Project Description

In order to address the climate emergency and prevent catastrophic climate change, we must reduce our greenhouse gas (GHG) emissions to net-zero as quickly as possible.  As humanity races to decarbonise all our activities, it has become apparent that although we must reduce GHG emissions in every sphere of our lives, some processes essential to our life on this planet are unlikely to ever become completely carbon neutral.  Therefore, in additional to a radical reduction in GHG emissions, IPCC (2018) predict that part of the solution to achieving a net-zero carbon world will be to remove carbon dioxide (CO2) directly from the air. 

Enhanced Rock Weathering (ERW) has been identified as a potentially promising technique for capturing CO2 from the atmosphere and sequestering it in soil, with a recent study claiming that ERW could meet 45% of the UK’s net-zero carbon removal target (Kantzas et al., 2022).  Natural rock weathering happens slowly with CO2 being removed from the atmosphere over thousands of years as silicate rocks, rich in either magnesium and/or calcium are chemically broken down to release base cations which can react with CO2 to produce carbonate minerals.  In ERW, pulverised silicate rocks are added to soils.  The high reactive surface area of the pulverised rock accelerates natural weathering processes and therefore has potential to sequester significant quantities of atmospheric CO2.  However, silicate rocks, including olivine-rich ultramafic and mafic rocks (basaltic) rocks, often contain trace metals including chromium (Cr) and nickel (Ni) that are toxic to humans and the environment at elevated levels (Cox et al., 2017).  These trace elements are likely to be released during the enhanced weathering process, and therefore excessive use of ERW may locally pose risks to human health and the environment.  

This PhD will investigate the risks to human health posed by Cr and Ni in soils enhanced with pulverised basalt.  This will be done by analysing for bioaccessible Ni and Cr concentrations using the Unified BARGE Method for bioaccessibility testing and considering whether the released Cr and Ni is available for plant uptake.  The rate of carbon sequestration in soils will be assessed using C and O isotope analysis.  The student will benefit from access to community gardens developed as part of a collaboration between QUB and Belfast City Council as part of the Horizon 2020 funded UPSURGE project and will work with GSNI to identify a suitable quarry to source local quarry dusts.  

Essential & desirable candidate skills

Essential: 2.1 Honours Degree  in Earth/Environmental Science or other related discipline. Experience in some of the following fields and a willingness to become familiar with the others: 

  • Laboratory techniques and extractions
  • Soil geochemistry
  • Statistical analysis of environmental and geospatial data.

 Ability to organise resources, manage time and meet deadlines. Good communication skills in English (written and verbal). Strong analytical and problem solving skills. Ability to logically conceptualise and summarise research findings. Be willing and able to carry out field work and spend time on secondment at UoA and engage with external organisations. 

Desirable: MSc or equivalent in relevant subject. Experience of environmental risk assessment. Experience of undertaking spatial, statistical and/or chemometric methods of analysis. Knowledge of weathering processes. Experience in using statistical software packages including ArcGIS or R. 


Siobhan Cox

Primary Supervisor:

Profile: Siobhan Cox
Institution: Queen's University, Belfast
Department/School: School of Natural and Built Environment

Alex Brasier

Secondary Supervisor:

Profile: Alex Brasier
Institution: University of Aberdeen
Department/School: School of Geosciences

Rory Doherty

Additional Supervisor:

Profile: Rory Doherty
Institution: Queen's University, Belfast
Department/School: School of Natural and Built Environment

Jennifer McKinley

Additional Supervisor:

Profile: Jennifer McKinley
Institution: Queen's University, Belfast
Department/School: School of Natural and Built Environment

Additional Supervisor:

Dr Mark Cooper  

Geological Survey of Northern Ireland 




Cox, S. F., Rollinson, G., McKinley, J. M. (2017) Mineralogical characterisation to improve understanding of oral bioaccessibility of Cr and Ni in basaltic soils in Northern Ireland. Journal of Geochemical Exploration, Volume 183, Part B, 166-177. 

Intergovernmental Panel on Climate Change (IPCC) (2018) Global Warming of 1.5 °C. An IPCC Special Report on the Impacts of Global Warming of 1.5 °C Above Pre-Industrial Levels and Related Global Greenhouse Gas Emission Pathways, World Meteorological Organization.  

Kantzas, E. P. et al. (2022) ‘Substantial carbon drawdown potential from enhanced rock weathering in the United Kingdom’, Nature Geoscience. Springer US, 15(5), pp. 382–389. doi: 10.1038/s41561-022-00925-2. 

Research Methods

The student will benefit from access to community gardens developed as part of a collaboration between QUB and Belfast City Council as part of the Horizon 2020 funded UPSURGE project.  It is anticipated that at least one plot at the site will be dedicated to this research, to allow the student to apply pulverised rocks to the soil, and compare growth of produce with amended soils, and take samples of soil and produce for laboratory analysis. 

It is anticipated the following laboratory work will be carried out: 

  • Oral bioaccessibility testing of Ni and Cr in soils and grown produce using the Unified BARGE Method (UBM) for bioaccessibility testing (Material Characterisation Laboratory, Queen’s University Belfast) 
  • Stable isotope measurements using C and O isotopes (Stable Isotope Laboratory, Queen’s University Belfast) 
  • Petrography of soil and plant samples (Scanning electron microscopy (SEM) including Energy Dispersive Spectroscopy (EDS)) (Aberdeen Centre for Electron Microscopy, Analysis and Characterisation (ACEMAC) facility at the University of Aberdeen). 

 There is also potential for enhanced weathering tests on amended soils to be carried out using environmental chambers available at QUB and for leaching tests to be carried out to determine how much Cr and Ni will be leached from the amended soils. 

 Using the findings of the field and laboratory analysis, the student will undertake a human health risk assessment to assess any risks posed from Cr and Ni in ERW amended soils.  


Impact on application of ERW to respond to the climate emergency 

A recent study claims that ERW could meet 45% of the UK’s net-zero carbon removal target (Kantzas et al., 2022).   This research will inform whether trace concentrations of Ni and Cr in basalts rocks pose a barrier to the utilisation in ERW.  It will inform the developing research related to ERW, and provide essential information to inform the discussion about whether these techniques could contribute to capture and sequestration of CO2 from the air.  It will prevent any unintended consequences resulting from application of ERW in inappropriate scenarios and potentially unlock ERW as a powerful tool to respond to the climate emergency. 

Academic impact 

The research carried out by the student will produce new understanding whether Cr and Ni in rocks proposed for use in ERW will cause risks to human health.  It will develop cross disciplinary research, bringing together the fields of environmental geochemistry, rock weathering and human health risk assessment to identify any limitations caused by Cr and Ni contamination on ERW.  

Proposed Supervision

The student will spend most of their time at Queen’s University Belfast, with additional time spent at University of Aberdeen. The primary supervisor will be Dr Siobhan Cox (QUB), who will be responsible for day-to-day activities, supervision on human health risk assessment, statistical methods and overall project management. Dr Rory Doherty and Prof Jennifer McKinley (QUB) will provide experience in chemical analysis, environmental geochemistry, compositional data analysis and using stable isotopes to quantify carbon sequestration. Dr Alexander Brasier (UoA) will provide expertise in stable isotope and elemental geochemistry, petrography (microscopy) and weathering processes and Dr Mark Cooper will provide expertise on identifying suitable quarries from which to source materials and characterising the basalt dusts.

Proposed Timetable

A proposed timetable for the research is set out below.  This will be reviewed and agreed with the student prior to differentiation. 


  • earth-systems
  • environmental-management


A project partnership is currently under discussion with Belfast City Council. An update will be provided in due course.

View All Projects