Tracing anthropogenic mercury in soils from Fe-Hg mining/smelting area: Isotopic and speciation insights.

Mercury (Hg) stable isotope ratios supplemented by Hg solid speciation data were determined in soils in a former Fe-Hg mining/smelting area (Jedová hora, Czech Republic, Central Europe). The dominant Hg phase in the studied soils was found to be cinnabar (HgS). A secondary form of soil Hg(II) was represented by Hg weakly and strongly bound to mineral (micro)particles, as revealed by thermo-desorption analysis. These Hg species probably play a key role in local soil Hg processes and biogeochemical cycling. The Hg isotopic data generally showed small differences between HgS (-1.1 to -0.8‰; δ202Hg) and the soil samples (-1.4 to -0.9‰; δ202Hg), as well as limited isotopic variability within the two studied soil profiles. On the other hand, the detected negative δ202Hg shift (∼0.4‰) in organic horizons compared to mineral soils in the highly contaminated profile suggests the presence of secondary post-depositional Hg processes, such as sorption or redox changes. For the less contaminated profile, the observed Hg isotopic variation (∼0.3‰; δ202Hg) in the subsurface mineral soil compared to both overlying and underlying horizons is likely due to cyclic redox reactions associated with Hg isotopic fractionation. We assume that the adsorption of Hg(II) to secondary Fe(III)/Mn(III,IV)-oxides could be of major importance in such cases.

An XAS study of Hg(II) sorption to Al-based drinking water treatment residuals.

Drinking water treatment residuals (DWTRs) are produced from the coagulation and flocculation processes in conventional drinking water treatment. The abundant metal oxide content of these materials resulting from the use of coagulants, like alum and ferric chloride, has driven strong research interest into the reuse of DWTRs as sorptive materials. Using a suite of aluminum-based DWTRs, we provide new insights into Hg(II) sorption mechanisms. Experiments performed at circum-neutral pH show that sorption capacities are related to the amount of organic carbon/matter present in DWTRs. We found that carbon rich samples can scavenge about 9000 mg/kg of Hg, in contrast to 2000 mg/kg for lime based DWTRs. X-ray absorption spectroscopy (XAS) at the Hg L3 edge further characterizes mercury coordination. X-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) results point to a partial association of mercury with sulfur at low mass loadings, transitioning to a full association with oxygen/carbon at higher concentrations of sorbed Hg(II) and in DWTRs with limited sulfur content. These results suggest that sorption of Hg(II) is primarily controlled by the carbon/organic matter fraction of DWTRs, but not by the coagulants.

Unveiling the Halogenation-Induced Formation of Hg3Se2X2 (X = Cl, Br, and I) Compounds for Multiphase Mercury Cycling.

The interaction between mercury (Hg) and inorganic compounds, including selenium (Se), sulfur (S), and halogens (X = Cl, Br, or I), plays a critical role in the global mercury cycle. However, most previously reported mercury compounds are susceptible to reduction, leading to the release of elemental mercury (Hg0) and causing secondary pollution. In this study, we unveil a groundbreaking discovery that underscores the vital role of halogenation in creating exceptionally stable Hg3Se2X2 compounds. Through the dynamic interplay of Hg, Se, and halogens, an intermediary stage denoted [HgSe]m[HgX2]n emerges, and this transformative process significantly elevates the stabilization of mercury. Remarkably, halogen ions strategically occupy pores at the periphery of HgSe clusters, engendering a more densely packed atomic arrangement of Hg, Se, and halogen components. A marked enhancement in both thermal and acid stability is observed, wherein temperatures ascend from 130 to 300 °C (transitioning from HgSe to Hg3Se2Cl2). This sequence of escalating stability follows the order HgSe < Hg3Se2I2 < Hg3Se2Br2 < Hg3Se2Cl2 for thermal resilience, complemented by virtually absent acid leaching. This innovative compound formation fundamentally alters the transformation pathways of gaseous Hg0 and ionic mercury (Hg2+), resulting in highly efficient in situ removal of both Hg0 and Hg2+ ions. These findings pave the way for groundbreaking advancements in mercury stabilization and environmental remediation strategies, offering a comprehensive solution through the creation of chemically stable precipitates.

DFT study of mercury adsorption on Al2O3 with presence of HCl.

mercury emission control from flue gas is a crucial issue for environment protection. Alumina is an important alkali metal oxide for mercury adsorption in particulate, meanwhile is the potential adsorbent for mercury removal. The cognition on mercury heterogeneous reaction mechanism with alumina in presence of hydrogen chloride is inadequate. In this work, the DFT calculation was applied to detect mercury's chlorides adsorption on α-Al2O3 (001) surface, the Bader charge analysis was used to estimate electron transfer and the transition state theory was used to clarify reaction pathway and energy barrier, besides, the kinetic analysis based on Gibbs free energy was conducted to study the impact of temperature on chemical reaction. The results show that Hg can be captured by weak chemisorption on α-Al2O3 (001) surface with the adsorption energy of -56.37 kJ/mol, HgCl, HgCl2 are intensively bonded on surface with adsorption energies of -276.90 kJ/mol and -231.87 kJ/mol, the surface unsaturated Al and O atoms are the active sites. Charge transfer and PDOS analysis prove that the forming of covalent bonding is responsible for Hg species adsorption. Two possible reaction pathways of Hg oxidization to HgCl2 are discussed, in which a smaller energy barrier of 0.1 eV implies the dominant pathway 1 via Eley-Rideal mechanism: two adsorbed HCl molecules dissociate on surface and then react with one Hg atom. High temperature can promote the reaction rate constants of pathway 1 and 2, but is only favorable for reducing energy barrier of pathway 2.

An Effective Selenium-Based Fluorescence Chemosensor for Selective Recognition of Hg2+ in Aqueous Medium: Experimental and Theoretical Studies.

We introduce a novel selenium-based compound [N-(Phenylcarbamoselenoyl) furan-2-carboxamide] for the optical and fluorimetric detection of Hg in an aqueous medium. The synthesized compound was characterized by different spectroscopic methods. The designed chemosensor FSU has shown a significant fluorescence quenching when Hg2+ ions were added to the sensing medium. Furthermore, Hg2+ ions provoked a 2:1 complex formation with the chemosensor FSU. It is found that the compound offers high selectivity over a variety of cations such as Co2+, Cr3+, Ni2+, Zn2+, Cu2+, Mg2+, Hg2+, Cd2+, Ca2+, Mn2+, Ga3+, Pb2+, Na+, Fe2+ and K+. The detection limit was calculated as 7.35 × 10-7 M. Also, FSU shows appreciable binding affinity towards Hg2+ ions with a binding constant value of 1.413 × 103 M-1. The ICT mechanism of mercury sensing was confirmed with spectroscopic techniques and DFT studies. Density functional theory was also implemented to investigate the structure of the Hg2+ complex and its electronic distribution in the aqueous medium. Finally, an MEP study was also carried out to obtain detailed information about the surface characteristics of the chemosensor FSU. Effectively, we have reported a potent chemosensor for Hg2+ in the aqueous medium.

New polluting metals. Quantification in herbal medicines by voltammetric and spectroscopic analytical methods.

A new application of voltammetric techniques in stripping mode to the quantitative determination of metals belonging to the platinum group (PGM) in herbal medicines, at the ultra-trace level, is reported. Pd (II), Pt (II) and Rh (III) are determined by means of square-wave adsorption voltammetry (SWAdSV); Os (VIII) and Ru (III) are determined through square-wave voltammetry in catalytic mode (SWCV); Ir (III) is determined through the application of square-wave catalytic voltammetry in adsorption mode (SWAdCSV). In all the applied methods, the voltammetric cell has the conventional setting with three-electrodes, which sees the presence of a suspended mercury-drop electrode (HMDE) or a glassy carbon electrode (GCE) as working electrodes for the determination of Ir (III). The auxiliary electrode was a platinum electrode, and an Ag∣AgCl∣KClsatd. electrode was employed as reference electrode. Validation of the analytical procedure here proposed has been achieved using reference standards: NIST-SRM 1570a (Spinach Leaves) and NIST-SRM 1573a (Tomato Leaves), both added with pure metal standards, obtaining satisfying precision values, better than the limits set for the validation of quantitative methods. Following the verification of the validity of the here presented procedure, commercially available herbal medicines, based on Eucalyptus globulus, Harpagophytum procumbens DC and Taraxacun officinale weber, were analyzed. Standard samples were also analyzed by atomic absorption spectroscopy, in order to have a reference technique for validating the entire procedure.

MALDI-TOF-MS and XAS analysis of complexes formed by metallothionein with mercury and/or selenium.

Mercury (Hg) is highly toxic while selenium (Se) has been found to antagonize Hg. Both Hg and Se have been found to induce metallothioneins (MTs). In this study, the complexes formed by metallothionein-1 (MT-1) with HgCl2 and/or Na2SeO3 was studied using matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) and X-ray absorption spectrometry (XAS). MALDI-TOF-MS and XAS indicated the formation of Hg-S bond or Se-S bond when MT-1 reacted with HgCl2 or Na2SeO3, respectively. The bond lengths of Hg-S and coordination number in MT-Hg are 2.41 ± 0.02 Å and 3.10 and in MT-Se are 2.50 ± 0.03 Å and 2.69. A MT-Se-Hg complex was formed when MT-1 reacted with both HgCl2 and Na2SeO3, in which the neighboring atom of Hg is Se, while the neighboring atoms of Se are S and Hg. Our study is an important step towards a better understanding of the interaction of HgCl2 and/or Na2SeO3 with proteins like MT-1.

Evaluating the spectrum-effect profiling and pharmacokinetics of Tieshuang Anshen Prescription with better sedative-hypnotic effect based on Fe2+ than Hg2.

Although Zhusha Anshen Pill (ZSASP) is a commonly used traditional prescription for insomnia, the safety of cinnabar in the formula has always been controversial since its initial application in medical fields. Here, we developed a new prescription, Tieshuang Anshen Prescription (TSASP), by improving ZSASP with Fe2+ instead of Hg2+. Besides, TSASP was further optimized by establishing and testing the HPLC fingerprint and its sedative-hypnotic effect of formulas with different compatibility ratios and performing correlation spectrum analysis. The safety of TSASP was also evaluated by HE staining of liver and kidney. In addition, a validated and robust UHPLC-MS/MS method was established to demonstrate the pharmacokinetic characteristics of berberine, palmatine, jatrorrhizine, ligustilide, catalpol, loganin, liquiritin and liquiritigenin after oral administration of TSASP. Our study originally provides a new non-toxic prescription, TSASP, with better sedative-hypnotic effect in comparison with ZSASP, revealing that Fe2+ could replace Hg2+ to eliminate its toxicity and play a sedative role. Meanwhile, we believe that our pharmacokinetics results may contribute valuable reference to both TSASP's specific mechanism of action and its further clinical efficacy and effectiveness research.

Investigation of the Hg(II) biosorption from wastewater by using garlic plant and differential pulse voltammetry.

In this work, the bio sorption of mercury ion by garlic bio-adsorbent was studied. A batch and a continuous up-flow fixed-bed column system were used in this report. Differential pulse voltammetry was used to detecting the amount of mercury ion. Using Differential pulse voltammetry prevents the production of carcinogenic mercury vapor. In the batch system, various doses of bio-adsorbent were investigated. After that, the experimental data was fitted using Langmuir and Freundlich models. The experimental data were also fitted to the Thomas, Bohart-Adams, and Yan models for the continuous mode in a fixed bed of garlic bio-adsorbent. The maximum adsorption capacity estimated by the Thomas models was 23.5 mg g-1 and τ was 135.3 min. This adsorbent is also suitable for absorbing mercury from a real-life well water sample. It is renewable and can be used to absorb mercury several times.

Highly efficient electrochemical gas reduction on a three-dimensional foam electrode: mechanism and application for the determination of hazardous mercury in complex matrix.

For the first time a nickel foam electrode (NFE) is applied in the field of electrochemical vapor generation (EVG) to carry out the electrochemical vapor phase conversion of mercury. Systematical electrochemical and morphological research has demonstrated that the specific surface area of the NFE was several times larger than that of the metal/non-metal electrode with the same geometric size. At the same time, the 3D porous channel composed of multi-layer nickel wire ensures the full contact between reactant and interface. The evident enhancement of spectral signals on a Ni electrode (283%), compared with Pt (27%) and graphite (109%), confirmed that the NFE effectively enhances the yield of mercury reduction. The NFE exhibits low limit of detection (0.017 µg L-1) and a wide linear range (0.2-20 µg L-1) with recoveries of actual samples in the range 87.8-117% towards Hg2+. Although the NFE has no advantage in electronic transmission and catalytic performance, its excellent stability, especially anti-interference and other characteristics, is sufficient for the analysis of hazardous mercury in complex matrix including certified reference materials and real samples.

Green and novel adsorbent from rice straw extracted cellulose for efficient adsorption of Hg (II) ions in an aqueous medium.

Cellulose nanofibrils (CNF) were extracted from rice straw, a waste lignocellulosic biomass, using soda cooking, which resulted in a reduction of the recalcitrance of biomass, leading to hydrolysis of hemicellulose into sugars, which was subsequently washed, leaving a residue of cellulose. FTIR confirmed the removal of lignin and hemicellulose to yield pure CNF while XRD, DTG and TGA results showed increased crystallinity and thus higher thermal stability. CNFs were functionalized using l-methionine, a natural amino acid, to graft sulfides and amino functional groups onto the surface of fibers. Structural and morphological changes induced by grafting were confirmed by FTIR, XRD, TEM, Mapping and Elemental analysis. Modified fibers exhibited a high adsorption capacity of 131.86 mg/g for Hg (II) ions even at low concentration i.e. 300 ppm owing to sulfides. Optimization of pH on adsorption behavior was established through extensive pH studies and adsorption kinetics. Adsorption follows pseudo second order kinetic model indicating chemisorption for removal of Hg (II) ions from simulated wastewater.

Colorimetric aptasensor for the detection of mercury based on signal intensification by rolling circle amplification.

Techniques that are sensitive to detect mercury ion (Hg2+) are very important, due to its serious threat to public health and food security. In this work, a colorimetric aptasensor was fabricated for the detection of Hg2+ based on rolling circle amplification (RCA). The aptamer was immobilized onto the microplate and hybridized with its complementary strand (cDNA1) which linked with a primer for triggering the RCA reaction of circular template. The successfully RCA process led to the formation of long ssDNA chains on the microplate, which created many hybridized DNA fragments for bio-cDNA2. The tagged amount of horseradish peroxidase (HRP) was enhanced through the avidin/biotin binding between avi-HRP and bio-cDNA2. In the addition of TMB-H2O2, HRP was catalyzed and generated an optical signal. However, in the presence of target, Hg2+ specifically and preferentially bound with aptamer and formed a strong and stable T-Hg2+-T complex, which led to the release of cDNA1 and HRP cluster. Consequently, the optical signal decreased. Our results showed that the limit of detection (LOD) of this system was 1.6 nM with excellent specificity, and that the detection signals were enhanced by up to 18 times under RCA conditions when compared with detections without RCA. This method has been successfully used to detect Hg2+ in water samples with a recovery of 98%-105.74%.

Selenium and mercury in dolphinfish (Coryphaena hippurus) from the Gulf of California: inter-annual variations and selenium health benefit value.

With the aim of determining the benefit from consumption of dolphinfish Coryphaena hippurus from La Paz and Cabo San Lucas in the southern area of the Gulf of California, mercury (Hg) and selenium (Se) were measured in liver and muscle of specimens (n = 362) collected between 2006 and 2013. Mean levels of Hg in muscle (0.61 µg g-1) and liver (0.42 µg g-1) of all individuals from La Paz were significantly higher (p < 0.05) than in fish from Cabo San Lucas; in the case of Se, mean concentrations in liver (1.54 µg g-1) of all individuals from La Paz were significantly higher (p < 0.05) than in fish from Cabo San Lucas. Hg levels in muscle were positively and significantly (p < 0.05) correlated with fork length and weight of fish; in liver, Hg and Se were significantly (p < 0.05) correlated with fork length and weight of specimens. Levels of Hg and Se in muscle and liver among years varied significantly (p < 0.05); although there was not a defined pattern of temporal fluctuations for both elements, the lowest Hg levels occurred in 2009 when surface water temperatures were the highest for the sampled years. With respect to the Se health benefit value (HBVSe), results were positive and above the unit in all cases; it implies that consumption of dolphinfish in the southern Gulf of California is beneficial.

Magnetite nanoparticle embedded Pectin-graft-poly(N-hydroxyethylacrylamide) hydrogel: Evaluation as adsorbent for dyes and heavy metal ions from waste water.

A pectin (Pec) based gel has been made by grafting N-hydroxyethylacrylamide (HEAA) on pectin using potassium peroxodisulphate as initiator and N,N-methylenebisacrylamide as crosslinker under microwave irradiation. The magnetite (Fe3O4) nanoparticles were incorporated within this gel via in situ diffusion of Fe2+ and Fe3+ followed by reaction with ammonia solution. The synthesized gel, pectin-graft-poly(N-hydroxyethylacrylamide) (Pec-g-PHEAA); and the magnetite containing composite (Pec-g-PHEAA/Fe3O4) were characterized by FTIR, TGA, XRD, BET and SEM techniques. The magnetic property measurement indicated ferromagnetic nature of the nanocomposite. The Pec-g-PHEAA and Pec-g-PHEAA/Fe3O4 systems were evaluated for removal of dye and metal ions from aqueous solution using Rhodamine 6G (R6G), a cationic dye; Cu(II) and Hg(II) ions. Both adsorbents showed significant adsorption capacity towards these species, with greater adsorption capacity in case of Pec-g-PHEAA/Fe3O4. Adsorption process is observed to follow both Langmuir and Freundlich isotherm models for R6G dye and Freundlich isotherm model for Cu(II) and Hg(II) ions. The adsorption was found to be a pseudo first order process for R6G and pseudo second order process for Cu(II) and Hg(II) ions. The positive values of ∆H0 and the negative values of ∆G0 indicated the adsorption process to be endothermic and spontaneous.

Exploiting the κ2 -Fashioned Coordination of [Se2 ]-Donor Ligand L3 Se for Facile Hg-C Bond Cleavage of Mercury Alkyls and Cytoprotection against Methylmercury-Induced Toxicity.

The Hg-C bond of MeHgCl, a ubiquitous environmental toxicant, is notoriously inert and exceedingly difficult to cleave. The cleavage of the Hg-C bond of MeHgCl at low temperature, therefore, is of significant importance for human health. Among various bis(imidazole)-2-selones Ln Se (n=1-4, or 6), the three-spacer L3 Se shows extraordinarily high reactivity in the degradation of various mercury alkyls including MeHgCl because of its unique ability to coordinate through κ2 -fashion, in which both the Se atoms simultaneously attack the Hg center of mercury alkyls for facile Hg-C bond cleavage. It has the highest softness (σ) parameter and the lowest HOMO(Ln Se)-LUMO(MeHgX) energy gap and, thus, L3 Se is the most reactive among Ln Se towards MeHgX (X=Cl or I). L3 Se is highly efficient, more than L1 Se, in restoring the activity of antioxidant enzyme glutathione reductase (GR) that is completely inhibited by MeHgCl; 80 % GR activity is recovered by L3 Se relative to 50 % by L1 Se. It shows an excellent cytoprotective effect in liver cells against MeHgCl-induced oxidative stress by protecting vital antioxidant enzymes from inhibition caused by MeHgCl and, thus, does not allow to increase the intracellular reactive oxygen species (ROS) levels. Furthermore, it protects the mitochondrial membrane potential (ΔΨm ) from perturbation by MeHgCl. Major Hg-responsive genes analyses demonstrate that L3 Se plays a significant role in MeHg+ detoxification in liver cells.

The total content of toxic elements in horsehair given the level of essential elements.

Elemental status of 214 mares aged 3-7 years from 11 breeds was studied: Arabian purebred (n = 20), Bashkir (n = 20), Kabarda (n = 20), Vyatka (n = 20), Tuva (n = 19), Yakutsk (n = 30), Mezenskaya (n = 20), Thoroughbred (n = 20), Akhal-Teke (n = 20), Russian trotter (n = 15), Soviet Heavy Draft (n = 10) bred in 13 regions of Russia. The research objective is to study the content of chemical elements in hair from the horse's mane, depending on the sum of toxic elements in animal hair expressed in moles. The elemental composition of the hair was defined by atomic emission and mass spectrometry (AES and MS). Elemental composition of biosubstrates was studied by 25 indicators (Al, As, B, Ca, Cd, Co, Cr, Cu, Fe, I, K, Li, Mg, Mn, Na, Ni, P, Pb, Se, Si, Sn, Hg, Sr, V, Zn). In the studies, an estimate of the total toxic load of the horse's body (∑tox) was given as the sum of mmoles of Al, Cd, Pb, Sn, Hg, and Sr in horsehair. Based on ∑tox percentile calculations, animals were divided into three groups up to 25 percentile (n = 54) with concentrations up to 1.09 mmol/kg, within the 25 and 75 percentile limits (n = 105) and over 75 percentile (n = 55) with a concentration above 6.08 mmol/kg. As follows from the obtained results, the ∑tox indicator in the mane's hair is closely connected with the total hair mineralization. For the studied range of ∑tox values, the relationship of this indicator with 13 essential and conditionally essential chemical elements is described. Moreover, as ∑tox increases, it indicates an increase in the concentration of eleven (Ca, P, Co, Cr, Fe, I, Mn, Li, Ni, V, As) and a decrease of two elements in hair (B, Si); for six elements (K, Mg, Na, Cu, Zn, Sn), such a connection was not revealed. At ∑tox values higher than 75 percentile, a critical increase in the exchange pools of two or more toxic elements in the body was observed in 85% of cases. Intensive exchange of selenium and iodine is observed; it is expressed by an increase in the number of animals with the content of these elements in hair beyond the "physiological standard," estimated as the range of 25-75 percentile.

Establishment of Logic Gates Based on Conformational Changes in a Multiple-Factor Biomolecule Interaction Process by Dual Polarization Interferometry.

DNA-based logic gates stimulate the development of molecular scale computers and show enormous potential in nanotechnology, biotechnology, and medicine. However, the reported detectors to date usually require one to label appropriate signal probes, resulting in not only a high cost but also potentially tedious manipulation. For the first time, we established a label-free logic gate by regarding the structure-related signal as output. Dual polarization interferometry (DPI) was employed to reveal the detailed conformational transitions occurring in the multiple-factor biomolecule interactions and then was utilized as a detection tool of logic gate. As a vital merit of this system, the dependence of the density output signal on the interaction with multiple-factor input can mimic the function of signal communication in OR, INHIBIT, and IDENTITY logic gates and the INHIBIT-OR cascade circuit. Additionally, the DPI signal with logic stringency can unambiguously distinguish conformational polymorphisms and compare structural stability. This study provides a new way for the construction of a label-free logic gate, supplements information deficiency of reaction details, and extends the application of DPI in logic operation.

Selenium and mercury concentration in drinking water and food samples from a coal mining area in Brazil.

Selenium (Se) is an essential element for human health and can also alleviate the toxicity of elements such as mercury (Hg), which is considered deleterious to health. The study area is an important coal mineral region in Brazil, generating 40% of all Brazilian coal. During the coal mining process, Se and Hg are released, which can induce potential human health risks via the food chain. The purpose of the present study is to determine total Se and its species and total Hg in drinking water and food locally produced from a coal mining area, to assess the impact of coal mining. The samples were collected in two cities, with and without coal mining influence. Total Se levels in drinking water and food were assessed by inductively coupled plasma mass spectrometry (ICP-MS) and its species by high-performance liquid-ICP-MS, while total Hg was determined by cold vapor atomic fluorescence spectrometry. Drinking water (1.1 ± 0.2 mg L-1 dry weight) (p = 0.02) and tomatoes (1.5 ± 0.1 mg kg-1 dry weight) (p = 0.01) from the coal mining area had higher total Se concentration than the control area. The highest Se concentrations were found in animal-based food (6.4 ± 0.8 mg kg-1 dry weight) with an important contribution of Se IV (65%). The analyzed sample did not accumulate a significant amount of Hg. Future studies on the estimates of daily intake of these elements and dietary pattern of the population are needed to make appropriate dietary recommendations and support public health action.

Mobilization of mercury species under dynamic laboratory redox conditions in a contaminated floodplain soil as affected by biochar and sugar beet factory lime.

Mercury and its species are toxic and therefore strategies to immobilize them or to impede the formation of bioaccumulative MeHg are a hot topic of ongoing research. Biochar (BC) and sugar beet factory lime (SBFL) are suggested to have the potential to meet these goals. However, their ability to restrain the mobilization of total Hg (Hgt), methylmercury (MeHg), and ethylmercury (EtHg) or the formation of MeHg and EtHg has not been examined to date. Moreover, the effect of systematically altered redox conditions on the release dynamics of Hgt, MeHg, and EtHg in a contaminated floodplain soil as affected by these soil amendments has not been studied. Therefore, we investigated the impact of pre-defined redox conditions on the release dynamics of Hgt, MeHg, and EtHg in a contaminated floodplain soil (CS) and the soil amended with either BC (CS+BC) or SBFL (CS+SBFL). The mobilization of Hgt, MeHg, and EtHg was generally higher at low redox potential (EH) and decreased with increasing EH, irrespective of soil treatment. Both BC and SBFL diminished the release of Hgt from soil but not the methylation and ethylation of Hg. In CS+SBFL approximately half of Hgt was found in solution compared to CS. However, higher methylation efficiency (MeHg/Hgt ratio) was found in CS+SBFL counterbalancing this benefit. Abundances of specific phospholipid fatty acids suggest the presence of sulfate-reducing bacteria, which are considered as primary Hg methylators. The results indicate that both BC and SBFL have the potential to curtail the release of Hgt from inundated soils, while SBFL was more efficient. However, these amendments had no marked effect on the MeHg and EtHg concentrations. Therefore, further research should be conducted to identify soil additives that are capable to reduce the release and formation of these Hg species.

Immobilization of elemental mercury by biogenic Se nanoparticles in soils of varying salinity.

Salinity can be a significant environmental stress which can govern the fate of nanoparticles in the environment as well as other factors such as pH, natural organic matter and minerals. In this research, the effects of salinity on the behavior of biogenic selenium nanoparticles (BioSeNPs) and consequences for elemental mercury (Hg0) immobilization in soil and soil solutions were investigated. It was found that homoaggregation and sedimentation of BioSeNPs were enhanced significantly with increasing salinity. Compression of the electric double layers of BioSeNPs at high ionic strengths resulted in attractive van der Waals forces dominating and leading to enhanced aggregation. Moreover, neutralization of the surface negative charge of BioSeNPs by divalent cations and the bridging of BioSeNPs via calcium binding to surface functional groups were also associated with enhanced aggregation. Such enhanced aggregation exerted inhibition of Hg0 immobilization in soil solutions/soils of varying salinity. These results indicate that salinity is an important environmental factor governing aggregation of BioSeNPs and therefore influencing the efficiency of Hg0 immobilization, and possible remediation treatments, as a consequence.