Arsenic-containing ribofuranosides and dimethylarsinic acid in green seaweed,Codium fragile

Three water-soluble arsenic compounds were isolated from the green seaweed Codium fragile. These compounds were identified as 1-glycerophosphoryl-2-hydroxy-3-[5′-deoxy-5′-(dimethylarsinoyl)-β-ribofuranosyloxy]propane (1a), 1′ -(1,2-dihydroxypropyl)-5′ -deoxy-5′ -(dimethylarsinoyl)-β-ribofuranoside (1b), and dimethylarsinic acid ((CH₃)₂AsOOH). The structures of these compounds were ascertained by ¹H NMR spectroscopy. Compounds 1a and 1b accounted for 60 % and dimethylarsinic acid for 5% of the water-soluble arsenic.     

Structural studies of spiroarsoranes derived from 2-aminophenols

This paper describes the structural studies of 2-phenyl-9,9′-dimethyl-2,2′-spirobis(1,3,2-λ⁵-benzoxazarsoline) 5, 2-phenyl-8,8′-dimethyl-2,2′-spirobis(1,3,2-λ⁵-benzoxazarsoline) 6 by ¹H,¹³C,¹⁵N NMR in [²H₆]DMSO and CDCl₃. The solid state studies were made by X-ray experiments. Infrared spectroscopy was obtained in CDCl₃ and the vibrational signals were assigned using DFT calculations. The nature of the As–N, As–C and As–O bonds in these compounds was established by NBO studies.     

Comparison of mild extraction procedures for determination of plant-available arsenic compounds in soil

In this work three mild extraction agents for determination of plant-available fractions of elements in soil were evaluated for arsenic speciation in soil samples. Pepper (Capsicum annum, L.) var. California Wonder was cultivated in pots, and aqueous solutions of arsenite, arsenate, methylarsonic acid, and dimethylarsinic acid, at a concentration of 15 mg As kg^–1 soil, were added at the beginning of the experiment. Control pots (untreated) were also included. Deionized water, 0.01 mol L^–1 CaCl₂, and 0.05 mol L^–1 (NH₄)₂SO₄ were used to extract the plant-available fraction of the arsenic compounds in soil samples collected during the vegetation period of the plants. Whereas in control samples the extractable arsenic fraction did not exceed 1% of total arsenic content, soil amendment by arsenic compounds resulted in extraction of larger amounts, which varied between 1.4 and 8.1% of total arsenic content, depending on soil treatment and on the extracting agent applied. Among arsenic compounds determined by HPLC–ICPMS arsenate was predominant, followed by small amounts of arsenite, methylarsonic acid, and dimethylarsinic acid, depending on the individual soil treatment. In all the experiments in which methylarsonic acid was added to the soil methylarsonous acid was detected in the extracts, suggesting that the soil bacteria are capable of reducing methylarsonic acid before a further methylation occurs. No significant differences were observed between analytical data obtained by using different extraction procedures.     

Gas generation and preconcentration coupled to gas phase molecular absorption spectrometry: a powerful tool for the simultaneous determination of analytes forming volatile compounds

Different methods for a simultaneous determination of several analytes forming volatile compounds at room temperature are described. The main steps of these methods are: continuous generation, collection in a cryogenic trap, revolatilization, measurement of the volatile compounds by Gas Phase Molecular Absorption Spectrometry and resolution by multi-wavelength methods. Several mixtures containing 2, 3 or 4 components have been studied: 1) elements forming covalent hydrides; 2) arsenic organometallic compounds forming volatile gases with a similar structure to arsine; and 3) sulphur species that can evolve volatile compounds. Under the optimum conditions obtained for each mixture, detection limits range from 0.8 ng/mL (dimethylarsinic acid) to 2 g/mL (SCN^-).     

Gas generation and preconcentration coupled to gas phase molecular absorption spectrometry: a powerful tool for the simultaneous determination of analytes forming volatile compounds

Different methods for a simultaneous determination of several analytes forming volatile compounds at room temperature are described. The main steps of these methods are: continuous generation, collection in a cryogenic trap, revolatilization, measurement of the volatile compounds by Gas Phase Molecular Absorption Spectrometry and resolution by multi-wavelength methods. Several mixtures containing 2, 3 or 4 components have been studied: 1) elements forming covalent hydrides; 2) arsenic organometallic compounds forming volatile gases with a similar structure to arsine; and 3) sulphur species that can evolve volatile compounds. Under the optimum conditions obtained for each mixture, detection limits range from 0.8 ng/mL (dimethylarsinic acid) to 2 microg/mL (SCN(-)).     

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 μg/L). The concentrations in the urine (3179 ± 2667 μg/L) and blood (44 ± 19 μg/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 μg/kg, kidney: 565 ± 193 μg/kg, muscle: 680 ± 224 μg/kg) and wool samples (10 470 ± 5690 μg/kg) show elevated levels which are also 100 times higher than the levels for the unexposed sheep. Received: 29 February 2000 / Revised: 26 April 2000 / Accepted: 1 May 2000     

Organoarsenic compounds in plants and soil on top of an ore vein

Plants and soil collected above an ore vein in Gasen (Austria) were investigated for total arsenic concentrations by inductively coupled plasma mass spectrometry (ICP‐MS). Total arsenic concentrations in all samples were higher than those usually found at non‐contaminated sites. The arsenic concentration in the soil ranged from ∼700 to ∼4000 mg kg⁻¹ dry mass. Arsenic concentrations in plant samples ranged from ∼0.5 to 6 mg kg⁻¹ dry mass and varied with plant species and plant part. Examination of plant and soil extracts by high‐performance liquid chromatography–ICP‐MS revealed that only small amounts of arsenic (<1%) could be extracted from the soil and the main part of the extractable arsenic from soil was inorganic arsenic, dominated by arsenate. Trimethylarsine oxide and arsenobetaine were also detected as minor compounds in soil. The extracts of the plants (Trifolium pratense, Dactylis glomerata, and Plantago lanceolata) contained arsenate, arsenite, methylarsonic acid, dimethylarsinic acid, trimethylarsine oxide, the tetramethylarsonium ion, arsenobetaine, and arsenocholine (2.5–12% extraction efficiency). The arsenic compounds and their concentrations differed with plant species. The extracts of D. glomerata and P. lanceolata contained mainly inorganic arsenic compounds typical of most other plants. T. pratense, on the other hand, contained mainly organic arsenicals and the major compound was methylarsonic acid. Copyright © 2002 John Wiley & Sons, Ltd.     

Methylation of inorganic arsenic by arsenic-tolerant freshwater algae

Five arsenic-resistant freshwater algae which had been isolated from an arsenic-polluted environment were studied for the biotransformation of arsenic compounds accumulated by them from the aqueous phase. The algal cells bioaccumulating arsenic were digested by 2 mol dm^?3 NaOH at 95°C, the As? C bonds except for As? CH₃ were cleaved by the treatment and the methylated arsenic compounds were reduced to the corresponding arsines by sodium borohydride (hydride generation). The arsines were chromatographically separated on the basis of their boiling-point difference and determined by atomic absorption spectrophotometry. Methylated arsenic compounds were found in all algal cells. The predominant arsenic species in the cells, however, were non-methylated arsenic compounds which were mainly present in the residue of a chloroform–methanol extract. The non-methylated arsenic compounds were found to be not present in the free inorganic arsenic substrate and to be bound strongly with proteins or polysaccharides in the cells. Methylated arsenic compounds were found mainly in the lipid-soluble fractions and the major form was a dimethylarsenic compound. Trimethyl- and monomethyl-arsenic compounds were detected but at very low level. The dimethylarsinic acid was not present in the free form in the lipid-soluble fraction and should be bound with a lipid molecule. It was also found that the accumulation of arsenic by Nostoc occurred only in living cells.     

Decomposition of organoarsenic compounds for total arsenic determination in marine organisms by the hydride generation technique

The conditions necessary for the complete decomposition of six organic arsenic compounds, namely methylarsonic acid (MMAA), dimethylarsinic acid (DMAA), trimethylarsine oxide, tetramethylarsonium iodide, arsenocholine bromide (AsC) and arsenobetaine (AB), were investigated. The degree of decomposition of the arsenic compounds was monitored using a hydride generation (HYD) technique, because the response from this system depends strongly on the chemical species of arsenic, with inorganic arsenic (the expected product from these decomposition experiments) giving a much more intense HYD signal than the organic arsenic compounds. The arsenic compounds were decomposed by heating them with three types of acid mixture, namely HNO₃? HClO₄, HNO₃? HClO₄? HF, or HNO₃? HClO₄? H₂SO₄. Both MMAA and DMAA were decomposed completely using any of the mixed acids at a decomposition temperature of 200 °C or higher. The HNO₃? HClO₄? H₂SO₄ mixture was the most effective for decomposing AsC and AB, which are the most difficult compounds among all types of organic arsenic compound to decompose and render inorganic. The complete decomposition of AB was only achieved, however, when the temperature was 320 °C or higher, and the sample was evaporated to dryness. When the residue from this treatment was examined by high‐performance liquid chromatography combined with inductively coupled plasma atomic emission spectrometry, all of the arsenic was found to be present as arsenic(V). The optimized conditions (HNO₃? HClO₄? H₂SO₄ at 320 °C) for decomposing AB were then used to determine the total amount of arsenic in marine organisms known to contain AB. Copyright © 2005 John Wiley & Sons, Ltd.     

Biomethylation and biotransformation of arsenic in a freshwater food chain: Green alga (chlorella vulgaris)→shrimp (neocaridina denticulata)→killifish (oryzias iatipes)

Tolerance, bioaccumulation, biotransformation and excretion of arsenic compounds by the fresh–water shrimp (Neocaridina denticulata) and the killifish (Oryzias latipes) (collected from the natural environment) were investigated. Tolerances (LC₅₀) of the shrimp against disodium arsenate [abbreviated as As(V)], methylarsonic acid (MAA), dimethylarsinic acid (DMAA), and arsenobetaine (AB) were 1.5, 10, 40, and 150μg As ml^?1, respectively. N. denticulata accumulated arsenic from an aqueous phase containing 1 μg As ml^?1 of As(V), 10 μg As ml^?1 of MAA, 30 μg As ml^?1 of DMAA or 150 μg As ml^?1 of AB, and biotransformed and excreted part of these species. Both methylation and demethylation of the arsenicals were observed in vivo. When living N. denticulata accumulating arsenic was transferred into an arsenic–free medium, a part of the accumulated arsenic was excreted. The concentration of methylated arsenicals relative to total arsenic was higher in the excrement than in the organism. Total arsenic accumulation in each species via food in the food chain Green algae (Chlorella vulgaris) → shrimp (N. denticulata) → killifish (O. latipes) decreased by one order of magnitude or more, and the concentration of methylated arsenic relative to total arsenic accumulated increased successively with elevation in the trophic level. Only trace amounts of monomethylarsenic species were detected in the shrimp and fish tested. Dimethylarsenic species in alga and shrimp, and trimethylarsenic species in killifish, were the predominant methylated arsenic species, respectively.     

Application of microwave digestion to the preparation of sediment samples for arsenic speciation

Several extraction procedures are described allowing arsenic speciation in sediments. The extraction of organometallic compounds such as dimethylarsinic acid or monomethylarsonic acid is quite simple since these compounds are stable in the different extraction media (HCl/ HNO₃, H₃PO₄, ammonium oxalate) and are easily released independent of the extraction mode (magnetic stirring or microwave solubilization). Extraction yields are higher than 96% for these two arsenic forms. An HCl/HNO₃ microwave solubilization procedure allows the quantitative solubilization of mineral arsenic, but the differentiation between the two oxidation states is not possible owing to the oxidation of As(III) to As(V). Extractions with orthophosphoric acid or ammonium oxalate allow the solubilization of mineral arsenic with extraction yields ranging from 90 to 95% and the differentiation between As(III) and As(V). Nevertheless, the amount of As(III) is underestimated owing to its partial oxidation. The usefulness and advantages of microwave solubilization compared with conventional extraction procedures are discussed. Received: 17 May 1996 / Revised: 19 September 1996 / Accepted: 25 September 1996     

Bioaccumulation and excretion of arsenic compounds by a marine unicellular alga,polyphysa peniculus

Polyphysa peniculus was grown in artificial seawater in the presence of arsenate, arsenite, monomethylarsonate and dimethylarsinic acid. The separation and identification of some of the arsenic species produced in the cells as well as in the growth medium were achieved by using hydride generation–gas chromatography–atomic absorption spectrometry methodology. Arsenite and dimethylarsinate were detected following incubation with arsenate. When the alga was treated with arsenite, dimethylarsinate was the major metabolite in the cells and in the growth medium; trace amounts of monomethylarsonate were also detected in the cells. With monomethylarsonate as a substrate, the metabolite is dimethylarsinate. Polyphysa peniculus did not metabolize dimethylarsinic acid when it was used as a substrate. Significant amounts of more complex arsenic species, such as arsenosungars, were not observed in the cells or medium on the evidence of flow injection–microwave digestion–hydride generation–atomic absorption spectrometry methodology. Transfer of the exposed cells to fresh medium caused release of most cell–associated arsenicals to the surrounding environment.     

The metabolism of methylarsine oxide and sulfide

Methylarsine oxide and sulfide are more toxic to Candida humicola than arsenite; the sulfide is rapidly metabolized to trimethylarsine (Me₃As) and methylarsine (MeAsH₂) and the oxide to dimethylarsinic acid [Me₂AsO(OH)]. Cell-free extracts of C. humicola also convert the oxide to Me₂AsO(OH). The glutathione (RSH) derivative Me₂AsSR is metabolized by C. humicola to Me₃As and Me₂AsH, but some other Me₂AsSR′ compounds are unaffected. Studies involving the interaction of the arsenic(III) compounds with natural ecosystems and other micro-organisms such as Scopulariopsis brevicaulis, Straptococcus sanguis, Escherichia coli, and Veillonella alcalescens are described.     

Application of microwave digestion to the preparation of sediment samples for arsenic speciation

Several extraction procedures are described allowing arsenic speciation in sediments. The extraction of organometallic compounds such as dimethylarsinic acid or monomethylarsonic acid is quite simple since these compounds are stable in the different extraction media (HCl/ HNO₃, H₃PO₄, ammonium oxalate) and are easily released independent of the extraction mode (magnetic stirring or microwave solubilization). Extraction yields are higher than 96% for these two arsenic forms. An HCl/HNO₃ microwave solubilization procedure allows the quantitative solubilization of mineral arsenic, but the differentiation between the two oxidation states is not possible owing to the oxidation of As(III) to As(V). Extractions with orthophosphoric acid or ammonium oxalate allow the solubilization of mineral arsenic with extraction yields ranging from 90 to 95% and the differentiation between As(III) and As(V). Nevertheless, the amount of As(III) is underestimated owing to its partial oxidation. The usefulness and advantages of microwave solubilization compared with conventional extraction procedures are discussed. Received: 17 May 1996 / Revised: 19 September 1996 / Accepted: 25 September 1996     

Metabolomics of arsenic based on speciation studies

Biomedical research on arsenic can be divided into three steps, i.e., speciation of the entirety of arsenic in a biological system (metallome), examination of the metabolism of arsenic based on the speciation of metallome (metabolomics), and examination of the metallomics underlying the mechanism that triggers biological/physiological/toxicological effects based on the metabolomics. In the present communication, the metabolic pathway for inorganic arsenic, a known human carcinogen, was explained based on current results of speciation. In addition to the consecutive reduction and oxidative methylation reactions converting inorganic arsenicals to the major urinary metabolite dimethylarsinic acid, the role of the conjugation reaction involving glutathione resulting in excretion from the liver was discussed. Furthermore, sulfur-containing arsenicals (thioarsenicals) identified as new metabolites in the livers of rats were characterized chemically and metabolically.     

Methyl transfer from a hydrophobic vitamin B12 derivative to arsenic trioxide

The methylation reaction of arsenic trioxide conducted at 37 °C and pH 7.0 for 24 h using hydrophobic methylated vitamin B₁₂, (methyl) (aquo) heptamethylcobyrinate perchlorate, CH₃B₁₂ ester, as a methyl donor in the presence of reduced glutathione (GSH) yielded monomethylarsonous acid (MMA), dimethylarsinic acid (DMA), and trimethylarsine oxide (TMAO) as products with a methylation rate over 95%. In contrast, when methylcobalamin (CH₃B₁₂) was used as the methyl donor, only MMA and DMA were produced and the methylation rate dropped to around 20%. Reductive demethylation of a methyl-corrinoid coordination complex mediated by GSH is suggested as a mechanism of methyl transfer to arsenic trioxide. The differences observed for different corrinoid coordination complexes with respect to the reactivity of methyl transfer to arsenic is ascribable to differences inherent in the base-on (CH₃B₁₂) and base-off (CH₃B₁₂ ester) natures of the compounds.     

Arsenic speciation in hair extracts

Ingested arsenic is known to be not only excreted by urine, but to be stored in sulphydryl-rich tissue like hair, nail or skin. We developed an extraction method for arsenic species from these tissues and studied the stability of different arsenic species during the extraction process. Inorganic and pentavalent methylated arsenic was found to be stable under the extraction conditions, whereas trivalent methylated arsenicals and the thio-analogue of DMA^V (DMAS) showed reduced stability. The absorption ability of hair for these different species was studied as well. Inorganic arsenic is better absorbed by hair than monomethyl- or dimethyl-arsenicals, whereby the trivalent forms are taken up better than the pentavalent forms. Independent of which methylated arsenical was used for the incubation, the pentavalent form was always the dominant form after extraction. Hair and nail samples from humans suffering from chronic arsenic intoxication contained dominantly inorganic arsenic with small and strongly varying amounts of DMA^V and MA^V present. DMAS was only found in some nail sample extracts containing unusually high amounts of DMA^V and is believed to be formed during the extraction process.     

Determination of ‘arsenosugars’ in algae with anion-exchange chromatography and an inductively coupled plasma mass spectrometer as element-specific detector

The retention behavior of four naturally occurring dimethylarsinoylribosides with –CH₂-CHOH-CH₂X (X = OH, HO₃POCH₂CHOHCH₂OH, SO₃H, OSO₃H) as aglycones, of arsenous acid, arsenic acid, methylarsonic acid, and dimethylarsinic acid was investigated on a Hamilton PRP-X100 anion-exchange column with aqueous solutions of ammonium dihydrogen phosphate (20 mmol/L) in the pH range of 3.8–9.0 as mobile phase. A HP 4500 inductively coupled plasma mass spectrometer (ICP-MS) served as arsenic-specific detector. The influence of pH, temperature, and the concentration of methanol in the mobile phase on the retention times of these arsenic compounds was explored. An aqueous 20 mM ammonium dihydrogen phosphate solution at pH 5.6 at a column temperature of 40?°C was considered optimal as it allowed ¶the separation of seven of the arsenic compounds within 16 min. Only arsenous acid and the ribose with the glycerol aglycone have overlapping signals with both migrating almost with the solvent front. At a concentration of 0.50 ng As mL^–1 the relative standard deviations (n = 3) of the signal areas of the eight arsenic compounds was in the range from 3.5 to 8.1%. The linear calibration curves (peak areas) from 0.5 to 10 ng/mL had correlation coefficients ¶> 0.997. Extracts obtained from the brown algae Fucus spiralis and Halidrys siliquosa were chromatographed under the optimized conditions. Both species contained the sulfate riboside as the major arsenic compound (～55% of total extractable arsenic) together with the sulfonate- and phosphate riboside. Arsenic acid was a significant constituent of Halidrys siliquosa (～6.5%), but was not detected in Fucus spiralis.     

Ascorbic Acid/Iodine and Triphenylphosphine/Iodine as Reducing Agents for the As(V)[dbnd]O Group

The scope of ascorbic acid/iodine and triphenylphosphine/iodine in methanol for the direct reduction of arsenic(V) compounds having the As[dbnd]O group has been investigated. Ascorbic acid/iodine reduces arsonic acids, diphenylarsinic acid (but not dimethylarsinic acid), and triphenylarsine oxide. The rates of reduction depend on the electronic effects of the ligands bound to arsenic and on the hydrogen-bonding strength of the species, when present. When the As(V) compound has an [sbnd]NH ₂ or an [sbnd]NH ₃ ⁺ group, the reduction product reacts with a ketonic form of dehydroascorbic acid, giving condensation product(s). Triphenylphosphine/iodine reduced slowly the zwitterionic o-aminophenylarsonic acid but reduced faster the hydrochloric acid salt of the same acid. It reduced dimethylarsinic acid as well because the powerful electron-withdrawing Ph ₃ P ⁺coordinated to As[dbnd]O seems to outweigh the electronic and hydrogen bonding effects.     

Analysis of the products of thermal decomposition of an aromatic polyamide fabric

The thermal degradation of an aromatic polyamide was studied under conditions of pyrolysis and oxidative degradation at 550°C and of flaming combustion. Techniques described elsewhere were used to determine the volatile compounds quantitatively by gas chromatography-mass spectrometry (GC–MS). The condensible material and the solid residue were characterized by infrared spectroscopy and MS, and in pyrolysis experiments 28 compounds were identified (CO, CO₂, H₂O, and C₆H₅CN were the primary products). Collectively, these compounds accounted for 79% of the sample weight loss. The remaining 21% was a condensible material that contained at least 17 compounds; the two major components were 1,3-dicyanobenzene and 3-cyanobenzoic acid. Most of the nitrogen content of the polymer remained as involatile residue. This study was sufficiently detailed to obtain a mass balance between the composition of the original polymer and the sum of the observed pyrolysis products. The major products observed in pyrolysis experiments supported a mechanism that involved the cleavage of an aromatic-NH bond and the loss of H₂O to form aromatic nitriles. Hydrolysis of the amide linkage, followed by decarboxylation of the product acid, accounted for the high concentrations of CO₂ observed. Oxidative degradation at 450°C yielded ten identifiable compounds and an additional 19 volatile compounds were formed at 550°C. The condensible fraction, which contained at least 20 compounds, was similar in composition to the fraction collected from the pyrolysis experiments. The sum of the carbon content from the two major volatile products of oxidative degradation (CO and CO₂) and from the solid residue quantitatively accounted for the carbon content in the original sample. Flaming combustion studies revealed a markedly different product distribution than was observed under nonflaming conditions, especially in regard to the higher-molecular-weight species.