Methylcyclopentadienyl manganese tricarbonyl (MMT): A science and policy review


MMT is an octane-enhancing gasoline additive that forms manganese particles when burned. It was widely introduced in the United States in the 1970s by the Ethyl Corporation when regulations restricting the use of tetraethyl lead first came into force.
Today health scientists and automobile manufacturers are strongly opposed to its use. Combustion of MMT releases manganese, a potent neurotoxin when inhaled. In vehicles it can leave deposits that degrade the performance of pollution control systems. Similar concerns regarding tetraethyl lead have led to a near global ban on its use. Alternatives to MMT are in widespread use and can cost-effectively achieve similar octane levels without the associated health risk. This report updates our 2004 Status Report on MMT, providing more detail on recent studies of the potential health impacts associated with its use.