Sorption of arsenic by iron oxides and oxyhydroxides in soils

Oxyanions of arsenic and selenium can be used in microbial anaerobic respiration as terminal electron acceptors. The detection of arsenate and selenate respiring bacteria in numerous pristine and contaminated environments and their rapid appearance in enrichment culture suggest that they are widespread and metabolically active in nature. Although the bacterial species that have been isolated and characterized are still few in number, they are scattered throughout the bacterial domain and include Gram-positive bacteria, beta, gamma and epsilon Proteobacteria and the sole member of a deeply branching lineage of the bacteria, Chrysiogenes arsenatus. The oxidation of a number of organic substrates (i.e. acetate, lactate, pyruvate, glycerol, ethanol) or hydrogen can be coupled to the reduction of arsenate and selenate, but the actual donor used varies from species to species. Both periplasmic and membrane-associated arsenate and selenate reductases have been characterized. Although the number of subunits and molecular masses differs, they all contain molybdenum. The extent of the environmental impact on the transformation and mobilization of arsenic and selenium by microbial dissimilatory processes is only now being fully appreciated.

Bacterial respiration of arsenic and selenium.

Recent improvements in sample collection and analytical techniques have suggested that As(III) is more prevalent in groundwater than previously believed. Indeed, reducing conditions in alluvial aquifers supplying single families may result in significant exposures to naturally occurring As(III). These results are noteworthy because As(III) is both more toxic and more mobile in the environment than As(V). The literature contains contradictory information concerning the appropriate preservation and analytical techniques for determining As(III). It appears that several previously reported occurrences of As(V) may have been predominantly As(III), but the samples were either not preserved or analyzed properly. For example, separation of arsenic species by ion exchange is apparently necessary to obtain reliable analytical results for certain environmental samples. The problems encountered with investigating As(III) in the environment are due to the complex series of geochemical reactions undergone by a...

A review of arsenic (III) in groundwater

Arsenic has a complex marine biogeochemistry that has important implications for its toxicity to marine organisms and their consumers, including humans. The average concentration of total arsenic in the ocean is about 1.7 μg/L, about two orders of magnitude higher than the U.S Environmental Protection Agency's human health criterion (fish consumption) value of 0.0175 μg/L. The dominant form of arsenic in oxygenated marine and brackish waters is arsenate (As V). The more toxic and potentially carcinogenic arsenite (As III) rarely accounts for more than 20% of total arsenic in seawater. Uncontaminated marine sediments contain from 5 to about 40 μg/g dry weight total arsenic. Arsenate dominates in oxidized sediments and is associated primarily with iron oxyhydroxides. In reducing marine sediments, arsenate is reduced to arsenite and is associated primarily with sulfide minerals. Marine algae accumulate arsenate from seawater, reduce it to arsenite, and then oxidize the arsenite to a large number of organoarsenic compounds. The algae release arsenite, methylarsonic acid, and dimethylarsinic acid to seawater. Dissolved arsenite and arsenate are more toxic to marine phytoplankton than to marine invertebrates and fish. This may be due to the fact that marine animals have a limited ability to bioconcentrate inorganic arsenic from seawater but can bioaccumulate organoarsenic compounds from their food. Tissues of marine invertebrates and fish contain high concentrations of arsenic, usually in the range of about 1 to 100 μg/g dry weight, most of it in the form of organoarsenic compounds, particularly arsenobetaine. Organoarsenic compounds are bioaccumulated by human consumers of seafood products, but the arsenic is excreted rapidly, mostly as organoarsenic compounds. Arsenobetaine, the most abundant organoarsenic compound in seafoods, is not toxic or carcinogenic to mammals. Little of the organoarsenic accumulated by humans from seafood is converted to toxic inorganic arsenite. Therefore, marine arsenic represents a low risk to human consumers of fishery products.

https://setac.onlinelibrary.wiley.com/doi/pdf/10.1002/etc.5620160511

Ecotoxicology of arsenic in the marine environment

Publisher Summary The chapter provides an overview of marine arsenic research and arsenic concentrations in the various marine compartments. General chemical and analytical characteristics of the arsenic compounds of significance in marine arsenic studies are mentioned in the chapter followed by an outline of their occurrence, distribution, and biotransformation in marine samples. Workers in the area have applied different scientific disciplines to advance various aspects of the problem over the years. For example, progress in biological and biochemical studies of the uptake of arsenic by algae was made following chemical studies identifying the natural arsenic constituents of algae. Subsequent chemical synthesis of the arsenic compounds enabled toxicological assessment and further biotransformation studies to be carried out. The presence of both arsenobetaine and arsenosugars in the one organism, particularly one from such an isolated and selfcontained environment, might be taken as support for the view that arsenosugars are serving as precursors to arsenobetaine.

Arsenic and Marine Organisms

Arsenic speciation data are presented for pore waters squeezed from some native and anthropogenically influenced sediments.

Arsenic speciation in marine interstitial water. The occurrence of organoarsenicals

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Arsenic speciation in marine interstitial water. The occurrence of organoarsenicals