Description

Sulfur dioxide (SO2) is a colorless, smelly gas in the sulfur oxide family of gases. Sulfur dioxide is formed when sulfur-containing fuels, such as coal and oil, are burned. The primary sources of SO2 emissions are power plants, refineries and copper smelting facilities. Sulfur dioxide is also found in the exhause of diesel fuel and gasoline. Volcanoes and decaying organic matter also produce SO2. However, man-made emissions of SO2 have been the cause of some of the worst air pollution episodes in the last century.

SO2 is one of the six major air pollutants in the U.S. Sulfur dioxide is a potent asthma trigger and can cause other respiratory health effects. In the atmosphere, sulfur dioxide can form dangerous sulfates, which can be breathed deep into the lungs, and sulfuric acid, the major acidic component of
acid rain. Acid rain can harm fish, damage forests and plants,and erode buildings.

Sulfur dioxide is also used to preserve foods. It is one of a group of sulfiting agents, used in wine, on many dried fruits and in numerous other foods. Asthmatics may be sensitive to sulfiting agents found in food.

Children living in urban areas are more likely to be exposed to air-borne sulfur dioxide and its byproducts. But any child living in a home where gas appliances are used may also be exposed. Because children breathe in more air for their body weight than adults do, children generally are more vulnerable to the effects of SO2 than adults.

Health Effects

Immediate Health Effects

If SWALLOWED, sulfur dioxide is Not Available
If ABSORBED THROUGH SKIN, sulfur dioxide is Not Available
If INHALED (SNIFFED OR BREATHED IN), sulfur dioxide is Not Available

Longterm or Delayed Health Effects

This chemical is considered an Unclassifiable Carcinogen by the World Health Organization, the U.S. Environmental Protection Agency, or another agency.
Allergen
Asthma Trigger

Other

Respiratory (breathing) effects. Breathing high levels of sulfur dioxide can constrict airways, causing wheezing, chest tightness, coughing, and breathing problems. This can aggravate existing respiratory diseases, such as bronchitis, asthma, or emphysema, and trigger asthma attacks. Chronic exposure may cause bronchitis. Sulfur dioxide exposure may also impair the respiratory system’s defenses against foreign particles and bacteria. Exposure to extremely high concentrations of SO2 can cause severe shortness of breath and pulmonary edema, a medical emergency characterized by fluid building up in the lungs.

Those most sensitive to sulfur dioxide exposure are children with asthma, the elderly, and individuals with asthma, cardiovascular or chronic lung disease (bronchitis, emphysema), or who are mouth-breathing, particularly when exercising. Exposure to SO2 while exercising can increase the likelihood of airway constriction. Possible effects of long-term exposure to SO2 during childhood are increased respiratory illness, wheezing fits, and respiratory-related
emergency room visits. Long-term exposure to SO2 can change a child’s ability to breathe deeply.
Low concentrations of sulfur dioxide in outdoor air can irritate the eyes, nose, throat, and respiratory tract, causing coughing and shortness of breath. Long-term exposure to low concentrations can cause headache, nausea, dizziness, and temporary loss of smell.
Breathing SO2 in polluted outdoor air may heighten sensitivities to other allergens, particularly in asthmatics.
Cancer. Inhaling sulfur dioxide has caused lung tumors in test animals. Some, but not all, studies of workers exposed to high levels of sulfur dioxide have found increased risk for lung, stomach and brain cancer.
Several studies have found higher death rates on days with elevated SO2 levels in outdoor air.
Some studies have found that exposure to increased SO2 levels from outdoor air pollution during pregnancy may be associated with an increased risk for low birth weight and premature birth. Long term exposure may decrease fertility in males and females.

How Exposures Occur

Industrial Pollution

Children can inhale sulfur dioxide from polluted
outdoor air, particularly if they live near industrial facilities that burn coal or oil, such as power plants and refineries, or near copper smelting plants, sulfuric acid manufacturers, fertilizer factories, paper pulp factories, or hazardous waste sites contaminated with sulfur dioxide. Because it increases breathing rates, exercising may increase the amount of sulfur dioxide entering the lungs if air pollution levels are high.

Vehicle Exhaust

Children can inhale sulfur dioxide from truck and car exhaust, especially in urban areas and near busy streets and highways. Diesel fuel, and to a lesser extent gasoline, contain sulfur and contribute to sulfur dioxide in the air. Recent studies show that diesel school buses is a source of exposure to school children.

Combustion Appliance

Children can inhale sulfur dioxide in homes
where fuel-burning appliances, including gas stoves, gas space heaters, kerosene heaters, furnaces, and wood stoves are used, especially if they are in disrepair, used improperly or without proper ventilation.

In Food

Children may ingest sulfur dioxide in foods preserved with it. Sulfur dioxide and five of its sulfite relatives are approved for use as preservatives in foods such as dried fruits (except prunes and black raisins), canned fruits and
vegetables, applesauce, wines, vinegar, pickled foods, instant potatoes and dried vegetables. Sulfur dioxide can also be applied to table grapes as a post-harvest fungicide. In sensitive individuals (particularly asthmatics), ingestion of sulfur dioxide and sulfites in food can cause asthma attacks, skin rashes and upset stomach.

Significant Statistics

In 1994, electricity generation was responsible for 70 percent of sulfur dioxide emissions. Of the top 50 individual sources of sulfur dioxide emissions in the U.S., all are electric power plants.

Risky Business: Hidden Environmental Liabilities of Power Plant Ownership. Natural Resources Defense Council, September 1996http://www.nrdc.org/air/energy/rbr/rbtinx.asp

Nationally, average SO2 concentrations in outdoor air have decreased by 50% from 1981 to 2000, and by 37% over the more recent 10-year period of 1991–2000. SO2 emissions decreased 31% in 1981-2000 and 24% in 1991-2000. Reductions in SO2 concentrations and emissions since 1994 are largely due to controls implemented under the U.S. Environmental Protection Agency’s Acid Rain Program, initiated in 1995.

National Air Quality Status and Trends 2000: Sulfur Dioxide. U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, 2000.http://www.epa.gov/oar/aqtrnd00/sulfur.html

Solutions

How to detect sulfur dioxide

Pay attention to local air pollution advisories and news bulletins, which alert citizens when levels of SO2 and other pollutants are elevated. While levels of sulfur dioxide in the air are typically highest during the winter months, human exposure to sulfur dioxide has been shown to be greatest during the summer months, when people enjoy being outdoors in
warm weather and are more likely to leave household windows open.
To find out the highest sources of sulfur dioxide pollution in your community, and how your region ranks nationwide for sulfur dioxide pollution, go to Environmental Defense Chemical Scorecard.
You can’t tell if sulfites are on foods by looking at them. Read food labels, which are required to list the use of sulfites. Look for sodium sulfite, sodium bisulfite, potassium bisulfite, potassium metabisulfite, sodium metabisulfite and sulfur dioxide in ingredient listings.

Sulfites may be used on salad bar and other buffets in delis and restaurants.

How to minimize exposure to sulfur dioxide

Children should be kept from doing moderate to strenuous exercise outdoors when air pollution levels are high. Children should also avoid exercising on playing fields near
highways or other busy roads.

Children with asthma or other respiratory difficulties should stay indoors and limit outdoor activities during local air pollution advisories, when high levels of sulfur dioxide may be present in the air.
Asthmatics should avoid foods preserved with sulfur dioxide or sulfites as a precaution against possible asthma attacks or allergic reactions.
Always operate combustion appliances according to manufacturer specifications. Use the proper fuel in
kerosene space heaters and never leave space heaters unattended. Choose properly sized wood stoves that are certified to meet EPA emission standards, and be sure doors on wood stoves fit tightly. Consider purchasing a vented space heater when replacing un-vented heaters.
Keep gas appliances properly maintained and in repair. Have gas appliances and furnaces inspected, cleaned and tuned at least once a year. Repair leaks promptly. In some areas, local gas companies perform this service.

When appliances are kept in good working condition, they produce few combustion pollutants such as nitrogen dioxide.
Make sure there is adequate ventilation when using combustion appliances.
-Use an exhaust fan vented to outdoors every time you use a gas stove. The exhaust fan should be located above the stove. If you do not have an exhaust fan over your gas stove, always open a window while cooking.
-Open flues when fireplaces are in use.
-Never leave a car or lawnmower engine running in a garage, shed or other enclosed spaces. Even if the garage door to the outside is open, fumes can build up very quickly in the garage and living area of your home. Don’t use gasoline-powered appliances, engines or tools (mowers, weed trimmers, snow blowers, chain saws, small engines or generators) in
enclosed or partly-enclosed spaces.

Alternatives

Using ovens and heating systems powered by electricity instead of fuels will reduce nitrogen dioxide emissions in the home; however,electric ovens are not as energy-efficient
as gas ovens. If you decide on gas appliances, choose appliances that vent their fumes to the outdoor whenever possible.
Use your car less. Take public transportation, walk, or ride a bicycle.
Fresh fruits and vegetables and organic grapes are not preserved with sulfur dioxide. Look for unsulphured dried fruits and vegetables.

For More information

Books, articles, factsheets and reports

Sulfur Dioxide Fact Sheet. Idaho Department of Health and Welfare, January 2001.

http://www2.state.id.us/dhw/BEHS/sulfur_dioxide.htm

Subtracting Sulfur: Reducing Diesel Sulfur Levels to Reduce Urban Pollution. Natural
Resources Defense Council, February 2002.

http://www.nrdc.org/air/transportation/psulfur.asp

What You Should Know About Combustion Appliances and Indoor Air Pollution. U.S. Consumer Product Safety Commission, U.S. Environmental Protection Agency, and The American Lung Association, Updated March 15, 1999.

http://www.epa.gov/iaq/pubs/combust.html