Arsenic metabolism in a freshwater food chain: Blue–green alga (Nostoc sp.)→ shrimp (Neocaridina denticulata)→ carp (Cyprinus carpio)

Bioaccumulation and biomethylation of inorganic arsenic were investigated in a three-step fresh-water food chain consisting of an autotroph (blue- green alga: Nostoc sp.), a herbivore (shrimp: Neocaridina denticulata) and a carnivore (carp: Cyprinus carpio). The autotroph, herbivore and carnivore survived in arsenic-containing water below 1000, 2 and 60 mg As(V) dm^?3, respectively. Bioaccumulation of arsenate by Nostoc sp. was decreased with an increase in the nitrogen concentration of the medium. Arsenic(V) was accumulated from the water phase and part-methylated by the carp, as well as by the algae and shrimp. Arsenic was mostly accumulated in the gut of the carp. The predominant arsenical in the guts was the monomethylarsenic species. Arsenic accumulation via food in the above three-step food chain decreased by one order of magnitude and the relative concentration of methylated arsenic to the total arsenic accumulated increased successively with an elevation in the trophic level. When arsenicals were transferred via the food chain, no monomethylarsenic, or only a trace amount, was detected in the three organisms. Dimethylarsenic in the alga, both dimethyl- and trimethyl-arsenic in shrimp, and trimethyl-arsenic in carp, were the predominant methylated arsenic species, respectively.     

Tolerance,bioaccumulation and biotransformation of arsenic in freshwater prawn (Macrobrachium rosenbergii)

Tolerance bioaccumulation and biotransformation of arsenic compounds by a freshwater prawn (Macrobrachium rosenbergii) were investigated. M. rosenbergii was exposed to 10, 20, 30 and 35 μg As cm⁻³ of disodium arsenate [abbreviated as As(V)], 25, 50, 100 and 120 μg As cm⁻³ of methylarsonic acid (MMAA), or 100,200, 300 and 350 μg As cm⁻³ of dimethylarsinic acid (DMAA). Tolerances (50% lethal concentration: LC₅₀) of the prawn against As(V), MMAA, and DMAA were 30, 100, and 300 μg As cm⁻³, respectively. The prawn accumulated arsenic compounds directly from aqueous phase and biotransformed them in part. Both methylation and demethylation of the arsenicals were observed in vivo. Highly methylated and less toxic arsenicals were less accumulated in M. rosenbergii.     

Seasonal dynamics of dimethylarsinic‐acid‐decomposing bacteria dominating in Lake Kahokugata

Decomposition processes of organoarsenic compounds significantly influence arsenic cycles in aquatic environments, and such processes depend on bacterial activity. However, the bacterial characteristics in these environments are obscure. Accordingly, we observed seasonal variations of arsenic species and the bacterial population decomposing dimethylarsinic acid (DMAA) in Lake Kahokugata from April 2002 to January 2003. Monitoring of bacterial biomass involving DMAA decomposition using the most probable number procedure showed that the bacterial cell densities ranged from 36 to 3600 ml^?1. On the other hand, methylated arsenic was not detected during the experimental period, although the inorganic arsenic concentration was over 4 nM . This suggests that bacteria remineralized methylated arsenic species to inorganic arsenic. Furthermore, the composition of bacterial communities involving DMAA decomposition was examined by restriction‐fragment‐length polymorphism analysis of the 16S rDNA nucleotide. As a result, a total of 49 isolates were classified into 10 type groups, and 32 of these isolates belonged to three dominant type groups. Phylogenetic analysis using 16S rDNA partial sequences (ca 320 bp) suggests that the representative isolates of the dominant type groups are specific to the summer or winter season. Moreover, as a result of the culture experiments to examine DMAA decomposition activity, the representative isolates decomposed 1 µM DMAA at a decomposition percentage of below 80%. In conclusion, some bacterial communities in a specific season can decompose DMAA to varying degrees, contributing to the annual cycle of arsenic species. Copyright © 2005 John Wiley & Sons, Ltd.     

Seasonal control of arsenic speciation in an estuarine ecosystem

Arsenic speciation in the Itchen estuary and Southampton Water (UK) has been shown to vary seasonally, with detectable (>0.02μg As dm^?3) dissolved arsenic(III) and methylated arsenic only being present from May to early October. This corresponds to the time period during which water temperatures exceed 12°C. For the remainder of the year, inorganic arsenic(V) was the only detectable species. At its peak, ca 30% of the dissolved arsenic was present as methylated forms with dimethylarsenic (DMAs) being the predominant bioarsenical. Significant quantities of monomethyl-arsenic (MMAs) and inorganic arsenic(III) were also present, however. The concentrations of the bioarsenical species varied with position in the estuary and generally increased with salinity. Measurements made during the period of peak algal activity implicated the highsalinity area of the estuary as the most probable region in which the methylated arsenicals are generated. At some sites, a distinct lag was observed between the appearance of dimethylarsenic and the detection of arsenic(III)and monomethylarsenic. Chlorophyll a concentration proved to be a poor predictor of the appearance of reduced and methylated arsenic in the water column. Possible sources of dissolved methylated arsenic are discussed.     

Distribution and cycle of arsenic compounds in the ocean

In order to understand the distribution and the cycle of arsenic compounds in the marine environment, the horizontal distributions of arsenic(V) [As(V)], arsenic(III) [As(III)], monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) in the Indian Pacific Oceanic surface waters have been investigated. This took place during cruises of the boat Shirase from Tokyo to the Syowa Station (15 November–19 December 1990), of the tanker Japan Violet from Sakai to Fujayrah (28 July–17 August 1991) and of the boat Hakuho-maru from Tokyo to Auckland (19 September–27 October 1992). Vertical distributions of arsenic in the west Pacific Ocean have also been investigated. The concentration of As(V) was found to be relatively higher in the Antarctic than in the other areas. Its concentration varied from 340 ng dm^?3 (China Sea) to 1045 ng dm^?3 (Antarctic). On the other hand, the concentrations of the biologically produced species, MMAA and DMAA, were extremely low in the Antarctic and southwest Pacific waters. Their concentrations in Antarctic waters were 8 ng dm^?3 and 22 ng dm^?3 and those in the southwest Pacific were 12 ng dm^?3 and 25 ng dm^?3. In the other regions the concentration varied from 16 ng dm^?3 (China Sea) to 36 ng dm^?3 (north Indian Ocean) for MMAA and from 50 ng dm^?3 (east Indian Ocean) to 172 ng dm^?3 (north Indian Ocean) for DMAA. As a result, with the exception of Antarctic and southwest Pacific waters, the percentages of each arsenic species in the surface waters were very similar and varied from 52% (east Indian Ocean) to 63% (northwest Pacific Ocean) for As(V), from 22% (northwest Pacific Ocean) to 27% (east Indian Ocean) for As(III) and from 15% (northwest Pacific Ocean) to 21% (north and east Indian Oceans) for the methylated arsenics (MMAA+DMAA). These percentages in Antarctic waters were 97%, 0.2% and 2.8%, respectively, and those in the southwest Pacific Ocean were 97% for As(V)+As(III) and 3% for MMAA+DMAA. The very low concentrations of the biologically produced species in Antarctic waters and that of methylated arsenic in southwest Pacific waters indicated that the microorganism communities in these oceans was dominated by microorganisms having a low affinity towards arsenic. Furthermore, microorganism activity in the Antarctic was also limited due to the much lower temperature of the seawater there. The vertical profile of inorganic arsenic was 1350 ng dm^?3 in surface waters, 1500 ng dm^?3 in bottom waters with a maximum value of 1700 ng dm^?3 at a depth of about 2000 m in west Pacific waters. This fact suggested the uptake of arsenic by microorganisms in the surface waters and the co-precipitation of arsenic with hydrated heavy-metal oxides in bottom waters. The suggested uptake of inorganic arsenic and subsequent methylation was also supported by the profile of DMAA, with a high concentration of about 26 ng dm^?3 in surface water and a significant decrease to a value of 9 ng dm^?3 at a depth of 1000 m.     

Arsenic speciation in aqueous samples using a selective As(III)/As(V) preconcentration in combination with an automatable cryotrapping hydride generation procedure for monomethylarsonic acid and dimethylarsinic acid

Differentiation between As(III) and As(V) is accomplished using earlier developed selective preconcentration methods (carbamate and molybdate mediated (co)precipitation of As(III) and As(V) respectively) follewed by AAS detection of the (co)precipitates. Apart from this, separation of methylated arsenic species is performed by an automatable system comprising a continuous flow hydride generation unit in which monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) are converted into their corresponding volatile methylarsines, monomethylarsine (MMA) and dimethylarsine (DMA) respectively. These species are cryogenically trapped in a Teflon-line stainless stell U-tube packed with a gas chromatographic solid-phase and subsequently separated by selective volatilization. A novel gas drying technique by means of a Perma Pure dryer was applied successfully prior to trapping. Detection is by atomic absorption spectrometry (AAS). MMAA and DMAA are determined with absolute limits of detection of 0.2 and 0.5 ng, respectively. Investigation of the behaviour of the methylarsines in the system was conducted with synthesized⁷³As labeled methylated arsenic species. It was found that MMA is taken through the system quantitatively whereas DMA is recovered for about 85%. The opumized system combined with selective As(III)/As(V) preconcentration has been tested out for arsenic speciation of sediment interstitial water from the Chemiehaven at Rotterdam. The obtained concentrations are 28.5, 26.8 and 0.60 ng·ml^–1 for As(III), As(V) and MMAA, respectively, whereas the DMAA concentration was below 0.16 ng·ml^–1.     

Intake of different chemical species of dietary arsenic by the japanese,and their blood and urinary arsenic levels

We calculated the intake of each chemical species of dietary arsenic by typical Japanese, and determined urinary and blood levels of each chemical species of arsenic. The mean total arsenic intake by 35 volunteers was 195±235 (15.8-1039) μg As day^?1, composed of 76% trimethylated arsenic (TMA), 17.3% inorganic arsenic (As_i), 5.8% dimethylated arsenic (DMA), and 0.8% monomethylated arsenic (MA): the intake of TMA was the largest of all the measured species. Intake of As_i characteristically and invariably occurred in each meal. Of the intake of As_i, 45-75% was methylated in vivo to form MA and DMA, and excreted in these forms into urine. The mean measured urinary total arsenic level in 56 healthy volunteers was 129±92.0 μg As dm^?3, composed of 64.6% TMA, 26.7% DMA, 6.7% As_i and 2.2% MA. The mean blood total arsenic level in the 56 volunteers was 0.73±0.57 μg dl^?1, composed of 73% TMA, 14% DMA and 9.6% As_i. The urinary TMA levels proved to be significantly correlated with the whole-blood TMA levels (r = 0.376; P<0.01).     

Lipophilic arsenic compound(s) in the liver of a tiger shark (Galeocerdo cuvier)

Homogenized aliquots (100 g) of the liver (8.4 kg, 5 m?g As g^?1) of a tiger shark (Galeocerdo cuvier) were extracted with chloroform/methanol, and the extracts purified by countercurrent extraction (hexane/87% ethanol), silica gel column chromatography (chloroform/methanol mixtures as mobile phases), and silica gel thin-layer chromatography (chloroform/methanol/acetic acid). The purified samples (24 mg arsenic g^?1) gave no ³¹P NMR signal, but gave ¹H and ¹³C NMR signals with similarities to those of dipalmitoylphosphatidic acid and salad on and also signals indicative of the presence of methylated arsenic compounds. The sample could contain a diacyl glyceride with a methylated arsenic group.     

Dual‐column capillary microextraction (CME) combined with electrothermal vaporization inductively coupled plasma mass spectrometry (ETV‐ICP‐MS) for the speciation of arsenic in human hair extracts

In this work, dual‐column capillary microextraction (CME) system consisting of N‐(2‐aminoethyl)‐3‐aminopropyltrimethoxysilane (AAPTS)‐silica coated capillary (C1) and 3‐mercaptopropyl trimethoxysilane (MPTS)‐silica coated capillary (C2) was developed for sequential separation/preconcentration of arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)] in the extracts of human hair followed by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV‐ICP‐MS) detection with iridium as permanent modifier. Various experimental parameters affecting the dual‐column microextraction of different As species had been investigated in detail. It was found that at pH 9, As(V) and MMA could be quantitatively retained by C1 and only As(III) could be quantitatively retained by C2. With the aid of valve switching, As(V)/MMA(V) retained on C1 and As(III) retained on C2 could be sequentially desorbed by 10 µl of 0.01 mol l^?1 HNO₃ [for As(V)], 0.1 mol l^?1 HNO₃ [for MMA(V)] and 0.2 mol l^?1 HNO₃‐3% thiourea (m/v) [for As(III)], respectively, the eluents were immediately introduced into the Ir‐coated graphite tubes for further ETV‐ICP‐MS detection. With two‐step ETV pyrolysis program, Cl^? in the sample matrix could be in situ removed, and the total As in the human hair extracts or digested solution could be interference‐free, determined by ETV‐ICP‐MS. DMA(V) in the human hair extracts was obtained by subtraction of total As in the human hair extracts from other three As species. Under the optimized conditions, the detection limits (3 σ) of the method were 3.9 pg ml^?1 for As(III), 2.7 pg ml^?1 for As(V), 2.6 pg ml^?1 for MMA(V) and 124 pg ml^?1 for total As with the relative standard deviations less than 7.0% (C = 0.1 ng ml^?1, n = 7), and the enrichment factor was 286, 262 and 260 for As(III), As(V) and MMA(V), respectively. The developed method was successfully applied for the speciation of arsenic in the extracts of human hair. Copyright © 2009 John Wiley & Sons, Ltd.     

Methylated arsenic species in estuarine porewaters

Inorganic arsenic, monomethylarsenic and dimethylarsenic species have been observed in samples of sediment porewater collected from the Tamar Estuary in South-West England. Porewater samples were collected using in situ dialysis. The arsenic species were separated by hydride generation and concentrated by liquid nitrogen trapping, prior to analysis by directly coupled gas chromatography-atomic absorption spectroscopy. The predominant dissolved arsenic species present was inorganic arsenic (5-62 m?g dm^?3). However, this is the first time significant concentrations of methylated arsenic species have been quantified in estuarine porewaters (0.04–0.70 m?g dm^?3), accounting for between 1 and 4% of the total dissolved arsenic. The presence of methylated arsenic compounds in porewaters is attributed to in situ environmental methylation, although the possibility of methylated arsenic species being derived from biological debris cannot be excluded.     

Synthetic and antimicrobial studies on new gold(I) complexes of imidazolidin‐2‐ylidenes

Six new 1,3‐diorganylimidazolidin‐2‐ylidene (NHC) gold(I) complexes of the type [Au(NHC)₂]⁺ (1–6), were synthesized by reacting [AuCl(PPh)₃] with 1,3‐dimesitylimidazolidin‐2‐ylidene or bis(1,3‐dialkylimidazolidin‐2‐ylidene). The complexes 1–6 were fully characterized by elemental analyses and spectroscopic data. The placement of mesityl or para‐substituted benzyl groups on the nitrogen atoms of the ring of the complexes leads to the particularly active antibacterial agents evaluated in this work. It is worth noting that the p‐methoxybenzyl derivative (2) inhibited the growth of Pseudomona aeruginosa, Staphylococcus epidermidis, Staphylococcus aureus and Enterococcus faecalis with minimum inhibitory concentration (MIC) values of 3.12 µg ml^?1, 6.25 µg ml^?1, 3.12 µg ml^?1 and 3.12 µg ml^?1 respectively. In contrast, the analogous p‐dimethylaminobenzyl derivative (3) is effective only against Escherichia coli (MIC = 3.12 µg ml^?1). Copyright © 2004 John Wiley & Sons, Ltd.     

Formation of methylated oxyarsenicals and thioarsenicals in wild-type and arsenic (+3 oxidation state) methyltransferase knockout mice exposed to arsenate

Arsenic (+3 oxidation state) methyltransferase (As3mt) plays a central role in the enzymatically catalyzed conversion of inorganic arsenic into methylated metabolites. Most studies of the metabolism and disposition of arsenicals following exposure to inorganic arsenic focus on the formation and fate of methylated oxyarsenicals. However, recent research has shown methylated thioarsenicals to be another important class of metabolites of inorganic arsenic. Here, we report on the presence of methylated oxy- and thioarsenicals in urine and liver from wild-type mice that efficiently methylate inorganic arsenic and from As3mt knockout mice that lack arsenic methyltransferase activity. Following a single oral dose of 0.5 mg of arsenic as arsenate/kg body weight, urine from wild-type mice contained methylated oxyarsenicals and unknown arsenicals. Further analysis identified one unknown arsenical in urine of wild-type mice as dimethylmonothioarsinic acid. In addition, another unknown arsenical in urine of wild-type mice that occurred in the urine of about 20 % of arsenate-treated mice. The presence of low levels of methylated arsenicals in liver digests of As3mt knockout mice may reflect the activity of other methyltransferases or the absorption of methylated arsenicals formed by the microbiota of the gastrointestinal tract. The lack of methylated thioarsenicals in urine of As3mt knockout mice suggests a close link between the processes that form methylated oxy- and thioarsenicals.     

Conversion of arsenite and arsenate to methylarsenic and dimethylarsenic compounds by homogenates prepared from livers and kidneys of rats and mice

Pooled livers and pooled kidneys from rats or mice were homogenized and spiked with arsenite or arsenate in the concentration range 1.3–20 μmol dm^?3. Methylarsenic and dimethylarsenic compounds were determined by the hydride generation technique in the homogenates after a 90 min incubation at 37°C. The rat homogenates methylated arsenite and arsenate more efficiently than the mouse homogenates. Monomethylated arsenic was present in larger amounts than dimethylated arsenic in the rat homogenates. In the absence of reduced glutathione (GSH), no methylation occurred. Addition of GSH promoted monomethylation and dimethylation, whereas dithiothreitol and mercaptoethanol (10 mmol dm^?3) fostered only monomethylation. The amounts of monomethylated arsenic in the rat liver homogenates increased with increasing arsenite concentration (1.3–20 μmol dm^?3) however, the percentage of arsenic that had been methylated decreased. A similar trend, but with much less monomethylarsenic formed, was observed for arsenate-spiked homogenates. Rat kidney homogenates methylated arsenite and arsenate to a much smaller extent than rat liver homogenates. The K_m values for the monomethylation in rat liver homogenates were found to be 5.3 μmol dm^?3 for arsenite and 59 μmol dm^?3 for arsenate.     

Seasonality in estuarine sources of methylated arsenic

The effect of seasonal temperature change on the release of methylated arsenic from macroalgae, phytoplankton and sediment porewaters has been investigated by a series of controlled laboratory experiments. The appearance of dissolved arsenic species in the overlying waters was monitored using a coupled hydride generation/GC AA analytical technique. The liberation of dissolved arsenic species by the macroalgae Ascophyllum nodosum was examined under estuarine conditions at 5 °C and 15 °C. At the lower temperature the release rates were 0.2 μg kg^?1 h^?1 (wet weight of material) for monomethylarsenic (MMA) and 0.5 μg kg^?1 h^?1 for dimethylarsenic (DMA), whereas at 15 °C the rates were 0.4 μg kg^?1 h^?1 and 3.2 μg kg^?1h^?1, respectively. Incubation experiments were also carried out at 15 °C using the diatom Skeletonema costatum. During the log growth phase, when chlorophyll a concentrations were in the range 1-5 μg dm^?3, the rate of appearance of DMA in the water was ～3 ng dm^?3 h^?1. Sediment samples from the freshwater and seawater end-members of the Tamar Estuary, UK, were incubated under natural conditions at 5 °C and 15 °C. The freshwater sediments released DMA in preference to MMA; the concentrations of both species increased exponentially and reached a steady state in the overlying water after 250 h. Considerably more DMA was produced at 15 °C than at 5 °C, whilst the amount of MMA produced appeared to be insensitive to the temperature increase. In contrast, the seawater sediments always produced more MMA than DMA and the increase in temperature had little effect on the production of either MMA or DMA. The results of the laboratory experiments were compared with field observations in temperate estuaries, including the Tamar Estuary. The implications of changes of water temperature on the fate of arsenic in estuaries is discussed and modifications to the estuarine arsenic cycle are proposed.     

Differential preconcentration of arsenic(III) and arsenic(V) with thionalide loaded on silica gel

2-Mercapto-N-2-naphtylacetamide (thionalide) on silica gel is used for differential preconcentration of μg l^?1 levels of arsenic(III) and arsenic(V) from aqueous solution. In batch experiments, arsenic(III) was quantitatively retained on the gel from solutions of pH 6.5–8.5, but arsenic(V) and organic arsenic compounds were not retained. The chelating capacity of the gel was 5.6 μmol g^?1 As(III) at pH 7.0. Arsenic retained on teh column was completely eluted with 25 ml of 0.01 M sodium borate in 0.01 M sodium hydroxide containing 10 mg l^?1 iodine (pH 10). The arsenic was determined by silver diethyldithiocarbamate spectrophotometry. Arsenic(V) was subsequently determined after reduction to arsenic(III) with sulphite and iodide. Arsenic(III) and arsenic(V) in sea water are shown to be < 0.12 and 1.6 μg l^?1, respectively.     

Determination of arsenic in glycerine by flow injection,hydride generation and inductively-coupled plasma/atomic emission spectrometry

The determination of low concentrations of arsenic in glycerine is investigated with flow injection for the introduction of analyte and tetrahydroborate reagent for arsine generation, separation in a vapor-liquid flow cell, and inductively-coupled plasma/atomic emission spectrometry (i.c.p./a.e.s.). Peak areas are used to quantify arsenic in the concentration range 0.12–3.0 μg ml^?1. Peak areas for prepared standards exhibited average deviations of about 1.4% for this concentration range. The slope and intercept for a least- squares fit of area (nanocoulombs) vs. concentration (μg ml^?1) were 10.9 ± 0.17 and 0.46 ± 0.3, respectively.     

A comparative study on acute toxicity of methylarsonic acid,dimethylarsinic acid and trimethylarsine oxide in mice

The acute toxicity of methylarsonic acid, CH₃AsO(OH)₂ (MAA), dimethylarsininc acid, (CH₃)₂AsO(OH) (DMAA), and trimethylarsine oxide, (CH₃)₃AsO (TMAO), were examined in mice with oral administration. The LD₅₀ values of MAA, DMAA and TMAO were 1.8, 1.2 and 10.6 g kg^?1 respectively. The toxicity of MAA and DMAA was very much lower than that for inorganic arsenic compounds. It was shown that TMAO has a similar acute toxicity to arsenobetaine. On the other hand, when the mice were administered 14.4 g kg^?1 of TMAO once only orally, a garlic-like odor (trimethylarsine, (CH₃)₃As) was definitely detectable in the exhalation of the animals by the human olfactory sense within about a few minutes.     

The Distribution of Arsenic Compounds in the Ocean: Biological Activity in the Surface Zone and Removal Processes in the Deep Zone

The vertical profies of inorganic arsenic [As(III)+As(V)], monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) were investigated at four sampling stations in the Pacific Ocean and a sampling station in the southern Tasman Sea. In addition, the concentrations of those compounds in surface waters of the Pacific Ocean and Tasman Sea have been determined. The vertical profiles of inorganic arsenic showed the low concentrations in both the surface and deep/bottom zones. The depleted concentrations in the surface zone varied from 1000 to 1700 ng dm⁻³ and that in the deep/bottom zone varied from 1300 to 2050 ng dm⁻³. The maximum concentrations that varied from 1500 to 2450 ng dm⁻³ were usually observed at a depth of about 2000 m. Both MMAA and DMAA were observed throughout the water column at sampling stations in the north-western and equatorial regions of the Pacific Ocean. At the sampling station in the central northern Pacific gyre, DMAA was the only methylated arsenic compound observed throughout the water column. On the contrary, at the sampling station in the southern Tasman Sea, the only detected methylated arsenic compound throughout the water column was MMAA. Their vertical profiles showed maximum concentrations in the surface water which abruptly dropped with depth from 0 to 200 m. The concentration in the surface water was close to 10 ng dm⁻³ for MMAA and varied from 27 to 185 ng dm⁻³ for DMAA. At depths greater than 100 m, MMAA and DMAA were at comparable concentrations which varied from 0.7 to 14 ng dm⁻³. The low inorganic arsenic concentration in the surface zone was due to biological activity. This activity resulted in the uptake of As(V) and subsequent reduction and methylation to MMAA and DMAA. DMAA was the main predominant arsenic compound resulting from biological activity in surface waters. The low inorganic arsenic concentrations in the deep and bottom zones were likely to be caused by the adsorption of dissolved inorganic arsenic onto sinking particulates rich in iron and manganese oxides.     

Ultrasound Assisted Emulsification Microextraction Based on dimetyl (E)‐2‐[(Z)‐1‐acetyl)‐2‐hydroxy‐1‐propenyl]‐2‐butenedioate for Determination of Total Amount of Iron in Water and Tea Samples

An ultrasound assisted emulsification microextraction (USAEME) is successfully used for extraction and determination of trace amount of iron in water and tea samples, followed by flame atomic absorption spectroscopy (FAAS). In this approach, a new synthetic ligand dimetyl (E)‐2‐[(Z)‐1‐acetyl)‐2‐hydroxy‐1‐propenyl]‐2‐butenedioate (DAHPB) is used as chelating agent and chloroform is selected as an extraction solvent. The factors influencing the complex formation and extraction by USAEME method are optimized. These factors are extraction solvent type as well as extraction volume, time, temperature, pH, and the amount of chelating agent. Under optimum conditions, an enrichment factor of 202.9 is obtained from only 7.1 mL of aqueous phase. The calibration graph using the preconcentration system for iron is linear between 40.0 and 800.0 μg L^?1 with a detection limit of 7.4 μg L^?1. The relative standard deviation (R.S.D) for ten replicate measurements of 500.0 μg L^?1 of iron is 2.5%.     

Speciation of Arsenic Compounds in the Urine of Rats Orally Exposed to Dimethylarsinic Acid Ion Chromatography with ICP–MS as an Element-Selective Detector

A combined ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP—MS) system as an element-selective detector has been used for the determination of arsenic compounds. Seven arsenic compounds were separated by cation-exchange chromatography. Subsequently, the separated arsenic compounds were directly introduced into the ICP—MS and were detected at m/z =75. Detection limits for the seven arsenic compounds ranged from 0.8 to 3.8 μg As/l. The IC–ICP–MS system was applied to the determination of arsenic compounds in the urine of dimethylarsinic acid (DMAA)-exposed rats. DMAA was the most abundant arsenic compound detected. Arsenous acid, monomethylarsonic acid and trimethylarsine oxide were also detected.