Free Ionic Species Research Articles

Assessment of water quality for mountainous high-elevated spring waters using self-organized maps

It is crucial to continuously evaluate the chemistry and quality of spring waters due to human activity, climate change, and environmental contamination in high-elevated areas. A total of 58 spring waters were collected from high-elevated areas in the Hamedan province, Iran. Different spring waters were divided into 4 clusters using the self-organizing map (SOM) and K-means clustering approach. The results from SOM indicated that the electrical conductivity (EC), magnesium (Mg2+), sodium (Na+), and potassium (K+) displayed relatively similar patterns, while the distribution patterns of pH, nitrate (NO3−), and phosphorus (P) were completely different from other variables. Factor analysis supported this conclusion as well, indicating that while pH, NO3−, and P were the results of human activity, the main cations and anions came from parent rocks. The weighted arithmetic water quality index (WQI) was also calculated based on measured parameters and spring waters were primarily categorized as excellent water. Every cation was predominantly found on its free ion species. The saturation indices for all minerals were negative, indicating the dissolution of all minerals. It was concluded that the characterization of spring waters is substantially influenced by the geological nature of the aquifer rocks. Also, the background levels of NO3− and P have been identified as ecological goal levels for spring water resource management in high-elevated areas.

Speciation of the binary Cr(III)-citrate system in the leachate samples of phosphate ore

This report focuses on the determination of chromium chemical forms in the lixiviates of phosphate ore using speciation modelling with the MATLAB 7.7 Language. Citric acid has been used as aleaching agent for the extraction of chromium (III) from phosphate ore. A computational approach was used to determine the concentration of differentionic species present in the Cr(III)-citric acid system. The results show that the main aqueous species identified in the systemwere both free and complex ions. In addition, it was found that the concentration of total chromium in the leachate was dependent on the concentration of citric acid.On the other hand, the formation of different species and the evolution of their concentration led to an increase in the ionic strength of the solution. The ionic complex CrHCit+ showed the highest activity coefficientamong the different Cr (III) species. It was also observed that free ionic species (H3O+, H2Cit-, Cr3+) have a higher activity than chromium ionic complexes (CrH3Cit3+, CrH2Cit2+, CrHCit+).

Charge and Electrical Double Layer Formation in a Nonpolar Solvent Using a Nonionic Surfactant.

In this work, we study the charge formation and the characteristics of the electrical double layer in a nonpolar medium using electrical impedance spectroscopy. To stabilize the free ionic species, a nonionic surfactant is added to the system. The conductivity and permittivity of the medium are obtained from high- to medium-frequency impedance data. Based on the correlation between (viscosity-adjusted) conductivity and surfactant concentration, we conclude that charge formation occurs due to a disproportionation mechanism. We accordingly estimate the concentration of the charge carriers in the sample and the Debye length of the diffuse double layer. The capacitance of the electrical double layer can be extracted from the low-frequency impedance data. We use this data to calculate the electrode distance of an equivalent parallel-plate capacitor. It is found that this distance is on the order of magnitude of Angstroms, indicating that the measured electrical double-layer capacitance is in fact the Stern layer capacitance.

Conventional and novel techniques for the determination of Hg uptake by lettuce in amended agricultural peri-urban soils

Peri-urban agriculture provides environmental benefits to the nearby urban areas. However, domestic and industrial infrastructures can be sources of pollution that can affect agricultural production. In this work, the diffusive gradient in thin film (DGT) technique was used to assess the bioavailability of mercury (Hg) in organic-amended agricultural soils, and uptake by lettuce. Two different amendments were studied individually in three different sets using a wood-based biochar at two rates (3% and 6%, w/w), and compost at one rate (30% w/w). The effect of the amendments on Hg bioavailability, mobility and uptake was investigated by means of both DGT analyses and accumulation of Hg by lettuce. DGT manufactured in-house devices with polyacrylamide gel using both open and restricted diffusive layers (ODL and RDL, respectively) were used to determine organic and inorganic Hg labile species in soils, respectively. The Hg concentration in lettuce leaves and roots were analyzed and compared with DGT measurements to predict the uptake of Hg from the different organic-amended soils and the non-amended soils. Results show that the application of biochar reduces the bioavailability of Hg in soil and, in consequence, the Hg uptake by lettuce. Inorganic Hg species were predominant in all the different sets of the experiment (62–97%), although the addition of the different amendments reduced the free ionic species in soil.

Trace metals pollution of waters and soils in Kardjali region, Bulgaria.

Trace metals pollution of surface waters and their nearby soils in the metallurgically polluted Kardjali region, Bulgaria, were studied. Thermodynamic modeling including the dissolved organic carbon (DOC) was carried out for evaluating the distribution of metal species in waters and soil solutions. Zn was found to be the most widespread pollutant in the water samples, followed by Cu, Mn, and Cd. Geoaccumulation indices of trace metals for the tested soils were calculated, indicating that regarding Al, Fe, Co, Ni, and Cu all soils are "uncontaminated". The most significant soil pollutant was found to be Cd, with all soils being either "extremely contaminated" by this metal or close to the limit, followed by Pb and Zn. The dynamics of trace metal chemical species distribution in surface waters and in the water-soluble soil fractions, as a result of possible spontaneous precipitations, was calculated by applying different thermodynamic models. Regarding Mn, Co, Ni, and Cd in waters and aqueous soil extracts and Zn in aqueous soil extracts, their free ion species prevailed, being more labile and hence toxic for the ecosystem. In the case of Al, Fe, Cu, Cd, and Pb in the waters and aqueous soil extracts and of Zn in waters, stable organic complexes with bidentate bonds, Me(OH)4- or Me(OH)02 prevailed.

Chemical speciation and complexation modeling of trace and rare earth elements in groundwater of Oban Massif and Mamfe mMbayment southeastern Nigeria

ABSTRACTChemical speciation was carried out on trace and rare earth elements on trace and rare earth elements data on water samples in Oban Massif and Mamfe Mbayment southeastern Nigeria. Product moment correlation showed significant correlation at r>0.7 between REEs Pr and Nd, Pr and Lu, Sm and Nd, Sm and Pr, Tb and Nd, Tm and Tb, and Yb and Nd. Speciation modeling result showed that free metal ionic species dominated boreholes and spring water samples. The predominant trace metal complex is the OH- ligand. Trace elements mineral saturation indexes in boreholes at oversaturation (S>1) predicted more mineral species than equilibrium saturation (S=0). Rare earth elements mineral oversaturation (S>1) in boreholes predicted least mineral species. Undersaturation (S<1) predicted highest range of rare earth elements minerals. Springs and streams at S>1, predicted more mineral range than equilibrium (S=O) while mineral prediction at S<1 were the highest. Rare earth elements are precipitated at undersaturated condition in the study area.

Atomistic simulation of calcite interaction with ionic species and oil components in water-flooding

Density functional theory (DFT) trends in Gibbs free energies and enthalpies were thoroughly studied in calcite. Different coordination was applied for ionic species that exist in smart-water as well as for carboxylic acids presented in crude oil at distinct two primary hydration sites: CO3H, CaOH. The studied hydration sites were proposed based on previous electro-kinetics besides surface titration experimental studies. Interfacial energy runs using molecular modeling approaches, with Becke's three parameter exchange and Lee Yang Parr corrected correlation functional (B3LYP) and 3-21G basis set, were performed to account for stability, reactivity and wettability alteration. The calculations predict the most stable complexes for calcite are, CO3H, CaO−, CO3Ca+, CO3Mg+, CaCO3−, CaHCO3, CaH2O+ and CaSO4−. We also demonstrate that free ion species are having a higher free energy in seawater than in case of a complex and thus indicates a more reactivity of complex species to interact with rock sites. This study proposes a numerical correlation between thermochemistry profiles and wettability alteration, which expresses to us how the surface affinity for a certain organic compound compares with its affinity for water. The calculations agrees with previous experiment findings especially in case of Ca+2, Mg+2, SO4−2, MgOH+1, OH−1, and NaCl. Some reversed trend can be explained by the smaller size of the basis set used in the calculations. The results of this insights help in understanding the interaction mechanism of this unique systems in order to modify reactivity for enhancing oil recovery (EOR) purposes, and to use the outcomes of this study to pose questions and directions for continuing theoretical efforts destined at linking macroscopic reactivity in case of altering wettability with molecular-level understanding.

Speciation and precipitation of heavy metals in high-metal and high-acid mine waters from the Iberian Pyrite Belt (Portugal).

Acid mine waters (AMW) collected during high- and low-flow water conditions from the Lousal, Aljustrel, and São Domingos mining areas (Iberian Pyrite Belt) were physicochemically analyzed. Speciation calculation using PHREEQC code confirms the predominance of Men+ and Me-SO4 species in AMW samples. Higher concentration of sulfate species (Me-SO4) than free ion species (Men+, i.e., Al, Fe, and Pb) were found, whereas opposite behavior is verified for Mg, Cu, and Zn. A high mobility of Zn than Cu and Pb was identified. The sulfate species distribution shows that Fe3+-SO42-, SO42-, HSO4-, Al-SO4, MgSO40, and CaSO40 are the dominant species, in agreement with the simple and mixed metal sulfates and oxy-hydroxysulphates precipitated from AMW. The saturation indices (SI) of melanterite and epsomite show a positive correlation with Cu and Zn concentrations in AMW, which are frequently retained in simple metal sulfates. Lead is well correlated with jarosite and alunite (at least in very acid conditions) than with simple metal sulfates. The Pb for K substitution in jarosite occurs as increasing Pb concentration in solution. Lead mobility is also controlled by anglesite precipitation (a fairly insoluble sulfate), where a positive correlation was ascertained when the SI approaches equilibrium. The zeta potential of AMW decreased as pH increased due to colloidal particles aggregation, where water species change from SO42- to OH- species during acid to alkaline conditions, respectively. The AMW samples were supersaturated in schwertmannite and goethite, confirmed by the Men+-SO4, Men+-Fe-O-OH, or Men+-S-O-Fe-O complexes identified by attenuated total reflectance infrared spectroscopy (ATR-IR). The ATR-IR spectrum of an AMW sample with pH 3.5 (sample L1) shows well-defined vibration plans attributed to SO4 tetrahedron bonded with Fe-(oxy)hydroxides and the Men+ sorbed by either SO4 or Fe-(oxy)hydroxides. For samples with lower pH values (pH~2.5-samples SD1 and SD4), the vibration plans attributed to Men+ sorption are not evidenced, indicating its release in solution. The sorption of heavy metals on the first precipitated simple metal sulfates was ascertained by scanning electron microscopy coupled with X-ray spectrometry (SEM-EDX), where X-ray maps of Cu and Zn confirm a distribution of both metals in the melanterite structure.

The structure investigations of dehydroacetic acid and 1,8-diaminonaphthalene condensation product by NMR, MS, and X-ray measurements

A new unexpected product of condensation reaction of 1,8-diaminonaphthalene (DAN) and carbonyl compound (here: dehydroacetic acid (dha)) was synthesized. Discussion about the molecular structure of possible products of this reaction was done on the base of NMR studies. The structure of the titled product in both DMSO solution and in the solid state was resolved by analysis of its spectral data (X-ray structure analysis, multinuclear NMR in solution and solid state spectra) and MS measurements. The presented studies provided clear evidence that the titled product exists in diluted DMSO solution as the mixture of two kinetic free ionic species whereas in concentrated DMSO solution as well as in the solid state this system forms associated ionic pairs bonded together by hydrogen bonds.

Low-voltage electrically driven homeostatic hydrogel-based actuators for underwater soft robotics

We present the synthesis, fabrication and electro-mechanical characterization of a novel electro-responsive hydrogel based on Na-4-vinylbenzenesulfonate (Na-4-VBS) that can operate as a fast response bending actuator in a low voltage regime (0.2–5V), in NaCl aqueous solutions. The bending speed can reach values up to 22°/s at 3V and of 2.7°/s at 1V. The responsive behavior of the benders was observed in physiological environments as well, such as phosphate buffer solution (PBS) and Dulbecco’s Modified Eagle’s Medium (DMEM) and exhibited similar performance. The material is a co-polymer comprising also hydroxyethyl methacrylate (HEMA) and acrylonitrile (AN), to confer high hydrophilicity to the structure and to enhance its elastic properties. According to the swelling and electro-mechanical testing results, the electrically driven deformation of the hydrogels was interpreted as a dynamic osmotic equilibrium effect taking place at the interface between the polymer and the surrounding medium, induced by the free ionic species migration throughout the polymer. This material constitutes a promising solution for the design and production of highly performing soft underwater actuators and biomimetic smart systems that can be controllably operated at the macro and mesoscale in fluids of biological interest, with minimal power consumption and below the standard potential of water electrolysis.

A method for measurement of free cadmium species in waters using diffusive gradients in thin films technique with an ion-imprinted sorbent

A diffusive gradients in thin films (DGT) device for the analysis of free Cd(II) species, based on Cd(II) ion-imprinted sorbent (IIS) as the binding agents and commercial polyethersulfone membrane (PES) as diffusion layer, was developed (PES/IIS-DGT). DGT time-series experiments showed that the mass of free Cd(II) species accumulated by PES/IIS-DGT was linear vs. time (R2 = 0.9953) and the concentration of free Cd(II) species by PES/IIS-DGT was in good agreement with the total dissolved concentrations of free Cd(II) species in simple synthetic solutions where free ionic species dominated. PES/IIS-DGT performance was independent in the range of pH 4.5–7.5 and ionic strength range from 1.0 × 10−3 to 0.7 mol L−1. The measurement of free Cd(II) species in synthetic solution containing different concentrations of ligands by PES/IIS-DGT showed an excellent agreement with the value measured by Cd(II) ion selective electrodes (Cd-ISE), indicating that PES/IIS-DGT method is more suitable than Cd-ISE for the measurement of low concentration of free Cd(II) species due to the enrichment of IIS for the analytes.

Cathodic Contact Glow Discharge Electrolysis for the Degradation of Liquid Ammonia Solutions

The application of 50 VDC cathodic contact glow discharge electrolysis for six hours in 1.0 mol/L KOH + 0.8, 0.4 and 0.08 g/L ammonia results in the removal of 66, 71 and 77% of ammonia, respectively, following pseudo first‐order kinetics at ca. 0.3 mol/kWh. The yields of dissolved NO2N and NO3N lie between 9 and 29% and are coupled with ammonia removal suggesting a nitrification process. Based on the near‐cathode UV–Vis emissions and ionization products of H2O and NH3 molecules, a mechanism is proposed along with the charge/energy transfer reactions between the plasma‐generated free radicals and ionic species. Joule heating and vaporization are also believed to physically remove ammonia.

Rare Earth Elements Fractionation in Native Vegetation from the Moncorvo Iron Mines, NE Portugal

Fractionation of Rare Earth Elements (REE) and the accumulation and translocation indexes were measured and determined in the native vegetation [Halimium lasianthum (Lam.) Spach subsp. alyssoides (Lam.) Greuter; Cytisus multiflorus (L’Hér.) Sweet; and Cistus monspeliensis L.; Cistus ladanifer subsp. ladanifer; Lavandula stoechas L.] from the iron mining area of Moncorvo (NE Portugal). There is no correlation between the amounts of REE in rhizosphere and in plants. The REE concentration as the fractionation follows roots>leaves>stems in plants. A slightly enrichment in HREE were found in rhizosphere and plants (roots and stems), whereas the leaves are enriched in LREE. The accumulation and translocation depend of internal complexes ligands. The redox and pH conditions of the rhizosphere conditioned the REE uptake. Greatest bioaccumulation ability of heavy REE (HREE) was found in C. monspeliensis, followed by H. lasianthum that also, has a high capacity of the REE translocation to the aerial parts, contrary to C. monspeliensis. An M-type tetrad effect was determined mainly for HREE (Gd-Ho series) indicating a complexation of REE. The greatest differences in the REE fractionation patterns (mainly for HREE) are observed in stems, as a consequence of the transport function of this organ. Cerium anomaly indicates that the pH and redox conditions affected the uptake of Ce by plants, where the free ionic species are dominated in roots and leaves (positive anomaly), and stems (negative anomaly). Also the Eu-anomaly is greater in roots and leaves than in steams probably by participation in metabolic functions due to similarity with calcium.

Modelling the speciation pattern of metals in Ondo coastal water with geochemical model – PHREEQCI

The speciation pattern of ten metals was studied in the coastal water of Ondo State, Nigeria using geochemical modelling software (PHREEQCI). The metals classified as macronutrients – Na, Ca, K, Mg; micronutrients – Fe, Cu, Mn, Zn; toxic metals – Cd, Pb were evaluated along with other general water quality parameters from ten sampling sites. The results served as input data for the modelling. The outcomes of the water speciation modelling revealed that the macronutrient metals exist as free ions which aid the reduction of free ion species of toxic metals. The micronutrients exist as neutral or complex salts which are less toxic according to free ion activity model theory. The self purification capacity of the coastal water was aided by the abundant formation of Fe-hydroxide precipitates; high alkalinity; pH; salinity of the coastal water which are responsible for the reduction of free ion specie of Pb and its ecotoxicity but increased the concentration of toxic Cd chloride species. Therefore, the prevailing biogeochemistry of the coast enhances demobilization of the metal contaminants and favours the reduction of their toxicity except Cd.

Fabrication of Aluminium Nitride by Electrophoretic Deposition

The electrophoretic deposition (EPD) technique has been developed to prepare AlN ceramics and the topic of this paper was the investigation of the AlN ceramic suspensions for electrophoretic deposition. The only addition of triethylamine didn’t promote the hydrolysis of AlN powder in 95% ethanol. The absorption of the polyacrylic acid (PAA) resulted in an increased Zeta potential, indicating that PAA is a very effective dispersant for the AlN and Y2O3 powders. Furthermore, by adding a combination of PAA and triethylamine, an stable AlN suspension could be obtained which was necessary for realising a high packing density in the electrophoretically deposited green bodies. The conductivity measurements indicated that suspension conductivity was lower than liquid conductivity. The lower conductivities of the suspensions could be explained by the fact that in concentrated suspensions the free ionic species are hindered in their movement by the particles. The conductivity of the centrifugate was higher than that of the suspension. It can be concluded that during the EPD the current in the suspension is mainly carried by the free ionic species. The transport of positively charged ionic species to the upper electrode (cathode) was slower than their consumption by the electrode reaction, an increased concentration overvoltage caused a significant increase in total electrical resistance due to the higher potential drop at the cathode. Finally, the EPD was usually stopped according to the increase in potential drop.

Enamel Subsurface Lesion Remineralisation with Casein Phosphopeptide Stabilised Solutions of Calcium, Phosphate and Fluoride

Casein phosphopeptide stabilised amorphous calcium phosphate (CPP-ACP) and amorphous calcium fluoride phosphate (CPP-ACFP) solutions have been shown to remineralise enamel subsurface lesions. The aim of this study was to determine the effect of ion composition of CPP-ACP and CPP-ACFP solutions on enamel subsurface lesion remineralisation in vitro. CPP-bound and free calcium, phosphate and fluoride ion concentrations in the solutions were determined after ultrafiltration. The ion activities of the free ion species present were calculated using an iterative computational program. The mineral deposited in the subsurface lesions was analysed using transverse microradiography and electron microprobe. CPP was found to stabilise high concentrations of calcium, phosphate and fluoride ions at all pH values (7.0–4.5). Remineralisation of the subsurface lesions was observed at all pH values tested with a maximum at pH 5.5. The CPP-ACFP solutions produced greater remineralisation than the CPP-ACP solutions at pH 5.5 and below. The mineral formed in the subsurface lesions was consistent with hydroxyapatite and fluorapatite for remineralisation with CPP-ACP and CPP-ACFP, respectively. The activity gradient of the neutral ion pair CaHPO₄⁰ into the lesion was significantly correlated with remineralisation and together with HF⁰ were identified as important species for diffusion.

Electronic structure and conformations of ortho-, meta-, and para-aminobenzensulfonic acid and its dimers

Geometric and electronic structures of some aniline derivatives have been obtained, aimed at a microscopic explanation of the observed electropolymerizability of these compounds. Monomers, dimers and their corresponding free radicals and ionic species, with the sulfonic acid group substituent located at various positions on the benzenoid ring, are considered. In this work we present an ab initio post-Hartree–Fock and density functional study of the ortho-, meta- and para-isomer of aminobenzenesulfonic acid (ortho-, meta-, and para-ABSA). To envisage a possible coupling scheme between ABSA molecules, we have obtained the equilibrium geometry and the electronic structure for monomers and dimers of ABSA as well as for the corresponding free radicals and ions.Based on the monomer-optimized geometries, atomic charges, bond orders and spin densities, a coupling scheme in the electrochemical polymerization is suggested. We have also calculated band gaps and ionization potentials. Some comments concerning the different theoretical methods used are made.

Electrophoretic Deposition of Ceramic Powders-Influence of Suspension and Processing Parameters

The electrophoretic deposition (EPD) of AlN, Al2O3 and SiC, respectively, from ethanolic suspensions stabilised by suitable organic additives has been investigated. A main topic of this paper is the EPD in the direction of the gravitational force. Using an AlN suspension, the deposit weight depending on the experimental parameters was determined. The deposition was carried out under constant voltage or constant current conditions. Several factors influencing the effective electric field strength will be discussed. It could be shown that the conductivity of the suspension results mainly from the free ionic species. By EPD from the different suspensions, green bodies with monomodal pore size distributions were produced. The electrophoretic deposition of alumina from an ethanolic and from an aqueous suspension of the same composition led to similar results regarding the homogeneity of the particle packing in the deposits. The SiC suspension was also used for infiltrating woven carbon fibre mats by EPD in order to fabricate ceramic matrix composites.

Photodegradation of Iron(III)-EDTA: Iron Speciation and Domino Effects on Cobalt Availability

Environmental Context. Aquatic life requires access to sufficient nutrients and trace metals in the surrounding waters. Measuring the speciation (in solution or precipitated, free ionic or complexed) of trace metals is a traditional procedure to assess the potential of waters for life. Iron, an important nutrient, is relatively insoluble, and metal–ligand complexes are required to keep the iron in solution and bioavailable. Sunlight often degrades these metal–ligand complexes, and the subsequently released iron can outcompete other (trace) metals for their ligands. A ‘domino’ effect on weaker metal–ligand complexes will occur which complicates the actual dynamic speciation and its measurements. Abstract. The effect of photodegradation of iron(iii)-EDTA on the chemical speciation of both iron and cobalt has been tested both in a simple medium and in a more complex algal growth medium. In both media, the photodegradation of iron(iii)-EDTA caused iron(iii) to be released as a free ionic species. Released iron(iii) could be modelled as engaged in precipitation and in competition with cobalt, initially also bound to EDTA. Cobalt appeared as free ionic species after a certain lag. The length of this lag phase was proportional to the amount of EDTA added to the media, which indicated that the surplus of EDTA was first targetted by iron(iii)-EDTA photodegradation, after which iron(iii) out-competed cobalt for the EDTA in the metal–EDTA pool. All data were fitted, using a model on speciation kinetics for cobalt-EDTA and iron(iii)-EDTA, taking into account photodegradation rates of iron(iii)-EDTA and precipitation of free iron(iii). The modelled rate of iron(iii)-EDTA photodegradation was compared to direct HPLC measurements of the disappearance of iron(iii)-EDTA due to photodegradation, the latter, however, with a different iron(iii)-EDTA concentration regime. The results suggest that photodegradation is a complex process which is greatly influenced by experimental conditions (e.g. light intensity/spectrum, iron(iii), and EDTA concentrations). Iron(iii)-desferrioxamine B (DFO-B) was suggested as a possible alternative for EDTA in experimental media: photostability was shown for prolonged experimental periods.

In situ trace metal speciation in a eutrophic lake using the technique of diffusion gradients in thin films (DGT)

We evaluated the application of DGT (diffusion gradients in thin films) as a tool to determine Cu, Zn, Ni, Cd, Pb and Mn concentrations and speciation in a hardwater eutrophic lake. This technique was used in situ during six sampling periods over one year in Lake Greifen. The DGT-labile species of Cu and Ni amounted to 15–25% of the total dissolved concentrations. Speciation by ligand-exchange/DPCSV indicated that Cu and Ni were predominantly organically complexed (>99%). Thus, the DGT-labile species for Cu and Ni were much more abundant than the free ionic and inorganic species determined by ligand-exchange/DPCSV. The results can be explained by incomplete metal exchange of very strong complexes with the chelating resin in the DGT devices, metal exchange of less abundant weaker complexes, and by slow diffusion of exchangeable organic complexes. For Zn (36 to >90% DGT-labile) and Mn (50 to 100% DGT-labile), the results indicated that these metals are less strongly organically complexed. A larger fraction of Zn occurred in DGT-labile species in the hypolimnion than it did in the surface water, probably due to a larger concentration of strong ligands in the productive surface water. DGT-labile Cd- (0.01–0.02 nM) and Pb-species (0.03–0.06 nM) were detected at very low levels. The combination of measurements of dissolved and DGT-labile species showed a decrease of Cu, Zn, Cd and Mn concentration at 2.5 m from June to August, which was probably linked to intensive sedimentation of organic matter during summer stagnation. Mixing and oxygenation of the lake in winter-spring led to an increase in dissolved and DGT-labile Ni, Zn and Cd, whereas Mn decreased in the hypolimnion.