Is methylcyclopentadienyl manganese tricarbonyl toxic to humans?

Yes. Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organomanganese compound antiknock agent used as an octane improver for unleaded gasoline. Using MMT can significantly reduce NOx emissions. Less than 15% of the manganese produced by the combustion of MMT is emitted from the tailpipe, mostly in the form of manganese phosphate in the PM2.5 component, with some manganese sulfate and very small amounts of manganese oxide. MMT has been used in almost all unleaded gasoline in Canada for about 20 years.

However, MMT is toxic to humans and can irritate the skin and eyes when exposed, and can irritate the nose and throat and cause coughing and wheezing when inhaled. Repeated exposure can cause headaches, nausea, weakness, tremors, dizziness, bluish skin (cyanosis), and convulsions. In vitro studies have shown that MMT has an LD50 of 50 mg/kg oral and 23 mg/kg intraperitoneal doses in rats and is teratogenic in animals. The main toxicological effects of manganese observed after long-term occupational exposure are on the lungs (manganese pneumonia) and the central nervous system (manganese poisoning). The main manifestations are bronchitis with cough, sputum and/or shortness of breath; personality changes, depression, anxiety or irritability; and damage to the liver and kidneys.

References:

[1] HINDERER R K. Toxicity studies of methylcyclopentadienyl manganese tricarbonyl (MMT).[J]. American Industrial Hygiene Association journal, 1979, 40 2: 164-167. DOI:10.1080/15298667991429462.

[2] RICHARD J. CLAY; John B M. Comparative pneumotoxicity of cyclopentadienyl manganese tricarbonyl and methylcyclopentadienyl manganese tricarbonyl[J]. Toxicology and applied pharmacology, 1989, 98 3: Pages 434-443. DOI:10.1016/0041-008X(89)90172-5.

[3] ABBOTT P J. Methylcyclopentadienyl manganese tricarbonyl (MMT) in petrol: The toxicological issues[J]. Science of the Total Environment, 1987, 67 2: Pages 247-255. DOI:10.1016/0048-9697(87)90215-4.

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