Hydrogen Sulphide (H2S)

Hydrogen sulfide occurs naturally through the breakdown of organic matter. It can be present in abandoned water wells, gas wells, sewers, sulfur springs, swamps, etc. It is also a by-product in many industrial plants, animal farms, and sewage treatment plants.

Hydrogen sulfide is part of the natural environment, and you will have had some exposure to it. Hydrogen sulfide usually breaks down in the air and hazardous exposure levels are only likely to occur if there is an ongoing source. It can enter your body 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. Hydrogen sulfide is a gas at room temperature and absorption through intact skin is minimal, so inhalation is the most likely route of exposure.

Absorbed hydrogen sulfide does not accumulate in the body, as it is rapidly metabolized by the liver into sulfate and excreted in the urine. The presence of hydrogen sulfide in confined spaces is of particular concern because high levels of the gas may accumulate. Hydrogen sulfide is slightly heavier than air and may accumulate in enclosed, poorly ventilated, and low-lying areas. Children are more vulnerable to exposure due to their shorter stature and greater lung surface area.

People usually can smell hydrogen sulfide 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. Hydrogen sulfide levels can change based on a variety of factors such as fluctuations from the source (i.e., a gas well), or from changes in weather patterns (i.e., wind direction).

It should be noted that there is no way to tell by smell alone if you are detecting low or high concentrations of hydrogen sulfide; in fact, concentrations around 100 ppm will temporarily hinder your ability to smell the gas. You cannot rely on your nose to tell you how much hydrogen sulfide gas is present.

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 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. Exposures to very high concentrations of hydrogen sulfide (750-1000 PPM) can cause a loss of consciousness, lung and breathing passage damage, and/or death from respiratory paralysis.

• Air pollution from H2S contributes to unpleasant odours and acid rain formation.
• H2S can contaminate water, harm aquatic life, and make water unsafe for consumption.
• Soil contamination from H2S affects plant life and can enter the food chain.
• Wildlife can be harmed or killed by exposure to H2S, disrupting ecosystems.

The ‘rotten egg’ smell of hydrogen sulfide, 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 odour may be more noticeable when you run hot water as heat forces the gas into the air. This may cause the odour to be especially offensive when showering. If there is an ongoing issue with hydrogen sulfide 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. Do not enter a well where hydrogen sulfide gas is suspected.

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

• Near your home, call the Spills Action Centre at 416-325-3000 or 1-800-268-6060 (toll-free)
• Inside your home, call your local fire department

GEPH does not offer testing for hydrogen sulfide or any other chemical. Chemical testing can be done for a fee through a licensed private laboratory. A list of licensed labs can be found online at List of Licensed Laboratories | ontario.ca.

GEPH does offer free bacteriological testing for private well owners.

• The Abandoned Works Program is a program offered by the Ministry of Natural Resources, to help Ontarians properly plug wells on their property. Landowners with gas wells can contact the Ministry to determine if their well qualifies for the program.  Please visit https://www.ontario.ca/page/abandoned-works-program for more information.
• The MAPSH (Monitoring Methane, Air pollutants, Soil quality and Human health) study aims to assess health symptoms experienced by participants in relation to indoor air quality and the presence of abandoned oil and gas wells. This study involves air monitoring within homes that may be impacted by abandoned gas or oil wells. H2S monitoring specifically can be included. For more information about the study and/or becoming a participant. Contact the MAPSH study team at 647-601-4641 or send an e-mail to elyse.caronbeaudoin@utoronto.ca.
• If you smell H2S (rotten eggs) near your home and suspect a leaking gas well, contact The Spills Action Centre (SAC) of the Ministry of the Environment, Conservation and Parks at 416-325-3000 or (toll-free) 1-800-268-6060 or (TYY) 1-855-889-5775.