Biogeochemical Cycling Of Arsenic Research Articles

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.

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.

Arsenic speciation in arsenic-rich Brazilian soils from gold mining sites under anaerobic incubation

Arsenic speciation in environmental samples is essential for studying toxicity, mobility and bio-transformation of As in aquatic and terrestrial environments. Although the inorganic species As(III) and As(V) have been considered dominant in soils and sediments, organisms are able to metabolize inorganic forms of arsenic into organo-arsenic compounds. Arsenosugars and methylated As compounds can be found in terrestrial organisms, but they generally occur only as minor constituents. We investigated the dynamics of arsenic species under anaerobic conditions in soils surrounding gold mining areas from Minas Gerais State, Brazil to elucidate the arsenic biogeochemical cycle and water contamination mechanisms. Surface soil samples were collected at those sites, namely Paracatu Formation, Banded Iron Formation and Riacho dos Machados Sequence, and incubated in CaCl2 2.5 mmol L(-1) suspensions under anaerobic conditions for 1, 28, 56 and 112 days. After that, suspensions were centrifuged and supernatants analyzed for soluble As species by IC-ICPMS and HPLC-ICPMS. Easily exchangeable As was mainly arsenite, except when reducible manganese was present. Arsenate was mainly responsible for the increase in soluble arsenic due to the reductive dissolution of either iron or manganese in samples from the Paracatu Formation and Riacho dos Machados Sequence. On the other hand, organic species of As dominated in samples from the Banded Iron Formation during anaerobic incubation. Results are contrary to the expectation that, in anaerobic environments, As release due to the reductive dissolution of Fe is followed by As(V) reduction to As(III). The occurrence of organo-arsenic species was also found to be significant to the dynamics of soluble arsenic, mainly in soils from the Banded Iron Formation (BIF), under our experimental conditions. In general, As(V) and organic As were the dominant species in solution, which is surprising under anaerobic conditions in terrestrial environments. The unexpected occurrence of organic species of As was attributed to enrollment of ternary organic complexes or living organisms such as algae or cyanobacteria. These findings are believed to be useful for remediation strategies in mine-affected regions, as the organic As species are in general considered to be less toxic than inorganic ones and even As(V) is considered less mobile and toxic than As(III).

Arsenic Species in a Rocky Intertidal Marine Food Chain in NSW, Australia, revisited

Environmental Context. The pathways by which arsenic is accumulated, biotransformed and transferred in aquatic ecosystems are relatively unknown. Examination of whole marine ecosystems rather than individual organisms provides greater insights into the biogeochemical cycling of arsenic. Rocky intertidal zones, which have a high abundance of organisms but low ecological diversity, are an important marine habitat. This study examines the cycling of arsenic within intertidal ecosystems to further understand its distribution and transfer. Abstract. The present study reports total arsenic and arsenic species in a short rocky intertidal marine food chain in NSW, Australia. Total mean arsenic concentrations increased up the food chain in the following order: 4 ± 2 µg g–1 in attached rock microalgae, 31 ± 14 µg g–1 in Bembicium nanum Lamarck, 45 ± 14 µg g–1 in Cellana tramoserica Sowerby, 58 ± 14 µg g–1 in Nerita atramentosa Reeve, 75 ± 15 µg g–1 in Austrocochlea constrica Lamarck (a herbivore) and 476 ± 285 µg g–1 in the carnivore Morula marginalba Blainville. Significant differences in arsenic concentrations of B. nanum, N. atramentosa and M. marginalba were found among locations and may be related to food availability, spawning or differences in age and/or size classes of individuals. Significant differences in arsenic concentrations were also found within locations among species, and increased in the order: rock microalgae < B. nanum < C. tramoserica < N. atramentosa < A. constricta < M. marginalba. Although small differences in total arsenic concentrations were found among locations for some gastropod species, arsenic species proportions were very consistent within gastropod species across locations. The majority of arsenic in Homosira banksii (macroalgae) was oxo-arsenoribosides, with thio-arsenoribosides making up ~10% of the total methanol–water extractable arsenic. The rock microalgae contained arsenobetaine (AB) (59 ± 5%) and arsenoribosides (36 ± 15%). The AB content of the herbivores B. nanum, N. atramentosa and A. constricta ranged from 71 to 95%, and that of the carnivore M. marginalba was 98%. Most gastropods contained thio-arsenosugars (up to 13 ± 3% of total extractable arsenic), with C. tramoserica containing higher proportions of thio-phosphate arsenoriboside (7 ± 2%) and lower proportions of AB (69 ± 4%). Glycerol trimethylarsonioribosides (1.4 ± 0.1%) were also found in most of the herbivorous gastropods. Oxo-dimethylarsinoylethanol (oxo-DMAE) was found in N. atramentosa (<1%).

Distribution and Speciation of Arsenic in Temperate Marine Saltmarsh Ecosystems

Environmental Context. The pathways by which arsenic is accumulated and transferred in aquatic ecosystems are relatively unknown. Examination of whole marine ecosystems rather than individual organisms provides greater insights into the biogeochemical cycling of arsenic. Saltmarshes with low ecological diversity are an important terrestrial–marine interface about which little is known regarding arsenic concentrations and species distribution. This study examines the cycling of arsenic within Australian saltmarsh ecosystems to further understand its distribution and trophic transfer. Abstract. This paper reports the distribution of total arsenic and arsenic species in saltmarsh ecosystems located in south-east Australia. We also investigated the relationship between arsenic, iron, and phosphorus concentrations in saltmarsh halophytes and associated sediment. Total mean arsenic concentrations in saltmarsh plants, S. quinqueflora and S. australis, for leaves ranged from 0.03 ± 0.05 to 0.67 ± 0.48 μg g−1 and 0.03 ± 0.02 to 0.08 ± 0.06 μg g−1, respectively, and for roots ranged from 2 ± 2 to 6 ± 12 μg g−1 and 0.39 ± 0.20 to 0.57 ± 1.06 μg g−1 respectively. Removal of iron plaque from the roots reduced the arsenic concentration variability to 0.40–0.79 µg g−1 and 0.95–1.05 µg g−1 for S. quinqueflora and S. australis roots respectively. Significant differences were found between locations for total arsenic concentrations in plant tissues and these differences could be partially attributed to differences in sediment arsenic concentrations between locations. For S. quinqueflora but not S. australis there was a strong correlation between arsenic and iron concentrations in the leaf and root tissues. A significant negative relationship between arsenic and phosphorus concentrations was found for S. quinqueflora leaves but not roots. Total mean arsenic concentrations in salt marsh animal tissues (7 ± 2–21 ± 13 µg g−1) were consistent with those found for other marine animals. The concentration of total arsenic in gastropods and amphipods could be partially explained by the concentration of total arsenic in the dominant saltmarsh plant S. quinqueflora. Of the extractable arsenic, saltmarsh plants were dominated by arsenic(iii), arsenic(v) (66–99%), and glycerol arsenoribose (17–35%). Arsenobetaine was the dominant extractable arsenic species in the gastropods Salinator soilda (84%) and Ophicardelus ornatus (89%) and the crab Neosarmatium meinerti (89%). Amphipods contained mainly arsenobetaine (44%) with some phosphate arsenoribose (23%). Glycerol trimethyl arsonioribose was found in both gastropods (0.7–0.8%) and the visceral mass of N. meinerti (0.1%). These results show that arsenic uptake into plants from uncontaminated saltmarsh environments maybe dependent on plant iron uptake and inhibited by high phosphorus concentrations. Arsenic in saltmarsh plants is mainly present as inorganic arsenic, but arsenic in animals that eat plant detritus is present as organo arsenic species, primarily arsenobetaine and arsenosugars. The presence of glycerol trimethyl arsonioribose poses the question of whether trimethylated arsonioriboses are transitory intermediates in the formation of arsenobetaine.

A novel arsenate respiring isolate that can utilize aromatic substrates

A novel anaerobic bacterium was isolated from the sediment of Onondaga Lake (Syracuse, NY), which can use arsenate [As(V)] as a respiratory electron acceptor. The isolate, designated strain Y5 is a spore-forming, motile rod, with lateral flagella. It is Gram-negative though it phylogenetically falls within the low G + C Gram-positive organisms. In addition to the more usual electron donors such as lactate and succinate, strain Y5 also can use H 2 + CO 2 chemoautotrophically and metabolize aromatic compounds such as syringic acid, ferulic acid, phenol, benzoate and toluene, coupled to arsenate reduction. Aside from As(V), nitrate, sulfate, thiosulfate and Fe(III) can also serve as electron acceptors. Based on 16S rDNA phylogeny and its physiological characteristics, strain Y5 was identified as most closely related to the genus Desulfosporosinus. The ability of microorganisms to reduce arsenate for respiration appears to be widely distributed and may be relevant in the biogeochemical cycling of arsenic in environments containing mixed contaminants.

Precipitation of Arsenic Trisulfide by Desulfotomaculum auripigmentum

A newly discovered bacterium, Desulfotomaculum auripigmentum, precipitates arsenic trisulfide (As(inf2)S(inf3)). Precipitation of As(inf2)S(inf3) by this organism results from its reduction of As(V) to As(III) and S(VI) to S(-II). At the As(III) concentration range of interest (0.1 to 1 mM), the stability of As(inf2)S(inf3) is highly sensitive to pH and [S(-II)]. Thus, the relative rates at which D. auripigmentum reduces As(V) and S(VI) are critical to its formation of As(inf2)S(inf3). Other As(V)- or S(VI)-reducing bacteria are unable to precipitate As(inf2)S(inf3) either due to their inability to reduce both As(V) and S(VI) or because they reduce S(VI) too rapidly. Electron microscopy of thin sections showed that the precipitate forms both intra- and extracellularly. Microbial As(inf2)S(inf3) formation nucleates precipitation of the mineral in the bulk milieu, whereas heat-killed cells alone do not serve as templates for its formation. Precipitation of As(inf2)S(inf3) by D. auripigmentum suggests that As(inf2)S(inf3) formation may be important in the biogeochemical cycle of arsenic.

Refractory arsenic species in estuarine waters

AbstractTotal digestion of estuarine water samples by dry ashing shows that a significant fraction of dissolved arsenic does not form hydrides with sodium tetrahydroborane (NaBH4) and is therefore not detected by the normal hydride generation‐atomic absorption analytical technique. It is also refractory to alkaline digestion with sodium hydroxide. Sequential ultrafiltration suggests a molecular weight below 210 for this new arsenic fraction. The magnitude and molecular weight of this fraction may open new perspectives on the biogeochemical cycling of arsenic. Ecological reasons can explain the discrepancy between these findings and previous research.

Arsenic in marine organisms

A review of the nature and accumulation of arsenic in marine organisms is presented. A study of the literature has revealed a lack of information about the mechanisms of uptake, molecular transformations, and biochemical associations of arsenic within organisms, and it remains unclear whether a few forms of arsenic are ubiquitous. The arsenic forms present in marine sediments and their role in the biogeochemical cycling of arsenic are also largely unknown.