Arsenic Speciation In Water Research Articles

Novel Preservation Methods for Inorganic Arsenic Speciation in Model and Natural Water Samples by Stripping Voltammetric Method

In this study, the preservation of As(III) in model solutions and natural groundwater samples from four locations in Croatia was conducted. Model laboratory samples were spiked with As(III) and As(V), and different complexing agents. Solutions were analysed in intervals of 24, 48 h and during ten days after preparation. Model samples containing citric acid, sodium citrate, sodium oxalate and potassium sodium tartrate in combination with acetic acid, spiked with As(III)and As(V), showed good species preservation. As(III), in model samples, was preserved for 7 days with citric acid, and citric acid in combination with acetic acid, as well as with tartrate. As(III), in natural samples, was preserved for 6 to 12 days with potassium sodium tartrate, citric acid, and citric acid in combination with acetic acid and showed improvement, compared with unpreserved samples (oxidation in 3 days). The results showed that acetic acid alone was not successful in preserving As speciation. Good resolution of inorganic arsenic species was achieved using differential pulse anodic stripping voltammetry technique (DPASV). Since this technique is comparatively cheaper and more convenient to use than other available techniques it could become a method of choice for arsenic speciation in water.

Seasonal impacts on arsenic mobility and geochemistry in streams surrounding a gold mineralization area, Paracatu, Brazil

Arsenic (As) is a trace element in the Earth's crust that often occurs with gold mineralization, where it is found in association with sulfide-bearing minerals such as pyrite (FeS2). Our study evaluated the mobility of As in creeks that traverse a gold mineralization area in Paracatu, Brazil. The results relate As mobility in water draining actively mined areas to season, wet and dry, and to the impact of in-stream channels lined with limestone that are used to neutralize acid mine drainage. Passage of the creek water through channels lined with limestone decreased soluble As to concentrations below the drinking water threshold in 13 out of 31 samples (10 μg.L−1). The soluble As concentrations were generally higher during the wet season. Arsenic speciation in water was mainly influenced by the season and by the proximity to mineralization zones in the areas that are actively mined. The organic arsenic species DMA (dimethylarsinate) was detected near the mineralized area during the wet season. Sediment-associated As varied with season and with sampling site, but was consistently high at one headwater spring; the highest observed value was 8750 mg As kg−1. We applied selective sequential extraction techniques to assess the portioning of As in the creek sediments. Two of the most mobile fractions of sediment-associated As, the adsorbed and very poorly crystalline fractions, showed a strong seasonal dependence which supported mobilization of As during the wet season. The amorphous Fe oxide fraction followed the same trend but contributed less As, and As associated with the crystalline Fe oxide fraction showed little fluctuation with season.

Selective speciation of inorganic arsenic in water using nanocomposite based solid-phase extraction followed by inductively coupled plasma-mass spectrometry detection

The multi-walled carbon nanotubes-branched polyethyleneimine (MWCNTs-BPEI) adsorbent composite material was employed to separate and pre-concentrate As(V) in water samples. The characterization of MWCNTs-BPEI by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy showed successful modification of the composite. The MWCNTs-BPEI composite exhibited selective retention of As(V) in the presence of As(III) in water samples of pH 7 using 40 mg of composite as adsorbent. The pre-concentrated As(V) was quantified using inductively coupled plasma-mass spectrometry (ICP-MS). A limit of detection (LOD) of 0.0537 µg L−1 and limit of quantification (LOQ) of 0.179 µg L−1 were achieved along with pre-concentration factor of 23.3. A percentage recovery of 81.0% confirm the accuracy of the method. The As(V) concentrations in water were in the range of 0.0612–3.65 µg L−1. The As(V) concentrations determined using solid-phase extraction (SPE) procedure were in good agreement with the concentrations obtained using high performance liquid chromatography hyphenated to inductively coupled mass-mass spectrometry (HPLC hyphenated to ICP-MS).

Ultrasound assisted deep eutectic solvent based on dispersive liquid liquid microextraction of arsenic speciation in water and environmental samples by electrothermal atomic absorption spectrometry

A green and highly efficient deep eutectic solvent ultrasound-assisted liquid phase microextraction (DES-UALPME) method have been developed for speciation of As(III) and As(V). Extraction of As(III) was observed by using sodium diethyldithiocarbamate (DDTC) as a chelating agent, choline chloride-phenol as extracting solvent and tetrahydrofuran (THF) as dispersive solvent. Arsenic concentration was determined by electrothermal atomic absorption spectrometry (ETAAS). The developed procedure established on significant recoveries of As(III) and also As(V) recoveries were obtained as <5%. Whereas the reduction of As(V) was achieved with potassium iodide and ascorbic acid. This technique was useful for the analysis of total arsenic. Whereas As(V) was originated as variation among total As and As(III) levels. The key factors affecting the microextraction efficiency including pH, ultrasonication time, and amount of ligand were studied and optimized. Under optimum conditions, limit of detection (LOD), limit of quantification (LOQ), preconcentration factor (PF) and relative standard deviation (RSD) were calculated as 10ng L−1, 33ng L−1, 25 and 4.3%, respectively. The accuracy of developed technique was carried through the analysis of certified reference materials. Technique was used for the speciation of As(III) and As(V) in water samples collected from Tokat, Turkey. It was also applied for the determination of total arsenic within food and environmental samples.

Arsenic speciation in water and biota samples at trace levels by ion chromatography inductively coupled plasma-mass spectrometry

ABSTRACTA sensitive, reliable, simple and rapid analytical method was developed for the determination of arsenite [As(III)], arsenate [As(V)] and arsenobetaine (AsB) species using ion chromatography combined with inductively coupled plasma-mass spectrometry (IC-ICP-MS). Inorganic and organic arsenic species were separated with an anion exchange column (Dionex AS9) and a 50 mM sodium bicarbonate mobile phase (pH 10) at a flow rate of 1.0 mL min−1. %RSD values were found to be lower than 5.1% for all arsenic species. The limits of detection (LOD) obtained for As(III), As(V) and AsB were 16.5 ng L−1, 14.1 ng L−1 and 6.2 ng L−1, respectively. The developed analytical method was tested using AsB certified reference material (NMIJ CRM 7901-a), and spring water certified reference material (UME CRM 1201) for accuracy check. This method was applied for the quantitative determination of arsenic species in different water samples and chicken samples as a solid matrix.

Human exposure assessment of different arsenic species in household water sources in a high risk arsenic area.

Understanding arsenic speciation in water is important for managing the potential health risks associated with chronic arsenic exposure. Most arsenic monitoring studies to date have only measured total arsenic, with few looking at arsenic species. This study assessed 228 ground water sources in six unstudied villages in Pakistan for total, inorganic and organic arsenic species using ion chromatography inductively coupled plasma collision reaction cell mass spectrometry. The concentration levels approached 3090μgL-1 (95% CI, 130.31, 253.06) for total arsenic with a median of 57.55μgL-1, 3430μgL-1 (median=52) for arsenate (As+5) and 100μgL-1 (median=0.37) for arsenite (As+3). Exceedance of the WHO provisional guideline value for arsenic in drinking water (10μgL-1) occurred in 89% of water sources. Arsenic was present mainly as arsenate (As+5). Average daily intake of total arsenic for 398 residents living in the sampled houses was found up to 236.51μgkg-1day-1. This exposure estimate has indicated that 63% of rural residents exceeded the World Health Organization's provisional tolerable daily intake (PTDI) of 2.1μgkg-1day-1 body weight. Average daily intake of As+5 was found to be 15.63μgkg-1day-1 (95% CI, 5.53, 25.73) for children ≤16 and 15.07μgkg-1day-1 (95% CI, 10.33, 18.02) for adults. A mean daily intake of 0.09μgkg-1day-1 was determined for As+3 for children and 0.26μgkg-1day-1 for adults. Organic arsenic species such as monomethylarsonic acid (MMA), dimethylarsinic acid (DMA) and Arsenobetaine (AsB) were found to be below their method detection limits (MDLs).

Fast arsenic speciation in water by on-site solid phase extraction and high-resolution continuum source graphite furnace atomic absorption spectrometry

A method of high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS-GFAAS), combined with on-site separation/solid phase extraction (SPE) has been developed for the speciation of inorganic As (iAs) in geothermal and drinking water samples. The HR-CS-GFAAS calibration curves were linear up to 200μg/L As, but using second order polynomial fitting, accurate calibration could be performed up to 500μg/L. It has been demonstrated that sample pH should not be higher than 8 for an accurate speciation of As(V) with a recovery of ≈95%. Geothermal water had fairly high salt content (≈2200mg/L) due to the presence of chlorides and sulfates at mg/L levels. Therefore, a two-fold dilution of these types of samples before SPE is recommended, especially, for total As determinations, when the As concentration is as high as 400μg/L. For drinking water, sampled from public wells with records of As concentrations higher than the 10μg/L in the past, the reduction of As contamination below the WHO's health limit value could be observed. However, the electrical conductivity was close to 2500μS/cm, i.e., the guideline limit for drinking water, which was due to their higher chloride content. The proposed fit-for-purpose SPE-HR-CS-GFAAS method could be a candidate for screening drinking water quality.

Arsenic speciation in water, suspended particles, and coastal organisms from the Taehwa River Estuary of South Korea

Water, suspended particulate matter (SPM), and biota samples were collected from the Taehwa River Estuary to determine the distributions, partitioning, and bioaccumulation of arsenicals. Six forms of As were quantitated by the use of HPLC-ICP/MS. As was found mainly near urban and industrial areas, and inorganic AsV was the predominant As form in both water and SPM. Particulate arsenicals were found at the greatest concentrations in coarse particles (>180μm), followed by medium (30–180μm) and fine (0.45–30μm) particles, in freshwater. Arsenical concentrations were similar across the three particle fractions in saltwater. Field-based distribution coefficient (Kd) values for As depended strongly on SPM, with a less robust dependence on salinity. Concentrations of As were greater in macroalgae than in marine animals, such as fishes, bivalves, crabs, shrimps, and gastropods. Overall, the results of the present study provide useful information on the behaviors and fate of arsenicals in an estuarine environment.

Development of a method for speciation of inorganic arsenic in waters using solid phase extraction and electrothermal atomic absorption spectrometry

ABSTRACTA solid phase extraction (SPE) procedure based on Amberlite IRA 900 resin was developed for speciation and separation of inorganic arsenic species (III, V) and total As in water samples. The As species and total As in eluent solutions were determined by electrothermal atomic absorption spectrometry (ETAAS) using Ni chemical modifier with 1200°C pyrolysis temperature. Experimental parameters such as pH value, sample volume, flow rate, volume and concentration of eluent solution for As(V) were optimised and 98.0 ± 1.9% recovery was found at pH 4.0. Experimental adsorption capacity of the resin for As(V) was investigated and 229.9 mg g–1 was found. Under optimised experimental conditions, instrumental parameters such as limit of detection (LOD) and limit of quantification (LOQ) found were 0.126 and 0.420 µg L–1, respectively. Interference effects of coexisting ions in the sample matrix on the recovery of As(V) were investigated. Concentration of As(III) was obtained by subtracting As(V) concentration found at pH 4.0 from total As(III + V) found at pH 8.0. The accuracy of the method proposed by using the resin was tested for analysing As species in a waste water standard reference material (SRM, CWW-TM-D) and spiked real water samples with recovery above 95%. The method proposed was also applied to the determinations of As species and total As in underground hot waters and tap water with relative error below 3%.

Measurement of labile arsenic speciation in water and soil using diffusive gradients in thin films (DGT) and X-ray absorption near edge spectroscopy (XANES)

Environmental context Both inorganic and organic arsenic species are toxic to the environment when labile. The Diffusive Gradients in Thin Films technique, equipped with ferrihydrite binding gel enables measurement of labile arsenic species from water and soil solutions. This study indicated that labile arsenic species are quantitatively adsorbed to the gel, and that they are stable for up to 2 weeks following deployment. Abstract Arsenic speciation was determined in the solution extracted from a ferrihydrite binding gel layer in a DGT unit (FB-DGT) deployed in water using coupled high-performance liquid chromatography and hydride generation atomic fluorescence spectrometry (HPLC-HG-AFS). However, the extent of change in arsenic speciation during the extraction process is unknown. By identifying the arsenic species in the FB-DGT gel directly, using X-ray absorption near edge spectroscopy (XANES) fitting with model arsenic compounds, we obtain a better understanding of the ability of FB-DGT to measure labile arsenic species in solution. The results presented herein confirm that FB-DGT accumulated labile inorganic and methylated arsenic species. Arsenic species bound to the FB-DGT gel were stable for up to 2 weeks following deployment. However, caution should be applied when interpreting the proportion of As species measured by HPLC-HG-AFS in solution extracted from FB-DGT because the distribution of arsenic species in extracted solutions was found to be modified by the extraction process. Some (~20%) of arsenate was converted into arsenite, and a significant amount (~25%) of dimethylarsinic acid (DMAsV) was converted into monomethylarsonic acid (MMAsV) or arsenate (AsV). Only inorganic arsenite (iAsIII) was stable during the extraction process. These findings suggested that, based on the XANES measurement, although As species were quantitatively accumulated in the FB-DGT gel, the FB-DGT technique was still unsuitable for studying As speciation. This is because changes in arsenic speciation were observed to occur during gel extraction, prior to HPLC-HG-AFS measurement, and because the XANES technique is available for routine measurements.

The Recent Advances and Applications of Arsenic Speciation in Water

Arsenic (As) is well known as a toxic element for human beings. The toxicity, mobility,and bioavailability of As compounds is highly dependent on its chemical forms and oxidation states. Speciation analysis of trace elements is an important issue in biomedical and environmental sciences. For the past few years many studies have been performed to determine As speciation in tap water, food chain and other environmental samples. This review provides the chemical speciation of As in water analysis in recent ten years, including the separation and preconcentration techniques, chromatographic techniques, detection techniques of inorganic As and organic As species (included As-containing chemical warfare agents). The advantages of various methods, insufficient, selectivity, sensitivity, limit of detection (DL) were reviewed.

Arsenic speciation in water by high-performance liquid chromatography/inductively coupled plasma mass spectrometry-method validation and uncertainty estimation

In order to obtain reliable analytical results for the separation and determination of arsenic species by high-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICP-MS), the analytical procedure must be fully validated and the measurement uncertainty of the analytical result should be estimated. The total arsenic concentration of the samples was determined by ICP-MS. Separation of the arsenic species, AsB, As(III), DMA, MMA and As(V), was accomplished by liquid chromatography, which was hyphenated to inductively coupled plasma mass spectrometry, used for detection purposes. Automated handling of these systems was achieved with Chromera software. The separation capability between the analytical signals of arsenic species, AsB-As(III), As(III)-DMA, DMA-MMA and MMA-As(V), was 1.3, 1.1, 5.1 and 4.6, respectively. The limit of detection (LOD) values ranged from 0.070 µg L(-1) for DMA to 0.13 µg L(-1) for MMA. The expanded uncertainty U [%] values for coverage factor k = 2 estimated for AsB, As(III), DMA, MMA and As(V) were 12 %, 13 %, 5.6 %, 9.6 % and 8.6 %, respectively. This study reports, for the first time, building the uncertainty budgets for five arsenic species and estimation of the expanded uncertainty (for k = 2). The qualitative and quantitative parameters determined in the validation process indicate that the presented analytical procedure can be applied for the determination of AsB, As(III), DMA, MMA and As(V) in water.

Arsenic speciation in water and snow samples by adsorption onto PHEMA in a micro-pipette-tip and GFAAS detection applying large-volume injection

A miniaturized solid phase extraction procedure has been developed for ultra-trace determination of inorganic arsenic species. Arsenic(III) as pyrrolidinedithiocarbamate complex was selectively adsorbed on 30mg poly(hydroxyethyl methacrylate) (PHEMA) micro beads, which is simply packed into a micro-pipette-tip. The adsorbed arsenic was quantitatively eluted by 700μL 0.25M NH3 and determined by graphite furnace atomic absorption spectrometry (GFAAS). Injection of larger volume (i.e., 50μL v.s. conventional 10–20μL) eluent into graphite furnace and the use of Mg(NO3)2 as chemical modifier have improved atomic absorption signal intensity (sensitivity as characteristic mass of 25pg) and precision (RSD of 2.6%, c=10μgL−1, n=11). Total arsenic amount was determined after reduction of arsenic(V) to arsenic(III) by thiourea-HCl system. As(V) concentration was calculated by the difference between As(III) and total arsenic. The detection limit (3s) of the method was found as 10ngL−1 As(III) with an enrichment factor of 86. The relative standard deviation and relative error for six replicate determinations of 0.5μgL−1 As(III) were found to be 4.0% and −0.7%, respectively. The method was successfully applied to drinking water, snow and reference water (SEM-2011) samples. When the samples were spiked with 0.5 and 1.0μgL−1 As(III) and As(V), the recoveries varied between 96 and 100%.

Field deployable method for arsenic speciation in water

Contamination of drinking water supplies by arsenic is a world-wide problem. Total arsenic measurements are commonly used to investigate and regulate arsenic in water, but it is well understood that arsenic occurs in several chemical forms, and these exhibit different toxicities. It is problematic to use laboratory-based speciation techniques to assess exposure as it has been suggested that the distribution of species is not stable during transport in some types of samples. A method was developed in this study for the on-site speciation of the most toxic dissolved arsenic species: As (III), As (V), monomethylarsonic acid (MMA) and dimethylarsenic acid (DMA). Development criteria included ease of use under field conditions, applicable at levels of concern for drinking water, and analytical performance. The approach is based on selective retention of arsenic species on specific ion-exchange chromatography cartridges followed by selective elution and quantification using graphite furnace atomic absorption spectroscopy. Water samples can be delivered to a set of three cartridges using either syringes or peristaltic pumps. Species distribution is stable at this point, and the cartridges can be transported to the laboratory for elution and quantitative analysis. A set of ten replicate spiked samples of each compound, having concentrations between 1 and 60 μg/L, were analyzed. Arsenic recoveries ranged from 78% to 112% and relative standard deviations were generally below 10%. Resolution between species was shown to be outstanding, with the only limitation being that the capacity for As (V) was limited to approximately 50 μg/L. This could be easily remedied by changes in either cartridge design, or the extraction procedure. Recoveries were similar for two spiked hard groundwater samples indicating that dissolved minerals are not likely to be problematic. These results suggest that this methodology can be use for analysis of the four primary arsenic species of concern in drinking water supplies.

Evaluation of liquid chromatography inductively coupled plasma mass spectrometry for arsenic speciation in water from industrial treatment of shale

This work describes an arsenic speciation analysis in aqueous effluent from a shale industrial plant using liquid chromatography coupled to inductively coupled plasma mass spectrometry (LC–ICP–MS). Arsenic species have been separated through an anion-exchange column and several parameters investigated, such as retention time, pH, flow rate and concentration of the mobile phase (ammonium carbonate), chloride interference and column conditioning time. The best conditions have been found by fixing the pH of the mobile phase at 8.7. Keeping the mobile phase flow rate at 1.5 ml min − 1 , arsenic species were separated by varying the concentration of the mobile phase and the time of elution, as follow: 1.5 mmol l − 1 for 10 min, 12 mmol l − 1 for 10 min and 20 mmol l − 1 for 10 min, respectively. Up to 13 As species present in the samples were separated under these conditions and the following species could be identified and quantified: arsenite [As(III)], dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and arsenate [As(V)]. The limits of detection of the LC–ICP–MS method were 0.02, 0.06, 0.04 and 0.10 μg l − 1 of As(III), DMA, MMA, and As(V), respectively. The concentration of these species in the samples were from 3.7 to 6.4 μg l − 1 , 6.9 to 13.2 μg l − 1 , 100 to 142 μg l − 1 and 808 to 1363 μg l − 1 for As(III), DMA, MMA and As(V), respectively. The accuracy, evaluated by recovery tests, varied from 94 to 105% and the precision, evaluated by the relative standard deviation was typically lower than 10%.

Speciation of Arsenic Using Chelation Solvent Extraction and High Performance Liquid Chromatography

AbstractResearch interest in speciation of arsenic stems from its species dependent behavior in the environment and in living organisms. The complexity of the matrix to be analyzed and low concentrations of target arsenic species that may be labile or difficult to chromatogram, indicate that a suitable pre‐treatment methodology is required. This study investigated the usefulness of chelation solvent extraction – high performance liquid chromatography (CSE‐HPLC) for the speciation of arsenic in water. It involved reacting arsenic with the chelant known for its affinity towards arsenic, followed by extraction, separation, and identification of the arsenic‐chelant‐arsenic complex. Arsenic species having different physicochemical properties were investigated. Species, such as, As2O3, As3O5, KH2AsO4, Na2HAsO4, and NaAsO2 were detected as a group of closely eluted peaks with different retention times and spectral properties, whereas, the organic arsenic species CH3Na2AsO3, o‐arsanilic acid, roxarson and triphenyl arsine separated quite well on the EnviroseP‐CM HPLC column. Key method parameters, such as, type of HPLC column, composition of mobile phase and organic solvents affecting peak resolution and sensitivity were optimized. Real environmental matrices contaminated with arsenic were analyzed under varying wavelengths (λmax = 190, 210, 220, 234, 244, and 282 nm), with good precision. Different arsenic species were detected in these samples with excellent background and signal‐to‐noise ratios demonstrating the robustness of the method. The detection limit, reproducibility, selectivity, accuracy, and dynamic range of the calibration curves were evaluated.

Inorganic arsenic speciation in water and seawater by anodic stripping voltammetry with a gold microelectrode

The determination of arsenic in sea and freshwater by anodic stripping voltammetry (ASV) was revisited because of problems related to unstable peaks and inconveniently strong acidic conditions used by existing methods. Contrary to previous work it was found, that As(III) can be determined by ASV using a gold microwire electrode at any pH including the neutral pH typical for natural waters. As(V) on the other hand, requires acidification to pH 1, but this is still a much milder condition than used previously. This is the basis of a new method for the chemical speciation of arsenic in natural waters. The limits of detection are 0.2 nM As(III) at pH 8 and 0.3 nM combined arsenic (III + V) at pH 1 with a 30 s deposition time. These limits are lowered by extending the deposition time. The detection step at pH 8 was stripping chronopotentiometry (SC) as this was found to give a lower detection limit than ASV. Copper is co-determined simultaneously with arsenic. The method was applied successfully to the determination of arsenic as well as copper in samples from the Irish Sea, mineral water and tap water.

Speciation of arsenic by ion chromatography inductively coupled plasma mass spectrometry using ammonium eluents

A method based on ion chromatography (IC) and inductively coupled plasma MS (ICP-MS) was developed for the speciation of arsenic in water and soil extracts. An anion-exchange column (G3154A/101) was used to separate As(III), As(V), dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA) with excellent resolution. Various ammonium salts, including NH4H2PO4, (NH4)2HPO4, (NH4)2CO3, and NH4HCO3, were examined as eluents to reduce matrix interference from chloride and to solve clogging problems. The best arsenic speciation was obtained within 9 min with excellent resolution and without interference from high chloride concentrations using an eluent containing 7.5 mM (NH4)2HPO4 at pH 7.9. The detection limits for the target arsenic species ranged from 0.1 to 0.4 microg/L with direct injection of sample without matrix elimination. The proposed method was effectively demonstrated by determining arsenic species in contaminated waters and soils of Bangladesh.

Arsenic Speciation Analysis in Water Samples: A Review of The Hyphenated Techniques

Interests in the determination of different arsenic species in natural waters is caused by the fact that toxic effects of arsenic are connected with its chemical forms and oxidation states. In determinations of water samples inorganic arsenate (As(III), As(V)), methylated metabolities (MMAA, DMAA) and other organic forms such as AsB, AsC, arsenosugars or arsenic containing lipids have the most importance. This article provides information about occurrence of the dominant arsenic forms in various water environments. The main factors controlling arsenic speciation in water are described. The quantification of species is difficult because the concentrations of different forms in water samples are relatively low compared to the detection limits of the available analytical techniques. Several hyphenated methods used in arsenic speciation analysis are described. Specific advantages and disadvantages of methods can define their application for a particular sample analysis. Insufficient selectivity and sensitivity of arsenic speciation methods cause searching for a new or modifications already existing techniques. Some aspects of improvement and modifications of the methods are highlighted.

Speciation of arsenic in water, sediment, and plants of the Moira watershed, Canada, using HPLC coupled to high resolution ICP-MS.

High-performance liquid chromatography (HPLC) coupled with high-resolution sector field ICP-MS was applied to the speciation of arsenic in environmental samples collected from the Moira watershed, Ontario, Canada. Arsenic contamination in Moira River and Moira Lake from historic gold mine operations is of increasing environmental concern to the local community. In this study, the current arsenic contamination status in water, sediment, and plants was investigated. Elevated levels of arsenic in the surface water of up to 75 ng mL(-1) in Moira River and 50 ng mL(-1) in Moira Lake were detected, 98% of which was present as arsenate. High concentrations of arsenic (>300 ng mL(-1)), mainly present as arsenite, were detected in sediment porewaters. A sediment profile of As from the West basin of Moira Lake showed lower As concentrations compared with data from the 1990s. An optimized extraction procedure using a phosphoric acid-ascorbic acid mixture demonstrated that an unknown "As-complex" which may consist of As, sulfide and organic matter is potentially responsible for the release of arsenite from the sediment to the overlying water column. Arsenic concentrations in plant samples ranged from 2.6 to 117 mg kg(-1), dry weight. Accumulation of arsenic was observed in submerged plants collected from Moira River and Moira Lake. Only a small part of the arsenic (6.3-16.1%) in the plants was extractable with methanol-water (9:1), and most of this arsenic (70-93%) was inorganic arsenic. A variety of organic arsenic compounds, including simple methylated compounds (methylarsonic acid and dimethylarsinic acid), trimethylarsine oxide, and tetramethylarsonium cation were detected at trace levels. No arsenobetaine and arsenocholine was found in any plant sample. An unknown compound, most probably an arsenosugar was detected in the two submerged plants, coontail ( Ceratophyllum demersum) and long-stemmed waterwort ( Elatine triandra). These submerged plants are constantly exposed to high arsenic concentrations in the surrounding water. Apparently, they are able to grow in this environment without invoking the same biochemical defence known from marine algae to detoxify inorganic arsenic. The detoxification mechanism of these plants remains unknown.