Radioactivity and the Environment


A mechanistic understanding of geochemical and microbial influences on radionuclide behaviour in soils

Dr Clare McCann, Newcastle

Environmental radiochemistry is driven by pH and redox conditions. Microbes create these conditions in the natural environment and vary them in time and space. Radiochemistry and microbiology are inextricably linked, but little is understood about these interactions in near surface natural environments. At Newcastle we are working to understand these links, which is vital to both the challenges of engineering geological disposal, and for predicating and remediating legacy contamination. Microbiological resources are the last unexploited and least understood frontier in engineering. This project will work towards a mechanistic understanding of radionuclide behaviour under relevant environmental perturbations (e.g. changing redox conditions) using a microcosm based approach investigating both geochemistry and microbiology with real UK contaminated soils. The bioavailability of radionuclides will be investigated and the effect of the chemical form of radionuclide contamination (organo-radionucide complexes, mineral associations / anthropogenic and geogenic) has upon in situ microbial communities will be combined with geochemical modelling. Additionally, key species, functional groups and metabolic pathways within the microbial populations will be characterised and their relationship to radionuclide speciation uncovered.

Arbuscular mycorrhizal fungal uptake and transport of radionuclides from natural environments to plant hosts

Dr Filipa Cox, Manchester University

Arbuscular mycorrhizal fungi (AMF) form mutualistic associations with the majority of flowering plants, and play a key role in the uptake of phosphorus and other nutrients from soil into the plant host. Little is currently known about how AMF are involved in the uptake and transport of radionuclides into host plants, although previous work has found that, in general, an association with AMF leads to a reduction in radionuclide concentration in above-ground plant tissues. The specific mechanisms behind this observation, however, are currently unknown. In this project, we are therefore focussing on the role of AMF in plant uptake of uranium and radium, addressing particularly the specific chemical species in which U and Ra are taken up and transported, and where in fungal/plant tissue these radionuclides become localised. In doing so, we will also produce input data for models predicting uptake at multiple scales, from the level of individual roots to whole plant systems.

To address these aims, we will focus on two UK sites with high natural abundance of radionuclides: 1) South Terras, an abandoned uranium/radium mine in Cornwall where concentrations of these radionuclides are subsequently technologically enhanced, and 2) Needles Eye, where a major vein of pitchblende provides naturally elevated levels of uranium in south west Scotland.

Soil collected from these sites will be used to establish experimental systems in which plant species, plant mycorrhizal status and radionuclide level can be manipulated. We will use plants that naturally occur at the study sites, as well as model plant species, in order to produce data that are both ecologically relevant as well as more broadly applicable for input into process models. A range of synchrotron, spectroscopy and molecular methods will be used on plants maintained with and without AMF, in order to establish the effects of mycorrhizal interactions on: rates of radionuclide uptake; concentrations of radionuclides in plant/fungal tissue; specific forms of U and Ra; localisation of U and Ra in plant/fungal tissue; and the AMF fungal communities associated with our experimental plants.

Determination of sediment radionuclide accumulation rates and geochemical controls on distribution

Dr Monica Felipe Sotelo, Loughborough University

The estuary of the river Esk in the north-west England presents enhanced levels of artificial radionuclides as a result of the historical authorized realise of liquid low level waste from the Sellafield reprocessing site. Studies carried out during the 80's and 90's [Oh et al., 2009 and references therein] provide data on the levels and distribution of the artificial radionuclide in at the Esk estuary as well as the factors affecting the transport of these radionuclides. The distribution seems to be affected mainly by association to fine particles and re-suspension processes. Other factors affecting the migration of the radionuclides are pH, Eh and salinity.

The aim of the present project is to assess whether some of the radionuclides have been reconcentrated in the sediments and how stable the accumulation is; this project will try to answer whether the sediments in this area act only as sink of radionuclides, or whether they can also behave as source at longer timescales. For this purpose a comprehensive sampling of the area will be carried out following a grid pattern, and taking sampling different depths, to a maximum depth of 30 cm. The sample will be analysed by gamma-spectrometry and X-ray fluorescence, and a subset of samples will be analysed for Pu by alpha-spectrometry. The results obtained will be compared with previous historical records of the distribution of radionuclides, in order to determine the rate of accumulation and the geochemical factors affecting the distribution. Chemometric tools will be employed to assess the association of the radionuclides to geochemical factors.

J.-S. Oh, P.E. Warwick, I.W. Croudace (2009) Spatial distribution of 241Am, 137Cs, 238Pu, 239,240Pu and 241Pu over 17 year period in the Ravenglass saltmarsh, Cumbria, UK. Applied Radiation and Isotopes, 67, 1484–1492Dr Clare McCann, Newcastle University.

Mechanistic models to study radionuclide migration in soil and uptake by plants by incorporating image based modelling techniques

Dr Shakil Masum, Southampton University and Cranfield University

Uptake of radionuclides by plants strongly depends on their mobility and bioavailability towards the plant roots. The transport of radionuclides in soil is affected by presence of various chemicals, minerals, soil organic matter, pH, CO2 etc. Within the scope of this project the aim is to develop mechanistic models to study radionuclide migration in soil and uptake by plants by incorporating image based modelling techniques. The modelling includes radionuclide transport processes in soil, mycorrhizal interaction, root-induced changes in soil biology and chemistry and root uptake. The key interest is on the processes those are taking place within the plant root/rhizosphere scale. Modelling using soil images provide realistic information on soil geometry, chemistry, root/mycorrhizas regarding the transport and fate of radionuclide in soil. To date the model is used to investigate the transport of a strongly sorbed solute under a simple chemical environment. Further development is underway to include more complex chemical processes together with mycorrhizal root growth modelling in soil. The developed model will be able to predict the transport of radionuclide in soil in presence of various chemical species and changing chemical environment and the influx towards the root or uptake by growing roots/mycorrhizas. The model will be tested using the experimental results obtained from other workstreams of the project. By sensitivity analysis minimal models will be developed describing the key processes which will then be used to explore other plant and soil conditions.

Mechanistic study of the speciation, physico-chemical transport and ecological transfers of long-lived radionuclides (14C, U/Ra etc.) in the marine environments of the Irish Sea and Scottish coastal waters

Dr Graham Muir, SUERC

My research, alongside the Scottish Association for Marine Science (SAMS) and Edinburgh University, is part of the marine workstream investigating Long-lived Radionuclides in the Surface Environment (LO-RISE). The marine component of LO-RISE is concerned with a mechanistic study of the speciation, physico-chemical transport and ecological transfers of long-lived radionuclides (14C, U/Ra etc.) in the marine environments of the Irish Sea and Scottish coastal waters. Specifically, my research focuses on (1) 14C speciation and distribution in Irish Sea sub-tidal sediments; 14C transfer to biota; and 14C transport in water within the Irish Sea to Scottish coastal waters. (2) 14C speciation and distribution and the role of organic matter in U transport within NE Irish Sea saltmarsh sediments. (3) Incorporation of data from this mechanistic understanding into predictive models of physico-chemical transport and ecological transfer processes within food webs of the Irish Sea.

U/Th/Ra behaviour at Needles Eye, South Terras, and in the Ravenglass estuary

Dr Adam Fuller, Manchester University

As the biogeochemistry/radiochemistry PDRA my role within LO-RISE is focused on gaining a process level understanding of radionuclide behaviour in the subsurface at the field sites. Specifically I am focusing on U/Th/Ra behaviour at Needles Eye, South Terras, and in the Ravenglass estuary. I will be investigating the geochemical properties of the field sites (e.g. pH, IS, redox) and how their properties govern the behaviour of the radionuclides (e.g. speciation, sorption). Additionally microcosm experiments will investigate the biotic contribution to these processes. All of this experimental data (and data from other investigators) will then assimilated into K1d reactive transport modelling of radionuclide mobility at the sites. These experimental and modelling outputs will then be fed into to the plant system models being constructed by other members of the consortia. My modelling should resolve the portion of the radionuclides that are held in the bioavailable pool(s) (i.e. those that are accessible to plants).

In addition to my personal work I will also be supporting other parts of the consortia by leveraging the radiochemical analysis capabilities of Centre for Radiochemistry Research (CRR).