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Development of Reference Doses for Mixtures: Risk Assessment of Cadmium, Iron and Zinc Interactions

   Postgraduate Training

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  Dr L Beesley, Dr R Hough  No more applications being accepted  Competition Funded PhD Project (European/UK Students Only)

About the Project


The risk assessment paradigm traditionally assesses the potential effects of single chemicals or toxicants in isolation of others. In recent years, there has been some movement towards assessing the compound toxicity arising from combinations of potentially toxic chemicals. While good progress has been made, these approaches are, by their nature, constrained to assuming static mixture exposure scenarios (i.e. specified ratios of different PTEs) as representative of reasonable worst-case scenarios in prospective chemical assessment. For site- or population-specific situations this is clearly unsatisfactory. Process-based models have been suggested as a way forward, but these are computationally intensive and require significant data resources beyond the scope of most risk assessments. As an alternative, Hough et al. (in press), suggested a simpler, more pragmatic way forward in which the reference dose (or “safe dose”) for a specific toxicant may be adjusted based on knowledge of interactions with other chemicals and/or nutrients that alter bioavailability. This approach is currently theoretical, and it is important to now validate the theory with experimental evidence.

Aims & Potential Outcomes
This study will develop a practicable approach to assessing compounded risks posed by concurrent exposure to multiple PTEs. This is one of the main challenges in human health risk assessment, and any progress in this area has potentially wide-reaching outcomes. This project could pave the way to a whole new way of assessing health risks from potentially toxic elements.

This project will build on previous theoretical work (Hough et al. in press) that investigated a new way to define reference doses for cadmium (Cd) that was dependent on iron (Fe) and zinc (Zn) status. The work will have three main activity strands:
Activity 1. Experimental studies to evaluate bioavailability/accessibility and absorption of Cd given different levels of dietary Fe and Zn.
Activity 2. A critical evaluation of the current Cd reference doses (RfDCD) for oral intake of water and food, based partly on the results from Activity 1.
Activity 3. Application of new Cd risk assessment models to test/validate the refined approach in a range of situations.

Supervisory Team:
Dr. Luke Beesley and Dr. Rupert Hough, The James Hutton Institute
Professor Neil Crout, University of Nottingham
Dr. Louise Ander, British Geological Survey

Funding Notes

The studentship is funded under the James Hutton Institute/University Joint PhD programme, in this case with the University of Nottingham and Prof. Neil Crout of the School of Biosciences as the primary university supervisor. Candidates are urged strongly to apply as soon as possible so as to stand the best chance of success. A more detailed plan of the studentship is available to suitable candidates upon application. Funding is available for European applications, but Worldwide applicants who possess suitable self-funding are also invited to apply.


1.Beesley, L., Inneh, O.S., Norton, G., Moreno-Jimenez, E., Pardo, T., Clemente, R., Dawson, J.J.C. 2014. Assessing the influence of compost and biochar amendments on the mobility and toxicity of metals and arsenic in a naturally contaminated mine soil. Environmental Pollution 186, 195-202

2.Moreno-Jimenez, E., Beesley, L., Lepp, N.W., Dickinson, N.M., Hartley, W. & Clemente, R. 2011. Field sampling of soil pore water to evaluate trace element mobility and associated environmental risk. Environmental Pollution 159, 3078-3085.

3.Beesley, L., Moreno-Jimenez, E., Clemente, R., Lepp, N. & Dickinson, N. 2010. Mobility of arsenic, cadmium and zinc in a multi-element contaminated soil profile assessed by in-situ soil pore water sampling, column leaching and sequential extraction. Environmental Pollution 158, 155-160.
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