate to high. This oxidation process can be seen in samples from hot springs in the Geysir geothermal area. While the thermodynamic modeling allows for a first-order estimation of the dominant species, discrepancies between the model results and the field data highlight the fact that for such dynamic chemical systems the exact speciation cannot be calculated, thus on-site and preferentially in-situ analysis is of crucial importance.

Comparison of Modifiers for Mercury Speciation in Water by Solid Phase Extraction and High Performance Liquid Chromatography–Atomic Fluorescence Spectrometry

Diethyldithiocarbamate and 2-mercaptoethanol modifiers were compared for the preconcentration of mercury species in water by C18 solid phase extraction (SPE). The recovery values of mercury species were determined by high performance liquid chromatography–atomic fluorescence spectrometry. The eluent type, pH, chloride ion concentration, humic acid concentration, and storage time were evaluated to compare the preconcentration efficiency. L-cysteine was employed to elute the mercury compounds. Less eluent was needed for 2-mercaptoethanol modified SPE than for diethyldithiocarbamate modified SPE at an L-cysteine concentration of 0.12%. Diethyldithiocarbamate modified SPE could be used over a wider pH range and higher humic acid concentrations, whereas 2-mercaptoethanol modified SPE was less affected by the chloride concentration. Both modified SPE systems stored mercury species for 5 days, but diethyldithiocarbamate modified SPE could be stored longer. Diethyldithiocarbamate SPE provided limits of detections of 3.5, 2.5, and 4 ng · L−1 and average recoveries of 90.78 ± 3.37%, 96.79 ± 5.12%, and 84.88 ± 5.37% for mercury(II), methylmercury, and ethylmercury, respectively. The relative standard deviation was less 6.5%. For 2-mercaptoethanol modified SPE, the limits of detection were 1.4, 1, and 1.6 ng · L−1 and the recoveries were of 87.66 ± 8.45%, 86.70 ± 2.61%, and 91.31 ± 6.98% for mercury(II), methylmercury, and ethylmercury, respectively, with a relative standard deviation below 9.7%. Water should be characterized for its physical and chemical characteristics before mercury preconcentration to choose the most suitable method.

Chemical speciation in fresh, saline and hyper-saline waters

AbstractA thermodynamic model is proposed, which combines the ion association and the ion interaction models using the extended database pit2010.dat for a more precise modeling of the chemical species of micro components in natural waters of varying ionic strength (fresh, saline and hyper-saline). Compared to the ion association model, the proposed combined model more adequately describes the complex character of the ionic interactions. The performance of the combined ion association/ion interaction model compared to that of the ion association model is illustrated in case studies of several Bulgarian natural water systems of different ionic strength and type of pollution. The results are interpreted in terms of the chemical behavior of the metals and of their chemical species in the water systems, which is defined by the redox potential, pH, cationic and anionic organic and inorganic composition of the water systems and by the ability of the metals to preferentially coordinate with some anions, as well as by the stability of the corresponding species. The affinity of the transition metals towards the ligands is explained by the “hardness-softness” factor and the crystal field stabilization energy (CFSE).

The Recent Advances and Applications of Arsenic Speciation in Water

Arsenic (As) is well known as a toxic element for human beings. The toxicity, mobility,and bioavailability of As compounds is highly dependent on its chemical forms and oxidation states. Speciation analysis of trace elements is an important issue in biomedical and environmental sciences. For the past few years many studies have been performed to determine As speciation in tap water, food chain and other environmental samples. This review provides the chemical speciation of As in water analysis in recent ten years, including the separation and preconcentration techniques, chromatographic techniques, detection techniques of inorganic As and organic As species (included As-containing chemical warfare agents). The advantages of various methods, insufficient, selectivity, sensitivity, limit of detection (DL) were reviewed.

Iodine and selenium speciation in natural waters and their concentrating at landscape-geochemical barriers

Drinkable waters in Bryansk oblast are generally poor in I and Se. Possible I and Se speciation in the drinkable waters and their means of migration and concentration in soils at geochemically contrasting conditions are analyzed, and the possible reason for the high mobility of I is demonstrated to be predetermined not only by its occurrence in the form of iodide and organic complexes but also by solute mineral species (CaI+ and MgI+), with the former and the latter types of the complexes spread more widely in the polessky and opolny landscape types, respectively. Iodine complexation with alkali-earth cations under reduced neutral-weakly alkaline conditions facilitates, on the one hand, vertical iodine migration and, on the other hand, its precipitation on the carbonate barrier. The predominant solute species of Se in these environments is hydroselenide, which can form FeSe in the presence of significant Fe concentrations and be precipitated on the reduced barrier in soils of hydromorphic landscapes. The generally low total I and Se concentrations in the drinkable waters and the migration of solute compounds of radioactive I in the form of organic and inorganic complexes could likely result in a higher thyroid morbidity rate over the whole territory of Bryansk oblast, including areas contaminated with radioactive I isotopes after the accident at the Chernobyl nuclear power plant.

Determination of arsenic speciation in sulfidic waters by Ion Chromatography Hydride-Generation Atomic Fluorescence Spectrometry (IC-HG-AFS)

A method for the analysis of arsenic species in aqueous sulfide samples is presented. The method uses an ion chromatography system connected with a Hydride-Generation Atomic Fluorescence Spectrometer (IC-HG-AFS). With this method inorganic AsIII and AsV species in water samples can be analyzed, including arsenite (HnAsIIIO3n−3), thioarsenite (HnAsIIIS3n−3), arsenate (HnAsVO4n−3), monothioarsenate (HnAsVSO3n−3), dithioarsenate (HnAsVS2O2n−3), trithioarsenate (HnAsVS3On−3) and tetrathioarsenate (HnAsVS4n−3). The peak identification and retention times were determined based on standard analysis of the various arsenic compounds. The analytical detection limit was ~1–3µgL−1 (LOD), depending on the quality of the baseline. This low detection limit makes this method also applicable to discriminate between waters meeting the drinking water standard of max. 10µgL−1 As, and waters that do not meet this standard. The new method was successfully applied for on-site determination of arsenic species in natural sulfidic waters, in which seven species were unambiguously identified.

Uranium distribution in the sediment of the Mianyuan River near a phosphate mining region in China and the related uranium speciation in water

To clarify the mechanisms of uranium distribution in river sediment and its speciation in river water near a phosphate mining region, the sediment and river water in the Mianyuan River in China were investigated. Using linear correlation analysis, it was determined that uranium distribution in upstream sediment is mainly controlled by the adsorption of organic compounds (RTOC-U2=0.848), whereas distribution is controlled by physical deposition of albite (RNa-U2=0.773) in downstream sediment. In addition, it was determined that Se and As had strong and positive linear correlations with uranium in sediment, regardless of whether it was upstream or downstream sediment. This type of relationship was also found in phosphate ores, which suggests that the ore is the common source of U, Se and As in the sediment. The results of speciation-solubility modelling suggest that no precipitation of uranium minerals occurred in river water and the dominant uranium species in river water included: UO2(HPO4)22−, Ca2UO2(CO3)3 and UO2(CO3)34−. In addition, our modelling indicated the relative species distribution was mainly affected by the pH and the total phosphate concentration.

Determination of Chromium Speciation in Tap Water Using Diffusive Gradients in Thin Film Technique

Abstract A dual diffusive gradients in thin film (DGT) device method for in situ fractionation of dissolved inorganic Cr was developed by simultaneously deploying two types of DGT devices with different binding phases in tap water. The concentration of Cr(III) in the tap water determined by a DGT device with sodium poly(aspartic acid) (PASP) solution as the binding phase (PASP DGT) was 3.18 µg L−1, and the recoveries of the spiked Cr(III) were 97.9%–105.3%; the concentration of Cr(VI) in the tap water determined by a DGT device with poly(quaternary ammonium) salt (PQAS) solution as the binding phase (PQAS DGT) was 2.92 µg L−1, and the recoveries of the spiked Cr(VI) were 98.2%–107.7%. The ratios of the total Cr measured by DGT to the total Cr measured by ICP-MS were 102.9%–105.7%.

Iodine speciation in coastal and inland bathing waters and seaweeds extracts using a sequential injection standard addition flow-batch method

The present work describes the development of a sequential injection standard addition method for iodine speciation in bathing waters and seaweeds extracts without prior sample treatment. Iodine speciation was obtained by assessing the iodide and iodate content, the two inorganic forms of iodine in waters. For the determination of iodide, an iodide ion selective electrode (ISE) was used. The indirect determination of iodate was based on the spectrophotometric determination of nitrite (Griess reaction). For the iodate measurement, a mixing chamber was employed (flow batch approach) to explore the inherent efficient mixing, essential for the indirect determination of iodate. The application of the standard addition method enabled detection limits of 0.14µM for iodide and 0.02µM for iodate, together with the direct introduction of the target water samples, coastal and inland bathing waters. The results obtained were in agreement with those obtained by ICP-MS and a colorimetric reference procedure. Recovery tests also confirmed the accuracy of the developed method which was effectively applied to bathing waters and seaweed extracts.

Spatial variability of total dissolved copper and copper speciation in the inshore waters of Bermuda

Total dissolved copper (Cu) and Cu speciation were examined from inshore waters of Bermuda, in October 2009 and July–August 2010, to determine the relationship between total dissolved Cu, Cu-binding ligands and bioavailable, free, hydrated Cu2+ concentrations. Speciation was performed using competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV). Mean total dissolved Cu concentrations ranged from 1.4nM to 19.2nM, with lowest concentrations at sites further from shore, consistent with previous measurements in the Sargasso Sea, and localized Cu enrichment inshore in enclosed harbors. Ligand concentrations exceeded dissolved [Cu] at most sites, and [Cu2+] were correspondingly low at those sites, typically <10−13 M. One site, Hamilton Harbour, was found to have [Cu] in excess of ligands, resulting in [Cu2+] of 10−10.7 M, and indicating that Cu may be toxic to phytoplankton here.

Arsenic speciation in water by high-performance liquid chromatography/inductively coupled plasma mass spectrometry-method validation and uncertainty estimation

In order to obtain reliable analytical results for the separation and determination of arsenic species by high-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICP-MS), the analytical procedure must be fully validated and the measurement uncertainty of the analytical result should be estimated. The total arsenic concentration of the samples was determined by ICP-MS. Separation of the arsenic species, AsB, As(III), DMA, MMA and As(V), was accomplished by liquid chromatography, which was hyphenated to inductively coupled plasma mass spectrometry, used for detection purposes. Automated handling of these systems was achieved with Chromera software. The separation capability between the analytical signals of arsenic species, AsB-As(III), As(III)-DMA, DMA-MMA and MMA-As(V), was 1.3, 1.1, 5.1 and 4.6, respectively. The limit of detection (LOD) values ranged from 0.070 µg L(-1) for DMA to 0.13 µg L(-1) for MMA. The expanded uncertainty U [%] values for coverage factor k = 2 estimated for AsB, As(III), DMA, MMA and As(V) were 12 %, 13 %, 5.6 %, 9.6 % and 8.6 %, respectively. This study reports, for the first time, building the uncertainty budgets for five arsenic species and estimation of the expanded uncertainty (for k = 2). The qualitative and quantitative parameters determined in the validation process indicate that the presented analytical procedure can be applied for the determination of AsB, As(III), DMA, MMA and As(V) in water.

XAS study of iron speciation in soils and waters from a boreal catchment

Iron (Fe) is a key element, strongly influencing the biogeochemistry of soils, sediments and waters, but the knowledge about the variety of Fe species present in these systems is still limited. In this work we have used X-ray absorption spectroscopy (XAS) to study the speciation of Fe in soils and waters from a boreal catchment in northern Sweden. The aim was to better understand the controls of Fe speciation across different, but adjacent landscape elements including soil, soil solution, groundwater and stream water draining catchments with contrasting land characteristics. Our results showed that all samples contained mixtures of Fe(II) and Fe(III). The soils consisted of Fe phyllosilicates, Fe (hydr)oxides and Fe complexed by natural organic matter (NOM). All aqueous samples contained Fe(II)– and Fe(III)–NOM complexes, often in combination with Fe(III) (hydr)oxides that were associated with NOM. The variation in contribution from Fe–NOM and Fe (hydr)oxides was controlled by pH and total concentrations of NOM. The XAS spectra suggested formation of mononuclear Fe–NOM complexes consisting of chelate ring structures, but it could not be determined whether they originated solely from Fe(III)– or from a mixture of Fe(II)/Fe(III)–NOM complexes. Our collective results showed that the Fe speciation was highly variable across the different landscape elements and streams. This variation was manifested both in the distribution between mononuclear Fe–NOM complexes and Fe (hydr)oxides associated with NOM and between Fe(II) and Fe(III). These results highlight the complexity of Fe speciation in natural environmental systems and thus the challenges in interpreting Fe reactivity.

DBP formation and speciation in a central anatolian dam water depending on pH, TOC level, fraction and chlorine dose

&lt;p&gt;The effects of pH, NOM concentration, fractions and the chlorine dose on the formation and speciation of THMs and HAAs were determined in Altinapa Dam water (Konya/Turkey). Water sample was isolated and chlorinated at different TOC levels and pH&amp;rsquo;s. The isolate was fractioned; THM and HAA species were measured after chlorination. THM increased with increasing pH (6 to 8) whereas a consistent pH tendency could not be inferred from the HAA changes. CF is the dominant THM specie which exerts up to 91% of the total THM. The majority of total HAAs composed of MCAA, DCAA and TCAA. The hydrophobic fraction was the main THM precursor under the studied conditions although their percentage was lower than hydrophilics, whereas, hydrophilic fraction had significant contribution to HAA formation, in contrast to the general tendency for HAA. High correlation (0.97) was calculated between total THMs and HAAs.&lt;/p&gt;

Polymeric ion-imprinted nanoparticles for mercury speciation in surface waters

Selective sorption and enrichment of Hg(II) were achieved by polymeric ion-imprinted nanoparticles, prepared by copolymerization of methacrylic acid (functional monomer), trimethylolpropane trimethacrylate (cross-linking agent), 2,2′-azo-bis-isobutyronitrile (initiator) and Hg(II) complexes with chelating agent 1-pyrrolidinedithiocarboxylic acid. The particles were characterized for their morphology, composition and structure by using AFM, FTIR and elemental analysis. Extraction efficiency and selectivity of ion imprinted sorbent toward Hg(II) were studied by batch procedures. Two distinct adsorption sites were identified on the surface of the polymeric nanoparticles through Scatchard analysis performed. Adsorption process was characterized by Langmuir isotherm model. Solid phase extraction procedure was developed for Hg speciation and determination in surface waters. The accuracy of the proposed speciation scheme was confirmed by the analysis of certified reference material. Limits of quantification achieved (0.015μgL−1 for Hg(II) and 0.02μgL−1 for methylmercury) and RSD values (7–12% for both species) completely satisfy requirements of European legislation for monitoring of surface waters.

Recovery of U(VI) from aqueous media with layered double hydroxides of Zn and Al, intercalated with complexones

The ability of layered double hydroxides (LDHs) with DTPA and EDTA complexones and carbonate ions in the interlayer space to sorb U(VI) was compared. The U(VI) sorption values correlate with the dissociation stability of the U(VI) complexes with these ligands in solution. The synthesized hydrotalcite-like sorbents intercalated with complexones showed high performance in sorption treatment of water to remove U(VI), irrespective of its speciation in natural waters (including di- and tricarbonate complexes). The carbonate form of LDH recovers only cationic uranyl species.

The behavior of rare-earth elements, Zr and Hf during biologically-mediated deposition of silica-stromatolites and carbonate-rich microbial mats

Venere Lake, in the Pantelleria Island thermal system (Central Mediterranean Sea) consists of a mix of seawater and hydrothermal volcanic fluids containing high levels of dissolved SiO2. Close to the lake's thermal springs, siliceous stromatolites are deposed under high bacterial activity conditions whereas roughly interlaminated Ca-carbonates and microbial mats are widely scattered in the lake. The dissolved REE speciation in lake waters is dominated by [REE(CO3)2]−, [REE(CO3)]+ and [REE(H3SiO4)]2+ complexes. On the contrary the most abundant Zr and Hf species are hydroxyl- and fluoride-complexes. The behavior of REE Zr and Hf in the Venere lake waters is controlled by precipitation of amorphous silica, carbonates and bacterial activity. Chondrite-normalized REE patterns in stromatolites are characterized by positive La anomalies, superchondritic Y/Ho ratios and negative Eu anomalies. The Eu depletion is also found in microbial mats where is associated to a “chondritic” Y/Ho signature. Zr and Hf differently behave in dissolved phase and in newly-formed siliceous and carbonatic material: Hf reacts easily into amorphous silica surfaces whereas Zr is preferentially partitioned onto phosphate binding sites on microbial cell surfaces similar to the observed behavior of heavy REE (HREE). We suggest that the Zr-Hf relationship reflect the interface processes between mineral phases and bacterial membranes or compounds produced by bacterial activity.