How can we predict soil-to-plant transfer risk of radiocesium? Dr Atsushi Nakao

Even nine years have already passed after the accident at the Fukushima Dai-ichi Nuclear Power Plant, radicesium contamination is still a public concern in Japan and other neighboring countries. Long before the accident, it is scientifically known that soil-to-plant transfer of radiocesium is generally very low due to strong retention by micaceous clay minerals in soil. Partially expanded micaceous clay minerals have a specific interlayer site with 1.1~1.2 nm d-spacing, named as a fayed edge site (FES). This site has much high ionic adsorption selectivity for Cs+ than other cations, thereby isolating radiocesium from nutrient cycles. In case of investigations in Europe after the Chernobyl accident, the FES content was found to be proportional to clay content. Relatively homogeneous clay mineralogy may be behind this simple relationship. However, in case of Japan, the FES content was highly variable and not related to clay content, which makes prediction of soil-to-plant transfer risk rather difficult. In this seminar, I will introduce the fundamental mineralogy related to the formation of FES in micaceous minerals, explain why the FES content is highly variable depending on soils in Japan, and then suggest the promising soil management strategy to prepare against radiocesium contamination.

Atsushi Nakao received his ph.D. in Agriculture from the Kyoto University in 2008. After completion of his degree, he was appointed as a Post-doc in the soil science laboratory of Kyoto University (2008-2009) and in the Institute for Environmental Sciences (2009-2011). In November 2011, he moved to Kyoto Prefectural University and was appointed as a faculty member of the Department of Life and Environmental Sciences, Kyoto University. His interests are focused on soil mineral functions to control elemental dynamics in the terrestrial ecosystems. In particular his laboratory is currently working on understanding the role of micaceous minerals controlling sol-to-plant transfer of radiocesium. His research and impact have been recognized through various awards including: The Incentive Award from JSSPN (2015); Japan Prize in Agricultural Sciences, Achievement Award for Young Scientists (2016).

Predicting contamination levels in foodstuffs in the longer-term after a nuclear accident. Prof. Nick Beresford

Following the 1986 Chernobyl accident restrictions were placed on the movement and slaughter of sheep in upland areas of the United Kingdom because of high 134,137Cs activity concentrations in their meat. It was stated that the restrictions would be in place for a matter of weeks, but, in actual fact restrictions were in place until 2012. Why were the original predictions so wrong? The answer is, models which were not fit for purpose.

The Chernobyl accident highlighted that some areas may be more ‘sensitive’ or ‘vulnerable’ (e.g. have comparatively high transfers to foodstuffs or contribute relatively high fluxes of radionuclides to the public via contaminated foodstuffs) to radiological contamination than other areas. Commonly used models to predict radionuclide activity concentrations in human foodstuffs tend to use empirical soil-to-plant transfer factors (or soil-plant concentration ratios) to describe the transfer of radionuclides from soil to crops. Such models cannot easily cope with variation in root uptake caused by variation in soil properties. In the late 1990’s – 2000’s, process-based soil-plant transfer models were developed that could be implemented spatially and predict radiocaesium transfer based upon relatively readily available soil properties (e.g. pH, soil organic matter content, clay content, exchangeable potassium).

The Fukushima accident renewed interest in process-based soil-plant models leading to their re-evaluation and the development of similar models for radiostrontium.

An overview, including potential future developments, of process-based soil-plant models will be given, with consideration about when such models are useful following an accidental release.

Prof. Nick Beresford leads the Environmental Contaminants Group at the UK Centre for Ecology & Hydrology’s Lancaster site. He has been a radioecologist for over 30 years and has an Honorary Professorship at the University of Salford. He is the Vice-President of the European Radioecology ALLIANCE (http://www.er-alliance.eu/) and an Associate Editor of the Journal of Environmental Radioactivity. In the 2000’s Nick was one of the developers of the ERICA Tool for the radiological assessment of wildlife and is now one of the group who maintains the tool and its under-pinning databases, as well as providing training on its use.

Current/recent projects include: investigations of wildlife in the Chernobyl Exclusion Zone; development of alternative approaches to model radionuclide transfer to wildlife and crops; application/development of process-based soil-plant models; working with local communities and government agencies to consider future management options for areas of the Ukraine abandoned after the Chernobyl accident. Nick is also contributing to the development of the ICRPs environmental protection framework and the IAEAs modelling approach for planned releases.

Nick has published around 190 referred papers and, with Prof. Jim Smith, wrote the book Chernobyl Catastrophe and Consequences. He currently co-supervises PhD-students at the universities if Salford and Stirling.