The methylation of arsenic in marine sediments

Laboratory studies have shown that microorganisms present in both natural marine sediments and sediments contaminated with mine-tailings are capable of methylating arsenic under aerobic and anaerobic conditions. Incubation of sediments with culture media produced volatile arsines [including AsH₃, (CH₃)AsH₂, and (CH₃)₃As] as well as the methylarsenic(V) compounds (CH₃)_nAs(O) (OH)_3?n (n = 1, 2, 3). The concentration of the arsines increased and then decreased in a growth and decay pattern reminiscent of the methylation and demethylation of mercury. Thus, arsenic speciation varied with time, being controlled by the biochemical activity of the dominant microbe(s) at the time of sampling, and changing in response to the ecological succession within the microbial community. The analysis of the interstitial waters of sediments collected from several British Columbia (Canada) coastal sites gave results that were consistent with the culture experiments, in that the methylarsenicals were ubiquitous, but present only in small amounts. It is estimated that methylarsenic(V) species account for less than 1% of the arsenic present in porewaters. The actual proportion was dependent on a number of factors but, contrary to prevailing viewpoints, there was no relationship to the organic content of the sediments, nor did methylation occur only in the presence of high arsenic concentrations. Instead, all of the evidence was consistent with in situ microbial methylation and demethylation processes that are similar to the arsenic transformations that occur in soil ecosystems. The results are discussed in terms of the cycling of arsenic in the marine environment and within the marine food web.     

Determination of arsenic and arsenic compounds in natural gas samples

Organic arsenic compounds (trialkylarsines) present in natural gas were extracted by 10 cm³ of concentrated nitric acid from 1 dm³ of gas kept at ambient pressure and temperature. The flask containing the gas and the acid was shaken for 1 h on a platform shaker set at the highest speed. The resulting solution was mixed with concentrated sulfuric acid and heated to convert all arsenic compounds to arsenate. Total arsenic was determined in the mineralized solutions by hydride generation. The arsenic concentrations in natural gas samples from a number of wells in several gas fields were in the range 0.01–63 μ As dm^?3. Replicate determinations of arsenic in a gas sample with an arsenic concentration of 5.9 μ dm^?3 had a relative standard deviation of 1.7%. Because of the high blank values, the lowest arsenic concentration that could be reliably determined was 5 ng As dm^?3 gas. Analysis of nonmineralized extracts by hydride generation identified trimethylarsine as the major arsenic compound in natural gas. Low-temperature gas chromatography-mass spectrometry showed more directly than the hydride generation technique, that trimethylarsine accounts for 55–80% of the total arsenic in several gas samples. Dimethylethylarsine, methyldiethylarsine, and triethylarsine were also identified, in concentrations decreasing with increasing molecular mass of the arsines.     

Distribution of inorganic arsenic and methylated arsenic in marine organisms

Inorganic arsenic and methylated arsenic compounds in 60 specimens of marine organisms were investigated by hydride generation derivatization and cold-trap gas chromatography–mass spectrometry (GC MS). Chloroform–methanol extracts from seaweeds, shellfish, fish, crustaceans and other marine organisms were separated into water-soluble and lipid-soluble fractions. The arsenic compounds in each fraction were identified and analysed as arsine, methylarsine, dimethylarsine and trimethylarsine. Trimethylarsenic compounds were distributed mainly in the water-soluble fraction of muscle of carnivorous gastropods, crustaceans and fish. The amounts of dimethylated arsenic compounds were found to be larger than that of trimethylated arsenic in the lipid-soluble fraction of fish viscera. Dimethylated arsenic compounds were distributed in the water-soluble fraction of Phaeophyceae.     

Arsenic speciation in water samples containing high levels of copper: removal of copper interference affecting arsine generation by continuous flow solid phase chelation

A simple continuous flow method is proposed to eliminate copper interference in arsenic speciation by hydride generation, based on the selective retention of this interfering ion in an iminodiacetate chelating resin previous to the hydride generation process. The arsines generated were cold trapped and measured by ICP/OES. The proposed method allows about 98% of the copper present in the samples to be removed. Minor co-retention of As(V) was observed as a result of electrostatic interaction between the arsenate anion and the nitrogen of the iminodiacetate group of the chelating resin Muromac A-1, the charge distribution of which is modified when copper is chelated. The species As(III), MMA and DMA were not retained in the microcolumn, probably because these species are mainly in the molecular form at the working pH value (4.5). In synthetic samples containing 50 g l^–1 of each arsenic species together with 100 mg l^–1 copper, the recoveries obtained were: As(V) 97.6%, As(III) 100%, MMA 99.8%, and DMA 99.9%. The method was applied to arsenic speciation in river water samples containing high levels of copper.     

Über cyclische tertiäre Arsine und sekundäre Arsenoxide

α,ω-Alkane-bis-diphenylarsines and -dimethylarsines, R₂AsC_nH_2nAsR₂, may be obtained from dichloroalkanes and sodium diorganyl-arsenides, R₂AsNa. The latter are prepared from tetraphenyl- and tetramethyl-diarsenic-sulphide, respectively, (R₂As)₂S. Elemental sodium eliminates on each As atom of the tetraphenyl-diarseno-alkanes one phenyl group, and on oxidation α,ω-alkane-diphenylarsenic acids are obtained. Reduction of these acids by means of SO₂ yields cyclic, secondary arsenic oxides, whereas H₃PO₂ gives cyclic arsines with As ? As bonds. Disodium-phenylarsenide, C₆H₅AsNa₂, prepared from (C₆H₅AsS)₄, reacts with longer dichloroalkanes to form cyclic tertiary phenylarsines which may contain, in addition to As, further heteroatoms such as N, O or S. Those arsines, which only contain carbon as the ring atoms, commutate with AsCl₃ to 1-chloro-arsolane and 1-chloroarsenane.     

Oxidative addition of substituted arsines and stibines with bis(trifluoromethyl)nitroxyl

Reactions of bis(trifluoromethyl)nitroxyl with a number of methyl- and trifluoromethyl- substituted arsines and stibines at room temperature lead to the formation of pentavalent arsenic and antimony derivatives, namely (CH₃)_3?n(CF₃)_nM[ON(CF₃)₂]₂ (M = As, n = 0, 1, 2; M = Sb, n = 0, 1). The derivatives yield bis(trifluoromethyl)- hydroxylamine and the corresponding dichlorides on treatment with hydrogen chloride. A free radical mechanism is proposed for the oxidative addition reactions.     

HPLC-ICP-MS for a comparative study on the extraction approaches for arsenic speciation in terrestrial plant, Ceratophyllum demersum

For the determination of arsenic compounds in terrestrial plant samples, a crucial step is the efficient extraction of arsenic from the solid plant matrix. However, the use of methanol-water extraction often resulted in low extraction efficiencies of less than 50%. In this study, eight solid-liquid extraction procedures (mainly based on mechanical mixing and sonication) were evaluated for the recovery of arsenic species from a submerged freshwater plant, coontail (Ceratophyllum demersum), collected in Moira River, Ontario, Canada. Speciation of As in the extracts was carried out with both anion-, and cation-exchange HPLC with sector-field inductively coupled plasma mass spectrometric (SF-ICP-MS) detection. The results obtained depended critically on the extraction solvents used in different extraction procedures. Extraction with methanol-water led only to 9%–44% recoveries of As. A high extraction yield (approximately 82%) was obtained by water extraction. Alkaline hydrolysis also resulted in high extraction efficiencies (86%–98%), but severe oxidation of As(III) to As(V) was observed. A protease enzymatic extraction led to a recovery of 48%. Approximately 0.5% of the total As in the plant sample was lipid-soluble. It was found that the extraction of inorganic arsenic species was suppressed by the presence of methanol in the extraction solvents, while high content of methanol in the extraction solvents was effective for the extraction of organic arsenic species. Therefore, it is recommended to perform the extraction both with water alone and with methanol-water (9+1, v/v), in order to obtain the complete As species profile in terrestrial plants.     

C−As Bond Formation Reactions for the Preparation of Organoarsenic(III) Compounds

Potential widespread applications of organoarsenic chemistry have been limited by the inherent lack of safe and effective As?C bond formation reactions. Several alternative reagents and methods have been developed in the last few decades to address the hazards and drawbacks associated with traditional arsenic synthetic strategies. Herein, this minireview summarizes the advances made in nucleophilic, electrophilic, radical and metal‐mediated As(III)?C bond formations while specifically highlighting the behavior of arsenic synthons with various well‐established reagents (eg. Grignard reagents, organolithium compounds, organometallic reagents, radical initiators and Lewis/Brønsted bases). Avenues for asymmetric synthesis are also discussed, as are recent advances in organoarsenic chemistry suggesting that arsines exhibit novel reactivities independent from that of other relatively more well explored Group V cogeners.     

液态石油烃的脱砷及砷化物与亚铜探针的相互作用

采用密度泛函理论B3LYP方法, 在6-311+G(2df,2p)基组水平上研究了液态石油烃体系中甲基胂化合物与过渡金属探针Cu+和CuCl的相互作用. 结果表明, 甲基胂化物与亚铜离子作用的最稳定模式为四面体构型, 随着烃基取代数增加, 砷化物同Cu+或CuCl的相互作用能(E0)更负, 配合物更稳定, 同时二者的相互作用轨道的能级差(△E)与E0值线性相关(R2≥0.99). Cu+配合物中, As—Cu成键轨道向C—As和/或H—As反键轨道形成电子反馈, 但是CuCl配合物中类似电子反馈则没有形成. 烃基取代并不降低活性组分对砷化物的吸附活性, 在活性组分满足砷化物选择性吸附的条件下, 液态石油烃脱砷的主要控制因素为砷化物在脱砷剂内部孔道中的扩散传输. 有机硫化物噻吩并不影响砷化物的选择性吸附分离, 硫醇类化合物则会影响单烷基砷化物的选择性吸附. 在进行脱砷剂开发时, 应拓宽载体孔道以提高流体传输效率, 并选择活性相组分与砷化物作用的△E相对较小, 配合物容易形成电子反馈, 且对硫醇类化合物的作用能力相对较弱, 对单烷基砷化物的作用能力相对较强的过渡金属组分.     

One pot synthesis from the elements of symmetrical and unsymmetrical triaryl-phospines, -arsines and -stibines by the SRN1 mechanism

The reactions of elemental phosphorus, arsenic and antimony with sodium metal in liquid ammonia form “M^?1“ species that react with haloarenes under irradiation to form symmetrical triaryl derivatives of these metals by the S_RN1 mechanism in fair to good yields. Further reaction with sodium metal gives a derivative nucleophile (diarylphosphide and diarylarsenide ions) that reacts with another haloarene under irradiation to form unsymmetrical phosphines and arsines.     

Determination of inorganic arsenic and organic arsenic compounds in marine organisms by hydride generation/cold trap/gas chromatography— mass spectrometry

The behavior of arsenite, methylarsonic acid, dimethylarsinic acid, trimethylarsine oxide, dimethyl-R-arsine oxides, and trimethyl-R-arsonium compounds (R = carboxymethyl, 2-carboxyethyl, 2-hydroxyethyl) toward sodium borohydride and hot aqueous sodium hydroxide was investigated. The arsines obtained by sodium borohydride reduction of the undigested and digested solutions were collected in a liquid-nitrogen cooled trap, separated with a gas chromatograph, and detected with a mass spectrometer in the selected-ion-monitoring mode. The investigated arsenic compounds were stable in hot 2 mol dm^?3 sodium hydroxide except arsenobetaine [trimethyl(carboxymethyl)arsonium zwitterion] that was converted to trimethylarsine oxide, and dimethyl(ribosyl)arsine oxides that were decomposed to dimethylarsinic acid. Hydride generation before and after digestion of extracts from marine organisms allowed inorganic arsenic, methylated arsenic, arsenobetaine, and ribosyl arsenic compounds to be identified and quantified. This method was applied to extracts from shellfish, fish, crustaceans, and seaweeds.     

Arsenic Compounds in Terrestrial Organisms I: Collybia maculata,Collybia butyracea and Amanita muscaria from Arsenic Smelter Sites in Austria

Three mushroom species from two old arsenic smelter sites in Austria were analyzed for arsenic compounds. The total arsenic concentrations were determined by ICP–MS. Collybia maculata contained 30.0 mg, Collybia butyracea 10.9 mg and Amanita muscaria 21.9 mg As kg⁻¹ dry mass. The arsenic compounds extracted with methanol/water (9:1) from the dried mushroom powders were separated by HPLC on anion-exchange and reversed-phase columns and detected by ICP-MS using a hydraulic high-pressure nebulizer. In Collybia maculata almost all arsenic is present as arsenobetaine. Collybia butyracea contained mainly arsenobetaine (8.8 mg As kg⁻¹ dry mass) and dimethylarsinic acid (1.9 mg As kg⁻¹). Amanita muscaria contained arsenobetaine (15.1 mg As kg⁻¹), traces of arsenite, dimethylarsinic acid and arsenate, and surprisingly arsenocholine (2.6 mg As kg⁻¹) and a tetramethylarsonium salt (0.8 mg As kg⁻¹). © 1997 by John Wiley & Sons, Ltd.     

Investigation of arsine-generating reactions using deuterium-labeled reagents and mass spectrometry

Mass spectrometry was used to detect transfer of deuterium from labeled reagents to arsines following hydride-generation reactions. The arsine gases liberated from the reactions of arsenite, arsenate, methylarsonic acid, and dimethylarsinic acid with HCl and NaBD(4) in H(2)O, or with DCl and NaBH(4) in D(2)O, were examined. Differences in the mode of deuterium incorporation for the various arsines were detected. These results may help explain some of the observed variations in arsine-generation efficiency for various arsenic compounds present in environmental and biological samples.     

Uptake and Reduction of Arsenate by Dunaliella sp.

Uptake and reduction of arsenate [AS(V)] by Dunaliella sp. cells were determined to investigate the metabolic processes of arsenic in the alga. Cellular uptake of arsenic by Dunaliella sp. cells was markedly affected by the form of arsenic in the medium. The content of arsenic taken up by Dunaliella sp. cells increased rapidly with time on addition of As(V) to the medium. However, in the case of addition of arsenite [As(III)], the gradient of arsenic uptake by Dunaliella sp. cells was low, and arsenic content was small. In the water-soluble fraction of arsenic taken up by Dunaliella sp. cells with exposure to As(V), arsenic was in the forms of organic arsenic, As(V) and As(III). The content of As(V) in the water-soluble fraction increased with exposure time. The content of As(III) also increased with time, but remained constant after 5 h of exposure. On the other hand, organic arsenic content was small and did not increase with time. It was found that Dunaliella sp. takes up As(V) and readily reduces it to As(III)     

Synthese und Eigenschaften von Bis(dialkylamino)-methylarsinen

Synthesis and Properties of Bis(dialkylamino)methylarsines The reactions of secondary amines with CH₃AsJ₂ lead to the formation of Bis(dialkylamino)methylarsines. Ten arsines have been prepared by this method and are described. IR and ¹H-NMR and mass spectral data are presented for these compounds and discussed. Acid molecules cleave the As? N bond. The reactions with halogen hydrides, water, alkoholes, thioles and amines are described.     

Desorption electrospray ionization mass spectrometry (DESI-MS) applied to the speciation of arsenic compounds from fern leaves

The different chemical forms of arsenic compounds, including inorganic and organic species, present distinct environmental impacts and toxicities. Desorption electrospray ionization mass spectrometry (DESI-MS) is an excellent technique for in situ analysis, as it operates under atmospheric pressure and room temperature and is conducted with no/minimal sample pretreatment. Aimed at expanding its scope, DESI-MS is applied herein for the quick and reliable detection of inorganic (arsenate—As(V): AsO₄ ^3? and arsenite—As(III): AsO₂ ^?) and organic (dimethylarsinic acid—DMA: (CH₃)₂AsO(OH) and disodium methyl arsonate hexahydrate: CH₃AsO₃·2Na·6H₂O) arsenic compounds in fern leaves. Operational conditions of DESI-MS were optimized with DMA standard deposited on paper surfaces to improve ionization efficiency and detection limits. Mass spectra data for all arsenic species were acquired in both the positive and negative ion modes. The positive ion mode was shown to be useful in detecting both the organic and inorganic arsenic compounds. The negative ion mode was shown only to be useful in detecting As(V) species. Moreover, MS/MS spectra were recorded to confirm the identity of each arsenic compound by the characteristic fragmentation profiles. Optimized conditions of DESI-MS were applied to the analysis of fern leaves. LC-ICP-MS was employed to confirm the results obtained by DESI-MS and to quantify the arsenic species in fern leaves. The results confirmed the applicability of DESI-MS in detecting arsenic compounds in complex matrices.     

The discovery of hidden arsenic species in coastal waters

The analysis of ultraviolet (UV)-irradiated and untreated seawater samples has shown that the dissolved arsenic content of marine waters cannot be completely determined by hydride generation–atomic absorption spectrophotometry without sample pretreatment. Irradiation of water samples obtained during a survey of arsenic species in coastal waters during the summer of 1988 gave large increases in the measured speciation. Average increases in the measured speciation. Average increases in total arsenic, monomethylarsenic and dimethylarsenic were 0.29 μg As dm^?3 (25%), 0.03 μg As dm^?3 (47%) and 0.12 μg As dm^?3 (79%), respectively. Overall, an average 25% increase in the concentration of dissolved arsenic was observed following irradiation. This additional arsenic may be derived from compounds related to algal arsenosugars or to their breakdown products. These do not readily yield volatile hydrides when treated with borohydride and are not therefore detected by the normal hydride generation technique. This has important repercussions as for many years this procedure, and other analytical procedures which are equally unlikely to respond to such compounds, have been accepted as giving a true representation of the dissolved arsenic speciation in estuarine and coastal waters. A gross underestimate may therefore have been made of biological involvement in arsenic cycling in the aquatic environment.     

Arsenic accumulation by arsenic-tolerant freshwater blue-green alga (Phormidium sp.)

Accumulation, biomethylation and excretion of arsenic by the arsenic-tolerant freshwater blue–green alga, Phormidium sp., which had been isolated from an arsenic-polluted environment, were investigated. The cellular growth curves were in fair agreement with a ‘logistic curve’ equation. The growth increased with an increase in the surrounding arsenic concentration up to 100 m?g g^?1. The cells survived even at 7000 m?g g^?1. The arsenic concentration of the cells increased with an increase of the surrounding arsenic concentration up to 7000 m?g g^?1. Phosphorus concentrations in the medium affected the growth and arsenic accumulation. No arsenic was accumulated by cells killed by ethanol. The arsenic was methylated to the extent of 3.2% of the total arsenic accumulated. When the cells were transferred into an arsenic-free medium, 85% of the arsenic accumulated was excreted; 58% of the excreted arsenic was in methylated form implying extensive methylation in the arsenic-free medium.     

Metabolism of arsenic compounds by the blue mussel mytilus edulis after accumulation from seawater spiked with arsenic compounds

Blue mussels (Mytilus edulis) were exposed to 100 μg As dm^?3 in the form of arsenite, arsenate, methylarsonic acid, dimethylarsinic acid, arsenobetaine, arsenocholine, trimethylarsine oxide, tetramethylarsonium iodide or dimethyl-(2-hydroxyethyl)arsine oxide in seawater for 10 days. The seawater was renewed and spiked with the arsenic compounds daily. Analyses of water samples taken 24 h after spiking showed that arsenobetaine and arsenocholine had been converted to trimethylarsine oxide, whereas trimethylarsine oxide and tetramethylarsonium iodide were unchanged. Arsenobetaine was accumulated by mussels most efficienty, followed in efficiency by arsenocholine and tetramethylarsonium iodide. None of the other arsenic compounds was significantly accumulated by the mussels. Extraction of mussel tissues with methanol revealed that control mussels contained arsenobetaine, a dimethyl-(5-ribosyl)arsine oxide and an additional arsenic compound, possibly dimethylarsinic acid. Mussels exposed to arsenobetaine contained almost all their experimentally accumulated arsenic as arsenobetaine, and mussels exposed to tetramethylarsonium iodide contained it as the tetramethylarsonium compound. Mussels exposed to arsenocholine had arsenobetaine as the major arsenic compound and glycerylphosphorylarsenocholine as a minor arsenic compound in their tissues. The results show that arsenobetaine and arsenocholine are efficiently accumulated from seawater by blue mussels and that in both cases the accumulated arsenic is present in the tissues as arsenobetaine. Consequently arsenobetaine and/or arsenocholine present at very low concentrations in seawater may be responsible for the presence of arsenobetaine in M. edulis and probably also among other marine animals. The quantity of arsenobetaine accumulated by the mussels decreases with increasing concentrations of betaine. HPLC-ICP-MS was found to be very powerful for the investigation of the metabolism of arsenic compounds in biological systems.     

The chemical form and acute toxicity of arsenic compounds in marine organisms

A method for the separation and identification of inorganic and methylated arsenic compounds in marine organisms was constructed by using a hydride generation/cold trap/gas chromatography mass spectrometry (HG/CT/GC MS) measurement system. The chemical form of arsenic compounds in marine organisms was examined by the HG/CT/GC MS system after alkaline digestion. It was observed that trimethylarsenic compounds were distributed mainly in the water-soluble fraction of muscle of carnivorous gastropods, crustaceans and fish. Also, dimethylated arsenic compounds were distributed in the water-soluble fraction of Phaeophyceae. It is thought that most of the trimethylated arsenic is likely to be arsenobetaine since this compound released trimethylarsine by alkaline digestion and subsequent reduction with sodium borohydride. The major arsenic compound isolated from the water-soluble fraction in the muscle and liver of sharks was identified as arsenobetaine from IR, FAB Ms data, NMR spectra and TLC behaviour. The acute toxicity of arsenobetaine was studied in male mice. The LD₅₀ value was higher than 10 g kg⁻¹. This compound was found in urine in the non-metabolized form. No particular toxic symptoms were observed following administration. These results suggest that arsenobetaine has low toxicity and is not metabolized in mice. The LD₅₀ values of other minor arsenicals in marine organisms, trimethylarsine oxide, arsenocholine and tetramethylarsonium salt, were also examined in mice.