Update: MMT

We’ve had requests for a September 2010 update on the situation regarding the fuel additive MMT that was inadvertently vaporized in the course of a website overhaul in late 2011. Text of the 2010 update appears below, supplemented by additional and more recent info on developments in China.


Manganese is a neurotoxin and heavy metal. The combustion of MMT in gasoline releases manganese phosphates, manganese sulfates, and manganese oxides into the air. When inhaled, these compounds may enter the bloodstream through the lungs and deliver dangerous doses of manganese to the brain, where accumulation can lead to Parkinsons-like symptoms including loss of motor control, memory loss, erratic behavior, and brain cell death. A recent study carried out in Mexico City found that exposure to both manganese and lead in early childhood led to exacerbated neurodevelopmental deficiencies and that the impacts of coexposure were more severe than expected based on exposure to each metal alone. There is no known treatment or cure.

The ICCT’s work in this area is summarized here and here.

A rare consensus exists among automakers, refiners, and the public health community in favor of restricting the use of manganese compounds in fuels. But regulation remains uneven, in part because of vigorous efforts by the manufacturer of MMT, Afton Chemical, to promote its use and contest proposed restrictions. This continues a pattern set by Afton’s predecessor the Ethyl Corporation, which for decades avoided restrictions on tetraethyl lead and manganese-based additives.

Public health professionals agree about the threat and the remedy. In 2003 the American Academy of Pediatrics recommended phasing out MMT from gasoline. The 2007 Brescia Declaration on Prevention of Neurotoxicity of Metals called for an immediate halt to the addition of organic manganese compounds to gasoline.

Automakers also want to eliminate MMT in fuels, for the very different reason that it damages emissions control components. To maintain emission and engine performance, BMW, General Motors, Honda, and Toyota and others have jointly defined standards for unleaded gasoline that explicitly exclude metallic additives, including MMT.

In 2009 the European Union adopted amendments to its fuel quality directive that set an interim limit on MMT in fuel of 6 mg of manganese per liter, falling to 2 mg/L in 2014, and also required labeling of fuel containing metallic additives. That put Europe in line with trends elsewhere, especially in the developed countries. The U.S. prohibits manganese entirely from reformulated gasoline, which constitutes more than 60 percent of the U.S. fuel supply, and California bans manganese entirely. Oil refiners voluntarily exclude manganese additives from the remainder of the U.S. supply, as well as from the fuel supply in Canada, the European Union, Japan, India, and Indonesia. The extent to which MMT is used in fuels elsewhere is impossible to determine with confidence, as Afton does not make public the list of countries where it is sold.

China gasoline fuel standard (2011)

On May 12, 2011, the Standardization Administration of China adopted the China IV standard for motor vehicle gasoline (GB17930-2011). This gasoline fuel quality standard will be implemented nationwide on January 1, 2014. Two points worth noting with regard to the fuel additive methylcyclopentadienyl manganese tricarbonyl (MMT):

  • The standard recommends a limit of 2 mg/liter of MMT for China V gasoline—the same limit set for the European Union in 2014 in the 2009 amendments to the Fuel Quality Directive.
  • The 2 mg/liter MMT limit for motor gasoline is also the same as that specified in the Hazardous Materials Control Standards for Motor Vehicle Gasoline (IV, V) adopted by the China Ministry of Environmental Protection (MEP) on Feb 14, 2011 (GWKB 1.1-2011). While the Hazardous Materials Control Standard is a voluntary standard, it serves as the reference fuel specification for city and provincial governments intending to adopt more stringent vehicle emissions and fuel standards ahead of the national schedule and before the China V standard is adopted nationally
  • Beijing proposes to adopt the China V gasoline standard, with a limit of 2 mg/liter of MMT, for implementation in 2012.

Reference standards lowered in Canada (2008) and California (2010)

In December 2008, the State of California Office of Environmental Health Hazard Assessment (OEHHA) lowered its reference exposure level (REL) for chronic inhalation of airborne manganese to 0.09 µg/m3 from 0.2 µg/m3, and set an REL for 8-hour exposure at a maximum level of 0.17 µg/m3. California also added manganese to its list of toxic air contaminants that may cause infants and children to be especially susceptible to illness. This requires that actions to control emissions of manganese must be adequate to protect the health of infants and children.

In June 2010, Health Canada lowered its reference concentration for airborne manganese—the concentration to which the general population and sensitive subgroups can be exposed for a lifetime without appreciable harm—to 0.05 µg/m3 in PM3.5. This is significantly lower than the previous standard of 0.11 µg/m3, which had been in place since 1994. The Canadian reference standard is now at a level on par with the US EPA reference standard.

Health-based limits on exposure to pollutants are an important complement to fuel regulations. In 1996 (a period when Canadian gasoline contained MMT), a Toronto study found that 10% of adults there were exposed to concentrations of ambient manganese greater than Health Canada’s new reference concentration of 0.05 µg/m3 in PM10.

EU limits withstand legal challenge (2009)

In 2009 the European Parliament adopted amendments to its Fuel Quality Directive that ordered an assessment of health and environmental risks from metallic additives in fuel (Directive 2009/30/EC). The results of that assessment, to be based on a test methodology developed specifically for the purpose, are to be delivered at the end of 2012. In the meantime, the directive limited the presence of MMT in fuel to 6 mg of manganese per liter in 2011, and 2mg/L in 2014. Those limits are to be revised based on the results of the required risk assessment, and could fall to zero. The directive further required that fuel containing metallic additives be labeled as such whenever it is made available to consumers.

Afton Chemical immediately sued on several grounds, the most important of which were that the directive improperly applied the precautionary principle and failed to comply with the principal of proportionality—i.e., that it exceeded the limits of what is appropriate and necessary to achieve a legitimate objective. In July, the High Court of Justice of England and Wales ruled against Afton Chemical, stating in part: “Where it proves to be impossible to determine with certainty the existence or extent of [an] alleged risk because of the insufficiency, inconclusiveness or imprecision of the results of studies conducted, but the likelihood of real harm to public health persists should the risk materialise, the precautionary principle justifies the adoption of restrictive measures. . . . In those circumstances, it must be acknowledged that the European Union legislature may, under the precautionary principle, take protective measures without having to wait for the reality and the seriousness of those risks to be fully demonstrated.”

The High Court’s judgment concisely summarizes the logic that the ICCT has consistently argued should govern regulation of MMT. As restrictions grow tighter in North America and Europe, industry will look elsewhere for markets, and policy makers should use their discretion to control the dangerous and unnecessary use of metallic fuel additives. As the Clean Air Initiative for Asia (CAI-ASIA) argues, “the environmentally responsible approach for Asian countries is to apply the precautionary principle for these metallic additives [MMT and ferrocene] and to not use them until and unless the scientific and health studies show that they are safe.”