Plant and associated arbuscular mycorrhizal fungi bioaccumulation of uranium, thorium and radium from natural environments containing elevated concentrations of radionuclides.

Abstract

Naturally occurring radionuclides, such as 238U, 232Th and 226Ra, are ubiquitous in the surface environment and at high concentrations, can become a significant environmental hazard, especially if they accumulate within biological food chains. In order to successfully manage ecosystems, which contain naturally occurring radioactive material (NORM) or technologically enhanced (TE-) NORM, it is critical that we understand the environmental behaviour and transfer of 238U, 232Th and 226Ra. Plants can bioaccumulate these biologically redundant elements and many previous studies have investigated radionuclide phyto-accumulation. However, few studies have investigated the role that arbuscular mycorrhizal (AM) fungi have on plant uptake of radionuclides: as AM fungi act as an extended root network for plants, affecting phyto-accumulation of soil elements, this has been a considerable oversight. Therefore the research presented in this thesis endeavoured to improve our current understanding behind the impacts that AM fungi have on 238U, 232Th and 226Ra plant uptake, with a particular focus on 238U. In the first of three data chapters, data is presented regarding the bioaccumulation of these radionuclides into mycorrhizal-associated plants, sampled from a NORM and TENORM environment, as well as soil- plant tissue transfer factors. These data showed that 238U was significantly partitioned in mycorrhizal plant roots. Principal component and linear regression analyses were also undertaken in order to try and determine the environmental factors affecting 238U, 232Th and 226Ra bioaccumulation into plant roots. Total organic carbon contributed significantly to the variation seen in radionuclide concentrations, whilst Cu and Pb in the soil were correlated with root 238U concentrations. In the second data chapter, high energy synchrotron radiation techniques were used to determine the intracellular localisation of U in mycorrhizal plant roots and thus elucidate the potential mechanisms behind AM fungal and plant root retention of U. However, the results were inconclusive. Data from an in vivo microcosm and heterogeneous mesocosm experiment, sampled from a TENORM environment, are also given in the second and third data chapter, respectively. Although significant challenges occurred, linear regression analyses of plant tissue concentrations from the microcosm experiment again indicated a positive correlation between Cu, Pb and 238U. As a whole, this research was approached using methods of greater environmental relevance than those undertaken previously, with a view to account for the broader ecological complexities of existing NORM and TENORM environments and AM fungal impacts on 238U, 232Th and 226Ra phyto-accumulation.

Date of Award	31 Dec 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Clare Robinson (Supervisor) & Jon Pittman (Supervisor)