What is the effect of sulphur dioxide (SO2) on the human body? Are any long-term effects known?


When people are exposed to pollution caused by sulphur dioxide (SO2), the compound turns into sulphuric acid on the moist surface of mucous membranes, which irritates the eyes, nose and throat. Most of the SO2, probably more than 85%, that enters the upper respiratory tract through the nose and mouth is absorbed through the mucous membranes. In the body, it is metabolized in the liver and excreted in the urine. Therefore, very little or almost no SO2 accumulates in the body and damage to internal organs has not been described. In addition to being absorbed by the respiratory tract, bacteria in the nose and throat produce various substances that bind SO2 and inactive it.

This is why guidelines for SO2 pollution emphasize that people breathe slowly, through their nose, and avoid heavy physical activity.
The harmful effects of SO2 are related to when the compound enters the lower respiratory tract, gets into the lungs and can then cause more serious symptoms such as asthma and pulmonary edema.

When assessing the risks and responses to SO2 pollution, various criteria or concentration levels of the compound have been defined that can be used as guidelines. For example, exposure limits per hour of 350 µg / m3 and 125 µg / m3 per day have been issued. However, it is difficult to associate certain levels directly with certain symptoms as the effects of SO2 vary for different individuals, one person may experience considerable symptoms but another person standing next to him or her will hardly notice anything.

The effects of SO2 can be divided into short-term effects due to sudden pollution, which lasts only for a few minutes or hours, and long-term effects that can occur when the pollution persists for days, months or even years.

The short-term effects at low concentrations are primarily irritation of the eyes, nose and throat and possibly headaches. At higher levels, for example above 500-600 µg / m3, coughing may be noticed, especially in people with underlying lung disease. Symptoms appear as soon as the pollution reaches levels that affect the individual, but also disappear as soon as the pollution goes away. When the concentration exceeds 2600 µ / m3, symptoms become universal, irritation of the respiratory tract, cough and headaches. Healthy individuals are unlikely to develop severe symptoms until the concentration approaches 9000 µ / m3. Life-threatening symptoms are not seen until the concentration exceeds 150,000 µ / m3.

During the time that the eruption in Holuhraun lava field lasted, in 2014 to 2015, no increase in serious respiratory symptoms was observed, even though SO2 pollution rose to several thousand µg / m3, although sensitive individuals certainly experienced considerable respiratory symptoms.

Theoretically, there are various indications that children are more sensitive than adults, for example, children breathe differently than adults, they breathe faster and the volume of air they absorb relative to body weight is greater than in adults. Also, it is more difficult to get children to breathe well through their nose. Therefore, some believe that children are more vulnerable than adults, but research has not confirmed this. In guidelines for responses to SO2 pollution published in Iceland, children enjoy the benefit of the doubt and their risk has been defined as for individuals with underlying diseases.

The long-term effects of SO2 on health have been researched in many studies. These studies differ in quality and the results are therefore often not the same. However, chronic SO2 pollution appears to cause persistent respiratory symptoms such as cough, runny nose and asthma. Many studies (not all) also show that SO2 pollution can cause growth retardation in fetuses of pregnant women and also premature births. However, there are no signs that SO2 causes cancer, but the question remains whether SO2 can cause high blood pressure and infertility, but that is not entirely clear.

Thorolfur Gudnason, 
Chief Epitemiologist

Fyrst birt 04.03.2021

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