Project Description

A full project description can be found on Find a PhD. Please see below for additional information about this 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) and 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/Irish 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.

Essential skills

  • The suitable candidate should have a solid background in environmental science with a demonstrable ability to conduct laboratory-based experiments.

Desirable skills

  • Experience in environmental analysis, inorganic chemistry, soil ecotoxicity, and dose response modelling.

Photo by Jan Kopřiva on Unsplash.


Lenka Mbadugha

Primary Supervisor:

Profile: Lenka Mbadugha
Institution: University of Aberdeen
Department/School: School of Biological Sciences

Paul N. Williams

Secondary Supervisor:

Profile: Paul N. Williams
Institution: Queen's University, Belfast
Department/School: School of Biological Sciences

Gareth Norton

Additional Supervisor:

Profile: Gareth Norton
Institution: University of Aberdeen
Department/School: School of Biological Sciences


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.

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.

Nkoa, R., 2014. Agricultural benefits and environmental risks of soil fertilizations with anaerobic digestates: a review. Agronomy and Sustainable Development 34, 473-492.

Research Methods

The research will be carried out at the School of Biological Sciences, University of Aberdeen, and led by Dr Lenka Mbadugha. The project co-supervisors are Dr Paul Williams (the Queen’s University Belfast), Dr Gareth Norton (the University of Aberdeen) and Lisa Black (AFBI).

The applicant will be integrated into the ‘Soil Biology’ research group based in Laboratory 2:05, Cruickshank Building, School of Biological Sciences, University of Aberdeen. The group has a long-standing expertise in pollution risk assessment and management and its research is supported by experienced laboratory technicians, Dr Hedda Weitz (with microbiology expertise) and Ms Jaime Buckingham (with expertise in soil characterisation and plant bioassays), who will train the student in laboratory techniques, bioassays and analytical methods.

The group holds regular laboratory meetings which enable timely overview of research work and its progress. Additional meetings with the supervisory team will be organised on demand.

The PhD student will gain advanced analytical skills (ICP-MS, F-AAS, LabTOC etc.) to assess heavy metal contamination in soils. Analytical skills will be complemented by 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. The applicant will also benefit from the strong training programme in QUADRAT, which will advance his/her personal and postgraduate skills.


Expected Training Provision

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 strong 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.


This project will address current knowledge gaps by deploying plant and microbial assays to soils contaminated with PTE mixtures. The outputs of laboratory tests will relate behaviour of PTE mixtures to changing physico-chemical parameters of soils, as well as effects on microorganisms and plants. The study outputs will elucidate potential impacts of PTE build-up in these soils on sustainability of agricultural practices related to the spreading of contemporary organic wastes on soils. It will also facilitate the critical appraisal of current soil guidance values. Currently, there is no consensus on how to approach this issue, both nationally and internationally.

Furthermore, the project addresses a number of Sustainable Development Goals (SDGs). Namely, SDG 2 – Zero Hunger, by investigating issues threating agricultural productivity and sustainable food production; SDG 3 – Good health and well-being by investigating soil contamination and its potentially effects on environmental and human health; and SDG 12 – Responsible production and consumption by informing on issues related to environmentally sound management of chemicals and organic wastes at the end of their life cycle.

Proposed Timetable

The project will start with the standard period of literature review confirming the best PTE candidates for experimental work, followed by laboratory induction. Subsequently, the PhD work will be split into focused periods of laboratory experiments followed by periods of data processing and academic writing.

The research work will commence by the analysis of samples from an organic manure trial in Northern Ireland. Soils will be assessed for the relative impact of 16 organic wastes on PTE content and behaviour in soils and their subsequent biological effect. The study will be complemented by the collection of agricultural soils of contrasting physico-chemical properties from affiliated farms in the NE Scotland. The soils will be fully characterised. Subsequently, the behaviour of single PTEs in soils and their effects on selected biological endpoints will be investigated during Year 1 of the PhD. This work will establish a solid baseline relatable to published literature.

The second year of PhD will be dedicated to ecological risk assessment of binary PTE mixtures. The laboratory work will focus on identification of synergism and antagonism in binary mixtures. The findings will be summarised in 24-month report.

Year 3 will consist of periods of laboratory work focused on risk assessment of tertiary PTE mixtures followed by periods of secondary data derivation and environmental modelling.

The last six months of the PhD will be dedicated to thesis writing.


  • biodiversity
  • environmental-management


CASE Partner: AFBI

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