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MMT Manganese in Gasoline

Potential Public Health Effects

Note: following this Position Paper is National PSR's 1996
Resolution on MMT in the United States Gasoline Supply

Gasoline pump on the highwayLead, an anti-knock additive, was finally phased out of use in non-aviation gasoline in 1995. Yet, that same year, another metal with potentially damaging health effects was cleared for addition to gasoline for the same purpose. In 1995, the EPA was forced by a federal judge to grant a waiver to the Ethyl Corporation allowing production and sale of methylcyclopentadienyl manganese tricarbonyl (MMT). Both the EPA and many health experts have serious concerns about the use of this compound in gasoline. MMT breaks down quickly on exposure to sunlight or in the car engine into compounds of the metal manganese.

Metabolism of Manganese

Unlike lead, manganese is normally present in food though it does not generally cause problems in adults, who are able to excrete excess manganese without difficulty. However, people with iron deficiency absorb oral manganese more avidly and may be more susceptible to adverse effects from this metal. Fetuses and newborns differ markedly from adults in that they absorb manganese more easily from the intestine and are not able to excrete any excess. Manganese passes from mother to infant across the placenta and in breast milk. Moreover, manganese crosses the blood-brain barrier and enters the brain much more easily in infants than in adults. These factors imply that infants and children may be disproportionately exposed and particularly susceptible to the toxic effects of manganese. The effects of early exposure may not appear until many years later. Manganese emitted from automobile tailpipes is in very fine particles and is carried to small airways deep in the lungs. While adults are generally able to eliminate manganese eaten in food, inhalation is an abnormal route of exposure. Inhaled manganese is absorbed through the lungs, less easily excreted, and accumulates in the body.

Health Effects of Manganese

Manganese has long been known to be a health hazard to workers at high doses. Its effects at low doses are poorly understood. There appear to be three major targets for toxicity: the brain, the lungs, and the testes. At high doses, such as those found in some workplaces, manganese causes a severe, degenerative neurologic condition almost indistinguishable from Parkinson's disease. This disease, known as manganism, begins as a loss of appetite, apathy, fatigue, psychotic behavior, and clumsiness. The final stages include an expressionless, mask-like face, difficulty initiating movements, a shuffling gait, and tremors. At lower levels of exposure, delayed reaction time, poor hand-eye coordination, memory loss and tremors have been reported.

Several studies suggest a subtle effect of manganese on behavioral characteristics and learning ability in children. Infants fed formula enriched with manganese have significantly higher hair manganese levels and more trouble with hyperactivity and learning disabilities.

Although infants are unquestionably a susceptible population, the elderly may also be at risk of accelerated neurologic decline from low-level manganese exposure. Victims of Parkinson's disease may be particularly susceptible.

Inhalation of manganese is toxic to the lungs, and produces an inflammatory reaction which increases susceptibility to pneumonia and bronchitis. Low level air exposures have been reported to increase the prevalence of respiratory symptoms (phlegm, wheezing, sore throat) in school children.

Animal studies have shown that exposure to manganese during fetal development at doses below those which cause other toxic effects retards growth of the testes and reduces testosterone concentrations. The research in male rats is supported by similar findings in human workers. In one study, workers exposed at levels averaging one fifth of the allowable workplace exposure limit had significantly fewer children during the period of exposure to the metal compared to similar unexposed workers. This finding suggests an adverse effect of manganese on male fertility.

Anticipated Exposures

Estimates of the amount of manganese that will enter the environment from the use of MMT in fuel are generally quite low. Studies in Canada where MMT has been used for several years in gasoline confirm that exposures are not high. However it is important to remember that environmental levels of manganese are normally extremely low. In the U.S., levels of airborne manganese fell substantially between 1970 and 1982 as a result of air pollution controls. The introduction of MMT would result in almost a tripling of current air levels.

Airborne manganese eventually settles to the ground where it contaminates the surface. A recent study showed strong correlations between manganese concentrations in soil and distance from major roadways. Over time, accumulation near roadways and in urban areas may lead to unacceptably high levels in the soil.

Manganese accumulation in the environment may result in significantly increased manganese levels in living organisms. It accumulates in certain plants, as demonstrated in an experimental study on oats and beans. A study of pigeons in Canada, where MMT is used, has shown that urban pigeons have higher manganese concentrations in their bodies than rural pigeons, showing that accumulation of manganese is possible. It is unclear whether most of the manganese emitted from automobiles will remain on surface dust where it may intermittently become airborne again, whether it will be mostly taken up by plants, or whether it will contaminate groundwater in significant amounts.


MMT fuel additive is likely to contribute to a small but significant increase in manganese concentrations in the environment. The health implications of this increase in ambient manganese are not yet certain. However, there are indications that some highly exposed or susceptible subpopulations might be at increased risk for neurological, respiratory, and reproductive toxicity from low level manganese exposure. Such at-risk populations include infants, the elderly, those with iron deficiency, people with Parkinson's disease, and workers exposed to gasoline or exhaust fumes.

While many petroleum refiners currently claim that they are voluntarily withholding MMT from their gasoline, there is still reason for concern and a need for more decisive action. The ready availability of alternative octane enhancers makes the case for adding MMT to gasoline almost exclusively a cost-savings argument. Minor cost-savings should not take precedence over potentially severe damage to human health.



  • Further research on the health effects of low-dose exposure to manganese.
  • Further investigation of the distribution, fate, and ecosystem effects of manganese.


  • Initiation of action by the EPA under section 211(c) of the Clean Air Act or under the Toxic Substances Control Act to withdraw licensing of MMT.
  • Pressure on Congress to clarify section 211(f)(4) of the Clean Air Act to allow EPA to consider public health effects of gasoline additives prior to licensing.

Individual and Local Action:

  • Pressure Ethyl Corporation to withdraw MMT from the market.
  • Pressure petroleum refiners to label MMT-containing gasoline and MMT- free fuel at the pump.
  • Pressure on cities and states to ban MMT via local ordinances.
  • Development and implementation of a rapid and simple test for the presence of manganese in gasoline to allow independent verification of the absence of MMT by public interest organizations.


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Lauwerys R. et al. Fertility of Male Workers Exposed to Mercury Vapor or to Manganese Dust: A Questionnaire Study. Am J Ind Med 7(1985):171-176.

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Loranger S. et al. The Pigeon (Columba livia) as a Monitor for Manganese Contamination from Motor Vehicles. Arch Environ Contam Toxicol. 27(1994): 311-317.

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Resolution on MMT in the United States Gasoline Supply

National Physicians for Social Responsibility

April 16, 1996

Whereas: Methylcyclopentadienyl manganese carbonyl (MMT) is an organic manganese compound formulated for use as a gasoline octane enhancer by the Ethyl Corporation, and marketed as HiTec 3000; and

Whereas: The widespread use of MMT in the U.S. gasoline supply might result in measurable increases in population exposure to manganese; and

Whereas: Manganese is recognized as a nervous system toxin at high levels of exposure, is also a pulmonary toxin, and may also be a reproductive and developmental toxin; and

Whereas: No available health data indicate that the widespread use of MMT as proposed is safe; and

Whereas: The widespread commercialization of MMT, without clear evidence of its safety, would represent a population-wide toxicologic experiment, performed without the informed consentof those who would be exposed, in violation of accepted norms of medical ethics; and

Whereas: Populations that may be at special risk of manganese toxicity from MMT use, and for which more data are especially necessary, include fetuses and children, the elderly, workers such as gasoline station attendants and mechanics with unusually high exposure, and persons with neurologic and respiratory diseases; and

Whereas: The United States Environmental Protection Agency was recently compelled by a Federal Appeals Court decision to permit the addition of MMT to the U.S. gasoline supply, despite its finding that available data preclude adequate assessment of MMT's risks;

Be it therefore resolved: The Physicians for Social Responsibility deplores the use of MMT in the U.S. gasoline supply without clear evidence of safety, and

urges the U.S. Congress and applicable state agencies to ban the addition of MMT into gasoline until its safety is clearly documented;

urges all refiners and sellers of gasoline to refrain from adding MMT to their products until its safety is clearly documented;

urges all refiners and sellers of gasoline to announce publicly their policies regarding the use of MMT;

urges all refiners and sellers of gasoline to label their product, at the point of retail sale, with regard to MMT content, so consumers will know whether they are purchasing gasoline with MMT added;

urges applicable government authorities to take steps to monitor the use of MMT by gasoline refiners and sellers in their jurisdictions, and to make this information available to the public;

urges further research into the health effects of manganese exposure, emphasizing the effects on vulnerable populations, with financial support from Ethyl Corporation but carried out completely independently of that corporation;

urges that health care providers and members of the public be fully informed about the potential health effects of MMT use.