Search

Environmental context The marine ecosystem is highly elevated in arsenic in comparison to the terrestrial environment. More than 100 different naturally occurring organoarsenic compounds have been found in different marine organisms. In order to understand how highly toxic AsHCs are formed and bioaccumulate in different marine organisms, large scale monitoring of AsHCs from a range of different laboratories is necessary. Despite their toxicity, AsHCs have not been extensively studied due in part to the lack of low-cost analytical methods and the lack of commercially available standards. Rational This study aims to develop a new analytical method for the quantitative determination of arsenic-containing hydrocarbons (AsHCs) with gas chromatography–mass spectrometry (GC-MS). The new method is an alternative approach to determine these compounds in environmental samples. Methodology AsHCs were extracted and purified from fish oil and seaweed samples. Due to the thermal conversion of oxo-AsHCs to their trivalent forms in the injection port of the GC, the conversion is incomplete resulting in low signal intensities and large carry overs. We therefore chemically reduced AsHCs to their trivalent forms and analysed them with GC-MS, gas chromatography–tandem mass spectrometry (GC-MS/MS) and high performance liquid chromatography–inductively coupled plasma mass spectrometry (HPLC-ICPMS). The possibility for compound independent quantification with commercially available standards was investigated. Results After optimisation of conditions for reduction of AsHCs, these compounds could be determined in marine samples using authentic standards with the new method. Results showed good agreement with results from HPLC-ICPMS. The novel GC-MS method showed compound independent quantification using triphenylarsine (TPA) as a commercially available standard. Discussion With the developed method we could demonstrate the applicability of GC-MS for the quantitative determination of AsHCs in marine samples for the first time. The compound independent quantification with TPA opens up a quantification for AsHCs species for which no standards are commercially available. The broad applicability might enhance screening for these toxic compounds in the environment.

Environmental context Arsenic exists in different chemical forms in our environment, among others as arsenolipids that are predominately found in appreciable quantities in various marine organisms (seafood). Their origin, biosynthetic pathway, toxicity and their potential biological role are not fully understood. We report purification strategies for environmental and human health relevant arsenolipids to broaden and support innovative arsenolipid research. Rational This study aims to isolate and purify common arsenolipids found in various seafood from commercially available marine sources to provide an alternative approach to the challenging chemical synthesis. Methodology Arsenic containing fatty acids and arsenic containing hydrocarbons were purified from salmon oil, and the edible dried seaweed Wakame was used for the purification of di-acyl arsenosugar phospholipids and arsenic containing hydrocarbons. The developed purification protocols apply and combine straightforward analytical techniques by means of chemical hydrolysis, solid–liquid extraction, solvent-partitioning, solid-phase extraction and preparative liquid chromatography. Elemental mass spectrometry and HPLC/mass spectrometry were used for the development of the purification protocols and the characterisation of purified natural extracts of arsenolipids. Results The salmon oil (20.0 kg) and Wakame (0.50 kg) samples contained 12.8 and 3.19 mg of lipid-soluble arsenic, respectively. The final purified extracts of arsenic fatty acids and arsenic hydrocarbons obtained from salmon oil contained 0.52 mg As in 85 mg of total mass and 2.19 mg As in 28 mg of total mass, respectively. Purification of di-acyl arsenosugar phospholipids and arsenic containing hydrocarbons from Wakame returned extracts containing 0.345 and 0.237 mg As in ≤20 mg of total mass, respectively. Discussion In a natural product approach, arsenic containing fatty acids, arsenic containing hydrocarbons and di-acyl arsenosugar phospholipids have been purified in a multi-stage process from fish oil and algae samples. In the final purified extracts, around 90% or more of the arsenic was present as mixtures of arsenolipids of their respective arsenolipid classes in only minute amounts of total mass. Application of the purified mixtures in toxicological and speciation studies will benefit the future investigation of arsenolipids.

Although the natural occurrence of arsenic-containing lipids (arsenolipids) in marine organisms is now well established, the possible role of these unusual compounds in organisms and in the cycling of arsenic in marine systems remains largely unexplored. We report the finding of arsenolipids in 61 plankton samples collected from surface marine waters of high- and low-nutrient content along a transect spanning the Gulf Stream in the North Atlantic Ocean. Using high-performance liquid chromatography (HPLC) coupled to both elemental and molecular mass spectrometry, we show that all 61 plankton samples contained six identifiable arsenolipids, namely, three arsenosugar phospholipids (AsPL958, 10–13%; AsPL978, 13–25%; and AsPL1006, 7–10% of total arsenolipids), two arsenic-containing hydrocarbons (AsHC332, 4–10% and AsHC360, 1–2%), and a methoxy-sugar arsenolipid that contained phytol (AsSugPhytol, 1–3%). The relative amounts of the six arsenolipids showed clear dependence on the nutrient status of the ambient water with plankton collected from high-nutrient waters having less of the arsenosugar phospholipids and more of the three non-P containing arsenolipids compared to low-nutrient waters. By combining these first field data of arsenolipids in plankton with reported global phytoplankton productivity, we estimate that the oceans’ phytoplankton transform per year 50 000–100 000 tons of arsenic into arsenolipids.

An inter-laboratory study was carried out to characterize a candidate hijiki seaweed for its concentrations of total arsenic and water-soluble arsenic compounds, particularly arsenosugar compounds. The candidate material, a dried hijiki seaweed powder, was analyzed by individual techniques in two laboratories. The water-soluble arsenic compounds were separated by anion exchange, and reversed-phase columns, and As(V), DMA and four kinds of arsenosugars, namely glycerol (-OH), phosphate (-PO4), sulfonate (-SO3), and sulfate (-SO4) types were detected by HPLC-ICP-MS. The methods applied were validated by analyzing a second sample, the NMIJ CRM 7405-a hijiki seaweed, which is certified for both total arsenic and As(V). Techniques for the inter-laboratory study, extraction efficiencies under different extraction conditions, some chromatographic techniques and sequential extraction were investigated. The results from the two laboratories for the candidate hijiki material showed good agreement within the measurement uncertainties for total and water-soluble arsenic compounds.

Environmental contextAlthough arsenic-containing lipids are widespread in marine environments, their origin remains unknown. We show that the arsenolipids in a filter-feeding bivalve mollusc closely match those found in marine food sources, including unicellular algae and bacteria. The results demonstrate the role of lower trophic levels in determining the forms of arsenic found in higher organisms. AbstractArsenic-containing lipids, arsenolipids, are widely found among marine organisms, but their origin and possible biochemical roles remain unknown This work describes the diversity and abundance of arsenolipids in the digestive gland and mantle of nine specimens of the Mediterranean mussel, Mytilus galloprovincialis. By using high performance liquid chromatography (HPLC) coupled to both elemental and high-resolution molecular mass spectrometry, we identified 36 arsenolipids including arsenic derivatives of fatty acids, hydrocarbons, sugar-phospholipids and sugar-phytol; 21 of these arsenolipids were identified for the first time and included a new group comprising ether-phospholipids. The arsenic compounds in the mussels show distinct profiles depending on the tissue type, which provide insight into the arsenolipid origin. The results suggest that the presence of some arsenolipids in the mussels is from direct uptake of the compounds, presumably from food, rather than biogenesis within the mussels.

Environmental contextArsenic is a globally distributed element, occurring in various chemical forms with toxicities ranging from harmless to highly toxic. We examined sediment samples from Great Salt Lake, an extreme salt environment, and found a variety of organoarsenic species not previously recorded in nature. These new compounds are valuable pieces in the puzzle of how organisms detoxify arsenic, and in our understanding of the global arsenic cycle. AbstractArsenic-containing lipids are natural products found predominantly in marine organisms. Here, we report the detection of known and new arsenolipids in sediment samples from Great Salt Lake, a hypersaline lake in Utah, USA, using high-performance liquid chromatography in combination with both elemental and molecular mass spectrometry. Sediments from four investigated sites contained appreciable quantities of arsenolipids (22–312ng As g−1 sediment) comprising several arsenic-containing hydrocarbons and 20 new compounds shown to be analogues of phytyl 2-O-methyl dimethylarsinoyl riboside. We discuss potential sources of the detected arsenolipids and find a phytoplanktonic origin most plausible in these algal detritus-rich salt lake sediments.

Arsenosugars are arsenic-containing ribosides that play a substantial role in arsenic biogeochemical cycles. Arsenosugars were identified more than 30 years ago, and yet their mechanism of biosynthesis remains unknown. In this study we report identification of the arsSgene from the cyanobacterium Synechocystissp. PCC 6803 and show that it is involved in arsenosugar biosynthesis. In the Synechocystissp. PCC 6803 arsoperon, arsSis adjacent to the arsMgene that encodes an As(III) S-adenosylmethionine (SAM) methyltransferase. The gene product, ArsS, contains a characteristic CX3CX2C motif which is typical for the radical SAM superfamily. The function of ArsS was identified from a combination of arsSdisruption in Synechocystissp. PCC 6803 and heterologous expression of arsMand arsSin Escherichia coli. Both genes are necessary, indicating a multistep pathway of arsenosugar biosynthesis. In addition, we demonstrate that ArsS orthologs from three other freshwater cyanobacteria and one picocyanobacterium are involved in arsenosugar biosynthesis in those microbes. This study represents the identification of the first two steps in the pathway of arsenosugar biosynthesis. Our discovery expands the catalytic repertoire of the diverse radical SAM enzyme superfamily and provides a basis for studying the biogeochemistry of complex organoarsenicals.

The release of a toxicant from a food matrix during the gastrointestinal digestion is a crucial determinant of the toxicant’s oral bioavailability. We present a modified setup of the human simulator of the gut microbial ecosystem (SHIME), with four sequential gastrointestinal reactors (oral, stomach, small intestine, and colon), including the salivary and colonic microbiomes. Naturally arsenic-containing rice, mussels, and nori seaweed were digested in the presence of microorganisms and in vitrooral bioaccessibility, bioavailability, and metabolism of arsenic species were evaluated following analysis by using HPLC/mass spectrometry. When food matrices were digested with salivary bacteria, the soluble arsenic in the gastric digestion stage increased for mussel and nori samples, but no coincidence impact was found in the small intestinal and colonic digestion stages. However, the simulated small intestinal absorption of arsenic was increased in all food matrices (1.2–2.7 fold higher) following digestion with salivary microorganisms. No significant transformation of the arsenic species occurred except for the arsenosugars present in mussels and nori. In those samples, conversions between the oxo arsenosugars were observed in the small intestinal digestion stage whereupon the thioxo analogs became major metabolites. These results expand our knowledge on the likely metabolism and oral bioavailabiltiy of arsenic during human digestion, and provide valuable information for future risk assessments of dietary arsenic.

The DNA-alkylating metabolite tilimycin is a microbial genotoxin. Intestinal accumulation of tilimycin in individuals carrying til+ Klebsiellaspp. causes apoptotic erosion of the epithelium and colitis. Renewal of the intestinal lining and response to injury requires the activities of stem cells located at the base of intestinal crypts. This study interrogates the consequences of tilimycin-induced DNA damage to cycling stem cells. We charted the spatial distribution and luminal quantities of tilmetabolites in Klebsiella-colonized mice in the context of a complex microbial community. Loss of marker gene G6pdfunction indicates genetic aberrations in colorectal stem cells that became stabilized in monoclonal mutant crypts. Mice colonized with tilimycin-producing Klebsielladisplayed both higher frequencies of somatic mutation and more mutations per affected individual than animals carrying a non-producing mutant. Our findings imply that genotoxic til+ Klebsiellamay drive somatic genetic change in the colon and increase disease susceptibility in human hosts.

Environmental context Arsenic biotransformation processes play a key role in the cycling of arsenic in aquatic systems. We show that a freshwater cyanobacterium can convert inorganic arsenic into arsenolipids, and the conversion efficiency depends on the arsenic concentration. The role of these novel arsenic compounds remains to be elucidated. Abstract Although methylated arsenic and arsenosugars have been verified in various freshwater organisms, lipid-soluble arsenic compounds have not been identified. Here, we report investigations with the model organism cyanobacterium Synechocystis sp. PCC 6803 wild type and ΔarsM (arsenic(III) S-adenosylmethionine methyltransferase) mutant strain, which lacks the enzymes for arsenic methylation cultured in various concentrations of arsenate (AsV). Although Synechocystis accumulated higher arsenic concentrations at the higher exposure levels, the bioaccumulation factor decreased with increasing AsV. The accumulated arsenic in the cells was partitioned into water-soluble and lipid-soluble fractions; lipid-soluble arsenic was found in Synechocystis wild type cells (3–35% of the total depending on the level of arsenic exposure), but was not detected in Synechocystis ΔarsM mutant strain showing that ArsM was required for arsenolipid biosynthesis. The arsenolipids present in Synechocystis sp. PCC 6803 were analysed by high performance liquid chromatography–inductively coupled plasma–mass spectrometry, high performance liquid chromatography–electrospray mass spectrometry, and high resolution tandem mass spectrometry. The two major arsenolipids were characterised as arsenosugar phospholipids based on their assigned molecular formulas C47H88O14AsP and C47H90O14AsP, and tandem mass spectrometric data demonstrated the presence of the phosphate arsenosugar and acylated glycerol groups.

Environmental contextAlthough organoarsenic compounds occur in marine organisms at high concentrations, the origin and role of these compounds is unknown. Arsenic-containing lipids (arsenolipids) are newly discovered compounds in fish. We identify a range of arsenolipids in algae and propose that algae are the origin of these unusual arsenic compounds in marine ecosystems. AbstractFourteen arsenolipids, including 11 new compounds, were identified and quantified in two species of brown algae, Wakame (Undaria pinnatifida) and Hijiki (Hizikia fusiformis), by high resolution mass spectrometry, high performance liquid chromatography–mass spectrometry and gas chromatography–mass spectrometry. Both algal species contained arsenosugar-phospholipids as the major type of arsenolipid, and arsenic-hydrocarbons were also significant components, particularly in Hijiki. The origin of the various arsenolipids, and the possible significance of their relative quantities, is briefly discussed.

Environmental contextDespite 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. AbstractTime 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.

The possible role of arsenosugars as precursors to arsenobetaine was investigated by feeding pure arsenosugar compounds to the shrimp, Crangon crangon, and monitoring the arsenic metabolites in muscle, midgut gland, gills, and ‘remainder’ tissues by HPLC–ICP MS. Control shrimps contained arsenobetaine (ca90% of the total As) as the major arsenic compound in all four tissues, and traces of tetramethylarsonium ion and two arsenosugars were also present. Shrimps accumulated only 0.9% of a dimethylated arsenosugar, mostly as unchanged compound, and conversion into arsenobetaine could not be detected. Dimethylarsinate and possibly dimethylarsinoylethanol were present as minor metabolites. Shrimps accumulated 4.2% of a trimethylated arsenosugar, and converted about half into arsenobetaine. The remainder of the arsenic was present as unchanged arsenosugar and several minor unidentified metabolites. The overall accumulation of arsenobetaine from ingested trimethylated arsenosugar was only about 2%, whereas shrimps fed arsenobetaine retained 57% of the dose. The undetectable (dimethylated) to low (trimethylated) conversion of the arsenosugars into arsenobetaine suggests that these compounds do not represent a major source of arsenobetaine for wild Crangon. Copyright © 1999 John Wiley & Sons, Ltd.

The possible role of arsenosugars as precursors to arsenobetaine was investigated by feeding pure arsenosugar compounds to the shrimp, Crangon crangon, and monitoring the arsenic metabolites in muscle, midgut gland, gills, and ‘remainder’ tissues by HPLC–ICP MS. Control shrimps contained arsenobetaine (ca 90% of the total As) as the major arsenic compound in all four tissues, and traces of tetramethylarsonium ion and two arsenosugars were also present. Shrimps accumulated only 0.9% of a dimethylated arsenosugar, mostly as unchanged compound, and conversion into arsenobetaine could not be detected. Dimethylarsinate and possibly dimethylarsinoylethanol were present as minor metabolites. Shrimps accumulated 4.2% of a trimethylated arsenosugar, and converted about half into arsenobetaine. The remainder of the arsenic was present as unchanged arsenosugar and several minor unidentified metabolites. The overall accumulation of arsenobetaine from ingested trimethylated arsenosugar was only about 2%, whereas shrimps fed arsenobetaine retained 57% of the dose. The undetectable (dimethylated) to low (trimethylated) conversion of the arsenosugars into arsenobetaine suggests that these compounds do not represent a major source of arsenobetaine for wild Crangon. Copyright © 1999 John Wiley & Sons, Ltd.

A method for the catalytic voltammetric determination of perchlorate using a carbon paste electrode modified with a liquid anion exchanger is presented. The fundamental catalytic effect is based on the chemical reoxidation of electrochemically generated Tl(O) by perchlorate which can be monitored by an increase of the corresponding current flow. Perchlorate can be preconcentrated, together with tetrachlorothallate(III) as a catalyst, from hydrochloric acid solutions onto the modified carbon paste electrode under open circuit conditions. For analytical purposes, the increase of the current response for the reoxidation of Tl(O) to Tl(I) is exploited for quantifications. Methodical parameters such as pH, ionic strength of the media, preconcentration time and thallium concentration are investigated; the influence of interferents is studied. The dependence of the current increase on the concentration of perchlorate with different accumulation times is presented. The detection limit (3) is 50 &(g)dot;l-1 ClO4- (12 min accumulation). To show the applicability of the method to the analysis of real samples spiked drinking water was investigated.

A method for the voltammetric determination of vanadium(v) using a carbon paste electrode in situ modified with cetyltrimethylammonium bromide (CTAB) is described. Vanadium is preconcentrated at the electrode surface via its anionic oxalate complex from acidic solution (0.01 M oxalic acid, 0.25 mM CTAB, pH 2.2) at a potential of −0.9 V [vs. the saturated calomel electrode (SCE)]. Simultaneously during accumulation, vanadium(v) in the complex is reduced to its tetravalent state. Differential pulse anodic stripping voltammetry exploiting the reoxidation can be used for the determination of trace levels of vanadium(v). Linearity between current and concentration exists for a range of 5 to 200 μg.L−1Vvwith a preconcentration time of 1 min. The limit of detection (calculated as 3 σ) is 0.07 μg.L−1with a preconcentration time of 10 min.

No Abstract

No Abstract

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.