Brombach, Christoph-Cornelius
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Brombach, Christoph-Cornelius
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Brombach, Christoph-Cornelius
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Item-typ:Veröffentlichung, Amorphous arsenic sulfide nanoparticles in a shallow water hydrothermal system(Elsevier Science, 2019-04-23); ; ; ; Hydrothermal fluids can contain trace elements such as arsenic (As), which are toxic to surrounding biota. In these kind of fluids, the bioavailability and biotransformation of As have been investigated but so far the ratio of total soluble As (<200 nm) versus the amount of As contained in a nanoparticulate phase has not been reported. Here, for the first time, the presence of As in the nanoparticulate fraction (between 200 and 20 nm) is described for arsenic-rich hydrothermal fluids in a marine shallow-water hydrothermal system. Samples of diffusively venting hydrothermal fluids, pore-water and seawater were collected in the hydrothermal system located in Paleochori Bay, Milos Island (Greece), and the fraction between 200 and 20 nm (As200-20) was studied. Up to 38% of the soluble arsenic was present within the As200-20 fraction in pore fluids, 10 to 20% in hydrothermal fluids and 5% in seawater. Identification and characterization of particles in hydrothermal fluid, pore-water and seawater was performed by scanning electron microscopy coupled to energy dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM) with selected area electron diffraction (SAED) and dynamic light scattering (DLS). The particles are of spherical morphology with a polydisperse size distribution (PDI: 0.37) and diameters close to 100 nm. EDX studies confirmed a chemical composition rich in As and S. The SAED pattern revealed absence of a crystal phase indicating the presence of an amorphous arsenic sulfide material. These results bring into discussion the role of the nanoparticulate fraction for As dispersion, bioavailability, and potentially harmful effects in marine coastal ecosystems.Wissenschaftlicher ArtikelBand:211100 155 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Mercury in the hydrothermal fluids and gases in Paleochori Bay, Milos, Greece(Elsevier Science, 2021-06-20); ; ; Seafloor hydrothermal activity may constitute a considerable mercury (Hg) source to the oceans, but the flux from marine shallow-water hydrothermal systems (MSWHS) remains poorly constrained to date. To study the presence of Hg in MSWHS in Paleochori Bay (Milos Island, Greece), sea surface, bottom, pore fluid and hydrothermal gas samples were collected in June of 2017, October of 2018 and July of 2020, and analyzed for Cl, Br, SO4, As, Ca, Fe, K, Mg, Mn, Na, Si, Sr, H2S, unfiltered total Hg (THg), and filtered Hg (Hgdiss). Specific sites were selected for the analysis of volatile elemental Hg (Hgo), dimethylmercury (DMHg), monomethylmercury (MMHg), and Hg in the gas phase (Hggas). Concentrations of THg observed in samples collected from the sea surface were elevated compared to surface samples taken outside Paleochori Bay. The highest surface water concentrations (~10 to 15 pM) were measured in samples collected directly above shallow-water hydrothermal discharge areas. Pore fluids outside Paleochori Bay were significantly lower in THg (0.8 to 8.6 pM) than those taken inside (17.4 to 1511 pM). Porewaters collected from areas with visible gaseous or fluid emission were highly variable but generally elevated in THg concentrations (185 to 5066 pM). Concentrations within gases ranged from 0.7 to 2791 nmol/m3. The vast majority of samples with highly elevated THg (> 100 pM) had low Na/K ratios (< 15), indicative of rapidly rising fluid. Concentrations of Hg0, DMHg, and MMHg were below detection limits in all samples. Bottom substrate type (e.g., rocky vs. sediment covered) likely affected infiltration rates of oxygenated seawater below the sediment-water interface, thereby affecting Hg speciation and removal by precipitation. Flux rates from porewaters compared to those with gaseous emission were high (12.56 to 1088 mol THg/year and 0.37 to 1.85 mol THg/year). Sites with slow gaseous emission rates are hypothesized to have extended subsurface reaction times, resulting in lower Hg concentrations emitted to bottom waters. However, increasing rates of gas emission did not necessarily indicate higher Hg concentrations. The scavenging of Hg in the sediments and advective flux out of Paleochori Bay likely prevent significant accumulations of THg in the water column of Paleochori Bay. The total atmospheric flux from Paleochori Bay using average flux calculations over the entire surface area would contribute 6 mmol Hg/year to the atmosphere. We hypothesize that Hg concentrations within the pore fluids of Paleochori Bay reflect a balance between mixing and precipitation in the subsurface. A three-component mixing system of vapor, brine and seawater determines THg concentrations; however, precipitation due to sulfur cycling, changes in redox conditions and temperature, all play a crucial role in removing Hg from emitted fluids and gases.Wissenschaftlicher ArtikelBand:23366 69 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Determination of ultra-low volatile mercury concentrations in sulfur-rich gases and liquidsDetermining mercury (Hg) concentrations in a wide range of naturally occurring liquids (i.e., groundwater, hydrothermal fluids, acid mine drainage, submarine groundwater discharge, etc.) and gases, (i.e., volcanic and hydrothermal emissions, flue gas, natural gas, land fill gas, etc.) has obstacles due to the presence of H2S in many of such samples. The classical approach of trapping Hg on gold traps comes up against its limits due to “poisoning” of the traps by H2S and problems for its determination by cold vapor atomic fluorescence spectrometry (CV-AFS). Due to low concentrations of Hg in these sample types it is often necessary to collect large amounts of liquid or gas in excess of 20 L, which makes transport to the laboratory difficult. With this in mind we developed a portable method for the collection of Hg from gases and liquids rich in H2S. The method uses an impinger set-up with an alkaline trap followed by two potassium permanganate - sulfuric acid traps. The potassium permanganate (KMnO4) oxidizes elemental Hg vapor to Hg2+, which remains in the KMnO4 solution and thus can be analyzed by CV-AFS. Thus, rather than 25 L of sample, only a few mL have to be transported to the laboratory. A possible caveat of this approach is that naturally occurring gases are generally a mixture of several different gases, such as H2, CH4, SO2 and H2S, which can react with and thus consume KMnO4. The influence of various gas compounds at different concentrations were tested for their effect on the trapping of Hg by KMnO4. Hydrogen and CH4 did not cause any interference, while SO2 did react with the KMnO4. When the oxidizing capacity in the first KMnO4-trap was depleted due to SO2, Hg was trapped in the second KMnO4-trap, which acted as a safety trap. Good recoveries of 99.5 % were achieved for the Hg collected in both KMnO4-traps. Nevertheless, when H2S was introduced into the system, Hg recovery dropped by almost 50 %. This observation was attributed to the formation of mercury sulfide (HgS) in the trap when the oxidation capacity of the KMnO4-trap was consumed. HgS cannot be reduced by stannous chloride (SnCl2), which is necessary for detection by CV-AFS. The problem was overcome by adding an alkaline trap with the reductant sodium borohydride (NaBH4) in front of the two KMnO4-traps. In this trap H2S was converted to S2-, which does not reach the KMnO4-trap while at the same time NaBH4 prevented the oxidation of Hg to Hg2+ followed by precipitation as HgS. Good recoveries of 98.05 ± 3.6 % (n = 3) were obtained for Hg when a volume of 1000 mL H2S was passed through the impinger train. Field testing of the method verified the effect of H2S on the trapping and ultimately the determination of Hg in the hydrothermal gas. With the alkaline trap we determined a Hg concentration of 358 ng m−3 Hg, while without the alkaline trap only 101 ng m−3 Hg. Thus, the set-up without the alkaline trap led to an underestimation of the real Hg concentration by 71.8 % and confirmed the necessity of an alkaline trap to overcome the interference of H2S.Wissenschaftlicher ArtikelBand:19953 80