University researchers uncover toxic legacy in Klip River

An environmental assessment study has found that the Klip River, which winds through Soweto and Lenasia and feeds into the Vaal river system, has an alarming presence of polycyclic aromatic hydrocarbons (PAHs) in its sediments.

The study by the University of Johannesburg (UJ) researchers said the cancer-causing organic pollutants were accumulating at levels high enough to potentially harm human health, animals and aquatic life. The researchers said the organic chemicals were 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 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 human health. 

Ambushe said the PAHs, notorious for their persistence and toxicity, primarily originated from oil spills, industrial runoff and leaking fuel tanks as well as from burning of coal, waste and biomass. These are common in urban and informal settlements, reminiscent of the activities in the vicinity of the water body.

“These toxins don’t just vanish. 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,” Ambushe said. 

Seopela said the problem was systemic.

“Urbanisation, inadequate waste management, and historical pollution have turned the Klip River into a chemical reservoir,” Seopela said. 

Seopela said contaminated sediments threatened communities using river water for drinking, laundry or irrigation and livestock grazing along banks, risking toxin transfers to meat and dairy. These PAHs also disrupted 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 shared about 70% of their genetic and physiological characteristics with humans, these findings strongly suggested 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,” Makobe said. 

Ambushe said the study was not just exposing the Klip River’s pollution crisis, but the research was 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,” Ambushe said. 

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