Controls on anthropogenic radionuclide distribution in the Sellafield-impacted Eastern Irish Sea

Ray, Daisy and Leary, Peter and Livens, Francis and Gray, Neil and Morris, Katherine and Law, Kathleen A. and Fuller, Adam J. and Abrahamsen-Mills, Liam and Howe, John and Tierney, Kieran and Muir, Graham and Law, Gareth T.W. (2020) Controls on anthropogenic radionuclide distribution in the Sellafield-impacted Eastern Irish Sea. Science of the Total Environment, 743. 140765. ISSN 1879-1026 (https://doi.org/10.1016/j.scitotenv.2020.140765)

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Abstract

Understanding anthropogenic radionuclide biogeochemistry and mobility in natural systems is key to improving the management of radioactively contaminated environments and radioactive wastes. Here, we describe the contemporary depth distribution and phase partitioning of 137Cs, Pu, and 241Am in two sediment cores taken from the Irish Sea (Site 1: the Irish Sea Mudpatch; Site 2: the Esk Estuary). Both sites are located ~10 km from the Sellafield nuclear site. Low-level aqueous radioactive waste has been discharged from the Sellafield site into the Irish Sea for >50 y. We compare the depth distribution of the radionuclides at each site to trends in sediment and porewater redox chemistry, using trace element abundance, microbial ecology, and sequential extractions, to better understand the relative importance of sediment biogeochemistry vs. physical controls on radionuclide distribution/post-depositional mobility in the sediments. We highlight that the distribution of 137Cs, Pu, and 241Am at both sites is largely controlled by physical mixing of the sediments, physical transport processes, and sediment accumulation. Interestingly, at the Esk Estuary, microbially-mediated redox processes (considered for Pu) do not appear to offer significant controls on Pu distribution, even over decadal timescales. We also highlight that the Irish Sea Mudpatch likely still acts as a source of historical pollution to other areas in the Irish Sea, despite ever decreasing levels of waste output from the Sellafield site.

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