Iodine-129 in the environment of a nuclear fuel reprocessing plant: I. 127I and 127I contents of soils,food crops and animal products

Concentrations of ¹²⁹I and ¹²⁷I in soils, food crops and animal products collected in the environment of the small Karlsruhe nuclear fuel reprocessing plant (WAK) were determined by neutron activation analysis. ¹²⁹I levels in all samples were found to be elevated by several orders of magnitude above current average biospheric background values. Resultant thyroid doses from consumption of food produced at locations in the vicinity of the Karlsruhe reprocessing plant are, however, small relative to the natural background dose.     

127I and 129I/127I isotopic ratio in marine alga Fucus virsoides from the North Adriatic Sea

The only stable iodine isotope is 127I and the natural 129I/127I ratio in the biosphere has increased from 10(-15)-10(-14) to 10(-10)-10(-9), mainly due to emissions from nuclear fuel reprocessing plants. In Europe they are located at La Hague (France) and Sellafield (England), where the ratio of 129I/127I is up to 10(-4). The marine environment, i.e. the oceans, is the major source of iodine with average concentrations of around 60 mirogL(-1) iodine in seawater. Brown algae accumulate iodine at high levels of up to 1.0% of dry weight, and therefore they are an ideal bioindicator for studying the levels of 127I and 129I in the marine environment. A radiochemical neutron activation analysis (RNAA) method, developed at our laboratory, was used for 129I determination in the brown alga Fucus virsoides (Donati) J. Agardh, and the same technique of RNAA was used for total 127I determination. The samples were collected along the coast of the Gulf of Trieste and the West coast of Istria in the North Adriatic Sea in the period from 2005 to 2006. Values of the 129I/127I ratio up to 10(-9) were found, which is in agreement with the present average global distribution of 129I. The levels of stable iodine found were in the range from 235 to 506 microg g(-1) and the levels of 129I from 1.7 to 7.3 x 10(-3)Bq kg(-1) (2.6-10.9 x 10(-7) microg g(-1)), on a dry matter basis.     

Areal distribution of 129I in west cumbrian solis

¹²⁹I has been released during operations at the BNFL nuclear fuel reprocessing plant at Sellafield in west Cumbria over the past thirty years with about 95% being discharged into the sea and 5% into the atmosphere. Soil samples have been taken within a 40 km radius of Sellafield to determine the extent to which the ¹²⁹I is deposited in the immediate vicinity of the plant. The ¹²⁹I content has been determined by a sensitive neutron activation technique and levels in soil were found to be elevated above global levels in all samples. The areal distribution of ¹²⁹I was consistent with direct deposition following release to the atmosphere from Sellafield and the relationship between ¹²⁹I activity and the distance from Sellafield was of a form predicted by atmospheric dispersion models. The absence of any observable return of ¹²⁹I from the sea has implications for assessments of dose.     

129I in the environment of the La Hague nuclear fuel reprocessing plant--from sea to land

In recent years, particular attention was paid to the long-lived radionuclides discharged with authorized low-level radioactive liquid and gaseous effluents by the nuclear spent fuel reprocessing plants of La Hague and Sellafield. The knowledge of (129)I (half-life=15.7 x 10(6) a) distribution in the environment is required to assess the radiological impact to the environment and population living in the area under the direct influence of La Hague NRP discharges. Measurement difficulties of (129)I in environmental matrices, where it is usually present at trace level, limited data published on (129)I activity levels in the European and more particularly in the French territory. Studies conducted to qualify a new alternative measurement method, direct gamma-X spectrometry with experimental self-absorption correction, led to test samples collected in the La Hague marine and terrestrial environment : seaweeds, lichens, grass, bovine thyroids, etc. All these results, often already published separately for analytical purposes and treated for intercomparison exercises, are presented here together in a radioecological manner. The levels of (129)I activity and (129)I/(127)I ratios in these samples show the spatial and temporal influence of the La Hague NRP in its local near-field environment as well as at the regional scale along the French Channel coast.     

Level and origin of iodine-129 in the Baltic Sea

Environmental samples, such as seawater, seaweed, lake water, lake sediment and grass collected from the Baltic Sea area were analyzed for 129I and 127I by radiochemical neutron activation analysis. In 2000, the concentration of 129I in the seawater from Borholm and M?en in the Baltic Sea has reached 6.0 x 10(-13) and 16 x 10(-13) g/l, respectively, these are more than two orders of magnitude higher than the global fallout level. The highest value of 270 x 10(-13) g/l being found in the seawater from the Kattegat. By comparison of the level of 129I in the lake water and precipitation in this region, it is estimated that more than 95% of 129I in the Baltic Sea originates from reprocessing emissions, especially from the French nuclear fuel reprocessing plant at La Hague. More than 30% of 129I in the south Baltic and 93% in the Kattegat directly originates from the marine discharges of the European reprocessing plants.     

Partition of iodine (¹²⁹I and ¹²⁷I) isotopes in soils and marine sediments

Natural organic matter, such as humic and fulvic acids and humin, plays a key role in determining the fate and mobility of radioiodine in soil and sediments. The radioisotope ¹²⁹I is continuously produced and released from nuclear fuel reprocessing plants, and as a biophilic element, its environmental mobility is strongly linked to organic matter.Due to its long half-life (15.7 million years), ¹²⁹I builds up in the environment and can be traced since the beginning of the nuclear era in reservoirs such as soils and marine sediments. Nevertheless, partition of the isotope between the different types of organic matter in soil and sediment is rarely explored. Here we present a sequential extraction of ¹²⁹I and ¹²⁷I chemical forms encountered in a Danish soil, a soil reference material (IAEA-375), an anoxic marine sediment from Southern Norway and an oxic sediment from the Barents Sea. The different forms of iodine are related to water soluble, exchangeable, carbonates, oxides as well as iodine bound to humic acid, fulvic acid and to humin and minerals. This is the first study to identify ¹²⁹I in humic and fulvic acid and humin. The results show that 30-56% of the total ¹²⁷I and 42-60% of the total ¹²⁹I are associated with organic matter in soil and sediment samples. At a soil/sediment pH below 5.0-5.5, ¹²⁷I and ¹²⁹I in the organic fraction associate primarily with the humic acid while at soil/sediment pH > 6 ¹²⁹I was mostly found to be bound to fulvic acid. Anoxic conditions seem to increase the mobility and availability of iodine compared to oxic, while subaerial conditions (soils) reduces the availability of water soluble fraction compared to subaqueous (marine) conditions.     

Level and origin of 129I and 137Cs in lichen samples (Cladonia alpestris) in central Sweden

Lichen is a symbiosis between algae and fungi. They have for decades been used as bioindicators for atmospheric deposition of heavy metals, organic compounds and radioactive elements. Especially the species Cladonia alpestris and Cladonia rangiferina are important for the food chain lichen-reindeer-man.The concentration of ¹²⁹I was determined in lichen samples (Cladonia alpestris) contaminated by fallout from atmospheric nuclear tests explosions and the Chernobyl accident. The samples were collected at Lake Rogen District (62.3°N, 12.4°E) in central Sweden in the periods 1961-1975 and 1987-1998, and analysed with accelerator mass spectrometry (AMS) at CNA (Seville) to study its distribution in different layers. Data on the ¹³⁷Cs activity measured previously were also included in this study. The ¹²⁹I concentration ranged from (0.95 ± 0.13) × 10⁸ at g⁻¹ in 1961 in the uppermost layer to (14.2 ± 0.5) × 10⁸ at g⁻¹ in 1987 in deepest layer. The ¹²⁹I/¹³⁷Cs atom ratio ranged between 0.12 and 0.27 for lichen samples collected in the period 1961-1975, indicating weapons tests fallout. For lichen samples collected between 1987 and 1998 the behaviour of ¹³⁷Cs concentrations reflected Chernobyl fallout. The concentrations of the two radionuclides followed each other quite well in the profile, reflecting the same origin for both.From the point of view of the spatial distribution in the lichen, it appears that ¹²⁹I was predominantly accumulated in the lowest layer, the opposite to ¹³⁷Cs for which the highest amounts were detected systematically in the topmost layer of lichen. This vertical distribution is important for radioecology because lichen is the initial link in the food chain lichen-reindeer-man, and reindeer only graze the upper parts of lichen carpets.     

Determination of 129I/127I in aerosol samples in Seville (Spain)

In this work we present results of the (129)I/(127)I ratio in aerosols of Seville, Southwest of Spain (37.4 degrees N,6 degrees W). A radiochemical method is applied to extract the iodine from the aerosols and prepare samples to be measured by accelerator mass spectrometry (AMS) at the ETH facility in Zürich. We have found the possibility of monitoring the (129)I/(127)I isotopic ratio on a two-days basis with sensitivities in the order of 10(4)-10(5) atoms (129)I/m(3), and values of 10(-8)-10(-9) for the isotopic ratio.     

A dynamic model of the global iodine cycle and estimation of dose to the world population from releases of iodine-129 to the environment

A dynamic linear compartment model of the global iodine cycle has been developed for the purpose of estimating radiological impacts on the world population from releases of ¹²⁹I to the environment. The time-invariant fractional transfer rates, which describe the transport of ¹²⁹I between environmental compartments comprising the atmosphere, hydrosphere, lithosphere, and terrestrial biosphere, are estimated from an analysis of available data on concentrations for naturally occurring stable iodine and data on the global hydrologic cycle. The global radiological impacts on man from a given release of ¹²⁹I are estimated from the calculated compartment inventories as a function of time and models for the intake of iodine by a reference adult. For a constrant population of 12.2 billion, the estimated worldwide complete population dose commitment to the thyroid is 76 man-Sv/GBq (2.8 × 10⁵ man-rem/Ci) released. Estimated values of the incomplete population dose commitment at various times after a global-scale release to the atmosphere are also presented.     

Monitoring iodine-129 in air and milk samples collected near the Hanford Site: an investigation of historical iodine monitoring data

While other research has reported on the concentrations of (129)I in the environment surrounding active nuclear fuel reprocessing facilities, there is a shortage of information regarding how the concentrations change once facilities close. At the Hanford Site, the Plutonium-Uranium Extraction (PUREX) chemical separation plant was operating between 1983 and 1990, during which time (129)I concentrations in air and milk were measured. After the cessation of chemical processing, plant emissions decreased 2.5 orders of magnitude over an 8-year period. An evaluation of (129)I and (127)I concentration data in air and milk spanning the PUREX operation and post-closure period was conducted to compare the changes in environmental levels. Measured concentrations over the monitoring period were below the levels that could result in a potential annual human dose greater than 1 mSv. There was a measurable difference in the measured air concentrations of (129)I at different distances from the source, indicating a distinct Hanford fingerprint. Correlations between stack emissions of (129)I and concentrations in air and milk indicate that atmospheric emissions were the major source of (129)I measured in environmental samples. The measured concentrations during PUREX operations were similar to observations made around a fuel reprocessing plant in Germany. After the PUREX Plant stopped operating, (129)I concentration measurements made upwind of Hanford were similar to the results from Seville, Spain.     

129I/127I, 129I/137Cs and 129I/99Tc in the Norwegian coastal current from 1980 to 1998

Discharges of the nuclides 129I, 137Cs and 99Tc from the nuclear reprocessing facilities at Sellafield (UK) and La Hague (France) are very useful as oceanic tracers. On the basis of 129I/127I, 137Cs and 99Tc measurements in archived seaweeds, the ratios of 129I/127I, 129I/137Cs and 129I/99Tc have been estimated in seawater at two locations (Utsira and Kiberg) in the Norwegian Coastal Current from 1980 to 1998. These ratios, which vary up to two orders of magnitude over this period, are potentially very interesting for determining "transit times" in the Arctic and North Atlantic oceans. While the long-term trends in these ratios are quite clear, measurements in monthly and bimonthly samples show considerable structure. Further studies are required to determine the exact origin of this structure, which may be a limiting factor in the time resolution that can be obtained with these parameters.     

Trends in the spatial and temporal distribution of 129I and 99Tc in coastal waters surrounding Ireland using Fucus vesiculosus as a bio-indicator

Spatial and temporal trends in (129)I and (99)Tc concentrations around the Irish coastline have been evaluated using Fucus vesiculosus as a bio-indicator. (129)I concentrations in a recent set of seawater samples have also been recorded and reveal an identical spatial pattern. Concentrations of (129)I in Fucus from the northeast coast of Ireland proved to be at least two orders of magnitude higher than concentrations in Fucus from the west coast. The (129)I content of Fucus increased significantly between 1985 and 2003, in line with increases in discharges of (129)I from the Sellafield nuclear reprocessing plant. Similar trends were observed in the case of (99)Tc. (129)I/(99)Tc ratios in Irish seawater were deduced from the Fucus data, and compared to ratios in discharges from Sellafield and from the French reprocessing plant at Cap de la Hague. Levels of (129)I and (99)Tc in Fucus from the west coast were found to be enhanced with respect to levels in seaweeds from other regions in the Northern Hemisphere unaffected by discharges from nuclear installations such as those referred to.     

Distribution and sources of (129)I in rivers of the Baltic region

The concentration of (129)I was measured in 54 river waters discharging into the Baltic Sea from Sweden, Finland, Estonia, Latvia, Lithuania, Poland and Germany. Sample collection was performed during a well-bracketed time interval (June-July 1999), thus allowing comparison of the rivers over a wide latitude range without the effect of long temporal spread. Although there is no direct input of anthropogenic (129)I in the watersheds, the concentration of the isotope is about two to three orders of magnitude higher than the expected pre-nuclear era natural values in the rivers of Finland and northern Sweden, and in the rivers of southern Sweden, Lithuania, Estonia, Latvia, Poland and Germany; the (129)I concentration may reach five orders of magnitude higher. Furthermore, there are significant correlations between the (129)I concentration and latitude and/or distance from the North Sea and between (129)I and Cl. These findings suggest seawater as a main source of (129)I to the rivers through atmospheric transport. Of the many chemical parameters investigated, the pH may account for some of the variability in (129)I concentrations of the rivers. The contribution from nuclear weapon tests and the Chernobyl accident to the riverine (129)I is insignificant compared to the releases from the nuclear fuel reprocessing facilities. The total flux of (129)I by rivers to the Baltic Sea and related basins represents minor amounts of the isotope pool in these marine waters. External radioactivity hazards from (129)I are considered to be negligible in the Baltic region. However, as the main (129)I intake to the human body is likely through water, due to the large amount of daily water consumption, more concern should be given to internal radioactivity hazard that may be associated with the isotope's localized elevated concentration in the human organs.     

Wet and dry deposition of 129I in Seville (Spain) measured by accelerator mass spectrometry.

Iodine-129 (T1/2 = 1.57 x 10(7) yr) concentrations have been determined by accelerator mass spectrometry in rainwater samples taken at Seville (southwestern Spain) in 1996 and 1997. This technique allows a reduction in the detection limits for this radionuclide in comparison to radiometric counting and other mass spectrometric methods such as ICP-MS. Typical 129I concentrations range from 4.7 x 10(7) 129I atoms/l (19.2%) to 4.97 x 10(9) 129I atoms/l (5.9%), while 129I depositions are normally in the order of 10(8)-10(10) atoms/m2d. These values agree well with other results obtained for recent rainwater samples collected in Europe. Apart from these, the relationship between 129I deposition and some atmospheric factors has been analyzed, showing the importance of the precipitation rate and the concentration of suspended matter in it.     

Chernobyl radionuclides in shellfish

Radionuclides from the Chernobyl accident arrived at Monaco on 30 April, 1986. A sample of Mytilus galloprovincialis collected six days later showed near-maximum levels of most radionuclides. Monitoring continued for seven months thereafter, peak concentrations being transiently as high as 480 Bq kg⁻¹ (all soft parts, wet weight) for ¹⁰³Ru. Other radionuclides detected included ¹³²Te, ^129mTe, ¹³¹I, ¹⁰⁶Ru, ¹³⁴Cs, ¹³⁷Cs, ^110mAg, ¹⁴⁰Ba, ¹²⁵Sb, ⁹⁵Nb and ¹⁴¹Ce. Biological half-lives for elimination in this environment were generally around 10 days or longer and most elimination curves contained a number of components. Radionuclide contents of the mussels were predicted quite accurately from concentrations observed on air filters collected simultaneously, but were not satisfactorily explained relative to total radionuclide concentrations in the seawater even three days after peak air filter activities. The use of concentration factors from the literature did not improve the latter predictions. This suggests that the radionuclides were absorbed very rapidly from the fallout particles, rather than from radionuclides first solubilised from particles. Patella lusitanica specimens contained activities about 20–50 times higher than those in the mussels.     

Sources of anthropogenic radionuclides in the environment: a review

Studies of radionuclides in the environment have entered a new era with the renaissance of nuclear energy and associated fuel reprocessing, geological disposal of high-level nuclear wastes, and concerns about national security with respect to nuclear non-proliferation. This work presents an overview on sources of anthropogenic radionuclides in the environment, as well as a brief discussion of salient geochemical behavior of important radionuclides. We first discuss the following major anthropogenic sources and current developments that have lead, or could potentially contribute, to the radionuclide contamination of the environment: (1) nuclear weapons program; (2) nuclear weapons testing; (3) nuclear power plants; (4) uranium mining and milling; (5) commercial fuel reprocessing; (6) geological repository of high-level nuclear wastes that include radionuclides might be released in the future, and (7) nuclear accidents. Then, we briefly summarize the inventory of radionuclides ⁹⁹Tc and ¹²⁹I, as well as geochemical behavior for radionuclides ⁹⁹Tc, ¹²⁹I, and ²³⁷Np, because of their complex geochemical behavior, long half-lives, and presumably high mobility in the environment; biogeochemical cycling and environment risk assessment must take into account speciation of these redox-sensitive radionuclides.     

Environmental radioactivity around tokai-works after the reactor accident at chernobyl

Following the reactor accident at Chernobyl, environmental samples of air, rain water and agricultural and marine products were collected and analyzed by gamma- and alpha-spectrometry. The highest concentrations of ¹³¹I in the environmental samples were as follows: 1·0×⁻¹ Bqm⁻³ (aerosol-associated in air); 3·0×10⁻¹ Bqm⁻³ (gaseous in air); 2·1×10² bq kg⁻¹ (plants); 1·4×10¹ Bq litre⁻¹ (milk). Other nuclides such as ⁹⁵Zr, ⁹⁵Nb, ¹⁰³Ru, ¹⁰⁶Ru, ¹²⁵Sb, ^129mTe, ¹³²I/¹³²Te, ¹³⁴Cs, ¹³⁷Cs, ¹⁴⁰Ba/¹⁴⁰La, ¹⁴¹Ce and ¹⁴⁴Ce were also observed in various environmental samples. ^110mAg was only detected in marine products such as cephalopoda and shellfish, ^239,240Pu and ²⁴¹Am originating from the accident were not identified.Based on the monitoring results at one dairy farm, we have derived an equation to model the transport of ¹³¹I from pasture grass to milk. This equation was then applied to the data from two other farms around Tokai-Works and the calculated ¹³¹I activities in milk were compared with those measured. The equation shows good predictive capabilities for quantification of the peak concentrations of ¹³¹I in milk but underestimates longer-term activities.     

Transfer of Chernobyl-derived 134Cs, 137Cs, 131I and 103Ru from flowers to honey and pollen

The activity concentrations of ¹³⁷Cs, ¹³⁴Cs, ¹³¹I and ¹⁰³Ru were determined separately in honey and pollen samples collected from a single bee colony during several months after the deposition of Chernobyl fallout. The source of each honey and pollen sample was determined by pollen analysis. Although the activity concentrations in honey and pollen varied with time, the concentrations of ¹³⁷Cs and ¹³⁴Cs were, in general, higher in pollen than in honey. For ¹⁰³Ru and ¹³¹I, these differences were comparatively small. The mean ¹³¹ I/¹³⁷Cs and ¹⁰³Ru/¹³⁷Cs ratios were about one order of magnitude higher in honey than in pollen. The mean ¹³¹I/¹⁰³Ru ratio was about the same for honey and pollen. This observation, in the light of the corresponding nuclide ratios found in the deposition, suggests that ¹³⁷Cs, ¹³⁴Cs, ¹³¹I and ¹⁰³Ru were taken up by the plant leaves and transported to nectar and pollen. The higher activity concentrations of ¹³⁷Cs and ¹³⁴Cs in pollen, relative to honey, indicate that these radionuclides behave analogously to potassium, which is also found in higher quantities in pollen.     

Verification of radionuclide transfer factors to domestic-animal food products, using indigenous elements and with emphasis on iodine

Recent reviews have established benchmark values for transfer factors that describe radionuclide transfer from plants to animal food product such as milk, eggs and meat. They also illustrate the paucity of data for some elements and some food products. The present study quantified transfer data using indigenous elements measured in dairy, poultry and other livestock farms in Canada. Up to 62 elements are reported, with particular emphasis on iodine (I) because of the need to accurately assess the behaviour of ¹²⁹I from disposal of nuclear fuel waste. There was remarkable agreement with the literature values, and for many elements the present study involved many more observations than were previously available. Perhaps the most important observation was that product/substrate concentration ratios (CR) were quite consistent across species, whereas the traditional fractional transfer factors (TF, units of d kg⁻¹ or d L⁻¹) necessarily vary with body mass (feed intake). This suggests that for long-term assessments, it may be advisable to change the models to use CR rather than TF.     

Natural radioactivity in refractory manufacturing plants and exposure of workers to ionising radiation

This paper shows the results of a survey carried out at some refractory manufacturing plants. During the first part of the survey, the concentration of natural radioactivity in raw materials and end-products, coming from four plants, was assessed. Several raw materials and, as a consequence, some end-products as well have shown activity concentrations exceeding a few hundreds of Bq kg⁻¹ of ²³⁸U and ²³²Th. In some important raw materials, such as bauxite and corundums, a remarkable radioactive disequilibrium was observed; this is probably due to the high temperature processes undergone by these materials. The second part of the survey focussed on the measurements of ambient equivalent dose rates, airborne dust concentrations and radon indoor. On the basis of results obtained, the effective dose for the standard worker was estimated. Two different types of refractory plants were investigated. Effective doses for both plants were lower than 1 mSv y⁻¹.