Species Of Cu Research Articles

Copper and cadmium, isolated and in the mixture, impact the Neotropical freshwater Calanoida copepod Notodiaptomus iheringi: A short-term approach with environmental concentrations

Metal discharges in aquatic ecosystems are of concern since they affect different trophic levels, altering the functioning of the aquatic food chain. The metals can interact among them and with other pollutants, resulting in complex mixtures whose effects on biota are unpredictable. The impacts of copper (Cu) and cadmium (Cd), isolated and combined, on the freshwater copepod Notodiaptomus iheringi were assessed in acute and sub-chronic exposures. Species sensitivity distribution (SSD) curves were constructed for both metals. In the acute tests antagonism was observed in mortality, while in sub-chronic, mortality was not affected; however, the eggs produced and percentage of viable eggs were significantly altered. Our data suggest that egg production can be a detoxification route in N. iheringi under Cu and mixture exposure. From the SSD curves, N. iheringi was the most sensitive Brazilian species for Cu and the second most sensitive for Cd.

Spatial Distribution, Speciation, and Ecological Risk Assessment of Heavy Metals in Surface Sediments of Dongjiang Lake, Hunan Province

To understand the heavy metal pollution status of Dongjiang Lake, the contents and species of heavy metals in the surface sediments were investigated during September 2021, and the heavy metal pollution level and potential ecological risk were evaluated. The results showed that Cd, Pb, As, Cu, Zn, Ni, and Cr contents were in the range of 0.40-34.1, 14.8-1688, 6.99-1155, 6.89-280, 26.2-1739, 6.29-55.4, and 23.3-44.8 mg·kg-1, respectively, with extremely uneven spatial distributions. The highest contents of Cd, Pb, As, Zn, Cu, and Ni were found in the site adjacent to Yaogangxian tungsten ore. The proportion of metal species with bioavailability was high, in which Cd in acid-soluble species was 46.7%-71.5% and Pb in reducible species was 46.8%-67.0%. The bioavailable species of Cu, Zn, Ni, and Cr were 35%-68%, 42%-72%, 26%-51%, and 6%-30%, respectively, although they primarily existed in residual species. According to the geo-accumulation index (Igeo), there was a moderate or extreme pollution status of Cd in all sites, moderate or extreme pollution status of Pb in 90% of sites, and moderate pollution status of As, Cu, and Zn in 30% of sites. The ecological risk factor (Eri) of Cd showed high potential ecological risk in all sites with significantly high potential ecological risk in 80% of sites. Moreover, As and Pb had significantly high potential ecological risk, and Cu had moderate potential ecological risk in S7, which was adjacent to Yaogangxian tungsten ore. There was a high total potential ecological risk in all sites and significantly high potential ecological risk in 50% of sites. Therefore, the surface sediments of Dongjiang Lake were under the combined pollution of Cd, Pb, As, Zn, and Cu with high bioavailability and high total potential ecological risk.

PEI-modified chitosan/activated carbon composites for Cu(II) removal from simulated pyrophosphate plating rinsing wastewater

It is a challenging task to remove heavy metal ions efficiently from the wastewater containing high concentrations of complexants. In this work, a novel PEI-modified chitosan/activated carbon composite adsorbent (PCA) was prepared and applied to the removal of Cu(II) from pyrophosphate plating rinsing wastewater. The main species of Cu(II) in the pyrophosphate wastewater was [Cu(HP2O7)2]4− or [Cu(P2O7)2]6−, which were denoted as [Cu(II)-PP] anions. The maximum adsorption capacity of PCA for Cu(II) reached 1.41 mmol g−1 under the condition of pH = 8 and molar ratio of pyrophosphate to Cu(II) = 4:1. The adsorption kinetic behavior of Cu(II) on PCA followed the Elovich model best and PCA attained adsorption equilibrium within 36 h. The thermodynamic studies showed that the adsorption process of Cu(II) by PCA was endothermic and spontaneous. The PCA fixed bed column was used to remove Cu(II) from simulated pyrophosphate plating rinsing wastewater. After three consecutive adsorption-desorption cycles, the adsorption performance, hydraulic conductivity, and mechanical stability of PCA column did not decrease. The FTIR and XPS analysis results indicated that [Cu(II)-PP] anions can be adsorbed on PCA by electrostatic attraction with protonated amine groups or coordination with the amine groups of PCA via ligand substitution.

Effect of dispersed species heterogeneity in carbon-based catalysts for near-infrared light-responsive synergistic antibacterial therapy

Due to their distinct properties, single atom and cluster catalysts have been intensively researched and developed in several fields. However, the mechanism by which the size of these dispersed species of single-atom and cluster catalysts, as well as conventional particulate catalysts, affects the properties remains ambiguous, especially in complex systems such as photothermal/photodynamic therapy. Therefore, carbon black is chosen as a substrate and loaded with two types of metals (Cu and Au) in sizes ranging from single atoms to nanoclusters and nanoparticles. The Cu-CBs and Au-CBs showed the opposite variation of antimicrobial activity to the dispersed species. The antimicrobial activity of the Cu-CBs decreased with the size of dispersed species from 100% to 99.48% and 99%. The increase in size enhanced the antimicrobial activity of Au-CBs from 95.1% to 97.4% and 98.8%. Characterization and theoretical calculations revealed that the dispersed species of Cu and Au affect the photothermal properties and photodynamic aspects to varying degrees. This work contributes to the development of single-atom and cluster nanomaterials as well as conventional catalysts and the investigation of related mechanisms.

Rational design of zero-valence and well-dispersed copper nanocluster stabilized by carbon-coated SiO2 for highly effective and ultrafast reduction of nitroarenes

In this work, we present a ligand modification strategy that allows for the regulation of the valence and dispersion state of Cu clusters in the final obtained Cu@C/SiO2 catalyst. Specifically, the phthalic acid (PA) ligand promotes the uniform anchoring of zero-valence Cu nanoclusters on Cu@C/SiO2, resulting in excellent catalytic activity in the selective reduction of toxic 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with a rate constant (k) of 19.06×10-3 s-1. This value was approximately 2.4- and 31.2-fold higher than that of the CuO/SiO2 and bare CuO catalysts, respectively. Additionally, no significant decline in activity was detected during six successful cycles. Through systematic analysis of structural and electronic properties of the catalyst, we confirmed that the coordination effect of the PA ligand and the carbothermic effect of its carbon derivatives effectively prevent particle aggregation and modulate the valence state of copper species in Cu@C/SiO2, resulting in superior catalytic performance.

Organic Wastes Augment the Eco-Restoration Potential of Bamboo Species on Fly Ash-Degraded Land: A Field Study

Rapid industrialization has been a major cause of land degradation and other environmental problems globally. Most energy inputs in industries depend on coal-burning power stations which release various pollutants into the environment. Among these pollutants, fly ash is a concerning pollutant for soil quality, as it occupies a voluminous area of land in India and renders it unproductive. Therefore, this work attempts to evaluate the organic amendment-facilitated bioremediation/phytoremediation of fly ash-degraded land through bamboo plantations under field conditions. Three species of bamboo, Bambusa balcooa, B. tulda, and B. bambos, were planted on fly ash dumpsite soil amended with a combined dose of pressmud and farmyard manure. Results demonstrate that after two years of plantation, all the physicochemical attributes of the degraded land were improved considerably compared to the initial observations. Although all the bamboo species exhibited promising phytoremediation potential, variations were observed in their phytoremediation mechanisms: B. balcooa was the most ideal phytostabilizer species for Cu, Zn, and Ni. B. bambos was found as an ideal phytostabilizer of Pb and Zn while B. tulda was found as a phytoextractor of Cr and Zn. Additionally, all the bamboo species sequestrated atmospheric CO2 considerably, resulting in overall environmental restoration of the degraded area; B. balcooa was the most ideal species. Moreover, B. balcooa exhibited the highest air pollution tolerance index compared to other species. This study, therefore, recommends that a comprehensive analysis of organic matter-mediated phytoremediation would assist environmental managers to formulate sustainable eco-restoration strategies, ensuring a sustainable solution to land degradation.

Multiple reinforcement of chloride ion on oxidizing acetaminophen with zero-valent copper particles: In-site formation and catalysis of hydrogen peroxide

Zero-valent copper particles (Cu0) used to degrade pollutant due to its in-site generation and activation of hydrogen peroxide (H2O2), while the disproportionation of Cu+ limited the efficacy. In this study, spiking chloride ion (Cl−) into zero-valent copper (Cu0) system (Cl−/Cu0 system) enhanced greatly acetaminophen degradation. The addition of Cl− not only reduced the dismutation reaction of Cu+, but also helped the comproportionation reaction of Cu0 and Cu2+, leading to much generation of Cu+ and H2O2. Hydroxyl radical (OH) and reactive chlorine species were identified as the dominant reactive oxidants in the Cl−/Cu0 system with its contribution ratio of degrading acetaminophen being respectively 73.4 % and 23.8 %. In the Cl−/Cu0 system, Cu+ was released by H+ corrosion from Cu0, and then Cu+ coupled with Cl− forming Cu-Cl complexes; Meanwhile, the reaction of O2 and the species of Cu+ (e. g. Cu-Cl complexes and Cu+) produced H2O2 and, then the species of Cu+ catalyzed H2O2 to form OH; Thereinto, partial OH was shifted by Cl− to reactive chlorine species. Except for fulvic acid, coexisting substrates such as sulphate, nitrate and phosphate ions had no obvious inhibition impact on oxidizing acetaminophen in the Cl−/Cu0 system. Furthermore, the Cl−/Cu0 system presented a good removal rate of acetaminophen in three actual water samples. Moreover, three kinds of dyes and painkillers was removed over 78 % in the Cl−/Cu0 system. The residual total dissolved copper was under II-level of environmental quality standards for surface water in China by alkali precipitation and filtration after reaction. Therefore, the study provided a new idea to enhance Cu0 for the purification of pollutants.

CsCu2I3 Nanoparticles Incorporated within a Mesoporous Metal-Organic Porphyrin Framework as a Catalyst for One-Pot Click Cycloaddition and Oxidation/Knoevenagel Tandem Reaction.

Metal-organic frameworks (MOFs) and metal halide perovskites are currently under much investigation due to their unique properties and applications. Herein, an innovative strategy has been developed combining an iron-porphyrin MOF, PCN-222(Fe), and an in situ-grown CsCu2I3 nontoxic lead-free halide perovskite based on an earth-abundant metal that becomes incorporated within the MOF channels [CsCu2I3@PCN-222(Fe)]. Encapsulation was designed to decrease and control the particle size and increase the stability of CsCu2I3. The hybrid materials were characterized by various techniques including FE-SEM, elemental mapping and line scanning EDX, TEM, PXRD, UV-Vis DRS, BET surface area, XPS, and photoemission measurements. Hybrid CsCu2I3@PCN-222(Fe) materials were examined as heterogeneous multifunctional (photo)catalysts for copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) and one-pot selective photo-oxidation/Knoevenagel condensation cascade reaction. Interestingly, CsCu2I3@PCN-222(Fe) outperforms not only its individual components CsCu2I3 and PCN-222(Fe) but also other reported (photo)catalysts for these transformations. This is attributed to cooperation and synergistic effects of the PCN-222(Fe) host and CsCu2I3 nanocrystals. To understand the catalytic and photocatalytic mechanisms, control and inhibition experiments, electron paramagnetic resonance (EPR) measurements, and time-resolved phosphorescence were performed, revealing the main role of active species of Cu(I) in the click reaction and the superoxide ion (O2•-) and singlet oxygen (1O2) in the photocatalytic reaction.

Chemical speciation of copper and manganese in solution of a copper-contaminated soil and young grapevine growth with amendment application

Copper (Cu)-based fungicide application to control foliar diseases in grapevine (Vitis vinifera L.) can increase soil Cu availability. Brazilian soils have high natural Cu and manganese (Mn) concentrations, increasing the potential for toxicity to grapevine plants. Application of amendment substances can reduce the concentrations of toxic chemical species of Cu and Mn in soil solution, especially for the soils grown with young plants. We evaluated the chemical speciation of Cu and Mn in soil solution and young grapevine growth using a contaminated soil with amendment application. Grapevine seedlings of Paulsen 1103 rootstock were grown for 12 months on an old vineyard (> 30 years of cultivation) soil without (control) and with vermicompost or limestone application. Grapevine dry matter, root morphological characteristics, and plant tissue Cu and Mn concentrations were evaluated. The cation and anion concentrations, dissolved organic carbon, pH, and chemical speciation of Cu and Mn in soil solution from different soil layers were analyzed. Vermicompost application did not reduce Cu and Mn phytotoxicity, and grapevine plants died after winter pruning. High soluble Mn concentration in soil (5.56 mg L–1 in 0–45 cm soil layer) and Mn concentration in plant tissue at pruning (380.8 mg kg–1) might be the primary cause of plant death. Limestone application reduced Cu2+ and Mn2+ chemical species in soil solution, thereby increasing plant growth. The Cu2+ and Mn2+ species were negatively correlated (P < 0.05) with grapevine shoot production at pruning (r = –0.92 and –0.97, respectively) and at the end of the trial (r = –0.73 and –0.51, respectively). Limestone application increased grapevine shoot and root dry matter production by 36% and 41%, respectively, while also presenting the highest root length and volume in the 5–10 cm soil layer. Limestone application is a viable and profitable alternative for reducing soil Cu and Mn availability and their phytotoxic effects.

Switching CO2 Electroreduction Selectivity Between C1 and C2 Hydrocarbons on Cu Gas‐Diffusion Electrodes

Regulating the selectivity toward a target hydrocarbon product is still the focus of CO2 electroreduction. Here, we discover that the original surface Cu species in Cu gas‐diffusion electrodes plays a more important role than the surface roughness, local pH, and facet in governing the selectivity toward C1 or C2 hydrocarbons. The selectivity toward C2H4 progressively increases, while CH4 decreases steadily upon lowering the Cu oxidation species fraction. At a relatively low electrodeposition voltage of 1.5 V, the Cu gas‐diffusion electrode with the highest Cuδ+/Cu0 ratio favors the pathways of hydrogenation to form CH4 with maximum Faradaic efficiency of 65.4% and partial current density of 228 mA cm−2 at −0.83 V vs RHE. At 2.0 V, the Cu gas‐diffusion electrode with the lowest Cuδ+/Cu0 ratio prefers C–C coupling to form C2+ products with Faradaic efficiency topping 80.1% at −0.75 V vs RHE, where the Faradaic efficiency of C2H4 accounts for 46.4% and the partial current density of C2H4 achieves 279 mA cm−2. This work demonstrates that the selectivity from CH4 to C2H4 is switchable by tuning surface Cu species composition of Cu gas‐diffusion electrodes.

The solubility of Cu, Ag and Au in magmatic sulfur-bearing fluids as a function of oxygen fugacity

Magma-derived fluids containing chlorine and sulfur are critical for the transport of ore metals to porphyry ore-forming environments. However, experimental data on the speciation and the solubility of ore metals in these fluids at conditions relevant to the arc magmatism are scarce. In particular, the effect of redox conditions on ore metal speciation and solubilities in sulfur-bearing fluids has not yet been experimentally constrained. We performed experiments to determine the effect of oxygen fugacity (fO2) on the solubility of Cu, Ag and Au in high-temperature, low- density, low-salinity fluids and hypersaline brine. The experiments were conducted at T = 900 °C, P = 2000 bar varying fO2 in 7 steps between 0.5 log units below the Ni-NiO buffer (NNO − 0.5) to NNO + 2.5. A prototype rapid-quench Molybdenum-Hafnium Carbide (MHC) externally heated pressure vessel assembly was used, which was fitted with a Shaw membrane for precise control of fO2. The fluid phase was sampled as synthetic fluid inclusions (SFI) by in situ fracturing of quartz chips during the experiments. As capsule material, Au97Ag2Cu1 alloy was used, which imposed activities of 0.962, 0.0082 and 0.0097 for Au, Ag and Cu, respectively. The apparent solubility of Cu and Ag at the imposed metal activities increases by a factor of 7 in the H2O-NaCl-KCl-S low-salinity fluid with fO2 increasing from NNO − 0.5 to NNO + 2.5. The addition of 0.198 m HCl increases the overall solubility of Cu by a factor of 1.2–2.4. The apparent solubility of Au decreases by a factor of 9 as fO2 changes from NNO − 0.5 to NNO + 2.5. The relationship between the logarithms of the apparent Cu and Ag solubilities and fO2 is linear and the slope of the fitted line corresponds to 1+ oxidation state of these metals indicating that they are dominantly complexed by ligands that are S-free (e.g., chloride). Thermodynamic model calculations indicate that the dominant species for Cu and Ag are NaCuCl2 and NaAgCl2, respectively. For Au, the dominant species is predicted to be NaAu(HS)2 at low and intermediate fO2 conditions, and AuCl and NaAuCl2 at oxidizing conditions. The measured gold solubilities at intermediate fO2 do not indicate significant Au complexation with S species containing S in intermediate oxidation states. Considering previous studies on silicate melts and our experimental data for volatiles, we conclude that Cu and Ag likely have constant fluid/melt partition coefficients in the typical fO2 range of arc magmatism because they dissolve in the same oxidation state in the fluid and the melt (1+) and are dominantly chloride complexed in the fluid.

Corrosion Mechanism of Microporous Nickel-Chromium Coatings: Part II. SECM Study Monitoring Cu2+ and Oxygen Reduction

The corrosion mechanism of microporous nickel-chromium multilayer coatings was studied at localised scale by Scanning Electrochemical Microscopy (SECM) after exposure to an aggressive electrolyte (chloride-based one at pH 3.1 containing cupric ions). The open circuit potential was initially monitored during 22 h, followed by a detailed characterisation using Glow Discharge-Optical Emission Spectroscopy and Field Emission Scanning Electron Microscope. Interestingly, Cu deposition occurs over the surface of the microporous nickel layer, and it is located on spots where micro-discontinuities (i.e., cracks and pores) of the outermost Cr layer are present. The application of different operation modes of the SECM (i.e., redox competition and surface generation/tip collection) not only reveals such copper deposits (which were identified after monitoring their catalytic capabilities for oxygen reduction reaction) but also confirms the stepwise reduction of Cu2+ to Cu0 (via intermediate species of Cu+) during the corrosion process. The impact of metallic copper particles in the local pH due to their catalytic activity could also explain why the microporous nickel layer is not corroded after exposure to such electrolyte.

The highly efficient electrocatalytic oxidation of 5-hydroxymethylfurfural on copper nanocrystalline/carbon hybrid catalysts: structure–function relations

The Cu species in Cu(NSD)/CP exhibit a high electrochemical specific surface area, which allows efficient transformation from Cu0and Cu1+species to Cu2+with high catalytic capacity, resulting in excellent catalytic performance (96% yield of FDCA).

Using modified Tessier sequential extraction to specify potentially toxic metals at a former sewage farm

The main objectives of this study were to evaluate the Cu, Zn, Pb, Cr and Ni mobility using modified Tessier sequential extraction procedure and to study the functional group changes affected by each extraction step using FTIR analysis in the soil of a former sewage farm sedimentation basin. Tessier extraction revealed element dependent fractionation of studied metals: Pb was mostly discovered in the residual fraction (77%) followed by Cr (53%), Cu (8%), and Zn (5%), while Ni was not extracted in this fraction. The organic matter-bound was the dominant species of Cu (77%). Zn and Ni exhibited the highest affinity for Fe/Mn oxides fraction (55% and 39%, respectively). The average recovery rate was 62–111%, whereas the lowest rate was obtained for Ni (62%) and the highest for Cu/Pb (110–111%). Results indicated elevated concentrations of studied elements, with the following order of mobility factor: Ni > Zn > Cu > PbCr. The preliminary interpretation of the sequential extraction FTIR spectral response revealed that DRIFT is applicable to interpret the sequential metal extraction and revealed three most profound changes correlated to the carbonate, Fe/Mn oxides, and OM fraction.

CO2 Hydrogenation to Methanol over Partially Reduced Cu-SiO2P Catalysts: The Crucial Role of Hydroxyls for Methanol Selectivity

The involvement of surface hydroxyl species in controlling methanol selectivity for a CO2 hydrogenation reaction was investigated over Cu-phyllosilicate (Cu-SiO2P) catalysts prepared by a urea-assisted hydrothermal synthesis method. The role of hydroxyls involvement was investigated by treating the Cu-SiO2P catalyst between 225 and 350 °C in H2 gas. The presence of Cu-containing phyllosilicate structures in Cu-SiO2P catalysts was confirmed through TEM and XPS analyses. As evidenced by in situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and X-ray absorption spectroscopy, Cu+ centers are dominant surface species for Cu in Cu-SiO2P catalysts during the hydrogenation reaction. Also, bidentate formate species are the prominent intermediates to direct methanol formation via methoxy intermediate species. The hydroxyl intervention in CO2 hydrogenation for a hydroxyl-abundant Cu-SiO2P catalyst reduced at 225 °C is confirmed by the appearance of a new band at 2944 cm–1 (−C–H) by high-pressure in situ DRIFTS CO2 hydrogenation experiments. H2/CO-TPR revealed the uniformity and presence of surface hydroxyls in Cu-SiO2P catalysts. The best catalyst Cu-SiO2P reduced at 225 °C gave a stable CO2 conversion of 3.5% and a methanol yield of 140 mg MeOH/g-cat.h (a methanol selectivity of 77%) at 225 °C and 3 MPa pressure for a 24 h reaction time. The presence of hydroxyls generated due to partial reduction of the Cu-SiO2P catalyst and surface enriched with Cu+ species could be the reasons for its superior catalytic performance.

Study the existing form of copper (p-type oxide/segregation) and its release mechanism from the passive film of Ti-7Cu alloy

The existing form of copper and its release mechanism from the passive film of Ti-7Cu alloy was studied by Quantitative analysis of depth profile and series of electrochemical tests. Results were interpreted within the Point Defect Model-II. Copper does not form any p-type (cuprous or cupric) oxide but preferentially oxidises at the metal/film interface and segregated as Cu interstitials Cui+ and become substituted as CuTix' in the oxygen-deficient TiO2-x barrier layer having n-type semiconducting character. Eventually, the segregated species of Cu preferentially dissolute through the film as Cu ions into the solution at film/solution interface via the Esaki-tunnelling effect.

Sensitivity of freshwater organisms to cadmium and copper at tropical temperature exposures: Derivation of tropical freshwater ecotoxicity thresholds using species sensitivity distribution analysis

Tropical freshwater ecosystems are increasingly influenced by chemical stressors including heavy metals posing threats to biodiversity. Adequate ecotoxicity data are not available for native tropical freshwater species for deriving water quality guidelines and for conducting ecological risk assessments. Objectives of this study were (i) to generate freshwater ecotoxicity data for cadmium (Cd) and copper (Cu) for tropical temperature exposures using standard laboratory bioassays with selected freshwater species and (ii) to derive ecotoxicity thresholds (protection concentrations, PC) for tropical freshwater life based on ‘tropical temperature-specific exposure’ ecotoxicity data. Estimated final chronic toxicity values of the six species tested in the study indicate that the most sensitive species was the crustacean, Moina macrocopa for both metals while the algae Chlorella vulgaris and the plant Lemna perpusilla showed highest tolerance to Cd and Cu respectively. Tropical temperature-specific exposure (25–30 °C) was used as the decision criterion for deriving ecotoxicity thresholds of Cd and Cu for protection of tropical freshwater life based on species sensitivity distribution analysis of the final chronic toxicity data sets which included published toxicity data of selected species in addition to the six species tested in this study. The derived PC99, PC95, PC90 and PC80 values for protection of tropical freshwater life under chronic exposure are 0.5, 1.2, 1.9 and 3.5 μg/L for Cd and 0.34, 0.84, 1.4 and 2.6 μg/L for Cu respectively. These derived threshold chronic values (PC99 and PC95) indicate that the established freshwater quality guidelines based on temperate species for Cu may not provide sufficient protection of the freshwater species in the tropics while the available freshwater guidelines for Cd would provide adequate protection for the tropical freshwater species. The tropical freshwater ecotoxicity thresholds derived in this study may be used with some caution as reference points for site specific ecological risk assessments in the tropics.

Mobilization mechanisms and toxicity risk of sediment trace metals (Cu, Zn, Ni, and Pb) based on diffusive gradients in thin films: A case study in the Xizhi River basin, South China

Identifying the mobilization mechanisms and predicting the potential toxicity risk of metals in sediment are essential to contamination remediation in river basins. In this study, a sequential extraction procedure and diffusive gradients in thin film (DGT) were employed to investigate the mobilization mechanisms, release characteristics, and potential toxicity of sediment metals (Cu, Zn, Ni, and Pb). Acid-soluble and reducible fractions were the dominant geochemical species of Cu, Zn, Ni, and Pb in sediments, indicating high mobility potentials for these metals under reducing conditions. In summer, the sediment acted as a source of water-column metals due to mineralization of organic matter and reductive dissolution of iron/manganese oxides in surface sediments, and the formation of metal sulfide precipitates markedly lowered DGT-labile metal concentrations with depth, while localized sulfide oxidation was responsible for fluctuating labile metal concentrations. Stable distribution patterns of labile metals resulted from the weak reducing conditions of sediment in winter, when the sediment shifted to a metal sink. The interstitial water criteria toxicity unit (IWCTU), calculated from DGT measurements, indicated no and low-to-moderate toxic risk of sediments in summer and winter seasons, respectively, and Pb was the major contributor to the predicted toxic effects in the soft interstitial water.

Metals Uptake by Sagittaria montevidensis in Contaminated Riparian Area of Matanza-Riachuelo River (Argentina)

The objective of this study was to evaluate the accumulation and uptake of Cr, Zn, Cu, Ni and Pb in Sagittaria montevidensis growing in highly contaminated riparian soils of Matanza Riachuelo Basin (MRB). It is a native and very abundant riparian plant exposed to heavy metal contamination. Samples of S. montevidensis, rhizosphere riparian soil and water were collected at three sites in the lower MR basin. The accumulation and the level of translocation of Cr, Zn, Cu, Ni and Pb in this species were determined. The soils were found to be the main reservoirs of metals (2225 mg Cr kg−1 d.w., 367 mg Cu kg−1 d.w., 61 mg Ni kg−1 d.w., 239 mg Pb kg−1 d.w., and 1495 mg Zn kg−1 d.w.). All studied metals were uptaken, but Zn and Cu were the most accumulated metals (426 ± 28 mg kg−1 d.w. and 129 ± 28 mg kg−1 d.w., respectively). S. montevidensis was an accumulator species for Cu and Ni (Translocation Factor (TF) > 1) and it showed an exclusionary behavior (TF < 1) for Cr, Pb, and Zn. Cu was mostly accumulated in the aerial biomass. The rest of the metals analyzed were mainly accumulated in the roots. The analyzed plant specimens did not show signs of stress, having completed their phenological states. This native species shows high tolerance of metals. Then the preservation and revegetation of this species in the riparian areas constitute a sustainable alternative for ecological restoration.

Benzyl alcohol oxidation mechanisms by one- and two-electron oxidized species of Cu(II)-salen complexes with para-R-substituents, [Cu(R-salen)]n+ (R = MeO, MeS; n = 1, 2)

Benzyl alcohol oxidation by one- and two-electron oxidized copper(II)-salen complexes with the para-substituted phenolate moieties, [Cu(R-salen)]n+ (H2R-salen = N,N’-bis(3-tert-butyl-5-R-salicylidene)ethylenediamine; R = methoxy (MeO), methylthio (MeS) groups; n = 1, 2) was kinetically investigated under the conditions with large excess of the substrate in comparison to the copper complex concentration (CBnOH ≫ CCu). The one- and two-electron oxidized complexes [Cu(R-salen)]n+ (n = 1 and 2) oxidized benzyl alcohol irrespective of R-groups to generate benzaldehyde and the Cu(R-salen) species in stoichiometries of complex : substrate = 2 : 1 and 1 : 1, respectively. Kinetic analyses for benzyl alcohol oxidation by the one-electron oxidized complexes [Cu(R-salen)]+ revealed significantly different kinetics depending on R-groups: one-step pseudo second-order kinetics was assigned for R = MeO, while two-step pseudo first-order kinetics was suitable for R = MeS. The reaction kinetics by two-electron oxidized complexes [Cu(R-salen)]2+ were assigned to two- and three-step first-order processes for R = MeO and MeS, respectively, in which the first step consists of parallel pathways of complex : substrate = 1:1 and 1:2 reactions to generate the one-electron oxidized complex intermediates irrespective of the R-group. However, the following steps were different depending on R-groups. Associating with the results of kinetic isotope effect (KIE) measurements, the reaction mechanisms were discussed and proposed.