129I in sediment cores from the Celtic Sea by AMS through a microwave digestion process
Ms Victoria Lérida-Toro1, Mr Unai Abascal-Ruiz1, Dr María Villa-Alfageme1,4, Dr Santiago Hurtado4, Dr Jessica Klar5, Dr Natalie Hicks6, Dr José María López-Gutiérrez1,2
1Centro Nacional de Aceleradores (Universidad de Sevilla, CSIC, Junta de Andalucía) , , Spain, 2Dpto. Física Aplicada I, ETSIA, Universidad de Sevilla , , Spain, 3Dpto. Física Aplicada I, Escuela Politécnica Superior, Universidad de Sevilla , , Spain, 4Dpto. Física Aplicada II, ETSI Edificación, Universidad de Sevilla , , Spain, 5Université de Perpignan UPVD – CEFREM , , France, 6School of Biological Sciences, University of Essex , , UK
The impact of the radioactive contamination in aquatic systems is often recorded in sediments. These, depending on their biogeochemical behaviour, they can give detailed information on the history of the discharges from the sources and the environmental processes related to the transportation of the radionuclides to the sediment. For long-lived radioisotopes as Iodine-129, only high sensitivity techniques as Accelerator Mass Spectrometry are able tocan measure its concentration at environmental levels.
To determine Iodine-129 in environmental samples, radiochemical methods are needed. In sediments, iodine can be associated to inorganic or organic matter and it presents several chemical forms. Therefore, a procedure designed to extract these different species from the matrix is necessary, together with a clean and little time-consuming radiochemical method.
In this work, two sediment cores from the Celtic Sea (core A and core I) have been analysed to determine the Iodine-129 concentration. While core I was a sandy sediment, core A was muddy and it had a high proportion of organic matter. For this reason, a conventional microwave digestion method was adapted for an optimum iodine extraction from the organic fraction. The performance of the different options considered for the iodine extraction will be shown in this work. Results show concentrations between 0.19 x 10^12 at/kg and 7.16 x 10^10 at/kg for core A and between 0.28 x 10^12 at/kg and 2.40 10^12 at/kg for core I. Despite an apparent diffusion in the deep layers, depth profiles accurately reproduced Sellafield discharges. The Iodine-129 concentrations will be compared to the Cesium-137 concentrations to calculate isotopic ratios in the cores and subsequently in the Sellafield nuclear fuel reprocessing discharges.
Victoria Lérida-Toro is part of the AMS group at the Centro Nacional de Aceleradores (CNA, Spain). She is currently a PhD student in the Physical Sciences and Technologies program at University of Seville and her research includes development of radiochemical methods, AMS technique and applications of iodine-129 in environmental samples.
Unai Abascal graduated in Physics and Electronic Engineering from the UPV/EHU. Current PHD student at the University of Seville in the group of AMS at the Centro Nacional de Aceleradores (CNA, University of Seville, Spain). His research focuses on the analysis of 129I by AMS in environmental samples. Now, he is involved in a project for the study of the Arctic Ocean and its connections.