• What are the main health hazards associated with breathing in sulfur dioxide?
• What happens when sulfur dioxide comes into contact with my skin?
• Can sulfur dioxide hurt my eyes?
• What happens if sulfur dioxide is accidentally swallowed (enters the digestive system)?
• What are the long term health effects of exposure to sulfur dioxide?
• Will sulfur dioxide cause cancer?
• Will sulfur dioxide cause any problems with my reproductive system?
• Will sulfur dioxide cause effects on the fetus/unborn baby?
• Will sulfur dioxide act in a synergistic manner with other materials (will its effects be more than the sum of the effects from the exposure to each chemical alone)?
• Is there potential for sulfur dioxide to build-up or accumulate in my body?

What are the main health hazards associated with breathing in sulfur dioxide?

Sulfur dioxide (SO₂) is a moderate to strong irritant. Most inhaled SO₂ only penetrates as far as the nose and throat with minimal amounts reaching the lungs unless the person is breathing heavily, breathing only through the mouth or the concentration of SO₂ is high.

Sensitivity varies among people, however, short exposure (1-6 hours) to concentrations as low as 1 ppm may produce a reversible decrease in lung function. A 10 to 30 minute exposure to concentrations as low as 5 ppm has produced constriction of the bronchiole tubes. Only one of eleven volunteers showed any effects at 1 ppm. A 20-minute exposure to 8 ppm has produced reddening of the throat and mild nose and throat irritation. About 20 ppm is objectionably irritating, although people have been reported to work in concentrations exceeding 20 ppm. 500 ppm is so objectionable that a person cannot inhale a single deep breath.

In severe cases where very high concentrations of SO₂ have been produced in closed spaces, SO₂ has caused severe airways obstruction, hypoxemia (insufficient oxygenation of the blood), pulmonary edema (a life threatening accumulation of fluid in the lungs), and death in minutes. The effects of pulmonary edema include coughing and shortness of breath which can be delayed until hours or days after the exposure. These symptoms are aggravated by physical exertion. As a result of severe exposures, permanent lung injury may occur.

What happens when sulfur dioxide comes into contact with my skin?

The gas will react with moisture on the skin and cause irritation. Liquid SO₂ may cause burns due to freezing. Symptoms of mild frostbite include numbness, prickling and itching in the affected area. The skin may become white or yellow. Blistering, necrosis (dead skin) and gangrene may develop in severe cases.

Can sulfur dioxide hurt my eyes?

Volunteers exposed to 5.4 ppm SO₂ experienced mild irritation, while 9.1 ppm cause moderate to severe irritation. At 8-12 ppm, smarting of the eyes and lachrymation (tears) began. There is strong irritation at 50 ppm. In severe cases, (very high concentrations in confined spaces), SO₂ has caused temporary corneal burns. Liquid SO₂ can burn the eye and permanently affect vision. Injury from contact with liquid SO₂ may not be immediately noticed by the victim because SO₂ damages the nerves of the eye. Any eye contact should be treated as very serious.

What happens if sulfur dioxide is accidentally swallowed (enters the digestive system)?

Not applicable. Ingestion of gaseous or liquid SO₂ is highly unlikely.

What are the long term health effects of exposure to sulfur dioxide?

RESPIRATORY EFFECTS: Several human studies have shown that repeated exposure to low levels of SO₂ (below 5 ppm) has caused permanent pulmonary impairment. This effect is probably due to repeated episodes of bronchoconstriction. One study has found a decrease in lung function in smelter workers exposed for over 1 year to 1-2.5 ppm SO₂. No effect was seen in the same study in workers exposed to less than 1 ppm. In another study, a high incidence of respiratory symptoms was reported in workers exposed to 20-30 ppm for an average of 4 years. Workers exposed to daily average values of 5 ppm SO₂ (with occasional peaks of 53 ppm) had a much higher incidence of chronic bronchitis than controls.

There are numerous studies on the potential effects of SO₂ as a component of air pollution. These studies are difficult to interpret because of confounding factors and uncertainty about exposure concentrations.

SKIN: There are two case reports of individuals developing skin eruptions after repeated inhalation of high concentrations. In later tests, it was found that as little as a 30-minute exposure to 10 ppm SO₂ or a 1-hour exposure to 4 ppm SO₂ could produce the skin eruptions. The eruptions disappeared after removal from exposure. These particular reactions are probably rare as there are no other reports of this type of reaction.

Will sulfur dioxide cause cancer?

Several epidemiological studies have examined the possibility that sulfur dioxide may cause cancers such as lung cancer, stomach cancer or brain tumours. In all of the studies, there were uncontrolled confounding factors, such as concurrent exposure to other chemicals. The International Agency for Cancer (IARC) has reviewed these studies and concluded there is inadequate evidence for carcinogenicity in humans. However, there is limited evidence of carcinogenicity in animals. Their overall evaluation is that sulfur dioxide is not classifiable as to its carcinogenicity to humans (Group 3).

Will sulfur dioxide cause any problems with my reproductive system?

A number of epidemiological studies have suggested that exposure to SO₂ may be related to adverse reproductive effects. However, it is not clear that SO₂ caused the effects observed in any of these studies. There are no relevant results from animal studies.

Will sulfur dioxide cause effects on the fetus/unborn baby?

No human information is available. In animal studies, no teratogenic effects were observed. However, slight fetotoxicity such as reduced birth weight and functional deficits have been reported at doses which were probably toxic to the mother.

Will sulfur dioxide act in a synergistic manner with other materials (will its effects be more than the sum of the effects from the exposure to each chemical alone)?

Insufficient information is available. Human studies have examined the effect of exposure to SO₂ along with other irritating gases such as ozone and nitrogen dioxide. No conclusive evidence of synergistic action has been seen in humans. In animal studies, it has been reported that exposure to SO₂ along with soluble particles such as ferrous iron and manganese and vanadium increases the toxic action of SO₂.

Is there potential for sulfur dioxide to build-up or accumulate in my body?

SO₂ may enter the body by the respiratory tract or following dilution in saliva. Most studies in both man and animals have indicated that 40-90% or more of inhaled SO₂ is absorbed in the moist upper respiratory tract. SO₂ is quickly converted to sulfurous acid upon contact with moist mucous membranes. Inhaled SO₂ is only slowly removed from the respiratory tract. After absorption in the blood stream, the sulfurous acid is widely distributed throughout the body, quickly converted to sulfite and bisulfite, which in turn is oxidized to sulfate and excreted in the urine.

Want more information?

Document last updated on December 29, 1997

Copyright ©1997-2013 Canadian Centre for Occupational Health & Safety