UNILORIN researchers identify heavy metal contamination in ground food
…. study warns of health risks from milling
By Mustafa Abubakar
Ten researchers from the University of Ilorin have identified potentially hazardous levels of metallic contaminants in ground food, warning that particles released from cast-iron grinding discs during milling could enter commonly consumed food and pose long-term health risks.
The researchers, in a study made available to UNILORIN Bulletin last Wednesday(September 9, 2026), said the research, funded by the Tertiary Education Trust Fund (TETFund) under the National Research Fund, documented contamination levels, sources and health risks associated with metallic wear from cast-iron grinding discs commonly used across Nigeria and other developing nations.
The team comprises the Principal Investigator, Prof. Sulaiman Abdulkareem of the Department of Mechanical Engineering, Prof. Ismaila Idowu Ahmed, Prof. Jamiu Kolawole Odusote, Prof. Rasheedat Modupe Mahamood, Dr Jeleel Adekunle Adebisi, Dr Segun Isaac Talabi, and Mr Taiwo Yahaya from the Department of Materials and Metallurgical Engineering.
Prof. Lawrence Aderemi Olatunji of the Department of Physiology and Dr Mariam Kehinde Sulaiman of the Department of Medical Microbiology & Parasitology contributed medical and biological expertise to the investigation, while Prof. Jamiu Adetayo Adeniran of the Department of Chemical Engineering was later invited to join the team, contributing environmental source apportionment and health-risk modelling expertise.
Speaking on behalf of the team, Prof. Abdulkareem said the findings highlighted the need for improved milling practices and stronger quality-control standards for grinding discs used in food processing.
The researchers found that up to 1.7 grams of metallic contaminants can be introduced into 10 kilograms of ground maize during dry grinding operations, according to the study published in Results in Engineering.
The team said the average contaminant particle size was approximately 43 micrometres, making the particles small enough to pass into the stomach unnoticed.
Prof. Abdulkareem said dry grinding produced significantly higher quantities of metallic contaminants than wet grinding, with water serving as a lubricant that reduces wear during the process.
The researchers said the research demonstrated significant corrosion susceptibility among all the grinding discs when exposed to simulated gastric solution, a fluid matching the human stomach environment at pH 1.7 and 37°C.
The team said corrosion occurred at varying degrees among the discs, with the imported sample showing the highest susceptibility, while the pit furnace-produced disc showed the most resistance.
According to the team, the health-risk assessments examined concentrations of eight potentially toxic elements in milled maize and found that the mean concentrations of lead, cadmium and arsenic exceeded permissible limits set by the Codex Alimentarius Commission of 0.2, 0.1 and 0.5 milligrams per kilogram, respectively.
The researchers said Positive Matrix Factorisation modelling identified grinding-disc wear as a significant contributor to contamination levels, alongside other sources including vehicle traffic emissions, application of pesticides and herbicides, use of manure and zinc-enriched fertilizer, irrigation with industrial wastewater, lubrication oil leakage and emissions from leaded-fuel combustion.
He said although the hazard-index assessments showed that immediate non-cancer risks were not significant, the potential for long-term accumulation of toxic elements, particularly cadmium, lead and arsenic, remained concerning.
The team said children were found to be 9.3 times more vulnerable than adults to health risks from the contaminants, saying that the ingestion pathway contributed over 94% of non-cancer risk and over 97% of cancer risk, making dietary exposure the primary concern.
The researchers also established that corrosion of metallic contaminants in simulated gastric solution followed an exponential trend, with hydrogen gas evolution occurring within 15 to 30 minutes of exposure to the acidic environment.
The team said a related study published in the Nigerian Journal of Technological Development demonstrated that adding ferrochromium to the cast iron used for grinding discs substantially improved performance.
They stated further that the study, which utilised recycled Toyota engine-block scrap as base material, found that hardness increased from 543 to 600 kgf/mm² with up to 1.5 weight percent ferrochromium addition.
The researchers said yield strength improved from 10 to 28 megapascals, while specific wear rate was reduced by approximately 27% at higher applied loads.
The team said corrosion resistance also improved significantly, with corrosion potential increasing from -0.91 to -0.69 volts.
The researchers called for multiple interventions based on their findings, including implementation of quality-control standards for grinding-disc manufacturing, promotion of wet grinding over dry grinding and adoption of ferrochromium-alloyed discs by local foundries.
The team also recommended the development of magnetic scavenging devices to capture metallic contaminants, public-awareness campaigns and further research into the long-term health effects of exposure to the contaminants.
According to him, the proposed solutions were practical and could be implemented using locally available materials and existing foundry equipment.
The researchers said the interventions would support safer food-processing practices and contribute to the objectives of United Nations Sustainable Development Goal 3 on healthy living and well-being.
