Dimethylarsinoylethanol Research Articles

Matrix-induced transformation of arsenic species in seafoods

The paper presents a study on the matrix-induced transformation of arsenic (As) species spiked into seafoods. Sixteen arsenicals were individually spiked into samples of finfish, crustaceans and molluscs. The spiked samples were subjected to hot water extraction at 90 °C, and extracts were analyzed by high pressure liquid chromatography (HPLC) interfaced with inductively coupled plasma mass spectrometry (ICP-MS). Arsenate (As5+), arsenobetaine (AsB), arsenocholine (AsC), dimethylarsinate (DMA), monomethylarsonate (MMA), tetramethylarsonium ion (TMA) and trimethylarsoniopropionate (TMAP) remained intact in all the matrices. Whereas arsenite (As3+), dimethylarsinoyl acetate (DMAA), dimethylarsinoyl ethanol (DMAE), dimethylarsinoyl propionate (DMAP), trimethylarsine oxide (TMAO) and glycerol-, sulfonate-, sulfate- and phosphate-arsinoylribosides (arsenosugars 328, 392, 408 and 482, respectively) were transformed to other forms in most finfish and crustaceans. The transformation of the arsenicals was discovered to be induced by matrix thiols. While As3+ was bound to sulfhydryl groups, DMAA, DMAE, DMAP, TMAO and arsenosugars 392, 408 and 482 were thiolated through conversion of their arsinoyl (As=O) functionalities to arsinothioyl (As=S). The newly formed arsinothioyl compounds were characterized by HPLC-ICP-MS and electrospray ionization high-resolution tandem mass spectrometry (ESI-HR-MS/MS) paired with HPLC. The observed matrix-induced transformation of the arsenic species could be prevented by treating the samples (prior to spiking) with a thiol-selective blocking agent, N-ethylmaleimide (NEM).

The formation and fate of organoarsenic species in marine ecosystems: do existing experimental approaches appropriately simulate ecosystem complexity?

Environmental context In marine environments, inorganic arsenic present in seawater is transformed to organoarsenic species, mainly arsenoribosides in algae and arsenobetaine in animals. These transformations decrease the toxicity of arsenic, yet the fate of arsenoribosides and arsenobetaine when marine organisms decompose is unknown. We review the current literature on the degradation of these organoarsenic species in marine systems detailing the drivers behind their degradation, and also discuss the environmental relevance of laboratory-based experiments. Abstract Despite arsenoribosides and arsenobetaine (AB) being the major arsenic species in marine macro-algae and animals they have never been detected in seawater. In all studies reviewed arsenoribosides from marine macro-algae were degraded to thio-arsenoribosides, dimethylarsinoylethanol (DMAE), dimethylarsenate (DMA), methylarsenate (MA) with arsenate (AsV) the final product of degradation. The use of different macro-algae species and different experimental microcosms did not influence the arsenoriboside degradation pathway. The use of different experimental approaches, however, did influence the rate and extent at which arsenoriboside degradation occurred. This was almost certainly a function of the complexity of the microbial community within the microcosm, with greater complexity resulting in rapid and more complete arsenoriboside degradation. AB from decomposing animal tissues is degraded to trimethylarsine oxide (TMAO) or dimethylarsenoacetate (DMAA), DMA and finally AsV. The degradation of AB unlike arsenoribosides occurs via a dual pathway with environmental or microbial community variability influencing the pathway taken. The environmental validity of different experimental approaches used to examine the fate of organoarsenic species was also reviewed. It was evident that although liquid culture incubation studies are cheap and reproducible they lack the ability to culture representative microbial communities. Microcosm studies that include sand and sediment are more environmentally representative as they are a better simulation of marine ecosystems and are also likely to facilitate complex microbial communities. An added benefit of microcosm studies is that they are able to be run in parallel with field-based research to provide a holistic assessment of the degradation of organoarsenic species in marine environments.

Total arsenic concentrations and arsenic species present in naturally decomposing Ecklonia radiata tissues collected from various marine habitats

To investigate the release and degradation of arsenoribosides associated with the brown alga Ecklonia radiata, tissues were collected in various marine micro-habitats (water column, sand intertidal, and rock platform intertidal) to establish the importance of decomposition stage and the micro-habitat in which decomposition occurs on arsenoriboside degradation. Total arsenic concentrations in E. radiata tissues varied in a similar pattern across all three sampling locations (Lake Tabourie, Burrill Lake, and Ulladulla Harbour) with concentrations in live tissues (53–124 μg As g−1 (dry mass)) greater than concentrations in tissues decomposing in the water column (28–90 μg As g−1 (dry mass)), which were in turn higher than concentrations in tissues decomposing in intertidal environments (16–21 μg As g−1 (dry mass)). Arsenoribosides, specifically sulfonate (SO3-), phosphate (PO4-), and glycerol (Gly-) accounted for all of the arsenic extracted from live E. radiata tissues. Arsenoribosides also accounted for 100 % of the extractable arsenic species in E. radiata tissues decomposing in the water column. The proportions of arsenic species in decomposing E. radiata tissue from intertidal environments varied with sampling location and therefore micro-habitat. In rock platform-based intertidal zones (Burrill Lake and Ulladulla harbour), considerable concentrations of unextractable arsenic (10–60 %) were present plus known arsenoriboside degradation products such as dimethylarsinoylethanol (DMAE), dimethylarsenate (DMA), and arsenate (As(V)). In sand/beach-based intertidal zones, however, the vast majority of arsenic (≈95 %) was unextractable with only small concentrations of arsenoribosides and As(V) present.

The degradation of arsenoribosides from Ecklonia radiata tissues decomposed in natural and microbially manipulated microcosms

Environmental context Arsenoribosides are the major arsenic species in marine macro-algae, yet inorganic arsenic is the major arsenic species found in seawater. We investigated the degradation of arsenoribosides associated with Ecklonia radiata by the use of microcosms containing both natural and autoclaved seawater and sand. The decomposition and persistence of arsenic species was linked to the use of autoclaved seawater and sand, which suggests that arsenoriboside degradation is governed by the microbial composition of microenvironments within marine systems. Abstract We investigated the influence of microbial communities on the degradation of arsenoribosides from E. radiata tissues decomposing in sand and seawater-based microcosms. During the first 30 days, arsenic was released from decomposing E. radiata tissues into seawater and sand porewaters in all microcosms. In microcosms containing autoclaved seawater and autoclaved sand, arsenic was shown to persist in soluble forms at concentrations (9–18µg per microcosm) far higher than those present initially (~3µg per microcosm). Arsenoribosides were lost from decomposing E. radiata tissues in all microcosms with previously established arsenoriboside degradation products, such as thio-arsenic species, dimethylarsinoylethanol (DMAE), dimethylarsenate (DMA) and arsenate (AsV) observed in all microcosms. DMAE and DMA persisted in the seawater and sand porewaters of microcosms containing autoclaved seawater and autoclaved sand. This suggests that the degradation step from arsenoribosides → DMAE occurs on algal surfaces, whereas the step from DMAE → AsV occurs predominantly in the water-column or sand–sediments. This study also demonstrates that disruptions to microbial connectivity (defined as the ability of microbes to recolonise vacant habitats) result in alterations to arsenic cycling. Thus, the re-cycling of arsenoribosides released from marine macro-algae is driven by microbial complexity plus microbial connectivity rather than species diversity as such, as previously assumed.

Closed Anaerobic Biotransformation Products of Organoarsenic Compounds inFucus distichus

The closed anaerobic decomposition extracts ofFucus distichusincubated with seawater and sediment, and without sediment as control, were subjected to extractions and isolation on Sephadex LH 20 and Cellulose Thin Layer Chromatography. The decomposition extracts and isolates were analyzed by using both the Hydride Generation Gas Chromatography Atomic Absorption Spectrometry (HG-GC-AAS) and High Performance Liquid Chromatography Inductively Coupled Plasma Mass Spectrometry (HPLC-ICPMS) to identify the arsenic species in the equilibrium mixtures of the seaweed and filtrates separately. In the methanol seaweed extract, equilibrium mixture of arsenosugars (AS) AS1 and AS2 and their biotransformation products of dimethylarsinoylethanol (DMAE) and dimethylarsinic acid (DMAA) were identified. In the methanol filtrate extract of the mixture, only DMAE and DMAA were identified. However, in the control methanol filtrate extract five organoarsenic species, AS1 and AS2, one unidentified hidden organoarsenic species, DMAE and DMAA were identified in the equilibrium mixture. This result confirmed that the hidden organoarsenic species inFucus distichus, AS1 and AS2, and an unidentified organoarsenic compounds are biotransformed to only DMAE and DMAA under an anaerobic condition. This also suggests that DMAE and DMAA are strong intermediate candidates for the generation of arsenobetaine, from arsenoribosides in the marine food webs.

Speciation of arsenic metabolites in the free-living mouse Mus spretus from Doñana National Park used as a bio-indicator for environmental pollution monitoring

AbstractA speciation approach based on orthogonal chromatographic systems coupled to inductively coupled plasma mass spectrometry (ICP-MS) was used to characterise the biological response of free-living mice Mus spretus to environmental pollution caused by arsenic in different areas of the Doñana National Park (south-west Spain). The relative presence of inorganic and organic forms of arsenic was studied in cytosolic extracts from high metabolic activity organs of Mus spretus mice: kidneys, liver, and brain. An instrumental coupling of size-exclusion chromatography with UV and collision/reaction cell-ICP-MS detectors (SEC-UV-ICP-ORC-MS) both in analytical and preparative scale was used for this purpose. The results showed the presence of low molecular mass (LMM) molecules linked to arsenic in these tissues especially in the kidneys, where the presence of these arsenic metabolites was higher. On the other hand, the presence of these arsenicals varied from one area to the other, which can be related to a different occurrence of contaminants. These low molecular mass fractions were collected by preparative SEC chromatography for later study with ion exchange chromatography and detection by ICP-ORC-MS, using both anionic and cationic columns. The results showed the higher presence of MMA and DMA in kidneys of mice caught in contaminated areas and the existence of small amounts of unidentified arsenicals when cation-exchange chromatography was used, which could be related to the presence of dimethylarsinoylethanol (DMAE), thioarsenic species, or arsenocholine (AsC).

Arsenic cycling in marine systems: degradation of arsenosugars to arsenate in decomposing algae, and preliminary evidence for the formation of recalcitrant arsenic

Environmental context Despite high levels of complex organoarsenic compounds in marine organisms, arsenic in seawater is present almost entirely as inorganic species. We examine the arsenic products from a marine alga allowed to decompose under simulated natural coastal conditions, and demonstrate a multi-step conversion of organic arsenicals to inorganic arsenic. The results support the hypothesis that the arsenic marine cycle begins and ends with inorganic arsenic. Abstract Time series laboratory experiments were performed to follow the degradation of arsenic compounds naturally present in marine algae. Samples of the brown alga Ecklonia radiata, which contains three major arsenosugars, were packed into 12 tubes open to air at one end only, and allowed to naturally decompose under moist conditions. During the subsequent 25 days, single tubes were removed at intervals of 1–4 days; their contents were cut into four sections (from open to closed end) and analysed for arsenic species by HPLC/ICPMS following an aqueous methanol extraction. In the sections without direct contact with air, the original arsenosugars were degraded primarily to arsenate via two major intermediates, dimethylarsinoylethanol (DMAE) and dimethylarsinate (DMA). The section with direct contact with air degraded more slowly and significant amounts of arsenosugars remained after 25 days. We also report preliminary data suggesting that the amount of non-extractable or recalcitrant arsenic (i.e. insoluble after sequential extractions with water/methanol, acetone, and hexane) increased with time. Furthermore, we show that treatment of the pellet with 0.1-M trifluoroacetic acid at 95°C solubilises a significant amount of this recalcitrant arsenic, and that the arsenic is present mainly as a cationic species of currently unknown structure.

Individual Variability in the Human Metabolism of an Arsenic-Containing Carbohydrate, 2′,3′-Dihydroxypropyl 5-deoxy-5-dimethylarsinoyl-β-d-riboside, a Naturally Occurring Arsenical in Seafood

We report studies on the variability in human metabolism of an oxo-arsenosugar involving the ingestion of a chemically synthesized arsenosugar and quantitative determination of the arsenic metabolites in urine and serum by HPLC coupled with arsenic-selective mass spectrometric detection (ICPMS, inductively coupled plasma mass spectrometry). The total, four-day, urinary excretion of arsenic for six volunteers ranged widely from ca. 4-95%. The arsenic metabolites present in the urine also showed great variability: high arsenic excretion was accompanied by almost complete biotransformation of the ingested oxo-arsenosugar into a multitude of metabolites (>10), whereas the subjects that excreted low amounts of arsenic produced low quantities of metabolites relative to unchanged oxo-arsenosugar and its thio-analogue. Major arsenic urinary metabolites were dimethylarsinate (DMA) and possible intermediates in the degradation of arsenosugar to DMA, namely, dimethylarsinoylethanol (DMAE) and dimethylarsinoylacetate (DMAA) present both as their oxo- and thio-analogues. Thio-DMAE and thio-DMAA were also found in blood serum indicating that these species were formed in the liver rather than on storage of the urine in the bladder. The large variability in the way individuals metabolize arsenosugars has implications for risk assessment of arsenic intake from seafood.

Hydride generation activity of arsenosugars and thioarsenicals

The major arsenosugar compounds have been reported to be hydride-generation-active, however to a lesser extent in comparison with the inorganic arsenicals. We report here for the first time the identity and quantity of the volatile arsenicals generated by As-sugar-SO(3), As-sugar-SO(4), dimethylarsinoyl acetic acid and dimethylarsinoyl ethanol. Only one major volatile compound was identified for all four compounds studied: dimethylarsine. This means that the As-C bond to the longer carbon chain was cleaved during the hydride-generation process. Theoretical calculations at the RHF/6-31G(d,p) ab initio level confirm that this As-C bond is much weaker than the As-CH(3) bonds. Furthermore, it was revealed that the sulphur analogue of dimethylarsinic acid (DMAS ) is hydride-generation-active at pH 7 in contrast to dimethylarsinic acid, despite the fact that arsenic is also pentavalent. This has been substantiated by the calculation of the change in susceptibility of the arsenic towards nucleophilic attack when oxygen is replaced by sulphur. Hence, DMAS can easily be mistaken for a trivalent arsenic species.

Report on three aliphatic dimethylarsinoyl compounds as common minor constituents in marine samples. An investigation using high‐performance liquid chromatography/inductively coupled plasma mass spectrometry and electrospray ionisation tandem mass spectrometry

Three water-soluble aliphatic arsenicals, dimethylarsinoyl acetate (DMAA), dimethylarsinoyl ethanol (DMAE), and dimethylarsinoyl propionate (DMAP), were identified in marine biological samples. Sample extracts in methanol/water (1 + 1) were analysed by cation-exchange high-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICPMS). Eluate fractions from the HPLC/ICPMS analyses containing the compounds in question were collected and subjected to analysis by electrospray ionisation tandem mass spectrometry (ESI-MS/MS), which provided supportive evidence for the structures of the three compounds. The concentrations of the three arsenicals were determined in 37 marine organisms comprising algae, crustaceans, bivalves, fish and mammals by HPLC/ICPMS. The three arsenicals DMAA, DMAE and DMAP, which occurred at microg kg(-1) concentrations, were detected in 25, 23 and 17 of the 37 samples analysed, respectively. The limits of detection were 2-3 microg kg(-1) dry mass. The data illustrate that the three compounds are common minor constituents in marine samples. This is the first report on DMAE and DMAP as naturally occurring species in marine samples. The presence of DMAA and DMAE supports a proposed biosynthesis of arsenobetaine (AB) from dimethylarsinoylribosides. Alternative proposals, which explain the presence of the compounds in marine samples, are addressed briefly in the paper.

Identification of some arsenic species in human urine and blood after ingestion of Chinese seaweed Laminaria

Algae contain high amounts of arsenic in the form of arsenosugars. The metabolism and toxicology of these arsenic species are not yet fully understood. Three sets of experiments have been conducted in which the alga Laminaria was ingested by 2 to 5 healthy volunteers. Total arsenic concentrations in urine and in blood, packed blood cells and serum have been determined using ICP-MS and HGAFS, respectively. Neutron activation analysis was used for the determination of the total arsenic content in algae samples. Speciation analysis of urine and serum samples has been carried out using HPLC-ICP-MS. HPLC-ES-MS/MS has been used for structural confirmation. The stability of the arsenosugars in simulated gastric fluid was studied for both boiled and unboiled seaweed. A maximum level of arsenic in urine appears within 15 to 25 h after ingestion. Total arsenic and speciation analysis revealed no marked increase in arsenic blood, serum and packed cells levels up to 7 h after ingestion. Dimethylarsinic acid (DMA), methylarsonic acid (MA) and dimethylarsinoylethanol (DMAE) have been positively identified in urine sampled after algae intake. Another 5 species remain unknown. In simulated gastric fluid incubated with algae, the larger share of the arsenosugars degrade within a short time span into a compound with a mass of 254 Da.

Metabolism of arsenic by sheep chronically exposed to arsenosugars as a normal part of their diet. 1. Quantitative intake, uptake, and excretion.

Information on the effects of long-term organoarsenical consumption by mammals is limited despite the fact that foodstuffs, especially seafood, often contain organoarsenicals at very high concentrations. Here we evaluate the intake, uptake, and excretion (urine and feces) of arsenic by sheep that live on North Ronaldsay in the Orkney Islands and naturally consume large amounts of arsenosugars through their major food source-seaweed. The sheep eat a broad variety of seaweed species, and arsenic concentrations were determined in all the species observed eaten by the sheep (5.7-74.0 mg kg(-1) dry mass). Because of preference and availability, they feed mostly on the seaweed species found to contain the highest arsenic concentrations: Laminaria digitata and Laminaria hyperborea (74 +/- 4 mg kg(-1) dry mass). To quantify the arsenic intake by the sheep, a feeding experiment reflecting natural conditions as close as possible was set up. In the feeding trial, the average daily intake of arsenic by 12 ewes was 35 +/- 6 mg (97% of water-extractable arsenic was present as arsenosugars) gained from feeding on the two brown algae. To test the possible influence of microflora on the metabolism of arsenosugars, six of the sheep were adapted to feeding on grass for 5 months before the start of the trial (control sheep), and the remaining six sheep were kept on their normal seaweed diet (wild sheep). No significant difference in seaweed/arsenic intake and arsenic excretion was found between the two groups of sheep. The arsenic excreted in the feces represents 13 +/- 10% (n = 12) of the total consumed, and on the assumption of that, the average urinary excretion is estimated to 86%.The main arsenic metabolite excreted in urine was dimethylarsinic acid (DMA(V)) (60 +/- 22%) and minor amounts of dimethylarsinoylethanol (DMAE), methylarsonic acid (MA(V)),tetramethylarsonium ion (TMA+), and arsenate (As(V)) together with seven unknown arsenic compounds were also excreted. The urinary arsenic excretion pattern showed a lag period (>4 h) before significant quantities appeared in the urine, an excretion rate that peaked between 4 and 28 h after seaweed intake and a relatively slow half-life (17 h) after end of intake.

Arsenic metabolism in seaweed-eating sheep from Northern Scotland.

Cation exchange and anion exchange liquid chromatography were coupled to an ICP-MS and optimised for the separation of 13 different arsenic species in body fluids (arsenite, arsenate, dimethylarsinic acid (DMAA), monomethylarsonic acid (MMAA), trimethylarsine oxide (TMAO), tetramethylarsonium ion (TMA), arsenobetaine (AsB), arsenocholine (AsC), dimethylarsinoyl ethanol (DMAE) and four common dimethylarsinoylribosides (arsenosugars). The arsenic species were determined in seaweed extracts and in the urine and blood serum of seaweed-eating sheep from Northern Scotland. The sheep eat 2-4 kg of seaweed daily which is washed ashore on the most northern Island of Orkney. The urine, blood and wool of 20 North Ronaldsay sheep and kidney, liver and muscle from 11 sheep were sampled and analysed for their arsenic species. In addition five Dorset Finn sheep, which lived entirely on grass, were used as a control group. The sheep have a body burden of approximately 45-90 mg arsenic daily. Since the metabolism of arsenic species varies with the arsenite and arsenate being the most toxic, and organoarsenic compounds such as arsenobetaine the least toxic compounds, the determination of the arsenic species in the diet and their body fluids are important. The major arsenic species in their diet are arsenoribosides. The major metabolite excreted into urine and blood is DMAA (95 +/- 4.1%) with minor amounts of MMAA, riboside X, TMA and an unidentified species. The occurrence of MMAA is assumed to be a precursor of the exposure to inorganic arsenic, since demethylation of dimethylated or trimethylated organoarsenic compounds is not known (max. MMAA concentration 259 microg/L). The concentrations in the urine (3179 +/- 2667 microg/L) and blood (44 +/- 19 microg/kg) are at least two orders of magnitude higher than the level of arsenic in the urine of the control sheep or literature levels of blood for the unexposed sheep. The tissue samples (liver: 292 +/- 99 microg/kg, kidney: 565 +/- 193 microg/kg, muscle: 680 +/- 224 microg/kg) and wool samples (10470 +/- 5690 microg/kg) show elevated levels which are also 100 times higher than the levels for the unexposed sheep.