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.     

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.     

Iodine-129 in the environment of a nuclear fuel reprocessing plant: II. Iodine-129 and iodine-127 contents of soils,forage plants and deer thyroids

Concentrations of ¹²⁹I and ¹²⁷I in soils, forage plants and deer thyroids collected in the environment of the small Karlsruhe nuclear fuel reprocessing plant (WAK) were determined by neutron activation analysis. Levels of ¹²⁹I in all samples were found to be elevated by several orders of magnitude above current average biospheric background values. In particular, deer thyroids were found to have very high ¹²⁹I levels and corresponding high ¹²⁹I/¹²⁷I ratios.Using all the analytical data for ¹²⁹I and ¹²⁷I concentrations in plants it seems probable that there is a correlation between the ¹²⁹I and the natural ¹²⁷I concentrations in plants.     

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.     

Carbon-14 discharges from the nuclear fuel cycle: 2. Local effects

Environemtnal ¹⁴C levels around various types of nuclear installations within the UK have been monitored during recent years. Enhanced ¹⁴C levels have been detected around both the nuclear fuel reprocessing plant as Sellafield and the thermal nuclear power station complex at Hunterston. From these measurements, the radiological impact of the ¹⁴C discharges on the local population is assessed. It is conservatively estimated that the ¹⁴CO₂ emissions from Sellafield between 1952 and 1985 could have delivered an 8·4 man Sv collective effective dose equivalent commitment to the population living within 40 km of the site. The maximum possible collective dose to the population within 15 km of Hunterston in 1984 was 15 × 10⁻³ man Sv. Conservative estimates of maximum annual effective dose equivalents to individuals around Sellafield and Hunterston are 0·2 mSv (in 1982) and 12 μSv (in 1984), respectively. These dose levels do not exceed the limits recommended by ICRP but the former value clearly indicates that, for the larger discharges at least, consideration and optimisation of ¹⁴C releases are fully justified. The same ¹⁴C measurements are also used to test the validity of two atmospheric dispersion models, the Gaussian plume and the so-called ‘hyperbolic’ models. The former is excellent in predicting downwind ¹⁴C levels around Hunterston but is unsatisfactory when applied to Sellafield, whereas the latter proves reliable at both sites. Further investigations suggest that the Gaussian plume model's poor performance at Sellafield can be explained by inaccurate input data.     

Some observations on the geochemistry and isotopic composition of uranium in relation to the reprocessing of nuclear fuels

In order to determine whether or not uranium depleted in ²³⁵U and derived from the British Nuclear Fuels Ltd (BNFL) nuclear fuel reprocessingg plant at Sellafield, Cumbria, UK can be detected in environmental samples, we have investigated the isotopic composition of uranium in ammonium carbonate leachates from marine and terrestial samples from near Sellafield. Some show a depletion in ²³⁵U and the presence of ²³⁶U which unequivocally identifies the presence of uranium derived from BNFL. The ²³⁴U/²³⁸U activity ratio and total uranium content of samples are not significantly different from those of natural uranium abundances. The highest concentrations of uranium are found in anaerobic organic-rich silts and the lowest in sandy silts and coarse-grained sands.     

Chemical associations of artificial radionuclides in Cumbrian soils

The distributions of radionuclides in the surface layer of four soils of contrasting types from west Cumbria, UK, have been studied in detail. All the soils contain enhanced levels of artificial radionuclides derived from low-level discharges both to sea and to atmosphere from the British Nuclear Fuels reprocessing plant at Sellafield. The bulk of the activity is held in the top 15 cm of soil profiles, suggesting that radionuclide mobility is limited. Sequential extraction experiments have identified major associations of plutonium with organic matter and of caesium with silicates but there is no preferential association of ruthenium with any single soil component.     

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.     

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.     

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.     

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.     

Airborne radioactivity on the Scottish Solway coast

A brief survey of the concentrations of radionuclides in surface air at five locations along the Scottish shoreline of the Irish Sea has been made in response to concern that airborne resuspension of marine radioactivity may be causing an inhalation hazard. Airborne concentrations of ⁴⁰K, ¹⁰⁶Ru, ¹³⁷Cs, ¹⁴⁴Ce, ²³⁸Pu, ^{239 + 240}Pu and ²⁴¹Am are reported. Plutonium isotopic ratios indicate the presence of radioactivity of marine origin attributable to low-level waste disposals from the fuel-reprocessing plant at Sellafield in Cumbria. Calculation of the dose resulting from inhalation shows that the risks to members of the public are negligible. Suggestions are made for development of these studies in future.     

Plutonium isotopes concentration in seawater and bottom sediment off the Pacific coast of Aomori sea area during 1991-2005

A radioactivity survey was launched in 1991 to determine the background levels of ^239+240Pu in the marine environment off a commercial spent nuclear fuel reprocessing plant before full operation of the facility. Particular attention was focused on the ²⁴⁰Pu/²³⁹Pu atom ratio in seawater and bottom sediment to identify the origins of Pu isotopes. The concentration of ^239+240Pu was almost uniform in surface water, decreasing slowly over time. Conversely, the ^239+240Pu concentration varied markedly in the bottom water and was dependent upon the sampling point, with higher concentrations of ^239+240Pu observed in the bottom water sample at sampling points having greater depth. The ²⁴⁰Pu/²³⁹Pu atom ratio in the seawater and sediment samples was higher than that of global fallout Pu, and comparable with the data in the other sea area around Japan which has likely been affected by close-in fallout Pu originating from the Pacific Proving Grounds. The ²⁴⁰Pu/²³⁹Pu atom ratio in bottom sediment samples decreased with sea depth. The land-originated Pu is not considered as the reason of the increasing ^239+240Pu concentration and also decreasing the ²⁴⁰Pu/²³⁹Pu atom ratio with sea depth, and further study is required to clarify it.     

Three-dimensional modelling of the tide-induced dispersion of radionuclides in the sea

A three–dimensional marine dispersion model for radionuclieds has been developed. The model solves the three–dimensional hydrodynamic equations and, simultaneously, the three–dimensional advective–diffusive dispersion equations. Thus the tide–induced dispersion of radionuclides is obtained. The equations are solved using a finite difference explicit scheme using a time step of a few seconds with appropriate boundary conditions. As an example the model has been applied to study the dispersion of ¹³⁷Cs in the Irish Sea which is released from the nuclear fuel reprocessing plant at Sellafield. Tidal amplitudes and current profiles obtained with the model have been compared with observations in the Irish Sea: both sets of data are in good agreement. Observed and computed ¹³⁷Cs distributions in waters have also been compared. The model gives a good representation of the dispersion of this radionuclide in the Irish Sea.     

Medical radioisotopes in the environment – following the pathway from patient to river sediment

Motivated by the detection of ¹³¹I in river sediment in routine long-term surveillance samples, a systematic short-term study of the wastewater treatment chain was planned and conducted. Inflow, effluent and primary sludge were collected on a daily basis during two weeks at a regional wastewater treatment plant. Samples were investigated by gamma spectroscopy. Four medically used isotopes could be identified (¹³¹I and ^99mTc regularly, ¹⁵³Sm and ¹²³I sporadically). The concentration levels coincide well with literature data for ¹³¹I, and with our own long-term data for ¹³¹I and ^99mTc for the same plant. Cosmogenic ⁷Be activity in primary sludge correlated well with rainfall intensity. Surface sediment was sampled at low tide at both shores of the river, up- and downstream of the plant. ¹³¹I was identified in all samples, with a sharp maximum (about 100 Bq kg⁻¹ d.m.) at the discharge point of the plant and lower levels elsewhere, decreasing monotonically in downstream direction. ⁷Be and ¹³⁷Cs showed the same behaviour, but no peak at the discharge point. Predictions from simple equilibrium models for the transport and sedimentation of ¹³¹I show good agreement with the experimental data and suggest that the wastewater treatment plant is the main source for this isotope.     

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.     

Spatio-temporal variations in the technetium-99 content of fucus serratus in the english channel during 1982–1984

Spatio-temporal variations in the technetium-99 content of Fucus serratus samples from the French coast of the English Channel were studied between 1982 and 1984 using various sampling strategies. The lack of constancy in measurements from within the seaweed zone of the same station is revealed by a variation of 18% in the mean contents of samples collected from different sampling levels, a variation which reaches 41% if the extreme values of all results are taken into account. Regional variations over the Channel as a whole show an asymmetric diminution of the ⁹⁹Tc content of the seaweed on the two sides of the liquid effluent discharge outlet from the reprocessing plant at La Hague and this confirms a predominant drift of Channel waters towards the North Sea. Variations with time at three stations during 1983 and 1984 have revealed that there is a time-lag between fluctuations observed in the discharges and those in F. serratus. In addition, a periodic component observed at the Roscoff and Wimereux stations, where the ⁹⁹Tc content of the seaweed varies by a factor of 2–3 between winter and summer periods, could be correlated with seasonal changes both in the metabolic state of F. serratus and in the currents to the south-west of Cap de La Hague. ⁹⁹Tc, which here has no radiological impact on man, would thus appear to be a radioactive label for sea waters and one which is particularly sensitive to variations in environmental conditions.     

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.     

Artificial radioactivity in Cumbria: Summary of an assessment by measurement and modelling

At the Harwell laboratory, the distributions of the artificial radionuclides discharged by British Nuclear Fuels at Sellafield have been measured within Cumbria, with particular emphasis on the transfer between environmental media. The results of the measurements have been incorporated into a model of the Cumbrian environment.The object of this work is to estimate the radiological impact upon man by exploring the pathways leading to external irradiation, to inhalation and to the ingestion of foodstuffs.Distributions have been established for caesium-137, plutonium isotopes and americium-241. Transfer from sea to land, of actinide radioactivity discharged to the sea, occures on a very small scale. The relative contributions to deposition and airborne radioactivity from sea-to-land transfer, fallout from nuclear weapons testing and atmospheric releases from Sellafield are compared. The dose resulting from sea-to-land transfer of actinides to a resident of Seascale peaked in 1973 at less than 1% of the ICRP annual limit for the general public and should fall steadily up to the year 2000.     

Geochemical associations of plutonium and γ-emitting radionuclides in caithness soils and marine particulates

Geochemical associations of plutonium and artificial γ-emitting radionuclides have been investigated in soils and marine particulate material from the immediate vicinity of the Dounreay Nuclear Power Development Establishment (DNPDE) Caithness. The artificial radionuclides present in these materials arise from a variety of sources: world-wide nuclear weapons test fallout, direct deposition from atmospheric discharges at DNPD, and the return to land of activity previously discharged to sea (containing contributions from Dounreay and Sellafield). The levels, although sufficient to permit satisfactorily low counting errors, are of negligible radiological significance, the plutonium being more than 1000 times less than the NRPB Generalised Derived Limit (GDL) for well-mixed soil. Sequential leaching using selective extractants was performed to quantify the percentages of each nuclide in the following notional fractions: (a) readily available, (b) exchangeable and bound at specific adsorption sites, (c) chelated as insoluble organic complexes, (d) associated with sesquioxides, and (e) residual. Plutonium was found to be associated mainly with phases (c) and (d), while the γ-emitters present in the marine particulate material showed quite varied distributions. The degree of chemical fixation in the particulates follows the sequence ⁴⁰K¹³⁷Cs¹⁰⁶Ru¹²⁵Sb^239,240Pu¹⁴⁴Ce⁶⁰Co^154,155Eu.