ATTENTION: News editors
Media Release
For Immediate Release
Tuesday, 25 March 2025
UJ study reveals alarming levels of cancer-causing chemicals in Gauteng’s Klip River that might be posing risks to communities, livestock, and ecosystems.
The Klip River, a lifeline winding through Soweto and Lenasia in the Gauteng Province, sustains families, livestock, and local ecosystems, is a critical water resource to the surrounding communities. The Klip River also feeds into the Vaal River System, a critical water source for millions.
But beneath its flowing surface lies a hidden danger: cancer-causing organic pollutants accumulating at levels high enough to potentially harm human health, animals, and aquatic life.
In an environmental assessment study, researchers from the University of Johannesburg (UJ) have exposed the alarming presence of polycyclic aromatic hydrocarbons (PAHs) in the river’s sediments. These are organic chemicals linked to organ damage, developmental disorders, and cancer.
Led by Samuel Makobe, Dr Mathapelo Seopela, and Prof Abayneh Ambushe from UJ’s Department of Chemical Sciences, the study analysed river sediments from nine sites along the Klip River, in wet and dry seasons.
Their findings, published in Environmental Monitoring and Assessment, reveal:
- Total concentrations of PAHs in river sediments reached up to 7.41 mg/kg—far exceeding environmental safety thresholds.
- High-risk toxins peak in dry seasons when water levels are lower and increasing the exposure risks as communities rely more heavily on the river.
- Zebrafish embryos exposed to sediments suffered severe malformations, delayed hatching, and 80% mortality, signalling dire risks for aquatic life and humans-health.
Prof Ambushe explains that PAHs, notorious for their persistence and toxicity, primarily originate from oil spills, industrial runoff, and leaking fuel tanks as well as from burning of coal, waste, and biomass—common in urban and informal settlements, reminiscent of the activities in the vicinity of the water body.
“These toxins don’t just vanish,” warns Prof Ambushe. “They linger in sediments, enter the food chain, and accumulate in humans and animals over time. This is a public health crisis in slow motion”.
Using percentage composition and diagnostic ratio analysis, the UJ team traced over 70% of PAHs to these dual sources. “The problem is systemic,” explains Dr Seopela. “Urbanization, inadequate waste management, and historical pollution have turned the Klip River into a chemical reservoir.”
Dr Seopela stressed that the Klip River feeds into the Vaal River System, a critical water source for millions. “Contaminated sediments threaten communities using river water for drinking, laundry, or irrigation; livestock grazing along banks, risking toxin transfer to meat and dairy; and biodiversity, with PAHs disrupting fish reproduction and amphibian survival.”
The toxicity study conducted using the zebrafish embryo development test highlighted that heart defects and spinal deformities were observed within days of exposure. Given that zebrafish share approximately 70% of their genetic and physiological characteristics with humans, these findings strongly suggest a high probability that similar developmental and cardiovascular impairments could occur in human populations exposed to PAH contaminated environments. “If these toxins can devastate aquatic life so quickly, imagine their long-term impact on humans,” says Makobe.
“The study isn’t just exposing the Klip River’s pollution crisis, but the research is leading the charge for solutions. By integrating advanced chemical analysis with bioassays, the research team pinpoints seasonal pollution hotspots for targeted cleanup, advocating for stricter industrial regulations, and empowering communities with data to demand safer water policies,” says Prof Ambushe.
Ends.
Note to the media: The research team responsible for this work is available for interviews. Please contact me to arrange.
Issued by:
Masego Panyane
Media Liaison
University of Johannesburg
Tel: +27 11 559-1571
Cell: + 27 84 067 7528
