Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Resolubilization of Protein from Water-Insoluble Phlorotannin-Protein Complexes upon Acidification
    Vissers, Anne M. ; Blok, Annelies E. ; Westphal, Adrie H. ; Hendriks, Wouter H. ; Gruppen, Harry ; Vincken, Jean Paul - \ 2017
    Journal of Agricultural and Food Chemistry 65 (2017)44. - ISSN 0021-8561 - p. 9595 - 9602.
    complexation - pH - phlorotannins - reversibility - solubility
    Marine phlorotannins (PhT) from Laminaria digitata might protect feed proteins from ruminal digestion by formation of insoluble non-covalent tannin-protein complexes at rumen pH (6-7). Formation and disintegration of PhT-protein complexes was studied with β-casein (random coil) and bovine serum albumin (BSA, globular) at various pH. PhT had similar binding affinity for β-casein and BSA as pentagalloyl glucose, as studied by fluorescence quenching. The affinity of PhT for both proteins was independent of pH (3.0, 6.0, and 8.0). In the presence of PhT, the pH range for precipitation of tannin-protein complexes widened to 0.5-1.5 pH units around the isoelectric point (pI) of the protein. Complete protein resolubilization from insoluble PhT-protein complexes was achieved at pH 7 and 2 for β-casein and BSA, respectively. It was demonstrated that PhT modulate the solubility of proteins at neutral pH and that resolubilization of PhT-protein complexes at pH deviating from pI is mainly governed by the charge state of the protein.
    Adsorption of levofloxacin onto goethite: Effects of pH, calcium and phosphate
    Qin, X.P. ; Liu, F. ; Wang, G.C. ; Weng, L. ; Li, L. - \ 2014
    Colloids and Surfaces. B: Biointerfaces 116 (2014). - ISSN 0927-7765 - p. 591 - 596.
    fluoroquinolone antibacterial agents - water interface - ciprofloxacin removal - antibiotic ofloxacin - humic substances - iron-oxides - sorption - complexation - tetracycline - speciation
    Adsorption of levofloxacin (LEV), one of the extensively used antibiotics, onto goethite was investigated using batch experiments. The adsorption of LEV on goethite was pH-dependent. A maximum adsorption was reached at pH 6. Above or below pH 6, the adsorption decreased. In the presence of calcium (Ca2+), a decrease in adsorption was observed, due to probably formation of Ca2+-LEV complexes in solutions. Phosphate also showed a significant inhibition on LEV adsorption over a pH range of 3-10. Phosphate competed with LEV for binding sites on the surface of goethite, and the electrostatic competition between LEV and phosphate on goethite surface might be another reason for the decrease in adsorption. These results indicated that Ca2+ and phosphate have a great influence on the distribution of LEV in soils and waters, which will eventually affect its antibacterial activity in the environment. (C) 2013 Elsevier B.V. All rights reserved.
    Electroactive behavior assessment of poly(acrylic acid)-graphene oxide composite hydrogel in the detection of cadmium
    Bejarano-Jimenez, A. ; Escobar-Barrios, V.A. ; Kleijn, J.M. ; Oritz-Ledon, C.A. ; Chazaro-Ruiz, L.F. - \ 2014
    Journal of Applied Polymer Science 131 (2014)19. - ISSN 0021-8995 - 10 p.
    carbon-paste electrodes - swelling properties - metal-ions - acid) - polymerization - gels - complexation - absorption - water - ph
    Super absorbent polymers of acrylic acid-graphene oxide (PAA-GO) were synthesized with different percentage of chemical neutralization (0, 10, and 20%) of the acrylic acid monomer before its polymerization. The influence of their swelling and adsorption/desorption capacity of cadmium ions in aqueous solutions were studied and revealed that the GO enables greater mechanical stability in the materials. The PAA hydrogels, with the same degrees of neutralization, were also prepared without GO to compare with the composites. Additionally, carbon paste electrodes (CPE) modified with the composites PAA-GO were used to asses and compare their adsorption properties with cadmium(II). The anodic stripping voltammetry (ASV) peak, in the differential pulse voltammetry mode, for cadmium oxidation was found to be influenced by the presence of GO into the polymer, and also by their percentage of neutralization. The accumulation of cadmium(II) on the surface of the modified CPEs was performed under open-circuit conditions taking an account the preconcentration time of the metal cation. The presence of GO enhances the electrical signal of the electrodes in short times of immersion in cadmium(II) solutions. This property contributed to get linear responses of the CPEs modified with the composites, which were influenced by their degrees of neutralization. The PAA-GO 10N electrode with 10% of neutralization combined the influence of GO and the degree of neutralization in the same matrix, and also showed good performance in terms of its mechanical stability, it was chosen for preliminary studies on the selectivity of the electrode toward Zn(II) and Cu(II).
    Interaction of flavan-3-ol derivatives and different caseins is determined by more than proline content and number of proline repeats
    Bohin, M.C. ; Vincken, J.P. ; Westphal, A.H. ; Tripp, A.M. ; Dekker, Peter ; Hijden, H.T.W.M. ; Gruppen, H. - \ 2014
    Food Chemistry 158 (2014). - ISSN 0308-8146 - p. 408 - 416.
    food proteins - binding - astringency - polymerization - precipitation - complexation - fluorescence - procyanidins - polyphenols - gallate
    Interactions of Type A and B flavan-3-ol dimers (procyanidins) and several monomeric flavan-3-ols, with a-casein and ß-casein, were investigated. Binding affinities measured were related to the ligands structure, including several properties (e.g. intrinsic flexibility (number of rotatable bonds) and hydrophobicity), and to the amino-acid composition of the caseins. A monomeric flavan-3-ol esterified with gallic acid (EGCG) had a five to ten times higher affinity to caseins compared to the non-galloylated dimeric flavan-3-ols. In this case, the larger number of rotatable bonds in EGCG might be accountable for this difference. Comparing flavan-3-ol dimers, intrinsic flexibility did not consistently promote interactions, as procyanidin A1 displayed a higher affinity to a-casein than the supposedly more flexible B-type dimers investigated. Despite its higher content of proline, compared to a-casein, ß-casein did not always have a higher affinity for the ligands investigated (e.g. no interaction with procyanidin A1 detected). These results suggest that more factors than proline content and the number of proline repeats govern phenolic–casein interactions.
    The effect of phosphorus binding clay (Phoslock) in mitigating cyanobacterial nuisance: A laboratory study on the effects on water quality variables and plankton
    Oosterhout, J.F.X. ; Lurling, M. - \ 2013
    Hydrobiologia 710 (2013)1. - ISSN 0018-8158 - p. 265 - 277.
    rare-earth-elements - organic-matter - lake restoration - eutrophication - microcystis - netherlands - sediments - blooms - complexation - speciation
    This laboratory study examined the lanthanum modified clay Phoslock® for its effectiveness to bind soluble reactive phosphorus (SRP), release of nutrients from this modified clay, its influence on water quality variables (pH, oxygen saturation %, conductivity and turbidity), effects on phytoplankton growth (green alga Scenedesmus obliquus, cyanobacteria Microcystis aeruginosa and Anabaena sp.), and, lastly, its effect on the population growth of the rotifer Brachionus calyciflorus. A clear dose–response for SRP binding by the modified clay was observed. A small amount of ammonium is released from Phoslock®. We found no effect of Phoslock® on pH or oxygen saturation. Conductivity increased with the increasing concentration of Phoslock®. An application of Phoslock® caused a transient increase of turbidity up to 211 NTU. However, due to rapid settlement, turbidity fell below 13 NTU (~1 m Secchi depth), after 6 h. Phoslock® addition caused a reduction in growth of all phytoplankton species tested that we attribute to the combined effects of light limitation, flocculation with the bentonite and binding of SRP to Phoslock®. We estimated the EC50 of Phoslock® on the population growth of rotifer B. calyciflorus to be 0.15 g Phoslock® l-1. Overall, the results of our study indicate Phoslock® seems to be suitable for field applications.
    Simultaneous analysis of small organic acids and humic acids using high performance size exclusion chromatography
    Qin, X.P. ; Liu, F. ; Wang, G.C. ; Weng, L.P. - \ 2012
    Journal of Separation Science 35 (2012)24. - ISSN 1615-9306 - p. 3455 - 3460.
    spectroscopic properties - molecular-weight - iron-oxide - adsorption - substances - goethite - matter - water - polydispersity - complexation
    An accurate and fast method for simultaneous determination of small organic acids and much larger humic acids was developed using high performance size exclusion chromatography. Two small organic acids, i.e. salicylic acid and 2,3-dihydroxybenzoic acid, and one purified humic acid material were used in this study. Under the experimental conditions, the UV peaks of salicylic acid and 2,3-dihydroxybenzoic acid were well separated from the peaks of humic acid in the chromatogram. Concentrations of the two small organic acids could be accurately determined from their peak areas. The concentration of humic acid in the mixture could then be derived from mass balance calculations. The measured results agreed well with the nominal concentrations. The detection limits are 0.05 mg/L and 0.01 mg/L for salicylic acid and 2,3-dihydroxybenzoic acid, respectively. Applicability of the method to natural samples was tested using groundwater, glacier, and river water samples (both original and spiked with salicylic acid and 2,3-dihydroxybenzoic acid) with a total organic carbon concentration ranging from 2.1 to 179.5 mg C/L. The results obtained are promising, especially for groundwater samples and river water samples with a total organic carbon concentration below 9 mg C/L.
    Predictive model of cationic surfactant binding to humic substances
    Ishiguro, M. ; Koopal, L.K. - \ 2011
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 379 (2011)1-3. - ISSN 0927-7757 - p. 70 - 78.
    natural organic-matter - metal-ion binding - nica-donnan model - proton binding - adsorption - acids - water - polyelectrolytes - complexation - competition
    The humic substances (HS) have a high reactivity with other components in the natural environment. An important factor for the reactivity of HS is their negative charge. Cationic surfactants bind strongly to HS by electrostatic and specific interaction. Therefore, a surfactant binding model is developed that takes both the specific and electrostatic interactions explicitly into account. The model is analogous to that of ion binding to HS with the NICA-Donnan model, but competition for the binding sites is not taken into account and the NICA-Donnan model reduces to the Langmuir–Freundlich–Hill–Donnan (LFH-D) model. The parameters of the LFH equation are the maximum binding, the affinity constant and the non-ideality constant. The non-ideality parameter accounts for both the site heterogeneity and the cooperativity due to hydrophobic interaction between surfactant molecules. The affinity constant incorporates the specific (e.g., hydrophobic) interactions between surfactant and HS. The Donnan part of the model accounts in a simple way for the electrostatic interactions by assuming that for a given set of conditions there is only one electrostatic potential that governs the behavior in the Donnan phase. The separation between the specific interactions (LHF) and the electrostatic interactions (D) is based on the so-called master curve (MC) procedure in which the binding is replotted as a function of the “free” surfactant concentration in the Donnan phase. The MC depends only on the specific interactions. Once the MC is obtained it can be fitted to the LFH equation to obtain the model parameters. Subsequently, the surfactant isotherms can be calculated with the LFH-D model. The model is tested using previously obtained data on dodecyl pyridinium chloride (DPC) and cetyl pyridinium chloride (CPC) binding to some purified humic and fulvic acids at pH about 5. The LFH-D model is well suited to describe the surfactant binding to HAs from very low concentrations up to the iso-electric point (IEP). The affinity of DPC for the different HAs allows ranking of the HAs according to their hydrophobicity. Prediction of DPC binding at other pH values also leads to good results for HA. For FAs the model can only describe the surfactant binding up to an adsorbed amount of 0.5 mol/kg. For higher binding values the LFH-D model underestimates the binding.
    Extraction of extracellular polymeric substances (EPS) from anaerobic granular sludges: comparison of chemical and physical extraction protocols
    Abzac, P. D'; Bordas, F. ; Hullebusch, E. ; Lens, P.N.L. ; Guibaud, G. - \ 2010
    Applied Microbiology and Biotechnology 85 (2010)5. - ISSN 0175-7598 - p. 1589 - 1599.
    activated-sludge - waste-water - polysaccharides - complexation - flocs - acid
    The characteristics of the extracellular polymeric substances (EPS) extracted with nine different extraction protocols from four different types of anaerobic granular sludge were studied. The efficiency of four physical (sonication, heating, cationic exchange resin (CER), and CER associated with sonication) and four chemical (ethylenediaminetetraacetic acid, ethanol, formaldehyde combined with heating, or NaOH) EPS extraction methods was compared to a control extraction protocols (i.e., centrifugation). The nucleic acid content and the protein/polysaccharide ratio of the EPS extracted show that the extraction does not induce abnormal cellular lysis. Chemical extraction protocols give the highest EPS extraction yields (calculated by the mass ratio between sludges and EPS dry weight (DW)). Infrared analyses as well as an extraction yield over 100% or organic carbon content over 1 g g(-1) of DW revealed, nevertheless, a carry-over of the chemical extractants into the EPS extracts. The EPS of the anaerobic granular sludges investigated are predominantly composed of humic-like substances, proteins, and polysaccharides. The EPS content in each biochemical compound varies depending on the sludge type and extraction technique used. Some extraction techniques lead to a slightly preferential extraction of some EPS compounds, e.g., CER gives a higher protein yield.
    Effects of extraction procedures on metal binding properties of extracellular polymeric substances (EPS) from anaerobic granular sludges
    Abzac, P. D'; Bordas, F. ; Hullebusch, E. ; Lens, P.N.L. ; Guibaud, G. - \ 2010
    Colloids and Surfaces. B: Biointerfaces 80 (2010)2. - ISSN 0927-7765 - p. 161 - 168.
    activated-sludge - titration data - biosorption - cadmium - complexation - adsorption - sorption - lead - cd - constants
    The effects of the extraction procedure of extracellular polymeric substances (EPS) on their proton/metal binding properties were studied. Nine extraction procedures (one control, four physical and four chemical procedures) were applied to four types of anaerobic granular sludges. The binding capacities between the EPS and lead or cadmium were investigated at pH 7 by a polarographic method. The composition of the EPS extracts varied according to the extraction technique and the origin of the sludge. This induced differences in the pK(a)s and the binding sites density of the EPS extracts. The carry-over of the extractant in the samples strongly affects the properties of the EPS from chemical extraction protocols. Lead and cadmium seem to be bound differently with the EPS, a higher binding capacity was observed for Pb2+ than for Cd2+.
    Uncertainly analysis of the nonideal competitive adsorption-Donnan model: effects of dissolved organic matter vaiability on predicted metal speciation in soil solution.
    Groenenberg, J.E. ; Koopmans, G.F. ; Comans, R.N.J. - \ 2010
    Environmental Science and Technology 44 (2010)4. - ISSN 0013-936X - p. 1340 - 1346.
    humic substances - fresh-waters - heavy-metals - ion-binding - sandy soil - cu - complexation - pb - parameters - acids
    Ion binding models such as the nonideal competitive adsorption-Donnan model (NICA-Donnan) and model VI successfully describe laboratory data of proton and metal binding to purified humic substances (HS). In this study model performance was tested in more complex natural systems. The speciation predicted with the NICA-Donnan model and the associated uncertainty were compared with independent measurements in soil solution extracts, including the free metal ion activity and fulvic (FA) and humic acid (HA) fractions of dissolved organic matter (DOM). Potentially important sources of uncertainty are the DOM composition and the variation in binding properties of HS. HS fractions of DOM in soil solution extracts varied between 14 and 63% and consisted mainly of FA. Moreover, binding parameters optimized for individual FA samples show substantial variation. Monte Carlo simulations show that uncertainties in predicted metal speciation, for metals with a high affinity for FA (Cu, Pb), are largely due to the natural variation in binding properties (i.e., the affinity) of FA. Predictions for metals with a lower affinity (Cd) are more prone to uncertainties in the fraction FA in DOM and the maximum site density (i.e., the capacity) of the FA. Based on these findings, suggestions are provided to reduce uncertainties in model predictions
    Evaluation of size exclusion chromatography (SEC) for the characterization of extracellular polymeric substances (EPS) in anaerobic granular sludges
    Simon, S. ; Pairo, B. ; Villain, M. ; Abzac, P. D'; Hullebusch, E. ; Lens, P.N.L. ; Guibaud, G. - \ 2009
    Bioresource Technology 100 (2009)24. - ISSN 0960-8524 - p. 6258 - 6268.
    activated-sludge - extraction methods - part i - exopolymers - biofilms - polysaccharides - complexation - separation - protocols - hplc
    The extracellular polymeric substances (EPS) extracted from three granular and one flocculant anaerobic sludges were characterised by size exclusion chromatography (SEC) using two serially linked chromatographic columns in order to obtain more detailed chromatograms. A Superdex peptide 10/300 GL (0.1-7 kDa) and Superdex 20010/300GL (10-600 kDa) from Amersham Biosciences were used in series with a mobile phase at pH 7 with an ionic strength of 0.223 M (phosphate buffer 50 mM and NaCl 150 mM). A part of the EPS molecules displays hydrophobic and/or ionic interactions with the column packing. Interactions could be modified by changing the mobile phase ionic strength or polarity (addition of acetonitrile). The detection wavelength (210 or 280 nm) affects strongly the EPS chromatogram. For a sludge originating from the same type of biofilms (i.e., anaerobic granules), the differences in EPS fingerprints are mainly due to differences in the absorbance of the chromatographic peaks, linked to EPS molecules content and composition. The EPS fingerprint changes significantly when the EPS originate from another type of anaerobic sludges. In addition, EPS fingerprints were affected by the extraction method used (centrifugation only; heat and centrifugation or cationic exchange resin and centrifugation). This phenomenon was observed mainly for the largest and smallest molecules and molecules which display interactions with column packing.
    Competition from Cu(II), Zn(II) and Cd(II) in Pb(II) binding to Suwannee River Fulvic Acid
    Chakraborty, P. ; Chakrabarti, C.L. - \ 2008
    Water Air and Soil Pollution 195 (2008)1-4. - ISSN 0049-6979 - p. 63 - 71.
    natural organic-matter - metal-ion binding - humic substances - physicochemical heterogeneity - site occupation - complexation - parameters - ligands - voltammetry - lead(ii)
    This is a study of trace metal competition in the complexation of Pb(II) by well-characterized humic substances, namely Suwannee River Fulvic Acid (SRFA) in model solutions. It was found that Cu(II) seems to compete with Pb(II) for strong binding sites of SRFA when present at the same concentration as Pb(II). However, Cd(II) and Zn(II) did not seem to compete with Pb(II) for strong binding sites of SRFA. These two metals did compete with Pb(II) for the weaker binding sites of SRFA. Heterogeneity of SRFA was found to play a crucial role in metal-SRFA interactions. The environmental significance of this research for freshwater is that even at relatively low Pb(II) loadings, the metals associated with lead in minerals, e.g. Cu(II), may successfully compete with Pb(II) for the same binding sites of the naturally occurring organic complexants, with the result that some of the Pb(II) may exist as free Pb2+ ions, which has been reported to be one of the toxic forms of Pb in aquatic environment.
    Modeling metal-particle interactions with an emphasis on natural organic matter
    Merdy, P. ; Huclier, S. ; Koopal, L.K. - \ 2006
    Environmental Science and Technology 40 (2006)24. - ISSN 0013-936X - p. 7459 - 7466.
    biotic ligand model - nica-donnan model - ion-binding - humic substances - fresh-waters - heavy-metals - adsorption - acid - charge - complexation
    Effect of accelerated aging of MSWI bottom ash on the leaching mechanisms of copper and molybdenum
    Dijkstra, J.J. ; Zomeren, A. van; Meeussen, J.C.L. ; Comans, R.N.J. - \ 2006
    Environmental Science and Technology 40 (2006)14. - ISSN 0013-936X - p. 4481 - 4487.
    natural organic-matter - humic substances - fulvic-acid - trace-elements - ion-binding - adsorption - surface - complexation - carbonation - speciation
    The effect of accelerated aging of Municipal Solid Waste Incinerator (MSWI) bottom ash on the leaching of Cu and Mo was studied using a "multisurface" modeling approach, based on surface complexation to iron/aluminum (hydr) oxides, mineral dissolution/precipitation, and metal complexation by humic substances. A novel experimental method allowed us to identify that the solid/liquid partitioning of fulvic acids (FA) quantitatively explains the observed beneficial effect of accelerated aging on the leaching of Cu. Our results suggest that iron/aluminum (hydr)oxides are the major reactive surfaces that retain fulvic acid in the bottom ash matrix, of which the aluminum (hydr)oxides were found to increase after aging. A new modeling approach, based on the surface complexation of FA on iron/aluminum (hydr) oxides is developed to describe the pH-dependent leaching of FA from MSWI bottom ash. Accelerated aging results in enhanced adsorption of FA to (neoformed) iron/aluminum (hydr) oxides, leading to a significant decrease in the leaching of FA and associated Cu. Accelerated aging was also found to reduce the leaching of Mo, which is also attributed to enhanced adsorption to (neoformed) iron/aluminum (hydr) oxides. These findings provide important new insights that may help to improve accelerated aging technology.
    Phase behavior of mixtures of oppositely charged nanoparticles: Heterogeneous Poisson-Boltzmann cell model applied to lysozyme and succinylated lysozyme
    Biesheuvel, P.M. ; Lindhoud, S. ; Vries, R.J. de; Stuart, M.A.C. - \ 2006
    Langmuir 22 (2006)3. - ISSN 0743-7463 - p. 1291 - 1300.
    bovine serum-albumin - protein solutions - colloidal crystals - osmotic-pressure - polyelectrolytes - sedimentation - adsorption - separation - complexation - equilibrium
    We study the phase behavior of mixtures of oppositely charged nanoparticles, both theoretically and experimentally. As an experimental model system we consider mixtures of lysozyme and lysozyme that has been chemically modified in such a way that its charge is nearly equal in magnitude but opposite in sign to that of unmodified lysozyme. We observe reversible macroscopic phase separation that is sensitive not only to protein concentration and ionic strength, but also to temperature. We introduce a heterogeneous Poisson-Boltzmann cell model that generally applies to mixtures of oppositely charged nanoparticles. To account for the phase behavior of our experimental model system, in addition to steric and electrostatic interactions, we need to include a temperature-dependent short-ranged interaction between the lysozyme molecules, the exact origin of which is unknown. The strength and temperature dependence of the short-ranged attraction is found to be of the same order of magnitude as that between unmodified lysozyme molecules. The presence of a rather strong short-ranged attraction in our model system precludes the formation of colloidal liquid phases (or complex coacervates) such as those typically found in mixtures of globular protein molecules and oppositely charged polyelectrolytes.
    Measuring free metal ion concentrations in situ in natural waters using the Donnan Membrane Technique
    Kalis, E.J.J. ; Weng, L.P. ; Dousma, F. ; Temminghoff, E.J.M. ; Riemsdijk, W.H. van - \ 2006
    Environmental Science and Technology 40 (2006)3. - ISSN 0013-936X - p. 955 - 961.
    dissolved organic-matter - speciation measurements - stripping voltammetry - humic substances - ligand-exchange - sandy soil - complexation - cadmium - binding - copper
    Metal toxicity is not related to the total but rather to the free or labile metal ion concentration. One of the techniques that can be used to measure several free metal ion concentrations simultaneously is the Donnan Membrane Technique (DMT) in combination with the inductively coupled plasma-mass spectrometer (ICP-MS). However, free metal ion concentrations in natural waters are commonly below the detection limit of ICP-MS. We decreased the detection limit by making use of a ligand, and we developed a field DMT cell that can be applied in situ in natural waters. A kinetic approach can be used to calculate free metal ion concentrations when the equilibrium time becomes too large. The field DMT measured in situ in natural waters a free metal ion concentration ranging from 0.015% (Cu) to 13% (Zn) of a total metal concentration ranging from 0.06 nM (Cd) to 237 nM (Zn). The free metal ion concentrations were difficult to predict using an equilibrium speciation model, probably due to the uncertainty in the nature of the dissolved organic matter or the presence of other reactive colloids. It is shown that DMT can follow changes in the free metal ion concentration on times scales less than a day under certain conditions.
    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.
    Heavy metals precipitation in sewage sludge
    Marchioretto, M.M. ; Rulkens, W.H. ; Bruning, H. - \ 2005
    Separation Science and Technology 40 (2005)16. - ISSN 0149-6395 - p. 3393 - 3405.
    soluble organic-matter - acid-mine drainage - complexation - chemistry
    There is a great need for heavy metal removal from strongly metal-polluted sewage sludges. One of the advantages of heavy metal removal from this type of sludge is the possibility of the sludge disposal to landfill with reduced risk of metals being leached to the surface and groundwater. Another advantage is the application of the sludge as soil improver. The use of chemical precipitation to remove dissolved heavy metals from sewage sludge implies a high cost for chemicals. This work shows, for real sewage sludge for the first time that the addition of NaOH as first precipitating agent considerably saves the addition of Na2S, that is one of the most effective metal precipitating agents and also expensive. After solubilization of heavy metals by chemical leaching with previous aeration, the next step was the separation of the sludge solids from the metalrich acidic liquid (leachate) by centrifugation and filtration. Afterwards, the filtered leachate was submitted to the application of NaOH and Na2S, separately and in combination, followed by filtration. The results showed that when iron and aluminium are present in the leachate, adsorption and/or coprecipitation of Cr, Pb, and Zn with Fe(OH)3 and Al(OH)3 might occur at increasing pH conditions. The combination of hydroxide and sulfide precipitation was able to promote an effective removal of heavy metals from leachate. Applying NaOH at a pH of 4-5 as a first precipitation step, followed by filtration and further addition of Na2S to the filtered liquid at pH of 7-8 as a second precipitation step, decreased considerably the dosage of the second precipitant (almost 200 times), compared to when it was solely applied. This has practical applications, as the claimed costs drawbacks of H2S addition is considerably reduced by the addition of the less expensive NaOH. The best removal efficiencies obtained were: Pb: ~ 100%, Cr: 99.9%, Cu: 99.7%, and Zn: 99.9%.
    Copper toxicity in relation to surface water-dissolved organic matter: biological effects to Daphnia magna
    Kramer, K.J.M. ; Jak, R.G. ; Hattum, B. van; Hooftman, R.N. ; Zwolsman, J.J.G. - \ 2004
    Environmental Toxicology and Chemistry 23 (2004)12. - ISSN 0730-7268 - p. 2971 - 2980.
    koper - toxiciteit - organische stof - waterverontreiniging - daphnia magna - biologische beschikbaarheid - nederland - waterbodems - copper - toxicity - organic matter - water pollution - daphnia magna - bioavailability - netherlands - water bottoms - biotic ligand model - humic-acid - ceriodaphnia-dubia - ion activity - metals - hardness - bioaccumulation - complexation - cadmium - speciation
    Water quality standards for copper are usually stated in total element concentrations. It is known, however, that a major part of the copper can be bound in complexes that are biologically not available. Natural organic matter, such as humic and fulvic acids, are strong complexing agents that may affect the bioavailable copper (Cu2+) concentration. The aim of this study was to quantify the relation between the concentration of dissolved natural organic matter and free Cu2+ in surface waters, and the biological effect, as measured in a standardized ecotoxicological test (48 h¿median effective concentration [EC50] Daphnia magna, mobility). Six typical Dutch surface waters and an artificial water, ranging from 0.1 to 22 mg/L dissolved organic carbon (DOC), were collected and analyzed quarterly. Chemical speciation modeling was used as supporting evidence to assess bioavailability. The results show clear evidence of a linear relation between the concentration of dissolved organic carbon (in milligrams DOC/L) and the ecotoxicological effect (as effect concentration, EC50, expressed as micrograms Cu/L): 48-h EC50 (Daphnia, mobility) = 17.2 × DOC + 30.2 (r2 = 0.80, n = 22). Except for a brook with atypical water quality characteristics, no differences were observed among water type or season. When ultraviolet (UV)-absorption (380 nm) was used to characterize the dissolved organic carbon, a linear correlation was found as well. The importance of the free copper concentration was demonstrated by speciation calculations: In humic-rich waters the free Cu2+ concentration was estimated at ¿10¿11 M, whereas in medium to low dissolved organic carbon waters the [Cu2+] was ¿10¿10 M. Speciation calculations performed for copper concentrations at the effective concentration level (where the biological effect is considered the same) resulted in very similar free copper concentrations (¿10¿8 M Cu) in these surface waters with different characteristics. These observations consistently show that the presence of organic matter decreases the bioavailability, uptake, and ecotoxicity of copper in the aquatic environment. It demonstrates that the DOC content must be included in site-specific environmental risk assessment for trace metals (at least for copper). It is the quantification of the effects described that allows policy makers to review the criteria for copper in surface waters.
    Application of the NICADonnan model for proton, copper and uranyl binding to humic acid
    Saito, T. ; Nagasaki, S. ; Tanaka, S. ; Koopal, L.K. - \ 2004
    Radiochimica Acta 92 (2004)9-11. - ISSN 0033-8230 - p. 567 - 574.
    metal-ion binding - fulvic-acids - humate interactions - substances - complexation - adsorption - parameters - heterogeneity - uranium(vi) - goethite
    Humic acids are natural organic materials that play an important role in the migration of heavy metal and actinide ions in aquatic and soil systems. In the present study, the binding of protons, copper ions and uranyl ions to the purified Aldrich humic acid (PAHA) is investigated and the results are modeled with the Non-Ideal Competitive Adsorption (NICA) model extended with electrostatic interactions according to the Donnan model (NICA-Donnan model). The NICA part of the model enables one to describe the competitive ion binding to a heterogeneous substrate taking into account a different stoichiometry per ion. The NICA-Donnan model can describe the binding of the ions to PAHA in large concentration ranges (3
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