Copper Speciation Research Articles

Determination of inert and labile copper on GEOTRACES samples using a novel solvent extraction method

Copper, in seawater, is predominantly bound by organic ligands of unknown composition. Complexation has been thermodynamically characterized using synthetic ligand competition experiments which assumes equilibrium among all chelators within the system. However, equilibration times are constrained by wall loss issues with the synthetic ligands. Here, a solvent extraction methodology, was utilized to avoid the wall-loss problems. Using an exceptionally high concentration of a strong copper chelator, oxine (8-hydroxyquinoline), at least six hours of equilibration time is required to reach steady state between the competing ligand and the labile copper in seawater. This is much longer than equilibration times used in previously published works. Our method was optimized by using samples from GEOTRACES expeditions in the North Pacific and North Atlantic Oceans. Surprisingly, 60–90% of the copper was not exchangeable with oxine under these conditions. We define this fraction as “inert”, and these data, which include profiles as deep as 1000 m in the North Pacific, suggest that this is a widespread feature. Our results suggest that there are two distinct pools of labile and inert copper, rather than an assemblage of similar complexes with incremental differences in stability constants. The results have important implications for the marine geochemistry of copper and its bioavailability. Complexation has been shown to limit copper bioavailability and influences scavenging and residence time. Moreover, a basic paradigm of copper speciation methodologies, that even strong Cu complexes are relatively labile, is likely incorrect.

CE-ICP-MS to probe Aβ1-42/copper (II) interactions, a complementary tool to study amyloid aggregation in Alzheimer's disease.

Copper (II) ions appear to be involved in the Alzheimer's disease and seem to influence the aggregation of the amyloid-β1-42 (Aβ1-42) peptide. However, data are not conclusive and still not subject to consensus, copper (II) being suspected to either promote or inhibit aggregation. To address this question, CE-ICP-MS (capillary electrophoresis-inductively coupled plasma-mass spectrometry) hyphenation was proposed as a complementary tool to follow the distribution of copper in the different oligomeric forms, at different substoichiometries and different incubation times. Results clearly indicated the formation of several negatively charged copper complexes and showed the enhancement of the aggregation rate with copper concentration. Moreover, the variations of copper (II) speciation suggest different aggregation pathway, even for substoichiometric ratios.

Structural charge location dictates speciation and lability of copper in swelling layer silicates

Clay minerals with high selectivity for metals have potential for remediating contaminated water and surface soils. A highly-charged swelling mica (Na-2-mica) and montmorillonite were assessed for their capacities to sorb Cu and resist subsequent desorption. Sorption onto Na-2-mica was studied at Cu loadings of 150, 500, 1500, and 5000 mg/kg in 10 g/L Na-2-mica suspensions with 1 mM KNO3 as the background electrolyte at pH 5. Copper sorption onto montmorillonite was tested under the same conditions at a Cu loading of 1500 mg/kg. Desorption was performed with 10 replenishments (i.e., desorption steps) of 1 mM KNO3 followed by 5 desorption steps with 0.1 M KNO3. About 1.3%–1.4% of the initial Cu was desorbed after 10 desorption steps with 1 mM KNO3 in both 1500 mg/kg clay systems. Subsequently, 5 desorption steps with 0.1 M KNO3 removed all the Cu from the montmorillonite, whereas approximately 23% of the Cu remained sorbed to Na-2-mica. The 500 mg/kg and 5000 mg/kg Cu Na-2-mica systems followed similar desorption trends as did the 1500 mg/kg Cu system. The resistance of Na-2-mica to Cu desorption was due to strong Cu retention mechanisms, including chemisorption and retention of partially hydrated and interacting Cu ions in a crowded interlayer space, as revealed by electron paramagnetic resonance spectroscopy (EPR). Strong retention of partially hydrated Cu by ion exchange is promoted by the high structural charge in the tetrahedral sheets of Na-2-mica. In contrast, montmorillonite reversibly retained fully hydrated Cu ions by electrostatic attraction (i.e., ion exchange), probably facilitated by structural charge located a greater distance from Cu in the octahedral sheet. Overall, the Na-2-mica's distinct electrostatic surface characteristics explain the lower degree of hydration and the greater strength of outer-sphere Cu complexes than those observed in the montmorillonite system. These results indicate that Na-2-mica shows more promise for Cu immobilization under acidic conditions.

Consistent controls on trace metal micronutrient speciation in wetland soils and stream sediments

Trace metal are essential for microbially-mediated biogeochemical processes occurring in anoxic wetland soils and stream bed sediments, but low availability of these elements may inhibit anaerobic element cycling and transformations. Solid-phase speciation is likely a critical control on trace metal availability but has seen limited study in anoxic systems having concentrations similar to geological background levels, where metal limitations may be most prevalent. We have investigated trace metal concentrations and solid-phase speciation in three freshwater subsurface aquatic systems: marsh wetland soils, riparian wetland soils, and the sediments of a streambed. These systems displayed low solid-phase trace metal concentrations, generally at or below geological background levels, which generally followed the trend Zn > Cu ≈ Ni > Co and showed no correlation with major element compositions. All soils and sediments were dominated by quartz but varied in clay mineralogy as well as the organic matter, total sulfur, and total iron contents. X-ray absorption near-edge structure (XANES) spectroscopy shows that sulfur speciation in both wetlands is dominated by organic sulfur. Elemental sulfur and iron sulfides together made up <25% of the sulfur in the wetland soils, but the distribution between inorganic and organic forms was reversed in the stream sediments. Ferrous and ferric iron in clay minerals were common species identified by both XANES and extended X-ray absorption fine structure (EXAFS) spectroscopies at all sites. Iron(III) oxides were substantial components in all but the marsh wetland soils. Quantitative analysis of copper, nickel, and zinc XANES spectra revealed similar metal speciation across all sites. Copper speciation was dominated by sulfides, adsorbed species, and minor amounts of copper bound to organic matter; no metallic copper was detected. Nickel speciation also varied little and was dominated by nickel in clay mineral octahedral sheets and nickel sulfide, with adsorbed species also present. Zinc speciation was slightly more varied, with the marsh wetland soils and stream bed sediments containing adsorbed species, zinc associated with clay mineral structures, and zinc bound to reduced sulfur groups on organic matter, whereas the riparian wetland soils lacked clay-associated zinc but contained zinc sulfide. Trace metals bound to reduced sulfur occurred at every site, with a greater sulfur-bound fraction for copper. The fractional abundance of sulfur-bound species showed no relationship with soil or sediment total sulfur content, which varied by two orders of magnitude. More broadly, the observations in this study suggest that trace metal speciation in freshwater wetland soils and stream sediments is consistently dominated by a small set of recurring components which are distinct for each metal. This may represent a general geochemical phenomenon in anoxic soils and sediments containing trace metals at background concentrations (as low as 3 µg g−1) that was not predicted from systems that are contaminated with or naturally-enriched in copper, nickel, or zinc.

In situ analysis of copper speciation during in vitro digestion: Differences between copper in drinking water and food

In recent years, the safety of copper in drinking water has increasingly been questioned. Copper speciation is an important factor that affects its bioavailability and toxicity; thus, it is critical to investigate the speciation of copper that is ingested from food and drinking water during in vitro digestion. After digestion, water- and food-derived copper formed 60 ± 4% 0.1–1 kDa and 49 ± 6% 10–1,000 kDa copper complexes, respectively. Under simulated fasting drinking water conditions, up to 90 ± 2% 0.1–1 kDa copper complexes formed. In addition, using ion selective electrode analysis, water-derived copper was detected that contained higher Cu2+ concentrations after digestion than those of food-derived copper. These results indicate that water-derived copper forms smaller-sized species and exhibits higher Cu2+ concentrations during digestion than those of food-derived copper, thereby highlighting the importance of reassessing the safety limit for copper in drinking water.

Elucidating the Significance of Copper and Nitrate Speciation in Cu-SSZ-13 for N2O Formation during NH3-SCR

Unwanted N2O formation is a problem that has been noted in selective catalytic reduction (SCR) where copper zeolite catalysts are utilized. With its immense global warming potential and long-term stability, elevated atmospheric N2O has already been identified as a future challenge in the war on climate change. This paper explores the phenomenon of N2O formation during NH3-SCR over Cu-SSZ-13 catalysts, which are currently commercialized in automotive emissions control systems, and proposes a link between N2O production and the local copper environment found within the zeolite. To achieve this, a comparison is made between two Cu-SSZ-13 samples with different copper co-ordinations produced via different synthesis methods. A combination of synchrotron X-ray absorption near-edge spectroscopy, UV–vis, Raman, and density functional theory (DFT) is used to characterize the nature of copper species present within each sample. Synchrotron IR microspectroscopy is then used to compare their behavior during SCR under operando conditions and monitor the evolution of nitrate intermediates, which, along with further DFT, informs a mechanistic model for nitrate decomposition pathways. Increased N2O production is seen in the Cu-SSZ-13 sample postulated to contain a linear Cu species, providing an important correlation between the catalytic behavior of Cu-zeolites and the nature of their metal ion loading and speciation.

Regeneration of sulfur-poisoned Cu-SSZ-13 catalysts: Copper speciation and catalytic performance evaluation

Regeneration of a sulfur-poisoned Cu-SSZ-13 catalyst via a temperature ramp in an inert atmosphere with subsequent holding under oxidizing conditions at 500 °C restores significant activity for NOx conversion under standard, fast, and NO2-rich SCR conditions. The N2O selectivity of the regenerated catalyst is higher than for the fresh catalyst under NO2-rich SCR conditions at 280 °C, while the opposite was observed for the standard and fast SCR conditions. Analysis of copper speciation showed that sulfur-free Cu species have different condition-dependent behavior in the fresh and regenerated catalysts. Heating the poisoned catalyst in an oxidizing atmosphere transforms a portion of ammonium sulfates into stable metal sulfates, while heating under inert or reducing conditions leads to more effective desulfation without the formation of stable metal sulfates. Reducing conditions result in desulfation at lower temperatures compared to inert conditions. These results contribute to the further development of regeneration strategies for Cu-SSZ-13 catalysts.

The influence of gastrointestinal pH on speciation of copper in simulated digestive juice.

Speciation can provide knowledge about absorption, reactivity to binding sites, bioavailability, toxicity, and excretion of elements. In this study, the speciation of copper in different model solutions under the influence of gastrointestinal (GI) pH was studied by ion selective electrode (ISE) and inductively coupled plasma optical emission spectrometry (ICP OES). It was found that the electrode response (mV) against Cu2+ decreased with the increase in pH and dropped to the lowest point at pH 7.5 in all model solutions. When amino acids and organic acids were present, the ratio of filtered copper (0.45 μm, pH 7.5) was more than 90%. When casein was present, whey protein, pancreatin, and starch were added, and the ratio of filtered copper was 85.6 ± 0.3, 56.7 ± 8.8, 38.5 ± 5.1, and 1.0 ± 0.3%, respectively. When there is not enough organic ligand, excessive copper will form copper hydroxide precipitation with the increase in pH, but it got the highest electrode response (mV) against Cu2+. From this study, it can be concluded that the speciation of copper in GI tract is strongly influenced by the pH and the composition of food. When there are few ligands coexisting in the GI tract, the concentration of copper ion may be relatively high.

A fit-for-purpose copper speciation method for the determination of exchangeable copper relevant to Wilson’s disease

Exchangeable copper (CuEXC), mainly comprised copper (Cu) bound to albumin, has been proposed as a specific marker of Cu overload in Wilson's disease (WD). To the author's knowledge, there are no methods capable of determining reliably CuEXC to meet the requirements and challenges faced by a clinical trial. The present work describes a novel speciation strategy for the determination of the main Cu-species in human serum by anion-exchange high-performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). A label-free protein quantification approach was conducted where the concentration of Cu associated to the protein fraction was based on its relative peak area distribution and the total Cu concentration in the sample. Such a methodology was characterized in terms of selectivity, sensitivity, precision, and robustness. Due to the lack of speciated Cu-reference materials, protein recovery was assessed by comparison with that of species-specific (SS) isotope dilution (ID). For this, a double SS HPLC-ICP-IDMS method for Cu-albumin was developed and presented here for the first time. Three human sera (two frozen LGC8211 and ERM®-DA250a, and the lyophilised Seronorm™ Human) were analyzed using both the relative and ID quantification methods. The validated relative approach, with relative expanded uncertainties (k = 2) between 5.7 and 10.1% for Cu-albumin concentrations ranging from 112 to 455 μg kg-1 Cu, was found to be able to discriminate between healthy and WD populations in terms of Cu-albumin content. Also, using such methodology, underestimation of CuEXC by the classical EDTA/ultrafiltration method was demonstrated. The methodology developed in this work will be invaluable for quality control assessment and WD drug monitoring. This work describes a Cu-protein quantification approach for the determination of exchangeable Cu relevant to Wilson's Disease.

Dissolved concentrations and organic speciation of copper in the Amazon River estuary and mixing plume

The Amazon is Earth's largest river by volume output, making it an important source of trace metals and dissolved organic matter (DOM) to the Atlantic Ocean. Despite major recent anthropogenic disruptions to the Amazon catchment area, data for trace metals such as copper (Cu) in the Amazon River estuary and associated mixing plume are still rare. Furthermore, there is currently no existing data in this region for Cu-binding ligands, which govern the amount of bioavailable Cu. To understand trace metal mixing and transport processes, the GEOTRACES process study GApr11 (cruise M147 with RV Meteor) was conducted in 2018 in the Amazon and Pará River estuaries and mixing plume in the tropical North Atlantic Ocean during high river discharge. Size-fractionated surface samples were collected along the full salinity gradient for concentrations of Cu, apparent Cu-binding organic ligands (LCu) and corresponding conditional stability constants (K′CuL, Cu2+cond), electroactive humic substances (eHS), solid phase extractable organic Cu (SPECu), dissolved organic carbon (DOC), chlorophyll a (Chl a) and macronutrients. Dissolved (<0.2 μm) and soluble (<0.015 μm) Cu correlated negatively with salinity and largely followed values expected from conservative mixing. Cu was primarily in the soluble fraction, with the exception of a minor fraction of large colloidal Cu at low salinity (S ≤ 10). Organic ligands (log K′CuL, Cu2+cond = 12.6–15.6) were present in excess of Cu and likely played a role in solubilizing Cu and preventing Cu being affected by colloidal flocculation. Cu-associated DOM (measured as LCu, eHS and SPECu) correlated negatively with salinity and appeared to be primarily governed by river input and mixing with seawater. However, an increase in the colloidal fraction for LCu and eHS observed at S ~ 6–10 was attributed to possible additional autochthonous (phytoplankton) ligand production. In all dissolved samples, organic complexation kept free Cu below levels potentially toxic for phytoplankton (<1 pmol L−1). Despite increasing anthropogenic activity over the past century, we find Cu concentrations remained similar to the 1970s, suggesting that the large overall river flow may so far minimize the impact of Cu pollution.

Fate of lead, copper, zinc and antimony during chemical looping gasification of automotive shredder residue

Gasification experiments in this study were performed in a 2–4 MW indirect gasifier coupled to a semi-commercial CFB combustor at Chalmers University of Technology. Experiments were carried out during 13 days with automotive shredder residue (ASR), giving a unique opportunity to investigate the bed material under realistic conditions and with long residence times. The metal rich ash was accumulated in the bed, gaining some oxygen carrying capabilities, creating a chemical looping gasification (CLG) process. This study aims to expand the knowledge about the chemistry of zinc, copper, lead and antimony during CLG of ASR. Several experimental methods have been utilized, such as XRD, SEM-EDX and XPS along with detailed thermodynamic calculations to study chemical transformations that can occur in the system. Thermodynamic calculations showed that the reduction potential affect the phase distribution of these elements, where highly reduction conditions result in heavy metals dissolving in the slag phase. Copper and zinc ferrites, lead silicates and antimony oxides were identified at the particle surfaces in the bottom ash. The formation of an iron rich ash layer plays an important role, especially for copper and zinc speciation. The main pathways in the complex CLG system have been discussed in detail.

Copper transformation, speciation, and detoxification in anoxic and suboxic freshwater sediments

The complex chemistry of copper (Cu) in freshwater sediments at low concentrations is not well understood. We evaluated the transformation processes of Cu added to freshwater sediments under suboxic and anoxic conditions. Freshwater sediments from three sources in Michigan with different characteristics (Spring Creek, River Raisin, and Maple Lake) were spiked with 30 or 60 mg kg−1 Cu and incubated under a nitrogen atmosphere. After 28-d, each treatment subset was amended with organic matter (OM) to promote anoxic conditions and evaluate its effects on Cu speciation. OM addition triggered a shift from suboxic to anoxic conditions, and sequential extractions showed that Cu accordingly shifted from acid-soluble to oxidizable fractions. Extended X-ray absorption fine-structure (EXAFS) spectroscopy revealed that Cu sulfides dominated all anoxic samples except for Spring Creek 30 mg kg−1, where Cu(I) was predominantly complexed to thiol groups of OM. Covellite and chalcopyrite (CuFeS2) were the predominant Cu species in nearly all anoxic samples, as determined by Raman spectroscopy, scanning electron microscopy, and X-ray absorption near-edge structure (XANES) spectroscopy. Copper reduction also occurred under suboxic conditions: for two of three sediments, around 80% had been reduced to Cu(I), while the remaining 20% persisted as Cu(II) complexed to OM. However, in the third coarsest (i.e., Spring Creek), around 50% of the Cu had been reduced, forming Cu(I)-OM complexes, while the remainder was Cu(II)-OM complexes. Toxicity tests showed that survival of H. azteca and D. magna were significantly lower in suboxic treatments. Anoxic sediments triggered a near-complete transformation of Cu to sulfide minerals, reducing its toxicity.

Copper entrapment and immobilization during cement hydration in concrete mixtures containing copper tailings

The use of copper tailings as supplementary cementitious material can reduce the environmental impacts of concrete production and the mining industry. A key concern limiting its application is the potential leaching of toxic metals from the cementitious matrix, especially copper. To analyze and reduce the risk of leaching, the mechanisms by which copper is entrapped in the cementitious matrix were investigated, by combining microscopic and spectroscopic approaches. Decreasing the water-to-binder ratio was statistically relevant to reduce copper leaching. Scanning Electron Microscope micrographs allowed to spatially localize enriched copper clusters within the cementitious hydration products. In the early stages of the cementitious hydration (i.e., 24 h), no spatial correlation between copper and hydration products was found; however, after seven days, copper was spatially associated with calcium silicate hydrates. Cu K-edge X-ray absorption near edge structure spectroscopy provided insights into the chemical speciation of copper in the cementitious matrix. It showed that copper sulfide and oxide phases persisted, whereas the copper sulfate phases were prone to dissolution and reprecipitation as cupric hydroxides induced by the relatively high pH from calcium hydroxides formed during hydration. Promoting the formation of hydration products can further reduce copper leaching from the alkaline cementitious matrix. A better understanding of metal entrapment mechanisms could lead to new strategies that reduce the mobility of toxic elements when using copper tailings, increasing their use as a replacement of cement. With this knowledge, it is expected to answer if it is possible to improve the copper entrapment into the cementitious matrix and if there is a risk of leaching once is entrapped.

Alteration of iron (Fe), copper (Cu), zinc (Zn), and manganese (Mn) tissue levels and speciation in rats with desferioxamine-induced iron deficiency.

The objective of the present study was to investigate the impact of iron deficiency and iron replenishment on serum iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn) speciation and tissue accumulation in a deferrioxamine-induced model of iron deficiency. A total of 26 male Wistar rats were divided into three groups: control; Fe-deficient; Fe-replenished (with iron (II) gluconate). Serum ferritin and transferrin levels were assessed using immunoturbudimetric method. Liver, spleen, and serum metal levels were assessed using ICP-MS. Speciation analysis was performed using a hyphenated HPLC-ICP-MS technique. Desferrioxamine injections resulted in a significant decrease in tissue iron content that was reversed by Fe supplementation. Iron speciation revealed a significant increase in serum transferrin-bound iron and reduced ferritin-bound Fe levels. Serum but not tissue Cu levels were characterized by a significant decrease in hypoferremic rats, whereas ceruloplasmin-bound fraction tended to increase. At the same time, Zn levels were found to be higher in liver, spleen, and serum of Fe-deficient rats with a predominant increase in low molecular weight fraction.Both iron-deficient and iron-replenished rats were characteirzed by increased transferrin-bound Mn levels and reduced low-molecular weight fraction. Hypothetically, these differences may be associated with impaired Fe metabolism under Fe-deficient conditions predisposing to impairment of essential metal handling. However, further studies aimed at assessment of the impact on Fe deficiency on metal metabolism are highly required.

Chemical and molecular scale speciation of copper, zinc, and boron in agricultural soils of the Canadian prairies

The general incidence of copper (Cu), zinc (Zn), and boron (B) deficiencies in soils of the Canadian prairies may be related to identifiable, highly variable, inherent soil attributes. The objective of this study was to investigate the variability of selected properties and their relationship with the bioavailability, forms, and distribution of Cu, Zn, and B in a range of prairie soils. The nature of these micronutrient distributions were evaluated by measuring extractable concentrations, supply rates, and by separation into various chemical pools through sequential extraction and spectroscopic speciation analyses. Soil pH was found to be the least variable property [coefficient of variation (CV) &lt; 13%], whereas carbonate content was the most variable (CV &gt; 130%). The Cu and B availability showed strong negative correlation with the sand content in all soils. Path coefficient results indicated that organic carbon had the highest positive direct effect on availability and supply of Cu and B in Grey soils. Extractable Zn was positively correlated with organic carbon content of Brown and Dark Brown soils. Overall, high sand content and low organic matter were identified as important soil properties contributing to the deficiency of Cu, Zn, and B. The major proportion of Cu, Zn, and B was found in the recalcitrant residual fraction (59%–88%), with the smallest proportions in labile soluble, exchangeable forms (2%–8%). The X-ray absorption near edge structure revealed that Cu and Zn associated with carbonate minerals were dominant forms of these micronutrients present in all soils. Chemisorption is likely a major process regulating the bioavailability of Cu and Zn in prairie soils.

Contribution of pristine and reduced microbial extracellular polymeric substances of different sources to Cu(II) reduction

Microbial extracellular polymeric substances (EPS) significantly influence metal behavior in the environment, but the electron transfer reaction between EPS and copper that determine the speciation and fate of copper is lacking. Here, we investigated the role of EPS from Shewanella oneidensis MR-1, Bacillus subtilis, and Saccharomyces cerevisiae and its redox state in the Cu(II) reduction under anoxic conditions. Both pristine and reduced EPS mediated copper transformation from Cu(II) to Cu(I) within 10 min. The Cu(II) reduction efficiency by the reduced EPS was ten times higher than that by the pristine EPS, which could be ascribed to the varied electron transfer ability of EPS. Multiple spectroscopic results indicated that c-type cytochromes and O-/N-containing groups were effective redox moieties responsible for copper transformation. The c-type cytochromes contributed for about 80% to the overall electron flux in S. oneidensis MR-1 EPS, which was significantly higher than in B. subtilis (27%) and S. cerevisiae EPS (22%). In contrast, functional groups such as phenolic and amide, dominated Cu(II) reduction for the B. subtilis and S. cerevisiae EPS. This study emphasizes the significant contribution of microbial EPS that serve as reducing agents and electron transfer mediators for cupric reduction and cuprous formation in the natural environments.

Evaluation and speciation of cobalt, copper, and zinc in saline soil bymicrowave‐assistedsingle extraction

AbstractThe present research assessed the chemical fractionation of Cobalt (Co), Copper (Cu), and Zinc (Zn), detected in saline soil samples of Hyderabad Pakistan. The partitioning of Co, Cu, and Zn in soil samples was carried by single‐step extraction using microwave irradiation energy. The validity of the methods was confirmed using the same operating conditions applied and checked as in BCR sequential extraction fractionation using certified reference material BCR‐701 and the standard method of addition (recoveries 96%–102%). Atomic absorption spectrometry was used to test extractable Co, Cu, and Zn contents obtained by the comparative method. Using compromised microwave conditions steps 1–3 of the sequential extraction (excluding hydrogen peroxide digestion in step 3) could be accomplished with an ultrasonic bath between 15 and 30 min, whereas 60–120 s were needed for microwave single‐extraction (MSE). The total concentrations of Co, Cu, and Zn extractable metals produced by three separate extractions ranged from 1.02–3.30, 5.02–9.95, and 3.97–8.01 μg/g respectively. Consequently, the use of single‐step extraction with the aid of microwave and ultrasound energy to reduce the time required for single‐step extraction based on the BCR sequential extraction method. However, with the aid of developed single‐step extraction methods, the obtained results were comparable to those values obtained from BCR sequential extraction method. For further study, the MSE can be frequently used to know the metal‐bound intensity with a different chemical fraction on environmental solid samples.

Organic Copper Speciation by Anodic Stripping Voltammetry in Estuarine Waters With High Dissolved Organic Matter.

The determination of copper (Cu) speciation and its bioavailability in natural waters is an important issue due to its specific role as an essential micronutrient but also a toxic element at elevated concentrations. Here, we report an improved anodic stripping voltammetry (ASV) method for organic Cu speciation, intended to eliminate the important problem of surface-active substances (SAS) interference on the voltammetric signal, hindering measurements in samples with high organic matter concentration. The method relies on the addition of nonionic surfactant Triton-X-100 (T-X-100) at a concentration of 1 mg L−1. T-X-100 competitively inhibits the adsorption of SAS on the Hg electrode, consequently 1) diminishing SAS influence during the deposition step and 2) strongly improving the shape of the stripping Cu peak by eliminating the high background current due to the adsorbed SAS, making the extraction of Cu peak intensities much more convenient. Performed tests revealed that the addition of T-X-100, in the concentration used here, does not have any influence on the determination of Cu complexation parameters and thus is considered "interference-free." The method was tested using fulvic acid as a model of natural organic matter and applied for the determination of Cu speciation in samples collected in the Arno River estuary (Italy) (in spring and summer), characterized by a high dissolved organic carbon (DOC) concentration (up to 5.2 mgC L−1) and anthropogenic Cu input during the tourist season (up to 48 nM of total dissolved Cu). In all the samples, two classes of ligands (denoted as L1 and L2) were determined in concentrations ranging from 3.5 ± 2.9 to 63 ± 4 nM eq Cu for L1 and 17 ± 4 to 104 ± 7 nM eq Cu for L2, with stability constants logK Cu,1 = 9.6 ± 0.2–10.8 ± 0.6 and logK Cu,2 = 8.2 ± 0.3–9.0 ± 0.3. Different linear relationships between DOC and total ligand concentrations between the two seasons suggest a higher abundance of organic ligands in the DOM pool in spring, which is linked to a higher input of terrestrial humic substances into the estuary. This implies that terrestrial humic substances represent a significant pool of Cu-binding ligands in the Arno River estuary.

Effect of modified biochar on the availability of some heavy metals speciation and investigation of contaminated calcareous soil

The aim of this study was to investigate the speciation of copper (Cu), lead (Pb), and cadmium (Cd) in a modified biochar amended soil in a long-term pot experiment. The efficiency of amendments was evaluated using the extraction of the sequence. Here, rice husk biochar was modified using three levels of cadmium nitrate salt (0, 40 and 80 mg kg−1 soil), copper sulfate salt (0, 50 and 200 mg kg−1 soil) and lead nitrate salt (0, 300 and 600 mg kg−1 soil). In addition, two levels (0 and 4 wt%) rice husk biochar was modified with Fe3O4, NaOH, and H2SO4 and applied each at three replicates. In order to study soil fractionation 5 months after incubation, chemical forms of cadmium, copper, and lead were determined by the fractionation method, a mobility factor and sequential extraction procedure were applied for appraising the effectiveness of the amendments. Based on the results, biochar modified with NaOH is the most effective and thus reduces lead release in solution and increases in residual form. The modified biochar decreases cadmium concentration and leads to increased copper concentration in the corn plant. Modified rice husk biochar decreased translocation factor, the least translocation factor was observed in NaOH-modified biochar.

Chlorophyll a π-Cation Radical as Redox Mediator in Superoxide Dismutase (SOD) Mimetics.

The extensive speciation of copper(II) chloride in organic solvents varies with concentration, temperature, pressure and oxygen content, providing the ability to switch between different chlorophyll transmetalation pathways. We found that one of them is exceptionally suitable for the formation and stabilisation of the chlorophyll π-cation radical. This is due to unique redox cycling, which is coupled to the generation and transformation of various reactive oxygen species. In the presence of a proton donor, our system shows behavior which resembles that of superoxide dismutase (SOD). Regardless of light, chlorophyll acts as an electron transfer mediator.