In-situ measurement of free trace metal concentrations in a flooded paddy soil using the Donnan Membrane Technique
Pan, Y. ; Koopmans, G.F. ; Bonten, L.T.C. ; Song, J. ; Luo, Y. ; Temminghoff, E.J.M. ; Comans, R.N.J. - \ 2015
Geoderma 241-242 (2015). - ISSN 0016-7061 - p. 59 - 67.
dissolved organic-matter - ray-absorption spectroscopy - copper redox transformation - reduced sulfur groups - ion activity model - sandy soil - humic substances - natural-waters - higher-plants - heavy-metals
The field Donnan Membrane Technique (DMT) has been used successfully to measure in-situ free trace metal concentrations in surface waters. However, it has not been applied previously in submerged soil systems including flooded paddy rice fields.Wetested this technique in a columnexperimentwith a flooded paddy soil contaminated with trace metals and compared the DMT measurements with predictions from a geochemical speciation model. Flooding led to a strong gradient in the redox potential (Eh) along the soil column, and the pH and concentrations ofMn, Fe, and dissolved organic carbon increased with decreasing Eh. Total dissolved tracemetal concentrations decreased from the overlying water layer to the soil layers, which might be ascribed to the elevated pH outweighing the effect of the increased DOC concentrations under anaerobic conditions. Also, free trace metal concentrations were lower in the soil solution of the upper and bottom soil layers than in the overlying water layer, largely due to the increased pH under anaerobic conditions. The DMT measurements and model predictions were similar in the aerobic water layer, except for Pb. In both anaerobic soil layers, however, Cu and Pb were poorly predicted. The applied geochemical modeling approach, which is frequently being used and performswell under aerobic conditions, does not fully capture all the chemical processes occurring under anaerobic conditions. Overall, the field DMT proved to be a useful tool for the in-situ measurement of free trace metal concentrations in flooded paddy soils.
Iron oxidation kinetics and phosphate immobilization along the flow-path from groundwater into surface water
Grift, B. van der; Rozemeijer, J.C. ; Griffioen, J. ; Velde, Y. van der - \ 2014
Hydrology and Earth System Sciences 18 (2014)11. - ISSN 1027-5606 - p. 4687 - 4702.
suspended sediment - ferrous iron - fresh-water - phosphorus limitation - nutrient dynamics - fe(ii) oxidation - arsenic removal - natural-waters - riparian zone - river
The retention of phosphorus in surface waters through co-precipitation of phosphate with Fe-oxyhydroxides during exfiltration of anaerobic Fe(II) rich groundwater is not well understood. We developed an experimental field set-up to study Fe(II) oxidation and P immobilization along the flow-path from groundwater into surface water in an agricultural experimental catchment of a small lowland river. We physically separated tube drain effluent from groundwater discharge before it entered a ditch in an agricultural field. Through continuous discharge measurements and weekly water quality sampling of groundwater, tube drain water, exfiltrated groundwater, and surface water, we investigated Fe(II) oxidation kinetics and P immobilization processes. The oxidation rate inferred from our field measurements closely agreed with the general rate law for abiotic oxidation of Fe(II) by O-2. Seasonal changes in climatic conditions affected the Fe(II) oxidation process. Lower pH and lower temperatures in winter (compared to summer) resulted in low Fe oxidation rates. After exfiltration to the surface water, it took a couple of days to more than a week before complete oxidation of Fe(II) is reached. In summer time, Fe oxidation rates were much higher. The Fe concentrations in the exfiltrated groundwater were low, indicating that dissolved Fe(II) is completely oxidized prior to inflow into a ditch. While the Fe oxidation rates reduce drastically from summer to winter, P concentrations remained high in the groundwater and an order of magnitude lower in the surface water throughout the year. This study shows very fast immobilization of dissolved P during the initial stage of the Fe(II) oxidation process which results in P-depleted water before Fe(II) is completely depleted. This cannot be explained by surface complexation of phosphate to freshly formed Fe-oxyhydroxides but indicates the formation of Fe(III)-phosphate precipitates. The formation of Fe(III)-phosphates at redox gradients seems an important geochemical mechanism in the transformation of dissolved phosphate to structural phosphate and, therefore, a major control on the P retention in natural waters that drain anaerobic aquifers.
Humic substances interfere with phosphate removal by lanthanum modified clay in controlling eutrophication
Lurling, M.F.L.L.W. ; Waaijenberg, G.W.A.M. ; Oosterhout, J.F.X. - \ 2014
Water Research 54 (2014). - ISSN 0043-1354 - p. 78 - 88.
waterbodems - fosfaten - eutrofiëring - bioremediëring - laboratoriumproeven - water bottoms - phosphates - eutrophication - bioremediation - laboratory tests - rare-earth-elements - phosphorus-binding clay - organic-matter removal - modified bentonite clay - natural-waters - cyanobacterial toxins - polyaluminum chloride - cation binding - ion-binding - fresh-water
The lanthanum (La) modified bentonite Phoslock® has been proposed as dephosphatisation technique aiming at removing Filterable Reactive Phosphorus (FRP) from the water and blocking the release of FRP from the sediment. In the modified clay La is expected the active ingredient. We conducted controlled laboratory experiments to measure the FRP removal by Phoslock® in the presence and absence of humic substances, as La complexation with humic substances might lower the effectiveness of La (Phoslock®) to bind FRP. The results of our study support the hypothesis that the presence of humic substances can interfere with the FRP removal by the La-modified bentonite. Both a short-term (1 d) and long-term (42 d) experiment were in agreement with predictions derived from chemical equilibrium modelling and showed lower FRP removal in presence of humic substances. This implies that in DOC-rich inland waters the applicability of exclusively Phoslock® as FRP binder should be met critically. In addition, we observed a strong increase of filterable La in presence of humic substances reaching in a week more than 270 µg La l-1 that would infer a violation of the Dutch La standard for surface water, which is 10.1 µg La l-1. Hence, humic substances are an important factor that should be given attention when considering chemical FRP inactivation as they might play a substantial role in lowering the efficacy of metal-based FRP-sorbents, which makes measurements of humic substances (DOC) as well as controlled experiments vital.
Quantification of Methylated Selenium, Sulfur, and Arsenic in the Environment
Vriens, B. ; Ammann, A.A. ; Hagendorfer, H. ; Lenz, M. ; Berg, M. ; Winkel, L.H.E. - \ 2014
PLoS ONE 9 (2014)7. - ISSN 1932-6203
plasma-mass spectrometry - atomic fluorescence spectrometry - solid-phase microextraction - gas-chromatography - speciation analysis - volatile selenium - natural-waters - icp-ms - elements - air
Biomethylation and volatilization of trace elements may contribute to their redistribution in the environment. However, quantification of volatile, methylated species in the environment is complicated by a lack of straightforward and field-deployable air sampling methods that preserve element speciation. This paper presents a robust and versatile gas trapping method for the simultaneous preconcentration of volatile selenium (Se), sulfur (S), and arsenic (As) species. Using HPLC-HR-ICP-MS and ESI-MS/MS analyses, we demonstrate that volatile Se and S species efficiently transform into specific non-volatile compounds during trapping, which enables the deduction of the original gaseous speciation. With minor adaptations, the presented HPLC-HR-ICP-MS method also allows for the quantification of 13 non-volatile methylated species and oxyanions of Se, S, and As in natural waters. Application of these methods in a peatland indicated that, at the selected sites, fluxes varied between 190–210 ng Se·m-2·d-1, 90–270 ng As·m-2·d-1, and 4–14 µg S·m-2·d-1, and contained at least 70% methylated Se and S species. In the surface water, methylated species were particularly abundant for As (>50% of total As). Our results indicate that methylation plays a significant role in the biogeochemical cycles of these elements
Speciation of heavy metals in River Rhine
Vega, F.A. ; Weng, L. - \ 2013
Water Research 47 (2013)1. - ISSN 0043-1354 - p. 363 - 372.
donnan membrane technique - field-flow fractionation - dissolved organic-matter - fresh-waters - trace-metals - chemical speciation - humic substances - model parameters - surface waters - natural-waters
Chemical speciation of Zn, Cu, Ni, Cd and Pb in River Rhine was studied by measuring free ion concentration and distribution in nanoparticles, and by comparing the measurement with speciation modeling. Concentrations of free metal ions were determined in situ using Donnan Membrane Technique (DMT). The percentage of free over total (filtered) metal concentration is 52%, 33%, 2.6%, 0.48% and 0.12% for respectively Zn, Cd, Ni, Pb and Cu, i.e. the degree of metal complexation in the river is the lowest for Zn and the highest for Cu. Metals in 1–300 nm particles were analyzed using Asymmetric Flow Field Flow Fractionation (AsF-FFF), but the overall recovery is quite low. The nano-sized Cu detected is mainly associated with DOM of 1–5 nm, whereas Pb and Zn are dominantly associated with particles of iron hydroxides and clay of larger size (30–100 nm). Free ion concentrations calculated with the speciation modeling are in good agreement with the measurements, except for Pb. Based on the model, DOM-bound is the most important complexed form for Cu and Cd, whereas formation of (bi)carbonate and EDTA complexes are more important for Ni and Zn. Adsorption of Pb to DOM is probably overestimated by the model, whereas Pb adsorption to iron hydroxides is underestimated.
Determinants of biodiversity in subtropical shallow lakes (Atlantic coast, Uruguay)
Kruk, C. ; Rodriguez-Gallego, L. ; Meerhoff, M. ; Quintans, F. ; Lacerot, G. ; Mazzeo, N. ; Scasso, F. ; Paggi, J.C. ; Peeters, E. ; Marten, S. - \ 2009
Freshwater Biology 54 (2009)12. - ISSN 0046-5070 - p. 2628 - 2641.
aquatic macrophyte richness - species richness - community structure - natural-waters - danish lakes - top-down - diversity - gradient - zooplankton - phosphorus
P> Shallow lakes and ponds contribute disproportionally to species richness relative to other aquatic ecosystems. In-lake conditions (e.g. presence of submerged plants) seem to play a key role in determining diversity, as has been demonstrated for temperate lakes. When water quality deteriorates and turbidity increases, conditions in such lakes are affected drastically resulting in a loss of diversity. However, it is not clear whether subtropical lakes show the same pattern and whether the richness of all groups reacts similarly to environmental changes. Our aim was to analyse the main factors explaining patterns of species richness in plankton, fish and submerged macrophyte assemblages in both turbid and clear subtropical shallow lakes. We analysed abiotic and biotic features of 18 subtropical, small- to medium-sized, shallow lakes along the Uruguayan coast. We compared both turbid and clear ecosystem states and evaluated the relative variance explained by the factors measured. Variables describing lake and catchment morphology, as well as the percentage of the water column occupied by submerged macrophytes (%PVI) and water turbidity, had strong effects on taxon richness. Interestingly, individual biotic groups had dissimilar richness patterns. Macrophyte %PVI decreased with increasing lake area, while fish species richness showed the opposite pattern. Phytoplankton species richness increased with macrophyte %PVI, while the zooplankton richness pattern varied depending on the taxonomic group considered. Overall, our results indicate that, as found for temperate lakes, a greater submerged plant cover promotes higher species richness in several groups, and that this may overwhelm the otherwise expected positive effect of lake size on species richness. On the other hand, small-bodied zooplankton predominated in lakes with high plant abundance. Our findings concur with recent studies, indicating that refuge capacity of aquatic plants might be weaker in (sub)tropical than in temperate shallow lakes. The extremely high plant cover, frequently observed in warm lakes, could potentially lead to different richness patterns in some groups. This conclusion has important consequences for local managers and conservationists.
Relationship between metal speciation in soil solution and metal adsorption at the root surface of ryegrass
Kalis, E.J.J. ; Temminghoff, E.J.M. ; Town, R.M. ; Unsworth, E.R. ; Riemsdijk, W.H. van - \ 2008
Journal of Environmental Quality 37 (2008). - ISSN 0047-2425 - p. 2221 - 2231.
donnan membrane technique - deposition potential sscp - stripping chronopotentiometry - contaminated soils - diffusive gradients - organic-matter - natural-waters - lolium-perenne - heavy-metals - trace-metals
Received for publication October 12, 2007. The total metal content of the soil or total metal concentration in the soil solution is not always a good indicator for metal availability to plants. Therefore, several speciation techniques have been developed that measure a defined fraction of the total metal concentration in the soil solution. In this study the Donnan Membrane Technique (DMT) was used to measure free metal ion concentrations in CaCl2 extractions (to mimic the soil solution, and to work under standardized conditions) of 10 different soils, whereas diffusive gradients in thin-films (DGT) and scanning chronopotentiometry (SCP) were used to measure the sum of free and labile metal concentrations in the CaCl2 extracts. The DGT device was also exposed directly to the (wetted) soil (soil-DGT). The metal concentrations measured with the speciation techniques are related to the metal adsorption at the root surface of ryegrass (Lolium perenne L.), to be able to subsequently predict metal uptake. In most cases the metal adsorption related pH-dependently to the metal concentrations measured by DMT, SCP, and DGT in the CaCl2 extract. However, the relationship between metal adsorption at the root surface and the metal concentrations measured by the soil-DGT was not¿or only slightly¿pH dependent. The correlations between metal adsorption at the root surface and metal speciation detected by different speciation techniques allow discussion about rate limiting steps in biouptake and the contribution of metal complexes to metal bioavailability.
Donnan effects in metal speciation analysis by DET/DGT
Yezek, L.P. ; Veeken, P.L.R. van der; Leeuwen, H.P. van - \ 2008
Environmental Science and Technology 42 (2008)24. - ISSN 0013-936X - p. 9250 - 9254.
low ionic-strength - in-situ measurement - thin-films - trace-metals - diffusive gradients - natural-waters - fresh-waters - performance-characteristics - dgt - hydrogels
Cross-linked polyacrylamide gels have found wide application in analytical techniques, such as diffusional equilibration in thin film (DET) and diffusive gradient in thin film (DGT). In these applications, the assumption is made that the gel matrix is effectively uncharged and chemically inert with respect to the species of interest. Recent data has shown significant nonideal behavior at low ionic strengths, which strongly suggests a finite structural charge within the gel matrix. The present investigation explores the possible ramifications of fixed charged sites within the gel on metal speciation analysis by DET and DGT. The results indicate that structural charge within the gel layer will give rise to different DET equilibrium concentrations than in the sample because of Donnan partitioning. The steady-state diffusion of ions through a diffusive gel (DGT) is also influenced by the gel charge, but the net effect will depend on the details of the speciation. The results indicate that for submillimolar ionic strength solutions the quantitative interpretation of DGT data benefits from combination with DET
Development of an automated system for isolation and purification of humic substances
Zomeren, A. van; Weij-Zuiver, E. van der; Comans, R.N.J. - \ 2008
Analytical and Bioanalytical Chemistry 391 (2008)6. - ISSN 1618-2642 - p. 2365 - 2370.
preparative isolation - natural-waters
Characterization of humic substances (HS) in environmental samples generally involves labor-intensive and time-consuming isolation and purification procedures. In this paper, the development of an automated system for HS isolation and purification is described. The novelty of the developed system lies in the way the multiple liquids and columns used in the isolation/purification procedure are handled in both forward and back-elution mode by solenoid valves. The automated procedure significantly reduces the total throughput time needed, from 6¿7 days to 48 h, and the amount of labor to obtain purified HS for further characterization. Chemical characterization of purified HS showed that results were in good agreement with previously published values for HS from a variety of sources, including the IHSS standard HS collection. It was also shown that the general properties of HS were consistent among the different source materials (soil, waste, aquatic) used in this study. The developed system greatly facilitates isolation and characterization of HS and reduces the risk of potential (time-dependent) alteration of HS properties in the manual procedure
Groundwater chemistry of Al under Dutch acid sandy soils: effects of land use and depth.
Fest, E. ; Temminghoff, E.J.M. ; Griffioen, J. ; Grift, B. ; Riemsdijk, W.H. van - \ 2007
Applied Geochemistry 22 (2007)7. - ISSN 0883-2927 - p. 1427 - 1438.
dissolved organic-matter - acid forest soils - aluminum solubility - bs horizons - unsaturated zone - natural-waters - surface waters - heavy-metals - nica-donnan - speciation
Aluminium has received great attention in the second half of the 20th century, mainly in the context of the acid rain problem mostly in forest soils. In this research the effect of land use and depth of the groundwater on Al, pH and DOC concentration in groundwater under Dutch sandy soils has been studied. Both pH and DOC concentration play a major role in the speciation of Al in solution. Furthermore, the equilibrium with mineral phases like gibbsite, amorphous Al(OH)3 and imogolite, has been considered. Agricultural and natural land use were expected to have different effects on the pH and DOC concentration, which in turn could influence the total Al concentration and the speciation of Al in groundwater at different depths (phreatic, shallow and deep). An extensive dataset (n = 2181) from the national and some provincial monitoring networks on soil and groundwater quality was used. Land use type and groundwater depth did influence the pH, and Al and DOC concentrations in groundwater samples. The Al concentration ranged from 7 to 1941 ¿mol L¿1 at pH <4; highest Al concentrations were found for natural-phreatic groundwater. The DOC concentration decreased and the median pH increased with depth of the groundwater. Natural-phreatic groundwater showed lower pH than the agricultural-phreatic groundwater. Highest DOC concentrations were found for the agricultural-phreatic groundwater, induced by the application of organic fertilizers. Besides inorganic complexation, the NICA-Donnan model was used to calculate Al3+ concentrations for complexation with DOC. Below pH 4.5 groundwater samples were mainly in disequilibrium with a mineral phase. This disequilibrium is considered to be the result of kinetic constraints or equilibrium with organic matter. Log K values were derived by linear regression and were close to theoretical values for Al(OH)3 minerals (e.g. gibbsite or amorphous Al(OH)3), except for natural-phreatic groundwater for which lower log K values were found. Complexation of Al with DOC is shown to be an important factor for the Al concentrations, especially at high DOC concentrations as was found for agricultural-phreatic groundwater.
Carbonate adsorption on goethite in competition with phosphate.
Rahnemaie, R. ; Hiemstra, T. ; Riemsdijk, W.H. van - \ 2007
Journal of Colloid and Interface Science 315 (2007)2. - ISSN 0021-9797 - p. 415 - 425.
surface structural approach - aqueous-solution interface - charge-distribution - vibrational spectroscopy - sulfate adsorption - pb(ii) sorption - ion adsorption - natural-waters - alpha-feooh - atr-ftir
Competitive interaction of carbonate and phosphate on goethite has been studied quantitatively. Both anions are omnipresent in soils, sediments, and other natural systems. The PO4¿CO3 interaction has been studied in binary goethite systems containing 0¿0.5 M (bi)carbonate, showing the change in the phosphate concentration as a function of pH, goethite concentration, and carbonate loading. In addition, single ion systems have been used to study carbonate adsorption as a function of pH and initial (H)CO3 concentration. The experimental data have been described with the charge distribution (CD) model. The charge distributions of the inner-sphere surface complexes of phosphate and carbonate have been calculated separately using the equilibrium geometries of the surface complexes, which have been optimized with molecular orbital calculations applying density functional theory (MO/DFT). In the CD modeling, we rely for phosphate on recent parameters from the literature. For carbonate, the surface speciation and affinity constants have been found by modeling the competitive effect of CO3 on the phosphate concentration in CO3¿PO4 systems. The CO3 constants obtained can also predict the carbonate adsorption in the absence of phosphate very well. A combination of inner- and outer-sphere CO3 complexation is found. The carbonate adsorption is dominated by a bidentate inner-sphere complex, (FeO)2CO. This binuclear bidentate complex can be present in two different geometries that may have a different IR behavior. At a high PO4 and CO3 loading and a high Na+ concentration, the inner-sphere carbonate complex interacts with a Na+ ion, probably in an outer-sphere fashion. The Na+ binding constant obtained is representative of Na¿carbonate complexation in solution. Outer-sphere complex formation is found to be unimportant. The binding constant is comparable with the outer-sphere complexation constants of, e.g., SO2¿4 and SeO2¿4.
Measurement of humic and fulvic acid concentrations and dissolution properties by a rapid batch procedure.
Zomeren, A. van; Comans, R.N.J. - \ 2007
Environmental Science and Technology 41 (2007)19. - ISSN 0013-936X - p. 6755 - 6761.
dissolved organic-matter - ion-binding - preparative isolation - natural-waters - bottom ash - substances - soil - carbon - copper - model
Although humic substances (HS) strongly facilitate the transport of metals and hydrophobic organic contaminants in environmental systems, their measurement is hampered by the time-consuming nature of currently available methods for their isolation and purification. We present and apply a new rapid batch method to measure humic (HA) and fulvic (FA) acid concentrations and dissolution properties in both solid and aqueous samples. The method is compared with the conventional procedures and is shown to substantially facilitate HS concentration measurements, particularly for applications such as geochemical modeling where HS purification is not required. The new method can be performed within 1.5-4 h per sample and multiple samples can be processed simultaneously, while the conventional procedures typically require approximately 40 h for a single sample. In addition, specific dissolution properties of HS are identified and are consistent with recent views on the molecular structure of HS that emphasize molecular interactions of smaller entities over distinct macromolecular components. Because the principles of the new method are essentially the same as those of generally accepted conventional procedures, the identified HA and FA properties are of general importance for the interpretation of the environmental occurrence and behavior of HS.
Adsorptive stripping chronopotentiometry (AdSCP). Part 2: Basic experimental features
Leeuwen, H.P. van; Town, R.M. - \ 2007
Journal of Electroanalytical Chemistry 610 (2007)1. - ISSN 1572-6657 - p. 17 - 27.
deposition potential sscp - competitive ligand-exchange - xylenol-orange - cyclic chronopotentiometry - diffusion-coefficients - natural-waters - voltammetry - speciation - complex - trace
AdSCP determines a metal ion, M, by reaction with added ligand, Lad, to form a surface active MLad which is accumulated on an electrode surface, then quantified by constant current reduction. The chronopotentiometric stripping curves for Pb(II), with xylenol orange (XO) as the added ligand, are scrutinized in the context of a recently developed theoretical framework. The experimental curves are well described by expressions for the general case of an adsorbed reactant and a dissolved product, Pb0, at a conventional mercury drop electrode. The shape of the potential/time transient is substantially influenced by convergency in the diffusion of Pb0 into the electrode volume. The mercury drop electrode lies in between the limits for a macroscale electrode (with planar diffusion) and a microelectrode (where diffusion of product is immaterial). Practical borders to the various experimental conditions are identified, e.g. in the maximum value of the stripping transition time as compared to the accumulation time, and in the strength of adsorption of PbXO to ensure a constant accumulation flux. The measured position of the E/t transient is in good agreement with that predicted on the basis of the extent of convergence together with the adsorption coefficient and the stability constant for PbXO. The suitability of the area under the dt/dE peak for obtaining the magnitude of the stripping transition time and the ensuing amount of PbXO is evaluated in detail.
Roles of metal ion complexation and membrane permeability in the metal flux through lipophilic membranes. Labile complexes at permeation liquid membranes
Zhang, Z. ; Buffle, J. ; Leeuwen, H.P. van; Wojciechowski, K. - \ 2006
Analytical Chemistry 78 (2006)16. - ISSN 0003-2700 - p. 5693 - 5703.
copper speciation - natural-waters - trace-metals - fatty-acid - separation - voltammetry - system - enrichment - transport - as(iii)
The various physicochemical factors that influence the flux of carrier-transported metal ions through permeation liquid membranes (PLM) are studied systematically. Understanding PLM behavior is important (i) to optimize the application of PLM as metal speciation sensors in environmental media and (ii) because PLM may serve as bioanalogical devices that help to elucidate the environmental physicochemical processes occurring at the surface of biological membranes. Diffusion of free and complexed metal ions in solution, as well as diffusion of the metal carrier complex in the membrane, is considered. The respective roles of diffusion layer thickness, ligand concentration, complex stability, carrier concentration, and membrane thickness are studied experimentally in detail and compared with theory, using various labile complexes, namely, Pb(II)-diglycolate, Cu(II)-diglycolate, and Cu(II)-N-(2-carboxyphenyl)glycine. Conditions where either membrane diffusion or solution diffusion is rate limiting are clearly discriminated. It is shown in particular, that, by tuning the carrier concentration or membrane thickness, either the free metal ion concentration or the total labile metal species are measured. PLM can thus be used to determine whether models based on the free ion activity in solution (such as BLM or FIAM models) are applicable to metal uptake by microorganisms in a real natural medium
Stripping chronopotentiometry at scanned deposition potential (SSCP). Part 8. Metal speciation analysis in gels.
Town, R.M. ; Yezek, L.P. ; Leeuwen, H.P. van - \ 2006
Journal of Electroanalytical Chemistry 589 (2006)2. - ISSN 1572-6657 - p. 203 - 211.
complex-systems - natural-waters - features - microelectrode - adsorption - parameters - diffusion - lability - ions - acid
In case of a finite negative Donnan potential difference, ¿D, metal speciation in a gel is significantly altered as compared to that in the surrounding aqueous medium. For anionic gels (e.g., typical biogels), ¿D leads to enhanced concentrations of positively charged species within the gel, and reduced concentrations of negatively charged ones. Thus both the absolute concentrations and the ratios of species are altered. Stripping chronopotentiometry at scanned deposition potential is shown to provide a reliable measure of the stability and lability of metal species in gels. Results are reported for labile, quasilabile and inert metal-ligand systems. Failure to take into account the Donnan partitioning leads to erroneous interpretations on the distribution and lability of species within the gel phase. Translation of the speciation measured within the gel to that in the surrounding medium is involved for chemically heterogeneous systems, e.g., natural waters. The results are of importance for interpretation of analytical signals from gel-integrated sensors and for understanding the behaviour of the different metal species in biogels
Model predictions of metal speciation in freshwaters compared to measurements by in situ techniques
Unsworth, E.R. ; Warnken, K.W. ; Zhang, H. ; Davison, W. ; Black, F. ; Buffle, J. ; Cao, J. ; Cleven, R.F.M.J. ; Galceran, J. ; Gunkel, P. ; Kalis, E.J.J. ; Kistler, D. ; Leeuwen, H.P. van; Martin, M. ; Noel, S. ; Nur, Y. ; Odzak, N. ; Pauy, J. ; Riemsdijk, W.H. van; Sigg, L. ; Temminghoff, E.J.M. ; Tercier-Waeber, M.L. ; Topperwien, S. ; Town, R.M. ; Weng, L.P. ; Xue, Hanbin - \ 2006
Environmental Science and Technology 40 (2006)6. - ISSN 0013-936X - p. 1942 - 1949.
donnan membrane technique - permeation liquid-membrane - dissolved organic-matter - biotic ligand model - humic substances - natural-waters - ion-binding - thin-films - diffusive gradients - acute toxicity
Measurements of trace metal species in situ in a softwater river, a hardwater lake, and a hardwater stream were compared to the equilibrium distribution of species calculated using two models, WHAM 6, incorporating humic ion binding model VI and visual MINTED incorporating NICA-Donnan. Diffusive gradients in thin films (DGT) and voltammetry at a gel integrated microelectrode (GIME) were used to estimate dynamic species that are both labile and mobile. The Donnan membrane technique (DMT) and hollow fiber permeation liquid membrane (HFPLM) were used to measure free ion activities. Predictions of dominant metal species using the two models agreed reasonably well, even when colloidal oxide components were considered. Concentrations derived using GIME were generally lower than those from DGT, consistent with calculations of the lability criteria that take into account the smaller time window available for the flux to GIME. Model predictions of free ion activities generally did not agree with measurements, highlighting the need for further work and difficulties in obtaining appropriate input data
Sulfide-iron interactions in domestic wastewater from a gravity sewer
Nielsen, A.H. ; Lens, P.N.L. ; Vollertsen, J. ; Hvitved-Jacobsen, Th. - \ 2005
Water Research 39 (2005)12. - ISSN 0043-1354 - p. 2747 - 2755.
afvalwater - sulfiden - zwavelwaterstof - ijzer - oxidatie - rioolwater - waste water - sulfides - hydrogen sulfide - iron - oxidation - sewage - hydrogen-sulfide - natural-waters - dissolved sulfide - reduction - kinetics - sediments - fe(iii)
Interactions between iron and sulfide in domestic wastewater from a gravity sewer were investigated with particular emphasis on redox cycling of iron and iron sulfide formation. The concentration ranges of iron and total sulfide in the experiments were 0.4-5.4 mg Fe L-1 and 0-5.1 mg S L-1, respectively. During anaerobic conditions, iron reduction kinetics were investigated and reduction rates amounted on average to 1.32 mg Fe L -1 d-1. Despite the very low solubility of iron sulfide, the reduced iron reacted only partly with sulfide to produce iron sulfide, even when dissolved sulfide was in excess. When a ferric chloride solution was added to sulfide containing anaerobic wastewater, the ferric iron was quickly reduced to ferrous forms by oxidation of dissolved sulfide and the ferrous iron precipitated almost completely as iron sulfide. During aerobic conditions, iron sulfide was oxidized with a half-life period of 11.7 h. The oxidation rate of iron sulfide was significantly lower than that reported for the oxidation of dissolved sulfide.
Dynamic aspects of metal speciation by competitive ligand exchange-adsoptive stripping voltammetry (CLE-AdSV)
Leeuwen, H.P. van; Jansen, S. - \ 2005
Journal of Electroanalytical Chemistry 579 (2005)2. - ISSN 1572-6657 - p. 337 - 342.
diffusion-coefficients - detection window - organic-ligands - natural-waters - trace - complexation - nickel - kinetics - systems - copper
Competitive ligand exchange¿adsorptive stripping voltammetry (CLE¿AdSV) measures speciation of a metal M via a bulk exchange reaction with an adsorptive ligand Lad followed by electrochemical detection of the adsorbed metal complex. Thermodynamic aspects of the detection window of the technique are well understood. Here, we analyse the kinetic aspects including those involved with the adsorptive accumulation step. The upper border of the kinetic detection window is defined by the requirement of equilibration before accumulation of the complex MLad at the electrode surface. Analysis of the exchange step demonstrates that complexes with sample ligands that remain unaffected by the exchange step are generally nonlabile and do not contribute to the AdSV signal. Any residual free metal, however, does contribute to the accumulation process, but this contribution will be negligible in the usual situation of a sufficiently strong complex MLad and an excess of Lad over M. The adsorption of the surface-active complex MLad is of a transient nature in the initial stage of the accumulation period, before the diffusive adsorption process approaches a steady-state nature.
Donnan effects in the steady-state diffusion of metal ions through charged thin films
Yezek, L.P. ; Leeuwen, H.P. van - \ 2005
Langmuir 21 (2005)23. - ISSN 0743-7463 - p. 10342 - 10347.
in-situ measurement - natural-waters - trace-metals - solute diffusion - hydrogels - gels - transport - dgt - electrolytes - membrane
The /teady-state diffusion of metals ions through thin films with fixed charged groups was investigated using diffusive gradients in thin films (DGT) measurements. Copolymers of acrylamide and sodium acrylate cross-linked with N,N'-methylenebisacrylamide were used as diffusive gels. The rate of diffusion of cadmium ions through the gels was measured by determining the mass of cadmium bound to a backing chelex resin after a known deployment time. Variation of the ionic strength as well as the fixed charge density and the thickness of the gel layer allowed evaluation of the impact of the Donnan partitioning and the diffusion layer in solution on the observed steady-state flux of ions through the layer. The results underscore that, as the Donnan partitioning increases, the impact of the diffusion layer in solution becomes more significant. At modest Donnan potentials, Donnan partitioning controls the net flux of metal ions, whereas at conditions of increasing Donnan potential, i.e., at decreasing ionic strength, the flux is increasingly limited by diffusion in solution. An analytical expression is developed to describe the influence of Donnan partitioning on the observed steady-state flux of metal ions.
Polystyrene film-coated glassware : a new means of reducing metal losses in trace metal speciation
Pinheiro, J.P. ; Bosker, W.T.E. - \ 2004
Analytical and Bioanalytical Chemistry 380 (2004)7-8. - ISSN 1618-2642 - p. 964 - 968.
natural-waters - stripping voltammetry - sea-water - adsorption - surfaces - storage - lead - silicon - samples - contamination
A recently developed process for coating a glass surface with polystyrene (PS) film, by use of a simple chemical process has been used to reduce trace metal adsorption by cell components. The glass coating is a two-step procedure consisting of covalent attachment of vinyl-terminated PS to Si atoms on the glass surface then adsorption of PS from solution to create a stable PS film. To assess the quality of the coating we used anodic stripping voltammetry to study the adsorption of lead and cadmium ions in coated and untreated glass cells. In both short and long-term (24 h) experiments we observed that the amount of metal adsorbed was considerably less for the PS film-coated glass cell than for the uncoated cell. Further experiments showed that metal desorption is faster and metal contamination after cleaning is significantly lower for the coated cells. The PS film was, moreover, stable over a period of 6 months within the pH range 3.5-9.