19 July 2005

Sulphur dioxide and trioxide poisoning – the facts

Sulphur dioxide and sulphur trioxide are potentially fatal gases. What effects do they have on people, and what should be done if exposure has occurred?

Sulphur dioxide and sulphur trioxide are potentially fatal gases. What effects do they have on people, and what should be done if exposure has occurred?

Possible effects of sulphur dioxide poisoning
Sulphur dioxide is a colourless gas with a pungent smell and comes from the burning of coal and oil. In the air, it can be converted to sulphuric acid, sulphur trioxide, and sulphates.

Exposure to very high levels of sulphur dioxide can be life threatening. Exposure to 100 parts of sulphur dioxide per million parts of air (100 ppm) is considered immediately dangerous to life and health. Burning of the nose and throat, breathing difficulties, and severe airway obstructions occurred in miners who breathed sulphur dioxide released as a result of an explosion in a copper mine.

Long-term exposure to persistent levels of sulphur dioxide can affect your health. Lung function changes were seen in some workers exposed to low levels of sulphur dioxide for 20 years or more. Asthmatics have also been shown to be sensitive to the respiratory effects of low concentrations of sulphur dioxide.

Animal studies also show respiratory effects from breathing sulphur dioxide. Animals exposed to high concentrations of sulphur dioxide showed decreased respiration, inflammation of the airways, and destruction of areas of the lung.

Children more sensitive to sulphur dioxide
Children who live in or near heavily industrialized areas where sulphur dioxide occurs may experience difficulty breathing, changes in the ability to breathe deeply, and burning of the nose and throat. It is not known whether children are more vulnerable to these effects than adults. However, children may be exposed to more sulphur dioxide than adults because they breathe more air for their body weight than adults do.

Long-term studies surveying large numbers of children indicate that children who have breathed sulphur dioxide pollution may develop more breathing problems as they get older, may make more emergency room visits for treatment of wheezing fits, and may get more respiratory illnesses than other children. Children with asthma may be especially sensitive even to low concentrations of sulphur dioxide.

The effects of sulphur trioxide poisoning
SO3 is formed when sulphur dioxide reacts with water in the air. SO3 is generally a colourless liquid but also exists as a gas. When SO3 is exposed to air, it rapidly takes up water and gives off white fumes. It can react with water to form sulphuric acid.

SO3 is also called sulphuric oxide and sulphuric anhydride. It is used in the production of sulphuric acid and other chemicals, and explosives.

Sulphuric acid is very corrosive and is used in many industrial processes including the manufacture of fertilizers. Sulphuric acid contributes to the formation of acid rain.

Breathing sulphuric acid can result in tooth erosion and respiratory tract irritation. People who have breathed large quantities of sulphuric acid at work have shown an increase in cancers of the larynx. The United States International Agency for Research on Cancer (US IARC) has determined that occupational exposure to strong inorganic acid mists containing sulphuric acid is carcinogenic to humans.

Children may have increased sensitivity to sulphuric acid in air, due to their smaller airway diameters and the fact that they breathe more air per kilogram of body weight than adults.

The US EPA limits the amount of sulphur dioxide that can be released into the air. This limits the amount of sulphur trioxide and sulphuric acid that form from sulphur dioxide in the air.


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