Government responds to ‘rotten egg’ smell in Gauteng

The department of forestry, fisheries and the environment is probing reports of a strong sulphurous odour detected across parts of Gauteng, particularly in Johannesburg and Ekurhuleni and believes the “rotten egg” smell is probably caused by hydrogen sulphide.

In a statement issued on Thursday, the department said it had received reports of the stench on 10 March and was analysing air quality data from the South African Air Quality Information System. 

Monitoring information showed that while sulphur dioxide levels were elevated, they remained within South Africa’s National Ambient Air Quality Standards.

However, hydrogen sulphide readings recorded noticeable peaks at several monitoring stations, among them Secunda, Springs, Irene in Pretoria, Midstream and Buccleuch in Johannesburg.

Although South Africa does not yet have national ambient air quality standards for hydrogen sulphide, the department said the concentrations detected were significantly higher than the World Health Organisation’s recommended nuisance odour threshold of 5.02 parts per billion.

The department said prevailing south-easterly winds probably carried polluted air from Mpumalanga into Gauteng, affecting communities across Ekurhuleni, Johannesburg and Pretoria.

This is not the first time residents have experienced such an episode. Similar sulphurous odours were reported across Gauteng and Mpumalanga in February 2022.

After that incident, the department said it had worked with air quality authorities from Mpumalanga, North West and Gauteng to investigate the source of the pollution. 

Particular attention was given to Sasol’s Secunda operations, which is one of the region’s largest industrial facilities and a significant contributor to sulphur dioxide and hydrogen sulphide emissions.

While the investigation found that Sasol was operating within the legally permitted emission limits, authorities concluded that the existing limits might not adequately protect public health, particularly for communities living near major industrial sites.

As a result, the department said the government had begun tightening emission standards for hydrogen sulphide produced during coal gasification processes.

In August last year, the minister of forestry, fisheries and the environment published a notice proposing that the allowable emission limit for hydrogen sulphide be reduced from 3 500mg/m³ to 600mg/m³.

The proposed changes were opened for public comment and will be published for a second round of consultations. The department expects the revised standards to be finalised and implemented this year.

Authorities are also working to introduce hydrogen sulphide as a “criteria pollutant” under the National Environmental Management: Air Quality Act. 

This would allow South Africa to establish national ambient air quality standards for the gas, aligned with international health protection guidelines. Consultations with provinces and municipalities on the proposed standards are under way.

“These regulatory changes are intended to provide long-term solutions to reduce hydrogen sulphide emissions and limit public exposure,” the department said.

Hydrogen sulphide is known for its distinctive “rotten egg” smell and can irritate the eyes and respiratory system. Possible health effects include headaches, dizziness, nausea, breathing difficulties and fatigue.

Children might be particularly vulnerable because they breathe more rapidly relative to their body size and might therefore receive higher exposure levels than adults in the same environment.

The department urged residents who noticed persistent strong odours to report them to local environmental health authorities, avoid prolonged exposure where possible and seek medical attention if they experience persistent respiratory discomfort.

Officials said the department would continue monitoring the situation and working with provincial and municipal authorities to identify the sources of emissions and ensure compliance with environmental regulations.

What is hydrogen sulphide

Hydrogen sulphide is a colourless, flammable, hazardous gas with a strong odour of rotten eggs. It is produced by the breakdown of animal wastes or manure. It is heavier than air and can collect in low-lying and enclosed, poorly ventilated areas such as reception pits, ditches or manholes. 

Exposure to hydrogen sulphide might cause irritation to the eyes and respiratory system. It can also cause apnoea, coma, convulsions, dizziness, headache, weakness, irritability, insomnia; stomach upset and if liquid, frostbite. 

Workers at risk of being exposed to H2S include factory workers in plants where rayon textiles are manufactured, petroleum and natural gas workers involved in drilling and refining, workers in wastewater treatment industries and agricultural workers on farms with manure storage pits or landfills.

What is sulphur dioxide

Sulphur dioxide is a colourless gas with a pungent odour.  Exposure to SO2 may cause irritation to the eyes, nose and throat. Symptoms include nasal mucus, choking, cough, and reflex bronchoconstriction and when liquid, frostbite. 

Inhalation is the major route of exposure. Most exposures are caused by air pollution and this has short-term and chronic health consequences for people with lung disease. 
Sulphur dioxide is used in many industries such as manufacturing sulfuric acid, paper and food preservatives. Examples of workers at risk of being exposed to SO2 include factory workers where it occurs as a by-product such as copper smelting or power plants, industry workers who make sulfuric acid, workers in plants that produce paper and workers who manufacture fertilisers.