Anthropogenic 236U and 129I in the Mediterranean Sea: First comprehensive distribution and constrain of their sources

The first basin-wide distribution of ²³⁶U/²³⁸U atom ratios and ¹²⁹I 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 ²³⁶U and ¹²⁹I in relation to the water masses, and to constrain their sources in this region. The ²³⁶U/²³⁸U atom ratios and the ¹²⁹I concentrations ranged from (710±40)×10^-12 to (2220±60)×10^-12 and from (4.0±0.1)×10⁷ to (13.8±0.3)×10⁷at·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 1000-2000m depth in the Eastern Basin. At greater depths, waters were relatively enriched in ²³⁶U and ¹²⁹I due to dense water formation occurring in both, the Eastern and Western Basins. The inventories of ²³⁶U and ¹²⁹I 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 ²³⁶U 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 ¹²⁹I 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.

Dose assessment to workers in a dicalcium phosphate production plant

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 ²³⁸U decay chain (around 10³ 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 ²³⁸U, ²³⁰Th, ²²²Rn, ²¹⁰Pb and ²¹⁰Po concentrations in aerosols (indoor and outdoor areas) are reported. Aerosols showed concentrations between 0.42-92 mBq·m^-3 for ²³⁸U, 0.24-33 mBq·m^-3 for ²³⁰Th, 0.67-147 mBq·m^-3 for ²¹⁰Pb and 0.09-34 mBq·m^-3 for ²¹⁰Po. Long-term exposure (four months) of passive ²²²Rn 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. ²²⁶Ra 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 ²²²Rn air concentrations were lower than the 300 Bq·m^-3 limit and therefore, according to European Directive 2013/59/EURATOM, ²²²Rn 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.

Influence of submarine groundwater discharge on (210)Po and (210)Pb bioaccumulation in fish tissues

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.

Chronological reconstruction of metal contamination in the Port of Maó (Minorca, Spain)

In this work we discuss the historical record of metals as derived from a sediment core from the Port of Maó (Minorca, Spain), the second natural largest harbour in Europe. The sedimentation rate derived from radionuclide profiles increased by a factor of five since the 1960s due to the urbanisation of the town waterfront. Metal concentrations showed two different trends: (i) Pb and Sn inputs started during the second half of the 19th century and remained relatively high until mid-20th century; and (ii) Ag, Cd, Ni, Zn, Cu and Cr accumulation began in the 1940s, peaking in the late 1970s. The commissioning of a submarine outfall in 1978 reduced metal concentrations in subsequently deposited sediments since, thereafter, urban and industrial wastes have been dumped out of the estuary. This study also shows that evaluating the quality of sediments on the basis of surface concentrations may be misleading.

Fluxes of 238U decay series radionuclides in a dicalcium phosphate industrial plant

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 (238,234)U, (230)Th, (226)Ra, (210)Pb and (210)Po at the different stages of the DCP production. Results showed highest activities of (238)U and (210)Pb were found in DCP (1500-2000 Bq kg(-1)); (230)Th and (210)Po were released together with the sludges (1600-2000 Bq kg(-1)) and (226)Ra presented particularly high activities in water (48 × 10(3) Bq m(-3)) and in the reactor scales (115 × 10(3) Bq kg(-1)). Fluxes of radionuclides showed that (238)U outflows were equally distributed between sludges (16 × 10(3) kBq h(-1)) and dicalcium phosphate (20 × 10(3) kBq h(-1)); (230)Th and (210)Po were almost entirely released in the sludges (30 × 10(3)kBq h(-1)) and the greatest (210)Pb outflow was the DCP current (25 × 10(3) kBq h(-1)). (226)Ra was mainly discharged through the water effluent (12 × 10(3) kBq h(-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.

Distribution and biokinetic analysis of 210Pb and 210Po in poultry due to ingestion of dicalcium phosphate

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 (210)Pb and (210)Po specific activities (approximately 2000 Bq.kg(-1)). Both (210)Pb and (210)Po 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 (210)Pb and (210)Po in chicken tissues during the first 42 days 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 42 days. The results show that diets containing enhanced concentrations of (210)Pb and (210)Po lead to larger specific accumulation in broiler tissues compared to the blank diet. Radionuclides do not accumulate homogeneously within the animal body: (210)Pb follows the calcium pathways to some extent and accumulates largely in bones, while (210)Po 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 (210)Pb and (210)Po 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.

Arctic Ocean sea ice drift origin derived from artificial radionuclides

Since the 1950s, nuclear weapon testing and releases from the nuclear industry have introduced anthropogenic radionuclides into the sea, and in many instances their ultimate fate are the bottom sediments. The Arctic Ocean is one of the most polluted in this respect, because, in addition to global fallout, it is impacted by regional fallout from nuclear weapon testing, and indirectly by releases from nuclear reprocessing facilities and nuclear accidents. Sea-ice formed in the shallow continental shelves incorporate sediments with variable concentrations of anthropogenic radionuclides that are transported through the Arctic Ocean and are finally released in the melting areas. In this work, we present the results of anthropogenic radionuclide analyses of sea-ice sediments (SIS) collected on five cruises from different Arctic regions and combine them with a database including prior measurements of these radionuclides in SIS. The distribution of (137)Cs and (239,240)Pu activities and the (240)Pu/(239)Pu atom ratio in SIS showed geographical differences, in agreement with the two main sea ice drift patterns derived from the mean field of sea-ice motion, the Transpolar Drift and Beaufort Gyre, with the Fram Strait as the main ablation area. A direct comparison of data measured in SIS samples against those reported for the potential source regions permits identification of the regions from which sea ice incorporates sediments. The (240)Pu/(239)Pu atom ratio in SIS may be used to discern the origin of sea ice from the Kara-Laptev Sea and the Alaskan shelf. However, if the (240)Pu/(239)Pu atom ratio is similar to global fallout, it does not provide a unique diagnostic indicator of the source area, and in such cases, the source of SIS can be constrained with a combination of the (137)Cs and (239,240)Pu activities. Therefore, these anthropogenic radionuclides can be used in many instances to determine the geographical source area of sea-ice.

Time-series sampling of 223Ra and 224Ra at the inlet to Great South Bay (New York): a strategy for characterizing the dominant terms in the Ra budget of the bay

Ra isotopes are a powerful tool for quantifying the flux of submarine groundwater discharge (SGD) into the sea. Previous studies of 223Ra and 224Ra mass balances in coastal embayments have shown that the Ra balance is dominated by supply via SGD, exchange with the open ocean and radioactive decay. The current study shows that a single time series over a tidal cycle at the principal inlet to Great South Bay (NY, US) is sufficient to determine the net flux of Ra across the inlet, and also can be used to estimate the decay of short-lived Ra in the bay. Estimates of the net Ra flux obtained from a single tidal time-series by using three different approaches agree with those determined from a more time-consuming survey of Ra within the bay, and may represent a first step of estimating SGD in bays and coastal lagoons.

Radioactivity contents in dicalcium phosphate and the potential radiological risk to human populations

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 (approximately 10(3) Bq kg(-1)), 210Pb (2 x 10(3) Bq kg(-1)) and (210)Po ( approximately 800 Bq kg(-1)); group B presents high activities of (238)U, (234)U and (230)Th (approximately 10(3) Bq kg(-1)). Group C was characterized by very low activities of all radionuclides (< 50 Bq kg(-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 x 10(3) and 10(3) Bq kg(-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 +/- 2 microSv y(-1). While these results suggest that human health risks are small, additional testing should be conducted.

Distribution of artificial radionuclides in deep sediments of the Mediterranean Sea

Artificial radionuclides enter the Mediterranean Sea mainly through atmospheric deposition following nuclear weapons tests and the Chernobyl accident, but also through the river discharge of nuclear facility effluents. Previous studies of artificial radionuclides impact of the Mediterranean Sea have focussed on shallow, coastal sediments. However, deep sea sediments have the potential to store and accumulate pollutants, including artificial radionuclides. Deep sea marine sediment cores were collected from Mediterranean Sea abyssal plains (depth >2000 m) and analysed for (239,240)Pu and (137)Cs to elucidate the concentrations, inventories and sources of these radionuclides in the deepest areas of the Mediterranean. The activity - depth profiles of (210)Pb, together with (14)C dating, indicate that sediment mixing redistributes the artificial radionuclides within the first 2.5 cm of the sedimentary column. The excess (210)Pb inventory was used to normalize (239,240)Pu and (137)Cs inventories for variable sediment fluxes. The (239,240)Pu/(210)Pb(xs) ratio was uniform across the entire sea, with a mean value of 1.24x10(-3), indicating homogeneous fallout of (239,240)Pu. The (137)Cs/(210)Pb(xs) ratio showed differences between the eastern (0.049) and western basins (0.030), clearly significant impact of deep sea sediments from the Chernobyl accident. The inventory ratios of (239,240)Pu/(137)Cs were 0.041 and 0.025 in the western and eastern basins respectively, greater than the fallout ratio, 0.021, showing more efficient scavenging of (239,240)Pu in the water column and major sedimentation of (137)Cs in the eastern basin. Although areas with water depths of >2000 m constitute around 40% of the entire Mediterranean basin, the sediments in these regions only contained 2.7% of the (239,240)Pu and 0.95% of the (137)Cs deposited across the Sea in 2000. These data show that the accumulation of artificial radionuclides in deep Mediterranean environments is much lower than predicted by other studies from the analysis of continental shelf sediments.