Hg Complexes Research Articles

Synthesis, Antioxidant, and Antibacterial Studies of Zn(II), Cd(II), and Hg(II) Complexes with 3-Formylpyridinethiosemicar bazone and Its N4-Methyl Analogue

Evaluation of stability constants of the complexes formed in solution by the biologically important ligands and metal ions can aid in understanding the application of metal complexes in chelation therapy. Hence, complexation equilibrium studies of the ligands (L), 3-formylpyridinethiosemicarbazone (H3FPT) and 3-formylpyridine-N4-methylthiosemicarbazone (H3FP4MT) with Zn(II) and Cd(II) metal ions (M) are carried out in 70% v/v DMF-water medium at 0.1M KNO3 ionic strength and the stability constants are determined pH-metrically at 303 K. The binary complexes are formed in 1: 1 (M: L) ratio and are fairly stable. The binary complexes of H3FPT and H3FP4MT (L) with Zn(II), Cd(II) and Hg(II) ions are synthesized and characterized by various analytical and spectral techniques including elemental analysis, molar conductance, LC-MS, TGA, IR and 1H NMR spectroscopy. According to the accumulated information, the complexes are polymeric (ML)n with n > 2, except that of Hg(II)-H3FP4MT, which is ML2. The antioxidant activity of the ligands and their Zn(II) and Hg(II) complexes demonstrate higher activity than their corresponding ligands Cd(II) complexes. Antibacterial activity of the ligands and the complexes is tested against gram positive: Staphylococcus aureus, Bacillus subtilis and gram negative: Escherichia coli and Klebsiella pneumonia bacterial strains. Activity of complexes is determined to be higher than that of the corresponding free ligands.

Synthesis and Antibacterial Activities of Novel Hg(II) and Zn(II) Complexes of Bis(Thiosemicarbazone) Acenaphthenequinone Loaded to MWCNTs

This paper describes a series of new polyamides containing bis(thiosemicarbazone) acenaphthenequinone (PA), bis(thiosemicarbazone) acenaphthenequinone zinc (Z-PA), and bis(thiosemicarbazone) acenaphthenequinone mercury (H-PA) complexes loaded onto MWCNTs synthesized via a chemical precipitation method in methanol followed by antimicrobial activity studies on the novel functionalized MWCNTs complexes. These complexes are characterized by FT-IR spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The antibacterial activity of free PA, Z-PA, and H-PA complexes loaded onto MWCNTs are studied against gram-positive and gram-negative bacteria. The results indicate that the HPA/MWCNT complex is the most effective growth inhibitor against Listeria monocytogenes and Pseudomonas aeruginosa, exhibiting the potential for the use as an antibacterial agent.

Metallobacitracins: Affinity and structural study in aqueous solution

Metallobacitracins are complexes with an extensive antimicrobial and biological activity. In this work, we investigated the metal complexation of bacitracin with several divalent metal ions in aqueous solution. The binding constants of Zn(2+), Cd(2+), Hg(2+), Cu(2+), Ni(2+), Pd(2+), Fe(2+), Mn(2+) and Mg(2+) to bacitracin were measured by UV/Vis spectroscopy, isotermic titration calorimetry (ITC) and potentiometry while the complexes were studied by Circular Dichroism and Nuclear Magnetic Resonance (15N HSQC) for Zn(2+), Cd(2+) and Hg(2+) at different pH. By UV/Vis spectroscopy the affinity is in the range 104 to 105 M−1 at pH 6 and follows the order Ni(2+) > Cd(2+) > Hg(2+) > Zn(2+) > Fe(2+). By potentiometry, the binding constants were determined in the pH range 2–12. Microcalorimetry shows that the stoichiometry of metallobacitracins investigated is 1:1 with binding constants in the range 105–102 M−1 at pH 6 and with an order of stability of Ni(2+) > Cd(2+) > Zn(2+) > Hg(2+); ΔS, ΔH and ΔG parameters were also determined. NMR spectroscopy lets us establish the binding site of the metal ion when comparing 15N HSQC of free bacitracin and complex in natural abundance; these findings agree with calorimetric results. Chemical shift changes in complexes containing Zn(2+) and Cd(2+) exhibit a similar behavior despite pH differences. Conversely, there is not a significant change for Hg(2+) complex. The obtained data contribute to understand the mechanism of the biological activity of the metallobacitracins and give the guideline for the design of more powerful metalloantibiotics.

2+2] or [4+4] metallamacrocycle: Synthesis and crystal structures of Hg(II) complexes derived from two flexible bis(pyridylurea) ligands

Two complexes, [Hg2(L1)2Br4]·4DMF·2H2O (1) and [Hg4(L2)4Br8]·8DMF·2H2O (2), have been synthesized and characterized from two flexible bis(pyridylurea) ligands (L1 and L2) with mercury(II) bromide respectively. Both the two complexes exist as centrosymmetric metallamacrocycles with four-coordination Hg(II) centers, but they present different architectures with slightly adjusted 3- and 4-position of nitrogen atom in the pyridyl rings from the two ligands. Complex 1 exists as a [2+2] metallamacrocycle with L1 as bidentate ligands bridging two HgBr2, while complex 2 exists as a novel 84-membered [4+4] metallamacrocycle, which indicates that the nature of the ligand plays an important role in the coordination networks.

Hydrogen storage capacities of some new Hg(II) complexes containing 2-acetylethiophene

Novel mercury divalent ion complexes with 2-acetylethiophene (AcT) were synthesized. The treatment of HgCl2 with AcT in ethanol at room temperature in 1:1 and 1:2 mercury to AcT ratios affords [Hg(AcT)Cl2] (1) and [Hg(AcT)2]Cl2 (2) respectively. Both complexes (1) and (2) were used as synthone for preparation the complexes of the type [Hg(AcT)(L-L)]Cl2 where the bidentate ligands were either aliphatic amines L-L; ethylenediamine (en) (3), N-methylethylenediamine (Men) (4), N-ethylethylene-diamine (Een) (5) and 1,3-diaminopropane (Dap) (6) or heterocyclic amines L-L; 2,2′-bipyridine (bipy) (7) and 1,10-phenanathroline (phen) (8). When complex (1) was used, the resulted complexes of the type [Hg(AcT)(L-L)]Cl2 were pure. Column chromatography packed with silica was used to separate the resulted complexes in pure form when complex (2) was used as a starting material. Furthermore, the treatment of complex (1) with two moles of triphenylephosphine (PPh3) results in the mixture of [Hg(AcT)(PPh3)2]Cl2 (9) and [Hg(AcT)(O = PPh3)2]Cl2 (10). These two complexes were separated using sephadex column depending on their molecular weight. The prepared complexes were characterized by molar conductivity, FT-IR, 1H-, DEPT 13C-{1H}, 31P-{1H}NMR and elemental analyses. The characterization results show that AcT behaves as a chelate bi-dentate ligand through sulfur and oxygen atoms in all complexes. The prepared complexes were characterized to be tetrahedral complexes. In order to take benefit of the prepared complexes, (1), (8) and (9) were selected to test their surface areas and hydrogen storage abilities. In addition, the thermodynamic properties of H2 adsorption (enthalpy and entropy) were determined at four different temperatures using the Clausius Clapeyron equation. The results prove that the prepared complexes were capable of storing the hydrogen.

Facile Fabrication of 3D Graphene⁻Silica Hydrogel Composite for Enhanced Removal of Mercury Ions.

Adsorption is a highly promising and widely used approach to remove Hg(II) ions from contaminated water. The key to this technology is exploring the effective adsorbent. The three-dimensional (3D) graphene as reduced graphene oxide hydrogel (rGH)-encapsulated silica gel (SG-PEI/rGH) was prepared by a moderate chemical reduction strategy using ascorbic acid. This composite structure was characterized by FTIR, XRD, and SEM analysis and used as adsorbents for Hg(II) ions. Its adsorption capacity toward Hg(II) ions was 266 mg/g and increased about 32% compared with the silica gel because of reduced graphene oxide hydrogel (rGH). Mechanism study showed that the high adsorption ability was due to the formation of an N–Hg complex with multi-amino groups on the surface of polyethyleneimine-modified silica gel (SG-PEI) and the rapid diffusion of adsorbed ions attributed to the rGH network structure. This composite SG-PEI/rGH would be a promising material for the removal of Hg(II) ions.

Effect of gamma irradiation on spectral, XRD, SEM, DNA binding, molecular modling and antibacterial property of some (Z)[sbnd]N-(furan-2-yl)methylene)-2-(phenylamino)acetohydrazide metal(II) complexes

A series of Ru(II), Pd(II),VO(II) and Hg(II) complexes with (Z)N-(furan-2-yl)methylene)-2-(phenylamino)acetohydrazide (HL) has been synthesized. Investigation of synthesized metal complexes was achieved by using elemental analyses, magnetic moment, molar conductance, FT-IR, 1H-NMR, UV–Vis., spectroscopy and thermal techniques. The effect of gamma irradiation on powder samples of [Ru(L)Cl]2·EtOH (B1), [Pd(L)Cl(H2O)]·H2O (B2), [(VO)(HL)SO4]·H2O (B3) and [Hg(HL)I(H2O)2] (B4) complexes was also investigated (hereafter referred to as (A1), (A2), (A3) and (A4), respectively). Spectral, thermal, powder X-ray diffraction patterns (XRD) and surface morphological studies were performed before and after irradiation. Irradiation causes changes in spectral features. XRD studies revealed the decrease in the crystalline size of sample (B2) from 43.3 nm to 30.6 nm upon irradiation and irradiation induced the crystallinity of the complexes. Surface morphology of [Pd(L)Cl(H2O)]·H2O (B2) before and after irradiation has been studied. Fluorescence studies revealed the possibility of the Pd(II) complex (B2) to form a binding mode with Heparin. In molecular modeling the possible structures of the ligand and its metal complexes were fully optimized with respect to the energy using the Hyper Chem. 8.03 molecular modeling program. Furthermore, the energies of highest occupied molecular orbital (EHOMO), energies of lowest unoccupied molecular orbital (ELUMO), energy gap (ΔE = ELUMO−EHOMO), the absolute electronegativity, χ, the chemical potential, Pi, the absolute hardness, η and the softness (σ) were obtained for the ligand and its complexes (B3), (B4). The antibacterial studies of the prepared compounds before and after gamma irradiation screened against both gram positive and gram negative bacteria proved that these compounds exhibit remarkable antibacterial activity and the irradiation improved the bioactivity for most complexes.

Mercury speciation, bioavailability, and biomagnification in contaminated streams on the Savannah River Site (SC, USA)

Water, sediment, and biota from two streams on the Savannah River Site were sampled to study mercury (Hg) biogeochemistry. Total and methyl- Hg (MHg) concentrations were measured for all samples, speciation models were used to explore Hg speciation in the water, and Diffusive gradients in thin films (DGT) were applied to indicate the vertical profiles of labile Hg (DGT-Hg). Trophic position (δ15N) was estimated for biota and used to establish MHg biomagnification model. The speciation model indicated Hg methylation in the water occurred on settling particles and the most bioavailable Hg species to bacteria were complexes of inorganic Hg and labile organic ligands. Correspondingly, dissolved organic carbon concentrations were positively related to MHg concentrations in the water. In the sediment, the sharp increase of DGT-Hg around the sediment water interface underscores the importance of this interface, which determines the differences in the accumulation and generation of labile Hg among different waterbodies. The positive correlation between sediment MHg and sulfate concentrations suggested possible methylation reaction by dissimilatory sulfate reducing bacteria in the sediment. The food web magnification factors of MHg were 9.6 (95% CI: 4.0–23.4) and 4.4 (95% CI: 2.5–7.7) for the two streams established with trophic data of biofilm, invertebrates, and fish. Meanwhile, DGT-Hg concentrations in the water were positively correlated to biofilm Hg concentrations, which can be combined with the MHg biomagnification model to generate a modified biomagnification model that estimate MHg bioaccumulation with only labile Hg concentrations in the water. With this approach, Hg accumulation in abiotic and biotic environmental compartments was connected and the different bioaccumulation patterns of Hg in different waterbodies were explained with both geochemical and biological factors.

Two Hg(II) complexes of 4-pyridinecarbacylamidophosphates: Synthesis, crystal structures, theoretical studies and in vitro antibacterial evaluation

Two new Hg(II) complexes of 4-pyridinecarbacylamidophosphate ligands, HgCl2(L1)2C1 (L1 = 4-NC5H4C(O)NHP(O)[NHC(CH3)3]2); [Hg(L2)Cl3]−[(L2)H]+C2 (L2 = 4-NC5H4C(O)NHP(O)[NHC5H9]2) were synthesized and characterized on the basis of elemental analysis, IR, UV–Vis, and multinuclear NMR spectroscopy. Molecular structures of C1 and C2 were determined by X-ray crystallography and revealed that coordination of ligands to Hg(II) has occurred from the nitrogen atom of the pyridine ring in neutral (C1) and ionic (C2) metal complexes. Coordination of L1 and L2 from Npyridine, as a monodentate ligand, resulted in infinite 1D and 2D hydrogen-bonded polymeric chains for C1 and C2, respectively. Mass spectral data further support the structure of the compounds and XRD indicates the crystalline state of metal complexes. The intermolecular hydrogen bonding interactions which connected the chains into 3D frameworks in both complexes were supported by Hirshfeld surface analysis and fingerprint plots. Also, natural bond orbital analysis divulges that the metal–ligand interaction in C1 and C2 is the LMCT. By using parameters derived from the quantum theory of atoms in molecules, the nature of Hg-ligand interaction is found to be mainly electrostatic with a small amount of covalent character. Hg(II) complexes and the corresponding ligands were also screened for their antibacterial activity against the selected Gram-positive and Gram-negative bacteria. Results indicated that C2 possess strong cytotoxic activity against the tested bacteria with MIC values ranging from 2.79 to 22.32 µg/ml. The activity of compounds was interpreted by their calculated descriptors, density, log P, and the lower unoccupied molecular orbital.

Environmental Mercury Chemistry - In Silico.

Mercury (Hg) is a global environmental contaminant. Major anthropogenic sources of Hg emission include gold mining and the burning of fossil fuels. Once deposited in aquatic environments, Hg can undergo redox reactions, form complexes with ligands, and adsorb onto particles. It can also be methylated by microorganisms. Mercury, especially its methylated form methylmercury, can be taken up by organisms, where it bioaccumulates and biomagnifies in the food chain, leading to detrimental effects on ecosystem and human health. In support of the recently enforced Minamata Convention on Mercury, a legally binding international convention aimed at reducing the anthropogenic emission of-and human exposure to-Hg, its global biogeochemical cycle must be understood. Thus, a detailed understanding of the molecular-level interactions of Hg is crucial. The ongoing rapid development of hardware and methods has brought computational chemistry to a point that it can usefully inform environmental science. This is particularly true for Hg, which is difficult to handle experimentally due to its ultratrace concentrations in the environment and its toxicity. The current account provides a synopsis of the application of computational chemistry to filling several major knowledge gaps in environmental Hg chemistry that have not been adequately addressed experimentally. Environmental Hg chemistry requires defining the factors that determine the relative affinities of different ligands for Hg species, as they are critical for understanding its speciation, transformation and bioaccumulation in the environment. Formation constants and the nature of bonding have been determined computationally for environmentally relevant Hg(II) complexes such as chlorides, hydroxides, sulfides and selenides, in various physical phases. Quantum chemistry has been used to determine the driving forces behind the speciation of Hg with hydrochalcogenide and halide ligands. Of particular importance is the detailed characterization of solvation effects. Indeed, the aqueous phase reverses trends in affinities found computationally in the gas phase. Computation has also been used to investigate complexes of methylmercury with (seleno)amino acids, providing a molecular-level understanding of the toxicological antagonism between Hg and selenium (Se). Furthermore, evidence is emerging that ice surfaces play an important role in Hg transport and transformation in polar and alpine regions. Therefore, the diffusion of Hg and its ions through an idealized ice surface has been characterized. Microorganisms are major players in environmental mercury cycling. Some methylate inorganic Hg species, whereas others demethylate methylmercury. Quantum chemistry has been used to investigate catalytic mechanisms of enzymatic Hg methylation and demethylation. The complex interplay between the myriad chemical reactions and transport properties both in and outside microbial cells determines net biogeochemical cycling. Prospects for scaling up molecular work to obtain a mechanistic understanding of Hg cycling with comprehensive multiscale biogeochemical modeling are also discussed.

Lignin xanthate resin-bentonite clay composite as a highly effective and low-cost adsorbent for the removal of doxycycline hydrochloride antibiotic and mercury ions in water.

Natural-occurring polymer intercalated inorganic clay composites have received increasing interests in water cleanup for the features of eco-friendliness, cost-effectiveness, and availability. Herein, a new lignin xanthate resin (LXR) intercalated bentonite clay composite (LXR-BT) for the adsorption of representative organic doxycycline hydrochloride (DCH) antibiotic and inorganic Hg(II) in water was created through a feasible process. Structural characterizations by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Thermo gravimetric analysis (TG), and scanning electron microscopy (SEM) confirmed LXR was successfully intercalated between the layers of bentonite clay. The adsorption performance of DCH/Hg(II) by LXR-BT was studied in detail with varied dosage, solution pH, contact time, and initial DCH/Hg(II) concentration. The results indicated that the adsorption capacities of DCH/Hg(II) on LXR-BT were much higher than that on bentonite, and the adsorption kinetics and isotherms followed the pseudo-second-order model and Langmuir model, respectively. X-ray photoelectron spectroscopy (XPS) analysis confirmed the adsorption mechanisms of DCH (or Hg(II)) was mainly due to π-π interaction and hydrogen bonding interaction of DCH (or the complexation of Hg(II)) with the functional groups in the LXR-BT. This study suggested the possibility of LXR-BT as a new cost-effective adsorbent for both organic and inorganic pollutants removal in water.

Novel Synthesized Benzesulfonamide Nanosized Complexes; Spectral Characterization, Molecular Docking, Molecular Modeling and Analytical Application

New series, for sulfa drug complexes, was prepared from Cu(II), Ag(I), Cd(II) and Hg(II) ions. The new sulfisoxazole derivative and its corresponding complexes were fully characterized through all, analytical, spectral and theoretical tools. The mode of bonding, is pentadentate mode, in all complexes, which having bi-central atoms. The coordination number four, was proposed with all complexes, except Cu(II) complex, which has square-pyramidal geometry. XRD patterns and SEM images, introduce, the nanocrystalline nature for all investigated compounds. Molecular modeling, was carried out for all compounds, to modulate the structural forms, the best method execute the aim, was, DFT/B3LYP. Utilizing frontier energy gaps, the following parameters, electronegativity (χ), chemical potential (μ), global hardness (η), global softness (S), global electrophilicity index (ω) and absolute softness (ϭ) were computed. The docking process, was executed from sulfa drug ligand, against pathogen proteins as, 1jm7, 2hq6 and 3lvq, which attributing for, breast, colon and liver tumors, respectively. The computed parameters, among them, the inhibition constant (1.09 KCal/uM), which displayed that, the tested sulfa drug derivative, is considered a promising anti-colon cancer. The antitumor screening against, MCF-7, HEPG-2 and HCT-116cell lines, displays promising results with Hg(II) and Cd(II) complexes covered all cell lines. IC50 values for them were ˂ 4, which considered, best toxic feature against tumor cells. A specific analytical application, was done, upon the use of sulfa drug ligand as an acid- base indicator. This study was carried out versus, different types of titrations, in comparing with referenced indicators (Me.O and Ph.Ph). High conformity in the titration end point, using the proposed indicator with that known, was obtained. It is worthy to note that, the compound achieved the exact end point for weak acid- weak base titration, which is considered a shining spot in the study.

Impact of dissolved organic matter on mercury and methylmercury sorption to activated carbon in soils: implications for remediation.

Activated carbon (AC) amendments have shown promise in reducing inorganic mercury (Hg(ii) complexes, "Hg") and methylmercury (MeHg) risk in contaminated soils. However, the effectiveness of AC in Hg and MeHg immobilization has varied among studies, suggesting that site biogeochemistry might dictate efficacy. In this study, we examined the effect of dissolved organic matter (DOM) on MeHg and Hg sorption to AC. We evaluated the impact of Suwannee River Humic Acid (SRHA) on sorption to AC directly using an isotherm approach and in a soil/AC mixture using slurry microcosms. Aqueous sorption coefficients to AC (log KAC) for Hg-SRHA and MeHg-SRHA complexes were one to two orders of magnitude lower (Hg-SRHA = 4.53, MeHgSRHA = 4.35) than those for chloride complexes (HgCl2 = 6.55, MeHgCl = 4.90) and more closely resembled the log KAC of SRHA (3.64). In anoxic, sulfidic soil slurries, the KAC for sulfide species appeared stronger than for chloride or SRHA species for both Hg and MeHg. AC significantly reduced porewater concentrations of both ambient MeHg and a fresh Me199Hg spike, and the addition of up to 60 mg L-1 SRHA did not reduce sorption to AC. The AC also reduced ambient Hg and 201Hg porewater concentrations, but as SRHA concentration increased, the magnitude of solid phase sorption decreased. Speciation modeling revealed that SRHA may have impacted Hg distribution to the solid phase by reducing HgS precipitation. This study highlights the need for site-specific evaluation of AC efficacy and the value in developing biogeochemical models of AC performance for Hg control.

Modulation of coordination in pincer-type isonicotinohydrazone Schiff base ligands by proton transfer

We report the synthesis and X-ray characterization and theoretical study of two Hg(ii) complexes with pincer-type isonicotinohydrazone Schiff base ligands to analyze chelate-ring π-stacked assemblies.

Synthesis and antibacterial activities of novel Hg(II) and Zn(II) complexes of bis(thiosemicarbazone) acenaphthenequinone loaded to MWCNTs

This paper describes a series of new polyamides containing bis(thiosemicarbazone) acenaphthenequinone (PA), bis(thiosemicarbazone) acenaphthenequinone zinc (Z-PA), and bis(thiosemicarbazone) acenaphthenequinone mercury (H-PA) complexes loaded onto MWCNTs synthesized via a chemical precipitation method in methanol followed by antimicrobial activity studies on the novel functionalized MWCNTs complexes. These complexes are characterized by FT-IR spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The antibacterial activity of free PA, Z-PA, and H-PA complexes loaded onto MWCNTs are studied against gram-positive and gram-negative bacteria. The results indicate that the HPA/MWCNT complex is the most effective growth inhibitor against Listeria monocytogenes and Pseudomonas aeruginosa, exhibiting the potential for the use as an antibacterial agent.

Highly selective metallogel from 4-biphenylcarboxy capped diphenylalanine and FeCl3

Gelation was observed selectively for FeCl3 and 4-biphenylcarboxy capped diphenylalanine, whereas Cd, Cu, Zn, Cr, Ni, Hg, Mg, Mn, Pb, and Pd complexes as well as Boc and acetyl capped diphenylalanine were not able to form a metallogel.

Synthesis, characterization, DFT molecular modeling and biological studies of Zn(II), Cd(II) and Hg(II) complexes of new polydentate thiosemicarbazide

The new ligand, 2,2'-(9,10-dihydro-9,10-ethanoanthracene-11,12-dicarbonyl)bis(N-ethyl hydrazine-1-carbothioamide) (H6ETS) and its complexes with Zn(II), Cd(II) and Hg(II) were synthesized and characterized using physicochemical techniques. The IR and 1H-NMR spectral data of the ligand indicated that it exists in two forms, keto- and enol-thione. The metal complexes spectral data revealed that in Zn(II) complex, the ligand acts as binegative hexadentate, while in the Hg(II) complex, it reacted in binegative tetradentate fashion. Moreover, the ligand chelated to the Cd(II) ion in neutral bidentate manner through the carbonyl and N2H groups. The thermogravimetric analyses of Cd(II) complex confirmed the absence of the water molecules outside or inside the coordination sphere. Furthermore, the thermodynamic parameters were evaluated using Coats-Redfern and Horowitz-Metzger methods. The bond lengths and angles for the ligand and its Cd (II) complex were calculated at Density Function Theory “DFT” level and showed very good agreement with the x-ray values of analogue compounds. The optical energy gap were calculated and compared with DFT estimated. The isolated compounds were examined to explore their antibacterial, DNA cleavage, superoxide dismutase (SOD) scavenging and hydroxyl radicals scavenging activities.

Carboxymethyl cellulose thiol-imprinted polymers: Synthesis, characterization and selective Hg(II) adsorption

Sulfur containing ion imprinted polymers (S-IIPs) were applied for the uptake of Hg(II) from aqueous solution. Cysteamine which was used as the ligand for Hg(II) complexation, was grafted along the epichlorohydrin crosslinked carboxylated carboxymethyl cellulose polymer chain through an amide reaction. The adsorption ability of S-IIPs towards Hg(II) was investigated by kinetic and isotherm models, which, corresponding, showed that the adsorption process followed a pseudo-second-order, fitted well with the Langmuir isotherm with a maximum adsorption capacity of 80 mg/g. Moreover, thermodynamic studies indicated an endothermic and spontaneous reaction with the tendency of an enhanced randomness at the surface of the S-IIPs with temperature increases. S-IIPs indicated a high degree of selectivity towards Hg(II) in the presence of Cu2+, Zn2+, Co2+, Pb2+ and Cd2+. Furthermore, the efficiency of S-IIPs was also evaluated against real samples showing 86.78%, 91.88%, and 99.10% recovery for Hg(II) wastewater, ground water and tap water, respectively. In this study, the adsorbent was successfully regenerated for five cycles, which allows for their reuse without significant loss of initial adsorption capability.

Application of hardwood biochar as a reactive capping mat to stabilize mercury derived from contaminated floodplain soil and riverbank sediments

Hardwood biochar (pyrolyzed at 700 °C), a potential candidate for Hg removal, has been proposed for use as reactive capping mats along groundwater discharge zones or riverbanks to control release of Hg from contaminated riverbank sediments. Frequent flooding and drainage in fluvial settings can influence the effectiveness of remediation systems in contaminated riverbank sediments and floodplain soils. This study evaluated the effectiveness of Hg removal using hardwood biochar under hydrogeochemical conditions representative of those present within a reactive capping mat installed in a fluvial setting. Two sets of treatment columns, containing 50% v.v biochar and quartz sand, were subjected to 100 weekly wetting/drying cycles that included dry air, water-saturated air, and drainage using leachate derived from two source columns as input solutions: 1. Passing simulated acid rain water through floodplain soil, 2. Passing river water through riverbank sediment. In both treatment columns, >80% of the Hg was retained on the biochar without promoting Hg methylation and the release of other unintended dissolved constituents (including N, P, DOC). Results from solidphase extraction analyses suggest that Hg accumulated near the air/biochar-sand interface (0–2 cm) in the treatment columns at low loadings but was present at greater depths at higher loadings. Results of micro X-ray fluorescence (μ-XRF) mapping and micro X-ray absorption near edge structure (μ-XANES) for the biochar collected at depths 0–2 cm in treatment columns suggest retention of Hg-bearing particles derived from riverbank sediment and floodplain soil within the pore structure of the biochar. Sulfur K-edge XANES analysis of the unused biochar and the biochar after treatment suggest formation of Hg complexes on the biochar surface. These results indicate that hardwood biochar is potentially an effective media for application in reactive mats for controlling Hg discharging from contaminated riverbank sediments.

Mercury Isotopic Fractionation during Pedogenesis in a Tropical Forest Soil Catena (French Guiana): Deciphering the Impact of Historical Gold Mining.

We used natural mercury (Hg) stable isotopes to investigate the Hg cycle in a rainforest soil catena (French Guiana) partially gold-mined during the early 1950s. Litterfall showed homogeneous Δ199Hg values [-0.18 ± 0.05‰, i.e., a modern gaseous elemental Hg (GEM) isotopic signature]. After litter decomposition, Hg bound to organic matter (OM) is mixed with Hg from pristine (-0.55 ± 0.22‰) or gold-mined (-0.09 ± 0.16‰) mineral materials. Negative Δ199Hg values in deep pristine mineral horizons (-0.60 ± 0.16‰) suggest the transfer of Hg bound to dissolved OM depleted in odd isotopes due to mass-independent fractionation during Hg abiotic reduction. Perennial palm tree leaves collected above gold-mined and pristine soil recorded contrasting Δ199Hg signatures likely resulting from GEM re-emission processes from soils and leaf surfaces. Upslope, soil δ202Hg signatures showed a negative shift (ε ∼ -1‰) with depth attributed to mass-dependent fractionation during Hg sorption and complexation onto iron oxides and dissolved OM. Downslope, higher δ202Hg values in soils resulted from hydromorphy [lower humification, greater Hg(II) reduction, etc.]. The unique Hg isotopic signatures of Amazonian soils probably result in multistep fractionation processes during pedogenesis (millions of years) and in a potentially different Hg isotopic signature of preanthropogenic background GEM.