Effects of adsorbent dose, its particle size and initial arsenic concentration on the removal of arsenic, iron and manganese from simulated ground water by Fe3+ impregnated activated carbon

This paper presents the observations of the study on arsenic removal from a contaminated ground water (simulated) by adsorption onto Fe³⁺ impregnated granular activated carbon (GAC-Fe). Fe²⁺, Fe³⁺ and Mn²⁺ have also been considered along with arsenic species in the water sample. Similar study has also been done with untreated granular activated carbon (GAC) for comparison. The effects of adsorbent dose, particle size of adsorbent and initial arsenic concentration on the removal of As(T), As(III), As(V), Fe²⁺, Fe³⁺ and Mn²⁺ have been discussed. Under the experimental conditions, the optimum adsorbent doses for GAC-Fe and GAC have been found to be 8 g/l and 24 g/l, respectively with an agitation time of 15 h. Particle size of the adsorbents (both GAC and GAC-Fe) has shown negligible effect on the removal of arsenic and Fe species. However, for Mn removal the effect of adsorbent particle size is comparatively more. Percentage removal of As(T), As(V) and As(III) increase with the decrease in initial arsenic concentration (As₀). However, the increase in percentage removal of all the arsenic species with decrease in As₀ are less for higher value of As₀ (3000–500 ppb) than those of the lower value of As₀ (500–10 ppb). The % removal of As(T), As(III), As(V), Fe, and Mn were 95%, 92.4%, 97.6%, 99% and 41.2%, respectively when 8 g/l GAC-Fe was used at the As₀ value of 200 ppb. However, for GAC these values were 55.5%, 44%, 71%, 98% and 97%. The pH and temperature of the study were 7 ± 0.1 and 30 ± 1 °C, respectively.     

Treatment of arsenic contaminated water in a laboratory scale up-flow bio-column reactor

The present paper describes the observations on the treatment of arsenic contaminated synthetic industrial effluent in a bio-column reactor. Ralstonia eutropha MTCC 2487 has been immobilized on the granular activated carbon (GAC) bed in the column reactor. The synthetic water sample containing As(T) (As(III):As(V)=1:1), Fe, Mn, Cu and Zn at the initial concentrations of 25, 10, 2, 5, 10 ppm, respectively, was used. Concentrations of all the elements have been found to be reduced below their permissible limits in the treated water. The significant effect of empty bed contact time (EBCT) and bed height on the arsenic removal was observed in the initial stage. However, after some time of operation (approximately 3-4 days) no such effect was observed. Removal of As(III) and As(V) was almost similar after approximately 2 days of operation. However, at the initial stage As(V) removal was slightly more than that of As(III). In absence of washing, after approximately 4-5 days of operation, the bio-column reactor was observed to act as a GAC column reactor based on physico-chemical adsorption. Like arsenic, the percent removals of Fe, Mn, Cu and Zn also attained minimum after approximately 1 day and increased significantly to the optimum value within 3-4 days of operation. Dissolved oxygen (DO) has been found to decrease along with the increasing bed height from the bottom. The pH of the solution in the reactor has increased slightly and oxidation-reduction potential (ORP) has decreased with the time of operation.     

Treatment of arsenic contaminated water in a batch reactor by using Ralstonia eutropha MTCC 2487 and granular activated carbon

This paper presents the observations on the bio-removal of arsenic from contaminated water by using Ralstonia eutropha MTCC 2487 and activated carbon in a batch reactor. The effects of agitation time, pH, type of granular activated carbon (GAC) and initial arsenic concentration (As(o)) on the % removal of arsenic have been discussed. Under the experimental conditions, optimum removal was obtained at the pH of 6-7 with agitation time of 100 h. The % removal of As(T) increased initially with the increase in As(o) and after attaining the maximum removal (~86%) at the As(o) value of around 15 ppm, it started to decrease. Simultaneous adsorption bioaccumulation (SABA) was observed, when fresh GAC was used as supporting media for bacterial immobilization. In case of SABA, the % removal of As(III) was almost similar (only ~1% more) to the additive values of individual removal of As(III) obtained by only adsorption and only bio-adsorption. However, for As(V) the % removal was less (~8%) than the additive value of the individual % removals obtained by only adsorption and bio-adsorption. Percentage removal of Fe, Mn, Cu and Zn were 65.17%, 72.76%, 98.6% and 99.31%, respectively. Maximum regeneration (~99.4%) of the used bio-adsorbent was achieved by the treatment with 5NH(2)SO(4) followed by 1N NaOH and 30% H(2)O(2) in HNO(3). The fitness of the isotherms to predict the specific uptake for bio-adsorption/accumulation process has been found to decrease in the following order: Temkin isotherm>Langmuir isotherm>Freundlich isotherm. For the adsorption process with fresh GAC the corresponding order is Freundlich isotherm>Langmuir isotherm>Temkin isotherm for As(V) and As(T). However, for As(III) it was Langmuir>Temkin>Freundlich.     

Effect of Mn substitution on the oxidation/adsorption abilities of iron(III) oxyhydroxides

In this study, divalent manganese ions [Mn(II)] were substituted a part of divalent iron ions [Fe(II)] present in Fe oxyhydroxides to prepare novel composites (Mn@Feox). The composites were prepared by (1) simultaneous hydrolysis of Fe(II) and Mn(II), and (2) rapid oxidation with H₂O₂. The resulting Mn@Feox prepared with different molar ratios of Fe and Mn was characterized and evaluated for their abilities to adsorb arsenic species [As(III) and As(V)] in aqueous solution. X-ray diffraction and field emission transmission electron microscope analyses revealed Mn@Feox has a δ-(Fe_1?x, Mn_x)OOH-like structure with their mineralogical properties resembling those of feroxyhyte (δ-FeOOH). The increase in Mn substitution in Mn@Feox enhanced the oxidative ability to oxidize As(III) to As(V), but it decreased the adsorption capacity for both arsenic species. The optimal Mn/Fe molar ratio that could endow oxidation and magnetic capabilities to the composite without significantly compromising As adsorption capability was determined to be 0.1 (0.1Mn@Feox). The adsorption of As(III) on 0.1Mn@Feox was weakly influenced by pH change while As(V) adsorption showed high dependence on pH, achieving nearly complete removal at pH?<?5.7 but gradual decrease at pH?>?5.7. The adsorption kinetics and isotherms of As(III) and As(V) showed good conformity to pseudo-second-order kinetics model and Freundlich model, respectively.     

Removal of arsenic from water by zero-valent iron

Batch and column experiments were conducted to investigate the effect of dissolved oxygen (DO) and pH on arsenic removal with zero-valent iron [Fe(0)]. Arsenic removal was dramatically affected by the DO content and the pH of the solution. Under oxic conditions, arsenate [As(V)] removal by Fe(0) filings was faster than arsenite [As(III)]. Greater than 99.8% of the As(V) was removed whereas 82.6% of the As(III) was removed at pH 6 after 9h of mixing. When the solution was purged with nitrogen gas to remove DO, less than 10% of the As(III) and As(V) was removed. High DO content and low solution pH also increased the rate of iron corrosion. The removal of arsenic by Fe(0) was attributed to adsorption by iron hydroxides generated from the oxic corrosion of Fe(0). The column results indicated that a filtration system consisting of an iron column and a sand filter could be used for treatment of arsenic in drinking water.     

Removal of As(V) and As(III) by reclaimed iron-oxide coated sands

This paper aims at the feasibility of arsenate and arsenite removal by reclaimed iron-oxide coated sands (IOCS). Batch experiments were performed to examine the adsorption isotherm and removal performance of arsenic systems by using the IOCS. The results show that the pH(zpc) of IOCS was about 7.0 +/- 0.4, favoring the adsorption of As(V) of anion form onto the IOCS surface. As the adsorbent dosage and initial arsenic concentration were fixed, both the As(V) and As(III) removals decrease with increasing initial solution pH. Under the same initial solution pH and adsorbent dosage, the removal efficiencies of total arsenic (As(V) and As(III)) were in the order as follows: As(V)>As(V)+As(III)>As(III). Moreover, adsorption isotherms of As(V) and As(III) fit the Langmuir model satisfactorily for the four different initial pH conditions as well as for the studied range of initial arsenic concentrations. It is concluded that the reclaimed IOCS can be considered as a feasible and economical adsorbent for arsenic removal.     

Biosorption of palladium(II) from aqueous solution by moss (Racomitrium lanuginosum) biomass: equilibrium, kinetic and thermodynamic studies

Arsenite (As(III)) and arsenate (As(V)) removal by direct contact membrane distillation (DCMD) were investigated with self-made polyvinylidene fluoride (PVDF) membranes in the present work. Permeability and ion rejection efficiency of the membrane were tested before the arsenic removal experiments. A maximum permeate flux 20.90 kg/m(2)h was obtained, and due to the hydrophobic property, the PVDF membrane had high rejection of inorganic anions and cations which was independent of the solution pH and the temperature. The experimental results indicated that DCMD process had higher removal efficiency of arsenic than pressure-driven membrane processes, especially for high-concentration arsenic and arsenite removal. The experimental results indicated that the permeate As(III) and As(V) were under the maximum contaminant limit (10 microg/L) until the feed As(III) and As(V) achieved 40 and 2000 mg/L, respectively. The 250 h simultaneous DCMD performance of 0.5mg/L As(III) and As(V) solution was carried out, respectively. The permeate arsenic was not detected during the process which showed the PVDF membrane had stable arsenic removal efficiency. Membrane morphology changed slightly after the experiments, however, the permeability and the ion rejection of the membrane did not change.     

Surface complexation modeling of the removal of arsenic from ion-exchange waste brines with ferric chloride

Brine disposal is a serious challenge of arsenic (V) removal from drinking water using ion-exchange (IX). Although arsenic removal with ferric chloride (FeCl(3)) from drinking waters is well documented, the application of FeCl(3) to remove arsenic (V) from brines has not been thoroughly investigated. In contrast to drinking water, IX brines contain high ionic strength, high alkalinity, and high arsenic concentrations; these factors are known to influence arsenic removal by FeCl(3). Surface complexation modeling and experimental coagulation tests were performed to investigate the influence of ionic strength, pH, Fe/As molar ratios, and alkalinity on the removal of arsenic from IX brines. The model prediction was in good agreement with the experimental data. Optimum pH range was found to be between 4.5 and 6.5. The arsenic removal efficiency slightly improved with higher ionic strength. The Fe/As ratios needed to treat brines were significantly lower than those used to treat drinking waters. For arsenic (V) concentrations typical in IX brines, Fe/As molar ratios varying from 1.3 to 1.7 were needed. Sludge solid concentrations varying from 2 to 18 mg L(-1) were found. The results of this research have direct application to the treatment of residual wastes brines containing arsenic.     

Arsenic removal from an aqueous solution by modified A. niger biomass: batch kinetic and isotherm studies

Batch studies were conducted to examine the adsorption kinetics and adsorption capacity of iron oxide-coated biomass (IOCB) for As(III) and As(V). The optimum pH for As(V) and As(III) removal was found to be 6. The equilibrium time for removal of arsenic was found to be approximately 7 h. The adsorption of As(V) on IOCB was rapid compared to that of As(III) adsorption. An increase in temperature (from 5 to 30 °C) was found to increase As(III) removal, whereas in the case of As(V), the removal increased with temperature from 5 to 10 °C, but remained relatively constant thereafter up to 30 °C. The pseudo-second order rate equation was found to describe better the kinetics of arsenic adsorption than other equations. The isotherm data for As(V) removal fitted better with the Langmuir equation compared with other tested models and the isotherm data for As(III) removal fitted better with Redlich–Peterson equation than other tested models. Iron oxide-coated fungal biomass (A. niger) was found to be efficient in removing arsenic from an aqueous solution.     

Pyridine sorption from aqueous solution by rice husk ash (RHA) and granular activated carbon (GAC): parametric, kinetic, equilibrium and thermodynamic aspects

The present study deals with the adsorption of pyridine (Py) from synthetic aqueous solutions by rice husk ash (RHA) and commercial grade granular activated carbon (GAC) and reports on the kinetic, equilibrium and thermodynamic aspects of Py sorption. Batch sorption studies were carried out to evaluate the effect of various parameters, such as adsorbent dose (m), initial pH (pH0), contact time (t), initial concentration (C0) and temperature (T) on the removal of Py. The maximum removal of Py is found to be approximately 96% and approximately 97% at lower concentrations (<50 mg dm(-3)) and approximately 79.5% and approximately 84% at higher concentrations (600 mg dm(-3)) using 50 kg m(-3) and 30 kg m(-3) of RHA and GAC dosage, respectively, at 30+/-1 degrees C. Adsorption of Py is found to be endothermic in nature and the equilibrium data can be adequately represented by Toth and Redlich-Peterson isotherm equations. Py can be recovered from the spent adsorbents by using acidic water and 0.1 N H2SO4. The overall adsorption of Py on RHA and GAC is found to be in the order of GAC>RHA. Comparative assessment of adsorbents used by various investigators available in literature showed the effectiveness of BFA and RHA over other adsorbents. Spent RHA can simply be filtered, dried and used in the boiler furnaces/incinerators. Thus, its heating value can be recovered.     

Arsenic removal by adsorption on iron(III) phosphate

Under natural conditions, arsenic is often associated with iron oxides and iron(III) oxidative capacity towards As(III) is well known. In this study, As(III) and As(V) removal was performed using synthesised iron(III) phosphate, either amorphous or crystalline. This solid can combine (i) As(III) oxidation by iron(III) and (ii) phosphate substitution by As(V) due to their similar properties. Results showed that adsorption capacities were higher towards As(III), leading to Fe2+ and HAsO4(2-) leaching. Solid dissolution and phosphate/arsenate exchange led to the presence of Fe3+ and PO4(3-) in solution, therefore various precipitates involving As(V) can be produced: with Fe2+ as Fe3(AsO4)2.8H2O(s) and with Fe3+ as FeAsO4.2H2O(s). Such formations have been assessed by thermodynamic calculations. This sorbent can be a potential candidate for industrial waste treatment, although the high release of phosphate and iron will exclude its application in drinking water plants.     

Modified aluminosilicates as low-cost sorbents of As(III) from anoxic groundwater

The utilization of low-grade clay materials as selective sorbents represents one of the most effective possibilities of As removal from contaminated water reservoirs. The simple pre-treatment of these materials with Fe (Al, Mn) salts can significantly improve their sorption affinity to As oxyanions. The natural kaolin calcined at 550 degrees C (mostly metakaolin) and raw bentonite (mostly montmorillonite) pre-treated with Fe(II), Fe(III), Al(III) and Mn(II) salts were used to remove of As from the model anoxic groundwater with As(III) concentration about 0.5 and 10 mg L(-1). All the pre-treating methods were appropriate for bentonite; the efficiency of As(III) sorption varied from 92 to >99%, by the sorption capacity higher than 4.5 mg g(-1). In the case of metakaolin, Fe(II)- and Mn(II)-treatments proved the high sorption efficiency (>97%), while only <50% of As was removed after Fe(III) and Al(III) pre-treatment. The sorption capacities of treated metakaolin ranged from 0.1 to 2.0 mg g(-1).     

Voltammetric speciation of arsenic species in plant biomaterial: bioremediation

Environmental pollution, as a consequence of the industrialization process, is one of the major problems that have to be solved and controlled. The heightened awareness regarding the high toxicity and biochemical behavior of the different arsenic species required to develop cost effective technologies for the speciation of arsenic species. Electrochemical techniques are found to be comparatively better tools for arsenic speciation. As (III) is electrochemically stable in the presence of ascorbic acid as supporting electrolyte, while As (V) is electrochemically inactive at the electrode surface. The present piece of work is an attempt to measure the two arsenic species in the elution of arsenic sorbed Leucaena leucocephala seed powder (LLSP), using square wave anodic stripping voltammetry. The strategy employed in this work is based on the determination of As (III) directly, while determining As (V) after reduction with sodium thiosulfate into As (III). The removal percentage of As (III) and As (V) using LLSP biomaterial was 83.18 and 95 %, respectively.     

Combined use of photocatalyst and adsorbent for the removal of inorganic arsenic(III) and organoarsenic compounds from aqueous media

A novel method for the removal of inorganic arsenic(III) (As(III)), monomethylarsonate (MMA), and dimethylarsinate (DMA) from aqueous media, was proposed and investigated. This method involves the combined use of TiO₂-photocatalyst and an adsorbent, which has a high ability of As(V) adsorption, under photo-irradiation. When an aqueous solution of As(III) was stirred and irradiated by sunlight or xenon lamp in the presence of TiO₂ suspension, the oxidation of As(III) into As(V) was effectively attained. By use of the same photocatalytic reaction, MMA and DMA were also degraded into As(V), while the total organic carbon (TOC) in the aqueous phase was decreased. When an aqueous solution of As(III) was stirred with a mixed suspension of TiO₂ and an adsorbent for As(V) (activated alumina) under sunlight irradiation, the arsenic removal reached 89% after 24 h. By use of the same photocatalyst–adsorbent system, 98% of MMA and 97% of DMA were removed. The mechanism of the removal of arsenic species by the photocatalyst–adsorbent system was discussed.     

Phosphorus removal performance of acid mine drainage from wastewater

Acid mine drainage (AMD) in Yunfu iron sulfide mine contain Fe(2+), Fe(3+), and Al(3+) up to 8000, 1700 and 1200 mg/L, respectively. Phosphorus removal from synthetic wastewater with 10mg/L of total phosphorus (TP) concentration and second municipal effluent with 3.5-4.0mg/L of TP concentration were conducted with the AMD by jar tests. Dosage of the AMD and initial pH of water are the two most important parameters affecting the performance of phosphorus removal of the AMD. The optimal phosphorus removal efficiency and residual iron ions (TFe) concentration are 97.0% and 3.0mg/L, respectively, at 1.61 Fe/P molar ratio and pH 8.03 for synthetic wastewater, and 92.1% and 0.32 mg/L, respectively, for second municipal effluent at 1.41 Fe/P molar ratio and pH 7.3. Resultant heavy metal concentration in effluents and precipitate was very low, and the risk of resultant heavy metal contamination was very small. The phosphorus removal performance of the AMD was much similar to that of ferric sulfate (FS) and polyferric sulfate (PFS), and better than that of FeSO(4). And residual TFe concentration in treated water arising from utilization of the AMD was similar to that of FeSO(4), and higher than that of FS and PFS. The AMD could be used as coagulant for phosphorus removal from wastewater directly due to the presence of Fe(2+), Fe(3+), and Al(3+) largely.     

Adsorptive removal of As(V) and As(III) from water by a Zr(IV)-loaded orange waste gel

Orange waste, produced during juicing has been loaded with zirconium(IV) so as to examine its adsorption behavior for both As(V) and As(III) from an aquatic environment. Immobilization of zirconium onto the orange waste creates a very good adsorbent for arsenic. Adsorption kinetics of As(V) at different concentrations are well described in terms of pseudo-second-order rate equation with respect to adsorption capacity and correlation coefficients. Arsenate was strongly adsorbed in the pH range from 2 to 6, while arsenite was strongly adsorbed between pH 9 and 10. Moreover, equimolar (0.27 mM) addition of other anionic species such as chloride, carbonate, and sulfate had no influence on the adsorption of arsenate and arsenite. The maximum adsorption capacity of the Zr(IV)-loaded SOW gel was evaluated as 88 mg/g and 130 mg/g for As(V) and As(III), respectively. Column adsorption tests suggested that complete removal of arsenic was achievable at up to 120 Bed Volumes (BV) for As(V) and 8 0BV for As(III). Elution of both arsenate and arsenite was accomplished using 1 M NaOH without any leakage of the loaded zirconium. Thus this efficient and abundant bio-waste could be successfully employed for the remediation of an aquatic environment polluted with arsenic.     

Assessing arsenic leachability from pulverized cement concrete produced from arsenic-laden solid CalSiCo-sludge

Synthetically prepared arsenic-laden CalSiCo-sludge was converted to pulverized cement concrete (PCC) using solidification/stabilization technology with cement. Batch leaching experiments were conducted to estimate the leaching of As(III) and As(V) from the CalSiCo-sludge as well as from the PCC. The leaching of As(III) and As(V) was found to be the function of time, pH and concentration of anions such as Cl(-), NO(3)(-), and SO(4)(2-) present in the extraction fluid. It is observed that from the CalSiCo-sludge the leaching of As(III) is >0.05mg/l (which is above the permissible limit for arsenic in drinking water) at any pH. But in case of As(V) the leaching is >0.05mg/l only at pH>8 and at pH<4. It is noted that maximum leaching occurs when the extraction liquid contains Cl(-). In contrary, NO(3)(-) and SO(4)(2-) have negligible effect on arsenic leaching from the CalSiCo-sludge. Extraction tests were carried out to determine the maximum leachable concentration under the chosen conditions of leaching medium and leaching time. Leaching of As(III) and As(V) from exhausted arsenic-laden CalSiCo-sludge and from PCC was carried out in both tap water and rain water. It was noticed that tap water has no effect in leaching of arsenic from CalSiCo-sludge but rain water causes significant amount of leaching, which is mostly due to pH effect. However, in all cases the leaching of As(III) was more than that of As(V). When compared with CalSiCo-sludge PCC showed negligible leaching of arsenic. It was noticed further that the variation of 28 days compressive strength was within 15% of the original strength after replacing 35% cement with exhausted CalSiCo-sludge.     

Characterization of Co-doped birnessites and application for removal of lead and arsenite

Nanostructured Co-doped birnessites were successfully synthesized, and their application for the removal of Pb(2+) and As(III) from aquatic systems was investigated. Powder X-ray diffraction, chemical analysis, nitrogen physical adsorption, field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the crystal structure, chemical composition, micromorphologies and surface properties of the birnessites. Doping cobalt into the layer of birnessite had little effect on its crystal structure and micromorphology. Both chemical and XPS analyses showed that the manganese average oxidation state (Mn AOS) decreased after cobalt doping. The Co dopant existed mainly in the form of Co(III)OOH in the birnessite structure. Part of the doped Co(3+) substituted for Mn(4+), resulting in the gain of negative charge of the layer and an increase in the content of the hydroxyl group, which accounted for the improved Pb(2+) adsorption capacity. The maximum capacity of Pb(2+) adsorption on HB, CoB5, CoB10 and CoB20 was 2538 mmol kg(-1), 2798 mmol kg(-1), 2932 mmol kg(-1) and 3146 mmol kg(-1), respectively. The total As(III) removal from solution was 94.30% for CoB5 and 100% for both CoB10 and CoB20, compared to 92.03% for undoped HB, by oxidation, adsorption and fixation, simultaneously.     

Studies on the removal of arsenic (III) from water by a novel hybrid material

The present work provides a method for removal of the arsenic (III) from water. An ion-exchanger hybrid material zirconium (IV) oxide-ethanolamine (ZrO-EA) is synthesized and characterized which is subsequently used for the removal of selective arsenic (III) from water containing 10,50,100 mg/L of arsenic (III) solution. The probable practical application for arsenic removal from water by this material has also been studied. The various parameters affecting the removal process like initial concentration of As (III), adsorbent dose, contact time, temperature, ionic strength, and pH are investigated. From the data of results, it is indicated that, the adsorbent dose of 0.7 mg/L, contact time 50 min after which the adsorption process comes to equilibrium, temperature (25 ± 2), solution pH (5-7), which are the optimum conditions for adsorption. The typical adsorption isotherms are calculated to know the suitability of the process. The column studies showed 98% recovery of arsenic from water especially at low concentration of arsenic in water samples.     

Separation and preconcentration of inorganic arsenic species in natural water samples with 3-(2-aminoethylamino) propyltrimethoxysilane modified ordered mesoporous silica micro-column and their determination by inductively coupled plasma optical emission spectrometry

A simple and sensitive method using micro-column packed with 3-(2-aminoethylamino) propyltrimethoxysilane (AAPTS) modified ordered mesoporous silica combined with inductively coupled plasma optical emission spectrometry (ICP-OES) for the speciation of inorganic arsenic (As(III) and As(V)) has been developed. The adsorption behaviors of As(III) and As(V) on AAPTS modified ordered mesoporous silica were investigated. It was found that As(V) can be selectively adsorbed on the micro-column within pH of 3-9, while As(III) could not be retained in the studied pH range and passed through the micro-column directly. Total inorganic arsenic was extracted after the oxidation of As(III) to As(V) with 50.0 micromol L(-1) KMnO(4). The assay of As(III) was based on subtracting As(V) from total As. The effect of various parameters on the separation/preconcentration of As(III) and As(V) have been investigated and the optimal experimental conditions were established. The adsorption capacity of AAPTS modified ordered mesoporous silica for As(V) was found to be 10.3 mg g(-1). The detection limit of the method for As(V) was 0.05 microg L(-1) with an enrichment factor of 100, and the relative standard deviation (R.S.D.) was 5.7% (n=7, C=1.0 microg L(-1)). In order to validate the developed method, a certified reference material GSBZ50004-88 environmental water sample was analyzed and the determined values were in good agreement with the certified values. The proposed method was successfully applied to the speciation analysis of inorganic arsenic in natural water samples.