title: Sellafield-derived 14C and 129I in the UK West Coast intertidal environment
Creators: name: Kinch, Helen Rose
Publisher: name: University of Glasgow
Year: 2019
Subjects: subject: Sellafield, radiocarbon, iodine, intertidal, seaweed, biota.

description: The Sellafield nuclear fuel reprocessing plant, situated on the west coast of the UK, releases both liquid and airborne discharges of radionuclides to the environment. Liquid discharges from Sellafield have been shown to travel up the west coast of the UK and out of the Irish Sea. The focus of this study was to investigate two long-lived radionuclides, 14C and 129I. 14C has a half-life of 5,730 years and is incorporated into the marine carbon cycle where it is readily bioavailable and thus becomes part of the entire food chain. It has a large impact on human populations as, in a global context, the collective dose from 14C, integrated over 10,000 years, comprises about 25% of the collective dose from the complete nuclear fuel cycle. 129I is of radiological importance as it is highly mobile and has a half-life of 15.7 million years. 95% of global anthropogenic 129I is discharged from Sellafield and AREVA NC (La Hague). Recent studies have been undertaken to understand 14C uptake by biota in the Irish Sea and west coast of Scotland but focussed on offshore samples while this study focussed on the intertidal environment. The principle aims of this research were to improve our understanding of the distribution and geochemical behaviour of long-lived Sellafield-derived radionuclides, 14C and 129I, mainly in the organic carbon reservoir of a range of intertidal sites situated between the Irish Sea and the Firth of Lorne, NW Scotland. Specifically, this research has compared the 14C in seaweeds collected from low tide and high tide areas of the intertidal environment, measured the 14C in a range of intertidal biota and measured the 129I in seawater. The main findings of this research were that both 14C and 129I show approximately exponential decreases in activity in the intertidal environment of the west coast of the UK with increasing distance from the Sellafield site. The halving distance for the dispersion of 14C was found to be between 68 km and 89 km while the halving distance for 129I was 64 km. In addition, there is a higher 14C activity in seaweed inhabiting the area of the intertidal environment near the low water mark when compared with seaweed inhabiting the area at the high water mark. It was also found that when seaweed samples from this study were compared to samples collected from 1988/1989, the 14C activities had decreased, despite the fact that the aqueous discharges are now higher, although a large difference in 14C activities was also observed in seaweed samples collected from the same site at different points in time throughout this study. All samples measured were found to have 14C activities above the UK background value (249 ± 1 Bq kg-1 C) and that the organic fraction of biota had predominantly higher 14C activities than the inorganic fraction. When comparing the 14C activity in biota collected from different sites; at Parton, the site closest to Sellafield, a pattern of decreasing activity was found in the biota as follows; seaweed &gt; starfish &gt; mussels &gt; whelks &gt; crabs &gt; winkles ≈ limpets &gt; sea anemones, whereas at Garlieston, the mid-range site, mussels had the highest activity and all other biota sampled were of similar 14C activities while at Port Appin, the site furthest from Sellafield, there was no discernible difference between 14C activities in biota. Finally, there appeared to be a relationship between diet and 14C activity in biota, with biota with a similar diet having similar 14C activities and similar 14C activities between organisms and their food source.