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High concentrations of arsenic in groundwater continue to present health threats to millions of consumers worldwide. Particularly, affected communities in the developing world need accessible technologies for arsenic removal from drinking water. We explore the application of cactus mucilage, pectic polysaccharide extracts from Opuntia ficus-indica for arsenic removal. Synthetic arsenate (As (V)) solutions were treated with two extracts, a gelling extract (GE) and a nongelling extract (NE) in batch trials. The arsenic concentration at the air-water interface was measured after equilibration. The GE and NE treated solutions showed on average 14% and 9% increases in arsenic concentration at the air-water interface respectively indicating that the mucilage bonded and transported the arsenic to the air-water interface. FTIR studies showed that the -CO groups (carboxyl and carbonyl groups) and -OH (hydroxyl) functional groups of the mucilage were involved in the interaction with the arsenate. Mucilage activity was greater in weakly basic (pH 9) and weakly acidic (pH 5.5) pH. This interaction can be optimized and harnessed for the removal of arsenic from drinking water. This work breaks the ground for the application of natural pectic materials to the removal of anionic metallic species from water.

Aquifer storage and recovery (ASR) is an aquifer recharge technique in which water is injected in an aquifer during periods of surplus and withdrawn from the same well during periods of deficit. It is a critical component of the long-term water supply plan in various regions, including Florida, USA. Here, the viability of ASR as a safe and cost-effective water resource is currently being tested at a number of sites due to elevated arsenic concentrations detected during groundwater recovery. In this study, we developed a process-based reactive transport model of the coupled physical and geochemical mechanisms controlling the fate of arsenic during ASR. We analyzed multicycle hydrochemical data from a well-documented affected southwest Floridan site and evaluated a conceptual/numerical model in which (i) arsenic is initially released during pyrite oxidation triggered by the injection of oxygenated water (ii) then largely complexes to neo-formed hydrous ferric oxides before (iii) being remobilized during recovery as a result of both dissolution of hydrous ferric oxides and displacement from sorption sites by competing anions.

Tens of millions of people in Southeast Asia drink groundwater contaminated with naturally occurring arsenic. How arsenic is released from the sediment into the water remains poorly understood. Here, we show in laboratory experiments that phosphate-limited cells of Burkholderia fungorum mobilize ancillary arsenic from apatite. We hypothesize that arsenic mobilization is a by-product of mineral weathering for nutrient acquisition. The released arsenic does not undergo a redox transformation but appears to be solubilized from the apatite mineral lattice during weathering. Analysis of apatite from the source area in the Himalayan basin indicates the presence of elevated levels of arsenic, with an average concentration of 210 mg/kg. The rate of arsenic release is independent of the initial dissolved arsenic concentration and occurs at phosphate levels observed in Bangladesh aquifers. We also demonstrate the presence of the microbial phenotype that releases arsenic from apatite in Bangladesh aquifer sediments and groundwater. These results suggest that microbial mineral weathering for nutrient acquisition could be an important mechanism for arsenic mobilization.

Monosodium methanearsonate (MSMA) is a commonly used herbicide on golf courses. To investigate the variation in abundance of arsenic (As) after MSMA application, 28 golf course lakes were monitored monthly for one year. The As concentrations varied substantially in and between individual lakes with values up to 124 microg/L (mean=10.9 microg/L, n=336). This is considerably higher than the As concentrations in comparable "non-golf course" lakes (up to 100-times) in the study area. The highest values of As in the lakes were generally observed in the late spring and early summer and corresponded to the intensity of MSMA applications. Arsenic seems to be sequestered by the golf course lake sediments with concentrations as high as 302 mg/kg, which were significantly higher than the 0.1 to 3 mg/kg expected for comparable sediments in central Florida. Arsenic correlates well with Fe in the top 15 cm of the lake sediments suggesting that As is sorbed by hydrous ferric oxides (HFO). As long as conditions are in favour of HFO stability, As is retained in the lake sediments preventing its migration into the Floridan aquifer systems. However, once the loading capacity of the sediment is reached or when as a result of changing physico-chemical conditions HFO may become unstable, As may enter the Floridan aquifer.

Elevated arsenic concentrations are common in water recovered from aquifer storage and recovery (ASR) systems in west-central Florida that store surface water. Investigations of the Suwannee Limestone of the Upper Floridan aquifer, the storage zone for ASR systems, have shown that arsenic is highest in pyrite in zones of high moldic porosity. Geochemical modeling was employed to examine pyrite stability in limestone during simulated injections of surface water into wells open only to the Suwannee Limestone with known mineralogy and water chemistry. The goal was to determine if aquifer redox conditions could be altered to the degree of pyrite instability. Increasing amounts of injection water were added to native storage-zone water, and resulting reaction paths were plotted on pyrite stability diagrams. Native storage-zone water plotted within the pyrite stability field, indicating that conditions were sufficiently reducing to allow for pyrite stability. Thus, arsenic is immobilized in pyrite, and its groundwater concentration should be low. This was corroborated by analysis of water samples, none of which had arsenic concentrations above 0.036 microg/L. During simulation, however, as injection/native storage-zone water ratios increased, conditions became less reducing and pyrite became unstable. The result would be release of arsenic from limestone into storage-zone water.

Groundwater monitoring relies on the acquisition of ‘representative’ groundwater samples, which should reflect the ambient water quality at a given location. However, drilling of a monitoring well for sample acquisition has the potential to perturb groundwater conditions to a point that may prove to be detrimental to the monitoring objective. Following installation of 20 monitoring wells in close geographic proximity in central Florida, opposing concentration trends for As and Mo were observed. In the first year after well installation As and Mo concentrations increased in some wells by a factor of 2, while in others As and Mo concentrations decreased by a factor of up to 100. Given this relatively short period of time, a natural change in groundwater composition of such magnitude is not expected, leaving well installation itself as the likely cause for the observed concentration changes. Hence, initial concentrations were identified as ‘false negatives’ if concentrations increased with time or as ‘false positives’ if concentrations decreased. False negatives were observed if concentrations were already high, i.e., the As or Mo were present at the time of drilling. False positives were observed if concentrations were relatively lower, i.e., As or Mo were present at low concentrations of approximately 1 to 2 μg/L before drilling, but then released from the aquifer matrix as a result of drilling. Generally, As and Mo were present in the aquifer matrix in either pyrite or organic matter, both of which are susceptible to dissolution if redox conditions change due to the addition of oxygen. Thus, introduction of an oxidant into an anoxic aquifer through use of an oxygen saturated drilling fluid served as the conceptual model for the trends where concentrations decreased with time. Mixing between drilling fluid and groundwater (i.e., dilution) was used as the conceptual model for scenarios where increasing trends were observed. Conceptual models were successfully tested through formulation and application of data-driven reactive transport models, using the USGS code MODFLOW in conjunction with the reactive multicomponent transport code PHT3D. [ABSTRACT FROM AUTHOR]

Lacking a connection to a municipal water supply, each household in the municipality of Lithia, approximately 30 km southeast of Tampa, Florida (USA), is responsible for its own supply of drinking water, causing a high-density of private domestic supply wells (DSW) in this area. There, a multilayered aquifer system exists, which can be subdivided into three distinct hydro stratigraphic units, which are, from the top down: the Surficial Aquifer System (SAS), the Intermediate Aquifer System (IAS), and the Upper Floridan Aquifer System (UFA). Despite the relatively small area, the geochemical and hydrogeological setting in Lithia is complex, consisting of: i) extensive cyclical pumping in a municipal well field to the west, ii) large seasonal changes in hydraulic head, ii) multiple aquifers with different hydraulic heads, and iv) a large density of domestic supply wells (DSW). Within the zone of highest As concentrations, there are approximately 100 wells in an area of 2.5 km × 1.5 km. Most of these wells have large open screened intervals, often open to all three aquifers, allowing the downward flow of oxygenated and upward flow of anoxic groundwater. A survey of groundwater quality found that As and Mo concentrations in the DSW were up to 371 μg/L and 4740 μg/L, respectively. To obtain information about the individual aquifers, 5 well clusters with 4 monitoring intervals (approximately 50 m, 65 m, 80 m and 95 m below surface) and 8 push core wells (approximately 9 m below surface) were installed and sampled. In those wells, As and Mo were only elevated in a permeable layer within the IAS at a depth of 50 m. Values were up to 195 μg/L for As and up to 5050 μg/L for Mo. Using the tritium-helium ( 3 H– 3 He) method, the ages of those samples high in As and Mo were determined to be 40, 30 and 30 years, respectively, while all other samples had ages older than 50 years. This indicated that mixing between young and old groundwater could be responsible for the high As and Mo concentrations. A good negative correlation for the whole data set was also observed between the concentration 3 H and δ 18 O values, which together with hydrogeological modeling confirmed that the increased permeability created by the high density of DSW resulted in flow paths that permitted the perpetual mixing of shallow and deep groundwater. The release of the As and Mo appeared to be a consequence of changes to the physicochemical conditions in the aquifer, either via the introduction of oxygen-rich fluids into the IAS or the mixing of different fluids in the IAS or the introduction of oxygen-depleted fluids into the IAS. While the mobilization of geogenic trace metals is often associated with pumping-induced hydraulic gradient changes, we found that a certain density of multi-aquifer wells can be sufficient to alter hydrologic flow paths and induce the mobilization of geogenic trace metals even in the absence of significant pumping. In Lithia, the DSW effectively increased the local scale permeability of the aquifer, causing the mixing of oxygen-rich surface and deeper anoxic groundwater across a confining unit. Because the alteration to the hydrologic flow paths was a consequence of changes to the physical structure of the aquifer system rather than due to pumping, the alteration is not easily reversible, thus significantly complicating site remediation. Our results provide a cautionary warning of the risks of undue private DSW development in rapidly growing communities. [ABSTRACT FROM AUTHOR]

The simultaneous preservation of the following redox couples was studied: As(III, V), Sb(III, V) and Se(IV, VI). Over a time period of 11 weeks the stability of these three redox couples was assessed in water samples with different dissolved oxygen content, i.e., groundwater, lake water and river water. High concentrations of Fe (25.0 mg L-1) and Mn (25.0 mg L-1) were added to each of the different matrices to simulate a Fe and Mn rich environment. In addition to their natural concentration, each sample was spiked with 5.0 μg L-1 As(III and V) and Sb(III and V) and 15.0 μg L-1 Se(IV and VI). As potential preservation strategies, EDTA alone and EDTA combined with HCl, HNO3, formic acid or acetic acid were investigated and compared to unpreserved samples. In addition, preserved samples were stored at 4°C in the dark, while unpreserved samples were stored at room temperature in the presence of light. The results showed that the addition of EDTA combined with acidification to a pH of 3 successfully preserved all three redox couples for at least 11 weeks stored at 4°C in the dark. EDTA alone (pH = 6) failed to preserve the As and Sb species, although it successfully preserved the Se species. Primarily based on observations made for the unpreserved samples, it was concluded that Sb(III) could be oxidized easier than As(III) and Se(IV) at neutral pH, and that the Se species in general were most stable. The formation of Fe-(oxy) hydroxide and possibly Mn-(oxy) hydroxide in the unpreserved samples also allowed an estimation of the relative adsorption behaviour. Arsenic(III), Sb(III), Se(IV)) and As(V) showed a strong adsorption affinity for Fe-(oxy) hydroxide and Mn-(oxy) hydroxide probably due to the fact that they all form inner sphere complexes, whereas Sb(V) and Se(VI) rarely adsorbed because they form outer sphere complexes and thus bond via weak electrostatic adsorption. Antimony(III) could chelate with EDTA and formed several complexes according to pH. The most stable species of Sb(III)Y− (Y = EDTA) existed at a pH range of 1.8 to 3.0. Apparently Sb(V), on the other hand, did not chelate with EDTA and thus should exist mainly in the form of Sb(OH)6− and minor Sb(OH)5 in this pH range. [ABSTRACT FROM AUTHOR]

Antimony (Sb) is a naturally occurring element of growing environmental concern whose toxicity, adsorption behavior and other chemical properties are similar to that of arsenic (As). However, less is known about Sb compared to As. Individual and simultaneous adsorption experiments with Sb(III) and Sb(V) were conducted in batch mode with focus on the Sb speciation of the remaining liquid phase during individual Sb(III) adsorption experiments. The simultaneous adsorption and oxidation of Sb(III) was confirmed by the appearance of Sb(V) in the solution at varying Fe/Sb ratios (500, 100 and 8) and varying pH values (3.8, 7 and 9). This newly formed Sb(V) was subsequently removed from solution at a Fe/Sb ratio of 500 or at a pH of 3.8. However, more or less only Sb(V) was observed in the liquid phase at the end of the experiments at lower Fe/Sb ratios and higher pH, indicating that competition took place between the newly formed Sb(V) and Sb(III), and that Sb(III) outcompeted Sb(V). This was independently confirmed by simultaneous adsorption experiments of Sb(III) and Sb(V) in binary systems. Under such conditions, the presence of Sb(V) had no influence on the adsorption of Sb(III) while Sb(V) adsorption was significantly inhibited by Sb(III) over a wide pH range (4–10). Thus, in the presence of ferrihydrite and under redox conditions, which allow the presence of both Sb species, Sb(V) should be the dominant species in aquatic environments, since Sb(III) is adsorbed preferentially and at the same time oxidized to Sb(V). [ABSTRACT FROM AUTHOR]

To investigate the potential of Mo and As as possible geogenic contaminants, three sediment cores were examined to evaluate their mineralogical association, distribution and mobility. The cores were described and analyzed for total organic carbon (TOC), Ca, Mg, Si, Al, P, Sr, As, Mo, Fe, and S content. Except in the uppermost segment, limestone was the main lithology with the occasional presence of dolomite and clay. That change in lithology was also observed in the bulk chemical composition, where Ca, Mg and Sr concentrations increased with depth, while Si, Al and P concentrations decreased with depth. Minor minerals included pyrite (FeS 2 ), powellite (CaMoO 4 ) and ferrihydrite. The minimum, maximum, median and standard deviations for all analyzed elements, including As and Mo were comparable for all three cores. Molybdenum and As, however, varied significantly with depth and median As and Mo values were above their respective crustal averages of approximately 1.1 mg/kg and 1.5 mg/kg. The median values for As were 1.9 mg/kg in core DEP-1, 3.3 mg/kg in DEP-2 and 1 mg/kg in DEP-5. The median values for Mo were 2.3 mg/kg in core DEP-1, 2.5 mg/kg in DEP-2 and 2.5 mg/kg in DEP-5. Maximum concentrations for As were 101.9 mg/kg, 47.5 mg/kg and 56.2 mg/kg in cores DEP-1, DEP-2 and DEP-5, respectively. Maximum concentrations for Mo were 880 mg/kg, 123 mg/kg and 225 mg/kg in cores DEP-1, DEP-2 and DEP-5, respectively. Electron microprobe analyses of individual minerals revealed variable concentrations of As ranging from approximately 300 to 9000 mg/kg, in pyrite and up to 17,600 mg/kg in powellite (CaMoO 4 ). The Mo concentration in pyrite was consistently below the detection limit of approximately 100 mg/kg. In powellite the Mo concentration was up to 42 wt%. A subset of 10 samples from different stratigraphic sections and with different As and Mo concentrations was further investigated to assess As and Mo mobility under changing physicochemical conditions. Leaching the aquifer matrix with a 1 M NaOAc solution at a pH of 8.1 removed more than 70% Mo in 8 of the 10 samples. The maximum value was 97%. In contrast to Mo, As was mobilized to a lesser degree. In 8 of the samples less than 30% were removed and the maximum was only 50%. Molybdenum, which seemed to be loosely bound to mineral and organic matter surfaces thus could easily be removed from the aquifer matrix, while As on the other hand should be much less mobile, because it occurred either tightly adsorbed by hydrous ferric oxide or as an impurity in pyrite. Thus, it is advisable to include Mo in the analytical program whenever elevated As concentrations are encountered in groundwater. [ABSTRACT FROM AUTHOR]

Abstract: Around Milos Island marine shallow-water hydrothermal activity can be found and in Paleochori Bay, where high arsenic concentrations were reported for the hydrothermal fluids. There the gastropod Cyclope neritea was present at high densities despite the extreme conditions associated with hydrothermal venting, feeding on white microbial mats. Surprisingly, C. neritea collected from the hydrothermal vent area accumulated comparatively less arsenic in its tissues than specimens of the same species collected from an area not affected by hydrothermal activity. Inorganic arsenic was found at high percentages with respect to the sum of arsenic species both in the gut and muscle of C. neritea and the amount of arsenobetaine (AB) was less than in specimens collected at an area away from hydrothermal activity. Trimethylarsoniopropionate (TMAP) was found at relatively high percentages in C. neritea and in the surrounding environment (sediment and plankton) in Paleochori Bay. Tetramethylarsonium ion (TETRA) was found at high percentages in the gut and muscle of C. neritea. It was most likely biosynthesized in the gastropod gut, and accumulated in the muscle, because it was not found in any other compartment studied. Based on these observations we conclude that C. neritea is arsenic tolerant. The data suggests that arsenic species distribution is strongly influenced by arsenic species exposure and/or different detoxifying mechanisms, although the exact metabolic pathways could not be completely resolved. [Copyright &y& Elsevier]

Hydrothermal fluids emerging at the seafloor near mid-ocean ridges (MOR) or in back-arc basins (BAB) and island arc (IA) settings are known to contain a considerable amount of dissolved metals (e.g. Fe, Zn, Cu, Cd) due to water–rock interaction at elevated temperatures and potentially magmatic degassing. The chemical input from these fluids plays an important role for ocean chemistry and the cycling of elements. Despite its notoriety as an environmental toxin and its abundance in hydrothermal ore deposits in combination with gold, arsenic (As) is one of the few elements, which has been rarely investigated. Compared to the amount of As in open ocean seawater of around 1.7μgL−1, hydrothermal fluids can have significantly higher concentrations. Fluids from MOR hydrothermal systems such as the East Pacific Rise can contain up to 80.5μgL−1 As and at the Mid-Atlantic Ridge the highest values were around 24μgL−1. Those values, although elevated are surpassed by As concentrations in BAB and IA hosted hydrothermal systems, which can be as high as 1386µgL−1 in BAB settings and even higher with values up to 5850µgL−1 (~3900-times seawater) in IA shallow-water settings, occurring near shore hydrothermal systems. The most important factors controlling the amount of As in hydrothermal fluids are the different – mostly physicochemical – conditions at and beneath the seafloor. These include temperature (controlling phase separation of the fluids and leaching processes in the host rock), pressure as a function of depth, pH directly influencing leaching processes, As mobility and speciation, reaction time and maturity of the system in combination with redox reactions and diverse chemical reactions like adsorption and desorption. The concentration of As in the underlying host rock may also play a role, although its mineralogical association may be more important than bulk rock concentration. Additional input of As could be caused by degassing magmatic metal-rich volatiles or sediment-fluid interaction in sediment covered hydrothermal systems. The contribution from magmatic volatiles is hard to quantify and therefore often neglected in calculations and discussions. Of the two As redox species, arsenate (AsV) and arsenite (AsIII), arsenite is easier transported in the vapor phase. However, As speciation has not been traditionally part of chemical analyses. Prior to discharge at the seafloor, the concentration of As in hydrothermal fluids may decrease rapidly, if precipitation of As-bearing and As-scavenging minerals, such as pyrite, orpiment, claudetite and hydrous ferric/manganese oxides, occurs in the shallow subsurface as shown by thermodynamic calculations. This is consistent to the observation that those hydrothermal fluids high in Fe and Mn are often low in As. Arsenic concentrations in fluids from shallow BAB/IA hydrothermal systems are higher than those in deep situated MOR hydrothermal systems most likely due to their different physicochemical conditions. Basaltic host rocks (MOR) and dacitic/andesitic host rocks (BAB/IA) have As concentrations which are more or less identical and cannot account for the huge differences in fluid As concentration. Arsenic is one of the few trace elements whose concentration in seawater is higher than in river water, which could be caused by the flux of As from hydrothermal systems. Estimating that between 3.0×103 and 1.25×108 kg As could be discharged at the MOR annually, which is a substantial amount compared to 53.9×106 kg transported annually by rivers. Higher flux can be expected at BAB and IA settings, however data is sparse. A single IA system, confined to a very small area of 60 by 100m (Tutum Bay, Papua New Guinea), discharges around 5.5×102 kg As annually. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the efficiency of a constructed wetland/filter basin (CW/FB) treatment system to improve the chemical composition of waste and surface waters. The system was constructed in closed phosphate mines used for clay settling and sand tailings. Monitoring was carried out for 18months to evaluate the CW/FB performance under a variety of climatic conditions. Water samples were taken bi-monthly. To evaluate possible groundwater input into and water leaking out of the wetland 6 monitor wells were installed along the flow path and sampled monthly. In order to estimate the change of water chemistry along the wetland flow path, water samples along a transect were taken during the dry and rainy seasons. The samples were analyzed for pH, T, oxidation–reduction potential (ORP), conductivity, total dissolved solids (TDS), dissolved oxygen (DO), Fe(II), H2S, major anions, major cations, arsenic, fecal and total coliform. The study showed the following changes in water quality between the input and output: (1) Substantial decrease of water temperature (up to 10°C); (2) Significant change in pH from about 9 to 6.5–7; (3) Negative ORP confirming the reducing conditions of the treatment system; (4) Substantial increase of H2S (up to 1060µg/L); (5) Reduction of As from 5 to <2µg/L (mostly <0.5); (6) Substantial reduction of SO4, F, Cl, NO3, NO2, Br, Na, K, Ca, and Mg; (7) Reduction of fecal and total coliform from 30–730 and 1000–7000 to <2 and <100count/100mL, respectively. In general, the performance of the CW/FB treatment system showed great potential to improve the water quality of industrial and municipal wastewater. Despite significant seasonal variations with respect to temperature, rainfall and humidity, the chemical/microbiological composition of the wetland output remained relatively constant. [Copyright &y& Elsevier]

Abstract: Arsenic (As) is being released from the Suwannee Limestone, Upper Floridan aquifer, during aquifer storage and recovery (ASR) cycle testing with concentrations of up to 130 μg/L in the recovered water. To determine the abundance and mineralogical association of As in the Suwannee Limestone matrix we have conducted a detailed mineralogical and geochemical study of 306 core samples. In addition to random sampling of core material, we also collected “targeted” samples of core material that contained organic material, hydrous ferric oxide, pyrite, phosphate minerals and clays. Bulk As concentrations were determined by acid digestion followed by hydride generation-atomic fluorescence spectrometry (HG-AFS). Specific mineral phases were analyzed using scanning electron microscopy (SEM) and electron-probe microanalyses (EPMA). The average As concentration for all 306 samples is 3.5 ppm, but only 1.7 ppm after exclusion of the “targeted” samples. The average for the “targeted” samples is 9.5 ppm. The detailed lithologic, mineralogical, and geochemical study of As in the Upper Floridan aquifer, Suwannee Limestone shows that: (1) Arsenic is present in the Suwannee Limestone in low concentrations, but is concentrated in minor mineral phases, particularly pseudo-framboidal pyrite. (2) Pyrite is generally As-rich and can contain concentrations between 100 and 11,200 ppm As (average 2300 ppm, n =25). (3) Compared to pyrite, other trace minerals contain much less As. (4) Pyrite is ubiquitous throughout the Suwannee Limestone, but is most abundant in high porosity zones. (5) Previously suggested hydrous ferric oxide, clay minerals and apatite are not an important source of As. This study also provided some insight into the question whether the interaction (reaction) of water with an aquifer matrix that contains only a few part per million As is capable of producing high-As concentrations in groundwater. Our findings indicate that it can be relatively easy to generate a high-As groundwater despite a low bulk As concentration in the aquifer matrix. A change in physico-chemical conditions that selectively affects the stability of As-bearing minerals is sufficient to increase As concentrations by several orders of magnitude. [Copyright &y& Elsevier]

Determines the role of hydrothermal iron III (Fe III) oxyhydroxide precipitates as sink for arsenic (As) in the coral reefs of Ambitle Island, Papua New Guinea. Environmental importance of hydrothermal Fe (III) oxyhydroxide; Mechanisms that control and buffer the As concentration; Retention of As in Fe (III) oxyhydroxide in natural marine environment.

Geochemical reactive transport modeling was coupled to bench-scale leaching experiments to investigate and verify the mobilization of geogenic arsenic (As) under a range of redox conditions from an arsenic-rich pyrite bearing limestone aquifer. Modeling and experimental observations showed similar results and confirmed the following: (1) native groundwater and aquifer matrix, including pyrite, were in chemical equilibrium, thus preventing the release of As due to pyrite dissolution under ambient conditions; (2) mixing of oxygen- and nitrate-rich surface water with oxygen-depleted native groundwater changed the redox conditions and promoted the dissolution of pyrite, and (3) the behavior of As along a flow path was controlled by a complex series of interconnected reactions. This included the oxidative dissolution of pyrite and simultaneous sorption of As onto neo-formed hydrous ferric oxides (HFO), followed by the reductive dissolution of HFO and secondary release of adsorbed As under reducing conditions. Arsenic contamination of drinking water in these systems is thus controlled by the re-equilibration of the system to more reducing conditions rather than a purely oxidative process. [ABSTRACT FROM AUTHOR]

Hydrothermal vents are often enriched in arsenic, and organisms living in these environments may accumulate high concentrations of this and other trace elements. However, very little research to date has focused on understanding arsenic bioaccumulation and biotransformation in marine organisms at deep-sea vent areas; none to date have focused organisms from back-arc spreading centers. We present for the first time concentration and speciation data for As in vent biota from several hydrothermal vent fields in the eastern Manus basin, a back-arc basin vent field located in the Bismark Sea, western Pacific Ocean. The gastropods Alviniconcha hessleri and Ifremeria nautilei , and the mussel Bathymodiolus manusensis were collected from diffuse venting areas where pH was slightly lower (6.2–6.8), and temperature (26.8–10.5 °C) and arsenic concentrations (169.5–44.0 nM) were higher than seawater. In the tissues of these organisms, the highest total measured As concentrations were in the gills of A. hessleri (5580 mg kg −1 ), with 721 mg kg −1 and 43 mg kg −1 in digestive gland and muscle, respectively. I. nautilei contained 118 mg kg −1 in the gill, 108 mg kg −1 in the digestive gland and 22 mg kg −1 in the muscle. B. manusensis contained 15.7 mg kg −1 in the digestive gland, followed by 9.8 mg kg - 1 and 4.5 mg kg - 1 in its gill and muscle tissue, respectively. We interpret the decreasing overall total concentrations in each organism as a function of distance from the source of hydrothermally derived As. The high concentration of arsenic in A. hessleri gills may be associated with elemental sulfur known to occur in this organism as a result of symbiotic microorganisms. Arsenic extracted from freeze-dried A. hessleri tissue was dominated by As III and As V in the digestive gland (82% and 16%, respectively) and gills (97% As III , 2.3% As V ), with only 1.8% and 0.2% arsenobetaine (As-Bet) in the digestive gland and gills, respectively. However, the muscle contained substantial amounts of As-Bet (42% As-Bet compared to 48% As III and 10% As V ), suggesting As-Bet is a metabolite. Trace arsenosugar (SO4-sug) was observed in digestive gland and gills only. The other snail, I. nautilei , was also dominated by As III and As V in digestive glands (82, 10%) and gills (80, 10%), with 6–9% As-Bet, but its muscle contained 62% As-Bet and 32% As III , with 7% trimethylarsoniopropionate (TMAP). Trace dimethylarsinic acid (DMA V ) was observed in its gills, and trace TMAP and arsenocholine (AC) was observed in digestive glands. The mussel B. manusensis was dominated by As-Bet in all three tissue types. Digestive gland and gills contained ~22% As III , 5–10% As V , 20–25% DMA V , along with some TMAP and tetramethylarsonium ion (TETRA). However, the muscle contained significantly more As-Bet (91.6%), with the only other species being As III (8.4%). Unfortunately, as is often the case in bioaccumulation and biotransformation studies, extraction efficiencies were low, limiting any rigorous interpretation of arsenic biotransformation patterns. Through process of elimination, we suggest that arsenosugars may be synthesized by H 2 S-oxidizing chemotrophic microbial mats, ultimately leading to the syntheses of As-Bet within vent organisms. However, because As-sugs rarely occur in deep-sea vent organisms, As-Bet, as well as TMAP, AC, and TETRA could also potentially be synthesized directly by the “Edmonds” pathway, the proposed arseno-analog to amino acid formation, without the necessity for arsenosugar formation as an intermediate. Future research should endeavor for more comprehensive extraction of organoarsenicals. [ABSTRACT FROM AUTHOR]

Abstract: The marine shallow-water hydrothermal system in Tutum Bay, Ambitle Island, Papua New Guinea discharges as much as 1.5kg of arsenic (As) per day into a coral reef ecosystem. Despite the amount of As released, coral reef organisms do not seem to be affected. We investigated the uptake and bioaccumulation of geothermally-derived inorganic As by the soft coral Clavularia sp., the calcareous algae Halimeda sp., and the sea squirt Polycarpa sp., by measuring the total As concentration (TAs) in tissues from each organism and comparing it to the same type of organism collected from a nearby control site. All organisms collected from the hydrothermal area displayed distinctly higher (2 to 20 times) TAs compared to the control site. Concentrations were typically higher in samples collected closer to the focused hydrothermal venting, which is the first direct evidence for enhanced bioaccumulation of As in organisms living within an area of hydrothermal influence. To assess As biotransformation to organoarsenicals, anionic and cationic As species were determined by IC-ICP-MS in methanol/water tissue extracts. The concentrations of several of the organoarsenic species were much higher at the hydrothermal vent site compared to the control site, and several organoarsenic species were present only in the hydrothermal samples, including some unidentifiable species. While intriguing, these speciation results cannot be interpreted robustly due to poor extraction efficiencies. Future researchers should attempt to improve the extraction efficiency to closer to 100%, which would allow a more accurate description of As biosynthesis pathways for the marine organisms living in these environments. [Copyright &y& Elsevier]

Abstract: Arsenic (As) is naturally enriched in most terrestrial and marine hydrothermal systems. Its discharge from shallow-sea hydrothermal vents into coastal marine environments can dramatically affect the surrounding ecosystems. Shallow-sea hydrothermal venting of acidic (pH~5), hot (40–116°C), and highly sulfidic (up to 3.1mM H2S) fluids occurs at Palaeochori and Spathi Bays, off the southeast coast of Milos Island, Greece. Two distinct types of fluids, both extremely As enriched, were collected from the submarine vents often within a few meters of each other: (1) a high-Cl fluid (enriched in Cl by up to 47% relative to seawater) depleted in Mg and SO4 and enriched in major (Na, Ca, K, B, Sr, and Br) and minor/trace elements (Si, Li, Rb, Ce, As, Fe, Mn, and Ba), and (2) a low-Cl fluid (depleted in Cl by up to 66% relative to seawater) also depleted in Na, Mg, SO4, and Br. The maximum concentration of As reached 39μM in the high-Cl fluids and up to 78μM in the low-Cl fluids. This is approximately 3000 times the concentration of As in seawater and far exceeds the concentrations typically found in mid-ocean ridge (MOR) and back-arc basin (BAB) fluids, which are typically <0.7 and <10μM, respectively. We used a combination of elemental analyses and stable and radiogenic isotope data (oxygen, deuterium, and strontium) to understand the primary controls on As enrichment. Those parameters all indicated that the fluids were a mixture of seawater and a hydrothermal fluid originally derived from seawater but altered by water–rock interaction, subcritical phase separation (boiling), and vapor/brine segregation. Since As was extremely enriched in both the high-Cl and the low-Cl thermal fluids, we conclude that this element readily partitions into the vapor phase in the Milos hydrothermal system. The original source of As is most likely the leaching of the greenschist facies metamorphic basement rocks transpierced by an abundance of secondary quartz and calcite veins rich in pyrite. It is possible that these veins were deposited from As-rich magmatic fluids, similar to some epithermal Au deposits. A poorly-crystalline orpiment precipitates as hydrothermal fluids mix with overlying seawater, and removes much of the dissolved As prior to discharge. [Copyright &y& Elsevier]