Residents across Gauteng, including parts of Pretoria, reported a strong sulphurous smell during the week of March 10–13.

National environmental authorities say elevated hydrogen sulphide levels were detected at several monitoring stations, including Irene in Pretoria, as pollution was carried into the province by prevailing winds from Mpumalanga.

The Irene monitoring station, located in the southern part of the metro, plays an important role in tracking pollution that may drift into Pretoria from industrial regions further east.

The Department of Forestry, Fisheries and the Environment (DFFE) confirmed that the odour, widely described as resembling that of rotten eggs, was most likely caused by hydrogen sulphide, a gas commonly associated with industrial emissions.

Reports of the smell began circulating on March 10, with residents in Johannesburg, Ekurhuleni, and the Tshwane metro noting the unusual odour during the day and evening.

Air quality monitoring data indicated that pollution levels were elevated across several monitoring stations in Gauteng, including the Irene station south of Pretoria, which monitors air quality affecting communities in the Tshwane metropolitan area.

DFFE spokesperson Zolile Nqayi said the department was aware of the incident and was monitoring the situation closely.

“The department can confirm that the stench experienced by residents in these areas is likely caused by hydrogen sulphide. DFFE wishes to assure the public that the matter is receiving attention.”

Monitoring data from the South African Air Quality Information System indicated elevated levels of the gas at multiple stations across the province, including Irene, Midstream, Buccleuch, Springs and Secunda.

Although the pollution was detectable by smell, the department said levels of sulphur dioxide remained within national standards.

“Air quality monitoring information from the South African Air Quality Information System showed that levels of sulphur dioxide, while elevated, remained in compliance with National Ambient Air Quality Standards during this period,” Nqayi said.

However, hydrogen sulphide levels showed noticeable spikes.

Hydrogen sulphide is a product and byproduct of coal pollution and coal-related activities.

While sulphur dioxide is the most commonly cited sulfur pollutant from coal combustion, hydrogen sulphide is released through various stages of the coal lifecycle.

“For hydrogen sulphide, monitoring data also showed elevated peaks especially in Secunda, Springs, Irene (Pretoria), Midstream and Buccleuch air quality monitoring stations,” Nqayi explained.

While South Africa does not yet have official ambient standards for hydrogen sulphide, the department said the levels recorded were higher than international guidelines for odour detection.

“Although there are no National Ambient Air Quality Standards for hydrogen sulphide for now, these pollution levels were all significantly higher than the World Health Organization’s recommended threshold for ambient nuisance odour of 5.02 parts per billion,” Nqayi explained.

Environmental officials believe prevailing weather conditions contributed to the spread of the smell across Gauteng.

“Meteorological conditions show prevailing south-easterly winds that allowed for the transportation of air pollution from Mpumalanga into Gauteng, particularly over the cities of Ekurhuleni, Johannesburg and Pretoria,” said Nqayi.

This means the odour detected in Pretoria may have originated from industrial activity outside the province.

The department noted that similar incidents have occurred in the past, including a major odour episode in 2022 that affected both Mpumalanga and Gauteng.

“At the time, investigations were conducted by DFFE together with air quality authorities from Mpumalanga, North West and Gauteng. Focus was given to Sasol Secunda Operations, which is a significant contributor to sulphur dioxide and hydrogen sulphide emissions,” he said.

Following the 2022 incident, the government established a multi-stakeholder task team to address the issue more effectively and develop long-term solutions to manage emissions of sulphur dioxide and hydrogen sulphide.

Since then, authorities have been working on strengthening regulations to limit the release of hydrogen sulphide into the atmosphere.

“In August 2025, the Minister of Forestry, Fisheries and the Environment published, for public comment, a notice of intention to tighten the permitted release of hydrogen sulphide from coal gasification processes in terms of Section 21 of the National Environmental Management: Air Quality Act,” Nqayi said.

The proposed changes would significantly lower the allowable emission levels.

“The proposed amendment seeks to reduce the emission limit of hydrogen sulphide from 3500mg per cubic metre to 600mg per cubic metre, which will significantly reduce pollution released into the environment,” he said.

According to the department, comments received during the first public consultation phase are currently being reviewed before a second round of consultations takes place.

“It is anticipated that these regulatory provisions will be finalised and implemented during 2026,” Nqayi said.

Another important step being considered by the government is the introduction of hydrogen sulphide as a formal criteria pollutant under the National Environmental Management: Air Quality Act.

This would allow South Africa to establish national ambient standards for the gas, similar to those that exist for other pollutants.

“The department is also in the process of introducing hydrogen sulphide as a criteria pollutant under the National Environmental Management: Air Quality Act,” said Nqayi.

“This will allow South Africa to establish National Ambient Air Quality Standards for hydrogen sulphide, aligned with international health protection guidelines.”

Authorities say this would strengthen monitoring and enforcement efforts across the country.

In the meantime, environmental officials have advised residents in affected areas, including Pretoria, to remain aware of potential health effects linked to exposure.

Hydrogen sulphide can irritate the eyes and respiratory system and may cause symptoms such as headaches, nausea, dizziness and breathing difficulties.

“The department therefore urges members of the public in affected areas to report persistent strong odours to local environmental health authorities or health authorities,” Nqayi said.

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