Correlation of phytoplankton satellite observations and radiological doses in molluscs.

In this work data of salinity, temperature, suspended particulate matter (SPM), chlorophyll-a, and phytoplankton concentration in the Gibraltar Strait coast, in the confluence of the Mediterranean Sean and the Atlantic Ocean, were analyzed together with 210Po, 40K, 210Pb and 234Th activity concentration in different types of bivalve molluscs at the same time-period. The physicochemical parameters were evaluated using the Copernicus Marine Environment Monitoring Service (CMEMS) products based on satellite observations. A multivariate statistical analysis, including contrasted natural radioactivity contents, allowed the discrimination of bivalve molluscs from Atlantic and Mediterranean coasts. Additionally, a cluster analysis determined a highly significant negative correlation 210Po concentration in molluscs and phytoplankton concentration suggesting that phytoplankton concentration in the water column is a determinant factor to regulate 210Po concentration in those animals. These results introduce a useful tool to calculate the radiological doses in seafood from chlorophyll satellite image.

The behaviour of 236U in the North Atlantic Ocean assessed from numerical modelling: A new evaluation of the input function into the Arctic.

A numerical model, previously validated with other radionuclides, was applied to simulate the dispersion of 236U released from European nuclear fuel reprocessing plants in the North Atlantic and Shelf Seas using a published reconstruction of Sellafield and La Hague releases. Model results are in better agreement with observations if the lowest estimation of such releases are used. This implies that approximately 40kg of 236U has been discharged from Sellafield. It was found that adsorption of 236U on bed sediments of the shallow European Shelf Seas plays an essential role in its dispersion patterns. This contrasts strongly with the more conservative behaviour of 129I in the same area. This has two important implications in the use of 236U as oceanographic tracer; i) special care must be taken in coastal areas, as sediments might act as sinks and sources of 236U; ii) the annual input function of 236U into the Arctic is not directly controlled by the annual discharges from Sellafield and La Hague, since sediments from the Irish, Celtic and North Sea modulate and smooth the signal. Only 52% of the total releases enter into the Arctic Ocean.

Natural and artificial radionuclides in a marine core. First results of 236U in North Atlantic Ocean sediments.

There are very few data available of 236U in marine sediment cores. In this study we present the results from the first oceanic depth profile of 236U in a sediment core sampled in the North Atlantic Ocean, at the PAP site (4500 m depth, Porcupine Abyssal Plain (PAP) site, 49°0' N, 16°30' W). Additionally, the sediment core was radiologically characterized through the measurement of anthropogenic 137Cs, 239Pu, 240Pu, 129I and 14C and natural 210Pb, 40K and 226Ra. The measured 236U concentrations decrease from about 90·106 at g-1 at the seafloor down to 0.5·106 at g-1 at 6 cm depth. They are several orders of magnitude lower than the reported values for soils from the Northern Hemisphere solely influenced by global fallout (i.e. from 2700·106 to 7500·106 at g-1). 236U/238U atom ratios measured are at least three orders of magnitude above the estimated level for the naturally occurring dissolved uranium. The obtained inventories are 1·1012 at m-2 for 236U, 80 Bq m-2 for 137Cs, 45 Bq m-2 for 239+240Pu and 2.6·1012 at m-2 for 129I. Atomic ratios for 236U/239Pu, 137Cs/236U and 129I/236U, obtained from the inventories are 0.036, 0.11 and 2.5 respectively. Concentration profiles show mobilization probably due to bioturbation from the abundant detritivore holothurian species living at the PAP site sea-floor. The range of 236U, 137Cs, 239+240Pu and 129I values, inventories and ratios of these anthropogenic radionuclides are more similar to the values due to fall-out than values from a contribution from the Nuclear Fuel Reprocessing Plants dispersed to the south-west of the North Atlantic Ocean. However, signs of an additional source are detected and might be associated to the nuclear wastes dumped on the Eastern North Atlantic Ocean.

A sequential determination of 90Sr and 210Po in food samples.

The latest EU Council Regulation 2016/52/Euratom updates the emergency limits on radionuclides in foods including 210Po and 90Sr, two of the most important radionuclides for radiological dose from the ingestion pathway. A novel and straightforward method has been developed for sequential determination of 90Sr and 210Po in food samples using ultra low-level liquid scintillation counting and alpha-particle spectrometry. For 90Sr analysis, the method makes use of stable strontium as yield tracer, and 210Po is determined through self-deposition using 209Po as a yield tracer. The quantification limit for this method is 25.0 and 2.0Bqkg-1 for 90Sr and 210Po, respectively. The proposed radiochemical separation can be completed within 2days for a batch of 12 samples. The radiochemical procedure was validated by its application for the measurement of IAEA certified reference materials, and through participation in a national intercomparison exercise. Results are also presented in seafood from the Mediterranean coast.

Rapid determination of (210)Pb and (210)Po in water and application to marine samples.

Measurement of radionuclides in marine samples, specifically radioactive pairs disequilibrium, has gained interest lately due to their ability to trace cutting edge biogeochemical processes. In this context, we developed a fast, direct method for determining (210)Pb and (210)Po water through the use of ultra low-level liquid scintillation counting and alpha-particle spectrometry respectively and through Eichrom Sr resins for the Po-Pb separation. For (210)Pb analysis, the method uses stable lead as a yield tracer measured by a robust ICP-MS technique, and (210)Po is determined through self-deposition using the conventional (209)Po yield tracer. The improvements of the method over other techniques are: a) the analysis can be completed within 6 days, simplifying other methods, b) very low limits of detection have been achieved -0.12 and 0.005mBqL(-1) for (210)Pb and (210)Po, respectively - and c) most of the method could be carried out in on-board analysis. We applied the method to different aqueous samples and specifically to marine samples. We determined (210)Pb and (210)Po in the dissolved fraction of Mediterranean Sea water and an estuary at the South-West of Spain. We found that it can be successfully employed to marine samples but we recommend to i) use a minimum of 20L water to measure the (210)Pb in the dissolved phase by LSC and lower volumes to measure total concentrations; ii) wait for (210)Pb and (210)Bi in secular equilibrium and measure the total spectrum to minimise the limit of detection and improve accuracy.