Radiation effects in the forest ecosystems: Acute irradiation.

The paper comprehensively brings together key data on radiation effects observed in the Russian studies with an acute forest irradiation. The experiments were based on the ecosystem approach, including an assessment of the radiation impacts based on a variety of the endpoints. The effects at the cellular level were observed at the lowest doses: a double increase of the chromosome aberrations in the apical meristem of pine were found at the site with the absorbed dose of 2.5 Gy. The effects at the tissues levels and trees mortality expressed in D50 were revealed for the trees received 20-50 Gy and a double reduction in a net primary radioactivity was observed at the doses of 14-38 Gy for pine and 280-750 Gy for birch. The seasonal differences in radiosensitivity of the forest ecosystems were noted: the radiosensitivity of the irradiated trees was 3-5 fold higher after the spring irradiation than that after autumn irradiation. An importance of the ecosystem endpoints is emphasized.

Optimising sampling strategies for emergency response: Vegetation sampling.

The lessons learned from the plant sampling campaigns implemented in the most Chernobyl affected countries are described. The variability of 137Cs activity concentrations in plants taken from a variety of sampling sites, as well as the uncertainties around the aggregated transfer factors (Tag) from soil to plants were estimated. The sampling sites covered both agricultural and natural lands in different landscapes: floodplain, plains, and watershed meadows. To determine parameters of the lognormal distribution of the 137Cs activity concentration in plants and the values of corresponding aggregated transfer factor (Tag) values, from 25 to 49 plant and soil samples were collected at each sampling site with the grid increment that varied from 1 to 10 m. The gradients of deposition i.e. monotonic changes (trends) of the contamination density conditioned by the global (in respect to study area) gradient of fallout were not observed in any of the study sites. Therefore, the variability of radionuclide contamination density (and activity concentrations in the soil) within the study sites were determined by only random factors such as microheterogeneity of radioactive deposition in a sampling point. The mean standard deviation of the logarithms of 137Cs activity concentrations in plants sampled in all such sites and the corresponding transfer factors were similar for all sites studied and were not dependent on the mean soil contamination density at the site, the type of radioactive fallout and the vegetation type. The values of the average standard deviation of the 137Cs activity concentration logarithms in plants and the corresponding transfer factors for the vegetation sampling area ≥1 m2 and the relative activity measurement uncertainties ≤10% were estimated as 0.4 ± 0.1 and 0.5 ± 0.1, respectively. A new simple method for optimization of the number of linked (conjugated) plant and soil samples as well as estimates of the activity concentration and transfer factor uncertainties when measuring composite samples were proposed. Based on the results of these studies, the recommendations were made to the sampling of plants for radionuclides.

Monitoring in animal breeding in response to nuclear or radiological emergencies: Chernobyl experience.

The main techniques of animal product sampling used in different time periods after the Chernobyl accident are summarised and lessons learned from this analysis are presented. It was shown that simple instruments for measurement γ-radiation in the environment can also be effectively implemented for measurement of γ-emitters in animal products even though these were not originally developed to measure radioactivity in food. The lessons learned related to the major tasks of the monitoring such "what to sample", "where to sample" and "when to sample". The role and example of application of supplementary data on radionuclide of concern properties for sampling planning are also discussed. Based on the statistical analysis of the data obtained in the affected settlement it was shown that radionuclide concentration in the animal products can be fitted by the log-normal distributions whilst the dispersion of the logarithms of the activity 137Cs concentrations in milk is not dependent on the local settlement specific factors. Based on these findings the novel approach for justification of the number of samples that should to be taken to obtain the GM estimate with predefined precision for given variability of the data is suggested.

Effects of radiation on radial growth of Scots pine in areas highly affected by the Chernobyl accident.

The effects of radiation on radial growth of Scots pine (Pinus sylvestris L.) affected by the Chernobyl accident were studied at five sites with different deposition levels. The study sites were chosen along a high gradient of depositions at the distance of a few hundred meters in the forests with similar forest characteristics. Air dose rates varied at the sites from the background values up to 30 µGy h-1 as of December 1, 2016. Scots pine trees exposed to sub-lethal doses of 8.6-13.2 Gy at the "Red Forest" site did not demonstrate deviations in formation of annual rings 30 years after the Chernobyl accident compared to trees with lower doses and control trees. Variation with time in annual rings thickness did reveal that the effect of radiation in trees growing at the sites with different contamination not detectable in 1986 and 1987. Conversely, the effects were clear observed in a later period in 1989-1991, i.e. 3-5 years after the accident. Until 2000, there were statistically significant differences in the annual rings growth rates of Scots pine trees exposed to external absorbed dose rates of 4.4-6.7 mGy h-1 as estimated for June 1, 1986 (or 19.5-30.0 µGy h-1 as of December 1, 2016) compared with the trees of the other sites studied. The results comply with the conclusions from research with acute pine exposure conducted in the Kyshtym area in 1975-1984.

Optimising sampling strategies for emergency response: Soil sampling.

The novel approach for optimising soil sampling strategies in areas affected by radionuclides is suggested. Major factors influencing the efficiency of soil sampling strategies, including (number of samples, sampling area size, sampling depth and spatial resolution of the sample sites are examined to provide optimisation of the soil sampling plan. The experimental field studies to validate the suggested approach were performed in 25 sampling units ranging from 1.2 × 1.2 m to 60 × 60 m size. The sampling units were selected on arable farmlands, natural meadow and former agricultural land), as well as coniferous and deciduous forests with contamination density of 137Cs ranging from 2.8 kBq·m-2 to 24.5 MBq·m-2. The studied areas were contaminated by both the global fallout and the Chernobyl radioactive particles of different types. To determine the values of standard deviation of the log of the soil contamination density of 137Cs, 25 to 256 soil samples were collected with an increment of 0.07-10 m within each sampling unit. It was found that the values of standard deviation of the log of the soil contamination density of 137Cs were not dependent on the mean contamination density, the type of radioactive deposition and the landscape features. The mean value of standard deviation calculated for all sites studied was estimated as 0.44 ± 0.15 and 0.30 ± 0.10 for the sampling area 0.001 m2 (∅37 mm) and 0.005 m2 (∅80 mm) at the relative measurement uncertainties lower than 10% (CI = 95%). Concentrations of 137Cs in the soil samples were statistically independent when sampling points were situated at a distance larger than 1 m one from each other. A simple method was developed for assessing minimum sample sizes required for estimation of the median or the geometric mean of radionuclide soil contamination with a relative uncertainty set by the user. The approach was also suggested for estimation of the uncertainty of soil contamination for the case of composite samples. The approach was implemented in the Ukrainian national requirements for assessment of quality of the soil.

Environmental behaviour of radioactive particles: Transfer to animals.

Field data on behaviour of artificial polydisperse radioactive silica particles in the components of the cattle food chain are presented. The model fused radioactive particles reproduced the spherical shape of particles in the local deposition during nuclear tests, including their specific gravity and polydispersity. It is shown that the composition of radioactive particles entering the body of animals differs from those initially deposited on the surface of pasture grass. The intake of particles into the body of animals decreased with increasing particle size. The intake for particles of 400-800 µm was about 10 times lower than that for fine particles sized 0-100 µm. It was found that the excretion rate of radioactive particles from the animal body also depends on particle size. The deposition of radioactive particles on the fundal surface of the wall of the ventral rumen sac and reticulum, as well as the long-term retention of radioactive particles of all sizes in the abomasum was noted. This can result in substantial damage in the GIT system, in particular, in these parts of the cattle digestive tract the focal ulcerative lesions of the mucous membrane can be formed by « hot ¼ radioactive particles.

Review of Russian research with radioactive particles: Foliar uptake.

Studies performed in the former Soviet Union were reviewed to provide interception and weathering values for radioactive particles. None of these studies were available in the English language literature before or were considered in the international reviews. The estimated mass interception fractions ranged 0.2-1.4 m2 kg-1 may be explained by the size of the particles used in the research. The interrelationships among the interception fractions, plants biomass and size of radioactive particles were determined for different plants: spring and winter wheat, maize, rice, pasture and sown grass. A filtration model rather accurately approximated data for pasture grass and some other crops but does not reflect properly patterns of the interception fraction dependence on biomass for perennial sown grass. The values derived have been compared with some expected values reported by the IAEA's Handbook of parameter values for the prediction of radionuclide transfer in temperate environments (TRS 472) where possible. The information presented can be used in the current updating of parameters recommended for environmental impact assessments.

Review of radiation effects in non-human species in areas affected by the Kyshtym accident.

The area affected by the Kyshtym accident in 1957 provided a unique opportunity for long-term studies of radiation effects in the environment. The biological effects observed in the area varied from deterministic lethal effects to an enhanced rate of mutations induced by radiation. This paper provides a comprehensive review of the long-term studies of biological effects in plants and animals inhabiting the Kyshtym affected areas over more than 50 years. Most of the observed effects were induced by the high irradiation during the 'acute' period after the accident. At the same time, some of the radiation effects were also because of long-term chronic exposure over many generations. Some phenomena such as (1) the increase of the mutation rate per unit dose with reduction of dose and dose rate, and (2) the radiodaptation of the affected populations to the chronic exposure were documented for the first time based on the radiobiological research performed in that area.

Review of Russian language studies on radionuclide behaviour in agricultural animals: Transfer to animal tissues.

Data on radionuclide transfer to animals from research performed in the former Soviet Union were reviewed to collate transfer coefficient values (Ff) to animal tissues such as liver, kidney and bone, but not muscle which has previously been reported. The derived values were compared with selected data published in the English language literature. The new data are mainly for 90Sr and 137Cs, although some data were also provided for 3H, 54Mn, 59Fe, 60Co, 22Na 65Zn, 131I and U. The Russian language data may provide a basis for better informed evaluation of radiation dose from the consumption of such animal products, which can form important components of the diet in some countries.

Harmonisation of standards for permissible radionuclide activity concentrations in foodstuffs in the long term after the Chernobyl accident.

The article critically examines the practice of post-Chernobyl standardisation of radionuclide concentrations (mainly 137Cs and 90Sr) in food products (FPs) in the USSR and the successor countries of Belarus, Russia and Ukraine. Recommendations are given on potential harmonisation of these standards of radionuclide concentrations in FPs among the three countries, taking into account substantial international experience. We propose to reduce the number of product groups for standardisation purposes from the current amount of several dozens to three to five groups to optimise radiation control and increase the transparency of the process. We recommend five product groups for the standardisation of 137Cs and three groups for 90Sr in food in radiocontaminated areas. The values of standards for individual product groups are recommended to be set proportionally to the measured specific activity in each of these groups, which will reduce unreasonable food rejection. The standards might be set for the entire country, and could be also used to control imports from other countries as well as exports to other countries. The developed recommendations were transferred in 2015-2016 to the regulatory authorities of the three countries.

Thirty years after the Chernobyl accident: What lessons have we learnt?

April 2016 sees the 30(th) anniversary of the accident at the Chernobyl nuclear power plant. As a consequence of the accident populations were relocated in Belarus, Russia and Ukraine and remedial measures were put in place to reduce the entry of contaminants (primarily (134+137)Cs) into the human food chain in a number of countries throughout Europe. Remedial measures are still today in place in a number of countries, and areas of the former Soviet Union remain abandoned. The Chernobyl accident led to a large resurgence in radioecological studies both to aid remediation and to be able to make future predictions on the post-accident situation, but, also in recognition that more knowledge was required to cope with future accidents. In this paper we discuss, what in the authors' opinions, were the advances made in radioecology as a consequence of the Chernobyl accident. The areas we identified as being significantly advanced following Chernobyl were: the importance of semi-natural ecosystems in human dose formation; the characterisation and environmental behaviour of 'hot particles'; the development and application of countermeasures; the "fixation" and long term bioavailability of radiocaesium and; the effects of radiation on plants and animals.

[Radiological Aspects of Transition of Russian Areas Affected by the Chernobyl Accident to Normal Activities].

Dynamics of radiation situation in settlements, agriculture and forestry on the Russian Federation areas af- fected by the Chernobyl accident is presented. A set of challenging problems on public radiation protection and rehabilitation of territories was determined. The main objective at a long-term period after the accident is a stage-wise return of the affected areas to normal activity without any radiological criteria restrictions. For practical realization of this process it is necessary to change the national statutes and regulations consid- ering the contemporary international approaches, to pass to the current exposure situation and to establish reference levels, to define criteria of transition of the areas affected after the Chernobyl accident to normal activity. The change of conceptual approaches will allow one to revise the boundaries of settlement zoning and to develop the regulatory framework on procedures of changing their status from radioactively contami- nated zone to normal activity zone; to develop the regulatory framework on the procedures of transition of agricultural and forest lands classified as radioactively contaminated zones to territories where the traditional husbandry is possible. The Russian Federation has positive experience of transition of areas contaminated as a result of the Chernobyl accident to normal activity.

Radionuclide biological half-life values for terrestrial and aquatic wildlife.

The equilibrium concentration ratio is typically the parameter used to estimate organism activity concentrations within wildlife dose assessment tools. Whilst this is assumed to be fit for purpose, there are scenarios such as accidental or irregular, fluctuating, releases from licensed facilities when this might not be the case. In such circumstances, the concentration ratio approach may under- or over-estimate radiation exposure depending upon the time since the release. To carrying out assessments for such releases, a dynamic approach is needed. The simplest and most practical option is representing the uptake and turnover processes by first-order kinetics, for which organism- and element-specific biological half-life data are required. In this paper we describe the development of a freely available international database of radionuclide biological half-life values. The database includes 1907 entries for terrestrial, freshwater, riparian and marine organisms. Biological half-life values are reported for 52 elements across a range of wildlife groups (marine = 9, freshwater = 10, terrestrial = 7 and riparian = 3 groups). Potential applications and limitations of the database are discussed.

Review of Russian language studies on radionuclide behaviour in agricultural animals: biological half-lives.

Extensive studies on transfer of radionuclides to animals were carried out in the USSR from the 1950s. Few of these studies were published in the international refereed literature or taken into account in international reviews. This paper continues a series of reviews of Russian language literature on radionuclide transfer to animals, providing information on biological half-lives of radionuclides in various animal tissues. The data are compared, where possible, with those reported in other countries. The data are normally quantified using a single or double exponential accounting for different proportions of the loss. For some products, such as milk, biological half-lives tend to be rapid at 1-3 d for most radionuclides and largely described by a single exponential. However, for other animal products biological half-lives can vary widely as they are influenced by many factors such as the age and size of the animal. Experimental protocols, such as the duration of the study, radionuclide administration and/or sample collection protocol also influence the value of biological half-lives estimated.

Radionuclide transfer from feed to camel milk.

The transfer of (137)Cs, (85)Sr, (131)I, (210)Po, (210)Pb and (238)U from feed to camel's milk was investigated in a pilot experiment with three lactating camels. For a period of 60 days, the animals were fed on spiked feed containing the studied radionuclides. They were subsequently returned to a contamination-free diet and monitored for another 90 days. The activity concentrations of (137)Cs, (85)Sr and (131)I in milk decreased with time and reached background levels after 20 days. Equilibrium transfer coefficients and biological half-lives were estimated and transfer coefficients were calculated as (8.1 ± 3.6) × 10(-4), (4.4 ± 1.6) × 10(-2), (7.8 ± 3.9) × 10(-4), (2.7 ± 3.5) × 10(-4), (1.8 ± 1.5) × 10(-4) and (7.0 ± 3.6) × 10(-3) d L(-1) for (85)Sr, (131)I, (137)Cs, (210)Po, (210)Pb and (238)U, respectively. The biological half-lives were estimated to be 6.4, 4.2, 8.9, and 53.3 days for (85)Sr, (131)I, (137)Cs, and (238)U, respectively. Estimates of the half-lives were based on a one component model: it was found that the half-life values measured for artificial radionuclides were slightly shorter than those for natural radionuclides. The data obtained in the study are the first published experimental data on radionuclide transfer to camel milk.

A new approach to predicting environmental transfer of radionuclides to wildlife: a demonstration for freshwater fish and caesium.

The application of the concentration ratio (CR) to predict radionuclide activity concentrations in wildlife from those in soil or water has become the widely accepted approach for environmental assessments. Recently both the ICRP and IAEA have produced compilations of CR values for application in environmental assessment. However, the CR approach has many limitations, most notably, that the transfer of most radionuclides is largely determined by site-specific factors (e.g. water or soil chemistry). Furthermore, there are few, if any, CR values for many radionuclide-organism combinations. In this paper, we propose an alternative approach and, as an example, demonstrate and test this for caesium and freshwater fish. Using a Residual Maximum Likelihood (REML) mixed-model regression we analysed a dataset comprising 597 entries for 53 freshwater fish species from 67 sites. The REML analysis generated a mean value for each species on a common scale after REML adjustment taking account of the effect of the inter-site variation. Using an independent dataset, we subsequently test the hypothesis that the REML model outputs can be used to predict radionuclide, in this case radiocaesium, activity concentrations in unknown species from the results of a species which has been sampled at a specific site. The outputs of the REML analysis accurately predicted (137)Cs activity concentrations in different species of fish from 27 Finnish lakes; these data had not been used in our initial analyses. We recommend that this alternative approach be further investigated for other radionuclides and ecosystems.

The IAEA handbook on radionuclide transfer to wildlife.

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.

Establishing a database of radionuclide transfer parameters for freshwater wildlife.

Environmental assessments to evaluate potentials risks to humans and wildlife often involve modelling to predict contaminant exposure through key pathways. Such models require input of parameter values, including concentration ratios, to estimate contaminant concentrations in biota based on measurements or estimates of concentrations in environmental media, such as water. Due to the diversity of species and the range in physicochemical conditions in natural ecosystems, concentration ratios can vary by orders of magnitude, even within similar species. Therefore, to improve model input parameter values for application in aquatic systems, freshwater concentration ratios were collated or calculated from national grey literature, Russian language publications, and refereed papers. Collated data were then input into an international database that is being established by the International Atomic Energy Agency. The freshwater database enables entry of information for all radionuclides listed in ICRP (1983), in addition to the corresponding stable elements, and comprises a total of more than 16,500 concentration ratio (CRwo-water) values. Although data were available for all broad wildlife groups (with the exception of birds), data were sparse for many organism types. For example, zooplankton, crustaceans, insects and insect larvae, amphibians, and mammals, for which there were CRwo-water values for less than eight elements. Coverage was most comprehensive for fish, vascular plants, and molluscs. To our knowledge, the freshwater database that has now been established represents the most comprehensive set of CRwo-water values for freshwater species currently available for use in radiological environmental assessments.