Methyl Mercaptan

Methyl mercaptan (also known as methanethiol is an organic compound with the chemical formula CH3SH (also written as CH4S). [fusion_builder_container hundred_percent=”yes” overflow=”visible”][fusion_builder_row][fusion_builder_column type=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none”][1]

At room temperature (above 43°F), methyl mercaptan is a colourless gas with an unpleasant odour described as rotten cabbage. It is slightly soluble in water. It is generally shipped as a liquefied compressed gas. When heated to decomposition, it emits toxic fumes, such as sulfur dioxide, and flammable vapours. [2] Methyl mercaptan is a natural substance found in the blood, brain, and other tissues of people and animals. It is released from animal faeces. It occurs naturally in certain foods, such as some nuts and cheese. [3]

 

Uses [4]

 

Methyl mercaptan is manufactured for use in pesticides, as a jet fuel additive, in the plastics industry, and in making methionine, a nutrient that is added to poultry feed. Methyl mercaptan is also released as a decay product of wood in pulp mills.

 

Sources and Routes of Exposure

 

Sources of Exposure [3]

 

 

  • Methyl mercaptan is always present in your body.
  • You may breathe it in the air if you live near a natural source of the gas, such as a marsh.
  • You may eat it in certain foods, such as nuts and cheese.
  • You may be exposed if you work at a wood-pulp mill or sewage treatment plant.
  • You could also be exposed if you work in a factory that uses it to make other products such as jet fuel, pesticides, or poultry feed.

 

Routes of Exposure [2]

 

  • Inhalation: Inhalation is the major route of exposure to methyl mercaptan. An odour threshold of 0.002 ppm has been reported for methyl mercaptan, but olfactory fatigue may occur and thus, it may not provide adequate warning of hazardous concentrations. Vapours of liquefied methyl mercaptan gas are heavier than air and spread along the ground. Exposure in poorly ventilated, enclosed, or low-lying areas can result in asphyxiation. Children exposed to the same levels of methyl mercaptan as adults may receive a larger dose because they have a greater lung surface area: body weight ratios and higher minute volume: weight ratios. In addition, they may be exposed to higher levels than adults in the same location because of their short stature and the higher levels of methyl mercaptan found nearer to the ground.
  • Eye/Skin Contact: Direct contact with liquid methyl mercaptan or the gas may cause frostbite injury or irritation of the eyes and skin.
  • Ingestion: Ingestion is unlikely to occur because methyl mercaptan is a gas at room temperature.

 

Health Effects [5]

 

  • Methyl mercaptan gas is irritating to the eyes, skin, and respiratory tract. Oedema of the airway and lungs can occur. Other possible effects include headache, dizziness, tremors, and seizures, and nausea and vomiting, and lack of coordination. The gas is rapidly absorbed in the lungs. Skin and eye absorption are minimal; however, upon direct contact with eyes or skin, liquefied methyl mercaptan will likely cause frostbite injury.
  • Methyl mercaptan is a central nervous system depressant that acts on the respiratory centre to produce death by respiratory paralysis.
  • Individuals with pre-existing respiratory, cardiac, nervous system, or liver impairment may be more susceptible to exposure to methyl mercaptan.

 

Acute Exposure

 

Methyl mercaptan inhibits mitochondrial respiration by interfering with cytochrome c oxidase. It also inhibits several enzyme systems such as carbonic anhydrase, beta-tyrosinase, and sodium+, potassium+ATPase. The enzyme inhibition appears to be related to a thiol-metal interference.

 

  • Respiratory: Acute inhalation exposure can irritate the mucous membranes of the respiratory tract. This may cause cough, dyspnea, a sensation of tightness of the chest, and subsequent cyanosis. Respiratory depression, apnoea, and pulmonary oedema were observed in animals.
  • Haematologic: Severe haemolytic anaemia may occur in people with glucose-6-phosphate dehydrogenase deficiency.
  • Neurologic: Restlessness, headache, staggering, and dizziness may develop; severe exposure may lead to convulsions and coma.
  • Dermal: Frostbite injury can occur from contact with the liquefied gas.
  • Ocular/Ophthalmic: High concentrations of methyl mercaptan can cause eye irritation.
  • Gastrointestinal: Although ingestion is unlikely, irritation of the mouth, throat, and oesophagus are possible. Nausea and vomiting may occur even with inhalation exposure to the gas.
  • Potential Sequelae: Methyl mercaptan exposure may result in altered heme synthesis.

 

Chronic Exposure

 

Dermatitis can occur with chronic exposure to methyl mercaptan.

 

Carcinogenicity

 

Methyl mercaptan has not been classified for carcinogenic effects.

 

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 [6]

 

First Aid Measures

 

  • If inhaled: If breathed in, move person into fresh air. If not breathing, give artificial respiration. Consult a physician.
  • In case of skin contact: Wash off with soap and plenty of water. Take victim immediately to hospital. Consult a physician.
  • In case of eye contact: Flush eyes with water as a precaution.
  • If swallowed: Do NOT induce vomiting. Never give anything by mouth to an unconscious person. Rinse mouth with water. Consult a physician.

 

Exposure controls & Personal Protection

 

Engineering Controls

 

  • Avoid contact with skin, eyes and clothing.
  • Wash hands before breaks and immediately after handling the product.

 

Personal Protective Equipment

 

  • Eye/face protection: Face shield and safety glasses 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: Use a complete suit protecting against chemicals or flame retardant or antistatic protective clothing. The type of protective equipment must be selected according to the concentration and amount of the dangerous substance at the specific workplace.
  • 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 [3,7]

 

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 [8]

 

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.

 

References

 

  1. http://en.wikipedia.org/wiki/Methanethiol
  2. http://www.atsdr.cdc.gov/MHMI/mmg139.pdf
  3. http://www.atsdr.cdc.gov/toxfaqs/tf.asp?id=223&tid=40
  4. http://www.atsdr.cdc.gov/phs/phs.asp?id=222&tid=40
  5. http://www.atsdr.cdc.gov/MMG/MMG.asp?id=221&tid=40
  6. http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=AU&language=en&productNumber=295515&brand=ALDRICH&PageToGoToURL=http%3A%2F%2Fwww.sigmaaldrich.com%2Fcatalog%2Fproduct%2Faldrich%2F295515%3Flang%3Den
  7. https://www.osha.gov/dts/chemicalsampling/data/CH_254300.html
  8. http://www.safeworkaustralia.gov.au/sites/swa/about/Publications/Documents/772/Workplace-exposure-standards-for-airborne-contaminants.docx

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