Heavy metal contamination is a ticking time bomb that is quietly accumulating in the environment and presenting a growing public health crisis, in South Africa and across the world. In her inaugural lecture at the University of Pretoria (UP) on 14 October 2024, Professor Nanette Oberholzer from UP’s Department of Anatomy, shared the latest research findings on the dangers posed by heavy metals such as mercury (Hg), cadmium (Cd), and lead (Pb).

Her presentation titled: ‘Integrative approaches in heavy metal toxicity research: Bridging animal models and ex vivo human blood studies,’ revealed the often-overlooked effects of these metals on human health.

Prof Oberholzer highlighted how rapid urbanisation, industrialisation, and modern agricultural practices have led to increased heavy metal pollution. While naturally occurring in the Earth's crust, these metals now find their way into drinking water, air, and food due to activities such as mining and industrial smelting.

"What makes these metals particularly dangerous is their ability to bioaccumulate, subtly disrupting vital biological processes, often at very low concentrations," Prof Oberholzer said.

Her research shows how this bioaccumulation — especially in South Africa, where mining is a key industry — puts communities at risk. The country holds the fifth-largest mining sector globally, with significant reserves of manganese, platinum and gold.

"People living near mining areas are among the most vulnerable. They are exposed to toxic metals on a daily basis," Prof Oberholzer revealed. Despite this widespread exposure, the full scope of long-term health effects remains poorly understood, she said.

Research knowledge gap

Prof Oberholzer's work addresses this knowledge gap through the innovative use of animal models and ex vivo studies on human blood. Ex vivo studies refer to experiments or procedures performed on tissues or organs extracted from a living organism and conducted outside the original biological context.

By using a combination of animal models and advanced microscopy techniques, Prof Oberholzer and her team have been able to closely study the impacts of metal exposure on critical biological systems such as the liver, heart, brain and lungs – which tend to be overlooked in toxicity studies.

“Animal models provide us with a controlled environment where we can replicate long-term exposure scenarios,” she explained. Her research found that even when standard blood tests appear normal, underlying tissue damage may still occur — leading to long-term health consequences such as cardiovascular disease.

Impacts on human health

The research conducted by Prof Oberholzer and her colleagues focuses on the complex and often underestimated reality of heavy metal exposure, where people are not exposed to single metals, but rather combinations at various concentrations.  

"The challenge is studying these combinations over long periods at concentrations that reflect real-world exposure," Prof Oberholzer said. Her team’s approach involved translating World Health Organisation (WHO) guidelines for safe drinking water into animal dosage models, allowing for a detailed investigation of how these metals affect specific organs and tissues.

One of the most concerning findings is how metal exposure, particularly cadmium and mercury, affects the cardiovascular system. “We observed profound effects on the fibrin network within the circulatory system,” Prof Oberholzer said. This resulted in the formation of fibrin networks with ultrastructural features indicative of a more thrombotic morphology, suggesting an increased risk of cardiovascular disease..

Using scanning electron microscopy (SEM), the researchers identified significant changes in the structure of red blood cells and platelets, further contributing to an increased risk of coagulation abnormalities.

Prof Oberholzer's research work where human blood samples were used to provide more direct insights into how metal exposure impacts human health revealed that exposure to metals such as cadmium and chromium not only activated platelets but also caused thicker fibrin fibres — tell-tale signs of a hypercoagulable state. A hypercoagulable state, also known as thrombophilia, is a medical condition characterised by an increased tendency for the blood to form clots.

"The human blood studies complement the animal models, helping us get a comprehensive view of how these metals affect the human body," she explained.

Contaminated water sources

South Africa's water sources are also bearing the brunt of this contamination. A study presented during the lecture revealed how river sediments in Mpumalanga’s Spekboom River have been highly contaminated with chromium (Cr) and nickel (Ni), while two other sites showed elevated levels of iron (Fe) and manganese (Mn).

Prof Oberholzer also cited research conducted in Kuils River, Western Cape, where arsenic (As) and zinc (Zn) levels in the soil samples of some pre-schools in the area exceeded recommended limits.

“In another study published in 2022 in the International Journal of Environmental Research and Public Health, the authors… collected samples from 34 preschools in the area and results indicated that metal levels in the soil were below the SA standard, however, at some of the pre-schools the levels of (arsenic and zinc) exceeded certain reference levels.”

Going forward

Prof Oberholzer called for future research to identify early biomarkers for heavy metal exposure and tissue damage. “By improving risk assessment and developing targeted interventions, we can mitigate the health effects of exposure in vulnerable populations,” she said.

South Africa, with its rich mining resources and vulnerable populations, is uniquely positioned to benefit from such enhanced assessments and targeted interventions.

“The goal is not only to understand the damage being done but to contribute to strategies that can ensure safer environments and healthier communities,” Prof Oberholzer concluded.