Quantification of methylmercury and geochemistry of mercury in sediments from a contaminated area of Descoberto (MG), Brazil     

《Applied Geochemistry》2016

In 2002, metallic Hg was found buried in a rural area of Descoberto city, Brazil. The origin of the Hg was a gold mining explotation plant established nearly one century ago. Although a number of studies have been conducted in order to assess the contamination of the area, none of them investigated the presence of methylated Hg in the hydric system. In this work methylmercury (CH₃Hg⁺) was determined using gas chromatography-pyrolysis-atomic fluorescence detection (CG-pyro-AFS) in material from rain sedimentation boxes and stream sediments near the contaminated area. Total Hg concentration (HgT) along with the chemical speciation by thermo-desorption were performed. HgT in material from the sedimentation boxes was found to be very high, up to 41,580 μg kg⁻¹, even in the rainy season, when in general HgT were much lower than in dry season. The samples from the Grama and Rico streams show a range of HgT from 5.8 to 266 μg kg⁻¹. The thermo-desorption analysis showed predominance of Hg²⁺, possibly linked to organic sulfur, suggested by a good positive correlation between Hg²⁺, HgT, organic mater (OM) and total S. The CH₃Hg⁺ concentration in stream sediment samples ranged from <0.07 to 1.87 μg kg⁻¹ and in the samples of sedimentation boxes the concentrations were 1.33 and 8.0 μg kg⁻¹ during dry season. The sample with the highest percentage of HgT as Hg²⁺ (98%) presented also the highest percentage of CH₃Hg⁺ (0.7%). These are high values, showing that care should be taken to avoid the transport of this material to the hydrological system. Further studies on the transfer through the food chain would be very important.  相似文献   

Extraction and distribution of soil organic and inorganic selenium in coal mine environments of Wyoming, USA     

S. Sharmasarkar  G. F. Vance 《Environmental Geology》1997,29(1-2):17-22

 Selenium (Se), an animal toxicant and aquifer contaminant, occurs in coal mine environments of Wyoming. There is a paucity of information on solution-phase Se speciation in mine soils. The objectives of this study were to compare Se extraction efficiencies of various reagents and to characterize SeO^2– ₃ (selenite), SeO^2– ₄ (selenate) and organic Se components in these extracts. Forty coal mine soils were extracted using DI (deionized) water, hot water (0.1% CaCl₂), AB-DTPA, NaOH, and KH₂PO₄. Each solution was analyzed for total dissolved Se, and inorganic and organic Se fractions. Both inorganic and organic Se fractions were detected in the soil extracts. The order of Se (total, inorganic, and organic) extraction efficiency for different reagents was DI water < hot water < AB-DTPA < NaOH < KH₂PO₄. The inorganic–organic Se ratios in DI water, hot water, AB-DTPA, NaOH, and KH₂PO₄ extracts were 60 : 40, 26 : 74, 61 : 39, 87 : 13, and 52 : 48, respectively, indicating predominance of inorganic Se in all but the hot water extract. Selenite was the dominant inorganic species in AB-DTPA and KH₂PO₄ extracts, while SeO^2– ₄ was the major Se species in the DI water, hot water, and NaOH extracts. Significant correlations (P<0.01) were observed among extractable inorganic Se [NaOH and KH₂PO₄ (r=0.95); hot water and AB-DTPA (r=0.89)], total soluble Se [DI water with hot water (r=0.98) and AB-DTPA (r=0.95)], and Se species [SeO^2– ₃ in AB-DTPA with SeO^2– ₄ in NaOH (r=0.94) and SeO^2– ₃ in KH₂PO₄ (r=0.88)]. These correlations are indicative of Se extraction efficiency, thermodynamically predicted chemical transformations (such as oxidation of SeO^2– ₃ to SeO^2– ₄), and probable interconversions between the organic and inorganic Se fractions (r=0.70 in KH₂PO₄ extracts); as a whole the correlations can be used as statistical validations of possible geochemical processes. Received: 21 August 1995 · Accepted: 16 October 1995  相似文献   

Thorium speciation in seawater   总被引：1，自引：4，他引：1  

P.H. Santschi  J.W. Murray  M. Baskaran  C.R. Benitez-Nelson  L.D. Guo  C.-C. Hung  C. Lamborg  S.B. Moran  U. Passow  M. Roy-Barman   《Marine Chemistry》2006,100(3-4):250

Since the 1960s, thorium isotopes occupy a special place in the oceanographer's toolbox as tracers for determining rates and mechanisms of oceanic scavenging, particle dynamics, and carbon fluxes. Due to their unique and constant production rates from soluble parent nuclides of uranium and radium, their disequilibrium can be used to calculate rates and time scales of sinking particles. In addition, by ratio-ing particulate ²³⁴Th (as well, in principle, other Th-nuclides) to carbon (and other elements), and linking this ratio to the parent–daughter disequilibrium in the water column, it is possible to calculate fluxes of carbon and other elements. Most of these applications are possible with little knowledge of the dissolved chemical properties of thorium, other than its oxidation state (IV) and tendency to strongly sorb to surfaces, i.e., its “particle- or surface-activity”. However, the use of any tracer is hindered by a lack of knowledge of its chemical properties. Recent observations in the variability of carbon to ²³⁴Th ratios in different particle types, as well as of associations of Th(IV) with various marine organic biomolecules has led to the need for a review of current knowledge and what future endeavors should be taken to understand the marine chemistry of thorium.  相似文献   

图们江口水中Zn,Cd,Pb,Cu的形式分析   总被引：1，自引：0，他引：1  

张首临  李泽林 《海洋科学》1992,16(5):47-50

本文用防吸附物理涂汞电极反问极谱对图们江口、东海及日本海水中Zn,Cd,Pb,Cu进行了形式分析,其不稳定态的平均浓度分别为5.9,0.071,0.039,0.69ug/L(占总量的15～27％),分布较为均匀,证实了痕量金属离子(自由离子及不稳定络离子的均匀分布规律。有机结合态Zn,Cd及Pb(10～30％)和颗粒态Zn,Cu和Cu(15～40％)的较高含量位于长江口、东海及图们江口。  相似文献   

Arsenic bioaccessibility and speciation in clams and seaweed from a contaminated marine environment     

Koch I  McPherson K  Smith P  Easton L  Doe KG  Reimer KJ 《Marine pollution bulletin》2007,54(5):586-594

The bioaccessible concentration and speciation of arsenic (soluble in a gastrointestinal medium and available for absorption into the bloodstream) were determined in softshell clams (Mya arenaria), harvested by local residents until 2005, and in seaweed (Fucus sp.) from an arsenic-contaminated marine site in Seal Harbour, Nova Scotia, Canada. Bioaccessibility extractions to simulate the human gastrointestinal environment (pH 1.5 and glycine for 1h followed by pancreatin, bile extract and pH adjustment to 7 for an additional 4h) and speciation of arsenic in extracts (HPLC-HG-AAS to target inorganic arsenic species) and whole samples (XANES) were carried out. Total arsenic for the clams from the contaminated area ranged from 218 to 228 ppm wet weight, with a bioaccessible fraction of 34-46%, and the major bioaccessible species of arsenic were inorganic. The seaweed from the contaminated area contained 27-43 ppm wet weight total arsenic, with the bioaccessible fraction ranging from 63% to 81%, and inorganic arsenic was also predominant. The predominantly inorganic nature of arsenic in the whole samples was confirmed by XANES. In concurrence with the closure of the area for clam harvesting, the clams and seaweed from Seal Harbour should probably not be used for human consumption.  相似文献   

Use of Pitzer Equations to Examine the Formation of Mercury(II) Hydroxide and Chloride Complexes in NaClO<Subscript>4</Subscript> Media     

Melchor González-Dávila  J. Magdalena Santana-Casiano  Frank J. Millero 《Aquatic Geochemistry》2007,13(4):339-355

The thermodynamic stability constants for the hydrolysis and formation of mercury (Hg²⁺) chloride complexes have been used to calculate the activity coefficients for Hg(OH) _n ^(2–n)+ and HgCl _n ^(2–n)+ complexes using the Pitzer specific interaction model. These values have been used to determine the Pitzer parameters for the hydroxide and chloro complexes and C _ML). The values of and have been determined for the neutral complexes (Hg(OH)₂ and HgCl₂). The resultant parameters yield calculated values for the measured values of log to  ±0.01 from I  =  0.1 to 3 m at 25°C. Since the activity coefficients of and are in reasonable agreement with the values for Pb(II), we have estimated the effect of temperature on the chloride constants for Hg(II) from 0 to 300°C and I = 0–6 m using the Pitzer parameters for complexes. The resulting parameters can be used to examine the speciation of Hg(II) with Cl⁻ in natural waters over a wide range of conditions.  相似文献   

Speciation of Polysulfides and Zerovalent Sulfur in Sulfide-rich Water Wells in Southern and Central Israel     

A. KamyshnyJr.  M. Zilberbrand  I. Ekeltchik  T. Voitsekovski  J. Gun  O. Lev 《Aquatic Geochemistry》2008,14(2):171-192

Zerovalent sulfur and inorganic polysulfides were determined in nine sulfide-rich water wells in central and southern Israel. Although the two locations belong to the same aquifer, they are characterized by different pH and hydrogen sulfide levels. Hydrogen sulfide in the central Israel wells ranged between 19 and 32 μM, and the pH was 7.26 ± 0.07. The southern basin is characterized by lower water circulation, lower pH (around 6.8), and higher hydrogen sulfide levels (>470 μM). Polysulfides were determined by a rapid single-phase methylation using methyl trifluoromethanesulfonate (methyl triflate) reagent. The summary polysulfide concentration for S₄²⁻–S₇²⁻ species was found to be around 0.14–0.75 μM in the central region of Israel and substantially higher, 2.3–4.6 μM in the southern region. The sum of polysulfide zerovalent sulfur and colloidal sulfur was quantitatively detected by cyanide derivatization and compared to polysulfide sulfur determined by methyl triflate derivatization and to the chloroform extraction of zerovalent sulfur. A method for the determination of sulfur undersaturation level—the ratio between dissolved elemental sulfur and its equilibrium concentration in the presence of solid sulfur—based on the observed levels of the major polysulfide species is described. The observed polysulfide speciation was compared with the predicted speciation under sulfur saturation conditions taking into account the water temperature, its ionic strength, and pH. Criteria for sulfur saturation versus unsaturated conditions were established based on (1) the chain length dependence of the ratio between the observed polysulfide concentrations and their predicted value under sulfur saturated conditions, and (2) the difference between the concentration of zerovalent sulfur, as determined by cyanolysis, and the total polysulfide sulfur. According to this dual criterion five of the water wells were classified as being undersaturated with respect to sulfur, though for all the examined water wells the majority of the zerovalent sulfur was in the form of polysulfide sulfur.  相似文献   

The impact of vegetation on fractionation of rare earth elements (REE) during water–rock interaction     

P. Stille  M. Steinmann  M.-C. Pierret  F. Gauthier-Lafaye  D. Aubert  A. Probst  D. Viville  F. Chabaux 《Journal of Geochemical Exploration》2006,88(1-3):341

Previous studies on waters of a streamlet in the Vosges mountains (eastern France) have shown that Sr and rare earth elements (REE) principally originate from apatite dissolution during weathering. However, stream water REE patterns normalized to apatite are still depleted in light REE (LREE, La–Sm) pointing to the presence of an additional LREE depleting process. Speciation calculations indicate that complexation cannot explain this additional LREE depletion. In contrast, vegetation samples are strongly enriched in LREE compared to water and their Sr and Nd isotopic compositions are comparable with those of apatite and waters. Thus, the preferential LREE uptake by the plants at the root–water–soil (apatite) interface might lead to an additional LREE depletion of the waters in the forested catchment. Mass balance calculations indicate that the yearly LREE uptake by vegetation is comparable with the LREE export by the streamlet and, therefore, might be an important factor controlling the LREE depletion in river waters.  相似文献   

Concentrations and speciation of arsenic along a groundwater flow-path in the Upper Floridan aquifer, Florida, USA     

S. E. Haque  K. H. Johannesson 《Environmental Geology》2006,50(2):219-228

Arsenic (As) concentrations and speciation were determined in groundwaters along a flow-path in the Upper Floridan aquifer (UFA) to investigate the biogeochemical “evolution“ of As in this relatively pristine aquifer. Dissolved inorganic As species were separated in the field using anion-exchange chromatography and subsequently analyzed by inductively coupled plasma mass spectrometry. Total As concentrations are higher in the recharge area groundwaters compared to down-gradient portions of UFA. Redox conditions vary from relatively oxic to anoxic along the flow-path. Mobilization of As species in UFA groundwaters is influenced by ferric iron reduction and subsequent dissolution, sulfate reduction, and probable pyrite precipitation that are inferred from the data to occur along distinct regions of the flow-path. In general, the distribution of As species are consistent with equilibrium thermodynamics, such that arsenate dominates in more oxidizing waters near the recharge area, and arsenite predominates in the progressively reducing groundwaters beyond the recharge area.  相似文献   

Metal speciation and attenuation in stream waters and sediments contaminated by landfill leachate     

Vojtěch Ettler  Marek Matura  Martin Mihaljevič  Petr Bezdička 《Environmental Geology》2006,49(4):610-619

The degree of metal contamination (Zn, Pb, Cu, Ni, Cd) has been investigated in the vicinity of an old unmonitored municipal landfill in Prague, Czech Republic, where the leachate is directly drained into a surface stream. The water chemistry was coupled with investigation of the stream sediment (aqua regia extract, sequential extraction, voltammetry of microparticles) and newly formed products (SEM/EDS, XRD). The MINTEQA2 speciation-solubility calculation showed that the metals (Zn, Pb, Cu, Ni) are mainly present as carbonate complexes in leachate-polluted surface waters. These waters were oversaturated with respect to Fe(III) oxyhydroxides, calcite (CaCO₃) and other carbonate phases. Three metal attenuation mechanisms were identified in leachate-polluted surface waters: (i) spontaneous precipitation of metal-bearing calcite exhibiting significant concentrations of trace elements (Fe, Mn, Mg, Sr, Ba, Pb, Zn, Ni); (ii) binding to Fe(III) oxyhydroxides (mainly goethite, FeOOH) (Pb, Zn, Cu, Ni); and (iii) preferential bonding to sediment organic matter (Cu). These processes act as the key scavenging mechanisms and significantly decrease the metal concentrations in leachate-polluted water within 200 m from the direct leachate outflow into the stream. Under the near-neutral conditions governing the sediment/water interface in the landfill environment, metals are strongly bound in the stream sediment and remain relatively immobile.  相似文献