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QUADRAT DTP: Quantitative environmental risk assessment of binary and tertiary heavy metal mixtures in agricultural soils

   School of Biological Sciences

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  Dr L Mbadugha, Dr P Williams, Dr Gareth Norton  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

The accumulation of potentially toxic elements (PTEs) in agricultural soils caused by intensive agriculture or ill-advised waste disposal practices is a well-recognised issue. Anthropogenic activities introduce a range of elements, but in practice the problems usually arise from a relatively small number of contaminants, such as copper (Cu), zinc (Zn) and manganese (Mn), but also lead (Pb), nickel (Ni) or cadmium (Cd). Copper, Zn and Mn are essential elements, but detrimental to soil biota when in excess. Consequently, the soil quality has to be protected. This is addressed by the implementation of national or international threshold values, i.e. maximum concentrations of PTEs deemed safe for agricultural production. However, while PTEs are almost invariably introduced to the environment in mixtures, they are generally regulated on an element-by-element basis. 

 Although PTE-mixture toxicity has received increasing attention, most interactions are reported for the aquatic environments. The PTE interactions might lead to synergism (i.e. enhanced toxicity of mixture) or result in antagonism (i.e. reduced toxicity of mixture). However, the PTE effects on biota are controlled not just by the PTE mixture composition, but also by the characteristics of receiving environment. This poses a formidable challenge for terrestrial risk assessment as soil properties vary. As a result, the soil-based PTE mixture toxicity data are limited and the joint effects of PTEs in Scottish soils remain largely unknown.  

 This study will evaluate the effect of binary and tertiary PTE mixtures on soil quality. A particular attention will be paid to the factors controlling sorption of PTE mixtures in soils, their partitioning into soil solution and subsequent detrimental effects on soil microorganisms and crops. The environmental fate of PTE mixtures will be assessed by distribution coefficients, which reflect the net effect of various reactions occurring at the soil solid-solution interface. The biological effects will be addressed by a suite of biological tools and quantified by ecotoxicity values and bioconcentration factors. 

 The research will be carried out at the School of Biological Sciences, University of Aberdeen, in collaboration with Agri-Food and Biosciences Institute (AFBI, Belfast, NI) and led by Dr Lenka Mbadugha (University of Aberdeen). The project co-supervisors are Dr Paul Williams (Queen's University Belfast) and Dr Gareth Norton (University of Aberdeen). 

 The suitable candidate should have a solid background in environmental sciences. The project will heavily engage with the disciplines of environmental chemistry and ecotoxicology. Consequently, demonstrable research experience in these disciplines is highly desired. The successful candidate will gain advanced analytical skills to assess PTE contamination in soils. Analytical skills will be complemented by a hands-on training in ecotoxicology. The School of Biological Sciences, University of Aberdeen, has a solid track record of bioassay development and optimisation, and hosts analytical facilities, which complement a wide range of environmental research. Benefitting from the strong training programme in QUADRAT, career opportunities on completion of the PhD span from further research and academic career to advanced environmental modelling in government organisations or consultancy firms. 

Candidate Background: The successful candidate should have a first degree in environmental science, environmental chemistry, biochemistry or ecotoxicology (or related). It is desirable that the candidate have research/laboratory experience in environmental chemistry and ecotoxicology.

Funding Notes

QUADRAT studentships are open to UK and overseas candidates. Funding covers:
• A monthly stipend for accommodation and living costs, based on UKRI rates (currently £17,668 pa for 2022/23, updated annually)
• Fees (home rate tuition fees and/or fee waiver for overseas fees, where applicable)
• Research and training costs
For further information before applying please check full funding and eligibility information:


1. Jegede, O.O., Awuah, K.F., Renaud, M.J., Cousins, M., Hale, B.A., Siciliano, S.D., 2020. Single metal and metal mixture toxicity of five metals to Oppia nitens in five different Canadian soils. Journal of Hazardous Materials 392, 122341.
2. Maderova, L., Paton, G.I., 2013. Deployment of microbial sensors to assess zinc bioavailability and toxicity in soils. Soil Biology and Biochemistry 66, 222-228.
3. Nkoa, R., 2014. Agricultural benefits and environmental risks of soil fertilizations with anaerobic digestates: a review. Agronomy and Sustainable Development 34, 473-492.
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