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The first basin-wide distribution of 236 U/ 238 U atom ratios and 129 I concentrations is presented for the Mediterranean Sea. During the GEOTRACES GA04S-MedSeA expedition in 2013 seawater was collected from 10 vertical profiles covering the principal sub–basins of the Mediterranean Sea. The main objective was to understand the distributions of 236 U and 129 I in relation to the water masses, and to constrain their sources in this region. The 236 U/ 238 U atom ratios and the 129 I concentrations ranged from (710 ± 40) × 10 − 12 to (2220 ± 60) × 10 − 12 and from (4.0 ± 0.1) × 10 7 to (13.8 ± 0.3) × 10 7 at·kg − 1 , respectively. The results show that radionuclide–poor Atlantic Water is entering at the surface through the Strait of Gibraltar whereas comparably radionuclide-enriched Levantine Intermediate Water is sinking in the Eastern Basin and flowing westward at intermediate depths. Low radionuclide levels were found in the oldest water masses at about 1000–2000 m depth in the Eastern Basin. At greater depths, waters were relatively enriched in 236 U and 129 I due to dense water formation occurring in both, the Eastern and Western Basins. The inventories of 236 U and 129 I cannot be explained only by global fallout from atmospheric nuclear bomb testings carried out in the 1950s and 1960s. We estimate that the liquid input of 236 U from the nuclear reprocessing facility of Marcoule (France), via the Rhône river, was of the same order of magnitude than the contribution from global fallout, whereas liquid and gaseous releases of 129 I from Marcoule were up to two orders of magnitude higher than global fallout. For both radionuclides, the contribution from the Chernobyl accident is found to be minor. [ABSTRACT FROM AUTHOR]

The first dataset of 236 U/ 238 U in the water column of the Arctic Ocean (AO) is presented and shows the widest range of ratios reported so far in the open ocean, from ( 5 ± 5 ) to ( 3840 ± 260 ) × 10 − 12 . Surface samples and depth profiles were collected during two GEOTRACES expeditions in 2011–2012 and analyzed for the concentrations of 236 U and 129 I, with the aim of investigating whether the combination of 236 U/ 238 U and 129 I/ 236 U can be used as a new oceanographic tool in the AO. Results show that the distributions of the 236 U/ 238 U and 129 I/ 236 U atomic ratios are consistent with the different water masses in the AO. High 236 U/ 238 U and 129 I/ 236 U ratios in the upper water column ( > 2000 × 10 − 12 and >200, respectively) illustrate the penetration of Atlantic waters (AW) into the AO. Lower values were found in Pacific waters (PW) and deep waters of the AO. Rivers seem to represent a temporally and spatially-constrained third anthropogenic source of 236 U but more data are needed to confirm this. In a simple mixing model, the combination of 236 U/ 238 U and 129 I/ 236 U reveals a high contribution (>99%) of natural background waters (pre-nuclear era) in the deep and bottom waters of the Amerasian basin, indicating an apparent water mass renewal time of >1000 years. Despite the relatively high apparent age of the Amerasian Basin deep waters, this work shows the potential of using the dual-tracer approach as a new oceanographic tool in the Arctic Ocean. [ABSTRACT FROM AUTHOR]

In this study the first comprehensive dataset of 236U in the North Atlantic Ocean is presented. 236U/238U ratios and 236U concentrations are determined in about 70 seawater samples collected from 9 depth profiles along a transect through the Northwest Atlantic Ocean during the first two legs of the GEOTRACES cruise GA02 in 2010. The cruise track was designed to follow the path of the North Atlantic Deep Water (NADW) from its formation region to the deep parts of the western Atlantic Ocean basins. Our results show that there is a strong North to South and surface to deep ocean gradient spanning a broad range of 236U/238U, from (44±15)×10−12 to (1477±91)×10−12 that correlates well with the distribution of water masses in this region. All measured ratios are above the theoretical pre-anthropogenic levels of 10−13 to 10−14, showing that the whole transect is dominated by anthropogenic 236U. Based on the calculated 236U inventories the 236U inputs of global fallout and direct releases from nuclear reprocessing plants could be constrained to a range from 1000 to 1400kg and from 115 to 250kg of 236U, from the two sources, respectively. Our results show that the 236U/238U atomic ratio can be used as a marker of North Atlantic water masses: with high ratios (>1000×10−12) characterizing northern water masses (LSW and DSOW); and lowest ratios (50–400×10−12) corresponding to the increasing influence of AABW and AAIW. [ABSTRACT FROM AUTHOR]

Abstract: This manuscript describes a protocol for the determination of U and Th isotopes via alpha spectrometry in NORM samples containing high concentrations of these radionuclides, up to kBqkg−1. This technique is based on extraction chromatography with UTEVA (Triskem Int.) resins and it has been tested using both NORM samples from a phosphate industry and reference materials. The results proved that this method is highly optimized in terms of accuracy and precision when dealing with NORM samples. Recycling of UTEVA columns was also checked using NORM samples and successful results were obtained for both U and Th isotopes, thus proving the feasibility of re-using these type of columns. [Copyright &y& Elsevier]

Abstract: The production of dicalcium phosphate (DCP) is part of the phosphate industry, which has been recently included in the positive list of the NORM industries defined in the revised version of the EU-BSS (Euratom 29/96). The objective of the present work is to study specific concentrations and fluxes of 238,234U, 230Th, 226Ra, 210Pb and 210Po at the different stages of the DCP production. Results showed highest activities of 238U and 210Pb were found in DCP (1500–2000Bqkg−1); 230Th and 210Po were released together with the sludges (1600–2000Bqkg−1) and 226Ra presented particularly high activities in water (48×103 Bqm−3) and in the reactor scales (115×103 Bqkg−1). Fluxes of radionuclides showed that 238U outflows were equally distributed between sludges (16×103 kBqh−1) and dicalcium phosphate (20×103 kBqh−1); 230Th and 210Po were almost entirely released in the sludges (30×103 kBqh−1) and the greatest 210Pb outflow was the DCP current (25×103 kBqh−1). 226Ra was mainly discharged through the water effluent (12×103 kBqh−1). This work highlights the importance of studying the industrial processes involving NORM, as minor changes in the production steps lead to different radionuclide distribution in the process. [Copyright &y& Elsevier]

Abstract: Dicalcium phosphate (DCP) is used as a calcium supplement for food producing animals (i.e., cattle, poultry and pig). When DCP is produced via wet acid digestion of the phosphate rock and depending on the acid used in the industrial process, the final product can result in enhanced 210Pb and 210Po specific activities (∼2000Bq·kg− 1). Both 210Pb and 210Po are of great interest because their contribution to the dose received by ingestion is potentially large. The aims of this work are to examine the accumulation of 210Pb and 210Po in chicken tissues during the first 42days of life and to build a suitable single-compartment biokinetic model to understand the behavior of both radionuclides within the entire animal using the experimental results. Three commercial corn-soybean-based diets containing different amounts and sources of DCP were fed to broilers during a period of 42days. The results show that diets containing enhanced concentrations of 210Pb and 210Po lead to larger specific accumulation in broiler tissues compared to the blank diet. Radionuclides do not accumulate homogeneously within the animal body: 210Pb follows the calcium pathways to some extent and accumulates largely in bones, while 210Po accumulates to a large extent in liver and kidneys. However, the total amount of radionuclide accumulation in tissues is small compared to the amounts excreted in feces. The single-compartment non-linear biokinetic model proposed here for 210Pb and 210Po in the whole animal takes into account the size evolution and is self-consistent in that no fitting parameterization of intake and excretions rates is required. [ABSTRACT FROM AUTHOR]

Abstract: Potentially harmful phosphate-based products derived from the wet acid digestion of phosphate rock represent one of the most serious problems facing the phosphate industry. This is particularly true for dicalcium phosphate (DCP), a food additive produced from either sulphuric acid or hydrochloric acid digestion of raw rock material. This study determined the natural occurring radionuclide concentrations of 12 DCP samples and 4 tricalcium phosphate (TCP) samples used for animal and human consumption, respectively. Metal concentrations (Al, Fe, Zn, Cd, Cr, As, Hg, Pb and Mg) were also determined. Samples were grouped into three different clusters (A, B, C) based on their radionuclide content. Whereas group A is characterized by high activities of 238U, 234U (∼103 Bqkg−1), 210Pb (2×103 Bqkg−1) and 210Po (∼800Bqkg−1); group B presents high activities of 238U, 234U and 230Th (∼103 Bqkg−1). Group C was characterized by very low activities of all radionuclides (<50Bqkg−1). Differences between the two groups of DCP samples for animal consumption (groups A and B) were related to the wet acid digestion method used, with group A samples produced from hydrochloric acid digestion, and group B samples produced using sulphuric acid. Group C includes more purified samples required for human consumption. High radionuclide concentrations in some DCP samples (reaching 2×103 and 103 Bqkg−1 of 210Pb and 210Po, respectively) may be of concern due to direct or indirect radiological exposure via ingestion. Our experimental results based on 210Pb and 210Po within poultry consumed by humans, suggest that the maximum radiological doses are 11±2μSvy−1. While these results suggest that human health risks are small, additional testing should be conducted. [Copyright &y& Elsevier]

The production of dicalcium phosphate (DCP) uses phosphate rock (PR) as a raw material. Sedimentary phosphate rocks are enriched with relevant concentrations of natural radionuclides from the 238 U decay chain (around 10 3 Bq·kg −1 ), leading to the need of controlling potential exposures to radiation of workers and members of the public in accordance with IAEA safety standards. Indeed, phosphate industries are classified as Naturally Occurring Radioactive Material (NORM) industries. Thus, the aim of this work is to assess the radiological risk of the workers in a DCP production plant located in the Iberian Peninsula (South-West Europe), which digests PR with hydrochloric acid. In the present study 238 U, 230 Th, 222 Rn, 210 Pb and 210 Po concentrations in aerosols (indoor and outdoor areas) are reported. Aerosols showed concentrations between 0.42–92 mBq·m −3 for 238 U, 0.24–33 mBq·m −3 for 230 Th, 0.67–147 mBq·m −3 for 210 Pb and 0.09–34 mBq·m −3 for 210 Po. Long-term exposure (four months) of passive 222 Rn detectors provided concentrations that ranged from detection limit (< DL) to 121 Bq·m -3 in outdoor areas and from < DL to 211 Bq·m −3 in indoor areas, similar to concentrations obtained from short-term measurements with active detectors from < DL to 117 Bq·m −3 in outdoor areas and from < DL to 318 Bq·m −3 in indoor places. 226 Ra accumulation in ebonite and pipe scales were the most important contributions to the ambient dose equivalent H*(10), resulting in 0.07 (background)–27 μSv·h −1 with a median value of 1.1 μSv·h −1 . Average 222 Rn air concentrations were lower than the 300 Bq·m −3 limit and therefore, according to European Directive 2013/59/EURATOM, 222 Rn concentration is excluded from the worker operational annual effective dose. Thus, considering the inhalation of aerosols and the external dose sources, the total effective dose determined for plant operators was 0.37 mSv·y −1 . [ABSTRACT FROM AUTHOR]

This study presents the results of the accumulation of 210 Po and 210 Pb in fish tissues and organs in a brackish-water marshland that is characterized by high concentrations of 222 Rn and 226 Ra supplied by submarine groundwater discharge (SGD). Tissues and organs from Cyprinus carpio , Chelon labrosus and Carassius auratus in the wetland were significantly enriched by both 210 Pb and 210 Po (up to 55 and 66 times, respectively) compared to blanks. The major input route of 210 Pb and 210 Po into the fish body seems to be through ingestion, due to the high levels of 210 Pb and 210 Po found in the gut content as well as in organs involved in digestion and metabolism (i.e. gut, kidney and hepatopancreas). Results showed that 210 Po was more accumulated in all fish tissues and organs except for the spine, which showed a higher affinity for 210 Pb, due to its capacity to replace Ca from apatite in bones. Over all the variables analyzed, fish tissues/organs and, secondarily, fish species were the most important factors explaining the concentration of radionuclides, whereas fish length and the sampling location played a minor role. The relationship of the two radionuclides varied markedly among tissues and their concentration levels were only correlated in gills, gut and, marginally, in spines. In general, the highest values of 210 Pb and 210 Po concentrations in tissues were found on C. labrosus tissues rather C. auratus and C. carpio . This study demonstrates that inputs of natural radionuclides supplied by SGD to coastal semi-enclosed areas (such as marshlands, lagoons or ponds) may significantly increase the contents of 210 Pb and 210 Po in fish tissues/organs. Thus, this study represents one of the first evidences of direct ecological effects derived from SGD. [ABSTRACT FROM AUTHOR]

Abstract: Liquid scintillation spectrometry is a fast competitive technique for the simultaneous evaluation of gross alpha and beta indexes. However, the implementation of this technique should not be considered as straightforward, and the pre-concentration methods to decrease the detection limit together with quenching and alpha, and beta crossover corrections should be carefully chosen according to the needs of the laboratory. Both aspects are being approached in this work as to find an easy and robust method for alpha/beta measurement in water samples, taking into account the quenching and alpha/beta crossover interferences effects. Results showed that most of the pre-concentration methods increased the quenching in the measurement, although HNO3 0.05M points to be the best solution for pre-concentration and re-dissolution of the sample as converges into low quenching and maximum recovery. Subsequently, in the measurement of water samples with different conductivities, the analysis of the raw counts to obtain gross alpha and beta indexes was carried out using different approaches to implement quenching and interference corrections. If quenching and salt content in the sample are relatively low, interference and quenching-efficiency corrections do not improve the accuracy of the results within the usual precision assumed for a result of gross alpha and beta index (25%). Special attention must be paid when corrections are applied to high quenched or saline samples and when alpha and beta activities values are different in several orders of magnitude. [Copyright &y& Elsevier]

We report dissolved concentrations of the long-lived radioisotope 236U measured in the water column along the 2013 US GEOTRACES Eastern Pacific Zonal Transect (GP16). This transect followed a 10–15°S line from Manta, Ecuador, to Papeete, Haiti, French Polynesia, crossing the southern East Pacific Rise, intercepting one of the largest hydrothermal plumes as well as a productivity gradient, which includes the upwelling zone and associated low oxygen waters offshore from Peru and the oligotrophic sub-tropical gyre. Accelerator Mass Spectrometry was used to measure dissolved seawater 236U concentrations as low as 1 × 103 atom kg−1, which are among the lowest levels reported to date. Differences in upper water column 236U distributions from east to west are a result of variable contributions from different surface and intermediate waters encountered along the transect. The distribution of 236U, both in depth and geographically, provides complementary information to that obtained from Δ14C and helium isotopes, demonstrating that 236U concentrations are diagnostic in the identification of and contributions from the different deep and bottom water masses encountered along the EPZT (Jenkins et al., 2017). For example, we observe minimum 236U concentrations along the EPZT between 2000 and 3000 m that are consistent with contributions attributed to Pacific Deep Water. We also observe increases in 236U below 3000 m at the eastern and western termini of the EPZT. This is consistent with contributions associated with Antarctic Bottom Water and Lower Circumpolar Deep Water. Our results indicate that 236U may be used in conjunction with Δ14C and 3He isotopes as an additional tool with which to identify and resolve contributions from different water masses in the Pacific Ocean. This article is part of a special issue entitled: "Cycles of trace elements and isotopes in the ocean – GEOTRACES and beyond" - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González. Unlabelled Image • 236U inventory in EPZT is one order of magnitude lower than in North Pacific. • 236U anthropogenic contribution at the EPZT is due to global fallout contribution. • AMS was used to measure dissolved 236U concentrations, which are among the lowest 236U values reported for seawater. • Lowest 236U concentrations were 1 × 103 at kg−1, measured between 2000 and 3000 m. • 236U distributions were used to identify deep and bottom water masses in EPZT. [ABSTRACT FROM AUTHOR]

This paper focuses on how a community of researchers under the COMET (CO-ordination and iMplementation of a pan European projecT for radioecology) project has improved the capacity of marine radioecology to understand at the process level the behaviour of radionuclides in the marine environment, uptake by organisms and the resulting doses after the Fukushima Dai-ichi nuclear accident occurred in 2011. We present new radioecological understanding of the processes involved, such as the interaction of waterborne radionuclides with suspended particles and sediments or the biological uptake and turnover of radionuclides, which have been better quantified and mathematically described. We demonstrate that biokinetic models can better represent radionuclide transfer to biota in non-equilibrium situations, bringing more realism to predictions, especially when combining physical, chemical and biological interactions that occur in such an open and dynamic environment as the ocean. As a result, we are readier now than we were before the FDNPP accident in terms of having models that can be applied to dynamic situations. The paper concludes with our vision for marine radioecology as a fundamental research discipline and we present a strategy for our discipline at the European and international levels. The lessons learned are presented along with their possible applicability to assess/reduce the environmental consequences of future accidents to the marine environment and guidance for future research, as well as to assure the sustainability of marine radioecology. This guidance necessarily reflects on why and where further research funding is needed, signalling the way for future investigations. [ABSTRACT FROM AUTHOR]

The 3D compartment model POSEIDON-R was applied to the Northwestern Pacific and adjacent seas to simulate the transport and fate of 90Sr in the period 1945-2010 and to perform a radiological assessment on the releases of 90Sr due to the Fukushima Dai-ichi nuclear accident for the period 2011-2040. The contamination due to runoff of 90Sr from terrestrial surfaces was taken into account using a generic predictive model. A dynamical food-chain model describes the transfer of 90Sr to phytoplankton, zooplankton, molluscs, crustaceans, piscivorous and non-piscivorous fishes. Results of the simulations were compared with observation data on 90Sr for the period 1955-2010 and the budget of 90Sr activity was estimated. It was found that in the East China Sea and Yellow Sea the riverine influx was 1.5% of the ocean influx and it was important only locally. Calculated concentrations of 90Sr in water, bottom sediment and marine organisms before and after the Fukushima Dai-ichi accident are in good agreement with available experimental measurements. The concentration of 90Sr in seawater would return to the background levels within one year after leakages were stopped. The model predicts that the concentration of 90Sr in fish after the Fukushima Dai-ichi accident shall return to the background concentrations only 2 years later due to the delay of the transfer throughout the food web and specific accumulation of 90Sr. The contribution of 90Sr to the maximal dose rate due to the FDNPP accident was three orders of magnitude less than that due to 137Cs, and thus well below the maximum effective dose limits for the public. [ABSTRACT FROM AUTHOR]

A numerical model consisting of a 3D advection/diffusion equation, including uptake/release reactions between water and sediments described in a dynamic way, has been applied to simulate the marine releases of 90Sr from the Fukushima power plant after the March 2011 tsunami. This is a relevant issue since 90Sr releases are still occurring. The model used here had been successfully applied to simulate 137Cs releases. Assuming that the temporal trend of 90Sr releases was the same as for 137Cs during the four months after the accident simulated here, the source term could be evaluated, resulting in a total release of 80 TBq of 90Sr until the end of June, which is in the lower range of previous estimates. Computed vertical profiles of 90Sr in the water column have been compared with measured ones. The 90Sr inventories within the model domain have also been calculated for the water column and for bed sediments. Maximum dissolved inventory (obtained for April 10th, 2011) within the model domain results in about 58 TBq. Inventories in bed sediments are 3 orders of magnitude lower than in the water column due to the low reactivity of this radionuclide. 90Sr/137Cs ratios in the ocean have also been calculated and compared with measured values, showing both spatial and temporal variations. [ABSTRACT FROM AUTHOR]