Will global warming affect soil-to-plant transfer of radionuclides?

Recent assessments of global climate/environmental change are reaching a consensus that global climate change is occurring but there is significant uncertainty over the likely magnitude of this change and its impacts. There is little doubt that all aspects of the natural environment will be impacted to some degree. Soil-to-plant transfer of radionuclides has long been a significant topic in radioecology, both for the protection of humans and the environment from the effects of ionising radiation. Even after five decades of research considerable uncertainty exists as to the interplay of key environmental processes in controlling soil-plant transfer. As many of these processes are, to a lesser or greater extent, climate-dependent, it can be argued that climate/environmental change will impact soil-to-plant transfer of radionuclides and subsequent transfers in specific environments. This discussion attempts to highlight the possible role of climatic and climate-dependent variables in soil-to-plant transfer processes within the overall predictions of climate/environmental change. The work is speculative, and intended to stimulate debate on a theme that radioecology has either ignored or avoided in recent years.     

An overview of the ERICA Integrated Approach to the assessment and management of environmental risks from ionising contaminants

The ERICA project (environmental risks from ionising contaminants: assessment and management, EC contract no. FI6R-CT-2004-508847) concluded with the publication of two main outputs: the ERICA Integrated Approach to the assessment and management of environmental risks from ionising radiation, of which also introduces the user to the second main output, the ERICA Tool, which is a software programme with supporting databases, that together with its associated help will guide users through the assessment process. More than 60 European scientists contributed to the ERICA Integrated Approach. In addition, a large number of experts, policy makers, and decision-makers in different areas have contributed views on the ERICA Integrated Approach and its associated Tool from the user's perspective, through participation in the End-Users Group set up under the ERICA project. Databases on transfer, dose conversion coefficients and radiation effects on biota have been developed specifically for the purpose of the Integrated Approach, and incorporated into, or interacting with, the Tool. Species sensitivity distributions of biological effects data have been performed and did not reveal, for chronic exposure, any statistical grounds for separation between terrestrial, marine and freshwater ecosystems in terms of species sensitivity to radiation; on the basis of such analysis a universal screening dose rate criterion of 10 microGy h(-1) incremental dose rate is suggested for exiting the assessment procedure while being confident that environmental risks are negligible. This criterion is used for the two first tiers (conservative assessment with limited data requirement and various possibilities of incorporating user-defined parameter values, including the screening dose rate criterion) of the assessment methodology. Exposure situations of concern are carried through a third tier, making use of all relevant databases and with a number of issues and options listed to support and guide decision-making. This article provides an overview to the ERICA Integrated Approach, whereas further articles of this special issue describe in-depth different vital aspects of the Integrated Approach.     

Soil availability,plant uptake and soil to plant transfer of 99Tc--a review

The fission yield of 99Tc from 239Pu and 235U is similar to that of 137Cs or 90Sr and it is therefore an important component of nuclear weapons fall-out, nuclear waste and releases from nuclear facilities. There is particular current interest in 99Tc transfer from soil to plants for: (a) environmental impact assessments for terrestrial nuclear waste repositories, and (b) assessments of the potential for phytoextraction of radionuclides from contaminated effluent and soil. Vascular plants have a high 99Tc uptake capacity, a strong tendency to transport it to shoot material and accumulate it in vegetative rather than reproductive structures. The mechanisms that control 99Tc entry to plants have not been identified and there has been little discussion of the potential for phytoextraction of 99Tc contaminated effluents or soil. Here we review soil availability, plant uptake mechanisms and soil to plant transfer of 99Tc in the light of recent advances in soil science, plant molecular biology and phytoextraction technologies. We conclude that 99Tc might not be highly available in the long term from up to 50% of soils worldwide, and that no single mechanism that might be easily targeted by recombinant DNA technologies controls 99Tc uptake by plants. Overall, we suggest that Tc might be less available in terrestrial ecosystems than is often assumed but that nevertheless the potential of phytoextraction as a decontamination strategy is probably greater for 99Tc than for any other nuclide of radioecological interest.     

The ecological relevance of current approaches for environmental protection from exposure to ionising radiation

This paper discusses the current approaches to environmental protection from ionising radiation from an ecological perspective, highlighting the need to understand fully what we are trying to protect. Ecologically relevant endpoints for environmental protection are discussed along with the need to integrate protection from ionising radiation with the approaches adopted for non-radioactive contaminants. A possible integrated assessment approach is outlined.     

Challenges in radioecology

Today, radioecology covers a broad scientific field; from the source to long term environmental impact from ionizing radiation. To summarize key challenges within radioecology, the present paper focuses upon knowledge gaps related to processes, mechanisms and variables contributing most to the overall uncertainties in environmental impact assessments. A series of sources related to the nuclear weapon cycle and the civil nuclear cycle has contributed, is still contributing or can potentially contribute to release of radionuclides to the environment in the future. The speciation of most radionuclides depends on the source and release conditions, and will influence ecosystem transport, biological uptake, doses and effects in flora and fauna. Radionuclides may also co-occur in contaminant mixtures (e.g., metals, organics), which potentially could lead to synergisms or antagonisms. Thus, challenges associated with the links between the source or release term – radionuclide speciation – ecosystem transfer – exposure – response relationships are highlighted.     

Assessment of radiological effects on the regional environment due to the operation of the Tokai Reprocessing Plant

The regional environmental radiological effects were assessed for the past 25-year operation of the Tokai Reprocessing Plant (TRP). The assessment was basically performed with the environmental radiological monitoring data around the TRP. For the environmental monitoring, various kinds of terrestrial and marine samples including air dust, surface soil, polished rice grain, leafy vegetable, milk, seawater, seabed sediments, fish, shellfish and seaweed were collected in the surrounding environment of the TRP. Radionuclides such as (3)H, (14)C, (90)Sr, (137)Cs and (239,240)Pu in the environmental samples were determined by radiochemical methods. However, they showed no significant short-term increase or long-term accumulation of radionuclides discharged from the TRP. Therefore, the public dose was evaluated using the mathematical models and the discharge data of radionuclides. The estimated annual effective dose for the public was about 0.1% of the annual effective dose limit recommended by the ICRP. The assessment showed that there were no significant radiological effects on the environment and the public due to the 25-year operation of the TRP.     

Protection of the environment from ionising radiation: ethical issues

The paper identifies some of the main ethical issues concerning the protection of the environment from radiation and suggests ways in which ethics can aid in developing a system of protection. After a presentation of background on ethical theory and environmental ethics, three main issues related to environmental protection are discussed: First, the question of valuing the environment and implications for the definition of harm and monetary valuation of environmental goods; second, difficulties with scientific uncertainty and applications of the precautionary principle; and third, issues concerned with the distribution of risk and its relevance for participation in decision-making. In summary, the paper argues that there are strong ethical grounds to provide for the protection of the environment and that, all other things being equal, there is no reason to treat ionising radiation differently to other environmental stressors.     

Assessing potential secondary effects of countermeasures in agricultural systems: a review.

Secondary effects are defined as any positive or negative impacts resulting from the application of countermeasures other than radiological benefits or direct costs. They are categorised into environmental, radioecological, economic and social effects. Impacts on the environment may include changes in water, air and soil pollution or in the conservation and amenity value of an area. Radioecological effects occur when the countermeasure unintentionally alters the behaviour of the target radionuclide or any other radionuclide present. Economic effects may range from changes in agricultural income to environmental costs (e.g. impact of soil erosion on fisheries). Social effects relate to the acceptability of countermeasures, for example in terms of consumer confidence and animal welfare. Recent research into the identification and assessment of secondary effects is summarised. Non-quantitative and quantitative approaches are explained and formal evaluation procedures involving decision matrices and decision support systems are introduced. Examples of recent experimental and modelling work focusing on radiocaesium are given for the following countermeasures: soil application of potassium, administration of AFCF to livestock and ploughing techniques.     

Regulation of nuclear radiation exposures in India

India has a long-term program of wide spread applications of nuclear radiations and radioactive sources for peaceful applications in medicine, industry, agriculture and research and is already having several thousand places in the country where such sources are being routinely used. These places are mostly outside the Department of Atomic Energy (DAE) installations. DAE supplies such sources. The most important application of nuclear energy in DAE is in electricity generation through nuclear power plants. Fourteen such plants are operating and many new plants are at various stages of construction. In view of the above mentioned wide spread applications, Indian parliament through an Act, called Atomic Energy Act, 1964 created an autonomous body called Atomic Energy Regulatory Board (AERB) with comprehensive authority and powers. This Board issues codes, guides, manuals, etc., to regulate such installations so as to ensure safe use of such sources and personnel engaged in such installations and environment receives radiation exposures within the upper bounds prescribed by them. Periodic reports are submitted to AERB to demonstrate compliance of its directives. Health, Safety and Environment Group of Bhabha Atomic Research Centres, Mumbai carries out necessary surveillance and monitoring of all installations of the DAE on a routine basis and also periodic inspections of other installations using radiation sources. Some of the nuclear fuel cycle plants like nuclear power plants and fuel reprocessing involve large radioactive source inventories and have potential of accidental release of radioactivity into the environment, an Environmental Surveillance Laboratory (ESL) is set up at each such site much before the facility goes into operation. These ESL's collect baseline data and monitor the environment throughout the life of the facilities including the decommissioning stage. The data is provided to AERB and is available to members of the public. In addition, a multi-tier system of AERB permissions is in place to ensure that all aspects of safety have been considered before permission to operate is granted. The stages where permission of AERB is essential are site selection, design data, and several stages during construction and operation. The details required by AERB include provision for treatment and storage of radioactive waste, de-commissioning procedures and provision of costs. In addition to AERB, nuclear power plants have to comply with the requirements of Ministry of Environment and Forests and get their clearance. This is given on the basis of Environmental Impact Assessment Report which should satisfy the authorities that no ecological damage will be caused and the facility will not have adverse effect on the environment. In addition, the State Pollution Control Board where the facility is to be located has to permit the site of the plant for its proposed discharges into the environment. It is largely due to the above comprehensive regulatory controls that none of the plants in India had any accident during the last 34 decades of operation. The type of measurements carried out by the ESL's and results from a few typical ESL's will be presented.     

The concentration of Cs in the surface of the Greek marine environment

The radiological status of the Greek marine environment, prior to the Chernobyl accident, was characterized mainly by the fallout from nuclear weapon tests. However, the release of radioactivity into the environment from the accident in the Chernobyl Nuclear Power Plant and its deposition in the Greek marine environment resulted in an increase of the ¹³⁷Cs activity concentration by approximately one order of magnitude. In addition, the direct transport of radiocaesium into the North Aegean Sea has been further influenced by the late impact of the Chernobyl accident on the Greek marine environment, related to the transfer of ¹³⁷Cs, mainly through the Dnieper but also the Danube rivers, to the Black Sea and further to the North Aegean Sea through the Straits of Dardanelles. The aim of this work is to provide a present day picture of the geographic variation of the concentration of ¹³⁷Cs in the surface layer of the Greek marine environment and hence, to evaluate the annual committed effective dose delivered to humans through the ingestion pathway from marine sources.     

Environmental radioactivity and thermoluminescence: A review

A close link exists between environmental radioactivity and thermoluminescence (TL) and this connection can be gainfully employed in (i) environmental radiation surveillance, (ii) radioactive prospecting and (iii) dating. The science of thermoluminescence dosimetry (TLD) is very well established for use in routine radiation monitoring. With the increased public awareness of health effects due to radioactivity releases from nuclear operations. TLDs have become indispensible ‘watchdogs’ in environmental surveillance; in high natural background areas such as the monazite regions, TLDs have yielded invaluable dosimetric data. Over large areas where the cosmic background can be assumed constant, the TLD-recorded radiation profiles can reflected the terrestrial gamma radioactivity distribution pattern and even seasonal variations in the radiation levels above ground may be delineated. A variety of natural materials like minerals, rocks, soils, sands, sediments, fossils, etc., as well as ancient artefacts like potteries and ceramic wares, yield TL even without any irradiation in the laboratory: the natural radioactivity in these materials, together with the radiation incident on them from the environment, causes a TL build-up during antiquity. It is possible to measure this natural TL and relate it to the natural radioactivity of the sample and hence to its age. In contrast, observations of a kind of anticorrelation between TL and a sample's radioactivity have also been made in recent times and the effect is mostly ascribable to alpha-radioactivity-induced damage effects.Typical results from recent investigations of the various aspects mentioned above are presented in this review, with particular emphasis on applications in India.     

Radioactive particles in dose assessments

Radioactive particles present a novel exposure pathway for members of the public. For typical assessments of potential doses received by members of the public, habit surveys and environmental monitoring combine to allow the assessment to occur. In these circumstances it is believed that the probability of encounter/consumption is certain. The potential detriment is assessed through sampling the use of environmental monitoring data and dose coefficients such as that in ICRP 60 [ICRP, 1990. 1990 Recommendations of the international commission on radiological protection. Publication 60. Annals of the ICRP 21 (1-3)]. However, radioactive particles often represent a hazard that is difficult to quantify and where the probability of encounter is less than certain as are the potential effects on health. Normal assessment methodologies through sampling and analysis are not appropriate for assessing the impact of radioactive particles either prospectively or retrospectively. This paper details many of the issues that should be considered when undertaking an assessment of the risk to health posed by radioactive particles.     

Applying radioecology in a world of multiple contaminants

This paper presents a review of the current status of radioecology and how it might be applied to contribute to a broader range of environmental pollution and contamination problems. In many respects radioecology is a unique and specialised branch of environmental science. However, radioecologists could be much more aware of the similarities and differences between their field and other fields of environmental pollution science. Areas of common interest described herein are exposure and risk assessment, and the problem of the bioavailability of potentially toxic substances in environmental media. It is concluded that radiometric methods and radioecological modelling methods can assist significantly with understanding and quantifying both these issues. The existence of multiple contaminants at many locations around the world dictates that assessment and remediation exercises should be carried out in an integrated fashion, as a partnership between scientific disciplines.     

Performance of data acceptance criteria over 50 months from an automatic real-time environmental radiation surveillance network

The automatic real-time environmental radiation surveillance network of Catalonia (Spain) comprises two subnetworks; one with 9 aerosol monitors and the other with 8 Geiger monitors together with 2 water monitors located in the Ebre river. Since September 2006, several improvements were implemented in order to get better quality and quantity of data, allowing a more accurate data analysis. However, several causes (natural causes, equipment failure, artificial external causes and incidents in nuclear power plants) may produce radiological measured values mismatched with the own station background, whether spurious without significance or true radiological values. Thus, data analysis for a 50-month period was made and allowed to establish an easily implementable statistical criterion to find those values that require special attention. This criterion proved a very useful tool for creating a properly debugged database and to give a quick response to equipment failures or possible radiological incidents. This paper presents the results obtained from the criterion application, including the figures for the expected, raw and debugged data, percentages of missing data grouped by causes and radiological measurements from the networks. Finally, based on the discussed information, recommendations for the improvement of the network are identified to obtain better radiological information and analysis capabilities.     

Sector field inductively coupled plasma mass spectrometry, another tool for plutonium isotopes and plutonium isotope ratios determination in environmental matrices

The transfer of radio nuclides into the different compartments of the environment are widely studied and leads to the elaboration of transfer models in order to evaluate potential impact onto the environment and humans. Accurate experimental data are needed to validate these models for all types of matrices (air, water, sediments, soils, biota and food...). Among these radionuclides, 238Pu, 239Pu, 240Pu and 241Pu, are often mentioned. They have been released into the environment by nuclear weapon tests, nuclear facilities, reactors or satellite accidents. These different sources have different 240Pu/239Pu ratios and therefore this ratio is used to provide information on the source of contamination into the environment. The most conventional analytical tools used for plutonium isotope determination are liquid scintillation and alpha spectrometry, and thermal ionisation mass spectrometry (TIMS) is still considered as the primary method for determination of plutonium isotope ratios. During the last decade, mass spectrometers equipped with plasma ion sources and sector field analysers were developed and can offer now another alternative method for the accurate determination of isotope content and ratios of long-lived radionuclides in environmental samples. This paper presents and discusses the results obtained for 239Pu, 240Pu and 241Pu content and isotope ratios by sector field ICP-MS in different environmental matrices.     

The development and purpose of the FREDERICA radiation effects database

Any system for assessing the impact of a contaminant on the environment requires an analysis of the possible effects on the organisms and ecosystems concerned. To facilitate this, the FREDERICA radiation effects database has been developed to provide an online search of the known effects of ionising radiation on non-human species, taken from papers in the scientific peer reviewed literature. The FREDERICA radiation effects database has been produced by merging the work done on radiation effects under two European funded projects (FASSET and EPIC) and making the database available online. This paper highlights applications for the database, gaps in the available data and explains the use of quality scores to help users of the database determine which papers may benefit their research in terms of techniques and reproducibility.     

Addressing uncertainties in the ERICA Integrated Approach

Like any complex environmental problem, ecological risk assessment of the impacts of ionising radiation is confounded by uncertainty. At all stages, from problem formulation through to risk characterisation, the assessment is dependent on models, scenarios, assumptions and extrapolations. These include technical uncertainties related to the data used, conceptual uncertainties associated with models and scenarios, as well as social uncertainties such as economic impacts, the interpretation of legislation, and the acceptability of the assessment results to stakeholders. The ERICA Integrated Approach has been developed to allow an assessment of the risks of ionising radiation, and includes a number of methods that are intended to make the uncertainties and assumptions inherent in the assessment more transparent to users and stakeholders. Throughout its development, ERICA has recommended that assessors deal openly with the deeper dimensions of uncertainty and acknowledge that uncertainty is intrinsic to complex systems. Since the tool is based on a tiered approach, the approaches to dealing with uncertainty vary between the tiers, ranging from a simple, but highly conservative screening to a full probabilistic risk assessment including sensitivity analysis. This paper gives on overview of types of uncertainty that are manifest in ecological risk assessment and the ERICA Integrated Approach to dealing with some of these uncertainties.     

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.     

Cytogenetic dose-response and adaptive response in cells of ungulate species exposed to ionizing radiation

In the studies reported here, the micronucleus assay, a common cytogenetic technique, was used to examine the dose-responses in fibroblasts from three ungulate species (white-tailed deer, woodland caribou, and Indian muntjac) exposed to high doses of ionizing radiation (1-4 Gy of (60)Co gamma radiation). This assay was also used to examine the effects of exposure to low doses (1-100 mGy) typical of what these species experience in a year from natural and anthropogenic environmental sources. An adaptive response, defined as the induction of resistance to a stressor by a prior exposure to a small "adapting" stress, was observed after exposure to low doses. This work indicates that very small doses are protective for the endpoint examined. The same level of protection was seen at all adapting doses, including 1 radiation track per cell, the lowest possible cellular dose. These results are consistent with other studies in a wide variety of organisms that demonstrate a protective effect of low doses at both cellular and whole-organism levels. This implies that environmental regulations predicated on the idea that even the smallest dose of radiation carries a quantifiable risk of direct adverse consequences to the exposed organism require further examination. Cytogenetic assays provide affordable and feasible biological effects-based alternatives that are more biologically relevant than traditional contaminant concentration-based radioecological risk assessment.     

Proposal for new best estimates of the soil-to-plant transfer factor of U,Th, Ra,Pb and Po

There is increasing interest in radiological assessment of discharges of naturally occurring radionuclides into the terrestrial environment. Such assessments require parameter values for the pathways considered in predictive models. An important pathway for human exposure is via ingestion of food crops and animal products. One of the key parameters in environmental assessment is therefore the soil-to-plant transfer factor to food and fodder crops. The objective of this study was to compile data, based on an extensive literature survey, concerning soil-to-plant transfer factors for uranium, thorium, radium, lead, and polonium. Transfer factor estimates were presented for major crop groups (Cereals, Leafy vegetables, Non-leafy vegetables, Root crops, Tubers, Fruits, Herbs, Pastures/grasses, Fodder), and also for some compartments within crop groups. Transfer factors were also calculated per soil group, as defined by their texture and organic matter content (Sand, Loam, Clay and Organic), and evaluation of transfer factors' dependency on specific soil characteristics was performed following regression analysis. The derived estimates were compared with estimates currently in use.