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.     

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.     

Distribution and behavior of long-lived radioiodine in soil

The concentration of¹²⁹I in soil in Japan was determined by neutron activation analysis. For the activation analysis, pre-irradiation chemical separation of the iodine was carried out by acid decomposition and distillation and post-irradiation treatment was performed by ion exchange and solvent extraction. The concentration of stable iodine and¹³⁷Cs were also determined and compared with the behavior of¹²⁹I in soil.Soil samples from Ibaraki, Fukui, Fukushima, and Nagasaki Prefectures were analyzed and¹²⁹I was detected in amounts ranging from 10^–7 to 10^–5 Bq/g soil in uncultivated surface soil. There are apparently small variations in the¹²⁹I concentrations in each of the regions analyzed.From depth profile studies in sandy soil, the iodide form of¹²⁹I was found to migrate downward at a relatively rapid rate while other species remain longer in the surface soil.     

Iodine separation procedure for the determination of129I and127I in soil by neutron activation analysis

A radiochemical neutron activation analytical method for the determination of¹²⁹I and¹²⁷I in soil samples was studied. Iodine was separated from the sample prior to the irradiation by volatilization, i.e. by combustion of the sample and trapping of the iodine in an alkaline solution together with a reducing agent. This method enables one to digest samples containing up to 100 g dry matter. The chemical yield was mostly more than 90%. After irradiation the iodine fraction was further purified by solvent extraction. The detection limit of the¹²⁹I/¹²⁷I ratio was 1×10^–9.     

A study on the association of two iodine isotopes,of natural127I and of the fission product129I,with soil components using a sequential extraction procedure

Sequential extraction techniques have been utilized in order to investigate the degree of binding or association of natural iodine¹²⁷I and the radioactive iodine isotope¹²⁹I with soil components. The results indicate that only a small fraction of natural iodine (2.5–4%) but a large fraction of the recently added radioactive¹²⁹I (38–49%) is water-soluble. The other forms of iodine which were determined for both iodine isotopes were exchangeable iodine, iodine bound to metal-oxides and iodine bound to organic matter.     

129I in soil and grass samples around a nuclear reprocessing plant

Neutron activation analysis was used to determine¹²⁹I in soil and grass samples around a reprocessing plant. The method involved wet oxidation of samples, using chromic acid, followed by distillation, collection of iodine in alkaline solution, loading on Dowex-1, irradiation and post-irradiation purification steps. The -activity of¹³⁰I isotope of the purified samples was measured for quantitative determination of¹²⁹I. The experimental results showed that¹²⁹I and the¹²⁹I/¹²⁷I atomic ratio in soil samples varied from 1.09×10^–4 to 5.33×10^–3 pCi g^–1 and 0.10×10^–6 to 6.12×10^–6, respectively. Further, the geometric mean of soil-to-plant transfer factor (Bv) for¹²⁹I was found to be 0.16 which was comparable with other published values.     

Iodine speciation in size fractionated atmospheric particles by isotope dilution mass spectrometry

An isotope dilution mass spectrometric method has been developed for the accurate and sensitive determination of iodide and iodate in aerosol particles of the atmosphere. The direct iodine speciation has been possible by the use of species specifically ¹²⁹I enriched spike solutions and separation of the isotope diluted species by anion exchange chromatography after water extraction of the filters. Size fractionated collection of aerosol particles by a six stage impactor system shows different distributions of iodide and iodate for particles of different size with specific patterns for anthropogenically influenced continental and unpolluted marine aerosols, respectively. The detection limit for particulate iodide and iodate has been (3–5) pg/m³ for sampling volumes of 3000 m³. Oil, used for heating plants, could be identified as one but not the only anthropogenic iodine source.Dedicated to Professor Dr. D. Klockow on the occasion of his 60th birthday     

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.     

Improved iodine-125 removal in anionic form of iodate by column method using laterite soil

Soil column experiments have been conducted to treat liquid wastes from hospitals containing¹²⁵I. Three sorbent samples of laterite clay materials with different contents of iron oxides (goethite, -FeOOH) and hydroxides were used to sorb anionic iodate. Post-treatment on effluent wastes with sodium hypochlorite (redox reagent) oxidized the iodide to the desirable iodate ion. Effluent pH after treatment ranges between 4.8 to 5.8, which does not vary much from the initial effluent pH of 4.5 before treatment. Results show that 90 to 97% sorption of iodine radionuclides with a decontamination factor ranges between 10–32 was obtained after the first two hours of experiments. Concentration has decreased from the initial 10 Bq/ml to concentration ranges of 0.3 to 0.9 Bq/ml. Batch experiments conducted using different sorbent masses of soils, show that there was a drop in sorption as the mass of soils fell below approximately 0 to 0.25 g. The sorption remains constant with the soil mass above 0.25 g. Another batch experiment using a different concentration shows that the adsorption capacity of the laterite soil was 1.1 Ci/g. The adsorption is about 96% with a distribution coefficient of 1170.     

Assessment of Iodine in the Diet of People Living Around a Nuclear Reprocessing Plant: Dose-Related Consequences of an Intake of 129I

It is important that in radioiodine dosimetry for low levels of daily intake, allowance must be made for the normal daily intake of stable iodine. This intake varies from one region to another, and variations are observed from one person to the next within a region, depending on eating habits. Measuring iodine in the urine over 24 hours can indirectly assess these variations. Analysis of the total iodine in the urine was carried out for 69 French people living in a temperate maritime region or in mainland France. This study justifies individual assessment of the coefficient of iodine transfer to the thyroid by means of this survey based on the urinary iodine analysis. The consequences for man of the release of ¹²⁹I around a nuclear reprocessing plant were analyzed by applying the methodology published previously by the authors. A software program based on the iodine biokinetic model recommended by the ICRP was used to calculate the daily urine excretion of ¹²⁹I for five different diets of total iodide in a ratio of 10^-4 for ¹²⁹I/¹²⁷I. This model makes it possible to set a practical detection limit of 20 mBq (0.003 µg). This approach is important from a practical point of view for health physicists involved in routine monitoring of workers in the nuclear field and members of the public exposed to radioiodine released into the environment.     

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.     

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.     

Reduction of iodate by hydrazine: Application of the iodide ion selective electrode to the uncatalyzed reaction

Summary The reduction of iodate by hydrazine was examined by use of the iodide ion selective electrode. The rate of reduction of iodate at iodide concentrations below 5 × 10^–5 M is controlled by the direct reduction by hydrazine. At higher iodide concentrations, the rate of reduction of iodate is controlled by the reduction of iodate by iodide with the subsequent reduction of iodine by hydrazine. Application of the reaction to the determination of g quantities of iodine is discussed.

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Zusammenfassung Die Reduktion von Jodat mit Hydrazin wurde mit Hilfe einer jodid-spezifischen Elektrode untersucht. Das Ausmaß der Jodatreduktion bei Jodid-konzentrationen unter 5·10^–5 Mol/l wurde durch direkte Reduktion mit Hydrazin kontrolliert. Bei höheren Jodidkonzentrationen wurde das Reduk-tionsausmaß des Jodats mit Hilfe der Jodat-Jodid-Reaktion und erst dann durch Reduktion des Jodids mit Hydrazin kontrolliert. Die Anwendung auf die Bestimmung von g-Mengen Jodid wurde diskutiert.

     

Tracer experiments for the determination of chemical forms of radioiodine in water samples

Two simple methods, (1) isotope exchange method and (2) anion exchanger column method, are developed for the determination of chemical forms of radioiodine (iodide and iodate) in water samples. Using these methods, transformations of chemical forms of iodine in various water samples were studied. It was observed that iodate in rain water (unfiltered) and milk tended to change iodide form, whereas iodide was converted to iodate form in seawater and tap water. After the Chernobyl accident both chemical forms of¹³¹I (iodide and iodate) were found in rain water samples collected in Japan.     

Gas chromatography–mass spectrometric identification of iodine species arising from photo-chemical vapor generation

Ultraviolet irradiation of aqueous solutions of iodide/iodate ion containing low molecular weight organic acids generates volatile iodine species that are amenable to detection by atomic spectrometry. In the presence of formic, acetic or propionic acids, photo-chemical generation results in the formation of HI, methyl- and ethyl-iodide respectively, the latter two products being directly identified by gas chromatography–mass spectrometry. Deuterium and ¹³C-labeled reagents were employed to elucidate the provenance of the alkyl group. Use of ¹³CH₃–COOH produced ¹³CH₃–I; deuterated acetic acid (D₃C-COOD) resulted in the formation of CD₃–I. These observations indicate direct transfer of the alkyl group from the carboxylic acid to iodide, consistent with the suggestion that the mechanism of synthesis involves radical induced reactions.     

Determination of 129I in Conifer Samples Around Nuclear Facilities in Argentina

An improved method has been developed that allows the determination of ¹²⁹I in conifers around nuclear facilities using neutron activation analysis. Pine and cedar needle samples were collected from the surroundings of Atucha and Embalse Nuclear Power Plants, Centro Atómico Ezeiza, as well as from background areas in Argentina. ¹³¹I was used as tracer. A chemical recovery of 98–100% was obtained for pre-irradiation distillations and total recovery was 70–85%. The minimal detectable amount (MDA) was 0.01 mBq/g of sample, depending on the total recovery, natural iodine concentration, irradiation time and neutron flux. The results presented in this paper are the first published from Argentina.     

Determination of ultratrace iodide in aqueous solution with a piezoelectric detector

Iodide is oxidized to iodate and, after destruction of excess oxidant, iodine is formed on addition of excess of iodide. This is extracted into toluene and detected by adsorption on the silver-plated electrode of the piezoelectric crystal. The resulting frequency change of the dry crystal after removal from the toluene is proportional to iodide concentration over the range 0.6–127 μg l^?1. No significant interferences were caused by other ions except bromide. The mechanism of iodine adsorption is investigated by cyclic voltammetry.     

Indirect amplification method for determining mercury by direct-current polarography. Application to organomercury compounds

An amplification method for the determination of 0.5–70 ppm (2.5 × 10⁻⁶ to 3.5 × 10⁻⁴ M) of Hg(II) is described. Hg(II) is reacted with a slight excess of KI, and the excess iodide is oxidized by bromine water and measured polarographically as iodate with sixfold amplification. Alternatively, the iodate formed is reacted to liberate iodine which is then reduced to iodide, and again oxidized to yield six iodate ions for every iodide ion originally present;

2. Microdetermination of Mercury in Organomercurial Compounds

polarographic reduction requires 36 electrons. Oxidation of the excess iodide with periodate yields four iodate ions for every iodide ion and therefore allows 24-fold amplification.Microdetermination of mercury in organomercurials is achieved using the sixfold method following closed flask combustion: the average percentage error for 10 determinations is ±0.40 and the time required for one sample run is 45 min.     

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.     

The use of charcoal from agriculture waste in the speciation of iodine from well and river waters

The concentrations of iodine in fresh waters are known to be within the range of 0.5 to 35 ng·ml⁻¹, much lower than in oceanic waters. The iodine concentrations, particularly that of¹²⁹I which is significant from the radiation safety aspect, in public drinking waters have to be specified in order to verify the required level before distribution for domestic use. A modified version of an established method was used in the adsorption of iodine, iodate, total inorganic iodine and charcoal-adsorbable iodine using activated carbon prepared from oil palm kernel wastes. A thorough investigation of the physical properties of the activated carbon was carried out to determine its viability as an adsorbent for volatile species such as iodine. The iodine species were preconcentrated from water samples collected from wells in villages and from water intake points along rivers. The quantitative analysis of the species adsorbed was done by irradiating the activated charcoal loaded with the respective species in a neutron flux of 5.1·10¹² n·cm⁻²·s⁻¹ from a TRIGA MkII, nuclear reactor. Recovery experiments using spiked samples was done to provide quality assurance controls.