Update of MMT Assessment

Methylcyclopentadienyl manganese tricarbonyl (MMT) is added to gasoline to increase its octane rating. As a metal additive with potential for widespread use and manganese (Mn) exposure implications, MMT has been the focus of numerous analyses and debates about its potential public health impacts. In 1994 ORD conducted a major reassessment of the potential health risks of MMT and concluded that “…a reasonable basis exists for concern regarding potential public health risks, especially for sensitive subpopulations….” However, as was also noted, “Until [previously identified] research and information needs are met, a high degree of uncertainty will attend any judgment of the potential risks to public health associated with the use of MMT.” In an agreement reached with Ethyl Corp. (now Afton Corp.) in 2000, EPA promised to reevaluate the conclusions of its 1994 assessment based on newer Mn exposure data submitted by Afton, as well as other information. Subsequently, Afton requested that EPA also consider human Mn PBPK modeling studies that were being conducted under contract to Afton. After completion of these studies, the results will be considered along with MMT emissions characterization data, Mn exposure estimates, Mn health effects data, and any other pertinent information in reevaluating the conclusions of the 1994 assessment. This work represents a coordinated effort among ORD labs/centers/offices to provide technical support to the Office of Transportation and Air Quality in EPA's Office of Air and Radiation.


U.S. EPA. Update of MMT Assessment. U.S. Environmental Protection Agency, Washington, DC.