The Fukushima Daiichi nuclear power plant was severely affected by the loss of on-site and off-site power and the incident caused the release of radioactive materials, resulting in a large scale contamination (650 km2). The large volume of contaminated soil, stored after its removal from contaminated ground, poses significant challenges for clean-up and waste management operations. A group of scientists from the University of Birmingham (UoB) are using ISIS to study how a biomineral could aid the clean-up effort.
Hydroxyapatite (HA), a biomineral similar to bones and teeth, can be produced by a species of Serratia bacteria and it is particularly suited for nuclear waste remediation and storage because it is stable over long geological periods, resistant to self-radiation and can incorporate radioactive metals into its structure [1]. Dr Stephanie Handley-Sidhu and scientists from the Unit of Functional Bionanomaterials at UoB are using ISIS to project how the HA-biominerals could be used to aid large scale decontamination efforts of Fukushima soils. They are particularly interested in the Serratia-HA because it can absorb up to 15 times more radionuclides than commercially produced hydroxyapatite; the specific structure of hydroxyapatite biominerals (such as amorphous content, large specific surface area and smaller crystallite size) is known to underlie these advantages [2, 3].
The growth and structure of the biomineral is controlled by the Serratia cells and their thick surrounding layer of extracellular polymeric substance (EPS). On the ISIS instrument, SANS2D, Stephanie and her team used small angle neutron scattering to follow, in-situ, the nucleation and growth of Bio-HAP as a function of time over 48 hours. They aim to understand the steps to biomineral formation so they can optimise synthesis conditions for improved radionuclide uptake.
“Small angle scattering is an ideal method because the technique probes the length scales we’re interested in, which is in the nanometre range. Neutrons are the only way to get more detail during real time biomineralisation on the bacterial surface. Real time is the key factor,” says Stephanie Handley-Sidhu.
Figure 1. Radionuclides stick to the top 10cm of the soil surrounding Fukushima.
The Birmingham group are working with the Japanese Atomic Energy Agency (JAEA) to investigate if these biominerals can be used to decontaminate soils. The problematic radionuclides stick to the top 10 cm of the soil (Figure 1) and this layer is removed during decontamination and stored in large black bags (Figure 2). The plan is to reduce this waste, by removing the radionuclide from the soils using oxalic acid. The aqueous radionuclides can then be concentrated onto biomineral sorbents. This reduced waste volume can then be safely disposed of into a waste repository. Stephanie will visit the JAEA in September 2013 and biominerals produced at Birmingham University will be used to clean up contaminated soils sampled from the Fukushima Prefecture.
Figure 2. Contaminated top soil is removed and stored in large black bags, where it is kept before treatment with oxalic acid
“We are already planning our next visit to ISIS” mentioned Prof. Lynne Macaskie, leader of the Unit of Functional Bionanomaterials. “A great thing about ISIS is the user friendliness. It is a two-way process with the instrument scientist, resulting in a potential collaborative paper. There is a lot of interaction, guidance and support on how to extract the information needed from the data”
The team grew the Serratia sp bacteria and undertook preparatory work in the ISIS biological support labs in Target Station 2, which they described as “a user friendly facility, well stocked with consumables and all the essential equipment.”
Emily Mobley and Stephanie Handley-Sidhu
Stephanie Handley-Sidhu et al.
Research date: June 2013
Further Information
References:
[1] Oelkers and Montel. (2008) Elements 4, 113-116.
Phosphate and Nuclear Waste Storage
[2] Handley-Sidhu et al., (2011) Environ. Sci. Technol. 45, 6985-6990.
Uptake of Sr2+ and Co2+ into Biogenic Hydroxyapatite: Implications for Biomineral Ion Exchange Synthesis
[3] Holliday et al., (2012) Langmuir, 28, 3845-3851
A New Incorporation Mechanism for Trivalent Actinides into Bioapatite: A TRLFS and EXAFS Study
