A new University of Cape Town study has found that pollution is building up in the False Bay seabed.

The study detected medicines, herbicides and metals in the bay’s waters and sediments. Researchers say the contaminants were found across parts of the seabed, raising concern about what is collecting beneath one of Cape Town’s most important coastal areas.

The field research sampled 19 stations between April and June 2021. It linked the contamination to wastewater discharges, stormwater runoff, harbour activity and urban development around Cape Town.

Medicines Found in Sediment

The study found several pharmaceutical compounds in the seabed, including diclofenac, acetaminophen and carbamazepine.

Researchers also detected herbicides, including atrazine and metolachlor.

Dr Buyani Mazeka said the research found that pharmaceuticals and herbicides were widespread across False Bay. He added that sediments appear to hold on to these contaminants for long periods.

That means pollution is not only moving through the water. It is also settling into the seabed, where it may remain over time.

Hotspots Near Muizenberg and Gordon’s Bay

The study found the highest water loads near Gordon’s Bay.

Sediment build-up was highest near Muizenberg and parts of the north-eastern coastline.

Researchers also found metals in sediment, including copper, iron, manganese, lead and zinc. Copper was found close to guideline limits.

The team described the seabed as a long-term reservoir for pollution. That matters because coastal pollution can build slowly and become harder to deal with once it settles into marine environments.

Researchers Call for Monitoring

The study did not find clear signs of immediate ecological harm in benthic communities.

However, researchers warned that pharmaceutical residues remain a concern and should not be ignored.

Mazeka described these residues as “contaminants of emerging concern” that need continued attention.

The research team called for long-term monitoring and wider contaminant screening in False Bay.

For everyday Cape Town residents, the warning is simple. What goes through wastewater systems, stormwater channels and urban spaces does not just disappear. In False Bay, some of it is ending up beneath the surface.