Role of natural organic matter in binding uranium and incorporating radiocarbon in soils and sediments

Authors: Michael Robert Muir (University of Edinburgh)
Co-authored by industrial partner: No

Type: Thesis

State: Published (Approved)
Published: July 2019

Abstract: The impact of long-lived radionuclides on human health depends on their behaviour in near-surface soils and sediments and the LORISE project aims to define the key controlling physical, chemical and biological processes at a number of ‘natural laboratories’ around the UK. Within this PhD project, the role of natural organic matter (NOM) is of especial importance because NOM can potentially facilitate the transport or attenuation of radiologically significant elements such as U and radiocarbon (14C). Peaty soils in the vicinity of natural uranium mineralisations are often highly enriched in U with concentrations of up to 3000 mg kg-1, 4000 mg kg-1 and 2500 mg kg-1 having been found in the US (Owen and Otten, 1995), Switzerland (Regenspurg et al., 2010), and the UK (Xu, 2013), respectively. The NOM within these soils has been implicated in U retention but the controlling processes and the nature of interactions are poorly characterised. The Needle’s Eye natural mineralisation, SW Scotland, provides a rare opportunity within the UK to investigate long-term U-NOM interactions. Similarly, the well characterised inputs of radiocarbon into the Irish Sea from the Sellafield nuclear reprocessing facility since the mid-1960s present an opportunity to investigate the transfer of anthropogenic 14C between environmental pools and trace its incorporation into coastal sediments. While the enrichment of sediment organic matter with anthropogenic 14C has been identified, (MacKenzie et al., 2004), the chemical and physical characteristics of NOM enriched with 14C have not been investigated. Currently, there is not a good understanding of which NOM components govern U binding or incorporate 14C, and therefore the implications of the influence of NOM on radionuclide mobilisation or immobilisation are hard to assess. In this study, the characteristics of organic matter from the Needle’s Eye natural analogue site have been examined and the relationship with the geochemical properties of the site and U binding have been investigated. Further to this, NOM extracted from the Needle’s Eye peat bog and from sediments of the Solway coast at the Southwick Merse has been fractionated and characterised using a range of spectroscopic techniques to identify the components of NOM which are responsible for binding U and those which incorporate anthropogenic 14C.

Subject Areas: Earth Science, Chemistry

Instruments: I18-Microfocus Spectroscopy