What's the Story? MMT

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What Is MMT?

MMT (methylcyclopentadienyl manganese tricarbonyl) is a fuel additive that has recently been approved by the Environmental Protection Agency (EPA) for use in unleaded gasoline in the United States. It has been used in Canada for nearly 20 years.

What Are the Benefits of MMT?

MMT improves the efficiency of petroleum processing and refining and reduces emissions from refineries. In automobiles MMT enhances fuel performance and also reduces emissions (primarily emissions of nitrogen oxides), thereby reducing urban smog.

What Are the Charges Leveled Against MMT?

MMT can be toxic, it's true; but the additive is almost completely burned during fuel combustion. This was evidenced by a 1979 study of ambient air collected on the streets of Toronto: Using procedures capable of detecting as little as 0.05 nanograms (a nanogram is one billionth of a gram) of MMT in a cubic meter of air, no MMT could be detected. Thus, human exposure to toxic levels of MMT would only be a concern in those confined occupational settings in which the additive is produced or in which it is mixed with fuels. And the Occupational Health and Safety Administration (OSHA) has set standards to protect workers in such settings.

Exposure to MMT thus is not a primary health concern for the general public. But some consumer activists and scientists are concerned about the public's exposure to manganese and especially to the manganese particulates produced when MMT is burned.

Opponents of MMT have charged that the manganese produced when MMT is burned will harm our children by causing learning disabilities and behavioral problems. These charges are based on studies of rats exposed deliberately to high levels of manganese and on studies of manganese miners and other workers exposed to thousands of times the doses the general population would receive.

In the occupationally exposed human population, excess manganese levels were shown to have detrimental effects on the nervous system. At their most severe the symptoms were similar to those of Parkinson's disease. But mild neurological symptoms, when caught early, were shown to be reversible or to cease to progress when the exposure was curtailed.

Although the EPA has reluctantly approved MMT (after receiving a court order to do so), the agency has objected to the additive's use. The EPA concedes that it "does not have data showing MMT to be a threat" to public health, but it also notes that it "does not have data proving MMT is not a threat." If the EPA waits for data to prove a negative, however that is, waits for evidence that MMT is not a health threat the agency will be both paralyzed and unable to rule on any question. But proving a negative is impossible: If 100 studies were to indicate that the use of a chemical was safe, critics could always charge that the 101st study might show otherwise.

What Are the Facts?

For any adverse health effects to result from MMT use, the population's exposure to the chemical or to its by-products must increase. Furthermore, that increase must be significant, because we are all continually exposed to trace levels of manganese the twelfth most abundant element in the earth's crust. Manganese is ubiquitous in the environment: it is in rocks and soil, in food and water and in living organisms. Manganese is, in fact, considered an element essential to humans for maintaining health.

Nearly 20 years of MMT use in Canada have not indicated that the exposure of the general population to manganese through the air or from the soil has increased. Furthermore, the proposed level of MMT to be added to gasoline in the United States is lower than the level added in Canada.

Studies in Canada have indicated that after years of MMT use a Canadian's average exposure to airborne manganese is less than the current EPA standard. Studies of garage mechanics and taxi drivers people in occupations having higher than average exposure to automobile exhaust have shown that even those individuals are not exposed to unsafe levels of manganese. In fact, even for people more highly exposed, manganese found naturally in the diet contributes far more to blood levels of the element than does manganese expo sure from MMT.

On average, food contributes 89 to 96 percent of human manganese exposure, with drinking water contributing another three to four percent. Manganese in the soil and in the air generally con tribute only a small fraction of exposure, except in cities with large manganese-emitting industries. In those localities, inhalation exposure may contribute up to 20 percent. In cities where MMT is used, however, the level of ambient manganese is not significantly different from that in cities where MMT is not used.

Manganese is present naturally in soil; Canadian soil levels average 520 micrograms per gram of soil (µg/g), with a range of 54 to 5740 µg/g (a microgram is one millionth of a gram). Levels in soil samples taken from Canadian urban areas in which MMT was used were found to be similar (522 µg/g in Montreal and 474 to 685 µg/g for street dust in Halifax). Thus, the 20-year use of MMT in Canada has not increased soil levels of manganese as compared to background levels.

Furthermore, various Canadian and international bodies have reviewed data from 20 years of Canadian use of MMT. According to Health Canada, an organization comparable to the U.S. Department of Health and Human Services, "All analyses indicate that the combustion products of MMT in gasoline do not represent an added health risk to the Canadian population."

When it comes to evaluating any theoretical toxicity for MMT either the additive itself or its combustion products it is important to consider the actual concentration or absorbed dose to which humans are exposed. While MMT and manganese may be toxic at high exposure levels, at low doses there are no measurable health risks. According to the World Health Organization, manganese exposure up to 100 times greater than that attributed to MMT use in Canada would still provide a sufficient margin of protection for the most sensitive population group.

The Bottom Line

Merely by allowing MMT on the market, the EPA does not lose its authority to further regulate or test the product.

Additional studies of MMT studies conducted both by MMT manufacturers and by independent researchers continue. If any significant hazards are revealed by that ongoing research, the EPA can change the status of MMT's approval. The real hazards apparent in the MMT story are not exposure levels but fears fears created by the exaggerated and erroneous propaganda of MMT's opponents and by the EPA's efforts to disallow a product with a history of safe use.

The bottom line? Studies indicate that 20 years of MMT use in Canada have presented no health hazard to the general public. And to deny consumers the benefits of innovative, beneficial products while forcing companies to prove the impossible that their product is completely safe and absolutely risk free is a prescription for disaster.