Iodine-129 in Thyroid Glands: A Sensitive Biological Marker of Fission Product Exposure

appeared in the Journal of Radioanalytical and Nuclear Chemistry, Vol. 243, No. 2 (2000) 467–472.During the electronic submission of the paper the file was damaged, and parts were left out. In order to correct this, we publish the correct paper as a whole.Iodine-129 may be no radiation hazard but it is a useful marker. Animal thyroids concentrate the isotope to 4 orders of magnitude greater than the intake. This results in a potential biological and physical indicator of radioactive contamination. Since 1943, ¹²⁹I/¹²⁷I ratio in animal thyroids from the Northern Hemisphere has increased 2 to 5 orders of magnitude. Since 1985, thyroids of deer, living near a nuclear reprocessing facility have contained ¹²⁹I which is 3 to 7 orders of magnitude greater than pre-nuclear levels. Limited measurements of ¹²⁹I in thyroids from the Southern Hemisphere have shown little increase. An appendix is presented to show that ¹²⁹I may be helpful to evaluate past radiation hazard from fission products.     

Iodine-129 and natural iodine-127 in deer thyroids from the environment of a small nuclear fuel reprocessing plant and from sites remote from nuclear facilities

Concentrations of the fission product¹²⁹I and natural¹²⁷I were determined in deer thyroids collected in the environment of the small Karlsruhe nuclear fuel reprocessing plant (WAK) and in a region remote from¹²⁹I sources of nuclear facilities. The isotopic ratio¹²⁹I/¹²⁷I in thyroids from the environment of WAK varies from 1.0×10^–6 to 12.9×10^–6, which is about one order of magnitude higher than the¹²⁹I/¹²⁷I ratios in thyroids from deer in a region remote from nuclear facilities. These ratios were between 0.2×10^–6 and 0.7×10^–6.     

Radioactive 129I in surface water of the Celtic Sea

Relatively large amounts of radioactive iodine ¹²⁹I (T _1/2  = 15.7 Ma) have been documented in seawater such as the English Channel, the Irish Sea and the North Sea. Data on the concentration of the iodine isotopes in waters of the Celtic Sea are missing. Aiming to provide first ¹²⁹I data in the Celtic Sea and compare them with levels in the other close-by seawater bodies, surface seawater samples were analyzed for the determination of ¹²⁷I and ¹²⁹I concentrations. The results revealed a high level of ¹²⁹I in these waters and suggest strong influence by liquid discharges from La Hague and Sellafield reprocessing facilities. ¹²⁷I concentrations are rather constant while the ¹²⁹I/¹²⁷I ratio reaches up to 2.8 × 10^?8 (ranging from 10^?10 to 10^?8), which is 2–4 orders of magnitude higher than pre-nuclear era natural level. Transport of ¹²⁹I to the Celtic Sea is difficult to depict accurately since available data are sparse. Most likely, however, that discharges originated from La Hague may have more influence on the Celtic Sea ¹²⁹I concentrations than the Sellafield. Comprehensive surface water and depth profiles ¹²⁹I data will be needed in the future for assessment of environmental impact in the region.     

Long-Lived Radioiodine in Japanese Environment

The amount of long-lived radioiodine, ¹²⁹I (half-life 1.57·10⁷ y) in the Japanese environment has been studied by measuring thyroids of humans and animals. The collected samples were thyroids of (1) humans in Ibaraki Prefecture, in Kanto district, the central part of Japan, (2) cattle in Aomori Prefecture, north part of Japan, and (3) wild deer in Chiba Prefecture, in Kanto district. The measured mean isotopic ratio ¹²⁹I/¹²⁷I for thyroids of cattle in Aomori Prefecture is 3.5±1.8·10^-9. A higher value of 14±5·10^-9 has been obtained for thyroids of wild deer in Kanto district. On the other hand, the measured ratio for human thyroids in Kanto district is 1±0.2·10^-9. This value is significantly lower than that of cattle thyroids in Aomori and also those reported for human thyroids in Europe and USA. The higher mean ratio for cattle thyroid in Kanto district is possibly explained by the influence of nuclear reprocessing plant. Lower mean ratio for human thyroid might be due to higher dietary intake of algae.     

Input of 129I into the western Pacific Ocean resulting from the Fukushima nuclear event

We present an initial characterization of the input of ¹²⁹I into the Pacific Ocean resulting from the 2011 Fukushima nuclear accident. This characterization is based primarily on ¹²⁹I measurements on samples collected from a research cruise conducted in waters off the eastern coast of Japan in June 2011. These measurements were compared with samples intended to reflect pre-Fukushima background that were collected during a May 2011 transect of the Pacific by a commercial container vessel. In surface waters, we observed peak ¹²⁹I concentrations of ~300 μBq/m³ which represents an elevation of nearly three orders of magnitude compared to pre-Fukushima backgrounds. We coupled our ¹²⁹I results with ¹³⁷Cs measurements from the same cruise and derived an average ¹²⁹I/¹³⁷Cs activity ratio of 0.442 × 10^?6 for the effluent from Fukushima. Finally, we present ¹²⁹I depth profiles from five stations from this cruise which form the basis for future studies of ocean transport and mixing process as well as estimations of the total budget of ¹²⁹I released into the Pacific.     

Determination of 129I in biomonitors collected in the vicinity of a nuclear power plant by neutron activation analysis

Neutron activation analysis (NAA) was used to determine ¹²⁹I and the ¹²⁹I/¹²⁷I ratio in bovine thyroid, moss, and river sediment samples collected in the vicinity of the Temelín nuclear power plant (NPP) in south Bohemia. The NAA procedures comprised pre-irradiation separation of ¹²⁹I by combustion of the samples in the stream of oxygen at 1,000 °C and trapping the liberated iodine in a LiOH/(NH₄)₂SO₃ solution. Post-irradiation separation of ¹³⁰I produced by the reaction ¹²⁹I(n,γ)¹³⁰I was carried out by extraction of elementary iodine with chloroform followed by precipitation of PdI₂. Nondestructive, epithermal NAA was used to determine ¹²⁷I employing the ¹²⁷I(n,γ)¹²⁸I reaction. The results showed that mean values of ¹²⁹I and the ¹²⁹I/¹²⁷I ratio in the bovine thyroids varied from 22 to 61 mBq kg^?1 (dry mass) and 2.8 × 10^?9 to 5.4 × 10^?9, respectively. These values are close to the lower end of results reported from various regions non-polluted with ¹²⁹I. No significant differences were found between ¹²⁹I concentrations and the ¹²⁹I/¹²⁷I ratios in the bovine thyroids collected prior to the start and after several years of operation of the NPP. The mean value and standard deviation of ¹²⁹I in mBq kg^?1, dry mass and the ¹²⁹I/¹²⁷I ratio in moss Pleurozium schreberi were 23 ± 16 and 2.3 × 10^?9, respectively, whereas values of ¹²⁹I in the river sediments were below 8–10 mBq kg^?1 (dry mass) after several years of the NPP operation.     

A review on speciation of iodine-129 in the environmental and biological samples

As a long-lived beta-emitting radioisotope of iodine, ¹²⁹I is produced both naturally and as a result of human nuclear activities. At present time, the main part of ¹²⁹I in the environment originates from the human nuclear activity, especially the releases from the spent nuclear fuel reprocessing plants, the ¹²⁹I/¹²⁷I ratios have being reached to values of 10⁻¹⁰ to 10⁻⁴ in the environment from 10⁻¹² in the pre-nuclear era. In this article, we review the occurrence, sources, inventory, and concentration level of ¹²⁹I in environment and the method for speciation analysis of ¹²⁹I in the environment. Measurement techniques for the determination of ¹²⁹I are presented and compared. An overview of applications of ¹²⁹I speciation in various scientific disciplines such as radiation protection, waste depository, and environmental sciences is given. In addition, the bioavailability and radiation toxicity (dose to thyroid) of ¹²⁹I are discussed.     

Analysis of low-level 129I in brine using accelerator mass spectrometry

An improved solvent extraction procedure for iodine separation from brine samples has been applied at Xi’an Accelerator Mass Spectrometry (AMS) center. Oil in the brine sample has to be removed to avoid appearance of the third phase during solvent extraction and to improve the chemical yield of iodine. The small amount of oil remained in the water phase was first removed by phase separation through settling down sufficiently based on their immiscibility, and then by filtration through a cellulose filter, on which oil was absorbed and removed. After oil removed, extraction recovery of iodine could achieve more than 90 %. The sodium bisulfite as an effective reductant should be added before acidification to avoid loss of iodine by formation of I₂ in sample via reaction of iodate and iodide at pH 1–2, and then pH was adjusted to 1–2 to reduce the iodate to iodide followed by oxidation of iodide to I₂ and solvent extraction to separate all inorganic iodine. As a pre-nuclear era sample, ¹²⁹I/¹²⁷I ratio in brine is normally more than two orders of magnitude lower than that in present surface environmental samples, so prevention of cross-contamination and memory effect in apparatus during processing procedure are very critical for obtaining reliable results, and monitoring the procedure blank is very important for analytical quality of ¹²⁹I. The ¹²⁹I/¹²⁷I isotopic ratio in the brine samples and procedure blank of iodine reagents were measured to be (1.9–2.7) × 10^?13 and 2.08 × 10^?13, respectively, 3–4 orders of magnitudes lower than that in environmental samples in Xi’an, and the result of procedure blank is in the same level as the previous experiments in past 3 years, indicating contamination is not observed in our method.     

Determination of129I and127I in environmental samples by neutron activation analysis (NAA) and inductively coupled plasma mass spectrometry (ICP-MS)

In order to assess the levels and behavior of¹²⁹I (half-life: 1.6×10⁷ y) and¹²⁷I (stable) in the environment, we have developed analytical procedures involving neutron activation analysis (NAA). Environmental samples collected around Tokaimura, Ibaraki Prefecture, Japan, have been analyzed using this method. Ranges of¹²⁹I and¹²⁷I concentrations in surface soil were 0.9–180 mBq kg^–1 and 1–60 mg kg^–1, respectively. Higher¹²⁹I concentrations were found in soil samples collected from coniferous forests, suggesting a contribution from tree canopies in the deposition of this nuclide. Most of the¹²⁹I in soil, was found to be retained in the first 10 cm. The¹²⁹I/¹²⁷I ratios in wheat fields were lower than those in rice paddy fields.A soil sample collected by IAEA from an area contaminated by the Chemobyl accident was also determined. The¹²⁹I concentration and the¹²⁹I/¹²⁷I ratio were 1.6 mBq kg^–1 and 1.7×10^–7, respectively. The¹²⁹I level in this sample was higher than the values obtained in areas far from nuclear facilities in Japan. It was suggested that the analysis of¹²⁹I in soils in the Chernobyl area may be useful in evaluating the¹³¹I levels at the time of the accident.Analyses of¹²⁹I and¹²⁷I by ICP-MS in water samples were also made. The analytical speed of this method was very high, i.e., 3 minutes for a sample. However, there is a sensitivity limitation for¹²⁹I detection due to interference from¹²⁹Xe with the¹²⁹I peak. The detection limits for¹²⁹I and¹²⁷I in water samples were about 0.5 mBq ml^–1 and 0.1 ng ml^–1, respectively.     

Chemical and nuclear interferences in neutron activation of129I and127I in environmental samples

A combination of neutron activation and gamma-ray coincidence counting technique is used to determine the concentration of both long-lived fission produced¹²⁹I and natural¹²⁷I in environmental samples. The neutron reactions used for the activation of the iodine isotopes are¹²⁹I(n, )¹³⁰I and¹²⁷I(n, 2n)¹²⁶I. Nuclear interferences in the activation analysis of¹²⁹I and¹²⁷I can be caused by production of¹³⁰I or¹²⁶I from other constituents of the materials to be irradiated, i.e. Te, Cs and U impurities and from the¹²⁵I tracer used for chemical yield determination. Chemical interferences can be caused by¹²⁹I and¹²⁷I impurities in the reagents used in the pre-irradiation separation of iodine. The activated charcoals used as iodine absorbers were carefully cleaned. Different chemical forms of added¹²⁵I tracer and¹²⁹I and¹²⁷I constituents of the samples can cause different behaviour of¹²⁵I tracer and sample iodine isotopes during pre-irradiation separation of iodine. The magnitude of the nuclear and chemical interferences has been determined. Procedures have been developed to prevent or control possible interferences in low-level¹²⁹I and¹²⁷I activation analysis. For quality control a number of biological and environmental standard samples were analyzed for¹²⁷I and¹²⁹I concentrations.     

Natural radioactivity of some local building materials in the middle Euphrates of Iraq

People are exposed to ionizing radiation from the radionuclides that are present in different types of a natural sources, of which building materials is one of the most important sources. Radionuclides in building materials belonging to ²³⁸U, ²³²Th series as well as radioisotope of Potassium ⁴⁰K are the major contributors of outdoor terrestrial natural radiation. This study is the first ever in Iraq. In order to estimate the radiological impact to the dweller, the activity concentration of radionuclides present in various Iraqi building materials were analyzed using Gamma-spectrometry. The radiation hazard indexes were calculated based on the above results. The results showed that the activity concentration of ²³⁸U, ²³²Th and ⁴⁰K was between 32.9 Bq/kg (Najaf gypsum)–179.32 Bq/kg (Karbala cement), 1.98 Bq/kg (Najaf sand)–17.43 Bq/kg (Qadisiya brick) and 108.73 Bq/kg (Karbala sand)–977.79 Bq/kg (Najaf brick), respectively. All values of Radium equivalent activities were found to be less than the maximum permissible limit and the internal hazard indexes (except Karbala cement) were less than unity for the radiation hazard. Some samples have external annual dose and external hazard index values greater than unity.     

Analysis of Iodine-129 in Environmental Materials: Quality Assurance and Applications

The long-lived radionuclide ¹²⁹I (T _1/2 = 15.7 My) occurs in the nature in very low concentrations. Since the middle of our century the environmental levels of ¹²⁹I have been dramatically changed as a consequence of civil and military use of nuclear fission. Its investigation in environmental materials is of interest for environmental surveillance, retrospective dosimetry and for the use as a natural and man-made fracers of environmental processes. We are comparing two analytical methods which presently are capable of determining ¹²⁹I in environmental materials, namely radiochemical neutron activation analysis (RNAA) and accelerator mass spectrometry (AMS). Emphasis is laid upon the quality control and detection capabilities for the analysis of ¹²⁹I in environmental materials. Some applications are discussed.     

Laser-induced surface migration via surface plasmons

A classical model coupling a charged adspecies to a laser-induced surface plasmon is presented. Such coupling can enhance the rate and specify the direction of surface migration. For the particular case of an atomic oxygen ion of charge ?1 adsorbed on aluminum which is exposed to CO₂ laser radiation of intensity 1 W/cm², the velocity of migration (61.3 μm/s) is five orders of magnitude greater than the usual thermal velocities observed at room temperature.     

Background-Free Detection of Spin-Exchange Dynamics at Ultra-Low Magnetic Field

Ultra-low field nuclear magnetic resonance spectroscopy (NMR) and imaging (MRI) inherently suffer from a low signal-to-noise ratio due to the small thermal polarization of nuclear spins. Transfer of polarization from a pre-polarized spin system to a thermally polarized spin system via the Spin Polarization Induced Nuclear Overhauser Effect (SPINOE) could potentially be used to overcome this limitation. SPINOE is particularly advantageous at ultra-low magnetic field, where the transferred polarization can be several orders of magnitude higher than thermal polarization. Here we demonstrate direct detection of polarization transfer from highly polarized ¹²⁹Xe gas spins to ¹H spins in solution via SPINOE. At ultra-low field, where thermal nuclear spin polarization is close to background noise levels and where different nuclei can be simultaneously detected in a single spectrum, the dynamics of the polarization transfer can be observed in real time. We show that by simply bubbling hyperpolarized ¹²⁹Xe into solution, we can enhance ¹H polarization levels by a factor of up to 151-fold. While our protocol leads to lower enhancements than those previously reported under extreme Xe gas pressures, the methodology is easily repeatable and allows for on-demand enhanced spectroscopy. SPINOE at ultra-low magnetic field could also be employed to study ¹²⁹Xe interactions in solutions.     

New measurement of <Superscript>129</Superscript>I in IAEA-375 reference material

Summary Under an IAEA project for upgrading of reference materials, a new determination of the ¹²⁹I concentration in the IAEA-375 reference material was performed. A chemical procedure was set up for the preparation of the AgI samples. Measurement of ¹²⁹I was carried out using the IsoTrace Tandetron AMS facility at University of Toronto. To ensure the accuracy of the calibration, the tuning of the AMS system was iterated using not only the QC (quality control) samples but also all unknown samples. To minimize any possible current-dependent effects between ¹²⁹I and ¹²⁷I ions in the injection magnet, low Cs⁺ sputtering beam intensity (10 μA) was used. The reproducibility in determining the ¹²⁹I/¹²⁷I ratio in the IAEA-375 AgI samples was less than 1%. The activity concentration (C_A) of ¹²⁹I in the IAEA-375 reference material was determined to be 1.59±0.08 mBq ^. kg^-1 at 95% confidence level. The present value is about 7% lower than the IAEA recommended value (1.7 mBq ^. kg^-1) listed in 2000 or 20% lower than the recommended value (2 mBq ^. kg^-1) listed in the IAEA AQCS Reference Material Catalogue (2002-2003). Since the IAEA recommended values for IAEA-375 materials was issued about 10 years ago and error range of the recommended values were large, the results we obtained might be useful in upgrading the recommended value.     

Determination of129I in ambient air by inductively coupled plasma mass spectrometry (ICP/MS)

The detection of¹²⁹I by Inductively Coupled Plasma Mass Spectrometry (ICP/MS) in environmental samples can be used to determine anthropogenic release of this long-lived radionuclide, which is a definitive indicator of certain nuclear activities. By using selective precipitation techniques with on-line ICP/MS detection, low levels of¹²⁹I can be detected. The major interference for the ICP/MS detection of¹²⁹I is due the presence of natural¹²⁹Xe found in water samples at a concentration of about 1 ng/ml. This work will demonstrate a instrument detection of less than 50 fg¹²⁹I from environmental air samples and shows promise for a rugged ICP/MS technique to monitor¹²⁹I levels in ambient air for nonproliferation monitoring purposes.     

Determination of 129I/127I ratios in environmental samplesusing neutron activation analysis

Studies on the behavior of ¹²⁹I in the environment are greatly enhanced when the concentration of the radioiodine can be related to stable ¹²⁷I. The background ratios of ¹²⁹I/¹²⁷I of 10^-10 and lower, found in uncontaminated areas, are best measured using accelerator mass spectrometry. However, there are many examples of studies where ratios higher than 10^-8 have been measured, even in places located remotely from nuclear reprocessing activities. In the vicinity of reprocessing plants it is possible to find ratios between 10⁰ and 10^-7, which can be detected easily using neutron activation analysis (NAA). Stable iodine is readily determined at concentrations below 1 mg/kg in environmental materials with instrumental NAA and radiochemical techniques can be used to measure ¹²⁹I to below mBq concentrations. Therefore, where there are elevated concentrations of ¹²⁹I it is possible to use a combination of neutron activation techniques to determine ¹²⁹I/¹²⁷I ratios. This paper describes how NAA is used to measure ¹²⁹I/¹²⁷I ratios in milk, vegetation, and atmospheric samples. Instrumental NAA is used to measure both ¹²⁹I and ¹²⁷I where the ratio is between 10⁰ and 10^-3. A radiochemical procedure is used to measure ¹²⁹I at ratios between 10^-3 and 10^-7, with a thermal neutron flux of 10¹⁶ m^-2·s^-1.     

Determination of129I in soils of Germany using radiochemical neutron activation analysis

At 5 sampling sites distributed throughout Germany the¹²⁹I concentrations in soils have been measured in individual depth intervals to a depth of 60 cm. These measurements are used to determine the total amount of¹²⁹I in a soil column of 60 cm depth. The data indicate that the¹²⁹I concentrations and the¹²⁹I/¹²⁷I isotope ratios are higher at the sampling locations near the coast compared to the sampling locations in Southern Germany. The total¹²⁹I inventories in the top 60 cm of soils are correlated with the¹²⁹I deposition through rainfall.     

Determination of iodine-129 and iodine-127 in environmental samples collected in Japan

Analytical method for the determination of¹²⁹I and¹²⁷I in environmental samples has been developed by using radiochemical neutron activation analysis. The¹²⁹I levels in the samples such as soil (0.9–41 mBq/kg), precipitation (0.002–0.11 mBq/kg), pine needles (1.2–32 mBq/kg) and seaweed (<0.1–17 mBq/kg) collected near the nuclear facilities in Tokaimura were higher than those from the other areas in Japan. The highest¹²⁹I concentration was found in surface soil (0–5 cm), and the highest¹²⁹I/¹²⁷I ratios were found in pine needles and precipitation. The¹²⁹I/¹²⁷I ratio was higher in rice paddy soil than those in wheat field soil collected around Tokaimura, while the concentration of¹²⁹I somewhat higher in wheat field soil.     

Application of 129I as an environmental tracer

¹²⁹I is produced naturally by cosmic-ray spallation of Xe and by spontaneous fission of ²³⁸U. In the environment ¹²⁹I is mainly due to nuclear weapon tests and reprocessing plants. The high water solubility of iodine makes ¹²⁹I a good oceanographic tracer. Long residence time and large air releases of ¹²⁹I from reprocessing plants allow ¹²⁹I to be used as a geochemical and metrological tracer. The same chemical and physical properties of ¹²⁹I and ¹³¹I enable one to use ¹²⁹I as a tool for the reconstruction of ¹³¹I doses after a nuclear accident. Some studies using ¹²⁹I as a tracer which were carried out in the author's laboratory, are summarized. This revised version was published online in July 2006 with corrections to the Cover Date.