Comparative analysis of corrosion resistance between beta titanium and Ti-6Al-4V alloys: A systematic review

BackgroundThe knowledge of the electrochemical property (corrosion resistance) of beta titanium alloys compared to Ti-6Al-4 V for implants is relevant because of the potential cytotoxic effects that the released ions could cause to long-term health.ObjectivesThe objective of this systematic review was to seek information on the electrochemical properties (corrosion resistance) of beta titanium alloys compared to Ti-6Al-4 V since the awareness of the electrochemical behavior of the implant surface in the medium is essential for the best indication of the alloys or compositional changes, which may promote benefits to bone-implant interaction in all areas that this procedure is required.MethodsThe PubMed, LILACS, COCHRANE Library, and Science Direct databases were electronically searched for the terms: dental implants AND beta-titanium AND Ti-6Al-4 V AND electrochemical technics. The inclusion criteria were research articles that studied beta-titanium compared to Ti-6Al-4 V using electrochemical techniques in electrolytes of chemical composition similar to body fluid, published in English, between 2000 and 2020. Articles that did not compare the corrosion resistance of these alloys in electrolytes similar to body fluids were excluded.ResultsA total of 189 articles were restored and selected by title and/or abstract according to the inclusion and exclusion criteria, which resulted in 15 articles that were reduced to 8 after read in full. The studies in vitro evaluated the corrosion resistance in electrolytes Hank, Ringer, SBF, and 0.9 % NaCl, between beta titanium alloys, obtained by arc fusion or bars stock, and Ti-6Al-4 V, for dental or biomedical implants submitted to surface treatments by heat treatment, plasma electrolytic oxidation (PEO), alkaline treatment, and thermomechanical.ConclusionThe evaluated literature allowed to determine that 1) The oxides Nb₂O ₅, Ta₂O _5, and ZrO₂ have higher stability and protection quality than that of TiO₂ modified by the oxides of Al and V; 2) A higher modulus of elasticity of the Ti-6Al-4 V alloy favors protection against corrosion by maintaining a thicker and more firmly adhered oxide layer; 3) The increase in the thickness of the Ti alloys superficial layer contributes to the improvement of the corrosion resistance.     

Room temperature solvent extraction for simple and fast determination of total concentration of Ca,Cu, Fe,Mg, Mn,and Zn in bee pollen by FAAS along with assessment of the bioaccessible fraction of these elements using in vitro gastrointestinal digestion

Background and aimBee pollen is recognized to be a source of different nutrients, including minerals. As a food supplement, its quality and safety due to concentrations of essential macro- and microelements, and harmful trace elements has to be verified. Fast and simple element analysis of bee-collected pollen can be regarded as an important part of its quality assurance and control. The present study aimed at developping a new method for determination of selected elements (Ca, Cu, Fe, Mg, Mn, Zn) of bee pollen based on solvent extraction and completely avoiding a high temperature treatment with concentrated reagents. In addition, in vitro gastrointestinal digestion was used to assess bioavailability of elements from this food supplement.MethodsBee pollen samples were dried and pulverized. Total concentrations of Ca, Cu, Fe, Mg, Mn, and Zn were determined by flame atomic absorption spectrometry (FAAS) in sample solutions obtained by wet digestion (WD) in concentrated HNO₃ or alternatively by solvent extraction (SE) with diluted solutions of HNO₃. Gastrointestinal digestion was mimicked using simulated solutions of gastric and intestinal juices followed by determination of Ca, Cu, Fe, Mg, Mn and Zn concentrations in the bioaccessible fraction by FAAS.ResultsA new simple and fast method for determination of total concentrations of Ca, Cu, Fe, Mg, Mn, and Zn in bee pollen was developed and validated. The method combined room temperature, two-hour SE with 0.5 mol L⁻¹ HNO₃ with FAAS measurements versus simple standard solutions. It provided precision within 1–5 % and trueness better than 8%, and was shown to be suitable for fast analysis of different polyfloral bee pollens. In vitro gastrointestinal digestion revealed that elements were well (70–85 % for Ca, Mg) and fairly (27–43 % for Cu, Fe, Mn, and Zn) bioaccessible from bee pollen. By pouring with water and swelling overnight, bioaccessibility of studied elements from such prepared bee pollen was increased on average by less than 15 % (Mn), 20 % (Ca, Cu, Fe, Zn) or 30 % (Mn).ConclusionsAvoiding long-lasting, high-temperature wet digestion with concentrated reagents, the proposed sample treatment along with FAAS provided precise and true results of total concentrations of Ca, Cu, Fe, Mg, Mn, and Zn in bee pollen. The method was simple and fast, and enabled to analyze a higher number of samples. Simulated gastrointestinal digestion of bee pollen have shown for the first time that Ca and Mg are the most bioaccessible from this bee product. Bioaccessibility of Cu, Fe, Mg, and Zn from bee pollen are close to or lower than 40 %.     

Galvanic Corrosion of Lithium‐Powder‐Based Electrodes

Lithium metal is considered to be the most promising anode for the next generation of batteries if the issues related to safety and low coulombic efficiency can be overcome. It is known that the initial morphology of the lithium metal anode has a great influence on the cycling characteristics of a lithium metal battery (LMB). Lithium‐powder‐based electrodes (Li_p‐electrodes) are reported to diminish the occurrence of high surface area lithium deposits. Usually, ultra‐thin lithium foils (<50 µm) and Li_p‐electrodes are prepared on a copper substrate, thus a metal–metal contact area is generated. The combination of these two metals in the presence of an electrolyte, however, can lead to galvanic corrosion. Herein, the corrosion behavior of Li_p‐electrodes is studied. The porosity of such electrodes leads to a high amount of accessible Cu surface in contact with electrolyte. As a consequence, Li_p‐electrodes aged for 1 week in the electrolyte show spontaneous lithium dissolution near the junction to copper and void formation on the lithium‐powder particles. This corrosion process affects the delivered capacity of Li_p‐electrodes and increases the overvoltage of the lithium electrodissolution process. The occurrence of corrosion at the Cu|Li_p interface raises concerns about the practicality of multi‐metallic component systems for LMBs.     

Chemical speciation distribution characteristics and ecological risk assessment of heavy metals in soil from Sunan mining area,Anhui Province,China

In this study, the content characteristics, comprehensive pollution assessment, and morphological distribution characteristics of heavy metals (Mn, Cd, Cr, Pb, Ni, Zn, and Cu) were researched based on the processes of field investigation, sample collection, and experimental analysis. Results showed that the mean concentrations of Mn, Pb, Cr, Cu, Cd, Zn, and Ni in surface soils were 522.77, 22.56, 55.10, 25.41, 0.25, 57.02, and 48.47 mg kg^?1, respectively. The surface soil from Sunan mining area was contaminated by Cu, Cd, and Ni in different degrees, and high CV values of Cd, Zn, Pb, and Ni were influenced by local human activities possibly. The evaluation results suggested that the mean I_geo values were in the sequence of Cd (0.657) > Ni (0.052) > Cu (?0.293) > Mn (?0.626) > Zn (?0.761) > Cr (?0.884) > Pb (?0.899). Besides, Cd was the most significant potential risk factor among all elements. Nevertheless, the Cd of bioavailable speciations with higher proportion had stronger migration and toxicity, and was more easier to be absorbed and enriched than other elements by some crops (e.g., vegetables, rice), and being at a relatively higher potential ecological risk in soil.     

Decreased expression of small-conductance Ca2+-activated K+ channels SK1 and SK2 in human chronic atrial fibrillation

AimsSmall-conductance Ca^2 +-activated K⁺ (SK) channels are recognized as new ion channel candidates in atrial fibrillation (AF), with pivotal implications as novel drug targets due to their atrial-selective distribution in humans. The purpose of this study was to investigate whether SK channels and the Ca^2 +-activated K⁺ current (I_K,Ca) are involved in electrical remodeling of human chronic AF (cAF) and whether they display the differential distribution between the right (RA) and left atria (LA).Main methodsThe right (RAA) and left atrial appendage (LAA) myocytes were obtained from 29 sinus rhythm (SR) and 22 cAF patients. The I_K,Ca and action potential (AP) were recorded using the patch-clamp technique. Three SK channel subtypes (SK1–3) expressions were assayed by western blot and real-time quantitative PCR analysis.Key findingsThe I_K,Ca was decreased and its role in AP repolarization was attenuated in cAF, concomitant with a significant decrease in protein and mRNA levels of SK1 and SK2. In either SR or cAF, there was no difference in the I_K,Ca density and protein and mRNA expression levels of SK1–3 between RAA and LAA myocytes.SignificanceOur results demonstrated that SK1 and SK2 are involved in electrical remodeling of cAF. SK1–3 and I_K,Ca do not display the inter-atrial differential distribution in SR or cAF. These findings provide a new insight into mechanisms of electrical remodeling of human cAF.     

Nitrogen fertilizers promote plant growth and assist in manganese (Mn) accumulation by Polygonum pubescens Blume cultured in Mn tailings soil

Abstract

This study examined how different nitrogen (N) forms and application levels promote plant growth and assist in manganese (Mn) remediation of Polygonum pubescens Blume (P. pubescens) cultured in soil with a high Mn level. The effects of ammonium chloride (a) and urea (u), at three application levels (10, 20, and 30?mg L^?1 N) and control (no N addition, CK) on the growth, Mn accumulation, and enzymatic anti-oxidative defenses of P. pubescens were examined. In general, both ammonium-N and urea-N promoted the plant mass and height of P. pubescens. The total Mn amount of roots, stems, and leaves in N treatments were higher (p?<?0.05) than that of CK. The ammonium-N treatments showed greater plant biomass and Mn accumulation compared to the urea-N ones. In general, the accumulations of Mn, Cr, Zn, and Cu were significantly lower (p?<?0.05) in the N fertilizer treatment than those in the control; while the accumulations of Pb were higher (p?<?0.05) in P. pubescens across all N fertilizer treatments than those in the control. The N addition decreased the contents of O₂^? and H₂O₂ in the leaves of P. pubescens, while increasing the activities of enzymatic anti-oxidative defenses.     

Leaching Behavior and Risk Assessment of Heavy Metals in a Landfill of Electrolytic Manganese Residue in Western Hunan,China

We analyzed the leaching behavior and chemical speciation of heavy metals in a landfill of electrolytic manganese residue (EMR). The results showed that most of Pb, Cr, As, Cu, and Zn were associated with F4 (residual fraction) and Mn and Co were mainly present in F1 (exchangeable and weak acid soluble fraction). In order to evaluate potential risks of heavy metals to the landfill, modified potential ecological risk index (MPER), potential ecological risk index (PER), index of geo-accumulation (I_geo) assessment, and risk assessment code (RAC) were employed. Ranking order for potential risk based on RAC assessment is Mn > Co > Zn > Cu > Cr = As = Pb. Results from I_geo assessment indicates that Mn poses a potential for high risk to human health and the ecosystem. MPER, which integrates the characteristics of PER and RAC, shows that the potential risks of heavy metals are in the order of As > Cu > Mn > Co > Pb > Cr > Zn. The analysis indicates that Mn, Co, As, and Cu within EMR pose a potential risk when this material is placed in landfills and that these metals should be given particular attention when managing the land disposal of EMR.     

Non-periodic trends in the oxidative dissolution of transition metals by manganese(III) acetate

As part of a study designed to synthesize the proposed high temperature superconductor MoN, molybdenum powder was reacted with manganese(III) acetate and sodium azide in refluxing glacial acetic acid. No MoN was found. Instead, rapid and complete oxidative dissolution of the metal to soluble forms of Mo(VI) were observed. Removal of the azide or replacement of the azide by chloride had no qualitative effect. Other metals were studied and four groups may be discerned: (1) quantitative dissolution in cold, pure acetic acid - Mn, Fe, Co; (2) quantitative dissolution in refluxing Mn(III) solution  Cu, Mo, In, Sn; (3) partial dissolution in refluxing Mn(III) solution  Ni, V; (4) no reaction  Ti, Zr, Nb, Ta, Cr, W, Re, Rh, Ru, and Pt. Use of preformed metal nitrides, e.g. MoN_0.6, and variation of the oxidant, e.g. replacing Mn(III) by Fe(III) or by Co(III), resulted in little qualitative change. Some unsuccessful attempts to explain this include literature periodic trends for transition metal chemistry and Pourbaix's electrochemical ‘thermodynamic and practical nobility scales’ for corrosion by aqueous media.     

Phthalocyaninato complexes with peripheral alkylthio chains: disk-like adsorbate species for the vertical anchoring of ligands on gold surfaces

Thin metalorganic films were prepared on gold by self-assembly of thioether-functionalised phthalocyaninato complexes from solution. The phthalocyaninato ligands used contain eight peripheral, β-positioned, alkylthio substituents SR (1a: R = n-C₈H₁₇, 1b: R = n-C₁₂H₂₅), which serve as headgroups for surface binding and promote lateral assembly, while the disk-like phthalocyaninato core offers the scope for the attachment of axial ligands to the adsorbed molecules. This process was mimicked by coordination of pyridine (Py) to [Zn(1a)] and [Zn(1b)], respectively. The crystal structures of the products [Zn(1a)(Py)] and [Zn(1b)(Py)] were determined. The crystal structures of 4,5-bis(octylthio)phthalodinitrile and 4,5-bis(dodecylthio)phthalodinitrile were also determined. The films fabricated from [Mn(1a)Cl] and [Mn(1b)Cl] on gold were characterised by XPS, ToF-SIMS and NEXAFS spectroscopy, which revealed the presence of well-defined and homogeneous self-assembled monolayers (SAMs), whose constituents are bound to the substrate by thioether-gold linkages. The orientation of the macrocycles is predominantly parallel to the surface. Strong electronic interaction of the manganese(III) centre with the substrate leads to Cl loss upon adsorption and its reduction to Mn^II.     

Inter-Subject Variability in Human Atrial Action Potential in Sinus Rhythm versus Chronic Atrial Fibrillation

Aims

Human atrial electrophysiology exhibits high inter-subject variability in both sinus rhythm (SR) and chronic atrial fibrillation (cAF) patients. Variability is however rarely investigated in experimental and theoretical electrophysiological studies, thus hampering the understanding of its underlying causes but also its implications in explaining differences in the response to disease and treatment. In our study, we aim at investigating the ability of populations of human atrial cell models to capture the inter-subject variability in action potential (AP) recorded in 363 patients both under SR and cAF conditions.

Methods and Results

Human AP recordings in atrial trabeculae (n = 469) from SR and cAF patients were used to calibrate populations of computational SR and cAF atrial AP models. Three populations of over 2000 sampled models were generated, based on three different human atrial AP models. Experimental calibration selected populations of AP models yielding AP with morphology and duration in range with experimental recordings. Populations using the three original models can mimic variability in experimental AP in both SR and cAF, with median conductance values in SR for most ionic currents deviating less than 30% from their original peak values. All cAF populations show similar variations in G_K1, G_Kur and G_to, consistent with AF-related remodeling as reported in experiments. In all SR and cAF model populations, inter-subject variability in I_K1 and I_NaK underlies variability in APD₉₀, variability in I_Kur, I_CaL and I_NaK modulates variability in APD₅₀ and combined variability in I_to and I_Kur determines variability in APD₂₀. The large variability in human atrial AP triangulation is mostly determined by I_K1 and either I_NaK or I_NaCa depending on the model.

Conclusion

Experimentally-calibrated human atrial AP models populations mimic AP variability in SR and cAF patient recordings, and identify potential ionic determinants of inter-subject variability in human atrial AP duration and morphology in SR versus cAF.     

Current-voltage analysis of apical sodium transport in toad urinary bladder: Effects of inhibitors of transport and metabolism

Summary The basal-lateral surface of the epithelium of the urinary bladder of the toad (Bufo marinus) was depolarized by exposure of the serosal surface to 85mm KCL and 50mm sucrose. The extent of depolarization appeared to be virtually complete, as evaluated by the invariance in the transepithelial electrical potential difference and conductance on addition of nystatin (a monovalent cation ionophore) to the serosal medium. The Na-specific current (I _Na) was defined as the current sensitive to the removal of Na from the mucosal medium or inhibitable by addition of amiloride to this medium. In the presence of the high K-sucrose serosal medium, rapid, serial, stepwise clamping of the transepithelial voltage (V) yielded a curvilinear dependence ofI _Na onV; which is taken to represent theI–V curve of the apical Na channels. The constant field equation (Goldman, D.E. 1943;J. Gen. Physiol. 27:37) fits theI–V data points closely, allowing estimates to be made of the permeability to Na of the apical membrane (P _Na) and of the intracellular Na activity (Na _c ). Exposure of the apical surface to amiloride (5×10^–7 m) decreasedP _Na in proportion to the decrease inI _Na (i.e., 70%) but decreased Na _c only 25%. In contrast, an equivalent lent reduction inI _Na elicited by exposure of the basallateral surface to ouabain was accompanied by only a 20% decrease inP _Na and a sixfold increase in Na _c . The effects of amiloride onP _Na and ouabain on Na _c are consistent with the primary pharmacological actions of these drugs. In addition,P _Na appears to be under metabolic control, in that 2-deoxyglucose, a specific inhibitor of glycolysis, decreasedI _Na andP _Na proportionately, and lowered Na _c marginally, effects indistinguishable from those obtained with amiloride.     

Ordering selected Zn(II), Cu(II), Pd(II) and Co(III) complex compounds: their separately and combinedly antibacterial therapy and DNA-binding studies

Abstract

In this study, four Co(III)-, Cu(II)-, Zn(II)- and Pd(II)-based potent antibacterial complexes of formula K₃[Co(ox)₃]·3H₂O (I), [Cu(phen)₂Cl]Cl·6.5H₂O (II), [Zn(phen)₃]Cl₂ (III) and [Pd(phen)₂](NO₃)₂ (IV) (where ox is oxalato and phen is 1,10-phenanthroline) were synthesized. They were characterized by elemental analysis, molar conductivity measurements, UV–vis, Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance (¹H-NMR) techniques. These metal complexes were ordered in three combination series of I+II, I+II+III and I+II+III+IV. Antibacterial screening for each metal complex and their combinations against Gram-positive and Gram-negative bacteria revealed that all compounds were more potent antibacterial agents against the Gram-negative than those of the Gram-positive bacteria. The four metal complexes showed antibacterial activity in the order I > II > III > IV, and the activity of their combinations followed the order of I+II+III+IV > I+II+III > I+II. The DNA-binding properties of complex (I) and its three combinations were studied using electronic absorption and fluorescence (ethidium bromide displacement assay) spectroscopy. The results obtained indicated that all series interact effectively with calf thymus DNA (CT-DNA). The binding constant (K_b), the number of binding sites (n) and the Stern–Volmer constant (K_sv) were obtained based on the results of fluorescence measurements. The calculated thermodynamic parameters supported that hydrogen bonding and van der Waals forces play a major role in the association of each series of metal complexes with CT-DNA and follow the above-binding affinity order for the series.

Communicated by Ramaswamy H. Sarma     

Multitracer study on biosorption of trace elements in yeastSaccharomyces cerevisiae

To estimate the applicability of yeastSaccharomyces cerevisiae as a radioisotope accumulator, biosorption of 18 radionuclides (isotopes of Be, Na, Sc, V, Cr, Mn, Fe, Co, Zn, As, Se, Rb, Sr, Y, Zr, Tc, Ru, and Rh) by the cells was tested using a multitracer technique. This technique enables us to examine the uptake of various elements under an identical condition. We showed that the yeast has ability to take up radioactive tracers of Be, Sc, V, Cr, Mn, Fe, Co, Zn, As, Se, Sr, Y, Zr, Ru, and Rh from an aqueous environment. Tracers of Be, Sc, Mn, Co, Zn, Se, Sr, Y, and Zr were distributed in both cell walls and other cell parts. Moreover, tracers of Sc, Mn, Co, Zn, Se, Sr, and Y were present as soluble and insoluble forms, and most of the Be and Zr were present as an insoluble form in the cells.     

Effects of chemical group specific reagents on sodium entry and the amiloride binding site in frog skin: Evidence for separate sites

Summary Previously we have shown that the inhibition of active transport by amiloride is noncompetitive with sodium inRana catesbeiana skin, suggesting that amiloride acts at a site separate from the sodium entry site (Benos, D.J., Mandel, L.J., Balaban, R.S. 1979,J. Gen Physiol. 73: 307). In the present study, the effects of a number of sulfhydryl, amino, and carboxyl group selective reagents were studied on short-circuit current (I _sc) as well as the efficacy of amiloride in bullfrog skin, to determine those functional ligands which may be involved with either of these processes.Addition of the sulfhydryl reagent PCMBS (1mm) to the outside bathing medium produced biphasic effects, initially reversibly increasingI _sc by an average 56% followed by a slower, irreversible decay to levels below baseline. In contrast, the addition of 0.1mm PCMB always resulted in a rapid, irreversible decrease inI _sc. When a 40,000 mol wt dextran molecule was attached to PCMB, a stable, reversible increase inI _sc was observed. These observations suggest that at least two populations of-SH groups are involved in Na translocation through the entry step. Amiloride was equally effective in inhibitingI _sc before and after treatment with PCMBS both during the stimulatory as well as the inhibitory phase. The sulfhydryl reducing agent DTT, and oxidizing agent DTNB had only minor influence onI _sc and did not alter the effectiveness of amiloride.Similarly, the amino reagents, SITS and TNBS did not affectI _sc. However, TNBS decreased the ability of amiloride to inhibit Na entry. These results suggest that an amino group may be involved in the interaction of amiloride and its site, without affecting Na entry.The carboxyl reagents EEDQ, TMO, and three separate carbodiimides were without effect onI _sc or amiloride inhibition. Methylene blue (MB), a molecule that interacts with both carboxyl and hydroxylspecific groups, inhibitedI _sc by 20% and decreased amiloride's ability to inhibitI _sc. These effects, however, are likely to occur from the cytoplasmic side as MB appears to enter into the cells.These results support the notion that amiloride and Na interact with the entry protein at different regions on the membrane.     

Elemental distribution in tissue components of N2-fixing nodules of Psoralea pinnata plants growing naturally in wetland and upland conditions in the Cape Fynbos of South Africa

There is little information on in situ distribution of nutrient elements in N₂-fixing nodules. The aim of this study was to quantify elemental distribution in tissue components of N₂-fixing nodules harvested from Psoralea pinnata plants grown naturally in wetland and upland conditions in the Cape Fynbos. The data obtained from particle-induced X-ray emission revealed the occurrence of 20 elements (Si, P, S, Cl, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, As, Br, Rb, Sr, Y, Zr, Mo and Ba) in nodule components. Although, in upland plants, the concentrations of S, Fe, Si, Mn and Cu showed a steady increase from the middle cortex to the medulla region of P. pinnata nodules, in wetland plants, only S, Fe and Mn showed an increase in concentration from the middle cortex to the bacteria-infected medulla of P. pinnata nodules. By contrast, the concentrations of Cl, K, Ca, Zn and Sr decreased from middle cortex to nodule medulla. The alkaline earth, alkali and transition elements Rb, Sr, Y and Zr, never before reported in N₂-fixing nodules, were found to occur in root nodules of P. pinnata plants grown in both wetland and upland conditions.     

Model of calcium-induced calcium release mechanism in cardiac cells

A model with which to elucidate the mechanism of Ca²⁺ release from, and Ca²⁺ loading in the sarcoplasmic reticulum (SR) by Ca²⁺ current (I _Ca) in cardiac cells is proposed. The SR is assumed to be comprised of three functional subcompartments: (1) the main calcium store (MCS), which contains most of the calcium (both free and bound); (2) the releasable terminal (RT), which contains the calcium readily available for release; and (3) the longitudinal network of the SR (LSR), which sequesters and the transfers the sarcoplasmic calcium to the RT. A rapid increase of the Ca²⁺ concentration at the outer surface of the SR (Ca_e) due to the fast component ofI _Ca activates and inactivates this surface, inducing the release of Ca²⁺ from the RT to the sarcoplasmic space. The RT in turn is further activated and inactivated by a increase in the concentration of sarcoplasmic Ca²⁺. The Ca²⁺ in the sarcoplasmic space is then sequestered by the LSR, leading to the reactivation of the RT. Further increase of Ca_e due to the slow component ofI _Ca enhances the entry of Ca²⁺ into the MCS to be bound by the binding substance. The free Ca²⁺ released from the Ca-binding substance complex is transferred to the RT for subsequent release. The activation, inactivation and reactivation are Ca²⁺-mediated and time-dependent. The proposed model yields simulation of the many events qualitatively similar to those observed experimentally in skinned cardiac cells.     

Moss and Peat Leachate Degradability by Heterotrophic Bacteria: The Fate of Organic Carbon and Trace Metals

The respiration of dissolved organic matter (DOM) by aerobic heterotrophic bacterioplankton in boreal surface waters is one of the major factors that regulate CO₂ exchange of lakes and rivers with the atmosphere in arctic and subarctic zones. The DOM that originates from topsoil leaching and vegetation degradation is brought to the lakes by surface flow and is subjected to coagulation and degradation by heterotrophic bacteria, which are well-established processes in the majority of boreal aquatic settings. The behavior of colloids and organic complexes of trace metals during this process is virtually unknown. In this work, we studied the interaction of two model heterotrophic bacteria, soil Pseudomonas aureofaciens and aquatic Pseudomonas reactans, with peat and Sphagnum moss leachates from the permafrost region under controlled laboratory conditions in nutrient-free media. The moss leachate was the better substrate for bacterial survival, with P. reactans exhibiting an order of magnitude higher live cell number compared with P. aureofaciens. In eight-day experiments, we analyzed organic carbon and ～40 major and trace elements (TEs) during heterotrophic bacteria growth. The total net decrease in the concentration of dissolved organic carbon (DOC) was similar for both bacteria and ranged from 30 mg g_wet^?1 to ≤10 mg g_wet^?1 during 8 days for the moss and peat leachate, respectively. Despite significant evolutions of pH, DOC, dissolved inorganic carbon (DIC), and cell number, most major (Mg, K, and Ca) and TEs remained nearly constant (within ±30% of the control). Only Fe, Al, P, Zn, Mn, Co, and Ba and to a much lesser extent Cd, Pb, Rare Earth Elements (REEs), U, Ti, and Zr were affected (p??1 to µg L^?1 and followed the order DOC >> P >> Ba > Zn ≥ Fe ≥ Al > Mn > Cu ≥ Sr > Zr ≥ Ti > Ni ≥ Co > REEs ≥ U > Hf～Th, which reflected the abundance of the elements in the two substrates. Generally, the soil exopolysaccharide producing bacterium P. aureofaciens in the peat leachate had the greatest impact of the four combinations investigated in this study (two bacteria with two substrates). Under ongoing environmental changes in the boreal zone, the autochthonous processes of bacterioplankton activity are able to decrease the concentrations of a very limited number of TEs, including mainly Fe and several macro- (P) and micro- (Zn, Mn, and Ba) nutrients.     

Distribution,pollution levels,toxicity, and health risk assessment of metals in surface dust from Bhiwadi industrial area in North India

Abstract

To understand distribution, toxicity, and health risk assessment of Cu, Ni, Cr, Pb, Zn, Fe, and Mn, 33 surface dust samples were collected during June 2015 from Bhiwadi Industrial Area (BIA) in north India. Average metal concentrations exceeded their corresponding values in upper continental crust depending upon metal(s) and sampling site(s). Industrial emissions resulted in high contamination factors and high pollution load index for metals. The BIA falls under least to moderately for Mn, unpolluted to heavily and extremely for Ni and Cu, Pb, and Zn and moderately to extremely polluted region for Cr. Inter-metal correlations and PCA indicated common and mixed sources for metals such Ni–Cr electroplating and alloys, battery recycling, stainless-steel, electrical wires, galvanizing, vehicular emissions, and wear and tear of vehicle parts. Non-carcinogenic health risk due to metals in surface dust was high in children compared to adults and major pathways were ingestion followed by dermal and inhalation. Surface dust in BIA falls under hazardous category as metals leached in toxicity characteristics leaching procedure and waste extraction test exceeded their prescribed regulatory limits. Leaching of metals can cause contamination of surface water, groundwater, and soils in surrounding areas, and can pose risk to human health and ecology.     

Potent inhibitory effects of benzyl and p-xylidine-bis dithiocarbamate sodium salts on activities of mushroom tyrosinase

A novel monofunctional benzyldithiocarbamate, C₆H₅CH₂NHCSSNa (I), and a bifunctional p-xylidine-bis(dithiocarbamate), NaSSCNHCH₂C₆H₄CH₂NHCSSNa (II), as sodium salts, were synthesized by reaction between p-xylylenediamine or benzylamine with CS₂ in the presence of NaOH. They were characterized by spectroscopic techniques such as ¹H NMR, IR, and elemental analysis. These water-soluble compounds were examined for their inhibition of both activities of mushroom tyrosinase (MT) from a commercial source of Agricus bisporus. l-3,4- Dihydroxyphenylalanine (L-DOPA) and l-tyrosine were used as natural substrates for the catecholase and cresolase enzyme reactions, respectively. Kinetic studies showed noncompetitive inhibition of I and mixed type inhibition of II on both activities of MT. The inhibition constant (K_I) of II was smaller than that of I. Raising the temperature from 27 to 37°C caused a decrease in K_I values of I and an increase in values of II. The binding process for inhibition of I was only entropy driven, which means that the predominant interaction in the active site of the enzyme is hydrophobic; meanwhile, the electrostatic interaction can be important for the inhibition of II due to the enthalpy driven binding process. Fluorescence studies showed a decrease of emission intensity without a shift of emission maximum in the presence of different concentrations of compounds. An extrinsic fluorescence study did not show any considerable change of the tertiary structure of MT. Probably, the conformation of inhibitor-bound MT is stable and inflexible compared with uninhibited MT.     

Chemical speciation of Zn in acidic soils: suitable soil extractant for assessing Zn availability to maize (Zea mays L.)

Abstract

Chemical fractions of soil Zn namely: water soluble (WS), exchangeable (EX), Pb displaceable (Pb-disp.), acid soluble (AS), Mn oxide occluded (MnOX), organically bound (OB), amorphous Fe oxide occluded (AFeOX), crystalline Fe oxide occluded (CFeOX), residual (RES) were determined in 20 surface (0–15 cm) samples of acidic soils from the provinces of Uttarakhand and Uttar Pradesh, India. The chemical fractions of soil Zn in acidic soils were found to be in the following descending order of Zn concentration: RES > CFeOX > Pb-Disp. > AFeOX > MnOX > AS > OB > EX > WS. These soil samples were also extracted by: DTPA (pH 7.3), DTPA (pH 5.3), AB-DTPA (pH 7.6), Mehlich 3 (pH 2.0), Modified Olsen, 0.01 N CaCl₂, 1 M MgCl ₂ and ion exchange resins. Chemical fractions and the soil extractable content of Zn estimated by different soil extractants were significantly correlated with some general soil properties. Maize (cv. Pragati) plants were grown in these soils for 35 days after emergence and Zn uptake by plants was compared with the amount of Zn extracted by different soil extractants and chemical fractions of Zn. Among chemical fractions of soil Zn, Pb-displaceable and acid soluble chemical fractions of soil Zn showed a significant and positive correlation with Zn uptake by maize. Path coefficient analysis also revealed that the acid soluble Zn fraction showed the highest positive and direct effect on Zn uptake (P=0.960). Among different multinutrient soil extractants evaluated for their suitability to assess Zn availability in acidic soils, DTPA (pH=5.3) was most suitable soil extractant, as the quantity of soil Zn extracted by this extractant showed a significant and positive correlation with the dry matter yield, Zn concentration and uptake by maize plants.