Global Lead Network: MMT Fact Sheet
MMT Fact Sheet
What Is MMT? Methylcyclopentadienyl manganese tricarbonyl (MMT) is a gasoline additive used to boost octane. When MMT is burned, manganese, a metal known to be a neurotoxin when inhaled, is emitted from the tailpipe.
Characteristics of Manganese. When ingested, manganese is beneficial to the human body – in fact, it is an essential dietary element. High levels of ingested manganese are easily processed by the liver and do not pose a health risk. In contrast, studies of factory workers and laboratory ani-mals have demonstrated that when manganese is inhaled, it causes “manganism.” The symptoms of manganism are similar to those caused by Parkinson’s disease – tremors, slowed reaction times, and difficulty learning. Even at levels of exposure too low to cause obvious symptoms, inhaled manganese can cause memory loss and reduced motor speed. Manganese exposure also may ad-versely affect the reproductive and respiratory systems.
Health Effects of MMT. In 1999 the American Medical Association Council on Scientific Af-fairs conducted a literature search and review of studies on manganese exposure, concluded that there is insufficient information to determine the risks of MMT, and recommended that research be carried out before the widespread introduction of MMT into the gasoline supply. No epidemi-ological studies have been conducted to determine the effects of low-level exposure to MMT over a lifetime. No studies have been done on the effects of such exposure on vulnerable populations, such as fetuses, children, and the elderly. Another unknown is the form of manganese that is emit-ted from the tailpipe when MMT is combusted (e.g., manganese oxide or manganese phosphate) and how the type of compound affects toxicity. Based on these findings, the AMA Council on Scientific Affairs recommended carrying out additional studies on MMT before adding it to the U.S. gasoline supply.
Environmental Effects of MMT. There is substantial evidence that MMT impairs vehicle cata-lyst and emission control system performance, which results in increased emissions. The Alliance of Automobiles Manufacturers, the Association of International Automobile Manufacturers and the Canadian Vehicle Manufacturers recently completed a comprehensive vehicle test program that demonstrated this impact on technologies prevalent in the U.S. since 1990. In addition, the test program showed MMT can foul spark plugs. This and other studies suggest MMT can inter-fere with on-board diagnostic systems. These effects would hinder continued progress to safer and cleaner air afforded by the switch from leaded to unleaded gasoline.
MMT Use. MMT has been added to unleaded gasoline in Canada for over 25 years and is legally allowed in the U.S., Argentina, Australia, Bulgaria, Russia, South Africa, and New Zealand. However, it is unclear if and how much MMT is being used in these countries – or for that matter, in other countries that may not have formal policies regarding MMT. Unlike leaded gasoline, which was clearly marked at the pump, it appears that no country has labeling requirements for gasoline containing MMT. The Ethyl Corporation, the manufacturer of MMT, closely guards where and how much MMT is being used.
Why MMT Use Is Allowed in the U.S. and Canada. MMT is allowed to be used in conven-tional (non-reformulated) gasoline in the U.S. and widely in Canada due to legal decisions rather than proof of its safety to the environment and public health. When Ethyl applied to the U.S. En-vironmental Protection Agency for a waiver under the Clean Air Act to market MMT as an addi-tive to unleaded gasoline, EPA denied the application based on evidence that MMT damaged cata-lytic converters. Ethyl then conducted studies purportedly showing that MMT does not interfere with catalytic converters (a claim vigorously disputed by automobile and catalytic converter manufacturers) and reapplied for a waiver. EPA denied the application again, but this time based on public health concerns. Ethyl sued EPA and the U.S. Court of Appeals ruled that, under the Clean Air Act, EPA did not have the authority to deny the waiver request based on health concerns – only on whether the additive causes or contributes to a failure of the vehicle’s emission control system. EPA did have authority to require additional health effects testing, however, which it did, and that testing is not yet complete. Despite the fact that MMT is allowed in the U.S. market, evi-dence suggests that most oil refiners are not using this product.
Canada attempted to ban MMT in 1996 with the passage Bill C-29, which made it illegal to import MMT into Canada and for it to be traded between provinces. Canada was apparently unable to ban MMT on health grounds due to a Health Canada report stating that MMT did not pose a risk to health. Unfortunately, this study was based on exposure assessments (i.e., measurements of the amount of airborne manganese inhaled by the typical individual) rather than epidemiological stud-ies of population health effects. Similarly, the government was unable to ban MMT on the grounds of environmental protection because the environmental ministry took the position that sufficient studies to determine the effects of MMT on emission control systems had not been car-ried out. Bill C-29 was challenged both by Ethyl (under Chapter 11 of the North American Free Trade Agreement), and those Canadian provinces with refineries. In 1998, the Canadian govern-ment decided to settle with Ethyl and allow MMT use to continue.
Resources
Davis, J. Michael. “Inhalation Health Risks of Manganese: An EPA Perspective.” NeuroToxi-cology 20 (April/June 1999): 511-518.
European Automobile Manufacturers Association, et al. World-Wide Fuel Charter. April 2000.
Frumkin, Howard and Solomon, Gina. “Manganese in the U.S. Gasoline Supply.” American Journal of Industrial Medicine 31 (1997): 107-115.
Lyznicki, James M., et al. “Manganese in Gasoline.” Journal of Occupational and Environmental Medicine 41 (March 1999): 140-143.
* For more information on MMT, see the Alliance’s Background Paper and Policy Statement, Don’t Repeat the Leaded Gasoline Experiment: Keep MMT out of Gasoline.
