Partitioning Of As Research Articles

Arsenic-poor fluids promote strong As partitioning into pyrite

Pyrite is a ubiquitous sulfide mineral found in diverse geological settings and holds great significance in the formation of Au deposits as well as the safe utilization of groundwater due to its remarkable ability to incorporate substantial amounts of As. However, despite its importance, there remains a dearth of fundamental data on the partitioning of As between pyrite and fluid, which is key for accurately modeling the As distribution in these environments.Here, we present new insights into the partitioning behavior of As between pyrite and fluid at conditions that mimic natural fluid systems. Pyrite was synthesized by replacement of natural siderite in hydrothermal experiments at 200 °C and pH 5 applying a wide range of fluid As concentrations, spanning from 0.001 to 100 µg/g. The As distribution and concentration in synthetic pyrite was analyzed by quantitative LA-ICP-MS mapping providing a high spatial resolution and sensitivity at 2–3 µm image pixel size at a detection limit of ∼1 µg/g at the single pixel scale. Pyrite-fluid partitioning coefficients (DAs(py/fluid)) between synthetic pyrite and experimental fluid agree with previously published data for high fluid As concentrations of 1 µg/g to 100 µg/g (DAs < 2000). However, at low As concentrations in the experimental fluid (<1 µg/g), a steep increase in the DAs(py/fluid) values of up to ∼30,000 was detected, demonstrating even stronger As partitioning into pyrite. This is confirmed by the analyses of natural pyrite that precipitated from As-poor fluids (0.3–0.4 ng/g) within a deep anoxic aquifer in SE Sweden. The discovery holds significant implications for the mobility and scavenging of As, which in turn is important for understanding the formation and fingerprinting of mineral deposits as well as for the secure utilization of groundwater resources.

Controls of Geochemical and Hydrogeochemical Factors on Arsenic Mobility in the Hetao Basin, China.

High arsenic (As) groundwater is frequently found in inland basins, but little is known about As pools in sediments and their influences on aqueous As distributions. The Hetao Basin is a typical inland basin, where groundwater As concentrations generally increase from alluvial fans to flat plain. Two sites are only 1700 m apart, but groundwater As concentrations at the depth range of 15 to 80 m are quite different, ranging from 7.0 to 31.7 μg/L at site B1 and from 5.2 to 99.8 μg/L at site B2. Sediment geochemistry and groundwater hydrochemistry at two sites were characterized. No distinct differences were observed in the bulk geochemistry of sediments. Sequential extractions of 39 sediments were conducted to determine why As was easily released to groundwater at one site and not the other. Results showed that at site B1 most of solid As was associated with amorphous Fe-(oxyhydr)oxides, whereas at site B2 the strong adsorption pool dominated. Furthermore, higher dissolved Fe2+ and lower ORP in groundwater at site B2 suggested more strongly reducing conditions compared to site B1. High concentrations of NH4 + and HCO3 - at site B2 were consistent with As release coupled to microbially induced reductive dissolution of Fe-(oxyhydr)oxides. Other processes, such as the competitive adsorption of HCO3 - , As desorption under weakly alkaline pH conditions, may also influence the partitioning of As between groundwater and sediments. This study highlights the differences in how As is associated with sediments between high and low As aquifers and the contribution of chemical characteristics to As release.

Validation of blood arsenic and manganese assessment from archived clotted erythrocyte fraction in an urban cohort of mother-child dyads

Exposure to arsenic (As) and manganese (Mn) from contaminated food, drinking water and dust are linked to a host of adverse health effects. The recent discovery of unmonitored community exposures to hazardous levels of metals, as seen in the Flint Water Crisis and East Chicago, have demonstrated a need for novel biomonitoring methods utilizing samples other than whole blood. Here, we present a method utilizing clotted erythrocyte fraction samples, a blood component commonly archived in biorepositories, to predict whole blood levels of As and Mn. This method would allow for innovative retrospective assessments of environmental exposures in previously unused samples. Whole blood and clotted erythrocyte fraction samples were simultaneously collected from 84 participants in the Airborne Exposure to Semivolatile Organic Pollutants (AESOP) cohort study of mother-child dyads in East Chicago. Clotted erythrocyte fraction samples were prepared by alkaline dilution and subsequently analyzed using inductively coupled plasma-mass spectrometry. A strong linear relationship was observed between whole blood and clotted erythrocyte fraction with Pearson correlation coefficients (r, p < 0.001) of 0.74, and 0.82 for As and Mn, respectively. Modeled whole blood Mn levels predicted from clotted erythrocyte fractions evaluated at a test threshold representing the NHANES median of 9.7 μg/L, were found to have diagnostic sensitivity of 88% and specificity of 71%. Clotted erythrocyte partitioning of As was tested on a wide range of oral gavage doses using a rat model. Results from this investigation demonstrate clotted erythrocyte fraction samples are a viable alternative biological sample for retrospective public health surveillance of environmental exposure to As and Mn.

Bioaccumulation and biotransformation of inorganic arsenic in zhikong scallop (Chlamys farreri) after waterborne exposure

Arsenic (As) and As speciation in marine bivalves have been widely investigated. However, little is known about the bioaccumulation and biotransformation of inorganic As in different tissues of scallops. Therefore, the tissue-specific accumulation, biotransformation and subcellular partitioning of As were investigated in Chlamys farreri following 12 d inorganic As [arsenite (AsⅢ) and arsenate (AsⅤ)] exposure and 30 d depuration. Total As levels were highest in the kidneys and lowest in the adductor muscle after 12 d exposure for both As (Ⅲ) and As (Ⅴ) treatment groups, and the bioavailability of As (Ⅲ) was significantly higher than that of As (Ⅴ) for C. farreri. After 30 d elimination, total As levels were significantly decreased to the control levels. The subcellular fate of As in five different tissues was similar for different inorganic As treatment groups. The greatest proportion of As was found in the metallothionein-like protein fraction (MTLP) and the second was the cellular debris (CD). A little part of As (Ⅲ) could be oxidized to As (Ⅴ) in the gill and digestive gland for As (Ⅲ) treatment groups, and the reduction of As (Ⅴ) to As (Ⅲ) happened in the gill and kidney under As (Ⅴ) exposure. Although a high methylation activity was found in C. farreri, it varied in different tissues with different inorganic As species exposure. The present results indicated that exposure to As (Ⅲ) and As (Ⅴ) could induce different responses in bioaccumulation and biotransformation in five tissues of C. farreri.

Partitioning of arsenic in low and high arsenic accumulating rice (Oryza sativa) cultivars

In view of limited information, an attempt has been made to work out the distribution pattern of arsenic (As) between root and shoot of high and low grain-As accumulating rice cultivars (HAC and LAC, respectively). For this purpose, a solution culture experiment was conducted at ICAR-Indian Agricultural Research Institute, New Delhi during kharif 2018-19 with two doses of As (@ 0 and 100 µg/L) and four rice cultivars comprising one HAC (IR-36) and three LACs (Khitish, Satabdi and Badshabhog). Results indicated that the biomass yields were not affected either by As or by cultivars. The highest root As content was recorded with Khitish (4.64 mg/kg), whereas, IR-36 showed the lowest value (2.00 mg/kg) but shoot As content did not vary with cultivars. Cultivars followed almost similar trends for As uptake. The highest translocation coefficient of As from root to shoot ranged from 0.52 (IR-36) to 0.31 (Khitish). It is clear from the study that LACs are more efficient in storing As in root, even though they uptake higher amount of As at the initial phase of growth, whereas, As is mobilized from root to above ground parts more efficiently in case of HACs. Thus, partitioning of As between root and shoot appears to be an important characteristic of rice (Oryza sativa L.) cultivars responsible for differential accumulation of As.

Redox Dependent Arsenic Occurrence and Partitioning in an Industrial Coastal Aquifer: Evidence from High Spatial Resolution Characterization of Groundwater and Sediments

Superlative levels of arsenic (As) in groundwater and sediment often result from industrial pollution, as is the case for a coastal aquifer in Southern Italy, with a fertilizer plant atop. Understanding conditions under which As is mobilized from the sediments, the source of that As, is necessary for developing effective remediation plans. Here, we examine hydrogeological and geochemical factors that affect groundwater As concentrations in a contaminated coastal aquifer. Groundwater has been subject to pump-and-treat at a massive scale for more than 15 years and is still ongoing. Nevertheless, As concentrations (0.01 to 100 mg/L) that are four orders of magnitude more than Italian drinking water standard of 10 μg/L are still present in groundwater collected from about 50 monitoring wells over three years (2011, 2016, and 2018). As was quantified in three different locations by sequential extractions of 29 sediment cores in 2018 (depth 2.5 m to −16.5 m b.g.l.), combined with groundwater As composition, the aqueous and solid partitioning of As were evaluated by partition coefficient (Kd) in order to infer the evolution of the contaminant plumes. Most sediment As is found in easily extractable and/or adsorbed on amorphous iron oxides/hydroxides fractions based on sequential extractions. The study shows that As contamination persists, even after many years of active remediation due to the partitioning to sediment solids. This implies that the choice of remediation techniques requires an improved understanding of the biogeochemical As-cycling and high spatial resolution characterization of both aqueous and solid phases for sites of interest.

Effect of chlorine, sulfur, moisture and ash content on the partitioning of As, Cr, Cu, Mn, Ni and Pb during bituminous coal and pickling sludge co-combustion

The effect of chlorine, sulfur, moisture and ash content in blended fuels on the partitioning of As, Cr, Cu, Mn, Ni and Pb during bituminous coal and pickling sludge co-combustion were studied in a horizontal tube furnace. Additives including NaCl, FeS2, water and kaolin were used to simulate coal with high chlorine, sulfur, moisture and ash content, respectively. The percentage of pickling sludge used in all conditions was 10%, and the additives added range was 1%–20%. The experimental results indicated that with increasing NaCl addition the percentage of As, Cu and Pb in bottom ash decreased significantly and the Mn percentage in fly ash increased slightly. Under FeS2 addition condition, Cu and Pb percentage in bottom ash increased significantly due to the incomplete decomposition of the generated CuFe2O4 and PbSO4 while the volatilization of As was promoted. With the increasing addition of water, a higher percentage of As moved into the fly ash from bottom ash, while the proportion of Pb in the fly ash decreased obviously. Under kaolin addition, the As partitioning showed a fluctuation trend, while for Pb and Cu the adsorption was the main effect and their distribution in bottom ash increased. Under all conditions, Cr and Ni partitioning were not affected by additives due to the non-volatility and stability of Cr, Ni and their compounds. Bottom ash XRD analysis results showed that CaF2 disappeared under NaCl addition condition and lots of Ca2Al2SiO7 generated. In addition, FeS2 addition caused more CaSO4 generated due to the sulfation reaction, while no obvious change of bottom ash composition was found under neither water nor kaolin addition.

Partitioning of arsenic between hydrothermal fluid and pyrite during experimental siderite replacement

Arsenian pyrite is the major host mineral of gold in Carlin type gold deposit (CTGD) and forms during the interaction of H2S bearing hydrothermal fluids with Fe-bearing carbonates (e.g., siderite, ankerite, Fe-rich dolomite) in the wall rock. Experimental replacement of siderite at hydrothermal conditions (i.e., 200 °C, Psat) was used to study the parameters that control the formation of CTGD pyrite (i.e., pH, time, aH2S) and the partitioning of As between the hydrothermal fluid and newly formed pyrite.Hydrothermal pyrite formed via replacement of siderite in experiments mainly occurs as two types: 1) porous, massive pyrite at alkaline pH conditions or 2) clusters of dense euhedral to anhedral pyrite grains at slightly acidic conditions (pH <6). Longer experimental run times (2 weeks) lead to formation of type 2 pyrite at alkaline conditions and an increase in euhedral grain sizes in all conditions.Concentration of As in newly formed pyrite depends strongly on the As concentration of the hydrothermal fluid used in the experiment. Calculated partition coefficients vary between 300 and 1700 with lowest D values at high As concentrations of the fluid. In the studied system As−1 substitutes for S−2 as indicated by the correlation of high As with low S concentrations. Experimental findings agree well with previous studies in natural CTGD on As substitution and the partitioning of As between ore stage pyrite and hydrothermal fluids trapped as fluid inclusions.The newly constrained partition coefficients for As help to explain the large heterogeneity in natural CTGD pyrite compositions which is caused by changes in the fluid composition due to the strong partitioning of As into the forming pyrite.

Subcellular partitioning of metals and metalloids (As, Cd, Cu, Se and Zn) in liver and gonads of wild white suckers (Catostomus commersonii) collected downstream from a mining operation

In the present study, we examined the subcellular distribution of metals and metalloids (As, Cd, Cu, Se and Zn) in the liver and gonads of wild white suckers (Catostomus commersonii) collected downstream from a metal mining operation (exposure area) and in a reference area. Metal partitioning among potentially metal-sensitive fractions (heat-denatured proteins (HDP), mitochondria and microsomes) and potentially biologically detoxified fractions (heat-stable proteins (HSP) and metal-rich granules) within cells was determined after differential centrifugation, NaOH digestion and heat-denaturation steps. Metal-handling strategies between liver and gonads, and between sexes, were examined. Hepatic metal concentrations were significantly higher in exposed compared to reference fish, especially for Se (14x), Cd (5x) and Cu (3x), and did not vary between sexes. In contrast, gonadal Cd, Cu, Se and Zn concentrations were consistently lower in testes than in ovaries; marked differences in Cd and Se concentrations between exposed and reference fish were observed for both sexes. Overall, metal-handling strategies were similar in both liver (male and female pooled) and female gonads, but differed from those in male gonads, likely due to the different functions assigned to ovaries and testes. Subcellular partitioning of As, Cd and Cu showed that the HSP fraction was most responsive to increased metal exposure, presumably reflecting Cu regulation, and possibly Cd and As detoxification. Zinc concentrations were tightly controlled and mainly found in the HDP fraction. Interestingly, changes in Cd-handling strategy in female gonads were particularly evident, with Cd shifting dramatically from the metal-sensitive HDP fraction in reference fish to the metal-detoxified HSP fraction in exposed fish. It seems that Cd detoxification in female gonads was not fully induced in the less contaminated fish, but became more effective above a threshold Cd concentration of 0.05 nmol/g dry weight. Partitioning of Se was different, with the largest contributor to the total liver and gonad Se burdens being the putative metal-sensitive HDP fraction, suggesting that excess Se in this fraction in exposed fish may lead to Se-related stress. The present subcellular partitioning results demonstrate that metal handling strategies vary among metals, between organs and (in some cases) as a function of metal exposure. They also show promise in identifying metals of potential concern in a risk assessment context.

Pathway analysis of neurodevelopment toxicity due to prenatal combined exposure to heavy metals and phthalates

The main goal of the present study was to assess accumulation, tolerance and sub-cellular partitioning of As, Hg, Cd and Pb in Venerupis corrugata. Results showed an increase of elements accumulation in V. corrugata with the increase of exposure. However, organisms presented higher capacity to accumulate Hg, Cd and Pb (BCF ≥ 12.8) than As (BCF ≤ 2.1) and higher accumulation rate for Cd and Pb than for Hg and As. With the increase of Hg exposure concentrations clams tended to increase the amount of metal bound to metal-sensitive fractions, which may explain the mortality recorded at the highest exposure concentration. Cd sub-cellular partitioning showed that with the increase of exposure concentrations V. corrugata increased the amount of metal in the cellular debris fraction, probably bound to the cellular membranes which explain the mortality recorded at the highest concentration. Results on As partitioning demonstrated that most of the metalloid was associated with fractions in the biologically detoxified metal compartment (BDM). Since high mortality was observed in clams exposed to As our results may indicate that this strategy was not enough to prevent clams from toxic effects and mortality occurred. When exposed to Pb most of the metal was in the BDM compartment, but in this case the metal was mostly in the metal-rich granules fraction which seemed to be efficient in preventing clams from toxicity, and no mortality was recorded. Our study further revealed that As and Hg were the most available elements to be biomagnified through the food chain.

Accumulation and sub-cellular partitioning of metals and As in the clam Venerupis corrugata: Different strategies towards different elements

The main goal of the present study was to assess accumulation, tolerance and sub-cellular partitioning of As, Hg, Cd and Pb in Venerupis corrugata. Results showed an increase of elements accumulation in V. corrugata with the increase of exposure. However, organisms presented higher capacity to accumulate Hg, Cd and Pb (BCF ≥ 12.8) than As (BCF ≤ 2.1) and higher accumulation rate for Cd and Pb than for Hg and As. With the increase of Hg exposure concentrations clams tended to increase the amount of metal bound to metal-sensitive fractions, which may explain the mortality recorded at the highest exposure concentration. Cd sub-cellular partitioning showed that with the increase of exposure concentrations V. corrugata increased the amount of metal in the cellular debris fraction, probably bound to the cellular membranes which explain the mortality recorded at the highest concentration. Results on As partitioning demonstrated that most of the metalloid was associated with fractions in the biologically detoxified metal compartment (BDM). Since high mortality was observed in clams exposed to As our results may indicate that this strategy was not enough to prevent clams from toxic effects and mortality occurred. When exposed to Pb most of the metal was in the BDM compartment, but in this case the metal was mostly in the metal-rich granules fraction which seemed to be efficient in preventing clams from toxicity, and no mortality was recorded. Our study further revealed that As and Hg were the most available elements to be biomagnified through the food chain.

Partitioning of selected trace elements in coal combustion products from two coal-burning power plants in the United States

Samples of feed coal (FC), bottom ash (BA), economizer fly ash (EFA), and fly ash (FA) were collected from power plants in the Central Appalachian basin and Colorado Plateau to determine the partitioning of As, Cr, Hg, Pb, and Se in coal combustion products (CCPs). The Appalachian plant burns a high-sulfur (about 3.9wt.%) bituminous coal from the Upper Pennsylvanian Pittsburgh coal bed and operates with electrostatic precipitators (ESPs), with flue gas temperatures of about 163°C in the ESPs. At this plant, As, Pb, Hg, and Se have the greatest median concentrations in FA samples, compared to BA and EFA. A mass balance (not including the FGD process) suggests that the following percentages of trace elements are captured in FA: As (48%), Cr (58%), Pb (54%), Se (20%), and Hg (2%). The relatively high temperatures of the flue gas in the ESPs and low amounts of unburned C in FA (0.5% loss-on-ignition for FA) may have led to the low amount of Hg captured in FA.The Colorado Plateau plant burns a blend of three low-S (about 0.74wt.%) bituminous coals from the Upper Cretaceous Fruitland Formation and operates with fabric filters (FFs). Flue gas temperatures in the baghouses are about 104°C. The elements As, Cr, Pb, Hg, and Se have the greatest median concentrations in the fine-grained fly ash product (FAP) produced by cyclone separators, compared to the other CCPs at this plant. The median concentration of Hg in FA (0.0983ppm) at the Colorado Plateau plant is significantly higher than that for the Appalachian plant (0.0315ppm); this higher concentration is related to the efficiency of FFs in Hg capture, the relatively low temperatures of flue gas in the baghouses (particularly in downstream compartments), and the amount of unburned C in FA (0.29% loss-on-ignition for FA).

Solid-solution partitioning of arsenic (As) in the paddy soil profiles in Chengdu Plain, Southwest China

To predict the long-term behavior of arsenic (As) in soil profiles, the solid-solution partitioning of As was studied in four paddy soil profiles obtained from agricultural areas in Chengdu Plain, Southwest China. Paddy soil profile samples were collected and soil solution samples were extracted. Total As contents in soil solution and soil solid were analyzed, along with the soil solid phase properties. The As in soil solution was significantly higher in the upper layer (0–20 cm) and had a definite tendency to decrease towards 40 cm regardless of the sampling locations. When the concentration of arsenic in soil solution decreased, its content in solid phase increased. Field-based partition coefficient (Kd) for As was determined by calculating the ratio of the amount of As in the soil solid phase to the As concentration in the soil solution. Kd values varied widely in vertical samples and correlated well with soil pH, total organic carbon (TOC) and total As. The results of this study would be useful for evaluating the accumulation trends of arsenic in soil profiles and in improving the management of the agricultural soils.

Changes in arsenic fractionation, bioaccessibility and speciation in organo-arsenical pesticide amended soils as a function of soil aging

Although organoarsenical pesticides are being phased out, sites with high concentrations of organic arsenical residues still exist due to the long-term application of these pesticides. The biotic and abiotic speciation of dimethylarsinic acid (DMA) can result in the formation of inorganic arsenic (As) species. Oxidation state, retention, and thereby persistence, varies according to temporal changes, influencing the availability and toxicity of contaminants. The current greenhouse study aimed at evaluating temporal changes in the oxidation state of As, geochemical partitioning, and bioaccessibility. Four soils with varying physiochemical properties were contaminated with DMA at two concentrations (675 and 1500mgkg−1 of As). Rice plants were grown for a 6months period, following which, the soils were allowed to age. The operationally defined forms of As and its bioaccessibility was analyzed at 0, 6months, 1year, and 3years. Changes in oxidation state of As were evaluated immediately after spiking and after 3years of soil-pesticide equilibration. Results show that geochemical partitioning of As was affected significantly (P<0.05) by soil type, loading rates, and equilibration time. Arsenic was bound mainly to the poorly-crystalline Fe/Al-oxyhydroxides in the soil. However, these interactions did not affect As bioaccessibility, presumably due to the dissolution of the bound fractions of As in the acidic stomach. While 74–94% of the total bioaccessible As was transformed to As(V), 4–19% was transformed to the more toxic As(III). This study indicates that although aging affected the geochemical partitioning of As in the soil, bioaccesibility was controlled by the gastric pH.

ChemInform Abstract: Arsenic Chemistry in Soils and Sediments

AbstractReview: 105 refs.

Fractionation and geochemical mobility of heavy elements in soils of a mining area in northern Kosovo

This paper reports the results of a geochemical study focusing on the partitioning of As, Cd, Cu, Pb, Sb and Zn in soils of the Kosovska Mitrovica mining area in northern Kosovo. The main objective was to define the element mobility in soil and potential bioavailability in relation to soil contamination levels. The Kosovska Mitrovica area is one of the main industrial sites in the former Yugoslavia and a world-class mining district in Europe. Extensive and locally very marked contamination mainly by Pb, Zn, Cd and Sb was found in soils, with the highest concentrations measured close to the Zvecan smelter. The study of As, Cd, Cu, Pb, Sb and Zn partitioning in the water soluble, extractable with 0.11 M acetic acid, reducible, oxidable and residual fractions of soils revealed that Pb was mainly associated with the reducible fraction, Cd with the extractable and reducible fractions, and As, Cu, Sb and Zn with the residual fraction. Heavy element fractionation in contaminated soils was influenced by the presence of owner mineralogical phases related to the emissions of the Zvecan smelter and to materials windborne from mining and industrial dumps, as well as originated by in situ processes. The order of mobility of these heavy elements in contaminated soils resulted as follows: Cd ≫ Zn ≫ Pb ≫ Sb > As > Cu. Anthropogenic amounts of heavy elements were distributed in all soil fractions, with the most relevant enrichments in the extractable and reducible ones. Anthropogenic inputs were responsible for some deviations from natural fractionation, mainly for Pb, Zn and Cd. A significant amount of Cd, Pb and Zn in contaminated soils was rather mobile, which suggests that these elements can be readily available to plants and soil organisms.

Speciation of trace metals in chromated-copper-arsenate contaminated sediment of Ogba River

The impact of storm water run-off from a location of intensive application of CCA in wood treatment on the quality of sediment of the receiving water body was examined. Sediment samples were collected along Ogba River. Physico-chemical characteristics as well as total levels of As, Cr and Cu in sediment samples were determined. Physico-chemical analysis of composite sediment samples upstream and downstream showed pH of sediments to be neutral (6.95 upstream and 6.90 downstream). The sand content for downstream sediment was 90.52 and 87.52% for upstream sediment sample. Total levels of 3.3–14.9 mg kg−1 As, 3.1–116.6 mg kg−1 Cr, and 13.7–16.4mg kg−1 Cu were obtained for downstream sediment samples and 2.2–2.3mg kg−1 As, 8.1–13.1 mg kg−1 Cr, and 6.0–7.4mg kg−1 Cu were obtained for upstream samples. Sequential extraction procedure involving six steps was used to evaluate the partitioning of As, Cr and Cu in the sediments. The results showed that the bioavailable fraction of sediment 20 m downstream was 10%, 100% and 20% of the total levels of As, Cr and Cu respectively in the sediment.

Geochemical changes in individual sediment grains during sequential arsenic extractions

High concentrations of As in groundwater frequently occur throughout the world. The dissolved concentration, however, is not necessarily determined by the amount of As in the ambient sediment but rather by the partitioning of As between different minerals and the type of fixation. Sequential extractions are commonly applied to determine associations and binding forms of As in sediments. Due to the operational nature of the extracted fractions, however, the results do not provide insight into how and where precisely As is bound within mineral grains and no information about elemental associations or involved mineral phases can be gained. Furthermore, little is known about possible geochemical alterations that actually occur within a single grain during sequential extraction. Therefore, micro-synchrotron X-ray fluorescence analysis was applied to study the micro-scale distribution of As and other elements in single sediment grains. Arsenic was found to be mainly enriched in Fe oxy-hydroxide coatings along with other heavy metals resulting in high correlations. Phosphate leached 34–66% of As from the studied grains. The release of As in this leaching step was accompanied by the disappearance of correlations between As and Fe as well as by a higher Fe/As ratio compared to untreated samples. During the Fe-leaching step the coatings were largely dissolved leading to much lower concentrations of As and Fe. The correlation between As and Fe was preserved only in association with K, indicating the presence of both elements in silicate structures. Several distinctive features were observed such as the release of Fe, Mn and Cr during phosphate leaching as well as the lowering of mean K concentrations due to the Fe-leaching which indicates that not only target mineral phases were dissolved in these extraction steps. The importance of re-precipitation processes during sequential extraction was indicated by a consistently observed increase of the Fe/As ratio from the untreated to the Fe-leached samples.

Mobilisation and transport of arsenic and antimony in the adjacent environment of Yata gold mine, Guizhou province, China

Arsenic and antimony distribution in water, sediment, soil and plants in the Yata gold mine and surrounding area, southwestern China, was investigated, so as to elucidate the mobilisation, transport, and distribution of As and Sb in mine environments. While oxidation of sulfide minerals mobilises both As and Sb, gold extraction by cyanidation is found to mobilise a large amount of Sb. Strontium concentration in water is proposed as an indicator for the oxidation of sulfide minerals in mine environments rich in carbonate. The partitioning of As, Sb, Fe, Cu, Zn and Sr between suspended particulate matter (SPM) and water shows a particle concentration effect. The partition coefficient (K(d)) decreases in the order Fe > Zn > Cu > As = Sb > Sr, consistent with the low affinity of As and Sb to SPM and the significant presence of As and Sb in soluble phase of water. During the transport of metalloids in water downstream of the mine area, As is released from the particulate or sediment to water as a result of the slight increase of pH, whereas Sb is not. The accumulation of As and Sb in soil and prevalent plants is minor with exceptions of rice root and Equisetumarvensel. The As and Sb concentration in the plants appears to be independent of the total As and Sb concentration in soil.

Geochemical processes underlying a sharp contrast in groundwater arsenic concentrations in a village on the Red River delta, Vietnam

Abstract The spatial variability of As concentrations in aquifers of the Red River Delta, Vietnam, was studied in the vicinity of Hanoi. Two sites, only 700 m apart but with very different As concentrations in groundwater (site L: NH 4 + (∼10 mg/L), HCO 3 - (500 mg/L) and dissolved P (600 mg/L), in addition to elevated As at site H are consistent with a release coupled to microbially induced reductive dissolution of Fe oxyhydroxides. Other processes such as precipitation of siderite and vivianite, which are strongly supersaturated at site H, or the formation of amorphous Fe(II)/As(III) phases and Fe sulfides, may also influence the partitioning of As between groundwater and aquifer sands. The origin of the redox contrast between the two sites is presently unclear. Peat was observed at site L, but it was embedded within a thick clayey silt layer. At site H, instead, organic rich layers were only separated from the underlying aquifer by thin silt layers. Leaching of organic matter from this source could cause reducing conditions and therefore potentially be related to particularly high concentrations of dissolved NH 4 + , HCO 3 - , P and DOC in the portion of the aquifer where groundwater As concentrations are also elevated.