What is that smell? Mystery rotten-egg stench triggers health concerns across Gauteng

Residents described the odour as sulphur, gas, cat urine, sewage and even old engine oil. A mysterious rotten-egg smell sweeping across parts of Gauteng has sparked health concerns, triggered widespread complaints and left residents searching for answers as authorities investigate the source of the lingering odour. Residents reported the pungent smell in areas including Randfontein, Krugersdorp, Muldersdrift, Fourways and other parts of Johannesburg. Foul smell Residents described the odour as sulphur, gas, cat urine, sewage and even old engine oil. Some initially blamed their pets or searched their homes for the source before realising the smell was affecting entire neighbourhoods. Security and risk intelligence company BCI Security said residents across parts of Johannesburg had reported a strong sulphurous or rotten-egg smell, but stressed that the source had not been confirmed. Precaution The company noted that similar odours have previously been associated with hydrogen sulphide (H₂S), a gas that can cause eye and respiratory irritation, headaches, dizziness, nausea and breathing difficulties depending on exposure levels. As a precaution, residents have been advised to limit time outdoors while the smell persists, keep windows and doors closed if the odour enters their homes and seek medical advice if they experience significant irritation or ongoing breathing problems. Complaints Adding to concerns, regional forecaster Gauteng Weather said east-south-easterly winds contributed to the strong sulphur smell across Gauteng on 28 October, resulting in unhealthy air-quality conditions for sensitive groups in some affected areas. Meanwhile, Refilwe Mahlangu, assistant to the media and public relations manager at Mogale City Local Municipality, said the municipality received numerous complaints from residents and stakeholders in and around Krugersdorp, The Citizen’s regional publication, Roodepoort Record,reported. Air quality Air-quality data from a monitoring sensor at the Krugersdorp Central Library recorded elevated PM2.5 and PM10 levels during the early hours of the morning before declining later in the day. “Following these complaints, readings from the low-cost sensor at the Krugersdorp Central Library were reviewed. The readings indicate spikes in PM2.5 and PM10 levels between 12am and 8am on Wednesday, followed by a decline after 8am,” Mahlangu said. Unknown Despite the complaints, the source of the smell remains unknown. “As the matter appears to involve transboundary pollution, the municipality will engage the relevant authorities, as the matter is regional in nature,” said Mahlangu. Investigations The mystery odour comes as Midvaal Local Municipality investigates recurring reports of ammonia-, sulphur- and rotten-egg-like smells in its area as part of a broader investigation into odour incidents affecting parts of Gauteng and Mpumalanga. For now, residents still have no answers as authorities work to determine what is behind the strange smell hanging over parts of the province.