Arsenic Cycling Research Articles

Arsenic-resistant bacteria isolated from agricultural soils of Bangladesh and characterization of arsenate-reducing strains

To analyse the arsenic-resistant bacterial communities of two agricultural soils of Bangladesh, to isolate arsenic-resistant bacteria, to study their potential role in arsenic transformation and to investigate the genetic determinants for arsenic resistance among the isolates. Enrichment cultures were performed in a minimal medium in the presence of As(III) and As(V) to isolate resistant bacteria. Twenty-one arsenic-resistant bacteria belonging to different genera of Gram-positive and Gram-negative bacteria were isolated. The isolates, with the exception of Oceanimonas doudoroffii Dhal Rw, reduced 2 mmol l(-1) As(V) completely to As(III) in aerobic conditions. Putative gene fragments for arsenite efflux pumps were amplified in isolates from Dhal soil and a putative arsenate reductase gene fragment was amplified from a Bacillus sp. from Rice soil. Phylogenetically diverse arsenic-resistant bacteria present in agricultural soils of Bangladesh are capable of reducing arsenate to arsenite under aerobic conditions apparently for detoxification purpose. This study provides results on identification, levels of arsenic resistance and reduction of arsenate by the bacterial isolates which could play an important role in arsenic cycling in the two arsenic-contaminated soils in Bangladesh.

Contamination levels and state assessment in the lakes of the Oliveri-Tindari Lagoon (North-Eastern Sicily, Italy)

The Oliveri-Tindari Lagoon, located in North-Eastern Sicily (Italy) and composed of six lakes, is subject to continuous environmental changes. An integrated study focusing on sediment features and levels of contamination was carried out for three of the six lakes, which are of ancient origin: Verde, Mergolo della Tonnara and Marinello. A high primary production (26.89 μg l−1) was detected at Lake Verde; texture classification showed a typical grain size in the sediments of all lakes; the study of macronutrients highlighted 17.08 of total carbon in sediments from Lake Mergolo della Tonnara; toxic elements were detected at higher concentrations in the sediments of Lake Marinello in comparison to the others, while arsenic was found in high concentrations in all the samples tested, especially in Lake Verde, with a mean value of 17.25 mg kg−1 dry weight (d.w.). All the organic contaminants, except 4, 4′-dichlorodiphenyldichloroethylene, were below the detection limits in the sediments. Minimal microbiological contamination was found in both water and sediment samples. In the latter, we isolated several bacterial strains thriving in the presence of arsenic, which play a role in the biogeochemical cycle of arsenic. These preliminary results, obtained for the first time using a multidisciplinary approach, provide general information about the Oliveri-Tindari Lagoon area.

Arsenic compounds in tropical marine ecosystems: similarities between mangrove forest and coral reef

Environmental context. Despite the widespread occurrence of arsenobetaine in marine animals the origin of this arsenic compound remains unknown. A current hypothesis is that arsenobetaine is formed from more complex arsenic compounds found in marine algae. To test this hypothesis, we examined the arsenic compounds in a mangrove ecosystem where algae play a limited role in primary productivity. Abstract. Marine algae are known to bioaccumulate arsenic and transform it into arsenosugars, which are thought to be precursors of the major arsenic compound, arsenobetaine, found in marine animals. Marine ecosystems based on mangrove forests have high nutrient input from mangrove leaves, and thus provide a unique opportunity to study the cycling of arsenic in a marine system where algae are not the dominant food source. Two mangrove forests in Phuket, Thailand were selected as sampling sites for this study. For comparison, samples were also collected from two coral reef sites at and near Phuket. The samples collected included mangrove leaves, corals, algae, molluscs, fish and crustaceans. Arsenic contents in the samples and in aqueous extracts of the samples were determined by hydride generation atomic absorption spectrometry following a dry-ashing mineralisation procedure, and arsenic species were determined in the aqueous extracts by HPLC-MS (mainly ICPMS). Mangrove leaves contained only low concentrations of total arsenic (0.10–0.73 mg kg–1 dry mass) and the aqueous extracts thereof contained inorganic arsenic species, methylarsonate and dimethylarsinate, but arsenosugars were not detected. The total mean arsenic contents (3.2–86 mg kg–1 dry mass) of the animals from the mangrove ecosystem, however, were typical of those found in animal samples from other marine ecosystems. Similarly the arsenic compounds present were typical of those in animals from other marine ecosystems comprising mainly arsenobetaine with smaller quantities of other common arsenicals including arsenosugars, arsenocholine, tetramethylarsonium ion, trimethylarsine oxide and dimethylarsinate. A trimethylated arsenosugar, which is not commonly reported in marine organisms, was a significant arsenical (6–8% of total As) in some gastropod species from the mangrove ecosystem. The coral samples contained mainly arsenosugars and arsenobetaine, and the other animals collected from the coral ecosystem contained essentially the same pattern of arsenicals found for the mangrove animals. The data suggest that food chains based on algae are not necessary for animals to accumulate large concentrations of arsenobetaine.

Treatment of Acute Promyelocytic Leukaemia in Jehovah's Witness(JW) Population

Treatment Of Acute Promyelocytic Leukemia (APML) In The Jehovah's Witness (JW) Population.Colm Keane, Peter Mollee, Paula Marlton, Devinder Gill.Background: Treatment of acute myeloid leukaemia in JW patients is challenging. The refusal to accept blood products is usually a contraindication to intensive chemotherapy and a potential cure.Methods: We review three cases of APML occurring in JW patients treated at our institution which demonstrate the benefit of newer targeted combination therapies that induce less marrow suppression. Suggested management principles are derived from these anecdotal rare cases. Case 1 was a 39 year old male who was initially treated with ATRA (25 mg/m2) and Darbopoietin 100μg twice weekly with arsenic added on day 10 (0.15mg/kg/day). He initially tolerated therapy well despite severe pancytopenia until (day 20) the hemoglobin fell to 52g/L when he developed chest pain. He was diagnosed to have had a myocardial infarct in the setting of fluid retention. His WCC was 10.4 × 109/L with platelet count of 20 × 109/L. He was managed conservatively with no anticoagulation. His hemoglobin nadir was 44 g/L before rising above 80 g/L by day 38 of therapy at which time he was in cytogenetic and molecular remission. He completed a further 28 weeks of consolidation with ATRA (45mg/m2 for 2 weeks every 4 weeks) and arsenic (0.15mg/kg/day Mon-Fri, d1-28 every 2 months for 4 cycles). He has completed 9 months of planned 2 yrs oral maintenance chemotherapy (ATRA, 6MP, MTX) without further incident. Case 2 was a 62 year old female who was treated with ATRA induction (initially at 25mg/m2 but increased to 45mg/m2 on day 18), plus Erythropoietin (Epo) 4,000U × 3 per week s/c. She was in complete cytogenetic remission on day 37 and complete molecular remission by day 87. She had a hemoglobin nadir of 60 g/L but remained asymptomatic. Consolidation therapy commenced on day 106 consisting 3 cycles of combination therapy with ATRA (45mg/m2/d po for 4 weeks) and arsenic (0.15mg/m2/d iv for 5d/week for 4 weeks). Between consolidation cycles there was a 3-week interval during which all therapy was ceased. This regimen was well tolerated. She remains in complete remission after 8 years. Case 3 was a 28-year-old male who was initially treated with ATRA, low dose cytarabine and Epo 4000U 3-times/week s/c. He developed symptoms of severe anemia when his hemoglobin dropped to 25g/L with syncopal episodes and hypotension. He was subsequently found to have t (11:17) mutation and the leukemia did not respond to ATRA. He died from severe anemia fourteen days after presentation. Case reports published subsequently have shown that ATRA resistance in t(11:17) APML may occasionally be overcome if combined with standard chemotherapy or GCSF. However to date Arsenic has not been useful in this variant form of APML. Recommendations:Therapy. Induction with ATRA 25mg/m2 followed on day 10 by arsenic 0.15mg/kg/day until morphologic remission. Consolidation with alternating cycles of ATRA and arsenic as per Case 1. Maintenance therapy with ATRA, 6MP and MTX for 2 years.Anemia. Our patients tolerated severe anemia reasonably well until hemoglobin dropped to approximately 50g/L (most deaths in the literature due to anemia in the JW population have occurred below this threshold). All JW patients receive maximal erythropoietin stimulation and sparing phlebotomy episodes using paediatric blood collection tubes.Thrombocytopenia and coagulopathy. Antifibrinolytics, DDAVP and newer agents such as FVIIa have been used successfully in JW patients undergoing high risk surgery and may be of benefit in the APML setting for patients with haemorrhagic complications.Differentiation syndrome (DS) Case 1 may have developed DS. The standard management of DS is to commence chemotherapy such as idarubicin, cytarabine or gemtuzumab ozogamicin but because of the potential prolonged myelosuppression such agents are not suitable options for JW patients. We would advocate corticosteroids for DS prophylaxis and if treatment of DS is required, hydroxyurea may be a safer option because of its limited and shorter duration of myelosuppression.Conclusion: Our series demonstrates the benefit of more targeted therapy in APML allowing patients who refuse transfusion of blood products a realistic chance of cure.

Anoxic oxidation of arsenite linked to denitrification in sludges and sediments

In this study, denitrification linked to the oxidation of arsenite (As(III)) to arsenate (As(V)) was shown to be a widespread microbial activity in anaerobic sludge and sediment samples that were not previously exposed to arsenic contamination. When incubated with 0.5 mM As(III) and 10 mM NO 3 −, the anoxic oxidation of As(III) commenced within a few days, achieving specific activities of up to 1.24 mmol As(V) formed g −1 volatile suspended solids d −1 due to growth (doubling times of 0.74–1.4 d). The anoxic oxidation of As(III) was partially to completely inhibited by 1.5 and 5 mM As(III), respectively. Inhibition was minimized by adding As(III) adsorbed onto activated aluminum (AA). The oxidation of As(III) was shown to be linked to the complete denitrification of NO 3 − to N 2 by demonstrating a significantly enhanced production of N 2 beyond the background endogenous production as a result of adding As(III)–AA to the cultures. The N 2 production corresponded closely the expected stoichiometry of the reaction, 2.5 mol As(III) mol −1 N 2–N. The oxidation of As(III) linked to the use of common-occurring nitrate as an electron acceptor may be an important missing link in the biogeochemical cycling of arsenic.

Ecophysiology and geochemistry of microbial arsenic oxidation within a high arsenic, circumneutral hot spring system of the Alvord Desert

Microbial metabolism of arsenic has gained considerable interest, due to the potential of microorganisms to drive arsenic cycling and significantly influence the geochemistry of naturally arsenic-rich or anthropogenically arsenic-polluted environments. Alvord Hot Spring in southeastern Oregon is a circumneutral hot spring with an average arsenic concentration of 4.5 mg L(-1) (60 microM). Hydrogeochemical analyses indicated significant arsenite oxidation, increased pH and decreased temperature along the stream channels flowing into Alvord Hot Spring. The dynamic range of pH and temperature over the length of three stream channels were 6.76-7.06 and 69.5-78.2 degrees C, respectively. Biofilm samples showed As(III) oxidation ex situ. 16S rRNA gene studies of sparse upstream biofilm indicated a dominance of bacteria related to Sulfurihydrogenibium, Thermus, and Thermocrinis. The lush downstream biofilm community included these same three groups but was more diverse with sequences related to uncultured OP10 bacterial phylum, uncultured Bacteroidetes, and an uncultured clade. Isolation of an arsenite oxidizer was conducted with artificial hot spring medium and yielded the isolate A03C, which is closely related to Thermus aquaticus based on 16S rRNA gene analysis. Thus, this study demonstrated the bacterial diversity along geochemical gradients of temperature, pH and As(III): As(V), and provided evidence of microbial arsenite oxidation within the Alvord Hot Spring system.

A New Role for Sulfur in Arsenic Cycling

Sulfur and arsenic often coexist in the environment and share similar microbial redox transformations. We examined the effects of sulfide on aerobic arsenite oxidation in alkaline lake water samples and in laboratory enrichment cultures. Significant arsenite oxidation occurred only in treatments with bacteria present, and production of arsenate was greatly enhanced by the addition of sulfide or thiosulfate. IC-ICP-MS analysis of samples showed that mono- and dithioarsenate formed in arsenite + sulfide amended lake water. Our data indicate that these two thioarsenic compounds are fairly stable in sterile alkaline solutions, but are transformed predominantly to arsenate when bacteria are present. Enrichment culture experiments suggest that sulfur-oxidizing bacteria use free or arsenic-bound sulfur as a growth substrate and directly or indirectly transform arsenite and thioarsenates to arsenate during growth. Increases in cell density resulted in more rapid conversion of arsenite and thioarsenates. The rate and extent of these processes appearto be controlled bythe concentration of bacteria and the ratio of reduced sulfur to arsenite present. Sulfur-driven arsenite oxidation and microbial thioarsenate transformation may be important biogeochemical processes in the arsenic cycle of our study site (Mono Lake, CA, USA) and other alkaline environments as well.

Uptake, transport and transformation of arsenate in radishes (Raphanus sativus)

The localization and identification of arsenic compounds in terrestrial plants are important for the understanding of arsenic uptake, transformation and translocation within these organisms, and contributes to our understanding of arsenic cycling in the environment. High performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS), and X-ray absorption near-edge structure (XANES) analysis identified arsenite, arsenate and arsenic(III)–sulphur compounds in leaf, stem and root sections of Rhaphanus sativus (radish) plants grown in both arsenic contaminated mine waste, and arsenic amended liquid cultures. The total arsenic distribution was similar between the plants grown in mine waste and those grown hydroponically. Arsenate was the predominant form of arsenic available in the growth mediums, and after it was taken up by roots, X-ray absorption spectroscopy (XAS) imaging indicated that some of the arsenate was transported to the shoots via the xylem. Additionally, arsenate was reduced by the plant and arsenic(III)–sulphur compound(s) accounted for the majority of arsenic in the leaf and stem of living plants. In this study the application of synchrotron techniques permitted the identification of arsenic(III)–sulphur species which were “invisible” to conventional HPLC-ICP-MS analysis.

Unusual arsenic speciation in sea anemones

Nine species of sea anemones ( Anthopleura asiatica, Actinia equina, Actinodendron arboreum, Phymanthus loligo, Entacmaea actinostoloides, Stichodactyla gigantea, S. haddoni, S. mertensii and Metridium senile) contained arsenic in the range of 1.6–7.0 μg As g −1 (wet mass basis). Irrespective of the species, water-soluble arsenic compounds accounted for more than 80% of the total arsenic. Analysis of water-soluble arsenic compounds by LC/ESI-MS revealed that four arsenicals, arsenobetaine (AB), trimethylarsoniopropionate, arsenocholine (AC) and tetramethylarsonium ion (TEMA), are contained in most species but arsenate, methylarsonic acid, dimethylarsinic acid and trimethylarsine oxide are absent in all species. Interestingly, compositional patterns of the four arsenicals greatly differed from species to species. Only three species ( S. gigantea, S. haddoni and M. senile) contained AB at the highest proportions, similar to the majority of marine animals. However, the remaining six species showed unusual compositional patterns of arsenic compounds; AC was most predominant in A. arboreum and P. loligo and TEMA in A. asiatica, A. equina, E. actinostoloides and S. mertensii. On the whole, high proportions (24.6–87.1% of the water-soluble arsenic) of TEMA appear to be a peculiar characteristic of many species of sea anemones. Thus, sea anemones are an important animal group in the arsenic cycling, especially in that they may be donors of TEMA to predators.

Speciation and Seasonal Variations of Dissolved Inorganic Arsenic in Jiaozhou Bay, North China

The distributions and biogeochemical cycles of arsenic in the aquatic environment have captured the interest of geochemists due to arsenic’s multiple chemical forms, the toxicity of certain arsenic species and large anthropogenic input. Seasonal variations in the dissolved inorganic arsenic concentration and speciation in Jiaozhou Bay, which is located on the west coast of the Yellow Sea in northern China, are presented here. Three cruises were carried out in Jiaozhou Bay under varying tidal regimes, one at neap tide and one at spring tide in August and one at spring tide in October of 2001. In addition to the transect surveys, the main sources of dissolved inorganic arsenate and arsenite in Jiaozhou Bay, including riverine input from five major tributary rivers, atmospheric dry and wet depositions, and groundwater and wastewater input, were collected in different seasons to estimate arsenic transport through different sources. The mean concentrations of total dissolved inorganic arsenic (TDIAs, As (V+III)) in Jiaozhou Bay were statistically comparable between summer and autumn, with higher concentrations at the northwest and northeast parts of the bay, reflecting human activities. The As (III)/TDIAs ratio ranged between 0.045 and 0.68, with an average of 0.16, implying that arsenate was the dominating species in Jiaozhou Bay. A preliminary box model was established to estimate the water-mass balance and arsenic budgets for Jiaozhou Bay, which demonstrated that river inputs and atmospheric depositions were the main sources of arsenic into Jiaozhou Bay. The concentrations of dissolved inorganic arsenic in Jiaozhou Bay have decreased in the last two decades. Compared with other areas in the world, the concentration of arsenic in Jiaozhou Bay remains at the natural level and this region can be characterized as a less disturbed area.

Determination of (Oxy)thioarsenates in Sulfidic Waters

Although it has long been known that soluble arsenic-sulfur (As-S) compounds exist in sulfidic waters and may play significant roles in several important processes in the biogeochemical arsenic cycle, no suitable analytical methods exist for their determination. We provide evidence that the four homologue (oxy)thioarsenates, mono-, di-, tri-, and tetrathioarsenate (AsO3S3-, AsO2S23-, AsOS33- and AsS43-), can be formed in geochemical model reactions between arsenite and sulfide under anoxic conditions (through currently unknown reaction mechanisms) and that these compounds appear to be major As species in natural sulfidic waters. These As-S species are quantified by anion-exchange chromatography-inductively coupled plasma mass spectrometry (AEC-ICPMS) with instrumental detection limits of approximately 0.1 nmol of As L(-1) in undiluted samples; arsenite, arsenate, and monomethylarsenate are quantified as well, but dimethylarsenate cannot be analyzed by this technique. Sulfur in the eluting peaks can be measured as SO+ with detection limits of approximately 0.1 micromol of S L(-1). The (oxy)thioarsenates were synthesized in solution and characterized by electrospray-tandem mass spectrometry (ES-MS-MS). In geochemical model solutions, we confirmed that both the AEC-ICPMS retention times and the ES-MS-MS spectra of the reaction products of sulfide and arsenite matched the synthesized (oxy)thioarsenate standards; for natural waters, the mass spectrometric confirmation was unsuccessful, due to matrix interferences.

Microbial Precipitation of Arsenic Sulfides in Andean Salt Flats

An abiotic origin has traditionally been assumed for the arsenic minerals realgar and orpiment associated with thermal springs. Microbial precipitation of arsenic, however, has been studied in pure cultures and the isotopic composition of arsenic sulfides associated with some borate deposits suggests a biotic origin for those minerals. The aim of the present study is to demonstrate the role of bacterial arsenic precipitation in the biogeochemical cycle of arsenic in such borate deposits. For this purpose both enrichment and pure cultures were obtained from the natural arsenic minerals and the composition and isotopic signatures of the arsenic sulfide minerals precipitated by the cultures and those associated with boron deposits from an Andean salt flat in northern Chile were compared. Based on the microbiological and chemical evidence gathered, it is concluded that bacteria contributed to the formation of the arsenic minerals. This interpretation is based on the consistent association of a variety of features that strongly indicate microbial involvement in the precipitation process. These include: (1) enrichment and isolation of cultures with arsenic precipitation capacity from arsenic mineral samples, (2) high numbers of arsenic-precipitating bacteria in the Andean minerals and brines, (3) chemical and mineralogical properties of precipitates experimentally formed under biotic and abiotic conditions, (4) similarities in stoichiometry between natural and laboratory obtained minerals, and (5) the consistent depletion in δ34S values for natural versus laboratory obtained sulfides. Thus, microbial precipitation of arsenic sulfides is a geochemically relevant metabolism.

Estimation of Biologic Gasification Potential of Arsenic from Contaminated Natural Soil by Enumeration of Arsenic Methylating Bacteria

Volatile arsenic species are found in gases released from natural environments as a result of natural ambient-temperature biomethylation of arsenic conducted by yeast, fungi, and bacteria. This process is part of arsenic transport in the arsenic geocycle. It is important to determine the flux of gasified arsenic released by microorganisms to determine the quantitative flux of arsenic cycle clearly and also to understand the effect of microorganisms on the transport and distribution of arsenic in the contaminated environment. In this study, biologic gasification potential of natural soil was determined by enumeration of arsenic methylating bacteria (AsMB). Enumeration of AsMB was conducted for 10 contaminated sites in Bangladesh where AsMB concentration varies from 0.2 x 10(4) to 7.8 x 10(4) most probable number (MPN) kg(-1) dry soil. The specific gasification rate of arsenic by microorganisms was estimated as 1.8 x 10(-7) microg As MPN(-1) d(-1) by incubation of soil in a laboratory soil column setup. Natural biologic gasification potential of arsenic was then calculated by multiplying the specific rate by the number of AsMB in different soils. The attempt of this study is a fundamental step in determining the volatilization flux of arsenic from land surface contributed by microorganisms.

Biosorption and Biovolatilization of Arsenic by Heat-Resistant Fungi (5 pp)

The aim of this work is to show the ability of several fungal species, isolated from arsenic polluted soils, to biosorb and volatilize arsenic from a liquid medium under laboratory conditions. Mechanisms of biosorption and biovolatilization play an important role in the biogeochemical cycle of arsenic in the environment. The quantification of production of volatile arsenicals is discussed in this article. Heat-resistant filamentous fungi Neosartorya fischeri, Talaromyces wortmannii, T. flavus, Eupenicillium cinnamopurpureum, originally isolated from sediments highly contaminated with arsenic (more than 1403 mg.l-1 of arsenic), and the non-heat-resistant fungus Aspergillus niger were cultivated in 40 mL liquid Sabouraud medium (SAB) enriched by 0.05, 0.25, 1.0 or 2.5 mg of inorganic arsenic (H3AsO4). After 30-day and 90-day cultivation under laboratory conditions, the total arsenic content was determined in mycelium and SAB medium using the HG AAS analytical method. Production of volatile arsenic derivates by the Neosartorya fischeri strain was also determined directly by hourly sorption using the sorbent Anasorb CSC (USA). Filamentous fungi volatilized 0.025-0.321 mg of arsenic from the cultivation system, on average, depending on arsenic concentrations and fungal species. The loss of arsenic was calculated indirectly by determining the sum of arsenic content in the mycelium and culture medium. The amount of arsenic captured on sorption material was 35.7 ng of arsenic (22nd day of cultivation) and 56.4 ng of arsenic (29th day of cultivation) after one hour's sorption. Biosorption of arsenic by two types of fungal biomass was also discussed, and the biosorption capacity for arsenic of pelletized and compact biomass of Neosartorya fischeri was on average 0.388 mg and 0.783 mg of arsenic, respectively. The biosorption and amount of volatilized arsenic for each fungal species was evaluated and the effect of initial pH on the biovolatilization of arsenic was discussed. The most effective biovolatilization of arsenic was observed in the heat-resistant Neosartorya fischeri strain, while biotransformation of arsenic into volatile derivates was approximately two times lower for the non-heat-resistant Aspergillus niger strain. Biovolatilization of arsenic by Talaromyces wortmannii, T. flavus, Eupenicillium cinnamopurpureum was negligible. Results from biosorption experiments indicate that nearly all of an uptaken arsenic by Neosartorya fischeri was transformed into volatile derivates. . Biovolatilization and biosorption have a great potential for bioremediation of contaminated localities. However, results showed that not all fungal species are effective in the removal of arsenic. Thus, more work in this research area is needed.

Geospeciation of arsenic using MINTEQA2 for a post-mining lake

The objective of this study was to investigate the cycling of arsenic in the water column of a post-mining lake. This study is part of a research project to develop health risk assessment for the surrounding population. Inductively Coupled Plasma-Mass Spectrophotometer (ICP-MS) and Capillary Electrophoresis (CE) have been used to analyze the total amount and speciation, respectively. A computer program, called MINTEOA2, which was developed by the United States Environmental Protection Agency (USEPA) was used for predicting arsenic, iron, and manganese as functions of pH and solubility. Studying the pH values and cycle of arsenic shows that the percentage of bound arsenate, As(V) species in the form of HAsO4- increases with range pH from 5 to 7, as well as Fe(II) and Mn(III). As expected phases of arsenic oxides are FeAsO4 and Mn3(AsO4), as a function of solubility, however none of these phases are over saturated and not precipitated. It means that the phases of arsenic oxides have a high solubility.

On the First Polyarsenic Organic Compound from Nature: Arsenicin A from the New Caledonian Marine Sponge Echinochalina bargibanti

Reported here is the first polyarsenic compound ever found in nature. Denominated arsenicin A, it was isolated along a bioassay-guided fractionation of the organic extract of the poecilosclerid sponge Echinochalina bargibanti collected from the north-eastern coast of New Caledonia. In defining an adamantine-type polyarsenic structure for this compound, deceptively simple NMR spectra were complemented by extensive mass spectral analysis. However, it was only the synthesis of a model compound that provided the basis to discriminate structure 4 from other spectrally compatible structures for arsenicin A; to this end, a comparative ab initio simulation of IR spectra for the natural and the synthetic compounds was decisive. Arsenicin A is endowed with potent bactericidal and fungicidal activities on human pathogenic strains. All this may revive pharmacological interest in arsenic compounds while prompting us to rethink the arsenic cycle in nature.

Simultaneous Microbial Reduction of Iron(III) and Arsenic(V) in Suspensions of Hydrous Ferric Oxide

Bacterial reduction of arsenic(V) and iron(III) oxides influences the redox cycling and partitioning of arsenic (As) between solid and aqueous phases in sediment-porewater systems. Two types of anaerobic bacterial incubations were designed to probe the relative order of As(V) and Fe(III) oxide reduction and to measure the effect of adsorbed As species on the rate of iron reduction, using hydrous ferric oxide (HFO) as the iron substrate. In one set of experiments, HFO was pre-equilibrated with As(V) and inoculated with fresh sediment from Haiwee Reservoir (Olancha, CA), an As-impacted field site. The second set of incubations consisted of HFO (without As) and As(III)- and As(V)- equilibrated HFO incubated with Shewanella sp. ANA-3 wild-type (WT) and ANA-3deltaarrA, a mutant unable to produce the respiratory As(V) reductase. Of the two pathways for microbial As(V) reduction (respiration and detoxification), the respiratory pathway was dominant under these experimental conditions. In addition, As(III) adsorbed onto the surface of HFO enhanced the rate of microbial Fe(III) reduction. In the sediment and ANA-3 incubations, As(V) was reduced simultaneously or prior to Fe(III), consistent with thermodynamic calculations based on the chemical conditions of the ANA-3 WT incubations.

Seasonal Dynamics of Dimethylarsenic Acid Degrading Bacteria Dominated in Lake Kibagata

Degradation processes of organoarsenic compounds significantly influence arsenic cycles in aquatic environments and would depend on the bacterial activities. The bacterial population involving dimethylarsinic acid (DMAA) degradation was investigated in Lake Kibagata from April to December in 2003. During the experimental period, the methylated arsenic was not detected, although the inorganic arsenic concentration ranged from 3.4 nM to 9.2 nM. Moreover, in the sample water of Lake Kibagata to which DMAA added, DMAA decreased while inorganic arsenic increased for 25 days. These facts suggested that the bacteria remineralized methylate arsenic species to inorganic arsenic. In fact, monitoring the use of Most Probable Number (MPN) procedure demonstrated that the DMAA-degrading bacteria exist at cell densities ranged from 41 cells/ml to 510 cells/ml. To determine the composition of DMAA-degrading bacteria, the total 110 isolates obtained as dominated bacterial species were analyzed by the restriction-fragment-length polymorphism (RFLP) analysis of 16S rDNA. As a result, total 110 isolates were classified into 12 types, of which 4 types dominated during the spring and/or fall seasons, and the rest 8 types dominated during summer season. DMAA degrading activities of the 110 isolates ranged at various degrees. Especially, the some isolates of fall season tend to show high degradation activities. The phylogenetic analysis using 16S rDNA revealed that the representative isolates formed several clusters in the gram-positive bacterial group and the proteobacteria subdivision. The diverse compositions of DMAA-degrading bacteria would seasonally change to control the rates of organoarsenic degradation in Kibagata.

Characterization of water‐soluble organoarsenic compounds in marine sponges

AbstractTo provide a better understanding of the arsenic cycle in the marine ecosystem and marine biotechnological viewpoints, the present study is intended to identify arsenic compounds contained in marine sponges. Marine sponges were collected off the coastal waters of Magsaysay Islet within Bohol Sea near Mindanao (Philippines) and in the Seto Inland Sea (Japan) by skin‐diving. Water‐soluble arsenic compounds were extracted with methanol–water (1: 1, v/v) from freeze‐dried samples of 13 marine sponges. The extracts were analyzed using high‐performance liquid chromatography (HPLC) with an inductively coupled plasma mass spectrometer (ICP/MS) serving as an arsenic‐specific detector. All marine sponges contained arsenobetaine [(CH3)3As+ CH2COO−], 2,3‐dihydroxypropyl 5‐deoxy‐5‐(dimethylarsinoyl)‐β‐ribofuranoside (arseno‐sugar X), and 3‐glycerophosphoryl‐2‐hydroxy‐1‐[5‐deoxy‐5‐(dimethylarsinoyl)‐β‐ribofuranosyloxy]propane (arseno‐sugar X1), among which arseno‐sugarX1 was most abundant in the Jaspis spp., Suberites spp. and four Japanese sponges. Also, a linear relationship existed between total water‐soluble arsenic and arsenobetaine Copyright © 2006 John Wiley & Sons, Ltd.

Geochemical Cycling of Arsenic in a Coastal Aquifer

Biogeochemically modified pore waters from subterranean estuaries, defined as the mixing zone between freshwater and saltwater in a coastal aquifer, are transported to coastal waters through submarine groundwater discharge (SGD). SGD has been shown to impact coastal and perhaps global trace metal budgets. The focus of this study was to investigate the biogeochemical processes that control arsenic cycling in subterranean estuaries. Total dissolved As, as well as a suite of other trace metals and nutrients, were measured in a series of wells and sediment cores at the head of Waquoit Bay, MA. Dissolved As ranged from below detection to 9.5 microg/kg, and was associated with plumes of dissolved Fe, Mn, and P in the groundwater. Sedimentary As, ranging from 360 to 7500 microg/kg, was highly correlated with sedimentary Fe, Mn, and P. In addition, amorphous Fe (hydr)oxides were more efficient scavengers of dissolved As than the more crystalline forms of solid-phase Fe. Given that dissolved As in the surface bay water was lower than within the subterranean estuary, our results indicate that the distribution and type of Fe and Mn (hydr)oxides in coastal aquifers exert a major influence on the biogeochemical cycling of As in subterranean estuaries and, ultimately, the fate of groundwater-derived As in marine systems influenced by SGD.