**3. Factors affecting biogeochemical cycling of iodine**

Iodine is a trace element present in the hydrosphere, lithosphere, atmosphere and biosphere at different concentrations and as different iodine species (Table 5). Speciation analysis of iodine was mainly done on stable 127I (Hou et al., 1997; dela Veija et al., 1997; Sanchez & Szpunar, 1999; Hou et al., 2000c; Leiterer et al., 2001; Schwehr & Santschi, 2003; Shah et al., 2005; Gilfedder et al., 2008), with some studies on 129I (Hou et al., 2001; Hou et al., 2003b; Schwehr et al., 2005; Englund et al., 2010b). Majority of researches performed on 127I and 129I are limited to fractionations of iodine – water soluble, exchangeable, bound to oxides, organic-inorganic fraction, etc. In general just the most abundant chemical forms of iodine – iodide (I-) and iodate (IO3-) are determined and the rest of total iodine content is associated with organic iodine. It is well known that organic iodine fraction mainly consist of iodine

**Sample 129I/127I (10-12) Reference** 

Russia, Bogoroditsk, 1909 25 Szidat et al., 2000a

USA, Pig, 1947 58 Szidat et al., 2000a

Moran et al., 1998 Mexico, Baja peninsula, depth: 415-420

1.48

1.40 0.55 0.52 0.67

Fehn et al., 2007

Cooper et al., 1998

1.87

1.00 3.69 1.35 1.37 1.92

Table 2. 129I/127I isotopic ratios in pre-nuclear age environmental and biological samples

Iodine is a trace element present in the hydrosphere, lithosphere, atmosphere and biosphere at different concentrations and as different iodine species (Table 5). Speciation analysis of iodine was mainly done on stable 127I (Hou et al., 1997; dela Veija et al., 1997; Sanchez & Szpunar, 1999; Hou et al., 2000c; Leiterer et al., 2001; Schwehr & Santschi, 2003; Shah et al., 2005; Gilfedder et al., 2008), with some studies on 129I (Hou et al., 2001; Hou et al., 2003b; Schwehr et al., 2005; Englund et al., 2010b). Majority of researches performed on 127I and 129I are limited to fractionations of iodine – water soluble, exchangeable, bound to oxides, organic-inorganic fraction, etc. In general just the most abundant chemical forms of iodine – iodide (I-) and iodate (IO3-) are determined and the rest of total iodine content is associated with organic iodine. It is well known that organic iodine fraction mainly consist of iodine

*TERRESTRIAL ENVIRONMENT* 

*MARINE ENVIRONMENT* 

Russia, Moscow, 1910 168

Russia, Lutovinovo, 1939 5.7

Species not given (USA), 1947 4.6

USA, Horse, 1947 1230

Peru, depth: 155-199 cm 1.50

Ecuador, depth: 315-320 cm 1.05

Hokkaido, 1883 Hokkaido, 1883 Miyagi, 1883 Miyagi, 1883

Miyagi, 1904

**3. Factors affecting biogeochemical cycling of iodine** 

Novaya Zemlya, 1930 Novaya Zemlya, 1931 White Sea, 1938 White Sea, 1930 White Sea, 1938

*Soil* 

*Thyroid powder* 

*Sediment* 

cm

*Algae*  Japan

*Pelvita* 

Russia

*Laminaria Japonica*

*Laminaria digitata* 


Table 3. 129I/127I isotopic ratios in nuclear age environmental and biological samples from marine compartments

The Potential Of I-129 as an Environmental Tracer 373

Hou et al., 2009

Hou et al., 2001

1995; Hou, 2004

Schmitz & Aumann, 1995

Muramatsu & Wedepohl,

Hou et al., 1997 Hou et al., 2000c Shah et al., 2005

Stibilj, 2008

dela Vieja et al., 1997

Wershofen & Aumann, 1989; Yoshida & Muramatsu, 1995

particle associated (aerosol); inorganic gaseous: I2, HI, HIO; organic gaseous: CH3I, CH2I2,

> I , - <sup>3</sup> IO ;

precipitation 1–6 ng mL-1 Yoshida & Muramatsu,

I , -

metal oxides, carbonates and

organic: bound to humic and

I , - <sup>3</sup> IO ; organic: iodo-amino acids (*Laminaria japonica*); bound to proteins, pigments, polyphenols\*

plants (terrestrial) <1 μg g-1 Hou et al., 2009

I organic: iodo-amino acids → iodo-thyronine and iodo-

I

0.017−0.49 μg mL-1

fresh water 1–3 ng mL-1 Hou et al., 2009

45–60 ng mL-1 Hou et al., 2009

0.5–40 μg g-1 Muramatsu & Yoshida,

10–6000 μg g-1 Hou & Yan, 1998; Osterc &

500–5000 μg g-1 Hou et al., 2003a

organic: bound to proteins\* Leiterer et al., 2001

1999

<sup>3</sup> IO , bound to

**Compartment Main iodine species Reference Concentration range**

CH3CH2CH2I, etc.

1–100 ng m-3

inorganic: -

organic: CH3I

inorganic: -

minerals;

fulvic acids

1998 metamorphic and

inorganic: -

inorganic: -

inorganic: -

Table 5. Concentrations of stable iodine in environmental compartments

tyrosine

surface sea sediment 1–2000 μg g-1

magmatic rocks <0.1 μg g-1

*Atmosphere*

*Hydrosphere* 

*Lithosphere* 

soil

*Biosphere* 

seaweed

thyroid gland

milk (bovine)

\*species not identified

oceans


\*The highest isotopic ratio (2.5 10-4) was obtained for an animal coming from Digulleville, a village 3 km to the north-east of the NFRP

Table 4. 129I/127I isotopic ratios in nuclear age environmental and biological samples from terrestrial compartments

**Sample 129I/127I (10-8) Reference** 

Spain, Seville, 2001 (n = 12) 0.29−2.72 Santos et al., 2005 Spain, Seville, 2001-2002 0.18−5.35 Santos et al., 2006 Sweden, Kiruna and Ljungbyhed, 1983-2008 0.5−147 Englund et al., 2010a

Spain, Seville, 1993-1994 and 1998 0.01−0.80 Santos et al., 2006

Germany, Hanover, 1986 16.6 Szidat et al., 2000a Germany, Lower Saxony, 1997 83.4 Germany, Upper Bavaria, 2003 14.6−38.6 Reithmeier et al., 2005 Spain, Seville, 1996-1997 0.23−52 Santos et al., 2006 Antartica, McMurdo Station, snowmelt 1999 0.004 Snyder et al., 2004 Antartica, Mt Erebus, snow, 2000 0.009

Germany, Lower Saxony, 1997 0.8 Szidat et al., 2000a

Germany, Harz, Okersee, June 1999 1.0 Snyder et al., 2004 USA, Oregon, Crater Lake, September 1996 0.9 USA, Colorado, Navajo Lake, June 2000 0.25 Snyder et al., 2003a Central America, Nicaragua, Lake Managua, 1998 0.029 Fehn & Snyder, 2000b South America, Chile, Lago Verde, Februar 1999 0.24 Snyder et al., 2004 Australia, New South Wales, Lake George, 1997 0.53 Fehn & Snyder, 2000b

Japan, Odanoike lake, May 2000 0.79 Snyder et al., 2004

England, London, river Thames, March 1999 1.9 Snyder et al., 2004 England, Cambridge, river Granta, March 1999 1.0

USA, Colorado, Pine River, June 2000 0.13 Snyder et al., 2003a USA, Colorado, Animas River, June 2000 0.08

India, Tista River, 1999 0.18 Snyder et al., 2004 India, Ganges River, 1999 0.03 Central America, El Salvador, Rio Lempa, 1999 0.058 Snyder et al., 2003b

Japan, Kugino river, May 2000 0.04 Snyder et al., 2004

(Bovine, n = 19) 100−25068\* Frechou et al., 2003 China (Tianjin), 1994-1995 (Human, male; n = 4) 0.04<sup>−</sup>0.09 Hou et al., 2000b China (Tianjin),1995 (Human, female; n = 2) 0.16<sup>−</sup>0.20

\*The highest isotopic ratio (2.5 10-4) was obtained for an animal coming from Digulleville, a village 3 km

Table 4. 129I/127I isotopic ratios in nuclear age environmental and biological samples from

England, rivers near Sellafield 2004-2005 (n = 4) 158-825 Atarashi-Andoh et al., 2007

England, lakes near Sellafield, 2004-2005 (n = 7) 24.8−638 Atarashi-Andoh et al., 2007 Germany, Munich, Kleinhesseloher See, July 1997 2.4 Fehn & Snyder, 2000b Germany, Malchow, Malchow See, July 1997 8.6

Denmark, 2000 (n = 7) 2.5−27.3 Hou, 2004 Lithuania, 1999 (n = 2) 6.6−7.3 Hou et al., 2002

New Zealand, Lake Taupo, 1999 0.005

Indonesia, Bali, Lake Beratan 0.032

Africa, Botswana, Thamakkane river, May 2000 0.10

Mongolia, Tuyu Gol River, January 2000 0.068

France, vicinity of La Hague (1−30 km), 1980-1999

*Aerosol* 

*Gas* 

*Precipitation*

*Shallow ground water*

*Lake water* 

*River water* 

*Thyroid*

to the north-east of the NFRP

terrestrial compartments


\*species not identified

Table 5. Concentrations of stable iodine in environmental compartments

The Potential Of I-129 as an Environmental Tracer 375

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

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

g g-1 (10-12) 129I/127I (10-12)

(AMS) and inductively coupled plasma mass spectrometry (ICP-MS) are also used.

**Analytical method/Sample Detection limit Reference** 

seaweed (400 g) 300 not given Lefevre et al., 2003

radioactive waste (coolant, 1 L) 23 not given Gudelis et al., 2006

soil (100 g) 0.05 5000 Osterc et al., 2007 soil (100 g) 0.015 10000 Muramatsu & Yoshida,

soil (80 g) 0.27 not given Michel et al., 2005 soil 0.13 410 Szidat et al., 2000b

commercial AgI not given 0.44 Suzuki et al., 2006 blank sample not given 0.50 Gomez-Guzman et al.,

blank sample not given 0.17 Muramatsu et al., 2008 soil (1 g) 0.0015 40 soil (80 g) 0.00015 5 Michel et al., 2005 Woodward Iodine\* not given 0.023 Reithmeier et al., 2005 Woodward Iodine not given 0.04 Buraglio et al., 2001 oil and gas hydrates not given 0.20 Alfimov & Synal, 2010 soil 0.000023 0.75 Szidat et al., 2000b

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

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

1995

2011

Aqueous solution 100 1000000 Muramatsu et al., 2008 Aqueous solution 0.8 not given Izmer et al., 2003 Aqueous solution (groundwater) 5 not given Brown et al., 2007 Sediment 30 not given Izmer et al., 2003 Sediment 0.4 not given Izmer et al., 2004

different analytical methods are compared in Table 6.

**4. Measurement of 129I** 

*γ-X spectrometry*

*LSC* 

*ICP-MS* 

*RNAA* 

*AMS*

lowest ratio is reported.

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 biological samples.

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

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