Arsenic speciation including ‘hidden’ arsenic in natural waters

Arsenic Speciation Including `Hidden' Arsenicin Natural WatersHiroshi Hasegawa,1* Masakazu Matsui,1 Shinsuke Okamura,2 Masashi Hojo,2

Nozomu Iwasaki2 and Yoshiki Sohrin3

1Institute for Chemical Research, Kyoto University, Uji, Kyoto 611, Japan2Faculty of Science, Kochi University, Akebono-cho, Kochi 780, Japan3Faculty of Engineering, Kanazawa University, Otateno, Kanazawa 920, Japan

Recent studies indicate the existence in naturalwaters of ‘hidden’ arsenic which had previouslybeen undetected by the hydride generation tech-nique. A speciation method for arsenic specieshas been developed in which hidden arsenic wasclassified into two fractions by their lability tothe photochemical degradation procedure: theultraviolet-labile fraction and the ultraviolet-resistant fraction. The ultraviolet-labile fractionwas the major fraction of hidden arsenic andcomprised 15–45% and 4–26% of the totalarsenic in Uranouchi Inlet and Lake Biwa(Japan), respectively. The highest concentrationof the ultraviolet-resistant fraction was observedin Uranouchi Inlet during the summer, in whichdimethylarsinic acid increased in the watercolumn. We discuss the hidden arsenic fractionas the key to explaining arsenic speciation innatural waters. Copyright # 1999 John Wiley &Sons, Ltd.

Keywords: arsenic; speciation; organoarseni-cals; ultraviolet irradiation; microwave diges-tion; methylation; natural water; hydridegeneration

Received 27 December 1997; accepted 28 September 1998

INTRODUCTION

Chemical speciation is the determination of theindividual concentrations of the various forms of anelement that together make up the total concentra-tion of that element. So far as arsenic species in

natural waters are concerned, the inorganic forms(arsenate [AsO(OH)3; As(V)] and arsenite[As(OH)3; As(III)]) and the methylated forms(methylarsonic acid [CH3AsO(OH)2; MMAA(V)]and dimethylarsinic acid [(CH3)2AsO(OH);DMAA(V)]) have been reported to be the mainspecies.1–4The bulk of the total dissolved arsenic isinorganic species in seawater1,2,6,7 and in freshwater,8,9 whereas methylarsenicals are found tocomprise significant amounts in the surfacelayers10–17 and above the sediment surface.16,17

The reported distributions suggest that the pre-dominant form of methylarsenic is consistentlyDMAA(V), followed by MMAA(V). The existenceof methylarsenic(III) species has also been demon-strated in the environment.15–19 Several observa-tions showed that methylarsenicals in surfacewaters exhibit a seasonal cycle in which themaximum concentrations of methylarsenicals ap-pear during the summer.13,15–17Although there isabundant evidence regarding methylarsenicals pro-duced biologically in natural waters,2,20–22apparentdifferences were observed in seasonal changes ofphytoplankton densities and methylarsenicals.

On the other hand, other organoarsenicals makeup the bulk of the arsenic stock in organisms.23,24

Arsenosugars are ubiquitous in algae25,26 andarsenobetaine is the predominant form in marineanimals.27,28 Arsenosugars and arsenobetaine can-not be detected with the conventional hydridegeneration analyses29,30which have been applied tonatural water samples. These facts suggest thepresence of additional organoarsenicals other thanmethylarsenicals in natural waters. Recently, tworesearch groups have revealed fractions of organo-arsenicals which were converted to hydride-reac-tive forms by ultraviolet irradiation31 or alkalinedigestion.32,33This ‘hidden’ or ‘refractory’ arseniccan be expected to offer the key to link arsenicspeciation in natural waters and biological produc-tion in organisms. The information on hidden

APPLIED ORGANOMETALLIC CHEMISTRYAppl. Organometal. Chem.13, 113–119 (1999)

Copyright# 1999 John Wiley & Sons, Ltd. CCC 0268–2605/99/020113–07 $17.50

* Correspondence to: H. Hasegawa, Institute for ChemicalResearch, Kyoto University, Uji, Kyoto 611, Japan.Contract/grant sponsor: Ministry of Education, Science, Sports andCulture, Japan; Contract/grant number: 09740557.

arsenicin naturalwatersis limited andits identityremainsunknown.

This paperdescribesthe speciationmethodforhiddenarsenicspeciesusingultraviolet irradiationand microwave digestion. Arsenic determinationwas performed by hydride generation atomicabsorptionspectrometry.We usedour speciationmethod to estimate the arsenic composition innaturalwaters.

EXPERIMENTAL

Sample collection and pretreatment

We collected surface water samples from twoeuphoticregions:the southernbasinof Lake Biwa(35° 06' N, 135° 56' E) and the deep part ofUranouchi Inlet (33° 25' N, 133° 21' E), Japan.Geographical data of the sampling sites aredescribedin detail elsewhere.15,34

The samplingsite of Lake Biwa is in a dredgedarea(depthca 12m) in thesouthernbasin,with anaverage depth of 3.5m. Thermal stratificationoccursfrom April to September,andthe dissolvedoxygenin the bottomlayer is extinguishedduringthe summer.Uranouchi Inlet is situated on thecentral coastof Tosa Bay. The water column isstratifiedasa resultof haloclineand/orthermoclineat a depthof 2–4m throughouttheyear.This inletleadsto theouterseathroughashallowmouthwitha depthof 2–4m, andthe deeppart hasa depthof10–20m. The salinity in UranouchiInlet is at thesamelevelsasthe outersea(26–34%),sincethereis no river from which waterflows into UranouchiInlet. The mean density of phytoplankton was2.5� 10ÿ9 and5.7� 10ÿ9 cells/m3 at thesamplingsite of Lake Biwa and Uranouchi Inlet, respec-tively. In both regions, the concentration ofarsenicalsfollows an annual cycle whereby themaximum concentrationsof methylarsenicalsap-pear with correspondingdecreasesin the As(V)level during thesummer.15,16

The sampleswere filtered with 0.45mm filters(Millipore) immediately upon collection. Bothfiltered and unfiltered sampleswere acidified topH 2 by the additionof 1 M hydrogenchloric acid,andstoredin acid-washedpolypropylenebottlesat5 °C in darkness.

Reagents

Stocksolutions(10ÿ2 M) for the identificationand

quantificationof arseniccompoundswerepreparedby dissolving the corresponding sodium salts[CH3AsO3Na2 preparedby Quick’s method,35 andNaAsO2,Na2HAsO4 and (CH3)2AsO2Na; NacalaiTesque],trimethylarsineoxide [(CH3)3AsO madeby Grignard synthesis] and arsenobetaine[(CH3)3As�CH2CO2

ÿ; Trichemical LaboratoryInc.] in 0.1M sodium hydroxide. These stocksolutions were standardized by using atomicabsorption spectrometry (Hitachi 180-70) andinductively coupledplasmaatomicemissionspec-trometry (ICP–AES;JapanJarrelAsh ICAP-500)afterdecompositionto As(V). Theyweredilutedtothe desiredconcentrationsjust beforeuse.For themicrowave digestion, the digestion reagentwasmadeby dissolvingpotassiumpersulphate(KantoChemical) in 0.15M sodium hydroxide (Merck).Sodium borohydride(Kanto Chemical)was usedfor hydride generation. A 3% (w/v) sodiumborohydridesolution,stabilizedin 10ÿ2 M sodiumhydroxide solution, was prepareddaily. Artificialseawaterwas preparedaccordingto Lyman andFleming36 anddistilled waterwasusedthroughout.Otherreagentswereof analyticalreagentgradeorbetter.

Arsenic analysis

Inorganic and methylarsenicalsAnalysis for inorganic and methylarsenicalswasperformedby modificationsof thehydridegenera-tion method(CT–HG–AAS),usinga apparatusandmaterials similar to those describedin previouspapers.19 In this technique,arsenicspecieswerereducedto the correspondingarsineswith sodiumborohydride, trapped in a U-tube with liquidnitrogen,andsequentiallyevolvedinto an electri-cally heatedquartzT-tube which wasmountedinthe atomicabsorptionspectrometer.The detectionlimits were 0.13–0.17nM and the reproducibilitywas3–6%for inorganicandmethylarsenicalsfor asamplesizeof 50ml.

Ultraviolet irradiationUltraviolet photolytic decompositionwas accom-plishedby useof a 400W high-pressuremercurylamp (Sigemi, AHH-400s) in a three-chamberreactionvesselconstructedfrom quartz.Sampleswere acidified to pH 2 by the addition of 1 Mhydrochloric acid and introduced into the outerchamber,cappedwith natural rubbersepta.Theywereirradiatedby a 400W high-pressuremercurylampmountedin thecentrechamber,with stirring.A Pyrex filter was attached,if necessary,in the

Copyright# 1999JohnWiley & Sons,Ltd. Appl. Organometal.Chem.13, 113–119(1999)

114 H. HASEGAWA ET AL.

centrechamberof thevessel.This filter cut off thelight under a wavelengthof 280nm. During theirradiation, cooling water at 25°C was circulatedinto the middle chamberfrom a constant-tempera-ture bath. Aliquots were taken at selectedtimeintervals.Analysisof thedigestatesfor arsenicwasperformedby CT–HG–AASasdescribedabove.

Total arsenicSamplesolution (20ml) and the digestionreagent(10ml) were introduced into a Teflon Beakerloosely closed with a Teflon watchglass.Sixsampleswere placedsymmetricallyin the micro-wave oven, and digestedat 500W for 10min.Followingashortcool-downperiod,10-mlportionsof 5 M hydrochloric acid were added and thebeakerswere set on a hotplate at 100°C for25min in order to decomposeexcesspersulphateand remove chlorine. After cooling to roomtemperature,the total arsenic concentrationwasmeasuredasAs(V) by CT–HG–AAS.

RESULTS AND DISCUSSION

Photolysis of arsenicals in naturalwaters

Figure 1 shows typical photoproductionof in-organic and methylarsenicspeciesin ultraviolet-irradiated samples. The water samples werecollected from surfacewaters in Uranouchi Inleton 30 April, 1997. Initially, both filtered andunfilteredsamplescontainedonly inorganicarsenic(9.3nM and11.5nM, respectively),andthemethy-larsenicconcentrationwasbelow detectionlimits.Inorganic and dimethylarsenicconcentrationsra-pidly increasedimmediatelyafter irradiation, andattainedequilibrium in 1–3h. The lake watersaswell asotherUranouchiwatersalsoshowedsimilarspeciation changes to those described above,although they varied as to their increments inarsenicconcentration.Our resultscoincidewith apreviousstudyin this respect:HowardandCombershowedthat irradiationof coastalseawaterfrom ashort-arcmercurylampgavelargeincreasesin themeasuredarsenicconcentration.31

Sampleswere adjustedto 0.01M hydrochloricacid solutionsto maintainthe pH conditionduringtheirradiation.All samplesremainedwithin thepHrange 2.00–2.10,even after 48h of irradiation.Howard and Comberreportedthat no increaseindimethylarsenic occurred in acidified samples

(about 0.011M hydrochloric acid) during ultra-violet irradiation.31 Underour conditions,suchaninhibition effect was not observedbelow at least0.1M. It seemsreasonableto supposethat thisdifferencewasdueto thewavelengthandintensityof the light. In Fig. 1, dimethylarsenicgraduallydecreasedbeyond4 h of irradiation by the high-pressuremercury light, althoughno decreasewasobservedin Howard’sexperiment.Brockbanketal.reportedthat methylarsenicwas demethylatedbyirradiation by 254nm ultraviolet light without adigestionreagent.37

Microwave digestion for thedetermination of total arsenic

The total arsenic bulk concentrationin naturalwaters was determinedby microwave digestionwith addedpotassiumpersulphatecombinedwith

Figure 1 Effect of irradiation time with a 400W high-pressuremercury lamp on arsenicspeciation.Sampleswerecollectedfrom surfacewaters(depth0 m) of the deeppart ofUranouchi Inlet, on 30 April 1997.*, Inorganic arsenicinfilteredsamples;*, inorganicarsenicin unfilteredsamples;&,dimethylarsenicin filtered samples;&, dimethylarsenicinunfilteredsamples.Monomethylarsenicwas below the detec-tion limit by CT–HG–AAS.


ARSENICSPECIATIONINCLUDING ‘HIDDEN’ ARSENIC 115

CT–HG–AAS. Organoarsenicalsare decomposedinto As(V) by persulphate,andmicrowaveirradia-tion speedstheoxidativedecompositionby its rapidheatingability. Bright et al. havedemonstratedtherelative efficacy of decompositionof microwavedigestionandotherdecompositionmethodsin porewater.38 Le et al. providea detaileddiscussionoffactorsthat influencethedecompositionof organo-arsenicals using microwave digestion.39 Whilemicrowave irradiation with persulphateis oftenused in the decompositionof an organic matrix,additionsarenecessaryfor speciationmeasurementby CT–HG–AAS.Whenthesolutionwasacidifiedwith hydrochloric acid for hydride generation,chlorine was slowly formed by the persulphateremaining in room temperature.This chlorineinterferedwith themeasurementof arsenicspeciesby CT–HG–AAS,since it oxidized arsinesin theU-tube.To removethe remainingpersulphate,thesolutionwasheatedat100°C aftertheacidificationwith hydrochloricacid. The digestionreagentwascompletelydecomposed,and the chlorine formedwaseliminatedby vaporization.

Therecoveryresultsobtainedby themicrowavedigestionmethodarepresentedin Table1. Micro-wave heating was applied for 10min to eachsampleadjustedto 0–0.10M potassiumpersulphatein 0.15M sodiumhydroxide.Thisdemonstratesthatcompletedigestionwas achievedin the rangeof0.03–0.10M potassiumpersulphate.If the persul-phate concentrationwas higher than 0.10M, theincreasedviscosityof thesamplesolutionmadethearsenic measurementby CT–HG–AAS difficult.Figure2 showsthe conversionsof arsenicspecies

upon decompositionof DMAA(V) and arsenobe-tainein distilled waterby themicrowavedigestionmethod.Thesecompoundsweredemethylatedstepby step,and quantitativelyconvertedinto the endproduct, As(V), over 6 min. When 300pmolportions of MMAA(V), DMAA(V) and arseno-betaine were spiked into 20ml portions ofUranouchiInlet waters,at least8 min of irradiationwasrequiredfor the quantitativedecompositionofthe orgnoarsenicals.We thereforedecidedthat thesample solution should be adjusted to 0.05Mpotassiumpersulphatein 0.15M sodiumhydroxideand irradiated for 10min. The blank value wasnegligible comparedwith the detection limit ofCT–HG–AAS. Relative standarddeviationswere

Table 1 Effect of initial potassiumpersulphate concentrationon therecoveryof arseniccompoundsby microwavedigestion

Arsenateconcentration(nM)

K2S2O8 (M) DMAA(V) a Seawaterb Freshwaterb

0 0 12.3 7.00.005 2.2 13.9 7.40.010 4.8 14.7 8.50.025 6.0 16.0 8.50.030 6.1 18.0 8.70.040 6.1 18.0 8.90.050 6.0 18.7 8.70.060 5.8 19.1 8.90.075 5.9 18.3 9.00.100 6.1 18.7 8.8

a 6.0nM dimethylarsonicacid in distilled water.b Sampleswerecollectedfrom surfacewaters(depth0 m) of thesouthernbasinof Lake Biwa on 24 April 1997,and the deeppart of UranouchiInlet on 22 October1996.

Figure 2 Effect of digestiontime on the decompositionoforganoarsenicalswith microwave digestion, using 0.05M

potassium persulphate and 0.15M sodium hydroxide asdigestion reagents. (a) DMAA(V) in distilled water; (b)arsenobetainein distilled water. *, Inorganic arsenic;~,monomethylarsenic;&, dimethylarsenic.



<4% for five measurementsof 1.0–10nMDMAA(V) standardsolutions.At the approximatedetectionlimit of 0.2nM, the standarddeviationswere20%in distilled waterandartificial seawater.

Arsenic speciation in natural waters

Hidden arsenicis definedas the fraction that hadpreviouslybeenundetectedby hydride generationatomic absorptionspectrometry.Our resultssug-gest that hidden arsenic can be classified intodifferent fractions by their lability to the photo-chemical degradationprocedure:the ultraviolet-labile fractionandtheultraviolet-resistantfraction.We estimatethe ultraviolet-labile fraction as theincrement in measurablearsenic concentrationbeforeandafter the 2.5h of ultraviolet irradiation,and the ultraviolet-resistantfraction as the differ-ence in measurablearsenic after the ultravioletirradiationandthemicrowavedigestion.

Figure3 showsthemeasuredarsenicfractionsinUranouchi Inlet and Lake Biwa. UV-InorgAs,

UV-MMA and UV-DMA are the correspondinginorganic,monomethyl-anddimethyl-arseniccon-centrationsin the ultraviolet-labile fraction. Theobserved results strongly suggest that hiddenarsenicexistsin both seawaterand in freshwater.UranouchiInlet clearly showedhigher concentra-tionsof hiddenarsenicthanLakeBiwa, in spiteofthe similar composition of the inorganic andmethylarsenicfractions.Thispatternwasconsistentwith thehigherdissolvedorganiccarbon(DOC) ofUranouchiInlet relativeto Lake Biwa. The valuesof DOC were2–4mg C 1ÿ1 and<0.3mg C 1ÿ1 inUranouchi Inlet and Lake Biwa, respectively.Between filtered and unfiltered samples, thedifferencein hiddenarsenicwas significantcom-paredwith that of inorganicandmethylarsenicals.It is likely that thehiddenarsenicin the>0.45mmsizefractionwasderivedfrom theorganoarsenicalsin biological organic detritus. Hanaoka et al.reported that arsenobetainewas decomposedbymarine microorganismsin sinking particles fromthe photic zone.40 Bright et al. suggestedthat

Figure 3 Meanconcentrationanddistributionof arsenicin naturalwaters.Sampleswerecollectedfrom surfacewaters(depth0 m)of (a) thedeeppart of UranouchiInlet on 30 April 1997,and(b) the southernbasinof Lake Biwa on 24 April 1997.



hiddenarsenicin interstitialwatersmightoccurin anumberof formssuchasarsenicalstightly adsorbedto organicmatter,or complexorganoarsenicals.38

In Fig 3, UV-InorgAs and UV-DMA were the

majorfractionsof hiddenarsenic,thoughlittle or noUV-MMA was detected. The ultraviolet-labilefractions comprised15–45% and 4–26% of thetotal arsenicin Uranouchi Inlet and Lake Biwa,respectively.It was reported that 25% and 18–420%increasesin theconcentrationof total arsenicwere observedin coastalwaters31 and interstitialwaters,38 respectively,beforeand after ultravioletirradiation.

On 23 June, the highest concentrationof theultraviolet-resistant fraction was observed inUranouchi Inlet with the highestdimethylarsenicconcentrationand a lower concentrationof theultraviolet-labile fraction. It appears that theincreaseddimethylarsenicconcentrationwas dueto photodegradationof hidden arsenicby strongsunlightin earlysummer.However,whenexposedto the filtered light abovea wavelengthof 280nmfrom a mercury lamp, both unfilteredsamples,ofseawaterandof freshwater,showedno significantchange in the arsenic speciation (Fig. 4). It isevident that photoproduction of UV-InorgAs,UV-MMA and UV-DMA occurred in responseonly to theultravioletregionof 250–280nmwhenahigh-pressuremercury lamp was used as anilluminator. These results indicate that photo-chemicaldegradationby sunlightrarelycontributesto the productionof methylarseniccompoundsinnaturalwaters.Anotherpossibilityis to assumethatdimethylarsenicwasproducedfrom theultraviolet-labile fraction by additional biological processessuch as bacterial decomposition,although theevidenceis not compelling.Clearly thereis muchto be learnedfrom further examinationof hiddenarsenicin naturalwaters.Furtheranalysesof otherwatersamplesarein progress.

Acknowledgements This researchwassupportedby a Grant-in-Aid for Encouragementof Young Scientists(09740557)from the Ministry of Education,Science,Sportsand Culture,Japan.

REFERENCES

1. M. O. Andreae,Deep-SeaRes.25, 391 (1978).2. M. O. Andreae,Limnol. Oceanogr.24, 440 (1979).3. M. O. Andreae,Organoarseniccompoundsin the environ-

ment.In: OrganometallicCompoundsin the Environment:PrinciplesReactions, Craig, P. J. (ed.), Longman,NewYork, 1986,pp. 198–228.

4. W. R. CullenandK. J.Reimer,Chem.Rev.89 713(1989).5. M. O. AndreaeandP.N. Froelich,Tellus36B, 101(1984).

Figure 4 Effect of irradiation time with a 400W high-pressuremercury lamp attacheda Pyrex filter on arsenicspeciationin unfilteredwaters.ThePyrexfilter cut off thelightbelow a wavelengthof 280nm. Sampleswere collectedfromsurfacewaters(depth0 m) of (a) UranouchiInlet on 30 April1997,(b) LakeBiwa on24April 1997,and(c) LakeBiwa on22July 1997.*, Inorganicarsenic;~, monomethylarsenic;&,dimethylarsenic.



6. M. L. Petersonand R. Carpenter,Mar. Chem.12, 295(1983).

7. G. A. Cutter,Mar. Chem.40, 65 (1992).8. P.SeylerandJ.M. Martin, Environ.Sci.Technol.23, 1258

(1989).9. A. Kuhn andL. Sigg,Limnol. Oceanogr.38, 1052(1993).

10. A. G. Howard, M. H. Arbab-Zavar and S. C. Apte,EstuarineCoastalShelfSci.19, 493 (1984).

11. L. C. D. Anderson and K. W. Bruland, Environ. Sci.Technol.25, 420 (1991).

12. G. F. Riedel,Estuaries16, 533 (1993).13. A. G. Howard,S. D. W. Comber,D. Kifle, E. E. Antai and

D. A. Purdie,EstuarineCoastalShelfSci.40, 435 (1995).14. S. J. Santosa,S. Wada,H. Mokudai andS. Tanaka,Appl.

Organometal.Chem.11, 403 (1997).15. H. Hasegawa,Appl. Organometal.Chem.10, 733 (1996).16. H. Hasegawa,Appl. Organometal.Chem.11, 305 (1997).17. Y. Sohrin, M. Matsui, M. Kawashima,M. Hojo and H.

Hasegawa,Environ.Sci.Technol., 31, 2712(1997).18. D. A. Bright,S.Brock,W. R.Cullen,G.M. Hewitt, J.Jafaar

andK. J.Reimer,Appl.Organometal.Chem.8, 415(1994).19. H. Hasegawa,Y. Sohrin, M. Matsui, M. Hojo and M.

Kawashima,Anal. Chem.66, 3247(1994).20. J. G. Sanders,Mar. Chem.17, 329 (1985).21. J. G. SandersandG. F. Riedel,Estuaries16, 521 (1993).22. A. G. Howard, S. C. Apte, S. D. W. Comberand R. J.

Morris, EstuarineCoastalShelfSci.27, 427 (1988).23. K. A. FrancesconiandJ.S.Edmonds,Adv.Inorg.Chem.44,

147 (1997).24. S. Maeda,Biotransformationof arsenicin the freshwater

environment. In: Arsenic in the Environment, Part I:Cycling and Characterization, Nraigu, J. O. (ed.), JohnWiley andSons,New York, 1994,pp. 155–187.

25. J.S.EdmondsandK. A. Francesconi,Nature(London)289,602 (1981).

26. J.S.EdmondsandK. A. Francesconi,J. Chem.Soc.PerkinTrans.I 2375(1983).

27. J.S.EdmondsandK. A. Francesconi,TetrahedronLett.18,1543(1977).

28. J. S. EdmondsandK. A. Francesconi,Experientia43, 553(1987).

29. M. O. Andreae,Anal. Chem.49, 820 (1977).30. R. S. Braman, D. L. Johnson,C. C. Foreback,J. M.

AmmonsandJ. L. Bricker, Anal. Chem.49, 621 (1977).31. A. G. HowardandS. D. W. Comber,Appl. Organometal.

Chem.3, 509(1989).32. A. M. M. de. Bettencourt and M. O. Andreae, Appl.

Organometal.Chem.5, 111 (1991).33. A. M. de.Bettencourt,M. H. Florencio,M. F.N. Duarte,M.

L. R. Gomesand J. F. C. Vilas Boasand,Appl. Organo-metal.Chem.8, 43 (1994).

34. Y. Sohrin,T. Tateishi,S. Mito, M. Matsui, H. Maeda,M.KawashimaandH. Hasegawa,LakesReserv.2, 77 (1997).

35. A. J. Quick and R. Adams, J. Am. Chem.Soc. 44, 805(1922).

36. J. LymanandR. H. Fleming,J. Mar. Res.3, 134 (1940).37. C. I. Brockbank,G. E. Batley andG. K.-C. Low, Environ.

Technol.Lett. 9, 1361(1988).38. D. A. Bright, M. DoddandK. J.Reimer,Sci.TotalEnviron.

180, 165 (1996).39. X. C. Le, W. R. Cullen and K. J. Reimer,Appl. Organo-

metal.Chem.6, 161 (1992).40. K. Hanaoka,T. Kaise,N. Kai, Y. Kawasaki,H. Miyashita,

K. Kakimoto and S. Tagawa,Appl. Organometal.Chem.11, 265 (1997).



Arsenic speciation including ‘hidden’ arsenic in natural waters

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