Methyl mercaptan, also known as methanethiol, is a colorless gas with the chemical formula CH₃SH. It has a strong, unpleasant odor, often compared to rotten cabbage. At room temperature (above 43°F), it exists as a gas but is commonly transported as a liquefied, compressed gas. Methyl mercaptan is slightly soluble in water and, when heated, releases toxic fumes such as sulfur dioxide.
This compound is found naturally in the body, particularly in the blood, brain, and other tissues, and is also released from animal waste. It is present in certain foods, including nuts and cheese, and occurs as a byproduct of wood decay in pulp mills.
What is Methyl Mercaptan used for?
Methyl mercaptan is widely used in industrial processes, including:
Pesticide production
Jet fuel additive
Plastics manufacturing
Methionine production (an essential nutrient in poultry feed)
Wood pulp industry (released as a decay byproduct)
Methyl mercaptan is widely used in jet fuel additives.
Sources & Routes of Exposure
Sources of Exposure
People may be exposed to methyl mercaptan in various ways:
It is always present in the human body.
It can be inhaled in areas near marshes or other natural sources.
It is found in certain foods like nuts and cheese.
Occupational exposure is common in wood pulp mills, sewage treatment plants, and factories producing pesticides, jet fuel, or poultry feed.
Routes of Exposure
Inhalation: The main route of exposure. The gas has a lowodour threshold (0.002 ppm), but prolonged exposure can cause olfactory fatigue, making detection difficult.Vapours of the liquefied gas are heavier than air and can accumulate in low-lying areas, leading to asphyxiation risks in poorly ventilated spaces.
Skin & Eye Contact: Direct exposure can cause irritation or frostbite injuries due to the cold temperature of the liquefied gas.
Ingestion: Unlikely, as methyl mercaptan is a gas at room temperature.
Children may be at greater risk than adults due to their higher breathing rates and shorter height, which exposes them to higher gas concentrations near the ground.
Health Effects
Irritates the eyes, skin, and respiratory tract.
Can cause lung and airway swelling (oedema).
Other symptoms: headache, dizziness, tremors, seizures, nausea, vomiting, and lack of coordination.
Rapidly absorbed by the lungs, but minimal absorption through skin and eyes.
Direct contact with liquefied methyl mercaptan may cause frostbite.
Acts as a central nervous system depressant, leading to respiratory paralysis and death.
Higher risk for individuals with pre-existing respiratory, heart, nerve, or liver conditions.
Acute Exposure
Affects mitochondria by interfering with cytochrome c oxidase and enzyme systems like carbonic anhydrase, beta-tyrosinase, and sodium-potassium ATPase.
Specific Effects
Respiratory: Can irritate airways, causing coughing, breathing difficulty (dyspnoea) chest tightness, and cyanosis. In severe cases, respiratory failure and lung swelling may occur.
Blood (Haematologic): Can cause severe anaemia in people with glucose-6-phosphate dehydrogenase deficiency.
Nervous System (Neurologic): May lead to restlessness, headaches, dizziness, staggering, convulsions, and coma.
Skin (Dermal): Liquefied gas can cause frostbite injuries.
Eyes (Ocular): High concentrations can cause eye irritation.
Digestive System (Gastrointestinal): Though ingestion is unlikely, it may cause irritation of the mouth, throat, and oesophagus as well as nausea and vomiting, even from inhalation.
Long-Term Effects: Can disrupt heme production in the body.
Chronic Exposure
Long-term exposure may lead to dermatitis (skin inflammation).
Carcinogenicity
Not classified as a cancer-causing substance.
Reproductive and Developmental Effects
No information is available regarding reproductive or developmental effects of methyl mercaptan in experimental animals or humans. Methyl mercaptan is not included in Reproductive and Developmental Toxicants, a 1991 report published by the U.S. General Accounting Office (GAO) that lists 30 chemicals of concern because of widely acknowledged reproductive and developmental consequences.
Safety
First Aid Measures
Inhalation: Move the affected person to fresh air. If they have trouble breathing, provide artificial respiration and seek medical attention immediately.
Skin Contact: Wash with soap and water. Seek medical help for frostbite injuries.
Eye Contact: Flush eyes with plenty of water for at least 15 minutes.
Ingestion: Although unlikely, do not induce vomiting. Rinse the mouth with water and get medical assistance.
Exposure Controls & Personal Protection
Engineering Controls
Avoid direct contact with the skin, eyes, and clothing.
Wash hands before eating or drinking after handling methyl mercaptan.
Personal Protective Equipment (PPE)
Eye/Face Protection: Safety glasses with side shields or a face shield. Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).
Skin Protection: Handle with gloves. Gloves must be inspected prior to use. Use proper glove removal technique (without touching glove's outer surface) to avoid skin contact with this product. Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices. Wash and dry hands. The selected protective gloves have to satisfy the specifications of EU Directive 89/686/EEC and the standard EN 374 derived from it.
Body Protection: Flame-retardant or chemical-resistant suits for handling high concentrations.
Respiratory Protection: Where risk assessment shows air-purifying respirators are appropriate use a full-face respirator with multi-purpose combination (US) or type AXBEK (EN 14387) respirator cartridges as a backup to engineering controls. If the respirator is the sole means of protection, use a full-face supplied air respirator. Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU).
Regulations
United States
OSHA: The Occupational Safety & Health Administration has established the following Permissible Exposure Limit (PEL) for methyl mercaptan:
ACGIH: The American Conference of Governmental Industrial Hygienists has set a Threshold Limit Value (TLV) for methyl mercaptan of: 0.5 ppm, 0.98 mg/m3 TWA
NIOSH: The National Institute for Occupational Safety and Health has established a Recommended Exposure Limit (REL) for methyl mercaptan of: 0.5 ppm, 1 mg/m3 Ceiling (15 Minutes)
EPA:The United States Environmental Protection Agency requires that discharges, spills, or accidental releases of 100 pounds or more of methyl mercaptan must be reported to the EPA.
Australia
Safe Work Australia: Safe Work Australia has set a Time Weighted Average (TWA) concentration for methyl mercaptan of 0.5 ppm, 0.98 mg/m3 for a 40 hour work week.
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