**4. Measurement of 129I**

374 Radioisotopes – Applications in Physical Sciences

bound to proteins – but these are still not identified for most environmental and biological samples, not for 127I and certainly not for 129I. The main problem is lack of appropriate standards for speciation analysis and very small amounts of 129I in environmental and

Iodine is released from marine environment to the atmosphere partly as aerosols formed from the sea spray – inorganic iodide and iodate – and mainly as volatile organic iodine compounds (VOIC) such as iodomethane (Baker et al., 2000; Leblanc et al., 2006, Chance et al., 2009). Bacteria, phytoplankton and brown algae present in marine environment are capable to reduce the most thermodynamically stable form of iodine, the iodate to iodide. On the other hand microalgae and macroalgae-seaweed accumulate iodide and transform it into VOIC – the most important are CH3I, CH2I2, CH2BrI and CH2ClI (Leblanc et al., 2006). The emitted organic iodine is decomposed by sunlight into inorganic iodine compounds. The photolytic lifetimes of VOIC differ; CH2I2 has a lifetime of 5 minutes, followed by CH2BrI with a lifetime of 45 minutes and CH2ClI with a lifetime of 10 h (Stutz, 2000). The longest photolytic lifetime of 14–18 days has CH3I (Stutz, 2000). During this process of photolization reactive iodine oxides such as HOI, I2O2 and IO2 form, which either form condensable vapours as nuclei for aerosols or react with ozone. From the atmosphere iodine enters the marine and terrestrial environment by processes of wet and dry deposition. In the iodine terrestrial cycle interactions between water and soil are most important (Santschi & Schwehr, 2004). Beside physical and chemical factors, biological processes especially promoted by microorganism influence the cycling of iodine. Microorganisms are involved in environmental processes as primary producers and also as consumers and decomposers. They have bioremedial and biotransformable potential and in this way affect the mobility of elements. Oxidation and reduction mechanisms contribute to transformations between soluble and insoluble forms. Experiments with 125I tracer showed the importance of microbial participation in iodine accumulation – sorption and desorption processes – in soil. Muramatsu et al. (1996) observed desorption of iodine from flooded soil during cultivation of rice plants. Microorganisms created reducing conditions in the flooded soil and iodine once adsorbed on the soils was desorbed (Muramatsu et al., 1996). Amachi et al. (2001) reported a wide variety of terrestrial and marine bacteria that are capable to produce CH3I under oligotrophic conditions. Aerobic bacteria showed significant production of CH3I, whereas anaerobic did not produce it. The methylation of iodide was catalysed

enzymatically with S-adenosyl-L-methionine as the methyl donor.

The biding of iodine by organic matter and/or iron and aluminium oxides has the potential to modify the transport, bioavailability and transfer of iodine isotopes to man (Santschi & Schwehr, 2004). Because of the same chemical properties 129I and 127I should behave similar in environmental processes. Major pathways are the volatilization of organic iodine compounds into the atmosphere, accumulation of iodine in living organisms, oxidation and reduction of inorganic iodine species, and sorption of iodine by soils and sediments. These

129I is gradually released in trace quantities into the atmosphere and aquatic environment from reprocessing plants. It is then physically transported in the air or water media under the influence of chemical and biological processes. Newly introduced 129I from NFRP is in volatile form and as such more mobile compared to 127I. By taking this aspect into account one cannot be sure that biogeochemical behaviour of 129I and 127I is the same. Even more, Santschi & Schwehr (2004) discussed that biogeochemical behaviour of iodine and its

processes are influenced or even controlled by microbial activities (Amachi, 2008).

isotopes appears to be different in North American and European waters.

biological samples.

129I decays by emitting beta particles (Eβmax = 154.4 keV), gamma rays (Eγ = 39.6 keV) and Xrays (29−30 keV) to stable 129Xe (Tendow, 1996). Therefore it can be measured by gamma and X-ray spectrometry and by beta counting using liquid scintillation counters (LSC).

Another method for determination of 129I is neutron activation analysis (NAA) that is based on neutron activation of 129I(n, γ)130I, which is measured by gamma spectrometry (Eγ = 536 keV (99 %). In recent year's mass spectrometry – such as accelerator mass spectrometry (AMS) and inductively coupled plasma mass spectrometry (ICP-MS) are also used.

For determination of 129I levels in environmental samples only two analytical methods are available, radiochemical neutron activation analysis (RNAA) and AMS. The main advantage of the AMS is the detection limit that is close to 10-14 expressed as 129I/127I ratio. RNAA can only measure 129I at elevated levels – nuclear era. AMS enables measurement of 129I in all environmental samples, also the natural, pre-nuclear levels, and the needed amount of sample is 10-100 times smaller than in the case of RNAA. Detection limits for 129I using different analytical methods are compared in Table 6.


\*Woodward Iodine is elemental iodine mined by Woodward Iodine Corp. in Oklahoma for which the lowest ratio is reported.

Table 6. Limits of detection for 129I in various samples using different analytical methods

The Potential Of I-129 as an Environmental Tracer 377

either quadropole type time-of-flight or combination of magnetic and electrostatic sector

Difficulties encountered when determining 129I with ICP-MS are low 129I quantities present with high 127I concentrations, isobaric and molecular ions interferences (129Xe+, 127IH2+), memory effects and tailing of 127I. To improve 129I/127I determination it was found that introduction of helium gas into collision cell reduces peak tail of a high-abundant isotope, 127I by up to three orders of magnitude. Detection limits have been improved by applying oxygen as collision gas for selective reduction of 129Xe (Izmer et al., 2003, Hou et

NAA enables determination of 129I in environmental samples at 10-10 129I/127I isotopic ratios. The concentration levels of 129I in environmental samples are very low and chemical separation/pre-concentration procedures have to be developed which can be used for a

Neutron activation analysis is based on induction of 129I with thermal neutrons – irradiation

( ) ( ) <sup>129</sup> <sup>13</sup><sup>0</sup> I n, I 12.36 hours, 536.1 keV *T E* <sup>½</sup>

129I is determined by measuring of 130I activity on a high purity Ge detector. Interfering nuclear reactions induced during irradiation of sample from other nuclides resulting in 130I production can influence the correct determination of 129I. These undesired nuclides are 235U, 128Te and 133Cs and nuclear reactions: 235U(n, f)129I(n,γ)130I, 235U(n,f)130I, 128Te(n,γ)129mTe(β- )129I(n,γ)130I and 133Cs(n,α)130I (Hou et al., 1999). They have to be removed from the sample

During irradiation radioactivity in sample is produced mainly due to the radioisotopes 23Na(n,γ)24Na (*T½* = 14.96 hours), 41K(n,γ)42K (*T½* = 12.36 hours) and 81Br(n,γ)82Br (*T½* = 35.30 hours) present in sample, which renders the direct measurement of 130I after irradiation and radiochemical separation of induced 130I after irradiation is necessary. Solvent extraction with CCl4 or CHCl3 are normally used to extract iodine (Osterc & Stibilj,

In first step pre-concentration of iodine from large amounts of sample is performed. Solid samples, such as soil, sediment, vegetation, biological samples can be decomposed by alkaline fusion (Hou et al., 1999, Osterc et al., 2007). The sample is mixed with potassium hydroxide/alkali solution and then gradually heated to 600 °C. Iodine is leached from the decomposed sample with hot water, isolated with solvent extraction and precipitated as PdI2 or MgI2 or trapped on activated charcoal (Fig. 2) (Hou et al., 1999, Osterc et al., 2007). Another method to separate iodine from solid samples is combustion at high temperature, ~1100 °C (Muramatsu & Yoshida, 1995). Released iodine is trapped in an alkaline solution or

The pre-concentrated iodine is than irradiated for up to 12 hours simultaneously with a 129I/127I standard. After radiochemical separation the 130I induced from 129I (see nuclear reaction 1) is counted on a high purity Ge detector and compared to standard of known

γ

= = (1)

and measured by an ion decetor (Hou et al., 2009).

**4.4 Neutron Activation Analysis (NAA)** 

in a nuclear reactor via following nuclear reaction:

before irradiation to avoid nuclear interferences.

γ

activity and corrected for chemical yield (Osterc et al., 2007).

wide variety of matrices.

2005; Osterc et al., 2007).

adsorbed on activated charcoal.

al., 2009).

### **4.1 Direct gamma and X-ray spectrometry**

Direct gamma-X spectrometry (Eγ = 39.6 keV; X-rays, 29−30 keV) is a non-destructive technique that is rapid and can be applied to different matrices. It is used for monitoring of environmental samples collected in vicinity of NFRP such as thyroid, urine, seaweed, and for nuclear waste by using high purity Ge or plenary Si detector (Suarez et al., 1996; Bouisset et al., 1999; Frechou et al., 2001; Lefevre et al., 2003; Frechou & Calmet, 2003; Barker et al., 2005). To lower the detection limits normally big samples (50−500 g) are used, which induces considerable attenuation at low energies. The attenuation depends on the matrix composition of the sample and geometric parameters of the container. Therefor the mass energyattenuation coefficient (self-absorption correction) at a given energy must be measured for all sample matrices with respect to that of the standard source. Experimentally obtained selfabsorption correction factors are used to obtain accurate results (Bouisset et al., 1999; Lefevre et al., 2003, Barker et al., 2005). To quantify self-absorption correction factors 210Pb (46.5 keV) and 241Am (59.6 keV), with gamma lines close to 129I are used. Detection limits as low as 2 Bq kg-1 dry mass can be reached for *Fucus sp.* samples (Bouisset et al., 1999).

Chemical separation of 129I from the sample matrix and interfering radionuclides – destructive method – improves the detection limit when using direct gamma-X spectrometry (Suarez et al., 1996).

By using direct gamma-X spectrometry 129I was determined in seaweed sample FC-98 Seaweed, which was prepared by Frechou et al. (2001), by using direct gamma –X spectrometry (Osterc & Stibilj, 2008).

#### **4.2 Liquid Scintillation Counting (LSC)**

Liquid scintillation counting is based on emissions of beta particles from radionuclides – beta decay (Eβmax = 154.4 keV). 129I has to be separated from the sample matrix and other radionuclides and dissolved or suspended in a scintillation cocktail containing an organic solvent and a scintillator. Beta particles emitted from the sample transfer energy to the solvent molecules, which in turn transfer their energy to the scintillator which relaxes by emitting light - photons. In a liquid scintillation counter each beta emission (ideally) results in a pulse of light, which is amplified in a photomultiplier and detected.

Recently extraction chromatographic resins for the separation and determination of 36Cl and 129I have been developed. First results show a promising potential to use the resins within the context of the monitoring of nuclear installations – during operation and especially during decommissioning (Zulauf et al., 2010).

### **4.3 Inductively Coupled Plasma Mass Spectrometry (ICP-MS)**

ICP-MS has been used to determine 129I in contaminated environmental samples with high level 129I content such as sediments, groundwater samples, soil and seaweed (Izmer et al., 2003; Izmer et al., 2004; Becker, 2005; Brown et al., 2007; Li et al., 2009). The lowest detection limit of the method reported as 129I/127I isotopic ratio is 10-7.

The method is based on iodine separation and injection to the machine as solution or gaseous iodine, I2. Iodine is decomposed into iodine atom and ionized to positive iodine ion at a temperature ~6000−8000 K. It is then extracted from the plasma into a high vacuum of the mass spectrometer via an interface. The extracted ions are separated by mass filters of

Direct gamma-X spectrometry (Eγ = 39.6 keV; X-rays, 29−30 keV) is a non-destructive technique that is rapid and can be applied to different matrices. It is used for monitoring of environmental samples collected in vicinity of NFRP such as thyroid, urine, seaweed, and for nuclear waste by using high purity Ge or plenary Si detector (Suarez et al., 1996; Bouisset et al., 1999; Frechou et al., 2001; Lefevre et al., 2003; Frechou & Calmet, 2003; Barker et al., 2005). To lower the detection limits normally big samples (50−500 g) are used, which induces considerable attenuation at low energies. The attenuation depends on the matrix composition of the sample and geometric parameters of the container. Therefor the mass energyattenuation coefficient (self-absorption correction) at a given energy must be measured for all sample matrices with respect to that of the standard source. Experimentally obtained selfabsorption correction factors are used to obtain accurate results (Bouisset et al., 1999; Lefevre et al., 2003, Barker et al., 2005). To quantify self-absorption correction factors 210Pb (46.5 keV) and 241Am (59.6 keV), with gamma lines close to 129I are used. Detection limits as low as 2 Bq kg-1

Chemical separation of 129I from the sample matrix and interfering radionuclides – destructive method – improves the detection limit when using direct gamma-X

By using direct gamma-X spectrometry 129I was determined in seaweed sample FC-98 Seaweed, which was prepared by Frechou et al. (2001), by using direct gamma –X

Liquid scintillation counting is based on emissions of beta particles from radionuclides – beta decay (Eβmax = 154.4 keV). 129I has to be separated from the sample matrix and other radionuclides and dissolved or suspended in a scintillation cocktail containing an organic solvent and a scintillator. Beta particles emitted from the sample transfer energy to the solvent molecules, which in turn transfer their energy to the scintillator which relaxes by emitting light - photons. In a liquid scintillation counter each beta emission (ideally) results in a pulse of light, which is amplified in a photomultiplier and

Recently extraction chromatographic resins for the separation and determination of 36Cl and 129I have been developed. First results show a promising potential to use the resins within the context of the monitoring of nuclear installations – during operation and especially

ICP-MS has been used to determine 129I in contaminated environmental samples with high level 129I content such as sediments, groundwater samples, soil and seaweed (Izmer et al., 2003; Izmer et al., 2004; Becker, 2005; Brown et al., 2007; Li et al., 2009). The lowest detection

The method is based on iodine separation and injection to the machine as solution or gaseous iodine, I2. Iodine is decomposed into iodine atom and ionized to positive iodine ion at a temperature ~6000−8000 K. It is then extracted from the plasma into a high vacuum of the mass spectrometer via an interface. The extracted ions are separated by mass filters of

**4.1 Direct gamma and X-ray spectrometry** 

spectrometry (Suarez et al., 1996).

spectrometry (Osterc & Stibilj, 2008).

detected.

**4.2 Liquid Scintillation Counting (LSC)** 

during decommissioning (Zulauf et al., 2010).

**4.3 Inductively Coupled Plasma Mass Spectrometry (ICP-MS)** 

limit of the method reported as 129I/127I isotopic ratio is 10-7.

dry mass can be reached for *Fucus sp.* samples (Bouisset et al., 1999).

either quadropole type time-of-flight or combination of magnetic and electrostatic sector and measured by an ion decetor (Hou et al., 2009).

Difficulties encountered when determining 129I with ICP-MS are low 129I quantities present with high 127I concentrations, isobaric and molecular ions interferences (129Xe+, 127IH2+), memory effects and tailing of 127I. To improve 129I/127I determination it was found that introduction of helium gas into collision cell reduces peak tail of a high-abundant isotope, 127I by up to three orders of magnitude. Detection limits have been improved by applying oxygen as collision gas for selective reduction of 129Xe (Izmer et al., 2003, Hou et al., 2009).

#### **4.4 Neutron Activation Analysis (NAA)**

NAA enables determination of 129I in environmental samples at 10-10 129I/127I isotopic ratios. The concentration levels of 129I in environmental samples are very low and chemical separation/pre-concentration procedures have to be developed which can be used for a wide variety of matrices.

Neutron activation analysis is based on induction of 129I with thermal neutrons – irradiation in a nuclear reactor via following nuclear reaction:

$$^{129}\text{I} \text{(n, } \text{\textgreatery)} ^{130}\text{I} \text{\textdegree T}\_{\text{\textquotedblleft}} = 12.36 \text{ hours}, E\_{\text{\textquotedblleft}} = 536.1 \text{ keV} \text{\textquotedblright} \text{\textquotedblright} \tag{1}$$

129I is determined by measuring of 130I activity on a high purity Ge detector. Interfering nuclear reactions induced during irradiation of sample from other nuclides resulting in 130I production can influence the correct determination of 129I. These undesired nuclides are 235U, 128Te and 133Cs and nuclear reactions: 235U(n, f)129I(n,γ)130I, 235U(n,f)130I, 128Te(n,γ)129mTe(β- )129I(n,γ)130I and 133Cs(n,α)130I (Hou et al., 1999). They have to be removed from the sample before irradiation to avoid nuclear interferences.

During irradiation radioactivity in sample is produced mainly due to the radioisotopes 23Na(n,γ)24Na (*T½* = 14.96 hours), 41K(n,γ)42K (*T½* = 12.36 hours) and 81Br(n,γ)82Br (*T½* = 35.30 hours) present in sample, which renders the direct measurement of 130I after irradiation and radiochemical separation of induced 130I after irradiation is necessary. Solvent extraction with CCl4 or CHCl3 are normally used to extract iodine (Osterc & Stibilj, 2005; Osterc et al., 2007).

In first step pre-concentration of iodine from large amounts of sample is performed. Solid samples, such as soil, sediment, vegetation, biological samples can be decomposed by alkaline fusion (Hou et al., 1999, Osterc et al., 2007). The sample is mixed with potassium hydroxide/alkali solution and then gradually heated to 600 °C. Iodine is leached from the decomposed sample with hot water, isolated with solvent extraction and precipitated as PdI2 or MgI2 or trapped on activated charcoal (Fig. 2) (Hou et al., 1999, Osterc et al., 2007). Another method to separate iodine from solid samples is combustion at high temperature, ~1100 °C (Muramatsu & Yoshida, 1995). Released iodine is trapped in an alkaline solution or adsorbed on activated charcoal.

The pre-concentrated iodine is than irradiated for up to 12 hours simultaneously with a 129I/127I standard. After radiochemical separation the 130I induced from 129I (see nuclear reaction 1) is counted on a high purity Ge detector and compared to standard of known activity and corrected for chemical yield (Osterc et al., 2007).

The Potential Of I-129 as an Environmental Tracer 379

An AMS facility is set up off injector and analyser linked with a tandem accelerator. The detector is either a combination of time-of-flight and silicon charged particle detector or gas ionization energy detector. Iodine has to be separated from the sample with same techniques as used for NAA, such as pyrohydrolysis at 1000 °C, and prepared as AgI targets (Muramatsu et al., 2008). Negative iodine ions are produced from AgI targets by Cs sputter

accelerated to positive high-voltage terminal converting negative ions to I3+, I5+ or I7+. The positively charged ions pass through a magnetic analyser where ions of 129I and 127I based on charge state and energy are selected and directed to a detector. AMS measures the 129I/127I isotopic ratio and the 129I absolute concentration is calculated by the 127I content determined in the sample and the chemical yield for separation of iodine from sample – preparation of

AMS is the only technique that enables measurement of pre-nuclear age samples and samples with low 129I content, below 10-10 129I/127I isotopic ratio (Moran et al., 1998; Fehn et al., 2000a; Buraglio et al., 2001; Alfimov et al., 2004; Santschi & Schwehr, 2004; Snyder & Fehn, 2004; Michel et al., 2005; Fehn et al., 2007; Hou et al., 2007; Keogh, et al., 2007; Muramatsu et al., 2008; Gomez-Guzman et al., 2011). Instrumental background of 10-14 129I/127I has been obtained (Buraglio et al., 2000). But the detection limit depends on the chemical separation before measurement and especially on addition of iodine carrier. When carrier and chemical processing are included the typical reported blank 129I/127I isotopic ratio is 1 · 10-13 (Buraglio et al., 2000). For environmental samples with a very low 129I/127I isotopic ratio Hou et al. (2010) reported a method for preparation of carrier free AgI targets based on co-precipitation of AgI with AgCl to exclude the influence of interferences from 129I and 127I in the carrier. They calculated a detection limit of 105 atoms, which corresponds to 2

To be able to determine 129I by RNAA in environmental samples from nuclear era preconcentration of iodine from large amounts of sample (up to 150 g) is needed. In this preconcentration step contamination of sample with 129I is possible. It is important to make a blank control when establishing a new method and verify the method by reference materials to evaluate possible contamination during the entire analytical process; including preconcentration, irradiation, radiochemical separation and gamma activity measurement. Also analysis of 129I by AMS requires intensive and continuous control – control charts of the analytical blank and verification of accuracy by analysis of reference materials, which has to be continued periodically also during routine operation (Szidat et al., 2000a). Influence of sample mass – AgI targets on accuracy of 129I determination was studied by Lu et al. (2007). They found that samples with masses above 0.3 mg did not show an influence on accuracy – ion current of the sample was constant, but it fell strongly for samples with masses below 0.3 mg. Samples wit masses below 0.1 mg did not produced sustainable currents for 129I determination. Presence of 5000 129I atoms or 50 µg in the target is sufficient for a successful 129I determination. To validate and or evaluate an analytical method, to run a laboratory inter-comparison, to check accuracy of analytical method, and ensure globally comparable and traceable results to stated references, as the SI units, certified reference materials are needed. Environmental samples represent a huge variety of different combinations of substances to be analysed and the matrices in which they are embedded. This countless combinations of substances –

and 127I-

ions are

ion source and injected into the tandem accelerator. The formed 129I-

**4.5 Accelerator Mass Spectrometry (AMS)** 

AgI targets (Hou et al., 2009).

**4.6 Quality assurance of 129I analyses** 

· 10-16 g of 129I.

Fig. 2. The scheme for pre-concentration of iodine from solid samples (Osterc et al., 2007)

For liquid samples, such as milk, urine and water samples anion exchange method using anion exchange resins can be applied. Adsorbed iodide is eluted and isolated from the eluate with solvent extraction and precipitated as PdI2 or MgI2 (Parry et al., 1995; Hou et al., 2001; Hou et al., 2003a).

Fig. 2. The scheme for pre-concentration of iodine from solid samples (Osterc et al., 2007)

2001; Hou et al., 2003a).

For liquid samples, such as milk, urine and water samples anion exchange method using anion exchange resins can be applied. Adsorbed iodide is eluted and isolated from the eluate with solvent extraction and precipitated as PdI2 or MgI2 (Parry et al., 1995; Hou et al.,

#### **4.5 Accelerator Mass Spectrometry (AMS)**

An AMS facility is set up off injector and analyser linked with a tandem accelerator. The detector is either a combination of time-of-flight and silicon charged particle detector or gas ionization energy detector. Iodine has to be separated from the sample with same techniques as used for NAA, such as pyrohydrolysis at 1000 °C, and prepared as AgI targets (Muramatsu et al., 2008). Negative iodine ions are produced from AgI targets by Cs sputter ion source and injected into the tandem accelerator. The formed 129I and 127I- ions are accelerated to positive high-voltage terminal converting negative ions to I3+, I5+ or I7+. The positively charged ions pass through a magnetic analyser where ions of 129I and 127I based on charge state and energy are selected and directed to a detector. AMS measures the 129I/127I isotopic ratio and the 129I absolute concentration is calculated by the 127I content determined in the sample and the chemical yield for separation of iodine from sample – preparation of AgI targets (Hou et al., 2009).

AMS is the only technique that enables measurement of pre-nuclear age samples and samples with low 129I content, below 10-10 129I/127I isotopic ratio (Moran et al., 1998; Fehn et al., 2000a; Buraglio et al., 2001; Alfimov et al., 2004; Santschi & Schwehr, 2004; Snyder & Fehn, 2004; Michel et al., 2005; Fehn et al., 2007; Hou et al., 2007; Keogh, et al., 2007; Muramatsu et al., 2008; Gomez-Guzman et al., 2011). Instrumental background of 10-14 129I/127I has been obtained (Buraglio et al., 2000). But the detection limit depends on the chemical separation before measurement and especially on addition of iodine carrier. When carrier and chemical processing are included the typical reported blank 129I/127I isotopic ratio is 1 · 10-13 (Buraglio et al., 2000). For environmental samples with a very low 129I/127I isotopic ratio Hou et al. (2010) reported a method for preparation of carrier free AgI targets based on co-precipitation of AgI with AgCl to exclude the influence of interferences from 129I and 127I in the carrier. They calculated a detection limit of 105 atoms, which corresponds to 2 · 10-16 g of 129I.

#### **4.6 Quality assurance of 129I analyses**

To be able to determine 129I by RNAA in environmental samples from nuclear era preconcentration of iodine from large amounts of sample (up to 150 g) is needed. In this preconcentration step contamination of sample with 129I is possible. It is important to make a blank control when establishing a new method and verify the method by reference materials to evaluate possible contamination during the entire analytical process; including preconcentration, irradiation, radiochemical separation and gamma activity measurement.

Also analysis of 129I by AMS requires intensive and continuous control – control charts of the analytical blank and verification of accuracy by analysis of reference materials, which has to be continued periodically also during routine operation (Szidat et al., 2000a). Influence of sample mass – AgI targets on accuracy of 129I determination was studied by Lu et al. (2007). They found that samples with masses above 0.3 mg did not show an influence on accuracy – ion current of the sample was constant, but it fell strongly for samples with masses below 0.3 mg. Samples wit masses below 0.1 mg did not produced sustainable currents for 129I determination. Presence of 5000 129I atoms or 50 µg in the target is sufficient for a successful 129I determination. To validate and or evaluate an analytical method, to run a laboratory inter-comparison, to check accuracy of analytical method, and ensure globally comparable and traceable results to stated references, as the SI units, certified reference materials are needed. Environmental samples represent a huge variety of different combinations of substances to be analysed and the matrices in which they are embedded. This countless combinations of substances –

The Potential Of I-129 as an Environmental Tracer 381

interesting as an oceanographic tracer, because the discharges from NFRP in La Hague and Sellafield increased since 1990 and highly sensitive analytical method, AMS, developed for

Concentrations and species of 129I and 129I/127I isotopic ratio were determined in many environmental and biological samples from marine environment, especially in areas influenced by NFRP. Results for Northeast Atlantic, Arctic and Baltic Seas indicate a strong influence of liquid discharges from NFRP in La Hague and Sellafield. Hou et al. (2000a) determined 129I concentrations in archived time series seaweed *Fucus vesiculosus* samples from Danish, Norwegian and Northwest Greenland coast collected in a period from 1980 to 1997 (Table 3). They used the 129I/99Tc ratio to estimate the origin of and transit times of 129I. Transit times were estimated to be 1−2 years from La Hague, 3−4 from Sellafield, to Denmark (Klint) and Norway (Utsira), and 9−14 years from La Hague, 11−16 from Sellafield,

Iodine exists in seawater mainly as dissolved iodate and iodide, and a small amount of organic iodine (Wong, 1991). Chemical speciation of 129I can be used to investigate the transport, dispersion, and circulation of the water masses – especially at the boundary of

129I was used in geochemical studies as a tracer for determining ages and migration of brines (Muramatsu et al., 2001, Snyder et al., 2003a, Fehn et al., 2007). Isolated system contain lower or close to estimated pre-nuclear 129I/127I ratio, 1.5 · 10-12. For correct interpretation of results – age calculation based on 129I one must consider the effect of possible fissiogenic production and initial concentration on isotopic ratios. The estimated pre-nuclear ratio can be disturbed along continental margins with lower isotopic ratios likely caused by releases of methanerich fluids with high stable iodine concentrations derived from old organic sources, where 129I already partly decayed. The isotopic ratio of the open ocean is not disturbed, justifying

Atmospheric releases of 129I from European and Hanford NFRP were much higher than from nuclear weapons tests and Chernobyl accident together (Table 1). Measurement of 129I in atmosphere and precipitation can be used to investigate the transport pathways of 129I from point sources, such as NFRP. But it is important to be aware that 129I levels in atmosphere and precipitation can originate either directly from atmospheric releases from NFRP, and from volatilization from seawater and terrestrial environment. To study transport pathways of 129I all of this aspects have to be considered and obtained results for atmospheric and precipitation samples compared to reported releases from NFRP in particular timescale. Many precipitation and atmospheric samples have to be measured

The same chemical and physical properties of isotopes of particular element enable to use 129I as a tool for the reconstruction of 131I doses after a nuclear accident. This was done after the nuclear accident in Chernobyl. Levels of 129I were determined in soils and from the measured 129I/131I ratio, 12−19 (Kutschera et al., 1988; Mironov et al., 2002), the long-lived

analysis (Hou, 2004).

to NW Greenland.

two or more sources. (Hou et al., 2001).

the use of estimated pre-nuclear ratio (Fehn et al., 2007).

continuously to establish a pattern or trend.

**5.4 129I for reconstruction of 131I dose** 

**5.2 129I as a geochemical tracer** 

**5.3 129I in precipitation** 

elements, radionuclides, contaminants – and matrices means that certified reference materials always lack.

The only reference material with a recommended value for 129I available on the market was the reference material IAEA-375 Soil – Radionuclides and Trace Elements in Soil. Top soil to a depth of 20 cm was obtained from the "Staryi Viskov" collective farm in Novozybkov, Brjansk, Russia in July 1990. Unfortunately this reference material is now out of stock.

Only informative and not certified values for 129I, determined in one laboratory, are reported for NIST SRM 4357 – Ocean Sediment Environmental Radioactivity Standard, which is a blend of ocean sediments collected off the coast of Sellafield, UK, and in the Chesapeake Bay, USA, and NIST SRM 4359 – Seaweed Radionuclide Standard, which is a blend of seaweed collected off the coast of Ireland and the White Sea.

Recently a new reference material, with a certified value for 129I, IAEA-418: I-129 in Mediterranean Sea Water was characterised in an interlaboratory comparison exercise. The used method was AMS (accelerator mass spectrometry).

Another new reference material for radionuclides in the mussel *Mytilus galloprovincialis* from Mediterranean Sea, IAEA-437 was characterised. They reported for the mussel sample collected in 2003 at Anse de Carteau, Port Saint Louis du Rhône, France an informative average massic activity of 0.8 ± 0.1 mBq kg-1 dry mass (Pham et al., 2010).

#### **5. Applications of I-129 as an environmental tracer**

Use of 129I as an intrinsic tracer for natural iodine kinetics was discussed as early as 1962 (Edwards, 1962). Already at that time two reprocessing plants, one for military purposes in Marcoule, France (from 1958) and one for nuclear fuel in Thurso, United Kingdom (from 1958) existed.

To be able to use 129I as an environmental tracer certain conditions have to be met. These are: (1) 129I must trace a single environmental process with a defined time scale; (2) 129I must be equilibrated with 127I; (3) The predominant chemical species of 129I and their geochemical properties must be known (Santschi & Schwehr, 2004); (4) Conservative behaviour, meaning relatively constant concentration in a reservoir over time, is desirable. The natural 129I/127I ratio has been strongly shifted by continuous additions from anthropogenic sources, which still persists. To trace existing and future global changes in inventories of anthropogenic 129I continuous monitoring and revised budget calculation are indispensable (Aldahan et al. 2007a). Recently also a prediction model system to better understand the dispersion of 129I from point sources (Sellafield and La Hague) to the northern North Atlantic Ocean has been developed (Orre et al. 2010).

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 2000) identifies as globally dispersed radionuclides 3H, 14C and 129I. Because of its very long half live is 129I one of the most important radionuclides in long-term radiological assessment of its discharges from nuclear fuel reprocessing plants. 129I is present in the environment in low quantities (in traces) and its increase in a particular compartment of the ecosystem can be instantly recognized.

#### **5.1 129I as an oceanographic tracer**

Transport, circulation and exchange of water masses in the Northeast Atlantic and Arctic Oceans has long been studied by using radionuclides such as 137Cs, 134Cs, 90Sr, 125Sb and 99gTc originating from reprocessing of spent nuclear fuel. In recent years 129I became

elements, radionuclides, contaminants – and matrices means that certified reference

The only reference material with a recommended value for 129I available on the market was the reference material IAEA-375 Soil – Radionuclides and Trace Elements in Soil. Top soil to a depth of 20 cm was obtained from the "Staryi Viskov" collective farm in Novozybkov, Brjansk, Russia in July 1990. Unfortunately this reference material is now out of stock. Only informative and not certified values for 129I, determined in one laboratory, are reported for NIST SRM 4357 – Ocean Sediment Environmental Radioactivity Standard, which is a blend of ocean sediments collected off the coast of Sellafield, UK, and in the Chesapeake Bay, USA, and NIST SRM 4359 – Seaweed Radionuclide Standard, which is a blend of

Recently a new reference material, with a certified value for 129I, IAEA-418: I-129 in Mediterranean Sea Water was characterised in an interlaboratory comparison exercise. The

Another new reference material for radionuclides in the mussel *Mytilus galloprovincialis* from Mediterranean Sea, IAEA-437 was characterised. They reported for the mussel sample collected in 2003 at Anse de Carteau, Port Saint Louis du Rhône, France an informative

Use of 129I as an intrinsic tracer for natural iodine kinetics was discussed as early as 1962 (Edwards, 1962). Already at that time two reprocessing plants, one for military purposes in Marcoule, France (from 1958) and one for nuclear fuel in Thurso, United Kingdom (from

To be able to use 129I as an environmental tracer certain conditions have to be met. These are: (1) 129I must trace a single environmental process with a defined time scale; (2) 129I must be equilibrated with 127I; (3) The predominant chemical species of 129I and their geochemical properties must be known (Santschi & Schwehr, 2004); (4) Conservative behaviour, meaning relatively constant concentration in a reservoir over time, is desirable. The natural 129I/127I ratio has been strongly shifted by continuous additions from anthropogenic sources, which still persists. To trace existing and future global changes in inventories of anthropogenic 129I continuous monitoring and revised budget calculation are indispensable (Aldahan et al. 2007a). Recently also a prediction model system to better understand the dispersion of 129I from point sources (Sellafield and La Hague) to the northern North Atlantic Ocean has been

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 2000) identifies as globally dispersed radionuclides 3H, 14C and 129I. Because of its very long half live is 129I one of the most important radionuclides in long-term radiological assessment of its discharges from nuclear fuel reprocessing plants. 129I is present in the environment in low quantities (in traces) and its increase in a particular compartment of the ecosystem can be

Transport, circulation and exchange of water masses in the Northeast Atlantic and Arctic Oceans has long been studied by using radionuclides such as 137Cs, 134Cs, 90Sr, 125Sb and 99gTc originating from reprocessing of spent nuclear fuel. In recent years 129I became

seaweed collected off the coast of Ireland and the White Sea.

**5. Applications of I-129 as an environmental tracer** 

average massic activity of 0.8 ± 0.1 mBq kg-1 dry mass (Pham et al., 2010).

used method was AMS (accelerator mass spectrometry).

materials always lack.

1958) existed.

developed (Orre et al. 2010).

**5.1 129I as an oceanographic tracer** 

instantly recognized.

interesting as an oceanographic tracer, because the discharges from NFRP in La Hague and Sellafield increased since 1990 and highly sensitive analytical method, AMS, developed for analysis (Hou, 2004).

Concentrations and species of 129I and 129I/127I isotopic ratio were determined in many environmental and biological samples from marine environment, especially in areas influenced by NFRP. Results for Northeast Atlantic, Arctic and Baltic Seas indicate a strong influence of liquid discharges from NFRP in La Hague and Sellafield. Hou et al. (2000a) determined 129I concentrations in archived time series seaweed *Fucus vesiculosus* samples from Danish, Norwegian and Northwest Greenland coast collected in a period from 1980 to 1997 (Table 3). They used the 129I/99Tc ratio to estimate the origin of and transit times of 129I. Transit times were estimated to be 1−2 years from La Hague, 3−4 from Sellafield, to Denmark (Klint) and Norway (Utsira), and 9−14 years from La Hague, 11−16 from Sellafield, to NW Greenland.

Iodine exists in seawater mainly as dissolved iodate and iodide, and a small amount of organic iodine (Wong, 1991). Chemical speciation of 129I can be used to investigate the transport, dispersion, and circulation of the water masses – especially at the boundary of two or more sources. (Hou et al., 2001).

### **5.2 129I as a geochemical tracer**

129I was used in geochemical studies as a tracer for determining ages and migration of brines (Muramatsu et al., 2001, Snyder et al., 2003a, Fehn et al., 2007). Isolated system contain lower or close to estimated pre-nuclear 129I/127I ratio, 1.5 · 10-12. For correct interpretation of results – age calculation based on 129I one must consider the effect of possible fissiogenic production and initial concentration on isotopic ratios. The estimated pre-nuclear ratio can be disturbed along continental margins with lower isotopic ratios likely caused by releases of methanerich fluids with high stable iodine concentrations derived from old organic sources, where 129I already partly decayed. The isotopic ratio of the open ocean is not disturbed, justifying the use of estimated pre-nuclear ratio (Fehn et al., 2007).

#### **5.3 129I in precipitation**

Atmospheric releases of 129I from European and Hanford NFRP were much higher than from nuclear weapons tests and Chernobyl accident together (Table 1). Measurement of 129I in atmosphere and precipitation can be used to investigate the transport pathways of 129I from point sources, such as NFRP. But it is important to be aware that 129I levels in atmosphere and precipitation can originate either directly from atmospheric releases from NFRP, and from volatilization from seawater and terrestrial environment. To study transport pathways of 129I all of this aspects have to be considered and obtained results for atmospheric and precipitation samples compared to reported releases from NFRP in particular timescale. Many precipitation and atmospheric samples have to be measured continuously to establish a pattern or trend.

#### **5.4 129I for reconstruction of 131I dose**

The same chemical and physical properties of isotopes of particular element enable to use 129I as a tool for the reconstruction of 131I doses after a nuclear accident. This was done after the nuclear accident in Chernobyl. Levels of 129I were determined in soils and from the measured 129I/131I ratio, 12−19 (Kutschera et al., 1988; Mironov et al., 2002), the long-lived

The Potential Of I-129 as an Environmental Tracer 383

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reprocessing facilities traced in precipitation and runoff in Northern Europe. *Environmental Science and Technology,* Vol. 35, No. 8, pp. (1579-1586), ISSN 0013-

transformations of inorganic iodine by marine macroalgae. *Estuarine, Coastal and* 

Iodine-129 and plutonium isotopes in Arctic kelp as historical indicators of

129I can be used to reconstruct 131I dose to thyroids. This method is limited only to areas that were relatively strong contaminated by fallout from Chernobyl like areas in Ukraine and Belarus (Michel et al., 2005; Straume et al., 2006).
