Compound Information

What is it?

• Hydrogen sulfide is a colorless, flammable gas with a rotten egg odor. It can be smelled at very low concentrations in air, at least 1,000 times below the level that would cause eye and lung irritation.

Where does it come from?

• There are natural and man-made sources of hydrogen sulfide. Natural sources of hydrogen sulfide include emissions from geothermal fields, volcanic gases, and the breakdown of animal and plant wastes. Because of the latter, hydrogen sulfide is present in emissions from swamps, sewers, sewage treatment facilities and landfills. Hydrogen sulfide occurs naturally in crude oil and natural gas depending on the level of sulfur in the source. Crude oil with a low concentration of sulfur is often referred to as “sweet crude,” and oil with a higher level of sulfur is known as “sour crude.” Common sources of hydrogen sulfide emissions at refineries are associated with the transfer, storage, and processing of crude oil and the combustion of natural gas.

Why measure it?

• Because hydrogen sulfide can be smelled at such low levels, its measurement can help identify potential leaks in order to address community odor concerns.

How might it affect my health?

• Hydrogen sulfide at high levels can cause watery eyes and/or induce symptoms related to the loss of sense of smell, including headache, nausea, or vomiting. At extremely high levels, hydrogen sulfide can be deadly, particularly in enclosed spaces—the gas is heavier than air and interferes with our ability to breathe oxygen.

Where can I learn more?

CDC has a hydrogen sulfide “ToxFAQs” fact sheet.

What is it?

• Sulfur dioxide is a colorless gas with a pungent odor. It is a liquid when under pressure, and it dissolves in water very easily. Sulfur dioxide in the air comes mainly from activities such as the burning of coal and oil at power plants or from copper smelting. In nature, sulfur dioxide can be released to the air from volcanic eruptions.

Where does it come from?

• Sulfur dioxide in the air comes mainly from activities such as the burning of coal and oil at power plants or from copper smelting. In nature, sulfur dioxide can be released to the air from volcanic eruptions.

Why measure it?

• When released into the environment, sulfur dioxide moves into the air. In the air, it can be converted to sulfuric acid, sulfur trioxide, and sulfates.
• Sulfur dioxide also dissolves in water. Once dissolved in water, sulfur dioxide can form sulfurous acid. Sulfur dioxide can also be absorbed into the soil, but we don't know if or how it moves in soil.

How might it affect my health?

• Exposure to sulfur dioxide occurs from breathing it in the air. It affects the lungs and at high levels may result in burning of the nose and throat, breathing difficulties, and severe airway obstructions. Exposure to very high levels of sulfur dioxide can be life threatening. Long-term exposure to persistent levels of sulfur dioxide can affect your health. Asthmatics have also been shown to be sensitive to the respiratory effects of low concentrations of sulfur dioxide.

Where can I learn more?

CDC has a sulfur dioxide “public health statement” for more information.