UNILORIN Researchers Raise Alarm Over Metal Contamination in Ground Food

Ten researchers from the University of Ilorin (UNILORIN) 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 foods and pose long-term health risks.

The researchers said metallic particles from grinding discs could contaminate milled maize, particularly during dry-grinding operations, with children potentially more vulnerable to the associated health risks.

The findings, contained in a study made available to the UNILORIN Bulletin on Wednesday, September 9, 2026, documented the levels, possible sources and health implications of metallic contamination associated with cast-iron grinding discs commonly used in Nigeria and other developing countries.

The research was funded by the Tertiary Education Trust Fund (TETFund) under its National Research Fund and was published in Results in Engineering.

According to the study, as much as 1.7 grammes of metallic contaminants could be introduced into 10 kilogrammes of ground maize during dry-grinding operations.

The researchers said the average size of the contaminant particles was approximately 43 micrometres, indicating that they were sufficiently small to become incorporated into food and ingested without being readily detected.

Speaking on behalf of the research team, the Principal Investigator, Prof. Sulaiman Abdulkareem of the Department of Mechanical Engineering, said the findings underscored the need for improved milling practices and stronger quality-control standards for grinding discs used in food processing.

He explained that dry grinding generated significantly higher quantities of metallic contaminants than wet grinding, noting that water acts as a lubricant and helps to reduce wear on the grinding discs.

The researchers also subjected the grinding discs to simulated gastric solution designed to replicate the human stomach environment at a pH of 1.7 and a temperature of 37°C.

They found that all the discs exhibited varying degrees of susceptibility to corrosion in the simulated gastric environment. The imported sample recorded the highest susceptibility, while the pit-furnace-produced disc demonstrated the greatest resistance.

The health-risk assessment examined concentrations of eight potentially toxicUNILORIN Researchers Raise Alarm Over Metal Contamination in Ground Food elements in milled maize.

The researchers reported that mean concentrations of lead, cadmium and arsenic exceeded permissible limits established by the Codex Alimentarius Commission, which are 0.2, 0.1 and 0.5 milligrams per kilogramme respectively.

Using Positive Matrix Factorisation modelling, the researchers identified grinding-disc wear as a significant contributor to the contamination.

Other identified sources included vehicle-traffic emissions, pesticide and herbicide applications, manure and zinc-enriched fertiliser, irrigation with industrial wastewater, lubrication-oil leakage and emissions associated with leaded-fuel combustion.

Although the hazard-index assessment indicated that immediate non-cancer health risks were not significant, the researchers expressed concern over the possibility of long-term accumulation of toxic elements, particularly lead, cadmium and arsenic.

The study further found that children could be 9.3 times more vulnerable than adults to the health risks associated with the contaminants.

According to the researchers, ingestion accounted for more than 94 per cent of the estimated non-cancer risk and more than 97 per cent of the cancer risk, making dietary exposure the major pathway of concern.

The researchers also observed that corrosion of the metallic contaminants in the simulated gastric solution followed an exponential pattern, with hydrogen gas evolution occurring within 15 to 30 minutes after exposure to the acidic environment.

The research team comprises Prof. Abdulkareem; Prof. Ismaila Idowu Ahmed; Prof. Jamiu Kolawole Odusote; Prof. Rasheedat Modupe Mahamood; Dr Jeleel Adekunle Adebisi; Dr Segun Isaac Talabi; and Mr Taiwo Yahaya, all 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 and Parasitology contributed medical and biological expertise to the study.

Prof. Jamiu Adetayo Adeniran of the Department of Chemical Engineering later joined the team, contributing expertise in environmental source apportionment and health-risk modelling.

The researchers also cited a related study published in the Nigerian Journal of Technological Development, which investigated ways of improving the performance and corrosion resistance of cast-iron grinding discs.

They said the related study found that adding ferrochromium to cast iron produced from recycled Toyota engine-block scrap significantly improved the material’s performance.

According to the researchers, hardness increased from 543 to 600 kgf/mm² with the addition of up to 1.5 weight per cent ferrochromium, while yield strength rose from 10 to 28 megapascals.

They added that the specific wear rate was reduced by approximately 27 per cent at higher applied loads, while corrosion resistance also improved significantly, with corrosion potential increasing from -0.91 to -0.69 volts.

Based on the findings, the researchers recommended the introduction and enforcement of quality-control standards for the manufacture of grinding discs used in food processing.

They also advocated greater use of wet grinding, adoption of ferrochromium-alloyed grinding discs by local foundries and the development of magnetic scavenging devices capable of removing metallic contaminants from milled food.

Other recommendations included sustained public-awareness campaigns on safer milling practices and further research into the long-term health effects of exposure to metallic contaminants in processed foods.

Prof. Abdulkareem said the proposed interventions were practical and could be implemented with locally available materials and existing foundry equipment.

He said the adoption of the recommendations would help promote safer food-processing practices while contributing to the achievement of United Nations Sustainable Development Goal 3, which focuses on healthy lives and well-being for all.