Adrien Mestrot IJA-CSIC-UB

ArsenicUbiquitous naturallyoccurringcontaminant– Earth’s crust andsedimentary rocks• Volcanic activity, soilerosion, leaching– Fossil fuel (mainlycoal), ores (mainlycopper ores)• Burning, roastingAlso (was) veryanthropogenic:– Herbicides, pesticides,wood preservativesMain problem isgroundwaterpollution, especiallyin India, Bangladeshand SE Asia, but alsoin South AmericaWater is used forcooking, drinking andalso irrigating ricepaddies– Biggest contaminationin the world!

ApproachSolid phase chemotrapping onsilver nitrate impregnatedsilica gel, previously used totrap As in natural gas.Quantification and qualification of all 4 arsines– Arsine: AsH 3 ,– Monomethylarsine: CH 3 AsH 2 ,– Dimethylarsine: (CH 3 ) 2 AsH,– Trimethylarsine (TMA): (CH 3 ) 3 As.-using offline hydride generation (HG) on solutions of As(III),monomethylarsenic acid (MMAA), dimethylarsenic acid(DMAA) and spiking of TMA ((CH 3 ) 3 As) solution (in pentane)into Tedlar Bags.Trap the content of the bags and assess recovery

ApproachElutionBoiling HNO 3 orBoiling H 2 O– with hot boiling solution of HNO 3 for totals,– with hot boiling water for speciation,– During trapping/elution process volatilespecies are converted to non volatilespecies.Measurements:– with HG-UV-AFS or ICP-MS for totals,– with HPLC-ICP-MS for speciation.

ExperimentsTotals:– 3 different experiments to assess recoveryon SKC traps, with 3 traps per species eachtime, analysis with UV-HG-AFS and ICP-MS.– Measure digests of traps to solve LODproblem.– Experiments on microcosms containing As.Speciation:– 4 species on a trap and 1 specie per trap.– Speciation on microcosms.

Recovery for totals:140120AsH387.8% ± 8.9140120(CH3)AsH295.6% ± 3.2100100Recovery (%)8060Recovery (%)80604040202001st exp 2nd exp 3rd exp average01st exp 2nd exp 3rd exp average120100(CH3)2AsH83.2% ±16.3120100(CH3)3As81.2% ± 20.18080Recovery (%)6040Recovery (%)6040202001st exp 2nd exp 3rd exp average01st exp 2nd exp 3rd exp average

LODsLOD(ng As trapped)Averageblank3xSDLOD(Avg+3xSD)Elution oftraps(n=8)11.805.9317.73Digestion of trapswithout glasswool (n=8)1.921.883.80Digest andmeasure allcompartments.Silica Gel180Repartition of the As in blank traps (n=5)GlassWoolFoam160Quantity of As (ng)140120100806040 Digest silica gel from SKC traps withblock digester after removal of theglass wool and the foam plug instead ofeluting.200Foam Silica Gel Glass Wool

Speciation analysis:Trapping 50 ng of each compound onto different traps andanalysis using HPLC ICP-MS, addition of 100 µL ofconcentrated H 2 0 2 .Speciation on a trap loadedwith the four arsine speciesMethod used:0.010HPLC (anion exchangeHamilton PRP X 100)Phosphate buffer (pH 6.2)Flow rate 1.0 ml/minICP-MSCPS As/RhGood separation0.0080.0060.0040.0020.000All four speciestrapped and eluted.(CH 3) 3Asas TMAO(CH 3) 2AsHas DMAATime (s)(CH 3)AsH 2as MMAAAsH 3as As(V)0 200 400 600 800 1000

Speciation analysis:Chromatograms of each specieOne specie pertrap.0.0140.012time (s) vs TMAOtime (s) vs DMAAtime (s) vs MMAAChromatogramsshow thatspecies are notfalling apart,the As-C bondremains intactwhen traps areeluted with hotboiling water.CPS As/Rh0.0100.0080.0060.0040.0020.000time (s) vs As (V)0 200 400 600 800 1000Time (s)

Volatilization measured onnon-spiked soil samplesBangladeshi paddysoils from an arsenicelevated tubewellwater irrigated paddyin Faridpur (24.2mg.kg -1 As).Traps were placedfor several weeks (1-33d and 34-61d) onthe inlet and theoutlet of thereactors.SoilTo pump@ 12ml/minWater

Influence of the flooding and themanure (cow dung):Two trappingperiods on themicrocosms: 1-33days and 34-61days.350300INLETOUTLETMF: Manured Flooded.MNF: Manured Non-Flooded.NMF: Non-ManuredFlooded.NMNF: Non-ManuredNon-Flooded.ng As trapped250200150Great influenceof the manureon thevolatilization,mainly infloodedconditions.100500MF 1-33dMF 34-61dMNF 1-33dMNF 34-61dNMF 1-33dNMF 34-61dNMNF 1-33dNMNF 34-61d

Speciation on MesocosmsTMA as (CH 3 ) 2 AsH as AsH 3 asManuredfloodedmicrocosms forthe secondtrapping period,34-61d.Main volatilespecies is TMAbut DMA is alsopresent and smallpeak of As(V)suggest traces ofAsH 3 .

Conclusions:Method allows for– Quantitative trapping of all 4 arsines down to a few ng(LOD=3.8ng),– Identification of all 4 species,– Sampling of environmental matrices (eg. Rice paddies,volcano fumes, hot springs etc…)– Determining key conditions for As volatilization.Method is simple, robust and can be easily deployedin the field where the real importance of Asvolatilization could be assessed.To be tested in the field…

Thank you for yourattention.We acknowledge funding from the EuropeanCommission (AquaTRAIN MRTN-CT-2006-035420).