As-rich Sediments Research Articles

Physiological response of adult Salix aurita in wetland vegetation affected by flooding with As-rich fine pyrite particles

An uncontrolled, natural episode of flooding with waters contaminated with As-rich pyrite (FeAsS) particles caused serious ecological damage leading to necrosis of plants growing in a fresh wet meadow located in an area characterized by unique geological structures rich in arsenopyrites. One of the few plant species capable of surviving this event was Salix aurita L., which grew in numbers in the analyzed area, but individual plants were affected differently by toxic flooding. No significant phenotypic changes (Group I), through partial leaf and/or stem necrosis (Group II) up to necrosis of the whole parental plant and root suckers (Group III), were observed for various willow clumps. These varied phenotypic responses of S. aurita to As-rich sediments were compared with the biochemical status of the foliage of willow trees, and with their rhizosphere physiological parameters.Our in situ study revealed that the biochemical status of leaves reflects the phenotypic damage incurred by adult willows growing in their natural environment and affected by the flooding. In leaves of willows with increasingly negative phenotypic changes (Groups I → II → III) as well as increasing levels of reactive oxygen species, malondialdehyde and decreased levels of glutathione and thiol groups were detected. Phytochelatins, commonly considered major As chelators, were not detected in S. aurita leaves. Despite a decrease in the size of leaves with the intensity of tree damage, all leaves expressed a normal level of leaf pigments.Phenotypic changes observed for particular willow clumps were only partly related to soil As levels. Moreover, As and S (but not Fe) foliar levels were related but did not correspond strictly with foliar biochemical features, or with soil As levels, soil pH or soil microbial activity, with the latter two drastically decreased in the rhizospheres of willows from Groups II and III.

Natural occurrence and controls of arsenic in groundwater in a semiarid basin in the Mexican Altiplano

The sources, mobility, and controlling processes of arsenic (As) in an aquifer system in the Cerritos-Guadalcazar area of Central Mexico were investigated. High As concentrations (up to 128 μg/L) in groundwater were found to be associated with both primary sources (rocks and tailings) and secondary sources (soil and sediments). The high As concentrations in the otherwise pristine Cerritos shallow granular aquifer are the result of a distant source of As-rich sediments eroded from a mineralized area in the recharge zone of a karstic aquifer. An intermediate groundwater flow system delivers the As load from the karstic to the granular aquifer. In addition, identification of a Na–Cl water type in the shallow granular aquifer indicates a regional flow; however, additional information is needed to corroborate this assumption. Local flows in the karstic aquifer are Ca–HCO3 water type with low (<1 μg/L) dissolved As concentrations. Principle axis factor analysis shows distinct groupings associated with different aquifer characteristics. The sulfate factor dominates in the southern area of the granular aquifer, which explains 30% of the total variance. The arsenic-uranium factor is expressed in samples from deep and dug wells tapping the basin sediments. A conceptual model was developed where the path of the As is shown. Three groups of samples showed negative correlation among deuterium excess and As concentrations. Evaporation modeling to simulate the As enrichment showed that evaporation processes play an important role in As behavior. This research can provide a tool for further studies in the Sierra Madre Oriental.

Winogradsky Bioelectrochemical System as a Novel Strategy to Enrich Electrochemically Active Microorganisms from Arsenic-Rich Sediments

Bioelectrochemical systems (BESs) have been extensively studied for treatment and remediation. However, BESs have the potential to be used for the enrichment of microorganisms that could replace their natural electron donor or acceptor for an electrode. In this study, Winogradsky BES columns with As-rich sediments extracted from an Andean watershed were used as a strategy to enrich lithotrophic electrochemically active microorganisms (EAMs) on electrodes (i.e., cathodes). After 15 months, Winogradsky BESs registered power densities up to 650 μWcm-2. Scanning electron microscopy and linear sweep voltammetry confirmed microbial growth and electrochemical activity on cathodes. Pyrosequencing evidenced differences in bacterial composition between sediments from the field and cathodic biofilms. Six EAMs from genera Herbaspirillum, Ancylobacter, Rhodococcus, Methylobacterium, Sphingomonas, and Pseudomonas were isolated from cathodes using a lithoautotrophic As oxidizers culture medium. These results suggest that the tested Winogradsky BES columns result in an enrichment of electrochemically active As-oxidizing microorganisms. A bioelectrochemical boost of centenarian enrichment approaches, such as the Winogradsky column, represents a promising strategy for prospecting new EAMs linked with the biogeochemical cycles of different metals and metalloids.

Review on the interactions of arsenic, iron (oxy)(hydr)oxides, and dissolved organic matter in soils, sediments, and groundwater in a ternary system

High concentrations of arsenic (As) in groundwater threaten the environment and public health. Geogenically, groundwater As contamination predominantly occurs via its mobilization from underground As-rich sediments. In an aquatic ecosystem, As is typically driven by several underlying processes, such as redox transitions, microbially driven reduction of iron (Fe) oxide minerals, and release of associated As. Notably, dissolved As mobilized from soils and sediments exhibits high affinity for dissolved organic matter (DOM). Thus, high DOM concentrations can increase As mobility. Therefore, it is crucial to understand the complex interactions and biogeochemical cycling of As, DOM, and Fe oxides. This review collates knowledge regarding the fate of As in multicomponent As–DOM–Fe systems, including ternary complexes involving both Fe and DOM. Additionally, the release mechanisms of As from sediments into groundwater in the presence of both Fe and DOM have been discussed. The mechanisms of As mobilization/sorption at the solid–water interface can be affected by negatively charged DOM competing for sorption sites with As on Fe (oxy)(hydr)oxides and may be further modified by other anionic ubiquitous species such as phosphate, silicic acid, or sulfur. This review emphasizes the need for a comprehensive understanding of the impact of DOM, Fe oxides, and related biogeochemical processes on As mobilization to aquifers. The review identifies important knowledge gaps that may aid in developing applicable practices for preventing the spread of As contamination in aquatic resources and traditional soil management practices.

Arsenic Transfer from As-Rich Sediments to River Water in the Presence of Biofilms

The influence of epipsammic biofilms on As release from river sediments was evaluated in a microcosm experiment where biofilms were grown on sediments containing 106 mg kg−1As, collected in the Anllóns River, and compared with control systems without biofilms. The As transfer to the water column was low (&lt;0.11% of total As in the sediment) and was further reduced by 64% in the presence of biofilms.AsVwas the predominant species in the overlying water in both systems.AsIIIconcentration was higher (up to 12% of total dissolved As) in the control systems than in the systems with biofilms, where this species was almost absent. This fact is of toxicological relevance due to the usually higher mobility and toxicity of the reducedAsIIIspecies. Control systems exhibited higher As mobility in water, in sulphate solution, and in weak acid medium and higher bioavailability in diffusive gradient in thin films (DGT) devices. Arsenic retained by the biofilm was equally distributed between extracellular and intracellular compartments. Inside the cells, significant concentrations ofAsIII, monomethylarsonic acid (MMAV), and dimethylarsinic acid (DMAV) were detected, suggesting that active methylation (detoxification) processes are occurring in the intracellular compartment.

Identifying sources of B and As contamination in surface water and groundwater downstream of the Larderello geothermal – industrial area (Tuscany–Central Italy)

Summary A study on the upper reaches of the Cecina River (Tuscany–Central Italy) and the associated unconfined aquifer was carried out from September 2007 to August 2008. The study aimed to identify the sources of B and As contamination in stream water and groundwater, and record contamination levels. The study area, which comprises a northern sector of the Larderello geothermal field, has in time been contaminated by both surface geothermal manifestations (now thought to have ceased) and anthropogenic activity. The latter refers to the disposal of spent geothermal fluids and borogypsum sludge, by-product of colemanite treatment with sulphuric acid, which until the late ‘70s were discharged in the Larderello area into the Possera Creek, a southern tributary of the Cecina River. A network of 22 stream sections and 9 observation wells was defined. Stream discharge (16 sites), well water levels and chemical concentrations (mainly B, As and anions) in water were measured monthly. Together, discharge and chemical concentrations were used to define the source of contamination by calculating the contaminant load in successive sections of the river network. Due to the stream’s intermittent flow, only 50% of the performed monthly surveys could be used in comparing the contaminant load at different sections. Both contaminant loads (referring to median to high flow conditions) and chemical concentrations suggest that B mainly derives from the leakage of a concentrated Na–SO4 water rich in B, SO4, NO3 likely from a small aquitard located in the Larderello area. The B load from this area is about 2 kg/h and increases to approximately 2.7 kg/h in the final section of the study area, likely due to contribution of groundwater. As mainly derives from dissolution and adsorption–desorption processes involving water and As-rich stream bed sediments. Of the total 15 g/h As load measured at the end section, only about 3 g/h derive from the Larderello area. Further to stream bed, As-rich sediments are also found at shallow depths in the area of the Cecina–Possera confluence and in the upper part of the aquifer skeleton. These sediments contribute to increase up to about 76 μg/L the As content of groundwater of the Cecina–Possera confluence area which, draining water from the Possera Creek, represents the aquifer root zone. This zone determines the B and As contents of groundwater which flows more or less parallel to the Cecina River, undergoes progressive dilution during its westward flow and locally supplies the same river. Most of the study stream water and groundwater in the study area cannot be exploited because mean B and As contents (respectively in the range 1.2–15.6 mg/L and 1.1–75.9 μg/L), are often well above the permissible limits for drinking water (1 mg/L for B, 10 μg/L for As).

Interrelationship of TOC, As, Fe, Mn, Al and Si in shallow alluvial aquifers in Chapai-Nawabganj, Northwestern Bangladesh: implication for potential source of organic carbon

Two boreholes and ten piezometers in the Ganges flood plain were drilled and installed for collecting As-rich sediments and groundwater. Groundwater samples from the Ganges flood plain were collected for the analysis of cations (Ca2+, Mg2+, K+, Na+), anions (Cl−, NO3−, SO42−), total organic carbon (TOC), and trace elements (As, Mn, Fe, Sr, Se, Ni, Co, Cu, Mo, Sb, Pb). X-ray powder diffraction was performed to characterize the major mineral contents of aquifer sediments and X-ray fluorescence (XRF) to analyze the major chemical composition of alluvial sediments. Results of XRF analysis clearly show that fine-grained sediments contain higher amounts of trace element because of their high surface area for adsorption. Relative fluorescence index (15–38 QSU) of humic substance in groundwater was measured using spectrofluorometer, the results revealed that groundwater in the Ganges flood plain contains less organic matter (OM). Arsenic concentration in water ranges from 2.8 to 170 μg/L (mean 50 μg/L) in the Ganges flood plain. Arsenic content in sediments ranges from 2.1 to 14 mg/kg (mean 4.58 mg/kg) in the flood plains. TOC ranges from 0.49 to 3.53 g/kg (mean 1.64 g/kg) in the Ganges flood plain. Arsenic is positively correlated with TOC (R2 = 0.55) in sediments of this plain. Humic substances were extracted from the sediments from the Ganges flood plain. Fourier transform infrared analysis of the sediments revealed that the plain contains less humic substances. The source of organic carbon was assigned from δ13C values obtained using elemental analysis-isotope ratio mass spectrometry (EA-IRMS); the values (−10 to −29.44‰) strongly support the hypothesis that the OM of the Ganges flood plain is of terrestrial origin.

Implications of organic matter on arsenic mobilization into groundwater: Evidence from northwestern (Chapai-Nawabganj), central (Manikganj) and southeastern (Chandpur) Bangladesh

Boreholes (50 m depth) and piezometers (50 m depth) were drilled and installed for collecting As-rich sediments and groundwater in the Ganges, Brahmaputra, and Meghna flood plains for geochemical analyses. Forty-one groundwater samples were collected from the three areas for the analyses of cations (Ca 2+, Mg 2+, K +, Na +), anions (Cl −, NO 3 −, SO 4 2−), total organic carbon (TOC), and trace elements (As, Mn, Fe, Sr, Se, Ni, Co, Cu, Mo, Sb, Pb). X-ray powder diffraction (XRD) and X-ray fluorescence (XRF) were performed to characterize the major mineral and chemical contents of aquifer sediments. In all three study areas, results of XRF analysis clearly show that fine-grained sediments contain higher amounts of trace element because of their high surface area for adsorption. Relative fluorescent intensity of humic substances in groundwater samples ranges from 30 to 102 (mean 58 ± 20, n = 20), 54–195 (mean 105 ± 48, n = 10), and 27–243 (mean 79 ± 71, n = 11) in the Ganges, Brahmaputra and Meghna flood plains, respectively. Arsenic concentration in groundwater (20–50 m of depth) ranges from 3 to 315 μg/L (mean 62.4 ± 93.1 μg/L, n = 20), 16.4–73.7 μg/L (mean 28.5 ± 22.4 μg/L, n = 10) and 4.6–215.4 μg/L (mean 30.7 ± 62.1 μg/L, n = 11) in the Ganges, Brahmaputra and Meghna flood plains, respectively. Specific ultra violet adsorption (SUVA) values (less than 3 m −1 mg −1 L) indicate that the groundwater in the Ganges flood plain has relatively low percentage of aromatic organic carbon compared to those in the Brahmaputra and Meghna flood plains. Arsenic content in sediments ranges from 1 to 11 mg/kg (mean 3.5 ± 2.7 mg/kg, n = 17) in the three flood plains. Total organic carbon content is 0.5–3.7 g/kg (mean 1.9 ± 1.1 g/kg) in the Ganges flood plain, 0.5–2.1 g/kg (mean: 1.1 ± 0.7 g/kg) in the Brahmaputra flood plain and 0.3–4.4 g/kg (mean 1.9 ± 1.9 g/kg) in the Meghna flood plain. Arsenic is positively correlated with TOC ( R 2 = 0.50, 0.87, and 0.85) in sediments from the three areas. Fourier transform infrared (FT-IR) analysis of the sediments revealed that the functional groups of humic substances in three areas include amines, phenol, alkanes, and aromatic carbon. Arsenic and Fe speciation in sediments were determined using XANES and the results imply that As(V) and Fe(III) are the dominant species in most sediments. The results also imply that As (V) and Fe (III) in most of the sediment samples of the three areas are the dominant species. X-ray absorption fine structure (EXAFS) analysis shows that FeOOH is the main carrier of As in the sediments of three areas. In sediments, As is well correlated with Fe and Mn. However, there is no such correlation observed between As and Fe as well as As and Mn in groundwater, implying that mobilizations of Fe, Mn, and As are decoupled or their concentrations in groundwater have been affected by other geochemical processes following reductive dissolution of Fe or Mn-hydroxides. For example, dissolved Fe and Mn levels may be affected by precipitation of Fe- and Mn-carbonate minerals such as siderite, while liberated As remains in groundwater. The groundwaters of the Brahmaputra and Meghna flood plains contain higher humic substances in relative fluorescence intensity (or fluorescence index) and lower redox potential compared to the groundwater of Ganges flood plain. This leads to the release of arsenic and iron to groundwater of these three plains in considerable amounts, but their concentrations are distributed in spatial variations.

THE ROLE OF ARSENIC-RICH MELTS AND MINERAL PHASES IN THE DEVELOPMENT OF HIGH-GRADE Pt-Pd MINERALIZATION WITHIN KOMATIITE-ASSOCIATED MAGMATIC Ni-Cu SULFIDE HORIZONS AT DUNDONALD BEACH SOUTH, ABITIBI SUBPROVINCE, ONTARIO, CANADA

At the Dundonald Beach South Ni-Cu occurrence in the western Abitibi subprovince, Ontario, Canada, komatiite-hosted magmatic sulfide mineralization (pentlandite-dominated; 0.5–7 ppm Pt + Pd) contains millimeter- to centimeter-size blebs of polycrystalline gersdorffite and nickeline. The gersdorffite-nickeline blebs are concentrated (~6 vol %) in a 10- to 20-cm-thick by 10-m-long lens that occurs at the base of a massive sulfide horizon. The lens is significantly more enriched in Pt and Pd (15–50 ppm Pt + Pd) than typical sulfide horizons in which sulfarsenide and arsenide phases occur only as trace to minor (up to 0.15 vol %) constituents. In the platinum group element (PGE)-rich lens, ~29 and ~74 percent of the bulk rock Pd and Pt, respectively, are dissolved in the sulfarsenide and arsenide minerals. Almost all the remaining Pd and Pt in the lens occur in inclusions of sperrylite, michenerite (PdBiTe), and an unidentified Pd-Bi-Te phase coexisting with inclusions of tellurobismuthite (Bi 2 Te 3 ), altaite (PbTe), and electrum that fill former open spaces (vugs) in gersdorffite and nickeline. In the surrounding sulfide mineralization, PGE mineral inclusions are 4 to 10 times less abundant, and the bulk PGE grade is an order of magnitude lower. Overall, PGE grade on a deposit scale may be controlled by the abundance of gersdorffite and nickeline. Even in minor abundances (e.g., ~1 wt %), sulfarsenide and arsenide minerals may produce economically favorable bulk PGE grades if dispersed throughout barren (PGE-poor) sulfide horizons. The PGE-rich lens may represent the accumulation of either crystallized droplets of an immiscible sulfarsenide melt phase or sulfarsenide phenocrysts that separated from a silicate or sulfide liquid. Arsenic-rich melt or mineral phases extracted (partitioned) the trace metals Pt, Pd, Au, Bi, Te, Sb, Pb, Zn, Ag, and Sn from non–As-bearing phases (silicate liquid, Fe-Ni-Cu sulfide liquid, or monosulfide solid solution [mss]) with inferred values of D As-phase/sulfide on the order of ~10 to 100. Textural, mineralogical, and geochemical observations highlight the importance of As-rich liquids or mineral phases as scavengers of the PGE and other chalcophile metals in komatiite-associated magmatic sulfide environments as well as the potential for high-grade PGE mineralization to occur where komatiites were contaminated by As-rich sediments or metasedimentary rocks.

Arsenic remobilization from sediments contaminated with mine tailings near the Adak mine in Västerbotten district (northern Sweden)

Weathering of mine tailings have resulted in high As concentrations in water (up to 2900 μg l − 1 ) and sediment (up to 900 mg kg − 1 ) samples around the Adak mine. Notably, As occurs as As(III) species (15–85%) in the oxic surface and ground water samples, which is not common. Time-series based sediment incubations were set up in the laboratory with contaminated sediments to study the microbial processes involved in transformation and remobilization of As across the sediment–water interface. The microcosm experiments indicate that microorganisms are capable of surviving in As-rich sediments and reduce As(V) to As(III). A decrease in total As concentration in sediments is coupled to an increase in As(III) concentration in the aqueous media. In contrast, the controls (treated with HgCl 2 and formaldehyde) did not show growth, and As(V) concentrations increased steadily in the sediments and aqueous medium. The results imply that active metabolism is necessary for As(V) reduction. These microorganisms possess reduction mechanisms that are not necessarily coupled to respiration, but most likely impart resistance to As toxicity.

Phosphate and arsenate retention in sediments of the Anllóns river (northwest Spain)

We have studied the distribution and sorption behavior of phosphate and arsenate in bed-sediments of the Anllóns river (NW Spain). As a consequence of the intense gold-mining activity in the past, substantial amounts of arsenic were found in the river sediments. For phosphorus, higher concentrations were found near two sources of P pollution. Sorption isotherms were described by the Freundlich, Langmuir and Tempkin equations. In general, the sediments sorbed more P than As. The equilibrium P concentration (EPC) reveals that sediments act as a scavenger for soluble P; by contrast, equilibrium As concentration (EAC) values were high for the As-rich sediments and correlates well with total arsenic content. Amorphous Fe oxides content, organic matter and fraction of clay plus silt were the main properties of the sediments related with the sorption of arsenate and phosphate. The results obtained provide a first estimate of the sorption behavior and availability of the phosphate and arsenate anions in the sediments of the Anllóns river.

Environmental Implications of Elements Associated with Pyrite Concentrates from Coal in the Sydney Coalfield (Upper Carboniferous), Nova Scotia, Canada

Abstract Pyrite concentrates were obtained from seven successive coal seams of Upper Carboniferous age in the Sydney Coalfield of Nova Scotia. These concentrates were analyzed for forty-nine trace metals and oxides using INAA and ICPES. The data indicate that trace amounts of other sulphide phases (inclusions as arsenopyrile, galena, chalcopyrite), presumed epigenetic clay minerals, and zircon inclusions are associated with pyrite concentrates. The content of rare earths and actinides in these pyrites are age dependent and tend to be more highly concentrated in the younger seams. Pyritic oxidation in coal and resultant formation and dissolution of secondary sulphate minerals are one mechanism for trace-metal dispersion into the surface-water environment. The pyrite concentrates on average are arsenic-rich (range 240-2900 ppm, mean 1556 ppm). However, this As may form insoluble, stable organic-complexes, which remain as As-rich sediments in situ.