Speciation Analysis of 129 I and Its Application as an Environmental Tracer

Transcription

1 Speciation Analysis of 129 I and Its Application as an Environmental Tracer Xiaolin Hou Risø National Laboratory for Sustainable Energy, Technical University of Denmark XIHO@risoe.dtu.dk

2 Isotopes of Iodine I (stable, 100% abundance) I (8 d), 125 I (56 d), 126 I (13 d), 124 I (4.2 d) I ( years ) - others (< 1 day)

3 Source of 129 I Natural process: Atmosphere Artificial process: Cosmic ray Xenon Neutron Induced fission of 235 U 129 I Spontaneous fission of 238 U 235 U(n, f) 129 I 239 Pu(n, f) 129 I

4 Inventory of 129 I by 2007 Reprocessing discharge to the sea (4750 kg) Reprocessing discharge to the atmosphere (230 kg) Weapon tests (63 kg) Chernobyl accident (1.3 kg) Nature (210 kg)

5 Level of 129 I in environment Source 129 I/ 127 I ratio in the Ocean 129 I concentration in seawater Nature ~ ~ atoms/l Nuclear waepon tests ~ ~ atoms/l Chernobyl accident Reprocessing plant (Marine discharge) by 2005 Reprocessing plants (air emission by 2006) ~10-6 (North Sea) 3~ (Kattegat) in ~10-6 (rain water in Europe) 2~ atoms/l (the Kattegat) 10 8 ~10 10 atoms/l (rain water)

6 Discharge of 129 I from reprocessing plant Sellafield marine discharg La Hague marine dischage Sellafield air release x10 La Hague air release x10 Discharges (kg/y) Year

7 Analytical Method for 129 I and their detection limits Method Liquid scintillation γ-spectrometry ICP-MS Radiochemical neutron activation analysis Accelerator mass spectrometry (AMS) Detection limit 129 I, atoms 129 I/ 127 I Ratio

8 PRINCIPLES OF AMS negative ions production (isobar elimination) charge exchange (breaking of molecular interference) high energy ions (unique ion identification) injector m 2 accelerator high energy analysis magnet m magnet Ion source 127 IH I +5 H 2 + electrostatic deflector sensitivity detector

9 ToF spectra of an AgI standard mixed with niobium (isotopic ratio = ) I Energy I Time

10 Method for Speciation of 129 I and 127 I in water (I) Anion exchnage The affinities of various anions to anion exchange resin AG-1: I - >HSO 4- >ClO 3- >NO 3- >Br - >CN - >HSO 3- >NO 2- >Cl - >HCO 3- >IO 3- >HCOO - >OH - >F Counts of 131 I (Bq) I - - IO 3 Fig. 1 The loading (1-50ml), washing (with deionized water ml and 0.5 mol/l KNO ml) and eluting (with 2.0 mol/l KNO ml) behavior of iodide and iodate in seawater in AG1 4 column using 131 I tracer Volume of eluate (ml)

11 Method for Speciation of 129 I and 127 I in water (I) Anion exchange seawater seawater Decomposition, KHSO 3 reduction Eluate by KNO 3 Eluate by KNO 3 KHSO 3 reduction IO 3 -+ Org. I I- Effluent Total iodine ICP-MS determination of 127 I Eluate by KNO 3 Add iodine carrier and extraction separation of iodine Org. I I- (IO 3 -) Hou, et al. Anal. Chem. 1999; Mar.Chem AgI add AgNO 3 AMS measurement of 129 I

12 The advantage and drawback of present method for the speciation analysis of 129 I Seawater Ion exchange separation of I - and IO 3 - Advantage: The present ion chromatography method has good separation efficiency and has been successfully used in the chemical speciation of I-129. CCl 4 /CHCl 3 extraction AgI precipiation AMS of AgI for 129 I - / 129 IO 3 - Drawback: The procedure is normally time consuming (3-12 hours depending on the sample size) Unsuitable for the in situ separation on board.

13 Method for Speciation of 129 I and 127 I in seawater (II) Co-precipiation Reactions: Ag + + I - = AgI Ksp= (Insoluble in acid and NH 3 ) Ag + + IO 3 - = AgIO 3 Ksp= (Insoluble in acid and NH 3 ) Ag + + Cl - = AgI Ksp= (Insoluble in acid, but soluble in NH 3 ) Note: M m A n =mm + (aq)+na - (aq) Ksp=[M+] m [A] n (solubility production)

14 AgI-AgCl co-precipitation for separation of iodide from IO 3 - recovery of iodine, % Ag+/I molecular ratio Iodide (125I-) Iodate (131IO3-) recovery of iodine, % Ag+/Cl molecular ratio Iodide (125I-) Iodate (131IO3-) Optimal precipitation condition: Iodide can be quantitatively separated from iodate and organic iodine by coprecipitation of AgI with AgCl. Ag/I ratio: Ag/Cl ratio: Salinity: >5 Precipitation time: h

15 Method for Speciation of 129 I and 127 I in seawater (II) Co-precipiation Seawater Add 127 I - carrier, adjust ph4-7, add AgNO 3 to Ag/Cl = , and I/Ag=50-200, stir for 1 h, centrifuge Add 127 I - carrier and Na 2 SO 3, adjust ph<2, add AgNO 3 to Ag/Cl = , and I/Ag=50-200, stir for 1 h, centrifuge supernatant AgI-AgCl precipitate Supernatant AgI-AgCl precipitate wash with NH 3 wash with NH 3 AMS of 129 Iodide (AgI) AMS of Total inorganic 129 I ( 129 I IO 3- )

16 Separation of iodide by extraction using CCl 4 water sample I- oxidation I 2 Oxidants: NaNO 2, H 2 O 2 CCl 4 (I 2 ) CCl 4 extraction Na 2 SO 3 back extraction 129 I - + Ag + Ag 129 I AMS of 129 I

17 Method for Speciation of 129 I and 127 I in seawater (II) extraction with NaClO as oxidant Seawater/Fresh water Aqueous phase Add 127 I - carrier, adjust ph4-7, add CCl 4, and 1% NaClO, extraction, repeat CCl 4 extraction until no I 2 in CCl 4 CCl 4 phase Add Na 2 SO 3 to back extract Aqueous phase Add 127 I - carrier and Na 2 SO 3, adjust ph<2, add CCl 4, and 1% NaClO, extraction, repeat CCl 4 extraction CCl 4 phase Add Na 2 SO 3 to back extract Decompose organic iodine by NaOH/UV, reduce all iodine to Iodide, extraction with CCl 4, back extraction with Na S 2O 3 Aqueous phase CCl 4 phase Aqueous phase Add Ag + to precipitate I - AMS of 129 Iodide CCl 4 phase AMS of Total inorganic 129 I Aqueous phase Add Ag + to precipitate I - Add Ag + to precipitate I - AMS of Total 129 I

18 Comparison of three methods for speciation of 129 I in seawater Seawater, English Channel, at/l Seawater, Kattegat(Denmark) at/l 129 I IO I IO 3 - Ion exchange 28.7± ± ± ±1.13 AgI-AgCl precipitate CCl 4 extraction with NaClO oxidation 26.9± ± ± ± ± ± ± ±1.43 Hou et al., Anal. Chem., 2009

19 Chemical species of iodine in seawater Iodine in Seawater (Total Iodine) Inorganic Iodine Organic Iodine I -, Iodide IO 3-, iodate

20 Variation of iodide and iodate with depth and latitude in seawater from Atlantic Ocean IO 3 - A high iodide concentration was found in the seawater from low latitude Iodide concentration is higher in surface water than in the deep water Truesdale et al

21 Property of iodide and iodate Iodide is a thermodynamically unstable species in oxygenated waters IO 3 - I - a thermodynamically unfavourable reaction I - IO 3 - a thermodynamically favourable reaction Where? (Origination of iodide) How? Conversion of iodine between different species, Stability and reaction kinetics of different species of iodine) Geochemical cycle of iodine --- transfer of iodine in different environment in the nature Investigation on this issue by speciation analysis of stable iodine in the seawater (Cannot identify the source and iodine, and convert, especially the new produced iodine species)

22 Eir e Sellafield North Sea ) German Bight Skagerrak Jutland Kattegat 49 Danm ark Baltic Sea La Hague 4 English Channel Belgique/België Ne de rland Luxembourg Deutschland Czech Republic Poland 1 France Fig. Sampling locations of surface water from the North Sea ( ), German Bight (o) in August 2005 and Danish coast in June 2000, the Kattegat and Belt Sea in November 1999( ). Slovakian

23 Fig. Distribution of 129 I (atoms/l) in the North Sea and English Channel High 129 I level in the English Channel and Southern North Sea and along the European continential coast. Verylow 129 I level in the south west of the English Channel and east sider of the northern North Sea.

24 Fig. Distribution of 127 I - in the North Sea Fig. Distribution of 129 I - in the North Sea Increased 129 I - concnetration occured in the Dutch coast and German Bight. Hou et al., Environ. Sci. Technol. 2007

25 Fig. Distribution of 127 I -/127 IO 3- in the North Sea Fig. Distribution of 129 I -/129 IO 3- in the North Sea Reduction of iodate or oxidation of iodide in the open sea seems to be a slow process. The reduction of iodate starts to occur in the Dutch coast and Germany Bight, this new produced 129 I - does not oxidized to 129 IO 3- during the movement northwards to the northern North Sea. No new production of 129 I - occurred during the transport of water from the German Bight to the northern North Sea.

26 Iodine cycle in nature I2, HI, HOI CH3I particulate I2 CH3I IOrganic-rich (little soil re-volatilization) IO3- Alkaline soil IO3- I2 Acidic soil (volatilization)

27 129 I/ 127 I in preciptiation from Roskilde, Denmark 129 I/ 127 I in precipitation, 10-8 atom/atom, Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Total iodine Iodate Sampling date (monthly) A 2-3 orders of magnitude increased 129 I level in precipitation in Denmark is attributed to the release of 129 I from reprocessing plants at La Hague and Sellafield.

28 Variation of deposition flux of 129 I and 127 I (10 9 atoms m 2 ) at Roskilde, Denmark in I deposition 129I deposition precipitation rate, mm 180 Deposition flux of 129 I (10 9 atoms m -2 ) or 127 I (μg m -2 ) Precipitation rate, mm 0 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 0 Sampling date (monthly) The deposition trend of 129 I does not follow the 127 I. The average annual deposition flux of 129 I is atoms m -2, the estimated annual deposition of 129 I over Europe is 3.0 kg in , while annual atmospheric emission of 129 I from two NRPs is only 3-4 kg in Considering the long distance of Risokilde to the two NRPs and the mainly local deposition of atmopheric emission 129 I. The contribution from atmospheric emision to the precipitation 129 I is limited.

29 Comparison of monthly variation of 129 I concentrations and 129 I/ 127 I atomic ratios in precipitate at Roskilde, Denmark and the atmospheric emission of 129 I from NRP at La Hague and Sellafield I concentration in precipitate total atmospheric releasr atmospheric release from Sellafield 129I/127I in precipitate atmospheric release from La Hague I concentration (10 9 atom L -1 ) or 129 I/ 127 I value (10-7 atom/atom) in precipitation, Monthly atmospheric emission of 129 I, kg month -1 0 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Sampling date (monthly) 0.00 The monthly variation trend of 129 I in precipitation does not follow the variation of atmospheric emission of 129 I from the two NRPs.

30 Correlation of chlorine with 127 I and 129 I in the precipitate 3.0 Cl-127I Cl-129I I concentration, ng ml R 2 = R 2 = I concentration, 10 9 atoms ml Chlorine, mg ml -1 0 Strong correlation between 129 I and Cl in precipitate. The measured ratio of 129 I/ 127 I in seawater from European Seas are , the estimated 129 I re-emitted from the European Seas is about 2-4 kg/y, which is comparable to the estimated 129 I deposition in Europe (3.0 kg/y). Indicating the marine source of 129 I in the precipitate from Roskilde.

31 Re-emission of 129 I from the coast of European water 129 I in European coastal water is 2-3 orders of magnitude higher than the central sea water, emission of 129 I from the coastal area of the seas may be a main contribution of iodine in the atmosphere. Iodide as the dominant species of 129 I in precipitation may be attributed to different sources as 127 I. Does biomass (seaweeds) has a major contribution to the re-emission of 129 I from the coastal water in the European water?

32 Speciation of 129 I in atmosphere collected from different distance to the North Sea Species of 129 I and 127 I Particle associated Iodine Inorganic gaseous iodine (I 2, HI, HIO) Organic gaseous iodine (CH 3 I, C 2 H 7 I, CH 2 BrI, etc.)

33 Speciation method for 129 I in air Glass filter (0.45 μm) for particles Two sets of NaOH/glycerin impregnated filter paper for inorganic gas iodine TEDA impregnated active charcocal (for organic gas iodine) To pump

34 Speciation method for 129 I in air

35

36 Air sampling locations HELSINKI OSLO STOCKHOLM TALLINN E RIGA A B C D R COPENHAGEN F VILNIUS BERLIN WARSAW

37 Sequential extraction for fractionation of 129 I in soil and sediment Soil sample, 30 g Water leaching Water soluble Residue NH 4 OAc (ph8.0) leaching Exchangable Residue NH 4 OAc (ph5.0) leaching Carbonate Metal oxides Organic matter Residue NH 2 OH HCl-HOAc (ph2.0) leaching Residue H 2 O 2 -HNO 3 leaching/naoh leaching Residue

38 Fig. Distribution of 129 I and 137 Cs in different fractions of soil from Chernobyl region I 137Cs Water soluable Exchangable Carbonate oxides Organic Residues Fraction Percentage %

39 Distribution of 129 I in different fractions of Chernobyl soil and Irish Sea sediment Soil Sediment percentage % Water soluable Exchangable Carbonate Oxides Organic Residues Fraction Hou et al. Sci. Total Environ., 2003

40 Englund, Hou, Aldahan, Environ. Sci. Technol Depth profile of 129 I fractionation in a lake sediment core from central sweden (Nylandssjön) 129 I and 127 I have a similar partitioning in the sediment. Iodine is mainly associated with organics in the sediment, the exchangable iodine counts only <6%. The feature of higher association of 129 I with organics in the sediment may be used for investiagtion of the organic carbon exchange, as well as for the age dating of the sediment.

41 More works on speciation of radionuclides Speciation of 129 I and 127 I in seaweeds, fish, and tissues Tc speciation in the environment (TcO 4-, TcO 2, organic Tc) Pu speciation in hot particles Pu, Np, Am speciation in environment (not only fractionation) Dynamic system for the fractionation of Pu in soil and sediment. Specaition related to depository of nuclear waste Hou et al., Anal. Chim Acta, (Review), 2009