Skip to Main Content Health Care Professionals Haldimand-Norfolk Health Unit Search

Hydrogen Sulphide (H2S)

Do you have questions about Hydrogen Sulphide (H2S)?

Hydrogen sulphide (H2S) is a colorless gas that smells like rotten eggs. At very high levels, hydrogen sulphide can be flammable.
Hydrogen sulphide often occurs naturally in some environments including abandoned water wells, gas wells, sulfur springs, and swamps. It is also produced by the breakdown of organic matter and can be associated with animal farms, industrial plants, sewers or sewage treatment plants.

Hydrogen sulphide is part of the natural environment. You can only be exposed to the gas when you come into direct contact with it by breathing it in, eating or drinking something contaminated with it, or when it touches your skin. Any absorbed hydrogen sulphide does not accumulate in the body as it is rapidly broken down into sulfate by the liver and excreted in the urine. Hydrogen sulphide usually breaks down in the air and therefore exposure is only a concern if a person is close to an ongoing source of that course is in a confined area.

People usually smell hydrogen sulphide even at very low concentrations in the air, ranging from 0.0005 to 0.3 parts per million (ppm). These levels in the air are not dangerous and will not cause negative health effects. It should be noted that there is no way to tell by smell alone if you are detecting low or high concentrations of hydrogen sulphide; in fact, concentrations around 100ppm will temporarily hinder your ability to smell the gas. You cannot rely on your nose to tell you how much hydrogen sulphide gas is present.

Hydrogen sulphide levels can change based on a number of factors such as fluctuations from the source (i.e. a gas well), or from changes in weather patterns (i.e. wind direction).

Exposure to low concentrations (10-100 ppm) of hydrogen sulfide may cause:

  • Irritation to the eyes, nose, or throat
  • Difficulty in breathing for some people with asthma
  • Headaches
  • Poor memory
  • Tiredness
  • Balance problems

Brief exposures to high concentrations of hydrogen sulfide (greater than 500 ppm) can cause a loss of consciousness. In most cases, the person will likely regain consciousness without any other effects. However, in some people, there may be permanent or long-term effects such as headaches, poor attention span, poor memory, and poor motor function. In very high concentrations, death is possible due to respiratory paralysis.

The ‘rotten egg’ smell of hydrogen sulphide, and its accompanying ‘sulfur water’ taste, will appear in water at low concentrations. Even at these low levels, water will become aesthetically unpleasant and most users will avoid drinking the water at that time. The odor may be more noticeable when you run hot water as heat forces the gas into the air. This may cause the odor to be especially offensive when showering. If there is an ongoing issue with hydrogen sulphide in your water supply, there are a variety of water treatment devices capable of removing it. Consult a licensed plumber or a water treatment company to determine what water treatment device will best suit your needs.

Water samples submitted to the HNHU are only sampled for bacteria at the Public Health Lab. Chemical sampling can be done for a fee through a licensed private lab. For more information about well water testing, the HNHU at 519-426-6170.

If you notice a rotten egg scent and suspect hydrogen sulphide:

  • Near your home, call the Spills Action Centre of the Ministry of Environment at 416.325.3000 or 1-800-268-6060 (toll-free)
  • Inside your home, call your local fire department — In Norfolk County In Haldimand County 


CAUTION: Confined Spaces

Small, enclosed spaces such as a cistern, septic tank, some farming and industrial equipment, well (dug / bored wells) or a well pit, may be considered Hazardous Confined Spaces and should never be entered by anyone other than a trained professional.   For more information on Hazardous Confined Spaces please visit:


Related Topics

  1. Abandoned Works Program is a program run by the Ministry to help Ontarians properly plug wells on their property. They will determine if our well qualifies and rank your well based on the risk to public safety. In addition, they will arrange for a certified well contractor to plug the well. For more information
  2. If you suspect you have an abandoned well on your property visit the site below for more information.
  3. The MAPSH study monitoring Methane, Air Pollutants, Soil quality and human health near abandoned oil and gas wells, is study is looking for participants to assess self-reported health symptoms in relation to indoor air quality and the presence of abandoned oil and gas wells. To sign up to participate, contact the MAPSH study team at 647-601-4641 or send an e-mail to [email protected]
  4. Spills Action Centre If you notice a rotten egg scent near your home an suspect hydrogen sulphide, call the Spills Action Centre of the Ministry of the Environment at 416-325-3000 or (toll-free) 1-800-268-6060 or (TYY) 1-855-889-5775