The use of the IAEA MARIS database in determining the variability of sediment distribution coefficients in the marine environment and potential implications for marine dispersion modelling.

A prototype tool has been developed for deriving sediment distribution coefficients,Kd, in the marine environment by harvesting simultaneous measurements of activity concentrations of radionuclides in seawater and sediments based on the International Atomic Energy Agency's Marine Radioactivity Information System (MARIS). As a case study, theKdvariability in the Baltic Sea was investigated as this region has been extensively monitored by HELCOM since 1984 resulting in a comprehensive dataset with good spatial and temporal coverage and required ancillary parameters. The prototype tool was used to derive a dataset ofin-situapparentKd(a)values derived from measurements of seawater and sediment in quasi-equilibrium conditions from the Baltic Sea over a period of approximately 35 years. For Cs, a comprehensive analysis of the Baltic SeaKd(a)dataset was undertaken, focusing on the temporal trend ofKd(a)and comparing the results toKdvalues derived elsewhere. For Sr and Pu, for which there were fewer data records available a more rudimentary analysis was carried out. The CsKd(a)median values derived from137Cs data in this study were estimated to be 2154 l kg-1for seabed sediment and 10 000 l kg-1for suspended sediment. The value derived for seabed sediment is in good agreement with the previously recommended ocean margin CsKdvalue of 4000 l kg-1. The analysis demonstrated the important distinction in the Baltic Sea betweenKdvalues for seabed sediment and suspended sediments, which differed by an order of magnitude. The analysis also highlighted the dependence ofKdvalues on the variation in both the salinity of seawater and the type of seabed sediment. Such variability can significantly influence outcomes when modelling the behaviour of radionuclides in marine dispersion modelling.

An approach to identifying the relative importance of different radionuclides in ecological radiological risk assessment: Application to nuclear power plant releases.

There is a need to prioritise the requirements for data to assess the radiological risk for fauna and flora, as inevitable large data gaps occur due to the large number of combinations of radionuclides and organisms for which doses need to be assessed. The potentially most important dose-forming radionuclide-pathways combinations need to be identified to optimize filling these gaps. Few attempts have been made to classify the importance of isotopes with regard to radiation protection of the environment. A hierarchical approach is described here for radionuclides that are potentially present in generic ecosystems (freshwater, marine or terrestrial) and is applied for scenarios considering ecologically relevant chronic exposure. In each ecosystem, the top ten radionuclides that may contribute to doses were identified using a qualitative Chronic Hazard Index. Including quantitative aspects by incorporating discharge quantities changed the priority list, and increased the relative importance of radionuclides contributing most to the authorized releases of nuclear facilities (14C and 3H followed by 60C). The potentially most important dose-contributing radionuclides in the framework of environmental radiation protection under a chronic exposure situation included isotopes of about 20 elements. The five most important in order of decreasing importance were: carbon, hydrogen, caesium, cobalt and americium. Consideration of acute exposure situations was hampered by data gaps that were even greater than that for chronic exposure situations, so it was only possible to consider the feasibility of developing a consistent approach.

Changes in the Soil to Brown Rice Concentration Ratio of Radiocaesium before and after the Fukushima Daiichi Nuclear Power Plant Accident in 2011.

Radiocaesium (RCs) mobility in soil is initially relatively high when the nuclide first comes into contact with soil, after which the mobile fraction decreases with time due to RCs fixation to soil particles (aging effect). Consequently, the RCs activity concentration in plants grown in soil was expected to decrease with time after the Fukushima Daiichi nuclear power plant accident in 2011. In this study, we collated data on concentration ratios (CR) of RCs between brown rice grain and paddy soil and compared CR values reported for periods before and after the accident. For this purpose, soil and rice data were collected after the accident specifically from paddy fields that did not have additional potassium fertilizer added (for remediation purposes). The geometric mean rice/soil CR of RCs for all types of soil was 1.2 × 10-2 in 2011 ( n = 62) and by 2013 the value had declined to 3.5 × 10-3 ( n = 32), which was similar to that for 1995-2007 of 3.4 × 10-3 ( n = 120). The comparison suggests that the mean soil-to-rice grain concentration ratio had returned to that prevailing before the accident after less than three years. It was also confirmed that CR values for rice sampled from paddy fields were lower than those obtained from pot experiments.

A Comparison of Remediation After The Chernobyl and Fukushima Daiichi Accidents.

Extensive remediation was conducted on contaminated landscapes after the Chernobyl accident in 1986 and the Fukushima Daiichi accident in 2011. A comparison is made of a range of different features relevant to each accident including the characteristics of the contamination and the landscapes affected, the radiological criteria, the designation of areas to be remediated and the remediation measures adopted.

How knowledge of the gastrointestinal absorption of elements could be used to predict transfer to milk.

The quality and quantity of data used to derive transfer parameter values for milk are variable and there are many data gaps for elements/radionuclides which may need to be considered for risk assessment of the agricultural foodchain. There has been a recent focus on critically evaluating current methods to fill data gaps and on identifying extrapolation methods to derive suitable values for the elements, and particularly radioisotopes, with no or sparse data. The relationship between fractional absorption of elements in the ruminant gastrointestinal tract and transfer to milk has been explored to determine whether knowledge of the former can be used to predict the latter. A relationship has been derived between fractional absorption of elements and two empirical ratios commonly used to quantify transfer to milk; transfer coefficients (element concentration in milk divided by element daily intake) and concentrations ratios (concentration in milk divided by concentration in feed). We propose that fractional absorption may be used to predict the order of magnitude of the transfer to milk of elements/radionuclides for which no relevant data have yet been identified or collated.

The Time-Dependent Transfer Factor of Radiocesium from Soil to Game Animals in Japan after the Fukushima Dai-ichi Nuclear Accident.

Since the Fukushima Dai-ichi accident, monitoring of tissues from hunted game animals ensures compliance with the standard food limits for radionuclides in Japan. We quantified the transfer of (137)Cs from contaminated land to game animals using the Aggregated transfer factor (Tag = activity concentration in meat [Bq kg(-1) fw]/amount in soil [Bq m(-2)]) of (137)Cs for Asian black bear, wild boar, sika deer, green pheasant, copper pheasant and wild duck, collected between 2011 and 2015. Open data sources were used from Fukushima, Miyagi, Ibaraki, Tochigi, and Gunma prefectures. Our initially compiled data showed that the maximum reported (137)Cs activity concentration in wild boar after the Fukushima Dai-ichi accident were lower than those reported after the Chernobyl accident. The geometric mean Tag values (m(2)kg(-1) fw) of (137)Cs in 2015 for Asian black bear, wild boar, sika deer and copper pheasant were similar (1.9-5.1) × 10(-3) while those for green pheasant and wild duck were about 1 order of magnitude lower at (1.0-2.2) × 10(-4). Effective half-lives were 1.2-6.9 y except for sika deer and copper pheasant where no decreases were found. In contrast to the Chernobyl accident, no seasonal change occurred in the meat (137)Cs activity concentrations of the wild animals during the study period.

Spatial trends on an ungrazed West Cumbrian saltmarsh of surface contamination by selected radionuclides over a 25 year period.

Long term spatial and temporal variations in radionuclide activity have been measured in a contaminated ungrazed saltmarsh near Ravenglass, Cumbria. Over a twenty-five year period there has been a decrease in activity concentration with (106)Ru and (137)Cs showing the highest rate of change followed by Pu alpha and (241)Am. A number of factors contribute to the reduction with time; including radiological half lives, discharge and remobilisation. For (241)Am the lower reduction rate is partially due to ingrowth from (241)Pu and partially as a result of transport of sediment from the offshore Irish Sea mud patch. Considerable spatial variation for the different radionuclides was observed, which with time became less defined. The highest activity concentrations of long-lived radionuclides were in low energy areas, typically where higher rates of sedimentation and vegetation occurred. The trend was reversed for the shorter lived radionuclide, (106)Ru, with higher activity concentrations observed in high energy areas where there was frequent tidal inundation. Surface scrape samples provide a pragmatic, practical method of measuring sediment contamination over large areas and is a sampling approach adopted by most routine environmental monitoring programs, but it does not allow for interpretation of the effect of variation in sedimentation rates. This paper proposes a method for calculating indicative sedimentation rates across the saltmarsh using surface scrape data, which produces results consistent with values experimentally obtained.

Time-dependent transfer of 137Cs, 85Sr and 65Zn to earthworms in highly contaminated soils.

The transfer characteristics of (137)Cs, (85)Sr and (65)Zn to earthworms (Eisenia andrei) in soils with different amounts of the radionuclides have been investigated. The time-dependent whole-body concentration ratios (CR) were derived for worms in artificially contaminated soils with three different activity concentrations. Two parameters of a first order kinetic model, the equilibrium concentration ratio (CR(eq)) and the effective loss rate constant (k), were estimated by a comparison of experimental CR results with model predictions. The estimated CR(eq) (Bq/kg fresh worm per Bq/kg dry soil) ranged from 3.9 × 10(-4) to 4.1 × 10(-3) for (137)Cs, 1.39 × 10(-3) to 2.94 × 10(-2) for (85)Sr, and 1.39 × 10(-3) to 5.0 × 10(-2) for (65)Zn, and consistently decreased with increasing soil activity concentration but the trend was not statistically significant. The CR(eq) for (137)Cs was one to two orders of magnitude lower than previously reported CR(wo-soil) values (based on field data with much less contaminated soil), that for (85)Sr was comparable with other reported values and for (65)Zn was less two to three orders of magnitude lower than CR(wo-soil) values for stable zinc. The estimated k (d(-1)) values ranged from 9 × 10(-2) to 1.4 × 10(-1) for (137)Cs, 7 × 10(-2) to 2 × 10(-1) for (85)Sr, and 6 × 10(-2) to 1.8 × 10(-1) for (65)Zn, and did not show a relationship with soil activity concentration. The effect of CR(eq) on the total dose rate was insignificant for (137)Cs or (65)Zn because external dose rates to the soil dwelling earthworms due to these radionuclides were much greater than the internal dose rate. In contrast, the total dose from (90)Sr was determined by the internal dose rate and therefore proportional to the CR(eq).

An overview of the transfer of radionuclides to farm animals and potential countermeasures of relevance to Fukushima releases.

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.

Whole-body to tissue concentration ratios for use in biota dose assessments for animals.

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.

Transfer of natural and anthropogenic radionuclides to ants, bryophytes and lichen in a semi-natural ecosystem.

Few data are available to quantify the transfer of both natural and anthropogenic radionuclides to detritivorous invertebrates to facilitate estimation of the internal dose to such biota in models used to assess radiation exposure. To enhance the available data, activity concentrations of (137)Cs, (40)K, (90)Sr, (239 + 240)Pu, (241)Am, (235)U and (238)U were measured in ants (Formicidae) and corresponding undisturbed soil collected from the Zlatibor mountain in Serbia and ant/soil concentration ratios (CR) calculated. The (241)Am concentration ratios for ants were fourfold higher than those calculated for ants in a previous study whereas they are similar to the more numerous data previously reported for a range of detritivorous invertebrates in other studies. CR values for (137)Cs in ants were similar to the few other reported values and slightly lower than those for a range of detritivorous invertebrates. Those for (239 + 240)Pu were slightly higher than those for ants in two other studies but they were close to upper limit of a range of data reported for detritivorous invertebrates. All the CR values will be included in a future revision of the ERICA Tool database and will particularly improve the information available for uranium.

Protection of the environment from ionising radiation in a regulatory context (protect): proposed numerical benchmark values.

Criteria are needed to be able to judge the level of risk associated with dose rates estimated for non-human biota. In this paper, European guidance on the derivation of predicted no-effect chemical concentrations has been applied to appropriate radiation sensitivity data. A species sensitivity distribution fitted to the data for all species resulted in a generic predicted no-effect dose rate of 10 microGy h(-1).Currently, data are inadequate to derive screening values for separate organism groups. A second, higher, benchmark could aid in decision making by putting results into context on the scale of no effect to a risk of 'serious' effect. The need for, meaning and use of such a value needs to be debated by the wider community. This paper explores potential approaches of deriving scientific input to this debate. The concepts proposed in this paper are broadly consistent with the framework for human protection.

An international comparison of models and approaches for the estimation of the radiological exposure of non-human biota.

Over the last decade a number of models and approaches have been developed for the estimation of the exposure of non-human biota to ionising radiations. In some countries these are now being used in regulatory assessments. However, to date there has been no attempt to compare the outputs of the different models used. This paper presents the work of the International Atomic Energy Agency's EMRAS Biota Working Group which compares the predictions of a number of such models in model-model and model-data inter-comparisons.

An extended critical review of twenty years of countermeasures used in agriculture after the Chernobyl accident.

A wide range of different countermeasures has been used to mitigate the consequences of the Chernobyl accident for agriculture in affected regions in Belarus, Russia and Ukraine. The paper comprehensively brings together key data on countermeasure application over twenty years for all three countries and critically evaluates the response to the accident with respect to agriculture. The extents of countermeasures implementation in various periods following the ChNPP accident are documented. Examples of best practices and drawbacks in remediation of affected areas are identified. Data on the effectiveness of agricultural countermeasures have been evaluated and the impact of countermeasures implementation to mitigate consequences of the accident has been assessed for the period 1986-2006. Implementation of agricultural countermeasures averted 30-40% of the internal collective dose that would have been received by the residents of affected regions without the use of countermeasures. The current situation in agriculture of areas subjected to contamination following the Chernobyl accident is described. Current and future needs for remediation, including a consideration of various strategies of rehabilitation of affected areas are presented.

Assessment of current exposure of the population living in the Techa River basin from radioactive releases of the Mayak facility.

Current doses arising from external and internal pathways have been estimated for the residents of two villages, Muslumovo and Brodokalmak, alongside the Techa River, which was contaminated by radioactive releases from the Mayak production facility. The dose estimates are based on numerous environmental measurements supplemented by further human whole body measurements and studies on occupational and dietary habits of Slavic and Turkish ethnic groups. Estimated doses arise mainly from use of the contaminated floodplains alongside the Techa River. The current average annual effective dose attributable to Cs and Sr in the environment, under conditions where restrictions on some river-related activities are in place, may exceed the Russian national action level of 1 mSv only in the hypothetical critical group of herdsmen in Muslumovo. The dose to this critical group in Brodokalmak is assessed to be 3 times less than that in Muslumovo and 2 fold below the action level. The external and internal exposures give comparable contributions to the total dose in both settlements and population groups: 47% and 53% in Muslumovo and 40% and 60% in Brodokalmak, respectively. About one quarter to one half of the internal dose in adults arises from the intake of Sr. In order to avoid substantial increases in the dose received by Muslumovo residents, it is expedient to prolong the current policy of restriction of some river-related population activities in this village.

Comparison of the accumulation of (137)Cs and (90)Sr by six spring wheat varieties.

The uptake of (137)Cs and (90)Sr by six varieties of spring wheat (Triticum aestivum) was compared in field trials on land contaminated by the Chernobyl accident. All the experimental varieties are officially adopted for agricultural use in Belarus and are used in large-scale production. Under identical conditions of nutrition, the productivity of the varieties varied significantly by a factor of 1.3. The extent of (137)Cs and (90)Sr accumulation by wheat grain, quantified as the concentration ratio, differed between the varieties by as much as a factor of 1.6, for both radionuclides. There was a significant linear positive correlation between the (90)Sr activity concentration in grain and straw, and the calcium concentration. The correlation between (137)Cs and potassium was not significant. The results suggest that certain varieties of spring wheat used in normal agricultural practice accumulate less (137)Cs and (90)Sr into grain than others. Some spring wheat varieties accumulated relatively less (137)Cs, but did not accumulate less (90)Sr. One variety, Quattro, had a significantly lower uptake of both (90)Sr (for grain) and (137)Cs (for both grain and straw) than that of the other varieties tested. The reduction efficiency achieved by the use of these varieties, however, is not as high as that achieved by soil amelioration techniques in the past. Nevertheless, since there are no additional costs or production losses associated with these varieties, their use in the contaminated areas is worth considering as a simple, practical, and effective contribution to reducing the uptake of both (90)Sr and (137)Cs and allowing farmers to produce food-grade grain.

Predicting radionuclide transfer to wild animals: an application of a proposed environmental impact assessment framework to the Chernobyl exclusion zone.

A number of assessment frameworks have been proposed to provide a mechanism to demonstrate protection of the environment from ionising radiation. Whilst some of these are being used for assessment purposes they have largely not been validated against field measurements. In this paper we compare the predictions of transfer parameters recommended by one of these frameworks (FASSET) with observed whole-body 90Sr and radiocaesium activity concentrations in a range of mammal and invertebrate species sampled within the Chernobyl exclusion zone. Predicted activity concentrations were generally within the observed ranges and mean predictions for reference organisms were similar to, or circa one order of magnitude higher than, the observed means. However, some predictions were more than one order of magnitude lower than observed values. No data were available to test predictions for the other radionuclides released by the Chernobyl accident. In a separate paper the outputs of this assessment will be used to estimate doses to reference organisms and compare these to observed radiation induced effects reported within the Chernobyl zone.