Speciation of five arsenic species (arsenite, arsenate, MMAA V, DMAA V and AsBet) in different kind of water by HPLC-ICP-MS

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1 Chemosphere 66 (2007) Specition of five rsenic species (rsenite, rsente, MMAA V, DMAA V nd AsBet) in different kind of wter by HPLC-ICP-MS Sébstien N. Ronkrt, *, Vincent Lurent b,1, Philippe Crbonnelle b,1, Nicols Mbon,2, Alfred Copin,2, Jen-Pul Brthélemy,2 Gembloux Agriculturl University, Unité de chimie nlytique et Phytophrmcie, Pssge des Déportés, 2, B-5030 Gembloux, Belgium b Lbortoire Centrl de l Société Wllonne Des Eux, Avenue de l Espérnce, B-6220 Fleurus, Belgium Received 22 Jnury 2006; received in revised form 19 July 2006; ccepted 20 July 2006 Avilble online 7 September 2006 Abstrct A method using Ion Chromtogrphy hyphented to n Inductively Coupled Plsm-Mss Spectrometer hs been developed to ccurtely determine rsenite (As III ), rsente (As V ), mono-methylrsonic cid (MMAA V ), dimethylrsinic cid (DMAA V ) nd rsenobetine (AsBet) in different wter mtrices. The developed method showed high sensitivity with detection limits for ech rsenic species close to 0.4 pg injected. Arsenite nd rsente were the mjor species found in surfce nd well wters, but AsBet nd DMAA V were found in some surfce wters, which hs never been reported before, while in some nturl minerl wters locted in volcnic region, the rsenic content exceeded the mximl dmissible rsenic content by Europen legisltion stndrds nd the predominnt form ws As V. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Arsenic; IC-ICP-MS; Specition; Trce nlysis 1. Introduction Arsenic exists under the form of vrious chemicl species differing, not only by their physicochemicl behviour, but lso in toxicity, biovilbility nd biotrnsformtion (Med, 1994). With more thn 20 rsenic compounds present in the nturl environment nd biologicl systems, it is importnt to identify ech individul chemicl species of the element in the smples (Le et l., 2004). For this reson, the notion of specition, defined s the determintion of ll the individul physicochemicl forms of n element, hs gined interest in recent yers. * Corresponding uthor. Tel.: ; fx: E-mil ddresses: ronkrt.s@fsgx.c.be (S.N. Ronkrt), lbo@swde. be (V. Lurent). 1 Tel.: ; fx: Tel.: ; fx: Arsenite (As III ) nd rsente (As V ) re the most toxic forms, considered nd clssified s humn crcinogen substnces nd re the predominnt forms found in wter. Biologiclly-medited methyltion rections, occurring in terrestril nd mrine orgnisms, convert rsenite nd rsente to methylted compounds of moderte toxicity, such s methylrsonic cid (MMAA V ) nd dimethylrsinic cid (DMAA V ). Arsenobetine (AsBet), more complex rsenic compound, ws identified essentilly in mrine biot (Goessler et l., 1998,b; Ackley et l., 1999; Kohlmeyer et l., 2002) or in mrine sediments (Tkeuchi et l., 2005) nd is considered to be reltively non-toxic (Kise et l., 1985). The dmissible level of rsenic in nturl minerl wter (Commission Directive 2003/40/CE of 16 My 2003) nd in wter intended for humn consumption (Commission Directives 98/83/CE of 3 November 1998), hs been lowered to 10 lg l 1 of totl rsenic. However, s reported previously in literture (Vn Holderbeke et l., 1999), some /$ - see front mtter Ó 2006 Elsevier Ltd. All rights reserved. doi: /j.chemosphere

2 S.N. Ronkrt et l. / Chemosphere 66 (2007) commercilly vilble nturl minerl wter exceeded this limit of 10 lg l 1. In order to ssess the individul forms of rsenic, which my be present in wter, nd thus the potentil toxicity, the nlyticl equipment must chieved very low detection limits. Hyphented nlyticl techniques re often necessry to chieve both selectivity nd sensitivity for rsenic specition t low concentrtion level. Numerous instrumentl methods for these five rsenic species specition re reported in the literture. Most of them re bsed on chromtogrphic seprtion techniques such s High Performnce Liquid Chromtogrphy (HPLC) (Giler nd Irgolic, 1996; Teräshde et l., 1996; Le nd M, 1997; Dgnc et l., 1999; Kohlmeyer et l., 2002) or Cpillry Zone Electrophoresis (Vn Holderbeke et l., 1999), coupled with selective nd sensitive detector such s Atomic Absorption Spectrometry (AAS) (Giler nd Irgolic, 1996) or Inductively Coupled Plsm-Mss Spectrometry (ICP- MS) (Teräshde et l., 1996; Kohlmeyer et l., 2002). Post column derivtiztion of rsenic species with formtion of the voltile rsine hydrides, hs been coupled with AAS (Le nd M, 1997), Atomic Fluorescence Spectrometry (Simon et l., 2004) or ICP-MS (Dgnc et l., 1999), but cnnot be used for quntifying AsBet without prior chemicl conversion (Slejkovec et l., 1999). The hyphented HPLC-ICP-MS technique is the most powerful method for rsenic specition, llowing detection limits generlly lower thn 0.5 lg l 1 (B Hymer nd Cruso, 2004, nd references therein). The dvntges ssocited with the HPLC-ICP-MS technique include high elementl specificity, the possibility to record rel time chromtogrms, the bility to seprte the signls of interfering species from the peks of interest, high liner rnge, multi-element cpbility nd the possibility of isotopic informtion. The high sensitivity of ICP-MS llows the nlysis of wter smples without time-consuming preconcentrtion nd derivtiztion steps. This considertion is crucil s species my be converted from one form to nother or lost during the pre-tretment of the smple (Gong et l., 2002). However, the use of ICP-MS s detector for HPLC gives rise to some constrints on the choice of chromtogrphic conditions concerning the nture nd concentrtion of the buffer slts of the mobile phse nd the presence of orgnic solvents. Moreover, becuse of its high sensibility, ICP-MS my suffer from mny isobric interferences cused minly by phenomen occurring either in the plsm or in the ion extrction device. For exmple, presence of chlorine in the smple my give rise to the formtion of 40 Ar 35 Cl + tht interferes strongly with the mono-isotopic 75 As + (Gry, 1986; Hywel Evns nd Giglio, 1993). For these resons, the im of this work ws to develop powerful specition method suitble for trce nlysis of ll rsenic species found in drinking nd surfce wter with pproprite performnce chrcteristics in order to identify nd quntify ech rsenic species. 2. Experimentl 2.1. Stndrds nd regents Stock solutions of rsenic species (1000 mg l 1 ) were prepred from NAsO 2 (rsenite, As III ), N 2 HAsO 4 Æ 7H 2 O (rsente, As V ), (CH 3 ) 2 AsO(OH) (dimethylrsinic cid, DMAA V ), CH 3 AsO(OH) 2 (mono-methylrsonic cid, MMAA V ) nd (CH 3 ) 3 As + CH 2 COO (rsenobetin, AsBet). As III, As V nd DMAA V were obtined from Sigm Aldrich (Steinheim, Germny) while MMAA V nd AsBet were obtined from Argus Chemicls (Florence, Itly). These individul stndrds were checked for purity by IC-ICP-MS, nd the stock solutions were stored t 4 C before nlysis. In these conditions, the stock solutions were stble for t lest one month. Anlyticl working solutions were prepred by diluting the stock solutions with ultrpure wter (18.2 MX cm 1, Millipore, Molsheim, Frnce) prior to nlysis. For the chromtogrphic mobile phse, NH 4 H 2 PO 4 (mmonium dihydrogen phosphte, >99%, Sigm Aldrich, Steinheim, Germny), NH 4 OH (mmonic 25%, Suprpur Ò, Merck, Drmstdt, Germny) nd methnol (Suprsolv Ò, Merck, Drmstdt, Germny) were used Instrumenttion The High Performnce Liquid Chromtogrphy (HPLC) module consisted of n Agilent 1100 Series (Agilent Technologies, Yokogw Anlyticl System Inc., Tokyo, Jpn) with hndheld control module. The seprtion of the rsenic species ws performed on Dionex AS7 nion-exchnge column (250 4 mm; 10 lm) bering lkyl quternry mmonium exchnge sites on styrenedivinylbenzene copolymer. 20 ll of the smple ws injected in the chromtogrphic column. The Inductively Coupled Plsm-Mss Spectrometry (ICP-MS) system consisted of n ICP-MS Hewlett-Pckrd 4500 Series 200 (Agilent Technologies, Yokogw Anlyticl System Inc., Tokyo, Jpn). A 40 cm PEEK Ò tubing (PolyEther Ether Ketone, 1/16 00 OD X ID Blue- Stripe) with pproprite fittings ws used to connect the outlet of the HPLC nlyticl column directly to the inlet of the ICP concentric nebulizer (Conikl Ò Concentric Nebulizer-STF, Glss Expnsion, Switzerlnd). A doublepss spry chmber nd qurtz torch were used in this study. The temperture of the spry chmber ws mintined t 2 C by cooling Peltier Effect. In ccordnce with B Hymer et l. (1998), this concentric nebulizer/double pss spry chmber combintion llows the best signl stbility. In ddition to the ICP-MS Hewlett-Pckrd 4500 Series 200 (only used for the coupling with HPLC), n ICP-MS Hewlett-Pckrd 4500 Series 100 (Agilent Technologies, Yokogw Anlyticl System Inc., Tokyo, Jpn) ws used for the totl rsenic concentrtion in wter. The ICP-MS Hewlett-Pckrd 4500 Series 100 ws equipped with Bbington nebulizer.

3 740 S.N. Ronkrt et l. / Chemosphere 66 (2007) Tuning nd dt cquisition Before ll nlyses, the instrument ws tuned using 10 lg l 1 lithium ( 7 Li), yttrium ( 89 Y), thllium ( 205 Tl) nd cerium ( 140 Ce) solution (ll Certipur Ò, obtined from Merck, Drmstdt, Germny). Resolution nd mss xis were optimized by monitoring m/z 7 Li, 89 Y nd 205 Tl. Sensitivity ws mximized t m/z 89 Y, llowing very high sensitivity for 75 As, nd thus very low detection limits, while mintining the rtio of oxides ( 140 Ce 16 O/ 140 Ce) nd doubly chrged ions ( 140 Ce 2+ / 140 Ce + ) t low level to minimize the potentil interferences. For IC-ICP-MS dt cquisition, the time resolved nlysis mode ws used. In ddition of the rsenic signl t m/z 75, the interferences from chloride were lso checked by monitoring m/z 35, 77, 82 nd 83. The quntifiction of the chromtogrphic peks ws bsed on the pek re Specition of rsenic in wter Surfce, well nd nturl minerl wter smples were nlysed by IC-ICP-MS. These smples were collected from severl loctions in the Wlloon Region (Belgium) nd stored in polyethylene flsks t 4 C without cidifiction to prevent chnges in species distribution. The nlyses were crried out within one week. Nturl minerl wters were obtined from locl mrket, nd covering different geologicl origins. The sum of rsenic species concentrtions ws compred to the totl rsenic content obtined by ICP-MS nlysis. All rel smples were filtered through 5, 0.45 nd 0.2 lm filter membrnes (ll Acrodisc Ò 25 mm Syringe filter with Verspor Ò membrne, Gelmn Sciences, MI, USA) directly into the uto smpler vil nd injected in the chromtogrphic system. All smples were nlysed in triplicte. 3. Results nd discussion The optimized chromtogrphic conditions nd the instrumentl prmeters used for IC-ICP-MS re summrized in Tble Set up of the chromtogrphic elution In HPLC, Ion Chromtogrphy (IC) is n ttrctive technique for elementl specition becuse it cn seprte chrged species. Except AsBet, which is zwitterion, ll the other rsenic species of this study hve rnge of dissocition constnts mking them suitble for nion exchnge column, s they exist in nionic form in lkline mobile phse (Teräshde et l., 1996). N 2 HPO 4 nd NH 2 PO 4 re often used s mobile phse for the rsenic species seprtion, but deposition of slt on the smpling interfce cuses rpid degrdtion nd instbility of the signl. For this reson, the selected mobile phse used in this study ws mmonium dihydrogen phosphte (NH 4 H 2 PO 4 ), less deposit ws observed together with good stbility of the signl. In the investigted NH 4 H 2 PO 4 concentrtion rnge (1 50 mm), the order of elution ws AsBet, DMAA V,As III, MMAA V nd As V (Fig. 1). NH 4 H 2 PO 4 5 mm gve the best compromise between good AsBet/DMAA V resolution nd minimum tiling for As III. Furthermore, the effect of the ph of the mobile phse ws tested (7.0, 8.0, 9.0 nd 10.0) by djusting with NH 4 OH 1.35 M. Incresing the Tble 1 Instrumentl settings Totl rsenic ICP-MS HP 4500 Series 100 Argon plsm gs flow rte (l min 1 ) 15 Argon crrier gs flow rte (l min 1 ) 1 Argon uxiliry gs flow rte (l min 1 ) 1 Peristltic pump flow rte (l min 1 ) 1 Power (W) 1400 Arsenic specition HPLC Agilent 1100 Series Anlyticl column Dionex IonPk AS7 (250 4 mm; 10 lm) Mobile phse A 2.5 mm NH 4 H 2 PO 4 ph 10.0 (NH 4 OH) Mobile phse B 50 mm NH 4 H 2 PO 4 Grdient progrm Time (min) A (%) B (%) ICP-MS HP 4500 Series 200 Argon plsm gs flow rte (l min 1 ) 15 Argon crrier gs flow rte (l min 1 ) 0.7 Argon uxiliry gs flow rte (l min 1 ) 1.0 Argon blend gs flow rte (l min 1 ) 0.5 Power (W) 1400 Monitored signls (dwell times in ms) 75 As (500), 35 Cl (100), 82 Se (100) nd 83 Kr (100)

4 S.N. Ronkrt et l. / Chemosphere 66 (2007) result of these ntgonist phenomenons. For this reson, 2.5 mm NH 4 H 2 PO 4 solution djusted to ph 10.0 with NH 4 OH llowing good AsBet/DMAA V seprtion together with minimum tiling for rsenite, ws selected. This mobile phse ws suitble for the seprtion of AsBet, DMAA V nd As III, but not for MMAA V nd As V due to the very long retention time. Consequently, n elution grdient with NH 4 H 2 PO 4 50 mm ws used. This grdient llowed correct seprtion of the five molecules within 30 min including column re-equilibrtion time. In order to improve the ionistion of rsenic in the plsm, 3% (v/v) of methnol hve been dded in the mobile phse (Beuchemin et l., 1989; Lrsen nd Stürup, 1994). In spite of the fct tht Brisbin et l. (2002) climed tht the use of crbonte s mobile phse brings less deposit thn phosphte, no signl decrese ws observed with ten repetitions. The reltive stndrd devitions of the pek re were 1.5, 1.5, 2.0, 0.8 nd 1.6% for AsBet, DMAA V,As III, MMAA V, nd As V, respectively. The stbility of the signl nd the low stndrd devition void the use of n internl stndrd Vlidtion of the method Fig. 1. Anion exchnge HPLC-ICP-MS chromtogrm of 20 ll injected stndrd solution contining 5 lg l 1 of ech rsenic species. Pek identifiction: (1) AsBet, (2) DMAA V, (3) As III, (4) MMAA V nd (5) As V. The nlysis ws performed ccording to the optimum conditions shown in Tble 1. ph of the mobile phse led to higher ionistion degree of rsenic compounds ccording to their pk nd should induced higher ffinity for the vilble exchnge sites on the column nd thus their retention time. But, the dissocition of the phosphte ions of the buffer, nd thus the eluent power of the mobile phse, lso incresed with the ph. The retention time obtined s function of the ph is the For the pplicbility of method to rel smples, vlidtion study is indispensble. Thus, the performnce of the method ws estimted by determining the limit of detection (LOD), the limit of quntifiction (LOQ), the linerity nd the precision (within-ssy nd between-ssy precision) of results following the XP T (1994) guideline nd clcultions ccording to ISO 5725 (1996) (Tble 2). The linerity ws checked in the concentrtion rnge lgl 1 for ech rsenic species by clculting the coefficient of determintion (R 2 ) of the liner regression bsed on six different concentrtions (three replictes) including the blnk. The liner regression equtions were y = x ; y = x ; y = x ; y = 19.09x nd y = x for respectively AsBet, DMAA V,As III, MMAA V nd As V. R 2 obtined fter liner regression were in ll cses better thn , clerly illustrting dequte linerity for ll the five rsenic species in the concentrtion rnge investigted. Precision ws expressed by within-ssy precision (WAP) nd between-ssy precision (BAP) nd were clculted ccording to Eqs. (1) nd (2), Tble 2 Within-ssy precision (WAP), between-ssy precision (BAP), limit of detection (LOD) nd limit of quntifiction (LOQ) of the method using conditions in Tble 1 Arsenic species b WAP BAP (%) LOD LOQ Reltive (ng l 1 ) Absolute (pg) Reltive (ng l 1 ) Absolute (pg) AsBet DMAA V As III MMAA V As V Concentrtions used for clculting these prmeters re expressed in lgl 1. b AsBet (rsenobetine), DMAA V (dimethylrsinic cid), As III (rsenite), MMAA V (methylrsonic cid), As V (rsente).

5 742 S.N. Ronkrt et l. / Chemosphere 66 (2007) Tble 3 Specition of the stndrd mteril wter nd comprison with the totl rsenic expecting concentrtion Wter smples IC-ICP-MS b Expecting vlue AsBet DMAA V As III MMAA V As V Totl Aquckeck ± ± ± ± 1.10 Aquckeck ± ± ± ± 0.49 Aquckeck ± ± ± ± 0.60 Aquckeck ± ± ± ± 1.15 The vlues re expressed in lg l 1. <LOD. b AsBet (rsenobetine), DMAA V (dimethylrsinic cid), As III (rsenite), MMAA V (methylrsonic cid), As V (rsente). vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi P k WAP ¼ 100 ðn j 1ÞS 2 j m j¼1 u t P k n j! k P k j¼1 BAP ¼ 100 ½n j ðm j mþ 2 Š m n j¼1 ð2þ k 1 where m is the used concentrtion; S 2 j is the intergroup vrince; n j is the number of the group j repetition; k is the number of the group (k = 4); m j is the verge of the j group; m is the verge m j nd n is the verge number of vlues per group. WAP nd BAP were determined t 0.1, 10 nd 50 lg l 1 with four nlysis groups. The first group included 10 repetitions, while for the three others, only six replictes were crried out. At concentrtions close to the LOQ, WAPs were <6%, showing good precision of the obtined results for trce rsenic nlysis. Moreover, BAPs were similr to WAPs, proving low vrition of the results in the course of time. Limit of detection nd quntifiction (LOD nd LOQ) were evluted by nlysing ten smples contining n rsenicl concentrtion close to the expected LOD nd LOQ in repetbility conditions nd using Eqs. (3) nd (4), LOD ¼ y signl þ 5 S signl ð3þ LOQ ¼ y signl þ 10 S signl ð4þ where y signl is the medium vlue nd S signl is the stndrd devition. LODs were closely the sme for ll the compounds nd mde the method prticulrly suitble for trce rsenic species determintion in rel wter smples nd were better thn detection limits previously reported in the literture. LOQ vlues were confirmed by nlysing ten replictes of solution contining ll the rsenic species t the LOQ. Vrition coefficient of 9.87, 8.38, 8.33, 12.3 nd 8.84% were obtined for respectively AsBet, DMAA V, As III, MMAA V nd As V Arsenic nlysis in reference mterils ð1þ Certified reference mterils for rsenic specition were not vilble for drinking wter. Therefore, interlbortory solutions with well estblished concentrtions for totl rsenic were selected, nmely Aqucheck Ò (Aqucheck Ltd, Bury Greter Mnchester, Englnd). The certified totl rsenic concentrtion grees closely with the specition results (Tble 3). However, simultneous presence of As III nd As V ws lso noticed, probbly Fig. 2. Anion exchnge HPLC-ICP-MS chromtogrm of 20 ll injected stndrd solution contining 10 lgl 1 of As V nd 200 mg l 1 of NCl. Pek identifiction: (1) Chloride nd (2) As V. The nlysis ws performed ccording to the optimum conditions shown in Tble 1.

6 S.N. Ronkrt et l. / Chemosphere 66 (2007) resulting from the oxidtion of the trivlent to the pentvlent form. Indeed, these solutions were prepred with n rsenite form nd this conversion cn be relted to the 2% Aqucheck Ò HNO 3 cidifiction nd prove the rsenic-form stbilistion problem in wter. This hypothesis ws confirmed by Bohri et l. (2001) who showed tht 0.5% HNO 3 cidifiction chnged rsenic specition fter ten dys of storge. Thus, it will be importnt to consider this spect for the preprtion of certified wter smples contining rsenic species, s this kind of smple does not exist yet Arsenic specition in rel smples The possible interference of 40 Ar 35 Cl + with the monoisotopic 75 As +, hs been studied by nlysing solutions contining incresed concentrtion (200, 500 nd 1000 mg l 1 ) of chloride nd compring the signl obtined t m/z 75 with the signl of blnk (Milli-Q wter) using t-test. This test ws of prticulr importnce since chloride eluted t the sme retention time s rsente (Fig. 2). We found tht there is no noticeble 40 Ar 35 Cl + interference up to 500 mg l 1 chloride. These results re in good greement with those published by Sverwyns et l. (1997) nd Pntsr-Kllio nd Mnninen (1997). Possible mtrix effects on the clibrtion were estimted by spiking representtive rel wter smples. These smples were collected t vrious loctions in order to hve different mtrix contents, e.g. high suspended colloids. Smples from ground, well nd surfce wter were spiked with stndrd mixture of the five rsenic species giving n dded rsenic concentrtion of 0.5 nd 5 lg l 1 ech. When the IC-ICP-MS procedure ws pplied to the nlysis of three spiked rel wter smples, recoveries were stisfctory with vlues rnging from 95% to 108%. Then, surfce, well nd nturl minerl wters were nlysed for the ntive rsenic species quntifiction (Tble 4). As III nd As V were the mjor rsenic species found in surfce nd well wters, but AsBet nd DMAA V were present only in surfce wter. To our knowledge, it ws the first time AsBet ws found in surfce wters, but the detection of this compound cn be relted to the fct tht the proposed method ws chrcterized by the lowest LOD in literture, permitting n AsBet ultr trce quntifiction. The presence of such methylted compounds probbly results from more intense biologicl ctivity in this kind of environment, s the bioccumultion of the methylted forms hs been lrgely discussed in terrestril nd mrine orgnisms. Moreover, Hnok et l., 1997 found AsBet in suspended prticles in mrine biot (probbly from degrded orgnisms), while Tkeuchi et l. (2005) climed n incorportion of this rsenic specie into the sediment. They quntified AsBet nd DMAA V s the mjor compounds in the sediment, lthough the concentrtion of these orgnorsenicls decresed with depth nd is considered to be degrded within 60 yers of deposition. In ddition, Hsegw (1997) found tht the detritus on the surfce of lke sediment ws consumed by the nerobic respirtion of bcteri. The methylrsenic species were degrdtion products nd/or the results of in situ bcteril methyltion nd were decomposed to inorgnic rsenic under noxic conditions by fculttive nd obligte nerobes. It ws lso reported tht portion of the DMAA V ws trnsformed in vitro to AsBet by some orgnisms (Kise Tble 4 Results of different nturl smple nlysis (concentrtion in lg l 1 ) Wter smples IC-ICP-MS ICP-MS AsBet DMAA V As III MMAA V As V Totl Drinking wters Well wter ± ± ± Well wter ± ± ± Well wter ± ± ± Surfce wter 1 b 0.12 ± ± ± ± Surfce wter 2 b b 0.11 ± ± ± Nturl minerl wters Smple 1 d 8.52 ± ± Smple 2 d 0.32 ± ± Smple 3 d 0.07 ± ± ± Smple 4 d ± ± Smple 5 e 0.25 Smple 6 c 0.08 ± ± 0.01 Smple 7 c Smple 8 d 7.59 ± ± Smple 9 d 0.55 ± ± Smple 10 d 3.57 ± ± <LOD. <LOQ. c Belgin minerl nturl wter. d French nturl minerl wter. e Itlin nturl minerl wter.

7 744 S.N. Ronkrt et l. / Chemosphere 66 (2007) et l., 1997). Indeed, orgnisms re trnsformed to prticulte or dissolved species fter their deth, nd experimentl studies in vitro demonstrted tht rsenobetine contined in orgnisms degrded to inorgnic forms vi DMAA V intermedites (Hnok et l., 1993, 1997). This mechnism could be t the origin of the low levels of AsBet nd DMAA V found in our study. This rsenic cycle shll explin why we detected both methylted nd inorgnic species in surfce wter. Depending on the geologicl origin of the nturl minerl wter, the rsenic content ws very vrible from one type of wter to the other (Tble 4). According to Vn Holderbeke et l. (1999), rsenic in such smples ws exclusively in the rsente form. Nevertheless, it ws very interesting to notice tht some nturl minerl wters hd totl rsenic content exceeding the 10 lg l 1 limit of the Europen Commission Directive 2003/40/CE (2003). The presence of rsenic t this concentrtion level should be ssocited with the geochemicl environment. Indeed, occurrence of rsenic in nturl wter depends on the locl geology, hydrology nd geochemicl chrcteristics of the quifer. In our study, the nturl minerl wters with the higher rsenic content were locted in volcnic region in Frnce. Thoms nd Snitechi (1995) reported tht some minerl or therml wter were exceeding the mximum drinking wter limit for rsenic vlues, e.g. spring wter from Puy du Dôme in the volcnic region of Mssif Centrl in Frnce. 4. Conclusions A method for rsenic specition by IC-ICP-MS ws developed which llowed the simultneous seprtion of five rsenic species (AsBet, DMAA V,As III, MMAA V nd As V ) in vrious types of wter smples with LODs close to 20 ng l 1 for ech rsenic compounds. In ech cse the totl rsenic concentrtion obtined by ICP-MS ws in good greement with the sum of the rsenic species obtined by IC-ICP-MS. Bsed on rsenic specition in well nd surfce wters, rsenite nd rsente were the mjor molecules, while in surfce wter, both DMAA V nd AsBet were found. The occurrence of these methylted forms ws probbly due to micro-orgnisms s in well nd nturl minerl wters, no methylted products were detected. The concentrtion of rsenic in some nturl minerl wters nlysed in this study exceeded the Europen Directive 2003/40/CE limit. The developed method is vilble to identify nd quntify the rsenic species present in nturl nd drinking wter t trce levels, which might be prticulrly importnt for the toxicity ssessment in regions tht my suffer of nturl rsenic contmintion. Acknowledgments The uthors re grteful to Mrs. Ptrici Pierre nd Mr. Léon Ronkrt for technicl ssistnce nd support during experimenttions nd the preprtion of the drft, nd to Prof. Georges C. Logny for criticl remrks during the writing of the mnuscript. 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