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

Strontium leaching from municipal waste subjected to incineration

The aim of the study was to determine the content and leachability of Sr in ashes obtained through combusting municipal waste in household furnaces. The waste had been collected as a mixed stream and as separate fractions (i.e. furniture, sponges, waste paper, PCV packaging, plastic-coated paper cartons, imitation leather, rubber, textiles and polystyrene). Using single-step chemical extractions, (HCl + HNO3, H2O, 0.01 M CaCl2, 0.1 M CH3COOH), we determined the total content of Sr (TC) and proportions of the following fractions: water-leachable, phytoavailable and easily soluble and bound to carbonates. We also analyzed the effect of reducing pH in the extraction solutions on St leachability from the study material. The study showed that Sr concentration in ash generated from the combustion of conventional fuels, alternative fuels and municipal waste ranged from 114 to 1006 mg/kg. The largest amounts of Sr were found in ash generated from the combustion of alternative fuels (coal pellets 488-1006 mg/kg), conventional fuels (hard coal 430-670 mg/kg) and mixed waste (237-825 mg/kg). The most mobile fraction of Sr (water-leachable) comprised from 1.3% to nearly 91% TC; the phytoavailable fraction and the ion-exchange and carbonate-bound fraction comprised 3-92% TC and 9-72% TC, respectively. We also found that the greatest pH reductions do not always entail the greatest amounts of extracted Sr. A much more significant factor in this respect is the mineral and chemical composition of primary materials, which can buffer changes in pH. The Risk Assessment Code (RAC) values pointed to a varied environmental risk and the highest RAC values (> 70) were found for coal pellets, wood pellets, straw, rubber and plastic containers for mixed oils.

Uptake from water and depuration of 137Cs and 90Sr by silver Prussian carp (Carassius gibelio)

To follow up field observations in the Chornobyl Exclusion Zone (ChEZ), a series of controlled model aquarium experiments were conducted to determine the uptake and depuration rates of 137Cs and 90Sr in silver Prussian carp (Carassius gibelio) in fresh water, varying in temperature from 5 to 27 °C, with daily feeding rates of 0-1.5 % fish weight day-1. In the present study, the 137Cs uptake rates in muscle tissues directly from water, 0.05-0.09 day-1 at temperatures of 5-27 °C, were significantly lower than previously reported for fish fed under natural conditions in contaminated lakes within the ChEZ. The rate of 90Sr uptake in bone tissues of silver Prussian carp varied from 0.055 day-1 at a water temperature of 5 °C and feeding rates ≤0.15 % fish weight day-1 to 1.5 ± 0.2 day-1 at a temperature of 27 ± 1 °С and at the highest tested feeding rate of 1.5 % day-1. The rate of decrease of 137Cs concentration in muscle tissues was kb = 0.0028 ± 0.0004 day-1 (T1/2 = 248 ± 35 days) at the lowest water temperature tested (5 °С). At water temperatures between 13 and 26 °С and a feeding rate of 0.15 % day-1, the rate increased to kb = 0.0071-0.0092 day-1 (T1/2 = 75-99 days). The rates of decrease of 90Sr activity concentration in bone tissues at water temperatures between 22 and 25 °С and a feeding rate of 0.5 % day-1 were kb=0.004-0.0014 day-1, and the associated biological half-life T1/2 ranged 50-160 days, respectively. The present work supported conclusions related to the main pathways of 137Cs and 90Sr uptake by silver Prussian carp, and demonstrated the usefulness of combining field and laboratory uptake and depuration experiments.

Long-term radiological assessment of a Mediterranean freshwater ecosystem surrounding a nuclear power plant

The radionuclide concentration of man-made radionuclides on non-human biota in freshwater ecosystems has been extensively studied in environments affected by the Chernobyl and Fukushima accidents, in both humid continental and subtropical climates, respectively. However, there are very few studies that assess the long-term effects of operating nuclear facilities in Mediterranean environments. In the present study, a temporal analysis of the impact on carp, cattail, and bulrushes in the cooling pond of the currently operating Almaraz nuclear power plant was investigated for the period 2000-2020. The results do not show a general trend in man-made radionuclide concentrations. Instead, depending on their availability and the type of organism, trends decrease over time. This is also reflected in the effective half-lives obtained, which are lower than the physical half-life for some radionuclides. Transfer coefficients for the main man-made radionuclides detected were obtained, and it was found that these were significantly lower than the typical ranges found for benthic fish and vascular plants in freshwater ecosystems. Finally, the internal and external doses received by the carp have been evaluated using ERICA tool, and it has been observed that the main contribution to the total dose is due to the internal dose (0.65-7.04) × 10-4 µGy/h.

Testing countermeasures to reduce 90Sr content in fish products

Activity concentrations of 90Sr in fish in lakes located within the Chornobyl Exclusion Zone (ChEZ) reach 100 kBq kg-1, which is several thousand times higher than the permissible level in Ukraine (35 Bq kg-1). This study was conducted in the natural conditions of the ChEZ to determine the effectiveness of keeping radioactively contaminated fish in "clean" water to reduce the 90Sr content of their muscle tissue, as previously shown in short-term laboratory experiments. It was found that transferring tench (Tinca tinca (Linnaeus, 1758)) from Lake Glubokoye one of the most contaminated lakes in the ChEZ, to a cage in the "clean" Lake Starukha for 45 days did not lead to a significant decrease in 90Sr content in both bone and muscle tissues. Establishing permissible levels of 90Sr concentration only in fish fillet, and not in the whole fish body (with bone tissue), is appropriate for human radiation protection, since the retention factors of 90Sr treatment for boiled bone tissue of crucian carp from the Chornobyl exclusion zone are less than 0.01, and up to 97% of strontium is contained in bone tissue.

The transfer of 137Cs and heavy metals to tissues within the organs of snails

This paper describes the dynamics of 137Cs accumulation and its concentration ratio as well as that of some stable elements in the body, shell, gastrointestinal tract and albumin gland of a particular species of snail (terrestrial gastropod), namely the Giant African snail (Lissachatina fulica), after the long-term ingestion of contaminated forage and/or soil. The activity concentration of 137Cs in the their bodies increased over the first 40 days of the experiment, after which the increase in the activity of this radionuclide significantly reduced. The distribution of 137Cs in the body of a snail decreases as follows: gastrointestinal tract ˃ body = albumin gland ˃ shell. It was found that the contribution of soil towards the contamination of their bodies by 137Cs is far less than that of forage. Although the biological availability of Pb and U in forage is one order of magnitude higher than in soil, the main contribution to the contamination of snails originates from soil.

Clean feed as countermeasure to reduce the 90Sr and 137Cs levels in fish from contaminated lakes

Glubokoye Lake situated within the Chernobyl Exclusion Zone is highly contaminated with respect to radioactive caesium and strontium isotopes, which also is reflected in the contaminated fish. To utilize the fish resources in contaminated lakes, the present work presents for the first time the effectiveness of using clean feed to counteract contamination of radionuclides in fish. The study is based on a series of repeated experiments with Prussian carp (Carassius gibelio (Bloch, 1782)) kept in cages in the contaminated Glubokoye Lake during summer 2018-2021. By the addition of clean feed, the activity concentration of ¹³⁷Cs in fish muscle tissues was lowered with a factor of 2-5 due to biodilution. Surprisingly, additional clean feed did not lead to further decrease in the uptake of ¹³⁷Cs in fish. In contrast to ¹³⁷Cs, the addition of clean feed increased the ⁹⁰Sr activity concentration in fish by a factor of 2-4 compared to fish fed with naturally occurring feed items. Radioactive strontium accumulated mainly in the fish bones and the muscle tissue level was 2 orders of magnitude lower, similar to the distribution observed for stable Sr. By utilizing a new kinetic model describing the dynamics of strontium isotopes in bone tissues of fish, predictions fitted well with site-specific data, taking growth rates and aging into account. Results showed that clean feeding can be used to counteract high activity concentration of ¹³⁷Cs in fish due to biodilution, but cannot counteract bioaccumulation of ⁹⁰Sr. Findings highlighted that it is essential to understand underlying factors influencing the uptake pathways for contaminants, as access to clean feed could increase the growth and thereby reduce the body activity concentration of dietary associated radionuclides such as ¹³⁷Cs (biodilution), as well as increase the transfer of dissolved compounds such as ⁹⁰Sr directly from water to fish.

Ensuring robust radiological risk assessment for wildlife: insights from the International Atomic Energy Agency EMRAS and MODARIA programmes

In response to changing international recommendations and national requirements, a number of assessment approaches, and associated tools and models, have been developed over the last circa 20 years to assess radiological risk to wildlife. In this paper, we summarise international intercomparison exercises and scenario applications of available radiological assessment models for wildlife to aid future model users and those such as regulators who interpret assessments. Through our studies, we have assessed the fitness for purpose of various models and tools, identified the major sources of uncertainty and made recommendations on how the models and tools can best be applied to suit the purposes of an assessment. We conclude that the commonly used tiered or graded assessment tools are generally fit for purpose for conducting screening-level assessments of radiological impacts to wildlife. Radiological protection of the environment (or wildlife) is still a relatively new development within the overall system of radiation protection and environmental assessment approaches are continuing to develop. Given that some new/developing approaches differ considerably from the more established models/tools and there is an increasing international interest in developing approaches that support the effective regulation of multiple stressors (including radiation), we recommend the continuation of coordinated international programmes for model development, intercomparison and scenario testing.

Best practices for predictions of radionuclide activity concentrations and total absorbed dose rates to freshwater organisms exposed to uranium mining/milling

Predictions of radionuclide dose rates to freshwater organisms can be used to evaluate the radiological environmental impacts of releases from uranium mining and milling projects. These predictions help inform decisions on the implementation of mitigation measures. The objective of this study was to identify how dose rate modelling could be improved to reduce uncertainty in predictions to non-human biota. For this purpose, we modelled the activity concentrations of ²¹⁰Pb, ²¹⁰Po, ²²⁶Ra, ²³⁰Th, and ²³⁸U downstream of uranium mines and mills in northern Saskatchewan, Canada, together with associated weighted absorbed dose rates for a freshwater food chain using measured activity concentrations in water and sediments. Differences in predictions of radionuclide activity concentrations occurred mainly from the different default partition coefficient and concentration ratio values from one model to another and including all or only some ²³⁸U decay daughters in the dose rate assessments. Consequently, we recommend a standardized best-practice approach to calculate weighted absorbed dose rates to freshwater biota whether a facility is at the planning, operating or decommissioned stage. At the initial planning stage, the best-practice approach recommend using conservative site-specific baseline activity concentrations in water, sediments and organisms and predict conservative incremental activity concentrations in these media by selecting concentration ratios based on species similarity and similar water quality conditions to reduce the uncertainty in dose rate calculations. At the operating and decommissioned stages, the best-practice approach recommends relying on measured activity concentrations in water, sediment, fish tissue and whole-body of small organisms to further reduce uncertainty in dose rate estimates. This approach would allow for more realistic but still conservative dose assessments when evaluating impacts from uranium mining projects and making decision on adequate controls of releases.

Parameter Values for Estimation of Internal Doses from Ingestion of Radioactive Fallout from Nuclear Detonations

ABSTRACT

This paper suggests values or probability distributions for a variety of parameters used in estimating internal doses from radioactive fallout due to ingestion of food. Parameters include those needed to assess the interception and initial retention of radionuclides by vegetation, translocation of deposited radionuclides to edible plant parts, root uptake by plants, transfer of radionuclides from vegetation into milk and meat, transfer of radionuclides into non-agricultural plants and wildlife, and transfer from food and drinking water to mother's milk (human breast milk). The paper includes discussions of the weathering half-life for contamination on plant surfaces, biological half-lives of organisms, food processing (culinary factors), and contamination of drinking water. As appropriate, and as information exists, parameter values or distributions are specific for elements, chemical forms, plant types, or other relevant characteristics. Information has been obtained from the open literature and from publications of the International Atomic Energy Agency. These values and probability distributions are intended to be generic; they should be reviewed for applicability to a given location, time period, or season of the year, as appropriate. In particular, agricultural practices and dietary habits may vary considerably both with geography and over time in a given location.

Planned release of contaminated water from the Fukushima storage tanks into the ocean: Simulation scenarios of radiological impact for aquatic biota and human from seafood consumption

The radiological impact for human and aquatic biota as a result of a planned release of contaminated water stored in tanks near the Fukushima Dai-ichi Nuclear Power Plant to the Pacific Ocean is assessed. The total activity for 10 dominant radionuclides (³H, ¹⁴C, ⁶⁰Co, ⁹⁰Sr, ⁹⁹Tc, ¹⁰⁶Ru, ¹²⁵Sb, ¹²⁹I, ¹³⁴Cs, ¹³⁷Cs) in tanks is estimated. The compartment model POSEIDON-R is applied to compute the concentration of activity for each radionuclide in water, bottom sediments, and biota, and corresponding doses to marine organisms and humans from seafood consumption. Predicted concentrations of activity in marine products in future will not exceed food safety limits in Japan. The computed maximum committed effective dose to humans is less than 1 μSv per year with the highest contribution from ¹²⁹I and ¹⁴C. Maximum absorbed doses to non-human biota are in the order of 0.05 to 20 μGy per year, meaning that no deleterious effects are expected.

Seasonal changes in uptake and depuration of 137Cs and 90Sr in silver Prussian carp (Carassius gibelio) and common rudd (Scardinius erythrophthalmus)

Dynamic transfer of radionuclides to fish was studied in a series of experiments under field condition in two lakes within the Chernobyl exclusion zone during 2016-2020. "Clean" common rudd (Scardinius erythrophthalmus) and silver Prussian carp (Carassius gibelio) were transported to the contaminated Glubokoye Lake and kept in cages during several months of exposure, while contaminated Glubokoye fish were kept in cages in the "clean" Starukha Lake. Radiocaesium (¹³⁷Cs) and radiostrontium (⁹⁰Sr) were determined in intestine contents, muscle and bone tissues based on repeated samples during several months of exposure. During summer, the activity concentrations of ¹³⁷Cs and ⁹⁰Sr increased with time of exposure in clean fish caged in the contaminated lake. During autumn and winter, however, minor changes in fish uptake occurred during several weeks of exposure to the contaminated water. Furthermore, depuration in the contaminated fish was significant during summer, while insignificant during winter when exposed in the «clean» water. The rate constant of ¹³⁷Cs uptake in muscle was between 8.0 and 22 day^-1 during summer, while 0.2 to 1.0 day^-1 during autumn-winter. Similarly, the rate constant of ⁹⁰Sr uptake in bone was between 1.4 and 1.6 day^-1, while 0.08-0.52 day^-1 during autumn-winter. Biological half-lives of ¹³⁷Cs in fish muscle tissue in summer were 77 ± 10 days, while exceeded 230 days during seasons at low water temperature. The results demonstrated that the transfer of ¹³⁷Cs and ⁹⁰Sr to fish was highly dependent upon seasons, in particular the water temperature. The transfer data obtained during low water temperature seasons deviated significantly from transfer data in literature and handbooks. Thus, seasonal changes in radionuclide transfer to fish should be taken into account when radiological impact to fish is assessed.

The excretion of 241Am and 137Cs from the broilers organs after long-term application

Data, despite being crucial for internal dose assessment, is lacking on the transfer of artificial radionuclides from the environment to the food supply. Expanding the available information on these factors is important for the improvement of dose models for specific scenarios. This paper describes the results of a 70 day field experiment with broiler chickens on the dynamics of excretion of ¹³⁷Cs and ²⁴¹Am from the muscle, liver and bone of broilers after a 30 day application of contaminated feed. The radionuclide concentrations in the feed and the thigh muscle, thigh bone and liver of 54 chickens divided between grass meal and soil contaminated feed groups were evaluated by gamma spectrometry for ²⁴¹Am and ¹³⁷Cs. The obtained results confirm previous data on the dynamics of the excretion of cesium from organs, which can be described with a fast and a slow exponential curve of excretion. On the 70th day, following the 30-days application, 2-8% of the first-day activity concentrations of ¹³⁷Cs in organs (muscle, liver, bone) were detected. In the first two days, activity concentration of ²⁴¹Am decreases twofold in both liver and bone. 35% of the maximum activity concentration of ²⁴¹Am remained in bone and 15% in liver on the last day of the experiment.

Differentiating Fukushima and Nagasaki plutonium from global fallout using 241Pu/239Pu atom ratios: Pu vs. Cs uptake and dose to biota

Plutonium (Pu) has been released in Japan by two very different types of nuclear events - the 2011 Fukushima accident and the 1945 detonation of a Pu-core weapon at Nagasaki. Here we report on the use of Accelerator Mass Spectrometry (AMS) methods to distinguish the FDNPP-accident and Nagasaki-detonation Pu from worldwide fallout in soils and biota. The FDNPP-Pu was distinct in local environmental samples through the use of highly sensitive ²⁴¹Pu/²³⁹Pu atom ratios. In contrast, other typically-used Pu measures (²⁴⁰Pu/²³⁹Pu atom ratios, activity concentrations) did not distinguish the FDNPP Pu from background in most 2016 environmental samples. Results indicate the accident contributed new Pu of ~0.4%-2% in the 0-5 cm soils, ~0.3%-3% in earthworms, and ~1%-10% in wild boar near the FDNPP. The uptake of Pu in the boar appears to be relatively uninfluenced by the glassy particle forms of fallout near the FDNPP, whereas the ^134,137Cs uptake appears to be highly influenced. Near Nagasaki, the lasting legacy of Pu is greater with high percentages of Pu sourced from the 1945 detonation (~93% soils, ~88% earthworm, ~96% boar). The Pu at Nagasaki contrasts with that from the FDNPP in having proportionately higher ²³⁹Pu and was distinguished by both ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu atom ratios. However, compared with the contamination near the Chernobyl accident site, the Pu amounts at all study sites in Japan are orders of magnitude lower. The dose rates from Pu to organisms in the FDNPP and Nagasaki areas, as well as to human consumers of wild boar meat, have been only slightly elevated above background. Our data demonstrate the greater sensitivity of ²⁴¹Pu/²³⁹Pu atom ratios in tracing Pu from nuclear releases and suggest that the Nagasaki-detonation Pu will be distinguishable in the environment for much longer than the FDNPP-accident Pu.

The transfer of 239+240Pu, 241Am, 137Cs and 90Sr to the tissues of horses

Horses are important food sources in several countries however, data on their radionuclide uptake is less available than for many other farm animals. Information on the transfer of artificial radioisotopes from the environment to the food supply is necessary for internal dose assessment and assuring the safety of the population relying on this food source. This study provides data for a less studied farm animal and, in the case of ²⁴¹Am and ^239+240Pu, relatively poorly studied radionuclides with respect to transfer to animal products. The transfer parameters for ^239+240Pu, ²⁴¹Am, ¹³⁷Cs and ⁹⁰Sr to the organs of 1-year old fillies, 10-year old mares and through the placental barrier into foetuses were quantified after 60-days feeding with contaminated soil or diet contaminated by a leachate solution. The transfer of radionuclides from ingested soil to tissues was generally lower, by up to three orders of magnitude, than from a diet contaminated by a leachate solution. The ingestion of soil is a particularly important source of radionuclide intake to grazing animals in the Semipalatinsk Test Site. For ²⁴¹Am there is a lack of available data, the two singular entries for mutton and beef in the IAEA handbook are higher than all values observed in the current study. The maximum observed transfer factor for ²⁴¹Am was 72 ± 22*10^-5 d kg^-1 FW in the liver of the mare fed with leachate contaminated feed. For ^239+240Pu the maximum transfer factor was 31.8 ± 8*10^-5 d kg^-1 FW observed also in the liver of the mare fed with leachate contaminated feed. The filly fed with leachate contaminated feed had the highest transfer parameter value for ¹³⁷Cs, 35.3*10^-3 d kg^-1 FW. The highest ⁹⁰Sr transfer factor was found in the ribs of the filly fed leachate contaminated feed, 720 ± 144 *10^-3 d kg^-1 FW. The results presented in this paper can be used to improve the current internal dose estimates from the ingestion of horse meat produced in the area, however they are based on a low sample size; future studies need to use a larger number of animals.

Radionuclides in sea turtles at the Montebello Islands former nuclear test sites: Current and historical dose rates for adults and embryos

Radionuclides from 1950s weapons testing at the Montebello Islands, Western Australia, may impact sea turtle embryos incubating within eggs laid in contaminated sands or be taken up into adult body tissues where they can contribute to radiation dose over a turtles' 60+ year lifespan. We measured plutonium in all local samples including turtle skin, bones, hatchlings, eggshells, sea sediments, diet items and beach sands. The amount of Pu in developing embryos/hatchling samples was orders of magnitude lower than that in the surrounding sands. These contaminated sands caused most dose to eggs (external dose from ¹³⁷Cs, ¹⁵²Eu), while most of the dose to adults was from internalised radionuclides (98%). While current dose rates are relatively low, local dose rates were high for about ten years following the 1950s detonations and may have resulted in lethality or health impacts to a generation of turtles that likely carry biomarkers today.

The transfer of 241Am and 137Cs to the tissues of broilers' organs

Data on the transfer of artificial radionuclides from the environment to the food supply is necessary for internal dose assessment. There is a necessity for expanding and improving the available information on these factors in order to make better dose models for specific scenarios. This paper describes the results of a field experiment with broiler chickens on the transfer factor (Ff) and concentration ratio (CR) for the long-term intake of 241Am and 137Cs with grass meal and soil. The broilers were divided into two groups, each group had nine subgroups and each subgroup had three broilers. The radionuclide concentrations in the feed and the thigh muscle, thigh bone, and liver of 54 broilers divided between the grass meal and soil groups were evaluated by gamma spectrometry for 241Am and 137Cs. The duration of feeding with "contaminated" sources ranged between 1-70 days. The equilibrium stage of 241Am in muscle and bone occurs on the 1st and 40th day, respectively; for 137Cs in muscle- 30th days of intake and for liver and bone- 7th days. For 241Am, the liver did not reach equilibrium stage during the 70 days of intake. Ff of 137Cs in the "forage-muscle" and "soil-muscle" systems were determined as 1.9±0.3 and 0.18±0.05; Ff of 241Am in the "soil-muscle" system was-7.5×10-5.

Whole organism concentration ratios in freshwater wildlife from an Australian tropical U mining environment and the derivation of a water radiological quality guideline value

More than 10,000 whole organism concentration ratio (CR_wo-water) values for freshwater wildlife were derived from radionuclide and stable element data representing an Australian tropical U mining environment. The CR_wo-water values were summarised into five wildlife groups (bird, fish, mollusc, reptile and vascular plant). The summarised CR_wo-water values represented 77 organism-element combinations. The CR_wo-water values for U decay series elements were used in a tier 3 ERICA assessment. The assessment results were used to derive a water radiological quality guideline value (GV) for radiation protection of freshwater ecosystems in the context of the planned remediation of the Ranger U mine. The GV was an above-background water ²²⁶Ra activity concentration of 14 mBq L^-1 (filtered fraction) or approximately 22 mBq L^-1 (total fraction). The GV was based on the results of mollusc-bivalve as the limiting organism for the freshwater ecosystem.

A comparison of methods to derive aggregated transfer factors using wild boar data from the Fukushima Prefecture

Aggregated transfer factors (T_ag; m² kg^-1) are often used to predict radionuclide activity concentrations in biota (Bq kg^-1) from soil contamination levels (Bq m^-2). Inherently large uncertainties in T_ag values severely limit their predictive power. Many published T_ag values have been derived from radionuclide deposition onto soil following weapons fallout, or the accidents at Chernobyl and Fukushima. In many cases the soil data used to derive a T_ag value were collected for other purposes, and the spatial resolution of the soil data is much less than that of the biota data to which it is paired. We hypothesized that this disassociation and imprecision in paring deposition density and biota data may contribute to the large variations observed in T_ag values. We tested the hypothesis by deriving T_ag values for Japanese wild boar in two ways. One method used paired deposition density-biota contamination levels, with the soil data collected from each boar trap site. The second method used a soil radioactivity density map, of relatively low spatial resolution, generated by the Japanese government agency MEXT for fallout from the Fukushima accident. We hypothesized that T_ag values derived from the method using paired deposition density-wild boar data would have less variation. Initial statistical test suggested significant differences in the predictive power of the two methods. However, removal of suspected outliers in the MEXT data set decreased the statistical differences and indicated that collecting ¹³⁷Cs soil deposition density measurements in the field did not reduce the large variation in our T_ag values. More importantly, both methods revealed that soil contamination levels are a poor predictor of radiocesium concentrations in boar (r² < 0.23). The inadequacies of T_ag to predict wild boar ¹³⁷Cs concentrations is an ominous indication of the lack of applicability of the T_ag model as a rigorous research parameter. T_ag values are best suited for their original intended purpose: upper tier, screening level computations. Further studies on how to reduce uncertainty when predicting ¹³⁷Cs concentrations in biota are needed to thoroughly understand the transfer of radiocesium within the environment.

The POSEIDON-R compartment model for the prediction of transport and fate of radionuclides in the marine environment

A detailed description of the advanced version of compartment model POSEIDON-R for the prediction of transport and fate of radionuclides in the marine environment is given. The equations of transfer of radionuclides in the water and bottom sediment compartments along with the dynamical food chain model are presented together with dose module to assess individual and collective doses to the population due to the regular and accidental releases of radionuclides. The method for the numerical solution of model equations is also presented. The modelling results for the northeast Atlantic shelf seas were compared with measurements of ¹³⁷Cs. •The three-dimensional compartment model POSEIDON-R describes the transfer of radionuclides and their daughter products in marine environment as a results of regular or accidental releases. This includes any transfer through the water column and sediments.•The model is complemented by a dynamic food chain model for transfer of radioactivity in pelagic and benthic food webs.•The dose module in the model calculates internal and external doses for humans and non-human biota.

Whole organism to tissue concentration ratios derived from an Australian tropical dataset

Whole organism to tissue concentration ratios (CR_wo-tissue) were derived for six wildlife groups (freshwater birds, freshwater bivalves, freshwater fishes, freshwater reptiles, freshwater vascular plants and terrestrial mammals). The wildlife groups and data represented species common to tropical northern Australia. Values of CR_wo-tissue were derived for between 6 and 34 elements, depending upon wildlife group. The values were generally similar to international reference values. However, differences for some element-tissue combinations could affect radiation dose estimates for wildlife in certain environmental exposure situations, including uranium mining, where these data are intended to be applied.

Whole-organism concentration ratios in wildlife inhabiting Australian uranium mining environments

Wildlife concentration ratios for ²²⁶Ra, ²¹⁰Pb, ²¹⁰Po and isotopes of Th and U from soil, water, and sediments were evaluated for a range of Australian uranium mining environments. Whole-organism concentration ratios (CR_wo-media) were developed for 271 radionuclide-organism pairs within the terrestrial and freshwater wildlife groups. Australian wildlife often has distinct physiological attributes, such as the lower metabolic rates of macropod marsupials as compared with placental mammals. In addition, the Australian CRs_wo-media originate from tropical and semi-arid climates, rather than from the temperate-dominated climates of Europe and North America from which most (>90%) of internationally available CR_wo-media values originate. When compared, the Australian and non-Australian CRs are significantly different for some wildlife categories (e.g. grasses, mammals) but not others (e.g. shrubs). Where differences exist, the Australian values were higher, suggesting that site-, or region-specific CRs_wo-media should be used in detailed Australian assessments. However, in screening studies, use of the international mean values in the Wildlife Transfer Database (WTD) appears to be appropriate, as long as the values used encompass the Australian 95th percentile values. Gaps in the Australian datasets include a lack of marine parameters, and no CR data are available for freshwater phytoplankton, zooplankton, insects, insect larvae or amphibians; for terrestrial environments, there are no data for amphibians, annelids, ferns, fungi or lichens & bryophytes. The new Australian specific parameters will aide in evaluating remediation plans and ongoing operations at mining and waste sites within Australia. They have also substantially bolstered the body of U- and Th-series CR_wo-media data for use internationally.

Calculating the radiological parameters used in non-human biota dose assessment tools using ERICA Tool and site-specific data

The substantial complexity in ecosystem-radionuclide interactions is difficult to be represented in terms of radiological doses. Thus, radiological dose assessment tools use typical exposure situations for generalized organisms and ecosystems. In the present study, site-specific data and radioactivity measurements of terrestrial organisms (grass and herbivore mammals) and abiotic components (soil) are provided. The retrieved data are used in combination with the ERICA Assessment Tool for calculation of radiological parameters. The process of radionuclide transfer within ecosystem components is represented using concentration ratios (CRs), while for the calculation of dose rates the dose conversion coefficient (DCC) methodology is applied. Comparative assessments are performed between the generic and assessment-specific radiological parameters and between the resulting dose rates. Significant differences were observed between CRs calculated in this study and those reported in the literature for cesium and thorium, which can easily be explained. On the other hand, CRs calculated for radium are in very good agreement with those reported in the literature. The DCCs exhibited some small differences between the reference and the assessment-specific organism due to mass differences. The differences were observed for internal and external dose rates, but they were less pronounced for total dose rates which are typically used in the assessment of radiological impact. The results of the current work can serve as a basis for further studies of the radiological parameters in environments that have not been studied yet.

A tool for calculating concentration ratios from large environmental datasets

This paper presents a tool for calculating concentration ratios from a large and structured environmental dataset of radionuclide activity and metal concentrations. The tool has been developed in MS Excel™ and includes a simple user interface for setting up queries. The tool is capable of matching environmental media samples to biota samples based on user-defined spatial and temporal criteria to derive a representative estimate of the environmental exposure conditions of an organism and its accumulation. Some potential benefits and uses of the tool are discussed.

Evaluation of factors influencing accumulation of stable Sr and Cs in lake and coastal fish

As a result of nuclear accidents and weapons tests, the radionuclides Cs-137 and Sr-90 are common contaminants in aquatic ecosystems. Concentration ratios (CR) based on concentrations of stable Cs and Sr in biota and media are used for the estimation of transfer of their radioisotopes for radiation dose calculations in environmental and human safety assessments. Available element-specific CRs vary by over an order of magnitude for similar organisms, thus affecting the dose estimates proportionally. The variation could be reduced if they were based on a better understanding of the influence of the underlying data and how that affects accumulation and potential biomagnification of stable Cs and Sr in aquatic organisms. For fish, relationships have been identified between water concentrations of K and CR of Cs-137, and between water concentrations of Ca and CR of Sr-90. This has not been confirmed for stable Cs and Sr in European waters. In this study, we analysed an existing dataset for stable Cs and Sr, as well as K and Ca, in four Swedish lakes and three Baltic Sea coastal areas, in order to understand the behaviour of these elements and their radioisotopes in these ecosystems. We found significant seasonal variations in the water concentrations of Cs, Sr, K and Ca, and in electrical conductivity (EC), especially in the lakes. CR values based on measurements taken at single or few time points may, therefore, be inaccurate or introduce unnecessarily large variation into risk assessments. Instead, we recommend incorporating information about the underlying variation in water concentrations into the CR calculations, for example by using the variation of the mean. The inverse relationships between fish CR(Cs)-[K]water and fish CR(Sr)-[Ca]water, confirmed that stable Cs and Sr follow the same trends as their radioisotopes. Thus, they can be used as proxies when radioisotope data are lacking. EC was also strongly correlated with K and Ca concentrations in the water and could potentially be used as a quick and cost-effective method to estimate water chemistry to obtain less variable CR. We also recommend some simple improvements to data collection that would greatly enhance our ability to understand Cs and Sr uptake by fish.

Radioactivity measurements and dose rate calculations using ERICA tool in the terrestrial environment of Greece

In the present study, the radioactivity levels to which terrestrial non-human biota were exposed are examined. Organisms (grass and herbivore mammals) and abiotic components (soil) were collected during the period of 2010 to 2014 from grasslands where sheep and goats were free-range grazing. Natural background radionuclides ((226)Ra, (228)Ra, (228)Th) and artificial radionuclides ((137)Cs, (134)Cs, (131)I) were detected in the collected samples using gamma spectrometry. The actual measured activity concentrations and site-specific data of the studied organisms were imported in ERICA Assessment Tool (version 1.2.0) in order to provide an insight of the radiological dose rates. The highest activity concentrations were detected in samples collected from Lesvos island and the lowest in samples collected from Attiki and Etoloakarnania prefectures. The highest contribution to the total dose rate was clearly derived from the internal exposure and is closely related to the exposure to alpha emitters of natural background ((226)Ra and (228)Th). The Fukushima-derived traces of (137)Cs, (134)Cs, and (131)I, along with the residual (137)Cs, resulted in quite low contribution to the total dose rate. The obtained results may strengthen the adaptation of software tools to a wider range of ecosystems and may be proved useful in further research regarding the possible impact of protracted low level ionizing radiation on non-human biota. This kind of studies may contribute to the effective incorporation of dosimetry tools in the development of integrated environmental and radiological impact assessment policies.

Voxel modeling of rabbits for use in radiological dose rate calculations

Radiation dose to biota is generally calculated using Monte Carlo simulations of whole body ellipsoids with homogeneously distributed radioactivity throughout. More complex anatomical phantoms, termed voxel phantoms, have been developed to test the validity of these simplistic geometric models. In most voxel models created to date, human tissue composition and density values have been used in lieu of biologically accurate values for non-human biota. This has raised questions regarding variable tissue composition and density effects on the fraction of radioactive emission energy absorbed within tissues (e.g. the absorbed fraction - AF), along with implications for age-dependent dose rates as organisms mature. The results of this study on rabbits indicates that the variation in composition between two mammalian tissue types (e.g. human vs rabbit bones) made little difference in self-AF (SAF) values (within 5% over most energy ranges). However, variable tissue density (e.g. bone vs liver) can significantly impact SAF values. An examination of differences across life-stages revealed increasing SAF with testis and ovary size of over an order of magnitude for photons and several factors for electrons, indicating the potential for increasing dose rates to these sensitive organs as animals mature. AFs for electron energies of 0.1, 0.2, 0.4, 0.5, 0.7, 1.0, 1.5, 2.0, and 4.0 MeV and photon energies of 0.01, 0.015, 0.02, 0.03, 0.05, 0.1, 0.2, 0.5, 1.0, 1.5, 2.0, and 4.0 MeV are provided for eleven rabbit tissues. The data presented in this study can be used to calculate accurate organ dose rates for rabbits and other small rodents; to aide in extending dose results among different mammal species; and to validate the use of ellipsoidal models for regulatory purposes.

Accumulation of plutonium in mammalian wildlife tissues following dispersal by accidental-release tests

We examined the distribution of plutonium (Pu) in the tissues of mammalian wildlife inhabiting the relatively undisturbed, semi-arid former Taranaki weapons test site, Maralinga, Australia. The accumulation of absorbed Pu was highest in the skeleton (83% ± 6%), followed by muscle (10% ± 9%), liver (6% ± 6%), kidneys (0.6% ± 0.4%), and blood (0.2%). Pu activity concentrations in lung tissues were elevated relative to the body average. Foetal transfer was higher in the wildlife data than in previous laboratory studies. The amount of Pu in the gastrointestinal tract was highly elevated relative to that absorbed within the body, potentially increasing transfer of Pu to wildlife and human consumers that may ingest gastrointestinal tract organs. The Pu distribution in the Maralinga mammalian wildlife generally aligns with previous studies related to environmental exposure (e.g. Pu in humans from worldwide fallout), but contrasts with the partitioning models that have traditionally been used for human worker-protection purposes (approximately equal deposition in bone and liver) which appear to under-predict the skeletal accumulation in environmental exposure conditions.

Making the most of what we have: application of extrapolation approaches in radioecological wildlife transfer models

We will never have data to populate all of the potential radioecological modelling parameters required for wildlife assessments. Therefore, we need robust extrapolation approaches which allow us to make best use of our available knowledge. This paper reviews and, in some cases, develops, tests and validates some of the suggested extrapolation approaches. The concentration ratio (CRproduct-diet or CRwo-diet) is shown to be a generic (trans-species) parameter which should enable the more abundant data for farm animals to be applied to wild species. An allometric model for predicting the biological half-life of radionuclides in vertebrates is further tested and generally shown to perform acceptably. However, to fully exploit allometry we need to understand why some elements do not scale to expected values. For aquatic ecosystems, the relationship between log10(a) (a parameter from the allometric relationship for the organism-water concentration ratio) and log(Kd) presents a potential opportunity to estimate concentration ratios using Kd values. An alternative approach to the CRwo-media model proposed for estimating the transfer of radionuclides to freshwater fish is used to satisfactorily predict activity concentrations in fish of different species from three lakes. We recommend that this approach (REML modelling) be further investigated and developed for other radionuclides and across a wider range of organisms and ecosystems. Ecological stoichiometry shows potential as an extrapolation method in radioecology, either from one element to another or from one species to another. Although some of the approaches considered require further development and testing, we demonstrate the potential to significantly improve predictions of radionuclide transfer to wildlife by making better use of available data.

A soil radiological quality guideline value for wildlife-based protection in uranium mine rehabilitation

A soil guideline value for radiological protection of the environment was determined for the impending rehabilitation of Ranger uranium mine in the wet-dry tropics of northern Australia. The guideline value was 1000 Bq kg(-1) of (226)Ra in the proposed waste rock substrate of the rehabilitated landform and corresponded to an above-baseline dose rate of 100 μGy h(-1) to the most highly exposed individuals of the limiting organism. The limiting organism was reptile based on an assessment using site-specific concentration ratio data.

Organ Dose-Rate Calculations for Small Mammals at Maralinga, the Nevada Test Site, Hanford and Fukushima: A Comparison of Ellipsoidal and Voxelized Dosimetric Methodologies

Radiological dosimetry for nonhuman biota typically relies on calculations that utilize the Monte Carlo simulations of simple, ellipsoidal geometries with internal radioactivity distributed homogeneously throughout. In this manner it is quick and easy to estimate whole-body dose rates to biota. Voxel models are detailed anatomical phantoms that were first used for calculating radiation dose to humans, which are now being extended to nonhuman biota dose calculations. However, if simple ellipsoidal models provide conservative dose-rate estimates, then the additional labor involved in creating voxel models may be unnecessary for most scenarios. Here we show that the ellipsoidal method provides conservative estimates of organ dose rates to small mammals. Organ dose rates were calculated for environmental source terms from Maralinga, the Nevada Test Site, Hanford and Fukushima using both the ellipsoidal and voxel techniques, and in all cases the ellipsoidal method yielded more conservative dose rates by factors of 1.2-1.4 for photons and 5.3 for beta particles. Dose rates for alpha-emitting radionuclides are identical for each method as full energy absorption in source tissue is assumed. The voxel procedure includes contributions to dose from organ-to-organ irradiation (shown here to comprise 2-50% of total dose from photons and 0-93% of total dose from beta particles) that is not specifically quantified in the ellipsoidal approach. Overall, the voxel models provide robust dosimetry for the nonhuman mammals considered in this study, and though the level of detail is likely extraneous to demonstrating regulatory compliance today, voxel models may nevertheless be advantageous in resolving ongoing questions regarding the effects of ionizing radiation on wildlife.

Time-dependence of ¹³⁷Cs activity concentration in wild game meat in Knyszyn Primeval Forest (Poland)

Wild game meat samples were analysed from the region of the Podlasie province (Knyszyn Primeval Forest). (137)Cs content in meat was determined by gamma spectrometry in 2003 (33 samples), 2009 (22 samples) and 2012 (26 samples). The samples were collected in the autumn of 2003, 2009 and 2012 and were compared with data from 1996. Mean concentrations of (137)Cs in the respective years were as follow: 42.2 Bq kg(-1), 33.7 Bq kg(-1) and 30.5 Bq kg(-1), respectively. On the basis of mean values of (137)Cs in the meat samples of red deer (Cervus elaphus), roe deer (Capreolus capreolus) and wild boars (Sus scrofa) between 1996/2012, the effective half-life of (137)Cs was determined for specific species. For red deer equaled 8.9 years, for roe deer 11.6 years while for wild boar it exceeded the physical half-life and equaled 38.5 years. Mean value CR obtained for all three species equaled 1.7 ± 1.5 out of 102 measurements in animals muscles.

Exposure of a herbivorous fish to ¹³⁴Cs and ¹³⁷Cs from the riverbed following the Fukushima disaster

Ayu Plecoglossus altivelis, a herbivorous fish, is an important fishery resource and key component of the foodweb in many Japanese streams. Radionuclide contamination of this species is likely transferred to higher trophic levels, include humans, in the food chain. After the Fukushima accident in March 2011, ayu were exposed to highly contaminated silt while feeding on algae attached to the riverbed stones. To understand the route by which herbivorous fish are exposed to radionuclides, the activity concentrations of sum of (134)Cs and (137)Cs (radiocesium) were analyzed in riverbed samples (algae and silt) and in the internal organs and the muscle of ayu in five river systems in the Fukushima Prefecture between summer 2011 and autumn 2013. Although there was a positive correlation between the radiocesium activity concentrations in the muscle and the internal organs of ayu, the median activity concentration in the muscle was much lower than those in the internal organs. The activity concentrations of radiocesium in the riverbed samples and the internal organs and the muscle of ayu were correlated with contamination levels in soil samples taken from the watershed upstream of the sample sites. The results of the generalized linear mixed models suggest that the activity concentrations in both the internal organs and the muscle of ayu declined over time. Additionally, the activity concentrations in the internal organs were correlated with those in the riverbed samples that were collected around the same time as the ayu. The activity concentrations in the muscle were correlated with ayu body size. Our results suggest that ayu ingest (134)Cs and (137)Cs while grazing silt and algae from the riverbed, and a part of the (134)Cs and (137)Cs is assimilated into the muscle of the fish.

Radiological dose rates to marine fish from the Fukushima Daiichi accident: the first three years across the North Pacific

A more complete record is emerging of radionuclide measurements in fish tissue, sediment, and seawater samples from near the Fukushima Daiichi Nuclear Power Plant (FDNPP) and across the Pacific Ocean. Our analysis of publicly available data indicates the dose rates to the most impacted fish species near the FDNPP (median 1.1 mGy d(-1), 2012-2014 data) have remained above benchmark levels for potential dose effects at least three years longer than was indicated by previous, data-limited evaluations. Dose rates from (134,137)Cs were highest in demersal species with sediment-associated food chains and feeding behaviors. In addition to (134,137)Cs, the radionuclide (90)Sr was estimated to contribute up to approximately one-half of the total 2013 dose rate to fish near the FDNPP. Mesopelagic fish 100-200 km east of the FDNPP, coastal fish in the Aleutian Islands (3300 km), and trans-Pacific migratory species all had increased dose rates as a consequence of the FDNPP accident, but their total dose rates remained dominated by background radionuclides. A hypothetical human consumer of 50 kg of fish, gathered 3 km from the FDNPP in 2013, would have received a total committed effective dose of approximately 0.95 mSv a(-1) from combined FDNPP and ambient radionuclides, of which 0.13 mSv a(-1) (14%) was solely from the FDNPP radionuclides and below the 1 mSv a(-1) benchmark for public exposure.

A new simplified allometric approach for predicting the biological half-life of radionuclides in reptiles

A major source of uncertainty in the estimation of radiation dose to wildlife is the prediction of internal radionuclide activity concentrations. Allometric (mass-dependent) relationships describing biological half-life (T1/2b) of radionuclides in organisms can be used to predict organism activity concentrations. The establishment of allometric expressions requires experimental data which are often lacking. An approach to predict the T1/2b in homeothermic vertebrates has recently been proposed. In this paper we have adapted this to be applicable to reptiles. For Cs, Ra and Sr, over a mass range of 0.02-1.5 kg, resultant predictions were generally within a factor of 6 of reported values demonstrating that the approach can be used when measured T1/2b data are lacking. However, the effect of mass on reptilian radionuclide T1/2b is minimal. If sufficient measured data are available for a given radionuclide then it is likely that these would give a reasonable estimate of T1/2b in any reptile species.

Regional long-term model of radioactivity dispersion and fate in the Northwestern Pacific and adjacent seas: application to the Fukushima Dai-ichi accident

The compartment model POSEIDON-R was modified and applied to the Northwestern Pacific and adjacent seas to simulate the transport and fate of radioactivity in the period 1945-2010, and to perform a radiological assessment on the releases of radioactivity due to the Fukushima Dai-ichi accident for the period 2011-2040. The model predicts the dispersion of radioactivity in the water column and in sediments, the transfer of radionuclides throughout the marine food web, and subsequent doses to humans due to the consumption of marine products. A generic predictive dynamic food-chain model is used instead of the biological concentration factor (BCF) approach. The radionuclide uptake model for fish has as a central feature the accumulation of radionuclides in the target tissue. The three layer structure of the water column makes it possible to describe the vertical structure of radioactivity in deep waters. In total 175 compartments cover the Northwestern Pacific, the East China and Yellow Seas and the East/Japan Sea. The model was validated from (137)Cs data for the period 1945-2010. Calculated concentrations of (137)Cs in water, bottom sediments and marine organisms in the coastal compartment, before and after the accident, are in close agreement with measurements from the Japanese agencies. The agreement for water is achieved when an additional continuous flux of 3.6 TBq y(-1) is used for underground leakage of contaminated water from the Fukushima Dai-ichi NPP, during the three years following the accident. The dynamic food web model predicts that due to the delay of the transfer throughout the food web, the concentration of (137)Cs for piscivorous fishes returns to background level only in 2016. For the year 2011, the calculated individual dose rate for Fukushima Prefecture due to consumption of fishery products is 3.6 μSv y(-1). Following the Fukushima Dai-ichi accident the collective dose due to ingestion of marine products for Japan increased in 2011 by a factor of 6 in comparison with 2010.

Plutonium in wildlife and soils at the Maralinga legacy site: persistence over decadal time scales

The mobility of plutonium (Pu) in soils, and its uptake into a range of wildlife, were examined using recent and ∼25 year old data from the Taranaki area of the former Maralinga weapons test site, Australia. Since its initial deposition in the early 1960s, the dispersed Pu has been incorporated into the soil profile and food chain through natural processes, allowing for the study of Pu sequestration and dynamics in relatively undisturbed semi-arid conditions. The data indicate downward mobility of Pu in soil at rates of ∼0.2-0.3 cm per year for the most mobile fraction. As a result, while all of the Pu was initially deposited on the ground surface, approximately 93% and 62% remained in the top 0-2 cm depth after 25- and 50-years respectively. No large-scale lateral spreading of the Taranaki plume was observed. Pu activity concentrations in 0-1 cm soils with biotic crusts were not elevated when compared with nearby bare soils, although a small number of individual data suggest retention of Pu-containing particles may be occurring in some biotic crusts. Soil-to-animal transfer, as measured by concentration ratios (CRwo-soil), was 4.1E-04 (Geometric Mean (GM)) in mammals, which aligns well with those from similar species and conditions (such as the Nevada Test Site, US), but are lower than the GM of the international mammal data reported in the Wildlife Transfer Database (WTD). These lower values are likely due to the presence of a low-soluble, particulate form of the Pu in Maralinga soils. Arthropod concentration ratios (3.1E-03 GM), were similar to those from Rocky Flats, US, while values for reptiles (2.0E-02 GM) were higher than the WTD GM value which was dominated by data from Chernobyl. Comparison of uptake data spanning approximately 30 years indicates no decrease over time for mammals, and a potential increase for reptiles. The results confirm the persistence of bioavailable Pu after more than 50 years since deposition, and also the presence of larger-sized particles which currently affect CRwo-soil calculations, and which may serve as an ongoing source of bioavailable Pu as they are subjected to weathering into the future.

Transfer parameters for ICRP reference animals and plants collected from a forest ecosystem

The International Commission on Radiological Protection (ICRP) have suggested the identification of a series of terrestrial, marine and freshwater sites from which samples of each Reference animal and plant (RAP) could be systematically collected and analysed. We describe the first such study in which six of the eight terrestrial RAPs, and associated soil samples, were collected from a site located in a managed coniferous forestry plantation in north-west England. Adult life stages of species representing six of the terrestrial RAPs (Wild grass, Pine tree, Deer, Rat, Earthworm and Bee) were sampled and analysed to determine concentrations of 60 elements and gamma-emitting radionuclides. The resultant data have been used to derive concentration ratios (CR(wo-soil)) relating element/radionuclide concentrations in the RAPs to those in soil. This paper presents the first-reported transfer parameters for a number of the RAP-element combinations. Where possible, the derived CR(wo-soil) values are compared with the ICRPs-recommended values and any appreciable differences discussed.

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.

Approaches to providing missing transfer parameter values in the ERICA Tool--how well do they work?

A required parameter for the ERICA Tool is the concentration ratio (CR), which is used to describe the transfer from environmental media to a range of organisms. For the original parameterisation of the ERICA Tool, 60% of these values were derived using a variety of extrapolation approaches, including the application of allometric models, the use of values for a similar organism or element with similar biogeochemical behaviour and the use of values from a different ecosystem. Although similar approaches are applied in other assessment systems, there has been little attempt to see how well these approaches perform. In this paper, CR values in the ERICA Tool derived using extrapolation approaches are compared to more recently available empirical data from the IAEA wildlife transfer database. The primary purpose of the default CR database in the ERICA Tool, and other models, is to enable the user to conduct conservative screening assessments. Conservatism was therefore introduced to the analyses by selecting the 95th percentile CR values for subsequent calculations. The extrapolation methodologies are not guaranteed to provide conservative estimates of empirical 95th percentile CRs. For the terrestrial ecosystem, the extrapolation methods provide underpredictions of empirical 95th percentiles as often as they produce overpredictions. In a few cases the underestimation of CR values, when considering all ecosystems, is substantial - by orders of magnitude - which is clearly unacceptable for a screening assessment. Thus, although extrapolation approaches will remain an essential component of screening assessments in the future, because data gaps will always be present, diligence is important in their application. Finally, by synthesizing the results from the current analyses and through other considerations, some recommendations are provided with regards to modifying the original guidance on use of extrapolation approaches in the ERICA Tool.

Whole-organism concentration ratios for plutonium in wildlife from past US nuclear research data

Whole-organism concentration ratios (CRwo-media) for plutonium (Pu) in wildlife were calculated using data from the broad range of organism types and environmental settings of the US nuclear research program. Original sources included site-specific reports and scientific journal articles typically from 1960s to 80s research. Most of the calculated CRwo-media values are new to existing data sets, and, for some wildlife categories, serve to fill gaps or add to sparse data including those for terrestrial reptile; freshwater bird, crustacean and zooplankton; and marine crustacean and zooplankton. Ratios of Pu concentration in the whole-organism to that in specific tissues and organs are provided here for a range of freshwater and marine fish. The CRwo-media values in fish living in liquid discharge ponds were two orders of magnitude higher than those for similar species living in lakes receiving Pu from atmospheric fallout, suggesting the physico-chemical form of the source Pu can dominate over other factors related to transfer, such as organism size and feeding behavior. Small rodent data indicated one to two order of magnitude increases when carcass, pelt, and gastrointestinal tract were included together in the whole-organism calculation compared to that for carcass alone. Only 4% of Pu resided in the carcass of small rodents compared to 75% in the gastrointestinal tract and 21% in the pelt.

An international database of radionuclide concentration ratios for wildlife: development and uses

A key element of most systems for assessing the impact of radionuclides on the environment is a means to estimate the transfer of radionuclides to organisms. To facilitate this, an international wildlife transfer database has been developed to provide an online, searchable compilation of transfer parameters in the form of equilibrium-based whole-organism to media concentration ratios. This paper describes the derivation of the wildlife transfer database, the key data sources it contains and highlights the applications for the data.

Evaluating summarised radionuclide concentration ratio datasets for wildlife

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

Marine and freshwater concentration ratios (CR(wo-water)): review of Japanese data

The water-to-organism (whole body) concentration ratio (CR(wo-water)), which is defined as the ratio of the concentration of a radionuclide in the biota (Bq kg(-1) fresh weight) to that in water (Bq L(-1)), has been used in mathematical models for environmental radiation protection. In the present paper, published global fallout (90)Sr, (137)Cs, (106)Ru, (144)Ce and (239+240)Pu activity concentration data and stable element concentration data for Na, K, Ca, Mg, Fe, Cu and Mn for organisms living in freshwater or seawater areas in Japan were collated. The data suitable for obtaining CR(wo-water) values were identified. CR(wo-water) values of (137)Cs were similar for pelagic fish, benthic fish and whitebait (immature, small fish) with respective geometric means of 30 (range: 4.4-69), 32 (range: 15-54) and 33 (range: 13-84). The calculated CR(wo-water) values of the other radionuclides and stable elements were generally similar to other previously reported values; with the exception that those for Ce were lower for marine biota and those of Cu were higher for freshwater fish.

TRS Cs CRwo-water values for the marine environment: analysis, applications and comparisons

A new TRS document on Transfer of radionuclides to Wildlife has compiled equilibrium CR(wo-media) values for a variety of radionuclides and ecosystems. Assessment tools such as the ERICA Tool use equilibrium whole organism concentration ratios (CR(wo-media)) to predict radionuclide activity concentrations in wildlife from those in media (e.g. water). The aim of this paper is to compare and contrast model predictions of doses from (137)Cs to marine organisms using three different approaches: (i) the ERICA Tool utilising the new TRS values to estimate internal and external doses to reference organisms for the Black sea and the Aegean Sea and for the sea close to the Fukushima Dai-ichi plant. (ii) a hydrodynamic site specific model for seawater for parts of the Aegean Sea, Greece which estimates radionuclide concentrations using site specific data and (iii) a biokinetic model for fish applied to the Fukushima releases to the Pacific. The advantages and limitations of these approaches are discussed with respect to determining doses to pelagic fish. The applicability of the three approaches will vary with the objective of an assessment. The site specific model can predict variation in (137)Cs with depth and uses site specific CR values. The application of the biokinetic model to predicted (137)Cs activity concentrations in seawater and fish due to near coastal inputs from Fukushima Dai-ichi showed that the maximum internal dose-rates in fish attributable to (137)Cs would be substantially lower than those determined using equilibrium assumptions in ERICA but the accumulative doses over 100 days were similar.

Estimating the biological half-life for radionuclides in homoeothermic vertebrates: a simplified allometric approach

The application of allometric, or mass-dependent, relationships within radioecology has increased with the evolution of models to predict the exposure of organisms other than man. Allometry presents a method of addressing the lack of empirical data on radionuclide transfer and metabolism for the many radionuclide-species combinations which may need to be considered. However, sufficient data across a range of species with different masses are required to establish allometric relationships and this is not always available. Here, an alternative allometric approach to predict the biological half-life of radionuclides in homoeothermic vertebrates which does not require such data is derived. Biological half-life values are predicted for four radionuclides and compared to available data for a range of species. All predictions were within a factor of five of the observed values when the model was parameterised appropriate to the feeding strategy of each species. This is an encouraging level of agreement given that the allometric models are intended to provide broad approximations rather than exact values. However, reasons why some radionuclides deviate from what would be anticipated from Kleiber's law need to be determined to allow a more complete exploitation of the potential of allometric extrapolation within radioecological models.

Chronic exposure by ingestion of environmentally relevant doses of (226)Ra leads to transient growth perturbations in fathead minnow (Pimephales promelas, Rafinesque, 1820)

PURPOSE

To assess the impact of environmentally relevant levels of ingested (226)Ra on a common freshwater fish species.

METHODS

Fathead minnow (Pimephales promelas, Rafinesque) were obtained at the first feeding stage and established on a commercial fish food diet containing (226)Ra in the activity range 10 mBq/g(-1), -10,000 mBq/g(-1). They remained on this diet for 24 months and were sampled invasively at 1,6,18 and 24 months to assess growth, biochemical indices and accumulated dose and non-invasively also at 12 and 15 months to assess growth.

RESULTS

Fish fed 10 and 100 mBq/g(-1) diet showed a small transitory deregulation of growth at 6 and 12 months. Fish fed higher activities showed less significant or insignificant effects. There was a trend at 18 months which was stronger at 24 months for the population distribution to change in all of the (226)Ra fed groups so that smaller fish were smaller and bigger fish were bigger than the controls. There were also significant differences in the ratios of protein:DNA at 24 months which were seen as a trend but were not significant at earlier time points.

CONCLUSIONS

Fish fed a radium diet for 2 years show a small and transitory growth dysregulation at 6 and 12 months. The effects predominate at the lower activities suggesting hormetic or homeostatic adjustments. There was no effect on growth of exposure to the high activities (226)Ra. This suggests that radium does not have a serious impact on the ecology of the system and the level of radium that would be transferred to humans is very low. The results may be important in the assessment of long-term environmental impacts of (226)Ra exposure.

Assessing radiation exposure of herbaceous plant species at the East-Ural Radioactive Trace

The East-Ural Radioactive Trace (EURT) is a result of the Mayak Production Association accident that occurred in 1957 in Russia. Radiological assessment improves the interpretation of biological effects of exposure to ionizing radiation. Therefore a modeling approach was used to estimate dose rates on Leonurus quinquelobatus, Silene latifolia, Stellaria graminea and Bromus inermis. Soil-to-organism transfer parameter values are delivered from empirical data of (90)Sr and (137)Cs soil and vegetative plant mass activity concentrations. External and internal whole-body dose rates were calculated using deterministic (The ERICA Tool-Tier 2 and R&D 128/SP1a) and probabilistic (The ERICA Tool-Tier 3) methods. The total dose rate for herbs was under 100 μGy h(-1) at the most polluted site. The total absorbed dose rates increased 43-110 times (Tier 3) for different herbaceous plant species along the pollution gradient. Based on these data, it can be concluded that herbaceous plant populations currently exist under low-level chronic exposure at the EURT area.

Ecological risk assessment of Central Asian mining sites: application of the ERICA assessment tool

Recent field expeditions to Central Asian mining sites have provided a wealth of data on radionuclide and metal concentrations in environmental media. In this paper the ERICA assessment tool was used to provide an assessment of the potential doses to non-human biota at the various sites. The aim was to identify the most exposed organism types and the radionuclides giving rise to the greatest doses. The measured media and biota activity concentrations were also used to compare site-specific Kds and CRs with default tool parameters. At all terrestrial sites, the maximum doses (up to ca. 600 μGy/h) were seen in lichens and bryophytes, with concentrations of radium in soils dominating the assessments. Internal alpha dose from (226)Ra was the biggest dose contributor, representing between 72 and 97% of the total dose, with U isotopes as the next most significant contributor. For aquatic organisms the highest calculated doses were obtained for aquatic plants (ca. 100 μGy/h), followed by molluscs, crustacean, zooplankton and insect larva, based on at site environmental media data. For aquatic plants, the internal alpha doses from uranium isotopes dominated the dose at most of the sites, hence the highest doses were seen at sites with the highest U concentrations. While the measured and modelled concentrations were usually in reasonable agreement, particularly for U and Ra in terrestrial plants, there were some differences, most notably for U and Po in the aquatic environment. Modelled concentrations of U in aquatic plants tended to be higher than those measured in site samples; while Po in fish was greater than modelled concentrations. Furthermore, not all the organisms listed in the ERICA tool had been sampled at the sites. Nevertheless, the assessment results should be of great benefit in identifying priority areas for future field studies.

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.