Evidence supporting the presence of dissolved dimethylarsinate in the marine environment

Experiments have been carried out to test the commonly held belief that the dissolved dimethylarsenic species present in marine waters is dimethylarsinate. By employing a novel combination of HPLC and cryogenic‐trap hydride generation atomic absorption spectroscopy (HG AA), the sensitivity limitations of conventional in‐line HPLC instrumentation can be overcome, permitting dimethylarsinate to be measured by HPLC at levels below 200 pg cm⁻³. A comparison of results obtained by this procedure with those obtained by direct cryogenic‐trap HG AA demonstrated that much of the dissolved dimethylarsenic present in the mouth of the Beaulieu River estuary (Hampshire, UK) had HPLC retention characteristics consistent with the presence of dimethylarsinate. Copyright © 1999 John Wiley & Sons, Ltd.     

Arsenic bioaccumulation and species in marine polychaeta

Published whole tissue arsenic concentrations in polychaete species tissues range from 1.5–2739 µg arsenic/g dry mass. Higher mean total arsenic concentrations are found in deposit‐feeding polychaetes relative to non‐deposit‐feeding polychaete species collected from the same locations. However, mean arsenic concentrations at some of the locations are skewed by the high arsenic concentrations of Tharyx marioni. There appears to be no direct correlation between sediment arsenic concentrations and polychaete arsenic concentrations. Arsenic bioaccumulation by polychaetes appears to be more controlled by the physiology of the polychaetes rather than exposure to arsenic via ingested material or the prevailing physiochemical conditions. Arsenic concentrations in polychaete tissues can vary greatly. Most polychaete species contain the majority of their arsenic as arsenobetaine (57–98%), with trace concentrations of inorganic arsenic (<1%) and other simple methylated species (<7.5%). However, this is not always the case, with unusually high proportions of arsenite (57%), arsenate (23%) and dimethylarsinic acid (83–87%) in some polychaete species. Arsenobetaine is probably accumulated by polychaetes via organic food sources within the sediment. The presence of relatively high proportions of phosphate arsenoriboside (up to 12%) in some opportunistic omnivorous Nereididae polychaete species may be due to ingestion of macroalgae, benthic diatoms and/or phytoplankton. Consideration of the ecology of individual polychaete species in terms of their habitat type, food preferences, physiology and exposure to arsenic species is needed for the assessment of arsenic uptake pathways and bioaccumulation of arsenic. Future research should collect a range of polychaete species from a wide variety of uncontaminated marine habitats to determine the influence of these ecological factors on total arsenic concentrations and species proportions. Copyright © 2005 John Wiley & Sons, Ltd.     

Tissue accumulation and distribution of arsenic compounds in three marine fish species: relationship to trophic position

In this study the accumulation and distribution of arsenic compounds in marine fish species in relation to their trophic position was investigated. Arsenic compounds were measured in eight tissues of mullet Mugil cephalus (detritivore), luderick Girella tricuspidata (herbivore) and tailor Pomatomus saltatrix (carnivore) by high performance liquid chromatography–inductively coupled plasma‐mass spectrometry. The majority of arsenic in tailor tissues, the pelagic carnivore, was present as arsenobetaine (86–94%). Mullet and luderick also contained high amounts of arsenobetaine in all tissues (62–98% and 59–100% respectively) except the intestines (20% and 24% respectively). Appreciable amounts of dimethylarsinic acid (1–39%), arsenate (2–38%), arsenite (1–9%) and trimethylarsine oxide (2–8%) were identified in mullet and luderick tissues. Small amounts of arsenocholine (1–3%), methylarsonic acid (1–3%) and tetramethylarsonium ion (1–2%) were found in some tissues of all three species. A phosphate arsenoriboside was identified in mullet intestine (4%) and from all tissues of luderick (1–6%) except muscle. Pelagic carnivore fish species are exposed mainly to arsenobetaine through their diet and accumulate the majority of arsenic in tissues as this compound. Detritivore and herbivore fish species also accumulate arsenobetaine from their diet, with quantities of other inorganic and organic arsenic compounds. These compounds may result from ingestion of food and sediment, degradation products (e.g. arsenobetaine to trimethylarsine oxide; arsenoribosides to dimethylarsinic acid), conversion (e.g. arsenate to dimethylarsinic acid and trimethylarsine oxide by bacterial action in digestive tissues) and/or in situ enzymatic activity in liver tissue. Copyright © 2001 John Wiley & Sons, Ltd.     

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.     

Specific determination of selenoaminoacids in whole milk by 2D size-exclusion-ion-paring reversed phase high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP MS)

A procedure was developed for the quantitative recovery of selenomethionine (SeMet) and selenocysteine (SeCys) from whole milk. It was based on the protein unfolding, carbamidomethylation of the aminoacid residues using iodoacetamide and proteolysis using Protease XIV. The selenoaminoacids were specifically determined by ion-paring reversed phase HPLC-ICP MS after their isolation from the post-reaction mixture by size-exclusion LC. Se(IV) present in the sample was derivatized as well and was determined along with the selenoaminoacids. The origin and identity of species were identified by the co-elution with the Se(IV), isotopically labelled selenomethionine, and with the synthetic standard of carbamidomethylated selenocysteine. The method development for SeCys was assisted by using glutathione peroxidise as the SeCys standard. SeMet, SeCys and Se(IV) were quantified by the method of standard additions. The mass balance provided a measure of the method validation. The method was applied to monitoring selenium speciation during supplementation of cows (dose-effect study) with Se-rich yeast containing feed and during milk processing.     

Biodegradation of arsenosugars in marine sediment

In the marine environment, arsenic accumulates in seaweed and occurs mostly in the form of arsenoribofuranosides (often called arsenosugars). This study investigated the degradation pathways of arsenosugars from decaying seaweed in a mesocosm experiment. Brown seaweed (Laminaria digitata) was placed on top of a marine sediment soaked with seawater. Seawater and porewater samples from different depths were collected and analysed for arsenic species in order to identify the degradation products using high‐performance liquid chomatography–inductively coupled plasma mass spectrometry. During the first 10 days most of the arsenic found in the seawater and the shallow sediment is in the form of the arsenosugars released from the seaweed. Dimethylarsenoylethanol (DMAE), dimethylarsinic acid (DMA(V)) and, later, monomethylarsonic acid (MMA(V)) and arsenite and arsenate were also formed. In the deeper anaerobic sediment, the arsenosugars disappear more quickly and DMAE is the main metabolite with 60–80% of the total arsenic for the first 60 days besides a constant DMA(V) contribution of 10–20% of total soluble arsenic. With the degradation of the soluble DMAE the solubility of arsenic decreases in the sediment. The final soluble degradation products (after 106 days) were arsenite, arsenate, MMA(V) and DMA(V). No arsenobetaine or arsenocholine were identified in the porewater. Copyright © 2005 John Wiley & Sons, Ltd.     

Determination of arsenic species in marine organisms by HPLC-ICP-OES and HPLC-HG-QFAAS

Separation and quantification of six arsenic species have been performed in cod, tuna and mussel samples by high performance liquid chromatography (HPLC) using inductively coupled plasma-optical emission spectrometry (ICP-OES) and hydride generation-quartz furnace atomic absorption spectrometry (HG-QFAAS) as detection techniques. It has been shown that arsenic extraction with a water-methanol (11) mixture is sufficiently quantitative for the cod and tuna, in which arsenic is mainly present as arsenobetaine (about 90% of total As extracted). In contrast, only 60% of the element is extracted from the mussels and the chromatograms obtained reveal the presence of an unknown compound. Detection limits are in the g ml^–1 range for the HPLC-ICP-OES technique (quantification of arsenobetaine and arsenocholine) and in the ng ml^–1 range for the HPLC-HG-QFAAS system (quantification of arsenite, arsenate, monomethylarsonic and dimethylarsinic acids).     

Analytical Methods for Speciation of Organotins in the Environment

The growing awareness over the environmental fate of organotin compounds is reflected in the large number of analytical methods developed for their separation. Organotin compounds have varying degrees of toxicological properties, depending on the nature and number of alkyl groups bonded to the tin atom. Most of the analytical speciation methods applied to actual environmental media have involved prior derivatization to transform organotin compounds into volatile hydrophobic analytes amenable to separation and identification by gas chromatography coupled to a sensitive and selective tin-detector. Evidence exists that members of the same homologous series are related by environmental degradation pathways. Chemical treatment prior to analysis, or high temperatures associated with gas chromatography separation, may alter the relative amounts of organotins in samples and blur the true environment picture. To avoid species redistribution that may occur during derivatization or gas speciation analysis, methods based on liquid chromatography and supercritical fluid chromatography have been investigated. This review documents analytical methods for determination of tin and speciation of organotin compounds, in the hope that it will be of value to those interested in initiating a programme for assessing the impact of such species on the environment.     

Ion chromatography–inductively coupled plasma mass spectrometry determination of arsenic species in marine samples

Arsenic speciation analysis in marine samples was performed using ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP‐MS) detection. The separation of eight arsenic species, viz. arsenite, monomethyl arsonic acid, dimethylarsinic acid, arsenate, arsenobetaine, tetramethylarsine oxide, arsenocholine and tetramethylarsonium ion was achieved on a Dionex AS4A (weaker anion exchange column) by using a nitric acid pH gradient eluent (pH 3.3 to 1.3). The entire separation was accomplished in 12 min. The detection limits for the eight arsenic species by IC–ICP‐MS were in the range 0.03–1.6 µ g l^?1, based on 3σ of the blank response (n = 6). The repeatability and day‐to‐day reproducibility were calculated to be less than 10% (residual standard deviation) for all eight species. The method was validated by analyzing a certified reference material (DORM‐2, dogfish muscle) and then successfully applied to several marine samples, e.g. oyster, fish muscle, shrimp and marine algae. The low power microwave digestion was employed for the extraction of arsenic from seafood products. Copyright © 2004 John Wiley & Sons, Ltd.     

Combination of LC-ICP-MS, LC-MS and NMR for investigation of the oxidative degradation of selenomethionine

Selenomethionine (SeMet) was oxidized by heating an acidic solution with hydrogen peroxide. Samples were taken before and during the oxidation process. The oxidation products were separated by cation exchange chromatography followed by ICP-MS detection to identify the selenium containing compounds as well as electrospray ionization MS detection to determine the masses of the degradation products. Furthermore, the samples were analyzed by ⁷⁷Se-NMR. The first appearing degradation product was selenomethionine selenoxide, which was converted via the deaminated selenoxide to methane seleninic acid and selenite.     

四川兴文地区硒的地球化学特征及生物效应

四川兴文土地质量调查显示:兴文县表层土壤中硒质量分数为0.075~2.540 mg/kg,平均值为0.43 mg/kg,富硒土地面积占调查面积53.25%,合计734.75 km^2。全区大米硒质量分数平均值为0.064 mg/kg,硒含量处于较为富足水平。水稻中的硒元素含量与根系土中硒元素呈明显正相关关系。根系土中水溶态硒和离子交换态硒含量高时,土壤容易产出富硒作物。     

Determination of Arsenic in Algae – Results of an Interlaboratory Trial: Determination of Arsenic Species in the Water-Soluble Fraction

Seven algae samples, five purchased from food stores and two reference algae (BCR 279 Sea Lettuce) were distributed as blind samples to 13 laboratories from which five labs attempted a full characterisation of the water-soluble fraction with respect to their arsenic species. The extraction efficiency is largely dependant on the algae and varied from 3% to 96%. Besides inorganic arsenic (mainly as As^(V)) DMA^(V) and, in particular, several arsenosugars were identified in all samples. From the five labs, three labs gave agreeable results in respect of the arsenic species identification and its quantification, although different chromatographic methods were used. Different Hijiki samples seem to contain largely different arsenic concentration (67–113 mg As/kg) which may also have an influence on the distribution of inorganic arsenic and arsenosugars.     

HPLC-ICP-MS测定植物样品中6种砷形态化合物

通过优化色谱分离、样品前处理条件,同时对比了电感耦合等离子体质谱的标准模式(STD)、碰撞模式(KED)、氧气反应模式(Oxygen-DRC)、甲烷反应模式(Methane-DRC)的检测结果,建立了一种有效分离植物样品中砷甜菜碱(AsB)、二甲基砷酸(DMA)、亚砷酸(As(Ⅲ))、砷胆碱(AsC)、一甲基砷酸(MM...     

Improvement of speciation analysis in environmental matrices. Identification of refractory arsenicals—some analytical difficulties

Arsenic species that do not form hydrides have been recently put in evidence in coastal seawater. This paper describes the procedures used in the first attempts to concentrate, purify and identify these forms as well as the difficulties that make this identification problematic. The rationale behind a new scheme under investigation based on solvent extraction/high-performance liquid chromatography/dynamic-flow-fast-atom-bombardment mass spectrometry is presented. Some alternatives that seem promising for the future are indicated.     

Speciation analysis to unravel the soil-to-plant transfer in highly arsenic-contaminated areas in Cornwall (UK)

Two areas near derelict calciners in Cornwall (UK) were chosen to study the uptake of arsenic from arsenic-contaminated soil into indigenous plants (heather, Calluna vulgaris; blackberry, Rubus ulmifulmus; gorse, Ulex europaeus). With total arsenic concentrations in soil ranging from 1240 to 2860 mg kg^?1 at Site 1 (Tuckingmill), no adverse effects on the growth of the plants studied were observed. Very low soil-to-plant transfer factors (0.01 to 0.03) were found although they were much higher when the extractable soil arsenic concentrations were taken into account (0.1 to 1.1). In the central dump area at Site 2 (Bissoe, 9.78% [w/w] arsenic in soil), the only plant to grow was heather, although it was severely impaired. However, heather was thriving at the edge of the dump where higher soil arsenic concentrations were found (10.32% [w/w]), indicating that arsenic is not a growth-limiting factor in itself. Soil-to-plant transfer factors in the range 2 × 10^?5–9 × 10^?4 confirm that arsenic is indeed effectively excluded from uptake, even taking into account extractable soil arsenic concentrations (9 × 10^?4–1.2 × 10^?2).

Extraction of bioavailable arsenic from soil using 0.05 mol L^?1 ammonium sulphate yielded recoveries from 1.18 to 3.34% of the total arsenic, predominantly in the form of arsenate. Extraction of arsenic and its metabolites from plants was achieved with water or a water/methanol mixture yielding recoveries up to 22.4% of the total arsenic, with arsenite and arsenate the predominant arsenic species and a minor fraction consisting of methylarsonic acid, dimethylarsinic acid and trimethylarsine oxide. The identity of the remainder of the non-extractable arsenic species still has to be revealed. Although the data suggest that higher plants synthesise organoarsenic compounds it cannot be excluded that symbiotic organisms have synthesised these compounds.     

Method for Determination of Selenium and Arsenic in Human Urine by Atomic Fluorescence Spectrometry

Abstract

The study presents the method for simultaneous determination of selenium and arsenic in human urine by atomic fluorescence spectrometry (AFS). According to the procedure developed, a sample is first digested in the microwave system, then chemically treated in the flow through a hydride generation system, and finally exposed to measurements in a double‐channel atomic fluorescence spectrometer. It has been revealed that selenium and arsenic can be accurately determined with detection limit of 0.13 and 0.16 µg/L and repeatability (RSD) of 1.0 and 1.2%, respectively. The urine samples taken from a control group and from persons subjected to a special diet were analyzed. The obtained results proved that the method developed was capable of controlling reliably even slight changes of both elements in a wide range of their concentrations, and, as such, that it can be recommended to be used for clinical and toxicological purposes.     

Profile distribution of As(III) and As(V) species in soil and groundwater in Bozanta area

The profile distribution of arsenic(III) and arsenic(V) species in soil and groundwater was investigated in the samples collected in 2005 from a hand-drilled well, in the Bozanta area, Baia Mare region, Romania. The total content of arsenic in the soil was in the range of 525–672 mg kg⁻¹ exceeding 21–27 times the action trigger level for sensitive soil. 0.9–11.3 % of the total content was soluble in water, 83.0–92.6 % in 10 mol dm⁻³ HCl and 2.6–13.3 % was the residual fraction. Arsenic(V) was the dominant arsenic species in the soil in the range of 405–580 mg kg⁻¹. The distribution and mobility of arsenic species was governed by soil pH and contents of Al, Fe, and Mn. The mobility of arsenic(V) decreased with depth, while that of arsenic(III) was high at the surface and in the proximity of groundwater. The total concentration of arsenic in groundwater was (43.40 ± 1.70) μg dm⁻³, which exceeded the maximum contaminant level of 10 μg dm⁻³. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

Characteristics of selenium in australian marine biota

The occurrence, distribution and speciation of selenium in Australian marine biota is discussed. Biochemical pathways for the accumulation of selenium by marine organisms are also postulated. Comparison of the levels of selenium in macroalgae, fish, crustaceans and molluscs indicates that preferential accumulation of selenium by particular taxa does not occur. Phaeophyta have significantly lower selenium concentrations than Rhodophyta and Chlorophyta. Fish have lower selenium contents in muscle tissues than molluscs and crustaceans. Marine animals with different dietary intake (planktonic vs herbivorous vs carnivorous) are not observed to have significantly different levels of selenium (P>0.05). Selenium in all the organisms studied was predominantly associated with free amino-acids or protein residues and was not present as characterizable inorganic selenium species (SeO₃^2?, SeO₄^2?). These results indicate that selenium is probably only incorporated into biota for specific biochemical purposes with any exces selenium being excreted or eliminated.     

HPLC–ICP–MS法测定地表水体中砷的形态

建立了高效液相色谱和电感耦合等离子体质谱联用技术测定水中砷形态的方法。对高效液相色谱和电感耦合等离子体质谱的实验条件如流动相的p H值及浓度、RF功率、采样深度、载气和补偿气流速等进行了优化。测定5种砷形态的线性范围为2.5~30.0μg/L,线性相关系数大于0.999,5种砷形态的检出限在0.10~0.15μg/L之间。对江、湖和河流3类地表水体样品分别加入2.0,5.0,15.0μg/L砷形态混合标准溶液进行回收试验,加标回收率为91.6%~104.5%,测定结果的相对标准偏差为1.5%~4.6%(n=6)。该方法灵敏、高效,适合于水中砷形态的测定。