Search

Experience after the Chernobyl accident has shown that restoration strategies need to consider a wide range of different issues to ensure the long-term sustainability of large and varied contaminated areas. Thus, the criteria by which we evaluate countermeasures need to be extended from simple cost-benefit effectiveness and radiological protection standards to a more integrated, holistic approach, including social and ethical aspects. Within the STRATEGY project, the applicability of many countermeasures is being critically assessed using a wide range of criteria. Attention is being given to issues such as practicability, feasibility, capacity and environmental side-effects, as well as social factors such as public perceptions of risk, communication of information and the need for dialogue and consultation with affected communities, and ethical aspects such as informed consent and the fair distribution of costs and doses. Although such socio-ethical factors are now the subject of a substantial field of research, there has been little attempt to integrate them in a practical context for decision makers. Within this paper, we specifically consider the ethical aspects of restoration strategies and suggest practical means by which these can be taken into account in the decision making process, introducing a value matrix. The paper covers two critical areas: evaluation of individual countermeasures, and use of the matrix to ensure transparent and systematic consideration of values in selection of a restoration strategy.

In this paper a compartment model of the highly vulnerable Arctic terrestrial food chain "lichen-reindeer-man" is outlined. Based upon an analysis of measured (137)Cs and (90)Sr contents in lichen and reindeer meat from 1961 up to 2001, site specific model parameters for two regions in north-western Arctic Russia and for Kautokeino municipality in Arctic Norway have been determined. The dynamics of radionuclide activity concentrations in the "lichen-reindeer-man" food chain for all areas was satisfactorily described by a double exponential function with short-term and long-term effective ecological half-lives between 1-2 and 10-12 years, respectively, for both (137)Cs and (90)Sr. Using parameter values derived from the model, life-time internal effective doses due to consumption of reindeer meat by reindeer-breeders after an assumed single pulse deposit of 1 kBq m(-2) of (137)Cs were estimated to be 11.4 mSv (Kola Peninsula), 5 mSv (Nenets Autonomous Area), and 2 mSv (Kautokeino, Norway). Differences in vulnerability to radiocaesium deposition were due to differences in transfer between lichen and reindeer and in diet between the three regions.

After the release of radionuclides into the environment it is important to be able to readily identify major routes of radiation exposure, the most highly exposed individuals or populations and the geographical areas of most concern. There have been significant recent improvements in our capability to estimate spatial variation in the environmental behaviour of radionuclides through better understanding of the underlying processes and an ability to spatially apply this knowledge by integrating relevant spatial information in the form of digital data sets using geographical information systems. Thus, it is now possible to refine the estimation of spatial variation in radiation exposure, both for routine releases and in accident situations. Within a recent EC-funded concerted action (the Radioecological Sensitivity Forum), there has been a renewed consideration of the concept of radioecological sensitivity with a particular focus on identifying sensitive areas as well as processes and communities. The concept should be relevant for both terrestrial and aquatic ecosystems, and might even be applied for consideration of doses to biota, although the current focus has been restricted to a consideration of human exposure. The conclusions of the action are outlined, considering the potential usefulness of the concept, and methods by which it can be applied. A framework for the estimation of radioecological sensitivity is proposed and the various measures by which it can be considered, including (i) aggregated transfer coefficients, (ii) action loads, (iii) fluxes and (iv) individual exposure of humans are discussed. The importance of spatial and temporal consideration of each of these outputs is emphasized.

Iceland was identified in the Arctic Monitoring and Assessment Report as one of the Arctic areas which received the most global fallout from atmospheric nuclear weapons tests, but measurements of contamination were sparse, and are difficult due to the remote and inaccessible terrain of much of the country. Measurements of global 1 3 7Cs deposition have been made at sites close to meteorological stations to ensure that precipitation data were of high quality. The measured data have been compared with different methods of predicting , 3 7Cs deposition. The AMAP modeling approach, based on fallout and precipitation data, was used based on a monitoring station near Reykjavik. The availability of good precipitation data and locally based estimates of time dependent ratios of 1 3 7Cs deposition to precipitation during the fallout period gave a better correlation between predicted and observed 1 3 7Cs deposition (1^=0.96) than that achieved using the heterogeneous set of data collected by AMAP over the whole of the Arctic. The method allows a fallout map to be produced for the whole of Iceland for any time period during or after deposition.

To sustain acceptable living and working conditions in areas contaminated by radioactivity, robust and effective restoration strategies need to consider different types of environment, land use and ways of life. The allocation of resources must take account of a range of requirements to ensure sustainable use, including social and ethical aspects, environmental considerations and quality of life. Current understanding of public perceptions and communication of technical information also needs to be integrated into the process so that the radiological situation is fully explained and any remediation measures are transparent to, and agreed by, affected populations. Many individual countermeasures have been developed and tested. Previously, the focus has been on evaluating their effectiveness, with some attention to cost. The current STRATEGY project aims to establish a more holistic decision framework for the selection of optimal remediation strategies for long-term sustainable management of contaminated areas. An initial step within this approach is a detailed evaluation of individual countermeasures; examples of which are provided here for an agricultural and urban countermeasure.

Previous discharges of radioactivity from the Mayak Production Association plant in the Urals have resulted in considerable radionuclide contamination of the Techa River, and consequent high radiation doses during the late 1940s and 1950s to residents of villages along the Techa river. The most contaminated villages close to the site were evacuated in the period 1954-1962. The objective of this recent study was to conduct a preliminary assessment of the current radioactive contamination of soil, vegetation and foodstuffs in the two remaining villages closest to the Mayak site, Muslyumovo and Brodokalmak. The highest contamination levels in soil were found in the floodplain at 5.5 MBq m(-2) for 137Cs and 1.0 MBq m(-2) for 90Sr. Radionuclide contamination in soil of the villages was much lower, but exceeded that expected from global fallout. Data from 1207 measurements of 137Cs in milk and 1180 for 90Sr in milk for the period 1992-1999 were collated. There was no change with time in the 90Sr or 137Cs activity concentration in milk over the measured period. There were significantly higher 137Cs activity concentrations in milk sampled during the housed winter period in Muslyumovo compared with the grazing summer period, but compared to that for Brodokalmak or for either settlement for 90Sr. The highest measured activity concentrations in food products of 137Cs and 90Sr were found in river fish, waterfowl, poultry and milk. The measured activity concentrations of 137Cs and 90Sr in some animal products were higher than that expected from soil and vegetation from fields and pasture in the villages (not including the floodplain) confirming that the highly contaminated floodplains are contributing to contamination of some animal products.

Arctic residents, whose diets comprise a large proportion of traditional terrestrial and freshwater foodstuffs, have received the highest radiation exposures to artificial radionuclides in the Arctic. Doses to members of both the average population and selected indigenous population groups in the Arctic depend on the rates of consumption of locally-derived terrestrial and freshwater foodstuffs, including reindeer/caribou meat, freshwater fish, goat cheese, berries, mushrooms and lamb. The vulnerability of arctic populations, especially indigenous peoples, to radiocaesium deposition is much greater than for temperate populations due to the importance of terrestrial, semi-natural exposure pathways where there is high radiocaesium transfer and a long ecological half-life for this radionuclide. In contrast, arctic residents with diets largely comprising marine foodstuffs have received comparatively low radiation exposures because of the lower levels of contamination of marine organisms. Using arctic-specific information, the predicted collective dose is five times higher than that estimated by UNSCEAR for temperate areas. The greatest threats to human health and the environment posed by human and industrial activities in the Arctic are associated with the potential for accidents in the civilian and military nuclear sectors. Of most concern are the consequences of potential accidents in nuclear power plant reactors, during the handling and storage of nuclear weapons, in the decommissioning of nuclear submarines and in the disposal of spent nuclear fuel from vessels. It is important to foster a close association between risk assessment and practical programmes for the purposes of improving monitoring, formulating response strategies and implementing action plans.

A recently developed semi-mechanistic temporal model is used to predict food product radiocaesium activity concentrations using soil characteristics available from spatial soil databases (exchangeable K, pH, percentage clay and percentage organic matter content). A raster database of soil characteristics, radiocaesium deposition, and crop production data has been developed for England and Wales and used to predict the spatial and temporal pattern of food product radiocaesium activity concentrations (Bq/kg). By combining these predictions with spatial data for agricultural production, an area's output of radiocaesium can also be estimated, we term this flux (Bq/year per unit area). Model predictions have been compared to observed data for radiocaesium contamination of cow milk in regions of England and Wales which received relatively high levels of fallout from the 1986 Chernobyl accident (Gwynedd and Cumbria). The model accounts for 56% and 80% of the observed variation in cow milk activity concentration for Gwynedd and Cumbria, respectively. Illustrative spatial results are presented and suggest that in terms of food product contamination areas in the North and West of England and Wales are those most vulnerable to radiocaesium deposition. When vulnerability is assessed using flux the spatial pattern is more complex and depends upon food product.

In the years following the Chernobyl accident the consumption of wild fungi has been shown to contribute significantly to the radiocaesium intake of humans in several countries. However, in Great Britain, the collection of wild fungi for consumption has generally been thought to be of minor importance and the pathway has not been considered in assessment of radioactivity to humans. The study reported here provides information on contamination levels and consumption rates of wild fungi. To gather the information required, two concurrent surveys were conducted. The first assessed the radiocaesium contamination levels present in commonly eaten fungal species where samples of wild fungi were collected from mainland Great Britain (in collaboration with the British Mycological Society's affiliated Fungus Groups). The second was a survey of consumption habits. The results show that it is not the actual amount of fungi consumed by individuals which determines their radiocaesium intake, but rather the species they select; mycorrhizal species, for example, have significantly greater 137 Cs activity concentrations than saprotrophic and parasitic species. It is concluded that the consumption of wild fungi would not currently be expected to appreciably increase the intake of radioactivity of most consumers above that attributable to the normal diet.

Over the last decade, there has been considerable progress in the development of countermeasures for preventing or reducing contamination of animal products by radioisotopes of iodine, caesium and strontium. In this paper, recent significant technical improvements are summarised and the current availability of countermeasures and their usefulness in the event of a nuclear accident reviewed. An improved understanding of factors controlling the metabolism of radioiodine and radiostrontium has enabled previously suggested countermeasures to be either optimised or dismissed. For radiocaesium in particular, experience since the Chernobyl accident has enabled effective and feasible countermeasures to be identified and successfully implemented in different situations. It has also been more widely understood that countermeasure effectiveness, although important, is not the only criterion which needs to be determined. In addition, cost and practical considerations such as availability, technical feasibility, acceptability and side-effects need to be taken into account. Evaluation of these factors has shown that some previously recommended countermeasures are unlikely to be feasible.

It is important to be able readily to identify major routes of exposure, the most highly exposed individuals or populations and the geographical areas of most concern arising from radioactive contamination. The critical group approach is used to identify sub-sections of the population who are likely to be most exposed. In this paper, the concept of radioecological sensitivity is explored with particular reference to methods of identifying spatial variation in radiation exposure. Radioecological sensitivity analysis attempts to integrate current knowledge on pathways, spatially attribute the underlying processes determining transfer and thereby identify the most radioecologically sensitive areas leading to high radiation exposure. This identifies where high exposure may occur and why, not only for humans, but also for other biota. It can consider single food products or species, or a number of key parameters to identify areas where a number of key pathways coincide. An example of radioecological sensitivity analysis is given for the Arctic. Prior identification of such areas and exposed individuals should improve the focus of emergency preparedness and planning, and contribute to environmental impact assessment for future facilities.

The transfer of radioactivity to the milk and meat of farm animals is likely be a major exposure pathway of human populations, following an environmental release of radioactivity. The importance of source-dependent bioavailability in determining absorption from the ruminant gastrointestinal tract of the radiologically significant radionuclides (radiocesium, radiostrontium, radioiodine, and plutonium) is reviewed. The requirements for and suitability of in vitro methods of determining bioavailability for absorption of these radionuclides is also assessed. Radiocesium absorption varies over a 50-fold range, depending upon dietary source. Source-dependent bioavailability is therefore an important factor in determining the radiocesium contamination of ruminant-derived food products, and reliable in vitro techniques have been developed to rapidly determine its bioavailability. In contrast, under conditions of adequate calcium intake, the absorption of radiostrontium will not be greatly influenced by the dietary source. Results of in vitro extractions of radiostrontium could be misleading, as they indicate differences in bioavailability that are not observed in the animal. Absorption of radioiodine is complete and independent of source. There is currently a lack of data on plutonium absorption in ruminants. However, on the basis of the limited data available, in vitro incubations provide a measure of the relative bioavailabilities of plutonium from different sources. The applicability of the techniques reviewed to the study of other radionuclides and heavy metals is discussed.

The influence of the stable iodine content in the diet on the absorption of radioiodine and its transfer to cow's milk was investigated for cows at different stages of lactation. Three different rates of stable iodine: a low intake rate of 4 mg d −1 , a moderate intake of 35 mg d −1 and a high rate of 75 mg d −1 were fed to two groups of three lactating cows in mid- and late-lactation. The transfer to milk of a single oral administration of radioiodine was measured for the three different intake rates. The lactation phase had no significant effect on iodine transfer to milk; therefore, the data from the two lactation groups were pooled for further statistical analyses. The mean transfer coefficient values for oral radioiodine to milk increased from 0.020 d l −1 for the low treatment to 0.024 d l −1 for the moderate stable iodine rate. There was a statistically significant decrease in the transfer to milk for the high stable dietary iodine intake rate (mean transfer coefficient=0.018 d l −1 ) compared with the moderate treatment. These differences were not due to effects on absorption since true absorption was complete for all three stable iodine treatments, but rather to differential affinities and saturation levels of the thyroid and milk pathways competing for the available iodine. The same behaviour and comparable values of transfer coefficients (range 0.015–0.020 d l −1 ) were observed for stable iodine.

A study conducted during summer 1993 to determine the bioavailability and transfer of 137 Cs and 90 Sr to dairy cattle from herbage collected from a pasture contaminated by particulate fallout is described. The study pasture was located 3.5 km from the Chernobyl nuclear power plant. The true absorption coefficient ( A t ) determined for 137 Cs (0.23) was considerably lower than previous estimates for radiocaesium incorporated into vegetation by root uptake. It is likely that the low dry matter digestibility of the diet and the potential presence of 137 Cs associated with adherent soil-associated fuel particles contributed to this low bioavailability. The A t value determined for 90 Sr (0.27) did not indicate a reduced bioavailability. It is suggested that the current and previous calcium status of the animals was the controlling influence on the transfer of 90 Sr from the diet to milk.

Food production and food harvesting systems common in the areas contaminated by the Chernobyl accident in Russia and Ukraine can be grouped into three major categories: collective farm produce, private farming produce and foods collected from natural ecosystems. The contribution of each of these sources to radiocaesium intake by people living in rural settlements in the mid 1990s has been estimated at two major study sites, one in each country. The collective farm system provided the smallest contribution (7-14%) to the intake of radiocaesium at both sites. Natural food was the major contributor to intake at the Russian site (83%). Whereas private farm produce was the major contributor (68%) at the Ukrainian study site. The difference between the two sites was mainly because private milk production was stopped at the Russian site due to the contamination in 1986. A retrospective assessment of the situation 1 year after the accident shows that collective farming could have been a minor contributor to radiocaesium intake (8%), whilst private farming would have been the major contributor wherever private milk production and consumption continued. The extent to which inhabitants consume natural foods from forests has a considerable effect on their radiocaesium intake. The comparative importance of food products from natural ecosystems increases with time due to the long effective ecological half-lives of radiocaesium in unimproved pastures and forests. Estimation of the fluxes of radiocaesium from the different production and harvesting systems showed that the contribution from private farming and food harvesting from natural ecosystems may be significant, contributing 14-30% to the total fluxes of radiocaesium from an area even if the quantity of food produced in these systems is small. However, the major contributor to the flux exported from an area was the collective farming system, accounting for about 70-86% of the total.

Evidence from research in the Pripyat catchment, reviewed here, indicates that under the ecological conditions prevalent in this area, radiocaesium (137Cs) is highly mobile in both river water and poorly drained organic soils. Data collected at three different spatial and temporal scales demonstrate the effects of hydrological events on 137Cs mobility. During the period 1988–1994, 137Cs contamination in some poorly drained organic soils in the Pripyat catchment and in the milk from cows grazing on these soils are generally declining much faster than the radioactive half life. However, sharp increases in levels of 137Cs in both floodplain soils and milk to 2–3 times that observed immediately after the initial deposition have been measured immediately after summer floods. The processes causing these observed changes have not yet been fully explained but the sites where enhanced 137Cs mobility has been detected are clearly associated with the spatial patterns of organic soils and river flooding.

A method of predicting the spatial distribution of 137Cs deposition in fallout in the Arctic from atmospheric nuclear weapons testing, developed during the Arctic Monitoring and Assessment Programme (AMAP), is described. The method uses a relationship between deposition and precipitation at Tromso (Norway) calculated for each year since 1955, which is spread over the Arctic using a global precipitation data set within a geographical information system. The advantages of this approach include the ability to cover the whole Arctic area and to predict 137Cs deposition, either integrated or decay corrected (cumulative), for any 0.5×0.5° unit for any year. For land north of 60°N, the areas with the lowest estimated ground 137Cs deposition from nuclear weapons testing are the Russian far north east, north Greenland and northern Canada. The highest estimated ground deposition occurred in the coastal areas of Alaska, the southern tip of Greenland, western Canada, Iceland and the western coast of Norway. Predicted differences in the spatial distribution of global fallout are generally consistent with the trends observed by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and with reported measurements in the region above 60°N. A comparison of the predicted cumulative 137Cs deposition with measured values gave a significant correlation (p

During the years after a nuclear accident, the bioavailability and environmental mobility of radiocesium declines markedly, resulting in large changes in contamination of foodstuffs, vegetation, and surface waters. Predicting such changes is crucial to the determination of potential doses to affected populations and therefore to the implementation of radiological countermeasures. We have analyzed 77 data sets of radiocesium (137Cs) activity concentrations in milk, vegetation, and surface waters after the Chernobyl accident. Our results show that the rate of decline in 137Cs during the years after Chernobyl is remarkably consistent in all three ecosystem components, having a mean effective half-life, Teff ≈ 2 years. By comparing changes in 137Cs availability with rates of diffusion of 40K (a close analogue) into the lattice of an illitic clay (1) we have, for the first time, directly linked changes in the environmental availability of 137Cs to fixation processes at a mechanistic level. These changes are co...

Hexacyanoferrates have been identified as highly effective radiocaesium binders which effectively reduce radiocaesium uptake and transfer to milk and meat. In Russia a hexacyanoferrate called ferrocyn has been produced for use as a countermeasure. In 1989-1992, experiments were undertaken in Russia to study the effectiveness of four different ferrocyn materials as 137Cs binders, their potential toxicity, effect on production rates of cow milk, effect on animal health and ease of implementation in routine agricultural practice. Four different ferrocyn delivery forms have been used: 98% pure powder, sustained release rumen boli (15% ferrocyn), salt licks (10% ferrocyn) and sawdust with 10% ferrocyn adsorbed (bifege). In initial experiments with different cows, sheep and pigs these four ferrocyn materials were effective in reducing radiocaesium transfer to animal products. Daily administration of ferrocyn powder at a rate of 3-5 g per cow reduced 137Cs transfer by up to 90% in milk. One single administration of three boli per cow (containing 30 g ferrocyn per boli) reduced 137Cs transfer by 50-75% for a period of 2 months. Salt licks containing 10% ferrocyn (0.22 kg ferrocyn per 2.2 kg briquette provided once) reduced transfer of 137Cs up to twofold for up to 10 days whilst bifege, given at a rate of 30-60 g day-1 (3-6 g day-1 ferrocyn), reduced 137Cs transfer by 90-95%. However, large-scale application of these ferrocyn materials on collective and private farms in agricultural trials in 1994 resulted in a lower effectiveness. Therefore, in 1996 a comparative assessment of the application of the four ferrocyn forms was made under carefully controlled conditions. The results fully validated the previous experimental data, and showed the importance of meeting recommended procedures for treatment, particularly when hexacyanoferrates are administered on a day-to-day basis.

The European Radiation Research Programme refocused some of its research effort within EU countries to consider the environmental consequences of the Chernobyl accident within the third framework period from 1985 to 1989. A gradual improvement in contacts with the Soviet Union occurred from 1990 and allowed the development of research collaboration between EC and Soviet scientists. In response, a programme of Experimental Collaborative Projects (ECP) and Joint Study Projects (JSP) were launched by the EC-DGXII’s Radiation Protection Research Action. Within these projects, Western European and Eastern European scientists collaborated on assessing the consequences of the accident, considering remedial actions and acquiring much basic scientific information on the behaviour of radionuclides in the contaminated territories in Ukraine, Belarus and the Russian Federation. The major goal of all these studies was to provide practical and theoretical assistance to the relevant authorities, based on a fundamental approach of understanding the environmental factors which control the different exposure rates to both the urban and rural populations living in the contaminated areas. The scientific results of the radioecological projects have been summarised at the First International Conference on the Radiological consequences of the Chernobyl accident. This Conference was organised by the European Commission and the Belarus, Russian and Ukrainian Ministries on Chernobyl affairs, Emergency Situations and Health. This paper summarises the achievements of the radioecological programme.

The results of a study in which groups of sheep were given single oral administrations of 14C, 3H and 35S and then slaughtered over a period of 1 year are reported. The experimental data were used to investigate the potential of metabolically based models for describing the transfer of the three radionuclides to sheep tissues. The structure of these models is based upon a simplified understanding of the transfer of the macro-elements C, H and S by processes such as respiration and protein synthesis/degradation. A consequence of this approach is that the three models have many common parameters. The models reproduced the general trends of the observations, accounting for 74%, 66%, and 58% of the observed variation in the 14C, 3H and 35S data, respectively, suggesting that they may provide a useful alternative approach to modelling the transfer of these radionuclides. The models presented are limited to the particular experimental situation for which they were developed, and further experimental work would be required to extend them. However, such metabolically based models have great potential: for example, they should be able to account for the influence of dietary intake, physiological status or the form of the radionuclide in the animals diet (e.g. tritiated water or organically bound tritium).

During the weeks to months after the deposition of radioactive fallout, the initial concentration of radioactivity in rivers and lakes declines as a result of flushing and removal to bottom sediments. In the long-term, however, radioactivity in the water body can remain at significant levels as a result of secondary contamination processes. In particular, it is known that soils contaminated by long-lived radionuclides such as 137Cs and 90Sr provide a significant source to surface waters over a period of years after fallout. Using The Land Cover Map of Great Britain, a satellite-derived land cover map as a surrogate indicator of soil type, we have related catchment land cover type to long-term 137Cs activity concentrations in 27 lakes in Cumbria, UK. The study has shown that satellite-derived maps could be used to indicate areas vulnerable to high long-term 137Cs transport to surface waters in the event of a nuclear accident. In these Cumbrian lakes, it appears that residual 137Cs levels are determined by transfers of 137Cs from contaminated catchments rather than within-lake processes. Only three of the cover types, open shrub moor, bog and dense shrub moor, as identified by the satellite, are needed to explain over 90% of the variation in long-term 137Cs activity concentrations in the lakes, and these have been shown to correlate spatially with occurrence of organic soils.

A number of radioisotopes of cerium, ruthenium and silver may be released into the environment and potentially contaminate foodstuffs. For ruminants, data on the absorption, transfer and excretion rates of these radionuclides are sparse and were previously insufficient to allow the development of reliable dynamic models to enable the prediction of contamination levels in food products. In this study, groups of sheep were given single oral administrations of radiocerium, radioruthenium, and radiosilver and slaughtered at various periods up to 1 year. The resulting data were used to develop compartment models to describe the transfer of the three radionuclides to sheep tissues. Values for gut absorption and transfer to muscle (the most important tissue in terms of contamination of the food chain) derived from the models were considerably lower than previously advised values for the radionuclides studied. For all three radionuclides there were certain organs which contained significantly higher activity concentrations than muscle. The models developed allow prediction of the likely levels of these radionuclides in the tissues of sheep as a result of single or continuous contamination events.

The activity concentrations of 137Cs,238 Pu, 239,240Pu and 241Am were measured in root mat and vegetation samples collected from tide washed pastures in 17 estuaries spanning the eastern seaboard of the Irish Sea, extending from the Solway in north-west England to St. David's Head in south Wales. Some of these estuaries had been investigated in previous surveys, but this study is unique in that it covered a wide geographic range using the same sampling and analytical methodology and within a comparatively short time scale. This allows for a valid comparison within the data set of the contamination levels at the different areas. Spatial distributions of the radionuclides were consistent with transport of radionuclides discharged to the Irish Sea from the Sellafield Nuclear Reprocessing Plant, with the highest activities occurring in the Esk estuary (closest to Sellafield) and lowest at the Welsh sites. Measurable activity concentrations of238 Pu and 239,240Pu were found in root mat samples from the Solway estuary to as far south as the Gwyrfai in Wales and showed an average238 Pu/239,240Pu ratio of 0.2, consistent with Sellafield-derived Pu. The ratios of137 Cs/241Am increased with distance from the source, with values of 1:1 in estuaries near Sellafield to ratios between 2 and 5 in estuaries further south and in excess of 10:1 in Wales. This is probably due to the more rapid movement of dissolved137 Cs in Irish Sea waters compared with the actinides. In contrast, 241Am and 239,240Pu behave similarly with consistent ratios of between 2:1 and 3:1, as both are associated with particulates. Dose assessment calculations suggest that external exposure would be a maximum of 530 µSv at the most contaminated spot at the Esk estuary. Relatively lower doses arise from the ingestion of animal products (along the soil-vegetation-grazing animal pathway) due to the low availability of sediment-associated radionuclides for gut transfer. The dose assessment calculations highlight the importance of using the appropriate transfer parameters that take into account this low bioavailability.

Ingestion of milk contaminated by radioiodine (most especially 131 I) represents an important potential route of radiation exposure to humans in the event of a nuclear accident. Oral administration of stable iodine to dairy ruminants has previously been suggested as an effective countermeasure to reduce radioiodine levels in milk. However, previous data on its effectiveness are contradictory, and little attention has been given to the most appropriate time to administer stable iodine relative to the time that an animal is first exposed to radioiodine. The effectiveness of 1g KI orally administered to lactating goats 12 h before and 12 h after contamination with pulse doses of radioiodine was investigated. Administration of KI prior to the ingestion of radioiodine was shown to reduce the transfer to milk by 50% compared to a reduction of approximately 40% when KI was administered 12 h after radioiodine. The administration of KI 12 h prior to radioiodine contamination effectively reduced the transfer of radioiodine to the thyroid by approximately 90%. When administered 12 h after radioiodine, the KI stopped subsequent uptake of radioiodine by the thyroid. The maximum level of iodine in milk, as a consequence of the administration of KI, was 20 mg I kg −1 . This was 40-fold higher than the maximum permissible level of iodine in milk of 0.5 mg l −1 currently set in some countries. Further consideration is required on stable iodine administration regimes for different scenarios and the consequent increase in the stable iodine content of the milk of different dairy animals.

In a study of transfer of Chernobyl radiocaesium to man, dietary surveys and whole body monitoring were conducted at two sites in the Bryansk Region of the Russian Federation. Radiocaesium activity concentrations in wild food products, especially mushrooms, were higher than those in agricultural products. The surveys revealed that consumption of highly contaminated wild mushrooms provided a significant contribution to ingested radiocaesium, accounting for 20–40% of the variability of radiocaesium activity concentrations in rural populations 8–9 years after the 1986 accident. Consumption of mushrooms was also the main reason for a 60–70% mean increase in radiocaesium activity concentrations in humans in autumn. Long term dose assessments after accidental releases of radiocaesium should therefore consider the potential contribution by mushrooms to ingested dose.

Following a large-scale release of radioactivity into the environment, food production systems and inhabited areas may be contaminated for many years. Accident response throughout Europe has tended to focus on management of the early phase, addressing issues such as evacuation, sheltering, restrictions on food and drinking water and provision of stable iodine tablets. Currently there is little systematic consideration of the long-term management to ensure the sustainability of contaminated areas. To sustain acceptable living and working conditions in such areas it is necessary to construct practicable restoration strategies that take into account the views of a wide range of stakeholders. Under the auspices of the European Commission’s 5th Framework Programme, funding was provided for two complementary projects (FARMING1 and STRATEGY2) to develop strategies for maintaining agricultural production and safe food supplies in the long term through stakeholder consultation. The FARMING project, which started in November 2000, established a network of stakeholder groups in the UK, Finland, Belgium, France and Greece, involving more than 100 individual stakeholders. The five national groups belonging to the FARMING network have met regularly since 2000 to discuss and evaluate countermeasure strategies. Much of the information on countermeasures for food

Concentration ratios (CRwo-media) are used in most radioecological models to predict\ud whole-body radionuclide activity concentrations in wildlife from those in environmental media. This\ud simplistic approach amalgamates the various factors influencing transfer within a single generic value\ud and, as a result, comparisons of model predictions with site-specific measurements can vary by orders\ud of magnitude. To improve model predictions, the development of 'condition-specific' CRwo-media\ud values has been proposed (e.g. for a specific habitat). However, the underlying datasets for most\ud CRwo-media value databases, such as the wildlife transfer database (WTD) developed within the IAEA\ud EMRAS II programme, include summarised data. This presents challenges for the calculation and\ud subsequent statistical evaluation of condition-specific CRwo-media values. A further complication is\ud the common use of arithmetic summary statistics to summarise data in source references, even though\ud CRwo-media values generally tend towards a lognormal distribution and should, therefore, be\ud summarised using geometric statistics. In this paper, we propose a statistically-defensible and robust\ud method for reconstructing underlying datasets to calculate condition-specific CRwo-media values from\ud summarised data and deriving geometric summary statistics. This method is applied to terrestrial\ud datasets from the WTD. Statistically significant differences in sub-category CRwo-media values (e.g.\ud mammals categorised by feeding strategy) were identified, which may justify the use of these CRwomedia\ud values for specific assessment contexts. However, biases and limitations within the underlying\ud datasets of the WTD explain some of these differences. Given the uncertainty in the summarised\ud CRwo-media values, we suggest that the CRwo-media approach to estimating transfer is used with\ud caution above screening-level assessments.

Limitations of existing methods to describe the bioavailability of dietary radionuclides to ruminants (the transfer coefficient and apparent absorption coefficient) have led to the alternative suggestion of using the true absorption coefficient (A(t)). Various approaches to estimating A(t) for radiocaesium, involving the intravenous administration of a second isotope, are presented and discussed with reference to results from studies in which a range of radiocaesium sources were examined in sheep. Although estimates of A(t) differed between the sources, they were reasonably consistent between measurement techniques. Those methods which involved the estimation of endogenous faecal excretion of radiocaesium could be used with previously contaminated animals and did not require continuous administrations of radiocaesium isotopes, but gave unreliable results for sources of low bioavailability. Methods based on estimating the turnover rate of dietary radiocaesium through blood plasma were sufficiently sensitive to measure A(t) for the range of sources studied. However, they require previously uncontaminated animals and continuous administration of both isotopes for approximately 7 days. Bioavailability is more effectively measured as A(t) than as the transfer or apparent absorption coefficients since A(t) does not incorporate factors relating to the metabolism of radiocaesium in the tissues of the animal. The results of these studies show that differences in transfer coefficients between sheep and cattle and between sheep of differing ages are not due to variation in absorption across the gut. The potential for applying these approaches to other radioactive elements is discussed.

Cation exchange resin saturated with H+ and Ca2+ was used to extract Cs-137 from peat soil at two sites in Britain affected by Cs-137 deposition following the Chernobyl accident. The technique identified three classes of Cs-137, similar to those observed for K+ in soils: 'Fast', 'Intermediate' and 'Slow'. These classes are probably related to the selectivity for Cs-137 Of the cation exchange sites on the organic matter and the clay minerals, and to the structure of the soil. With one exception, most Cs-137 was in the 'Slow' form and was only very slowly released to the resins, if at all. However, there was enough Cs-137 in the 'Fast' and 'Intermediate' forms to contaminate pasture and thus grazing animals for some years. Based on the resin technique, it is estimated that contamination will persist for several decades in uplands contaminated at these activity concentrations.

The model of radiocaesium transfer to sheep presented by Galer et al. [1] provides reliable predictions only for sheep of a similar body weight to those used in the development of the model (approximately 30 kg). To extend the applicability of the model, it was necessary to re-parameterise it in terms of activity concentrations in tissues rather than total activities within them (although for gut compartments the use of activity has been retained). The rate coefficients for the new model have been estimated by fitting the model to the data used by Galer et al. [1] which was derived from a single “calibration” experiment. The new model was found to account for 94% of the observed variation in the data (n=42), a result similar to that obtained by Galer et al. [1]. The model has also been tested against data not used in its development but obtained from four separate experiments undertaken by three different laboratories. Good agreement between the predictions of the new model and observations was found for most circumstances and for several breeds of sheep with different body weights. It is concluded that the new model provides a useful dynamic description of radiocaesium transfers to the tissues of sheep of different breeds and under different contamination scenarios.

The validity of an in vitro extraction technique to predict the availability for absorption of radiocaesium in the sheep gut has been assessed. The technique (a 2-h extraction with caesium chloride) was found to be valid for sources with a low availability for transfer across the gut, but inappropriate for ionic radiocaesium or radiocaesium incorporated internally within herbage. For such radiocaesium sources, which have a high in vitro availability, no correlation was found between in vitro extraction and true absorption measurements. A true absorption value of 0.80 is recommended for these sources, although values for individual sheep in the range 0.60 to 1.00 should be expected.

International audience; With intentions of integrating a portion of their respective research efforts into a trans-national programme that will enhance radioecology, eight European organisations recently formed the European Radioecology ALLIANCE (www.er-alliance.org). The ALLIANCE is an Association open to other organisations throughout the world with similar interests in promoting radioecology. The ALLIANCE members recognised that their shared radioecological research could be enhanced by efficiently pooling resources among its partner organizations and prioritising group efforts along common themes of mutual interest. A major step in this prioritisation process was to develop a Strategic Research Agenda (SRA). An EC-funded Network of Excellence in Radioecology, called STAR (Strategy for Allied Radioecology), was formed, in part, to develop the SRA. This document is the first published draft of the SRA. The SRA outlines a suggested prioritisation of research topics in radioecology, with the goal of improving research efficiency and more rapidly advancing the science. It responds to the question ". What topics, if critically addressed over the next 20 years, would significantly advance radioecology?" The three Scientific Challenges presented within the SRA, with their 15 associated research lines, are a strategic vision of what radioecology can achieve in the future. Meeting these challenges will require a directed effort and collaboration with many organisations the world over. Addressing these challenges is important to the advancement of radioecology and in providing scientific knowledge to decision makers. Although the development of the draft SRA has largely been a European effort, the hope is that it will initiate an open dialogue within the international radioecology community and its stakeholders. This is an abbreviated document with the intention of introducing the SRA and inviting contributions from interested stakeholders. Critique and input for improving the SRA are welcomed via a link on the STAR website (www.star-radioecology.org). © 2012 Elsevier Ltd.

An IAEA handbook presenting transfer parameter values for wildlife has recently been produced. Concentration ratios (CRwo-media) between the whole organism (fresh weight) and either soil (dry weight) or water were collated for a range of wildlife groups (classified taxonomically and by feeding strategy) in terrestrial, freshwater, marine and brackish generic ecosystems. The data have been compiled in an on line database, which will continue to be updated in the future providing the basis for subsequent revision of the Wildlife TRS values. An overview of the compilation and analysis, and discussion of the extent and limitations of the data is presented. Example comparisons of the CRwo-media values are given for polonium across all wildlife groups and ecosystems and for molluscs for all radionuclides. The CRwo-media values have also been compared with those currently used in the ERICA Tool which represented the most complete published database for wildlife transfer values prior to this work. The use of CRwo-media values is a pragmatic approach to predicting radionuclide activity concentrations in wildlife and is similar to that used for screening assessments for the human food chain. The CRwo-media values are most suitable for a screening application where there are several conservative assumptions built into the models which will, to varying extents, compensate for the variable data quality and quantity, and associated uncertainty. © 2012 Elsevier Ltd.

It is difficult to measure transfer of radiocaesium to the tissues of forest ruminants because they can potentially ingest a wide range of plant types. Measurements on undomesticated forest ruminants incur further difficulties. Existing techniques of estimating radiocaesium intake are imprecise when applied to forest systems. New approaches to measure this parameter are discussed. Two methods of intake estimation are described and evaluated. In the first method, radiocaesium intake is estimated from the radiocaesium activity concentrations of plants, combined with estimates of dry-matter (DM) intake and plant species composition of the diet, using plant and orally-dosed hydrocarbons (n-alkanes) as markers. The second approach estimates the total radiocaesium intake of an animal from the rate of excretion of radiocaesium in the faeces and an assumed value for the apparent absorption coefficient. Estimates of radiocaesium intake, using these approaches, in lactating goats and adult sheep were used to calculate transfer coefficients for milk and muscle; these compared favourably with transfer coefficients previously obtained under controlled experimental conditions. Potential variations in bioavailability of dietary radiocaesium sources to forest ruminants have rarely been considered. Approaches that can be used to describe bioavailability, including the true absorption coefficient and in vitro extractability, are outlined.

The transfer coefficient of 110mAg to a range of sheep tissues and its biological half-life in these tissues has been determined. Liver was shown to be the major site of 110mAg deposition and retention, with a transfer coefficient of Ff 7.1 d kg-1 and a biological half-life of 79 d. These results also suggest that previous estimates of the transfer of silver to muscle were too high, although further work would be required to confirm this. There is a need for accurate data which can be used to predict the transfer of 110mAg to food-producing animals.

Atmospheric testing of nuclear weapons began in 1945 and largely ceased in 1963. Monitoring of the resulting global fallout was carried out globally by the Environmental Measurements Laboratory and the UK Atomic Energy Research Establishment as well as at national level by some countries. A correlation was identified between fallout deposition and precipitation and an uneven distribution with latitude. In this study, the available data from 1954 to 1976 for 90 Sr and 137 Cs were reanalysed using analysis of covariance (ANCOVA) and logarithmically transformed values of the monthly deposition density as the response variable. Generalized additive models (GAM) were used to explore the relationship of different variables to the response variable and quantify the explanatory power that could be achieved. The explanatory variables which consistently explained most of the variability were precipitation at each site, latitude and change with time and a simple linear model was produced with similar explanatory power as the GAM. The estimates improved as the temporal resolution of the precipitation data increased. A good log–log fit could be obtained if a bias of about 1–6 mm precipitation per month was added, this could be interpreted as dry deposition which is not otherwise accounted for in the model. The deposition rate could then be explained as a simple non-linear power function of the precipitation rate ( r 0.2–0.6 depending on latitude band ) . A similar non-linear power function relationship has been the outcome of some studies linking wash-out and rain-out coefficients with rain intensity. Our results showed that the precipitation rate was an important parameter, not just the total amount. The simple model presented here allows the recreation of the deposition history at a site, allowing comparison with time series of activity concentrations for different environmental compartments, which is important for model validation.

Radiological doses to terrestrial wildlife were examined in this model inter-comparison study that emphasised factors causing variability in dose estimation. The study participants used varying modelling approaches and information sources to estimate dose rates and tissue concentrations for a range of biota types exposed to soil contamination at a shallow radionuclide waste burial site in Australia. Results indicated that the dominant factor causing variation in dose rate estimates (up to three orders of magnitude on mean total dose rates) was the soil-to-organism transfer of radionuclides that included variation in transfer parameter values as well as transfer calculation methods. Additional variation was associated with other modelling factors including: how participants conceptualised and modelled the exposure configurations (two orders of magnitude); which progeny to include with the parent radionuclide (typically less than one order of magnitude); and dose calculation parameters, including radiation weighting factors and dose conversion coefficients (typically less than one order of magnitude). Probabilistic approaches to model parameterisation were used to encompass and describe variable model parameters and outcomes. The study confirms the need for continued evaluation of the underlying mechanisms governing soil-to-organism transfer of radionuclides to improve estimation of dose rates to terrestrial wildlife. The exposure pathways and configurations available in most current codes are limited when considering instances where organisms access subsurface contamination through rooting, burrowing, or using different localised waste areas as part of their habitual routines.

Initial information since the releases of radioactive materials from the Fukushima Daiichi nuclear power plant, in Japan, shows that some animal food products are contaminated with 131I (mostly milk) and, to a lesser extent with 134Cs and 137Cs. Current knowledge on the transfer of these radioisotopes to animal products and available relevant countermeasures and management options to reduce radiation doses to humans are summarized. Much of this knowledge was obtained during the years of global fallout from atmospheric nuclear weapons tests and the response to the Chernobyl accident, in Ukraine in 1986.

The aim of the Relative Effectiveness of Agricultural Countermeasures Techniques workshop (REACT) was to provide a forum in which to evaluate current knowledge of different agricultural countermeasures. Initial decisions about the possible need for intervention in a particular area will be made at national or regional government level. The arguments that underlie these decisions were outside the remit of this workshop. Instead, attention was directed towards the basis for practical decisions about countermeasures that could be employed in a particular situation. Countermeasures differ, both in their effectiveness and their economic, ecological and social impact. In certain situations countermeasures developed before and since the Chernobyl accident have general applicability. However, this is not always the case and in general a fundamental understanding of the processes involved is needed to predict the effect that a given countermeasure might have under a range of different circumstances.

A sward will often have significant amounts of soil adhered to the vegetation surfaces which will be ingested by grazing animals. If the soil is contaminated by radioactive fallout then it can serve as a dietary source of radionuclides, in addition to any root uptake by the plants. This study is an attempt to quantitatively assess the importance of soil adhesion as a source of radiocaesium to sheep using the RUINS model which simulates radiocaesium transfer in grazing systems. The method of simulating the contamination of vegetation surfaces used by the RUINS model is described, and the importance of the availability of radiocaesium associated with adhered soil relative to plant incorporated radiocaesium discussed. Two sets of simulations are presented: one in which the soil is treated as a medium providing a uniform availability of radiocaesium, and the second in which account is taken of the partitioning of radiocaesium in the soil between ‘fixed’ and ‘labile’ phases. The results demonstrate that, because of the reduced absorption in the gut of radiocaesium associated with soil, animals grazing pastures with significant amounts of radiocaesium associated with adhered soil will not be as contaminated as radiocaesium activity concentrations measured in bulk vegetation samples would suggest. Therefore, the extent of soil adhesion needs to be considered if predictions of radiocaesium contamination of animal products are to be made on the basis of measured activities of sampled vegetation. However, soil adhesion is unlikely to be a significant dietary source of available radiocaesium, unless the soil concerned exhibits an unusually high bioavailability of radiocaesium. Moreover the simulation results indicate that differences in availability between soil types observed experimentally are consistent with the partitioning between fixed and labile soil compartments made by the RUINS model.

An experiment was carried out to provide a data set specifically designed to allow the development of a model to describe the dynamic behaviour of radiocaesium in sheep tissues. A single intraruminal dose of 134CsCl was given to each of 15 Scottish Blackface ewes, aged 1–2 years. Radiocaesium activity concentrations were measured at various time intervals after dosing in blood, faeces and urine and, after slaughter, in a range of tissues and digestive tract contents. A first order compartment model was developed comprising nine compartments representing various organs and tissues in the body. Rate constants for the model were obtained by optimisation to the experimental results. A limited validation of the model was carried out by using it to calculate tissue transfer coefficients (Ff) and biological half-lives (0.5) of radiocaesium in sheep. The values generated compare favourably with published figures. Applications for the model and constraints on its usage are examined along with possibilities for further development.

The transfer of 131I to sheep milk was measured in a controlled feeding experiment using herbage recently contaminated by fallout from the Chernobyl accident. The transfer coefficient (fm) of131I from the Chernobyl-contaminated herbage was 0·29±0·017 day litre−1. The daily proportion of 131I intake which was secreted in milk was 56±0·035%. This is an order of magnitude higher than for cattle and agrees with the higher transfer of stable iodine from plasma to milk which occurs in sheep and goats. At the same time the biological half-life of 131I was measured in ewes which had been grazing outside during deposition of the Chernobyl fallout and were then housed and fed an 131I-free diet. The loss of 131I in sheep milk was described using a double exponential relationship. The calculated biological half-life for the first component in the milk was 1 day, accounting for 97.4% of the reduction in the concentration of 131I activity in the milk. The 131I-free diet had a comparatively high stable iodine content since it was saltmarsh vegetation. however, the calculated half-life was similar to previously estimated values for goats. The transfer parameters presented here, which have been estimated using measured dietary intakes and milk outputs, appear to be the first such dates reported for sheep for an environmentally contaminated source.

Under the International Atomic Energy Agency (IAEA)'s EMRAS (Environmental Modelling for Radiation Safety) programme, activity concentrations of (60)Co, (90)Sr, (137)Cs and (3)H in Perch Lake at Atomic Energy of Canada Limited's Chalk River Laboratories site were predicted, in freshwater primary producers, invertebrates, fishes, herpetofauna and mammals using eleven modelling approaches. Comparison of predicted radionuclide concentrations in the different species types with measured values highlighted a number of areas where additional work and understanding is required to improve the predictions of radionuclide transfer. For some species, the differences could be explained by ecological factors such as trophic level or the influence of stable analogues. Model predictions were relatively poor for mammalian species and herpetofauna compared with measured values, partly due to a lack of relevant data. In addition, concentration ratios are sometimes under-predicted when derived from experiments performed under controlled laboratory conditions representative of conditions in other water bodies.

The outcome of the PROTECT project (Protection of the Environment from Ionising Radiation in a Regulatory Context) is summarised, focusing on the protection goal and derivation of dose rates which may detrimentally affect wildlife populations. To carry out an impact assessment for radioactive substances, the estimated dose rates produced by assessment tools need to be compared with some form of criteria to judge the level of risk. To do this, appropriate protection goals need to be defined and associated predefined dose rate values, or benchmarks, derived and agreed upon. Previous approaches used to estimate dose rates at which there may be observable changes in populations or individuals are described and discussed, as are more recent derivations of screening benchmarks for use in regulatory frameworks. We have adopted guidance and procedures used for assessment and regulation of other chemical stressors to derive benchmarks. On the basis of consultation with many relevant experts, PROTECT has derived a benchmark screening dose rate, using data on largely reproductive effects to derive species sensitivity distributions, of 10μGyh-1 which can be used to identify situations which are below regulatory concern with a high degree of confidence. © 2010 IOP Publishing Ltd.

Dose rate benchmarks are required in the tiered approaches used to screen out benign exposure scenarios in radiological ecological risk assessment. Such screening benchmarks, namely the predicted no-effect dose rates (PNEDR), have been derived by applying, as far as possible, the European guidance developed for chemicals. To derive the ecosystem level (or generic) PNEDR, radiotoxicity EDR10 data (dose rates giving a 10% effect in comparison with the control) were used to fit a species sensitivity distribution (SSD) and estimate the HDR5 (the hazardous dose rate affecting 5% of species with a 10% effect). Then, a multi-criteria approach was developed to justify using an assessment factor (AF) to apply to the HDR5 for estimating a PNEDR value. Several different statistical data treatments were considered which all gave reasonably similar results. The suggested generic screening value of 10 μGyh-1 (incremental dose rate) was derived using the lowest available EDR10 value per species, an unweighted SSD, and an AF of 2 applied to the estimated HDR5. Consideration was also given to deriving screening benchmark values for organism groups but this was not thought to be currently appropriate due to few relevant data being currently available. © 2010 IOP Publishing Ltd.

Environmental monitoring programs often measure contaminant concentrations in animal tissues consumed by humans (e.g., muscle). By comparison, demonstration of the protection of biota from the potential effects of radionuclides involves a comparison of whole-body doses to radiological dose benchmarks. Consequently, methods for deriving whole-body concentration ratios based on tissue-specific data are required to make best use of the available information. This paper provides a series of look-up tables with whole-body:tissue-specific concentration ratios for non-human biota. Focus was placed on relatively broad animal categories (including molluscs, crustaceans, freshwater fishes, marine fishes, amphibians, reptiles, birds and mammals) and commonly measured tissues (specifically, bone, muscle, liver and kidney). Depending upon organism, whole-body to tissue concentration ratios were derived for between 12 and 47 elements. The whole-body to tissue concentration ratios can be used to estimate whole-body concentrations from tissue-specific measurements. However, we recommend that any given whole-body to tissue concentration ratio should not be used if the value falls between 0.75 and 1.5. Instead, a value of one should be assumed.

The uptake into vegetation of radiocaesium originating from the Chernobyl accident and from previous sources was compared at two upland sites in west Cumbria during November/December 1989. Both sites were in an area where restrictions are in place on the movement and slaughter of sheep due to high radiocaesium activities, and were known to have received comparatively high levels of deposition from both the 1957 Windscale accident and weapons fallout. The proportion of Chernobyl derived radiocaesium in the total radiocaesium inventory at each site was estimated using a 134Cs:137Cs ratio of 0–53 in Chernobyl fallout. Aged radiocaesium, mostly present for over 20 years, accounted for 59 ± 2·3 and 44 ± 2·8% (mean ± SE) of the 137Cs deposit at the two sites. Initially, after the Chernobyl accident, the transfer of the recently deposited radiocaesium was reported to be greater than that of aged deposits. However, four years after the accident, the extent of transfer of Chernobyl radiocaesium from the top 4 cm of soil to vegetation is now similar to that of the aged radiocaesium. The similarity in behaviour of Chernobyl derived and aged radiocaesium suggests that future reductions in radiocaesium levels in vegetation, and therefore in sheep, will be slow. The total deposit, measured per square metre down to bedrock or 40 cm. of aged radiocaesium was less available for plant uptake than that from Chernobyl. This is because a greater proportion of the earlier deposit has migrated further down the soil profile. The movement of Chernobyl radiocaesium down the soil profile and its radioactive decay will be the two major factors which contribute to its decline in vegetation and hence sheep.