Task team appointed to investigate source of sulphur dioxide and hydrogen sulphide smell experience by the public in North West and Gauteng
10 June 2022
A task team has been established to investigate the complaints about the stench experienced over parts of Gauteng and North West in the past week.
The task team, comprising environmental and air quality officials from the Department of Forestry, Fisheries and the Environment and the provincial departments in Mpumalanga, Gauteng, North West and the Free State will also devise a proactive long-term program to improve the management of sulphur dioxide and hydrogen sulphide emission sources beyond the responses triggered by public complaints.
The meeting on 9 June 2022 formally initiated an investigation into the origins of the sulphurous odour, which is thought to be, in all likelihood, due to a combination of above average ambient levels of sulphur dioxide (SO2) and or hydrogen sulphide (H2S) in the air given the nature of this odour.
During February 2021, similar sulphurous odour episodes were experienced over Mpumalanga and Gauteng. Investigations by the department and atmospheric emission licencing authorities in the two provinces had focussed on the Sasol Secunda operations, because these facilities are known to be the significant contributors of sulphur dioxide and hydrogen sulphide emissions. These investigations were, however, inconclusive and no further action could be taken.
Following complaints this week about the strong sulphuric smell over Gauteng and parts of North West, officials have undertaken to immediately probe the possible source and cause of the stench, but also to submit a detailed report on the matter by next week.
The task team will investigate possible upset conditions experienced or reported by atmospheric emission licence holders over the past month that have had the potential to release large quantities of sulphur dioxide or hydrogen sulphide into the atmosphere.
Ambient air quality monitoring reports on the state of air in the region over the past month will be studied focusing on sulphur dioxide and hydrogen sulphide. Ambient air quality monitoring observations on the South African Air Quality Information System (SAAQIS) show that sulphur dioxide ambient levels, while elevated, are compliant with ambient standards in Gauteng. However, preliminary results show significantly elevated levels of hydrogen sulphide around the Irene monitoring station in Centurion on 7 June 2022. Possible sources that could influence such levels will be identified from the meteorological assessment.
The task team will also probe possible sources through inspections and compliance assessment of emission monitoring reports against atmospheric emission licence requirements. Where non-compliances are identified, enforcement action will be taken.
For the long-term plan, the officials will undertake a detailed assessment of hydrogen sulphide sources in the four provinces. Atmospheric emission licence holders, wastewater treatment facilities and landfill sites will be prioritised as they are the most significant contributors. For the atmospheric emission licence holders, emission reductions and management plans will be established to improve the monitoring and management of hydrogen sulphide to reduce the risks of ongoing pollution episodes that are affecting the provinces.
The long-term plans will strengthen the implementation of the Air Quality Management Plans in priority areas to ensure the reduction of air pollution once the priority area regulations come into effect.
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Through the implementation of the Air Quality Act, standards and regulations related to the levels of NOx and SO2 levels, the Department of Forestry, Fisheries and the Environment ensures that all industries comply with national ambient air quality standards.
Hydrogen sulphide (H₂S)
Hydrogen sulphide (H₂S) is a colourless, flammable, extremely 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 may 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 may be harmed from exposure to hydrogen sulphide. The level of exposure depends upon the dose, duration, and work being done.
Hydrogen sulphide is used in many industries. For example, it’s used to produce textiles. Some examples of workers at risk of being exposed to hydrogen sulphide include the following:
- Factory workers in plants where rayon textiles are manufactured
- Petroleum and natural gas workers involved in drilling and refining
- Workers in wastewater treatment industries
- Agricultural workers on farms with manure storage pits or landfills
Sulphur dioxide (SO₂)
Sulphur dioxide (SO₂) is a colourless gas with a characteristic, irritating, pungent odour. Exposure to sulphur dioxide may cause irritation to the eyes, nose, and throat. Symptoms include nasal mucus, choking, cough, and reflex bronchi constriction, and when liquid: frostbite. Workers may be harmed from exposure to sulphur dioxide. The level of exposure depends upon the dose, duration, and work being done.
Sulphur dioxide is used in many industries. It’s used to manufacture sulfuric acid, paper, and food preservatives. Some examples of workers at risk of being exposed to sulphur dioxide include the following:
- Factory workers in industries where it occurs as a by-product, such as copper smelting or power plants
- Industry workers that manufacture sulfuric acid
- Workers in plants that produce paper
- Food processing to preserve foods, such as dry fruits
- Workers who manufacture fertilisers
Inhalation is the major route of exposure to sulphur dioxide. The odour threshold is 5 times lower than, for example, the US’ permissible exposure limit of 5 ppm. Most exposures are due to air pollution, and this has both short-term and chronic health consequences for people with lung disease. Inhaled sulphur dioxide readily reacts with the moisture of mucous membranes to form sulphurous acid (H2SO3), which is a severe irritant. People with asthma can experience increased airway resistance with sulphur dioxide concentrations of less than 0.1 ppm when exercising. Healthy adults experience increased airway resistance at 5 ppm, sneezing and coughing at 10 ppm, and bronchospasm at 20 ppm. Respiratory protection is required for exposures at or above 20 ppm. Exposures of 50 to 100 ppm may be tolerated for more than 30 to 60 minutes, but higher or longer exposures can cause death from airway obstruction. Sulphur dioxide is heavier than air; thus, exposure in poorly ventilated, enclosed, or low-lying areas can result in asphyxiation.
Children exposed to the same levels of sulphur dioxide as adults may receive a larger dose because they have greater lung surface area: body weight ratios and increased minute volumes: weight ratios. In addition, they may be exposed to higher levels than adults in the same location because of their short stature and the higher levels of sulphur dioxide found nearer to the ground and because they are slow to leave the site of an exposure.