Allometric-kinetic model predictions of radionuclide dynamics across turtle taxa

Chelonians (turtles, tortoises, and sea turtles; hereafter, turtles) inhabit a wide variety of ecosystems that are currently, or have the potential in the future to become, radioactively contaminated. Because they are long-lived, turtles may uniquely accumulate significant amounts of the radionuclides, especially those with long half-lives and are less environmentally mobile. Further, turtle shells are covered by scutes made of keratin. For many turtle taxa, each year, keratin grows sequentially creating annual growth rings or layers. Theoretically, analysis of these scute layers for radionuclides could provide a history of the radioactivity levels in the environment, yet there are few previously published studies focused on the dynamics of radionuclide intake in turtles. Using established biochemical and ecological principles, we developed an allometric-kinetic model to establish relationships between the radionuclide concentrations in turtles and the environment they inhabit. Specifically, we calculated Concentration Ratios (CRs - ratio of radionuclide concentration in the turtle divided by the concentration in the soil, sediment, or water) for long-lived radionuclides of uranium and plutonium for freshwater turtles, tortoises, and sea turtles. These CRs allowed prediction of environmental concentrations based on measured concentrations within turtles or vice-versa. We validated model-calculated CR values through comparison with published CR values for representative organisms, and the uncertainty in each of the model parameters was propagated through the CR calculation using Monte Carlo techniques. Results show an accuracy within a factor of three for most CR comparisons though the difference for plutonium was larger with a CR ratio of about 200 times for sea turtles, driven largely by the uncertainty of the solubility of plutonium in sea water.

A comprehensive probabilistic approach for integrating and separating natural variability and parametric uncertainty in the prediction of distribution coefficient of radionuclides in rivers

A geochemical speciation model was developed to predict Distribution coefficients (K_ds) of radionuclides (RNs) in rivers. The model takes into account complexation of RNs with inorganic ligands, sorption of RNs with hydrous ferric oxides, complexation of RNs with dissolved and particulate organic carbon (DOC and POC) and sorption and/or co-precipitation of RNs to carbonates. A sorption model of Cs onto clay was also integrated. The tool is also designed to conduct uncertainty and sensitivity analysis. Sensitivity analysis follows a stepwise structured approach, starting from computationally 'inexpensive' Morris method to most costly variance-based EFAST method. A nested Monte Carlo approach was also implemented to separate natural variability and lack of knowledge in global uncertainty assessment. As case studies, K_d distributions were estimated for Co, Mn, Ag and Cs in seven French rivers. Uncertainty analysis allowed to quantify K_d ranges that can be expected when considering all the sensitive parameters together.

A 40-year marine record of 137Cs and 99Tc transported into the Danish Straits: Significance for oceanic tracer studies

This work reports comprehensive time-series datasets for 137Cs and 99Tc in marine samples from the Danish Straits over the past 40 years, where dynamic inputs from the two European nuclear reprocessing plants Sellafield (SF) and La Hague (LH) and Chernobyl accident are clearly archived. Distinct seasonal variations between 137Cs and 99Tc are observed in Fucus vesiculosus (F. vesiculosus), which needs to be taken into account when using F. vesiculosus as a bio-monitor to represent the concentration of radionuclides in seawater. Comparable transfer factor (TF) for 99Tc from SF to Kattegat between our calculation and earlier studies indicates a relatively steady water mass transport over the past decades. Three distinct events are observed in the temporal evolution of 99Tc/137Cs activity ratio in F. vesiculosu with the first event corresponding with the increased 99Tc discharge from SF, while the other two are very likely related to the major Baltic inflow (MBI) events. The correlation between the 99Tc/137Cs activity ratio and salinity fits well into the binary mixing line with the North Sea (NS) and the Baltic Sea (BS) as end members. A model simulation indicates that water mass from NS constitutes less than 50% in the surface water and 50-100% for most locations in the bottom water of the Danish Straits. Overall observations show that 137Cs and 99Tc in marine samples, especially 99Tc/137Cs isotope ratios, serve as useful oceanic tracers to study different natural processes, such as water mixing and transport dynamics.

Transport and fate of 137Cs in the Mediterranean and Black Seas system during 1945-2020 period: A modelling study

The compartment model POSEIDON-R with an embedded dynamic food web model was used to assess ¹³⁷Cs distributions in the Mediterranean and Black Seas during 1945-2020 due to the weapon testing and accident at the Chernobyl nuclear power plant. Three maximums of contamination of surface waters can be identified from 1950 in the Mediterranean Sea system. Two of them (in 1959 and 1963) were caused by atmospheric deposition due to the nuclear weapon testing. Third maximum in 1986 was related with the Chernobyl accident. Maximum of inventory of ¹³⁷Cs in the Mediterranean Sea (11461 TBq) was achieved in 1968, whereas secondary maximum caused by Chernobyl accident in 1986 was almost the same (11460 TBq). The corresponding maximum in the Black Sea (3703 TBq) was reached in 1986. It is approximately two times larger than nuclear weapon tests maximum. The results of simulations conducted with generic parameters agreed well with measurements of ¹³⁷Cs concentrations in the water, bottom sediments, and in marine organisms. The inventory in the Mediterranean Sea is most sensitive to the global deposition, whereas water exchange with Atlantic Ocean and the Black Sea plays minor role. The cumulative individual dose for the period 1945-2020 from consumption of marine products contaminated by ¹³⁷Cs was in the range 41-130 μSv in the Mediterranean Sea and 213-274 μSv in the Black Sea. The dose increased up to 40% due to Chernobyl accident in the Mediterranean countries and 66-103% in the Black Sea countries comparatively with dose from the global deposition. A useful application of the modelling for monitoring purposes was selection of representative regions in the Mediterranean Sea (5 regions) and in the Black Sea (4 regions) using "etalon" method for classification.

A modeling approach to estimate the 137Cs discharge in rivers from immediately after the Fukushima accident until 2017

We developed a simple model to evaluate and predict the ¹³⁷Cs discharge from catchments using a tank model and the L-Q equation. Using this model, the ¹³⁷Cs discharge and discharge ratio from the Abukuma River and 13 other rivers in the Fukushima coastal region were estimated from immediately after the Fukushima accident up to 2017. The ¹³⁷Cs discharge (and discharge ratio to the deposition inventory in the catchment) of the Abukuma River and 13 other rivers in the Fukushima coastal region during the initial six months after the accident were estimated to be 18 TBq (3.1%) and 11 TBq (0.79%), respectively. These values of ¹³⁷Cs discharge ratio were 1-2 orders of magnitude higher than those observed after June 2011 in previous studies (Ueda et al., 2013; Tsuji et al., 2016; Iwagami et al., 2017a), indicating that the initial ¹³⁷Cs discharge from the catchments through the rivers was significant. The simulated initial ¹³⁷Cs discharge rates for the initial six months after the Fukushima accident were about 9-30 times larger in each catchment than those after that point until 2017, though initial ¹³⁷Cs concentration in river water was derived from an extrapolation of data based on a two exponentially decreasing fitting. However, it was found that the impact on the ocean from the initial ¹³⁷Cs discharge through the rivers can be limited because the ¹³⁷Cs discharge from the Abukuma River and the 13 other rivers in the Fukushima coastal region (29 TBq) was two orders of magnitude smaller than the direct release from Fukushima Dai-ichi Nuclear Power Plant (FDNPP) into the ocean (3.5 PBq) and from atmospheric deposition into the ocean (7.6 PBq) (Kobayashi et al., 2013). This model is expected to be useful to evaluate and predict ¹³⁷Cs discharge from catchments in future water management and in the estimation of ¹³⁷Cs discharge into reservoirs and the ocean.

Fukushima 137Cs releases dispersion modelling over the Pacific Ocean. Comparisons of models with water, sediment and biota data

A number of marine radionuclide dispersion models (both Eulerian and Lagrangian) were applied to simulate ¹³⁷Cs releases from Fukushima Daiichi nuclear power plant accident in 2011 over the Pacific at oceanic scale. Simulations extended over two years and both direct releases into the ocean and deposition of atmospheric releases on the ocean surface were considered. Dispersion models included an embedded biological uptake model (BUM). Three types of BUMs were used: equilibrium, dynamic and allometric. Model results were compared with ¹³⁷Cs measurements in water (surface, intermediate and deep layers), sediment and biota (zooplankton, non-piscivorous and piscivorous fish). A reasonable agreement in model/model and model/data comparisons was obtained.

Radiocesium in seawater, sediments, and marine megabenthic species in coastal waters off Fukushima in 2012-2016, after the 2011 nuclear disaster

In bottom-sediment samples collected in 2012 from a coastal strip (∼30 km × 120 km) off the Fukushima Daiichi Nuclear Power Plant (FDNPP), radiocesium activity concentrations were generally higher south of the FDNPP, with high activity concentration patches in the north. In periodic surveys conducted at nearshore sites during 2012-2016, no clear temporal trends were observed in radiocesium activity concentrations in seawater or bottom sediment, and activity concentrations were higher in fish than in invertebrates. During 2012-2014, radiocesium activity concentrations tended to decrease in fish, but during 2012-2013 in the south, some increases were observed. Radiocesium activity concentrations were significantly higher in some fish (e.g., Okamejei kenojei) directly offshore and south of the FDNPP than in the north. Activity concentrations in fish stomach contents were significantly correlated with those in muscle tissue, suggesting that the consumption of contaminated prey contributed greatly to radiocesium contamination in demersal fish.

Radionuclide concentration processes in marine organisms: A comprehensive review

The first measurements made of artificial radionuclides released into the marine environment did reveal that radionuclides are concentrated by marine biological species. The need to report radionuclide accumulation in biota in different conditions and geographical areas prompted the use of concentration factors as a convenient way to describe the accumulation of radionuclides in biota relative to radionuclide concentrations in seawater. Later, concentration factors became a tool in modelling radionuclide distribution and transfer in aquatic environments and to predicting radioactivity in organisms. Many environmental parameters can modify the biokinetics of accumulation and elimination of radionuclides in marine biota, but concentration factors remained a convenient way to describe concentration processes of radioactive and stable isotopes in aquatic organisms. Revision of CF values is periodically undertaken by international organizations, such as the International Atomic Energy Agency (IAEA), to make updated information available to the international community. A brief commented review of radionuclide concentration processes and concentration factors in marine organisms is presented for key groups of radionuclides such as fission products, activation products, transuranium elements, and naturally-occurring radionuclides.

Applicability of Kd for modelling dissolved 137Cs concentrations in Fukushima river water: Case study of the upstream Ota River

A study is presented on the applicability of the distribution coefficient (K_d) absorption/desorption model to simulate dissolved ¹³⁷Cs concentrations in Fukushima river water. The upstream Ota River basin was simulated using GEneral-purpose Terrestrial Fluid-flow Simulator (GETFLOWS) for the period 1 January 2014 to 31 December 2015. Good agreement was obtained between the simulations and observations on water and suspended sediment fluxes, and on particulate bound ¹³⁷Cs concentrations under both base and high flow conditions. By contrast the measured concentrations of dissolved ¹³⁷Cs in the river water were much harder to reproduce with the simulations. By tuning the K_d values for large particles, it was possible to reproduce the mean dissolved ¹³⁷Cs concentrations during base flow periods (observation: 0.32 Bq/L, simulation: 0.36 Bq/L). However neither the seasonal variability in the base flow dissolved ¹³⁷Cs concentrations (0.14-0.53 Bq/L), nor the peaks in concentration that occurred during storms (0.18-0.88 Bq/L, mean: 0.55 Bq/L), could be reproduced with realistic simulation parameters. These discrepancies may be explained by microbial action and leaching from organic matter in forest litter providing an additional input of dissolved ¹³⁷Cs to rivers, particularly over summer, and limitations of the K_d absorption/desorption model. It is recommended that future studies investigate these issues in order to improve simulations of dissolved ¹³⁷Cs concentrations in Fukushima rivers.

Temporal and spatial variations of 134Cs and 137Cs levels in the Sea of Japan and Pacific coastal region: Implications for dispersion of FDNPP-derived radiocesium

To investigate the dispersion of Fukushima Dai-ichi Nuclear Power Plant (FDNPP)-derived radiocesium in the Sea of Japan and western Pacific coastal region and determine the sources of radiocesium in these areas, we examined the temporal and spatial variations of ¹³⁴Cs and ¹³⁷Cs concentrations (activities) during 2011-2016 in seawaters around the western Japanese Archipelago, particularly in the Sea of Japan. In May 2013, the surface concentration of ¹³⁴Cs was ∼0.5 mBq/L (decay-corrected to March 11, 2011), and that of ¹³⁷Cs exceeded the pre-accident level in this study area, where the effects of radiocesium depositions just after the FDNPP accident disappeared in surface waters in October 2011. Subsequently, radiocesium concentrations gradually increased during 2013-2016 (∼0.5-1 mBq/L for ¹³⁴Cs), exhibiting approximately homogeneous distributions in each year. The temporal and spatial variations of ¹³⁴Cs and ¹³⁷Cs concentrations indicated that FDNPP-derived radiocesium around the western Japanese Archipelago, including the Sea of Japan, has been supported by the Kuroshio Current and its branch, Tsushima Warm Current, during 2013-2016. However, in the Sea of Japan, the penetration of ¹³⁴Cs was limited to depths of less than ∼200 m during three years following the re-delivery of FDNPP-derived radiocesium.

Norwegian monitoring (1990-2015) of the marine environment around the sunken nuclear submarine Komsomolets

Norway has monitored the marine environment around the sunken Russian nuclear submarine Komsomolets since 1990. This study presents an overview of 25 years of Norwegian monitoring data (1990-2015). Komsomolets sank in 1989 at a depth of 1680 m in the Norwegian Sea while carrying two nuclear torpedoes in its armament. Subsequent Soviet and Russian expeditions to Komsomolets have shown that releases from the reactor have occurred and that the submarine has suffered considerable damage to its hulls. Norwegian monitoring detected ¹³⁴Cs in surface sediments around Komsomolets in 1993 and 1994 and elevated activity concentrations of ¹³⁷Cs in bottom seawater between 1991 and 1993. Since then and up to 2015, no increased activity concentrations of radionuclides above values typical for the Norwegian Sea have been observed in any environmental sample collected by Norwegian monitoring. In 2013 and 2015, Norwegian monitoring was carried out using an acoustic transponder on the sampling gear that allowed samples to be collected at precise locations, ∼20 m from the hull of Komsomolets. The observed ²³⁸Pu/^239,240Pu activity ratios and ²⁴⁰Pu/²³⁹Pu atom ratios in surface sediments sampled close to Komsomolets in 2013 did not indicate any releases of Pu isotopes from reactor or the torpedo warheads. Rather, these values probably reflect the overprinting of global fallout ratios with fluxes of these Pu isotopes from long-range transport of authorised discharges from nuclear reprocessing facilities in Northern Europe. However, due to the depth at which Komsomolets lies, the collection of seawater and sediment samples in the immediate area around the submarine using traditional sampling techniques from surface vessels is not possible, even with the use of acoustic transponders. Further monitoring is required in order to have a clear understanding of the current status of Komsomolets as a potential source of radioactive contamination to the Norwegian marine environment. Such monitoring should involve the use of ROVs or submersibles in order to obtain samples next to and within the different compartments of the submarine.

Ecotracer: analyzing concentration of contaminants and radioisotopes in an aquatic spatial-dynamic food web model

Ecotracer is a tool in the Ecopath with Ecosim (EwE) software package used to simulate and analyze the transport of contaminants such as methylmercury or radiocesium through aquatic food webs. Ecotracer solves the contaminant dynamic equations simultaneously with the biomass dynamic equations in Ecosim/Ecospace. In this paper, we give a detailed description of the Ecotracer module and analyze the performance on two problems of differing complexity. Ecotracer was modified from previous versions to more accurately model contaminant excretion, and new numerical integration algorithms were implemented to increase accuracy and robustness. To test the mathematical robustness of the computational algorithm, Ecotracer was tested on a simple problem for which we know an analytical solution. These results demonstrated the effectiveness of the program numerics. A much more complex model, the release of the cesium radionuclide ¹³⁷Cs from the Fukushima Dai-ichi nuclear accident, was also modeled and analyzed. A comparison of the Ecotracer results to sampled ¹³⁷Cs measurements in the coastal ocean area around Fukushima show the promise of the tool but also highlight some important limitations.

Marine ecological risk assessment methods for radiation accidents

Ecological risk assessment (ERA) is a powerful technical tool that can be used to analyze potential and extreme adverse environmental impacts. With the rapid development of nuclear power plants in coastal areas around the world, the establishment of approaches and methodologies for marine ERA with a focus on radiation accidents is an urgent requirement for marine environmental management. In this study, the approaches and methodologies for ERA pertaining to marine radiation accidents (MRA) are discussed and summarized with applications in case studies, such as the nuclear accident in Fukushima, Japan, and a hypothetical accident in Daya Bay, China. The concepts of ERA and Risk Degree of ERA on MRA are defined for the first time to optimize the ERA system. The results of case studies show that the ERA approach and methodology for MRA are scientifically sound and effective in both the early and late stage of MRAs along with classic ERA Approach and the ERICA Integrated Approach. The results can be useful in the decision-making processes and the risk management at the beginning of accident as well as the ecological restoration after the accident.

U isotopes distribution in the Lower Rhone River and its implication on radionuclides disequilibrium within the decay series

The large rivers are main pathways for the delivery of suspended sediments into coastal environments, affecting the biogeochemical fluxes and the ecosystem functioning. The radionuclides from ²³⁸U and ²³²Th-series can be used to understand the dynamic processes affecting both catchment soil erosion and sediment delivery to oceans. Based on annual water discharge the Rhone River represents the largest river of the Mediterranean Sea. The Rhone valley also represents the largest concentration in nuclear power plants in Europe. A radioactive disequilibrium between particulate ²²⁶Ra_(p) and ²³⁸U_(p) was observed in the suspended sediment discharged by the Lower Rhone River (Eyrolle et al. 2012), and a fraction of particulate ²³⁴Th was shown to derive from dissolved ²³⁸U_(d) (Zebracki et al. 2013). This extensive study has investigated the dissolved U isotopes distribution in the Lower Rhone River and its implication on particulate radionuclides disequilibrium within the decay series. The suspended sediment and filtered river waters were collected at low and high water discharges. During the 4-months of the study, two flood events generated by the Rhone southern tributaries were monitored. In river waters, the total U_(d) concentration and U isotopes distribution were obtained through Q-ICP-MS measurements. The Lower Rhone River has displayed non-conservative U-behavior, and the variations in U_(d) concentration between southern tributaries were related to the differences in bedrock lithology. The artificially occurring ²³⁶U was detected in the Rhone River at low water discharges, and was attributed to the liquid releases from nuclear industries located along the river. The (²³⁵U/²³⁸U)_(d) activity ratio (=AR) in river waters was representative of the ²³⁵U natural abundance on Earth. The (²²⁶Ra/²³⁸U)_(p) AR in suspended sediment has indicated a radioactive disequilibrium (average 1.3 ± 0.1). The excess of ²³⁴Th in suspended sediment =(²³⁴Th_xs(p)) was apparent solely at low water discharges. The activity of ²³⁴Th_xs(p) was calculated through gamma measurements and ranged from unquantifiable to 56 ± 14 Bq kg^-1. The possibility of using ²³⁴Th as a tracer for the suspended sediment dynamics in large Mediterranean river was then discussed.

Radiation hazards and lifetime risk assessment of tap water using liquid scintillation counting and high-resolution gamma spectrometry

In this work, two complementary techniques, viz. liquid scintillation counting and high-resolution gamma spectrometry are utilized to analyze radionuclides concentrations in tap water of Irbid governorate, Jordan, and study their correlation. Gross alpha and gross beta concentrations, in the tap water samples collected from the nine districts of Irbid governorate, ranged from <82 to 484 mBq/L with a mean of 295 mBq/L and from <216 to 984 mBq/L with a mean of 611 mBq/L, respectively. Furthermore, gamma spectrometry analysis, for the tap water samples, shows that the activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K ranged between <19 and 302 mBq/L, 24 to 119 mBq/L, and <101 to 342 mBq/L, respectively. There was a weak or even no correlation among the identified natural radionuclides with no trace of artificial radioactivity. In addition, the results of both techniques show that storing tap water in drilled wells leads to higher levels of radioactivity concentrations beyond the international permissible limits. Furthermore, the average lifetime risk and annual effective dose received by age-grouped inhabitants due to direct and indirect tap water consumption are evaluated, where most of the received dose is attributed to ²²⁶Ra.

Cancer Incidence after In Utero Exposure to Ionizing Radiation in Techa River Residents

Health effects of in utero exposure to ionizing radiation, especially among adults, are still unclear. The aim of this study was to analyze cancer risk in a cohort of subjects exposed in utero due to releases of nuclear waste into the Techa River in the Southern Urals, taking into account additional postnatal exposure. Analysis for solid cancer was based on 242 cases among 10,482 cohort members, accumulating 381,948 person-years at risk, with follow-up from 1956-2009, while analysis for hematological malignancies was based on 26 cases among 11,070 persons, with 423,502 person-years at risk, with follow-up from 1953-2009. Mean doses accumulated in soft tissues and in red bone marrow during the prenatal period were 4 mGy and 30 mGy, respectively. Additional respective mean postnatal doses received by cohort members were 11 and 84 mGy. Poisson regression analysis was used to estimate the excess relative risk (ERR) of cancer incidence related to in utero and postnatal doses. No association was observed for in utero exposure with solid cancer risk [ERR per 10 mGy: -0.007; 95% confidence interval (CI): <-0.107; 0.148] or with hematological malignancy risk (ERR/10 mGy: -0.011; 95% CI: <-0.015; 0.099). However, ERR of solid cancer increased significantly with increasing postnatal dose (ERR/10 mGy: 0.11; 95% CI: 0.04; 0.22). The very wide confidence intervals in these ERR results are similar to those of studies performed on the LSS cohort and the offspring of the Mayak Female Worker Cohort, as well as case-control studies of effects after in utero medical exposure. There were limitations of this study, with decreased statistical power, due to the low prenatal doses received by most of the cohort members, the small number of cancer cases and the absence of cohort members over the age of 59 years (living cohort members had reached 49-59 years of age). Further aging of the cohort and extension of the follow-up period will enhance the statistical power of this study in the future. There is a shortage of cohort studies reporting on the effects of prenatal radiation exposure, as well as information on chronic exposure during the prenatal period. Therefore, further research of this unique cohort will be a useful addition to the published literature on this subject, and a valuable means of elucidating the long-term effects of low-dose radiation exposure in the fetus.

Long term changes in the concentration of radium in discharge waters of coal mines and Upper Silesian rivers

According to the latest guidelines of the International Atomic Energy Agency (IAEA, 2016), coal mining is one of the most important contributors to occupational exposure. Coal mining contributes about 45% of the total annual collective dose obtained by workers due to the exposure at places of working. One of the sources of exposure in mining are formation brines with elevated concentrations of natural radionuclides, the most common are radium ²²⁶Ra and ²²⁸Ra. Radium isotopes often occur in formation waters in underground collieries in the Upper Silesian region (USCB) in Poland. Significant amounts of radium remain underground in the form of radioactive deposits created as a result of spontaneous deposition or water treatment. This phenomenon leads to the increase of radiation hazard for miners. The remaining activities of ²²⁶Ra and ²²⁸Ra are released into the rivers with mine effluents, causing the contamination of bottom sediments and river banks. The results of radioactivity monitoring of effluents and river waters are presented here to illustrate a trend of long-term changes in environmental contamination, caused by mining industry in the Upper Silesian Region.

Improving transfer functions to describe radiocesium wash-off fluxes for the Niida River by a Bayesian approach

This paper proposed methodological refinements of the generic transfer function approach to reconstruct radiocesium wash-off fluxes from contaminated catchments, by the integration of hydrological descriptors (passed volume of water, flow rate fluctuations and antecedent flow conditions). The approach was applied to the Niida River (Fukushima prefecture, Japan) for the period 03/2011-03/2015, for which daily flow rate (m³/s) and infrequent total radiocesium concentration (Bq/L) values were available from literature. Three models were defined, generic TF (Φ₀), flow-corrected time variant (Φ₁) and antecedent-flow corrected variant (Φ₂). Calibration of these models' parameters was performed with a Bayesian approach because it is particularly adapted to limited datasets and censored information, and it provides parameters distributions. The model selection showed strong evidence of model Φ₂ (indicated by marginal likelihood), which integrates current and recent hydrology in its formulation, and lower prediction errors (indicated by RMSE and ME). Models Φ₁ and Φ₂ better described wash-off dynamics compared to model Φ₀, due to the inclusion of one or several hydrological descriptors. From March 2011 to March 2015, model Φ₂ estimated ¹³⁷Cs export from Niida catchment between 0.32 and 0.67 TBq, with a median value of 0.49 TBq, which represents around 0.27% of the initial fallout and could represent a significant source-term to the Ocean compared to the direct release from Fukushima Dai-ichi Nuclear Power Plant (FDNPP). Moreover the remaining 99% of the initial radiocesium fallout within the catchment may constitute a persistent contamination source for wash-off. Although the proposed methodology brought improvements in the assessment of wash-off fluxes, it remains an empirical interpolation method with a limited predictive power, particularly for recent low activities. To improve predictions, modelling approaches require more observed data (particularly more activity values corresponding to more hydrological conditions), and the inclusion of more hydrological descriptors.

Impacts on the marine environment in the case of a hypothetical accident involving the recovery of the dumped Russian submarine K-27, based on dispersion of 137Cs

There is increasing concern regarding the issue of dumped nuclear waste in the Arctic Seas and in particular dumped objects with Spent Nuclear Fuel (SNF). Amongst dumped objects in the Arctic, the dumped Russian submarine K-27 has received great attention as it contains two reactors with highly enriched fuel and lies at a depth of about 30 m under water. To address these concerns a health and environmental impact assessment has been undertaken. Marine dispersion of potentially released radionuclides as a consequence of different hypothetical accident scenarios was modelled using the model NAOSIM. The outputs from the dispersion modelling have been used as inputs to food-chain transfer and environmental dosimetry models. The annual effective doses for subsistence fishing communities of the Barents-Kara seas region do not exceed 0.6 mSv for hypothetical accidents located at Stepovogo fjord or the Barents Sea. For high rate consumers of fish in Norway, following a potential accident at the Gremikha Bay, annual effects doses would be at around 0.15 mSv. Accumulated doses (over 90 days) for various organisms and for all release scenarios considered were never in excess of 150 μGy. The levels of ¹³⁷Cs derived for marine organism in areas close to Norway were not values that would likely cause concern from a regulatory perspective although for subsistence fishing communities close to the considered accident locations, it is not inconceivable that some restrictions on fishing etc. would need to be introduced.

Impacts on the terrestrial environment in case of a hypothetical accident involving the recovery of the dumped Russian submarine K-27

Objects containing radioactivity have been routinely dumped in Arctic waters near NW Russia up until the 1990s. One of the most radioactive objects in this region, the nuclear submarine K-27, was dumped in Stepogovo Fjord and contained spent nuclear fuel (SNF). Although the two K-27 submarine reactors were mothballed before dumping, concerns about the potential long term risks of contamination remain and plans to retrieve and decommission K-27 exist. In this article, human dose and environmental impact aseessments are presented for two possible future scenarios involving: (1) an ingress of water into a reactor in situ leading to a spontaneous chain reaction (SCR) and (2) an on-board fire when SNF is being removed at the mainland decommissiong site at Gremhika Bay on the Kola Peninsula. Assessments have been completed using conservative assumptions, focusing on possible effects to Norwegian territory. Atmospheric transport and deposition of radioactivity was modelled near field and regionally, using appropriate models, whilst human doses and environmental exposures were modelled using a standard IAEA approach and the ERICA tool, respectively. Results indicate that large areas of Norwegian territory could be affected by fallout from the Gremhika scenario, especially in the north, though at levels two orders of magnitude lower than those observed after the Chernobyl accident. Potential doses, primarily due to ground shine, to a critical group of personnel on-site at Stepogovo resulting from a SCR could require preventative measures based on ICRP recommendations (20-100 mSv). Doses to non-human biota in Norway for the Gremhika scenario would be negligible, typical of background dose rates for terrestrial organisms.

Radioecological investigation of 3H, 14C, and 129I in natural waters from Fuhrberger Feld catchment, Northern Germany

Ongoing radionuclide releases from nuclear facilities, e.g. from reprocessing plants, but also from nuclear reactors require monitoring of the environment. Particularly drinking water reservoirs are prone to possible radionuclide accumulation fostering the need for routine surveillance. In this work, we investigated tritium (³H), radiocarbon (¹⁴C), and iodine-129 (¹²⁹I) activity levels in natural aquatic samples at the water protection area of Fuhrberger Feld near Hannover city, Northern Germany. For that aim, a low-level liquid scintillation counting (LSC) technique was used to measure ³H in the water samples based on a distillation process after alkaline permanganate treatment. Isotopic ratios for both ¹⁴C and ¹²⁹I were measured by accelerator mass spectrometry (AMS) after chemical separation and purification of the samples. Mean ³H levels in precipitation (8.8 ± 3.4 TU) were found to be comparable to its levels in precipitation data in Germany. Rivers and small streams revealed similar mean ³H value (11.0 ± 3.3 TU) as in lake water (10.6 ± 3.4 TU). Variations in ³H concentrations in groundwater samples were observed and discussed. ¹⁴C levels in all groundwater samples were below the atmospheric natural level of 100 pMC indicating no anthropogenic input of radiocarbon. The ¹²⁹I/¹²⁷I isotopic ratios in all investigated water samples were in the order of 10^-8 to 10^-7, which is significantly higher than the pre-nuclear natural equilibrium isotopic ratio (∼1.5 × 10^-12). In strong contrast to all other regional groundwaters, the Fuhrberger Feld groundwater has much higher values of ¹²⁹I concentration and ¹²⁹I/¹²⁷I isotopic ratio close to the ones of surface water. The overall annual effective dose via ingestion for all nuclides in the investigated groundwater remains substantially below the reference dose level of 0.1 mSv a^-1.

Probabilistic assessment of the influence of lake properties in long-term radiation doses to humans

The assessment processes concerning the safety of nuclear waste repositories include the modelling of radionuclide transport in biosphere and the evaluation of the doses to the most affected humans. In this paper, a scenario, in which a contaminated lake is the water source for drinking water, irrigation water and watering of livestock, is presented. The objective of the paper is to probabilistically study the influence of lake properties as parameters in the assessment scenario. The properties of the lake are a result of previously conducted probabilistic studies, where the land uplift of the terrain surrounding the repositories and the formation of water bodies were studied in a 10,000-year time span using Monte Carlo simulation. The lake is formed at 3000 years from present day and the changing properties of the lake have been used in the study. The studied radionuclides ³⁶Cl, ¹³⁵Cs, ¹²⁹I, ²³⁷Np, ⁹⁰Sr, ⁹⁹Tc and ²³⁸U enter the lake with a rate of 1 Bq/year. The transport process from the lake water to humans is described and the doses (dose conversion factors) to adult humans are evaluated based on a study on average food consumption. Sensitivity analysis is used for identifying the parameters having the most influence on the outcome of the dose. Based on the results from the sensitivity analysis, the volumetric outflow rate of the lake and the volume of the lake were taken into closer consideration. The results show the influence of probabilistically derived geomorphic lake input parameters on the dose.

Environmental evolution records reflected by radionuclides in the sediment of coastal wetlands: A case study in the Yellow River Estuary wetland

Vertical profiles of environmental radionuclides (²¹⁰Pb, ¹³⁷Cs, ²³⁸U, ²³²Th, ²²⁶Ra and ⁴⁰K) in a sediment core (Y1) of the Yellow River Estuary wetland were investigated to assess whether environmental evolutions in the coastal wetland could be recorded by the distributions of radionuclides. Based on ²¹⁰Pb and ¹³⁷Cs dating, the average sedimentation rate of core Y1 was estimated to be 1.0 cm y^-1. Vertical distributions of natural radionuclides (²³⁸U, ²³²Th, ²²⁶Ra and ⁴⁰K) changed dramatically, reflecting great changes in sediment input. Concentrations of ²³⁸U, ²³²Th, ²²⁶Ra and ⁴⁰K all had significant positive relationships with organic matter and clay content, but their distributions were determined by different factors. Factor analysis showed that ²³⁸U was determined by the river sediment input while ²²⁶Ra was mainly affected by the seawater erosion. Environmental changes such as river channel migrations and sediment discharge variations could always cause changes in the concentrations of radionuclides. High concentrations of ²³⁸U and ²²⁶Ra were consistent with high accretion rate. Frequent seawater intrusion decreased the concentration of ²²⁶Ra significantly. The value of ²³⁸U/²²⁶Ra tended to be higher when the sedimentation rate was low and tide intrusion was frequent. In summary, environmental evolutions in the estuary coastal wetland could be recorded by the vertical profiles of natural radionuclides.

Impact of the Fukushima accident on marine biota, five years later

In a previous commentary written in 2011 in the aftermath of the Fukushima accident in Japan, I summarized what was then understood about the effects of accidental radioactive discharges to marine life and forecasted into the future how the marine environment would likely be affected. Since that time, several studies have been conducted on the impact of the accident on marine organisms, and radiation doses arising thereof. I developed a dynamic transfer model for studying the bioaccumulation of Fukushima radionuclides in marine biota and assessed the impact and likelihood of effects to marine life. In the present article, I highlight the lessons learned over the past 5 years. I address whether the environmental consequences in the marine environment are as significant as initially feared and, with respect to the current situation, what remains to be investigated as the radioactivity continues to spread in the marine environment. Integr Environ Assess Manag 2016;12:654-658. © 2016 SETAC.

Fukushima nuclear accident: preliminary assessment of the risks to non-human biota

This study assesses the 'radio-ecological' impacts of Fukushima nuclear accident on non-human biota using the ERICA Tool, which adopts an internationally verified methodology. The paper estimates the impacts of the accident on terrestrial and marine biota based on the environmental data reported in literature for Japan, China, South Korea and the USA. Discernible impacts have been detected in the marine biota around Fukushima Daiichi nuclear power plant. This study confirms that the Fukushima accident had caused heavier damage to marine bionts compared with terrestrial flora and fauna, in Japan.

Predicting exposure of wildlife in radionuclide contaminated wetland ecosystems

Many wetlands support high biodiversity and are protected sites, but some are contaminated with radionuclides from routine or accidental releases from nuclear facilities. This radiation exposure needs to be assessed to demonstrate radiological protection of the environment. Existing biota dose models cover generic terrestrial, freshwater, and marine ecosystems, not wetlands specifically. This paper, which was produced under IAEA's Environmental Modelling for Radiation Safety (EMRAS) II programme, describes an evaluation of how models can be applied to radionuclide contaminated wetlands. Participants used combinations of aquatic and terrestrial model parameters to assess exposure. Results show the importance of occupancy factor and food source (aquatic or terrestrial) included. The influence of soil saturation conditions on external dose rates is also apparent. In general, terrestrial parameters provided acceptable predictions for wetland organisms. However, occasionally predictions varied by three orders of magnitude between assessors. Possible further developments for biota dose models and research needs are identified.

Site-specific water quality guidelines: 2. Development of a water quality regulation framework for pulse exposures of mine water discharges at a uranium mine in northern Australia

The Ranger Uranium Mine, in northern Australia, is monitored by the Supervising Scientist Division (SSD) of the Australian Government to ensure that it does not impact on the highly valued aquatic ecosystems of Kakadu National Park. In 2010, the SSD adopted the continuous monitoring of electrical conductivity (EC) and turbidity, in combination with event-triggered automated grab samples, as its primary water quality monitoring method. The continuous monitoring of EC has shown that mine discharges typically occur over short-term 'pulse' durations of minutes to hours. Given that magnesium (Mg) is the most likely mine-derived solute to approach or exceed the applicable water quality limit value, the focus has been on developing a pulse exposure assessment framework for Mg, as represented by its proxy EC, which is tracked by the continuous monitoring system. This study presents a possible ecotoxicologically derived Mg pulse exposure limit and trigger regulation framework for Magela and Gulungul Creeks and an assessment of historic continuous monitoring EC data from these creeks. This framework demonstrates potential to supersede the current EC guideline and associated trigger levels, which are statistically derived from historic grab sample data.

Uranium in Kosovo's drinking water

The results of this paper are an initiation to capture the drinking water and/or groundwater elemental situation in the youngest European country, Kosovo. We aim to present a clear picture of the natural uranium concentration in drinking water and/or groundwater as it is distributed to the population of Kosovo. Nine hundred and fifty-one (951) drinking water samples were analyzed by inductively coupled plasma mass spectrometry (ICPMS). The results are the first countrywide interpretation of the uranium concentration in drinking water and/or groundwater, directly following the Kosovo war of 1999. More than 98% of the samples had uranium concentrations above 0.01 μg L(-1), which was also our limit of quantification. Concentrations up to 166 μg L(-1) were found with a mean of 5 μg L(-1) and median 1.6 μg L(-1) were found. Two point six percent (2.6%) of the analyzed samples exceeded the World Health Organization maximum acceptable concentration of 30 μg L(-1), and 44.2% of the samples exceeded the 2 μg L(-1) German maximum acceptable concentrations recommended for infant food preparations.

Baseline concentrations of strontium and 90Sr in seawater from the northern Gulf

Baseline concentration of strontium and Sr-90 in Gulf is presented. The strontium concentration is much higher than reported for other oceanic waters, while the Sr-90 concentration is low at 0.7-1.0 mBq l(-1), that represents the background level following nuclear tests and can be used as an effective tracer in case of any radioactive release in the region. The strontium concentration is primarily related to the increasing salinity off the Gulf coast.

Iodine-131 in sewage sludge from a small water pollution control plant serving a thyroid cancer treatment facility

Iodine-131 (half-life = 8.04 d) is the most widely used radionuclide in medicine for therapeutic purposes. It is excreted by patients and is discharged directly to sewer systems. Despite considerable dilution in waste water and the relatively short half-life of I, it is readily measured in sewage. This work presents I concentrations in sewage sludge from three water pollution control plants (WPCPs) on Long Island, NY. Iodine-131 concentrations ranged from 0.027 ± 0.002 to 148 ± 4 Bq g dry weight. The highest concentrations were measured in the Stony Brook WPCP, a relatively small plant (average flow = 6.8 × 10 L d) serving a regional thyroid cancer treatment facility in Stony Brook, NY. Preliminary radiation dose calculations suggested further evaluation of dose to treatment plant workers in the Stony Brook WPCP based on the recommendations of the Interagency Steering Committee on Radiation Standards.

Artificial radionuclides ⁹⁰Sr and ²⁴¹Am in the sediments of the Baltic Sea: total and spatial inventories and some temporal trends

The Baltic Sea was contaminated by radioactivity following global nuclear fallout and later by the Chernobyl accident. Despite the decrease of radioactivity caused by radioactive decay, radionuclides have a prolonged residence time in the water of the Baltic Sea due to slow water exchange and relatively rapid sedimentation. Very little is known about the amounts or spatial differences of ⁹⁰Sr and ²⁴¹Am in the Baltic Sea sediments. In this study, 20 sediment cores taken around the Baltic Sea were investigated to estimate inventories of these radionuclides. The rough results show that the Chernobyl fallout added the amount of ⁹⁰Sr in the same areas where the increase of ¹³⁷Cs can be detected, whereas this is not the case for ²⁴¹Am which is more evenly distributed in the sea bottom. In addition, local differences occur in the concentrations. These results are an important amendment to the radioactivity baseline of the Baltic Sea.

Variations of 210Po and 210Pb concentration in mussels (Mytilus galloprovincialis) from Didim and Izmir Bay (Turkish coast of Aegean Sea)

In this study, the activity concentrations of (210)Po and (210)Pb were determined in mussels (Mytilus galloprovincialis) collected from Didim and Izmir Bay (Turkish coast of Aegean Sea) during the period of April 2006-March 2007. The concentrations activity of (210)Po were determined spectroscopically through its 5.30 MeV alpha particle emission, using (209)Po as an internal tracer. The (210)Pb activity concentrations were determined from the ingrowth of (210)Po, assuming zero initial (210)Po activity. The results of (210)Po and (210)Pb activity concentrations were found to vary between 34 ± 9 and 1855 ± 98 Bq kg(-1) dry weight and ND (lower than limit of detection) - 64 ± 6 Bq kg(-1) dry weight, respectively. (210)Po/(210)Pb ratio ranged between 1.00 and 106.87. The highest (210)Po activities were found in mussels collected from Didim.

Evaluation of surface water quality in aquatic bodies under the influence of uranium mining (MG, Brazil)

The quality of the water in a uranium-ore-mining area located in Caldas (Minas Gerais State, Brazil) and in a reservoir (Antas reservoir) that receives the neutralized acid solution leaching from the waste heaps generated by uranium mining was investigated. The samples were collected during four periods (October 2008, January, April and July 2009) from six sampling stations. Physical and chemical analyses were performed on the water samples, and the data obtained were compared with those of the Brazilian Environmental Standards and WHO standard. The water samples obtained from waste rock piles showed high uranium concentrations (5.62 mg L(-1)), high manganese values (75 mg L(-1)) and low average pH values (3.4). The evaluation of the water quality at the point considered the limit between the Ore Treatment Unit of the Brazilian Nuclear Industries and the environment (Consulta Creek) indicated contamination by fluoride, manganese, uranium and zinc. The Antas reservoir showed seasonal variations in water quality, with mean concentrations for fluoride (0.50 mg L(-1)), sulfate (16 mg L(-1)) and hardness (20 mg L(-1)) which were low in January, evidencing the effect of rainwater flowing into the system. The concentrations for fluoride, sulfate and manganese were close or above to the limits established by current legislation at the point where the treated mining effluent was discharged and downstream from this point. This study demonstrated that the effluent discharged by the UTM affected the quality of the water in the Antas reservoir, and thus the treatments currently used for effluent need to be reviewed.

Relative importance of direct and trophic uranium exposures in the crayfish Orconectes limosus: Implication for predicting uranium bioaccumulation and its associated toxicity

Pollutants that occur at sublethal concentrations in the environment may lead to chronic exposure in aquatic organisms. If these pollutants bioaccumulate, then organisms higher in the food chain may also be at risk. Increased attention has thus been focused on the relative importance of dietary uptake, but additional knowledge of the cellular distribution of metals after dietary exposure is required to assess the potential toxicity. The authors address concerns relating to increasing uranium (U) concentrations (from 12 µg/L to 2 mg/L) in the freshwater ecosystem caused by anthropogenic activities. The objective of the present study is to compare uranium bioaccumulation levels in tissues and in the subcellular environment. The authors focused on the cytosol fraction and its microlocalization (TEM-EDX) in the gills and the hepatopancreas (HP) of the crayfish Orconectes limosus after 10 d of direct exposure (at concentrations of 20, 100, and 500 µg/L) and five trophic exposure treatments (at concentrations from 1 to 20 µg/g). Results indicated that adsorption of uranium on the cuticle represents the main contribution of total uranium accumulation to the animal. Accumulation in the gills should be considered only as a marker of waterborne uranium exposure. Accumulation in the HP after trophic environmental exposure conditions was higher (18.9 ± 3.8 µg/g) than after direct exposure. Moreover, no significant difference in the subcellular distribution of uranium (50%) in HP was observed between animals that had been exposed to both types of treatment. A potential toxic effect after uranium accumulation could therefore exist after trophic exposure. This confirms the need to focus further studies on the metal (uranium) risk assessment.

Fish pollution with anthropogenic 137Cs in the southern Baltic Sea

This paper presents the results of a study on changes in (137)Cs activity concentrations in three fish species from the southern Baltic Sea: cod (Gadus morhua), herring (Clupea harengus) and flounder (Platichtys flesus), in the period 2000-2010. During the study period a marked decline in cesium activity concentration in fish muscle tissue was observed, which reflected changes in radionuclide activity concentration in seawater. No statistically significant temporal trends were determined in changes of concentration factors (CF(fish/seawater)) calculated for the examined fish species. The analysis of (137)Cs activity as a function of ichthyological parameters revealed the lack of a relationship between radionuclide activity concentrations in herring muscle tissue and the fish age in an narrow age range (2-4 years). However, a reverse proportionality of total fish mass, as well as body length, against (137)Cs activity concentrations in muscles was well documented. The latter observation can be the direct result of the dilution effect related to the increase of fish body weight. (137)Cs activity concentration in muscle tissue of the five fish species forms a declining sequence: Gadus morhua, Platichthys flesus, Clupea harengus, Perca fluviatilis and Neogobius melanostomus.

Activity levels of (210)Po and (210)Pb in some fish species of the Izmir Bay (Aegean Sea)

Concentrations of ²¹⁰Po and ²¹⁰Pb were determined in the edible muscle tissue of twelve species of marine fish collected from Izmir Bay in the Aegean Sea Region of Turkey during the 2006-2007. ²¹⁰Po activity concentrations in fish samples were found to vary from ND to 400±9 Bq kg⁻¹ dry weight and ²¹⁰Pb activity concentrations were found to vary from ND to 15±3 Bq kg⁻¹ dry weight. The highest dose contribution due to ²¹⁰Po to humans was found to be 8.908 μSv y⁻¹.

Radionuclides in resident and migratory fishes of a wedge bank region: Estimation of dose to human beings, South India

Baseline activity concentration of (137)Cs, (210)Po and (210)Pb was determined for 25 resident and 22 migratory fish species collected in a so-called wedge bank region in the extreme south of India. A nuclear power station is now under construction at Kudankulam near the target region and the data provide background information on the radionuclide activity concentration in the region. Three-way ANOVA revealed no significant variation in the concentrations of (137)Cs, (210)Po and (210)Pb between species based on feeding habit, habitat and migratory pattern except the effect of feeding habit on (210)Po concentration (p<0.05). The annual dose due to radionuclide ingestion through the fishes was calculated based on the survey results of fish consumption rates for the local population. The dose due to (137)Cs was negligibly small while those due to (210)Po and (210)Pb varied from 1.2 to 36.9 and 0.2 to 2.9μSv yr(-1), respectively.

235U, 238U, 232Th, 40K and 137Cs activity concentrations in marine sediments along the northern coast of Oman Sea using high-resolution gamma-ray spectrometry

The natural radioactivity levels in sediment samples of the northern coast of Oman Sea, covering the coastal strip from Hormoz canyon to Goatr seaport, as the first time has been determined. The results of measurements will serve as background reference level for Oman Sea coastlines. Sediments from 36 coastal and near shore locations were collected for analysis. Analysis on the collected samples were carried out to determine (235)U, (238)U, (232)Th, (40)K and (137)Cs using two high purity germanium detectors with 38.5% and 55% relative efficiencies. The concentration of (235)U, (238)U, (232)Th, (40)K and (137)Cs in sediment samples ranged between 1.01 and 2.87 Bq/kg, 11.83 and 22.68 Bq/kg, 10.7 and 25.02 Bq/kg, 222.89 and 535.07 Bq/kg and 0.14 and 2.8 Bq/kg, respectively. The radium equivalent activity was well below the defined limit of 370 Bq/kg. The external hazard indices were found to be less than 1, indicating a low dose.

Concentration of selected radionuclides in seawater from Kuwait

No baseline existed for the radionuclides in Kuwait territorial water. With changing trend in the region to embrace nuclear energy, the baseline study is imperative to create a reference and to record the influence-functioning of upcoming power plants. The first one in Bushehr, Iran is ready to start and several more are likely to come-up in UAE, Saudi Arabia and Kuwait. The present baseline concentration of the four considered radionuclide's show low concentration of tritium, polonium, strontium and cesium; their concentration is comparable to most oceanic waters.

Tritium release during nuclear power operation in China

Overviews were evaluated of tritium releases and related doses to the public from airborne and liquid effluents from nuclear power plants on the mainland of China before 2009. The differences between tritium releases from various nuclear power plants were also evaluated. The tritium releases are mainly from liquid pathways for pressurised water reactors, but tritium releases between airborne and liquid effluents are comparable for heavy water reactors. The airborne release from a heavy water reactor is obviously higher than that from a pressurised water reactor.

Biomonitoring fallout 137Cs in resident and migratory fishes collected along the southern coast of India and assessment of dose

The globally distributed fallout radionuclide (137)Cs was monitored in 25 resident and 22 migratory fish species collected from some regions of west and east coast of southern India to establish a baseline data. The samples were collected during June 2008 to June 2009. Higher level of (137)Cs was noted in planktivorous fishes and lower level in herbivores. A significant variation in (137)Cs was observed between fishes with different feeding habits and different migratory pattern. Oceanodromic migratory fishes displayed higher cesium levels than other migratory types. Similarly, migratory fishes displayed higher (137)Cs concentration compared to resident fishes. The overall range of (137)Cs varied from 0.06 to 0.3 Bq/kg in fishes. The biological concentration varied from 55 to 250. The average external dose rate to fishes was calculated to be 2.7 × 10(-7) μGy/h, while the internal dose rate varied from 8.50 × 10(-6) to 5.27 × 10(-5) μGy/h. The hazard quotient for fishes was found to be less than 1. The average intake of (137)Cs via fishes to the public was calculated to be 3.5 Bq/year and subsequently the committed effective dose was 0.05 μSv/year. The data obtained were less than global average and comparable to those of many regions.

Spatial and temporal distribution of Pu in the Northwest Pacific Ocean using modern coral archives

Historical (239)Pu activity concentrations and (240)Pu/(239)Pu atom ratios were determined in skeletons of dated modern corals collected from three locations (Chuuk Lagoon, Ishigaki Island and Iki Island) to identify spatial and temporal variations in Pu inputs to the Northwest Pacific Ocean. The main Pu source in the Northwest Pacific is fallout from atmospheric nuclear weapons testing which consists of global fallout and close-in fallout from the former US Pacific Proving Grounds (PPG) in the Marshall Islands. PPG close-in fallout dominated the Pu input in the 1950s, as was observed with higher (240)Pu/(239)Pu atom ratios (>0.30) at the Ishigaki site. Specific fallout Pu contamination from the Nagasaki atomic bomb and the Ivy Mike thermonuclear detonation at the PPG were identified at Ishigaki Island from the (240)Pu/(239)Pu atom ratios of 0.07 and 0.46, respectively. During the 1960s and 1970s, global fallout was the major Pu source to the Northwest Pacific with over 60% contribution to the total Pu. After the cessation of the atmospheric nuclear tests, the PPG again dominated the Pu input due to the continuous transport of remobilised Pu from the Marshall Islands along the North Equatorial Current and the subsequent Kuroshio Current. The Pu contributions from the PPG in recent coral bands (1984 onwards) varied over time with average estimated PPG contributions between 54% and 72% depending on location.

Anthropogenic Pu distribution in Tropical East Pacific

The geographical distribution of the anthropogenic radionuclides (238)Pu and (239+240)Pu in the Tropical East Pacific in 2003 was studied from the viewpoint of material migration. We measured the contents of Pu isotopes in seawater and in sediment from the sea bottom. The distributions of Pu isotopes, together with those of coexisting nitrate and phosphate species and dissolved oxygen, are discussed in relation to the potential temperature and potential density (sigma-θ). The Pu contents in sediment samples were compared with those in the seawater. Horizontal migration across the Equator from north to south was investigated at depths down to ~800m in the eastern Pacific. The Pu distribution at 0-400m correlated well with the distribution of potential temperature. Maximum Pu levels were observed in the subsurface layer at 600-800m, corresponding to the depth where sigma-θ≈27.0. It is suggested that the Pu distribution depends on the structure of the water mass and the particular temperature and salinity. The water column/sediment column inventory ratio and the vertical distribution of Pu may reflect the efficiency of scavenging in the relevant water areas.

Modelling the biological half-life and seasonality of ¹⁴C in Fucus vesiculosus from the east coast of Ireland: implications for the estimation of future trends

Radiocarbon levels were recorded in Fucus vesiculosus samples collected on a monthly basis over a three-year period at a site on the east coast of Ireland. The resulting data was analysed using a numerical model which estimates the transit times from the Sellafield plant to the sampling location, and the mean availability time of ¹⁴C in seaweed. With the inclusion of a model parameter allowing for seasonal variability in uptake by the Fucus, good correlation was observed between the predicted and measured concentrations. Future temporal trends of ¹⁴C Fucus concentrations along the eastern Irish coastline were modelled with the application of three possible prospective discharge scenarios, predicting ¹⁴C Fucus concentrations to reduce to ambient background levels within 2.5-years of discharges being set to zero. Such projections may prove helpful in assessing the consequences of discharge management and policy making in the context of the OSPAR convention.

Assessment of health safety from ingestion of natural radionuclides in seafoods from a tropical coast, India

The activities of ²¹⁰Po and ²¹⁰Pb were determined in commonly consumed seafoods to evaluate the internal exposure and risk to humans residing Kudankulam coast where a mega nuclear power plant is under construction. The concentration of ²¹⁰Po in seafoods ranged from 1.2 ± 0.7 to 248 ± 8.1 Bq kg⁻¹. Meanwhile, ²¹⁰Pb ranged between 1.1 ± 0.05 and 14.8 ± 1.6 Bq kg⁻¹. The committed effective dose (CED) due to ²¹⁰Po and ²¹⁰Pb varied from 11.04 to 515.6 and 3.93 to 23.5 μSv yr⁻¹, respectively. The lifetime cancer risk for the public due to ²¹⁰Po was in the range of 3.47 × 10⁻⁵- 1.62 × 10⁻³ and it was 4.03 × 10⁻⁵ - 1.96 × 10⁻⁴ due to ²¹⁰Pb. The activity intake, effective dose and cancer risk was found lesser than international guidelines and the seafood intake was considered to be safe for human consumption.

Concentrations of 137Cs, 90Sr, 108m Ag, 239+240 Pu and atom ratio of 240Pu/239Pu in tanner crabs, Chionoecetes japonicus and Chionoecetes opilio collected around Japan

The anthropogenic radionuclides, (137)Cs, (90)Sr, (108m)Ag, (239+240)Pu, were measured in two Chionoecetes species, red queen crab (Chionoecetes japonicus) and snow crab (Chionoecetes opilio) collected around Japan during 1996-2007. There was no increase in the concentrations of these radionuclides and no large variation of the atom ratio of (240)Pu/(239)Pu during this research period. These results indicated that the source of the radionuclides was not the radioactive wastes dumped by the former USSR and Russia and originated from past nuclear weapon tests. The higher atom ratio in the crab species than that from global fallout would be contributed by the Pacific Proving Grounds close-in fallout. The variability of the concentration of radionuclides in the crab species would result from the variability of the composition and quantity in the diet. However, the decrease in the concentration of radionuclides with sampling depth would depend on the concentration in the seawater and diet.

Temporal variation of 240Pu/239Pu atom ratio and 239+240Pu inventory in water columns of the Japan Sea

The (239+240)Pu concentrations and (240)Pu/(239)Pu atom ratios were determined by alpha spectrometry and double-focusing SF-ICP-MS for seawater samples obtained in 1984 and 1993 from the Yamato and Tsushima Basins of the Japan Sea in the western North Pacific margin. The total (239+240)Pu inventories in the whole water columns were approximately doubled during the period from 1984 to 1993 in the two basins. The increasing rates were estimated to be 5.1 Bq m(-2)yr(-1) in the Yamato Basin and 4.2 Bq m(-2)yr(-1) in the Tsushima Basin and they corresponded to ~0.02% of the annual (239+240)Pu inflow rate into the Japan Sea through the Tsushima Strait. The mean (240)Pu/(239)Pu atom ratios were ~0.240 and significantly higher than the mean global fallout ratio of 0.18. Furthermore, there were no temporal or spatial variations of (240)Pu/(239)Pu atom ratios during this period in the Japan Sea. The total (239+240)Pu inventories originating from the close-in fallout increased from 17.6 Bq m(-2) to 34.6 Bq m(-2) in the Yamato Basin and from 20.1 Bq m(-2) to 34.6 Bq m(-2) in the Tsushima Basin; however, the relative percentage of ~40% from the close-in fallout was unchanged during this period. A likely mechanism for the increasing Pu inventory would be the continuous inflow of the Tsushima Current from the western North Pacific, and the removal of Pu from surface waters by scavenging onto the settling particles, followed by regeneration of Pu from the settling particles during the downward transport.

Reconstructing the abundance of Dounreay hot particles on an adjacent public beach in Northern Scotland

Following the discovery of a number of hot particles in the offshore environment of Dounreay on the North Coast of Scotland in 1997, the Dounreay site operator was required to introduce rapid and extensive beach monitoring. Since the introduction of vehicular based beach monitoring in 1999 there have been two further generations of beach monitoring equipment, developed to satisfy regulatory requirements for particle detection and in response to the recommendations of the Dounreay Particles Advisory Group (DPAG). This paper reports the results of DPAG's review of beach monitoring capabilities, evaluating the factors influencing detection capability, assessing the likely monthly particle abundance and whether there has been any real change in particle arrivals with time. The incorporation of real time kinematic GPS has enabled changes in beach elevation to be mapped, and thus allowed the assessment of whether particles detected have recently arrived or may have been buried undisturbed for extended periods of time. The results focus on Sandside Beach from which, between 1984 and December 2009, 150 particles have been recovered. This is by far the largest number of particles found on a Caithness Beach with the exception of the Foreshore of the Dounreay site. The results suggested that there is no evidence for a change in the rate of particle arrivals and DPAG estimated that there is a 1 in 20 million chance of encountering a relevant particle via contact with the skin on Sandside Beach.