MMT: Questions and Controversies

Posted: 01-Jan-1994; Updated: 05-Feb-2002

What is MMT? MMT stands for methylcyclopentadienyl manganese tricarbonyl, a chemical compound that is added to gasoline to enhance octane under the name HiTEC 3000. It is manufactured by the Ethyl Corporation, which for many decades also manufactured lead additives for gasoline.

Who is worried about MMT and why? The U.S. Environmental Protection Agency, environmentalists and public health advocates share concerns that grow out of three undisputed facts:

• First, putting manganese into gasoline means that manganese will come out of car tailpipes, increasing manganese levels in air and resulting in manganese accumulations over time in dust (since manganese, as an element, cannot biodegrade).

• Second, airborne manganese, unlike manganese in the diet, can unquestionably harm the human brain and nervous system. Workers highly exposed to airborne manganese develop symptoms that are similar to Parkinson's disease. Workers with moderate exposures suffer from impairments in neuromotor function (e.g., hand-eye coordination, reaction time), and in lung function.

• Third, almost no studies have been done, in either humans or animals, on the effects of long term exposures to the levels of airborne manganese that MMT use will cause. No studies at all have been conducted on exposures that start in childhood and continue for years.

Given these facts, additional toxicity data is needed before MMT is put into gasoline (specific data needs were identified in an international scientific meeting in 1991). After all, neurologic diseases already cost America more than $100 billion annually -- the last thing America needs is to allow preventable exposures to a known neurotoxin.

Why hasn't EPA required more information on the safety of MMT? EPA tried to do exactly that, but the courts held that the relevant statutory provision (section 211(f) of the Clean Air Act) barred EPA from considering health issues in deciding whether to allow marketing of MMT. The court said that EPA could only evaluate MMT's effect on pollution-control devices; in a separate case, the court held that EPA's new rules that require pre-market testing of new gasoline additives did not apply to MMT because the MMT application was filed before the new rules took effect. (Ethyl v. EPA, D.C. Cir. No. 94-1505, decided April 14, 1995; Ethyl Corp. v. EPA, D.C. Cir. No. 94-1516, decided Oct. 20, 1995). After the court's rulings, EPA had no choice but to register MMT for use as a gasoline additive, effective December 13, 1995.

Which companies are now using MMT? The public doesn't know. Although refiners must notify EPA when they start using a new additive, at least four companies initially blocked release of that information when it was sought under the Freedom of Information Act, by claiming it as confidential business information (three other small refineries did not claim confidentiality, namely Navajo Refining, Flying J. Inc., and Pride Companies). In any event, there is no requirement for gas stations to let consumers know whether gas at particular gasoline pumps contains MMT. However, EPA statistics indicate that only .02 percent of the U.S. gasoline supply currently contains MMT.

But isn't manganese required in the diet? There's a key distinction between breathing manganese and eating it. Eating trace amounts is necessary to good health, but the body handles manganese in a very different way depending on whether it's breathed in or eaten. Breathing manganese puts it on a fast track to the brain, which of course is the target organ for neurotoxic effects.

And the effects of manganese may also depend on the age at which exposure occurs. While its neurotoxic mechanism of action is not fully understood, manganese kills brain cells. That's bad news, because brain cells, unlike virtually all others in the body, aren't replaced. And while there are billions of cells in the brain, over time the brain's total capacity can be depleted, leading to critical problems. That's what happens with Parkinson's disease -- after 80% of the relevant neural pathways degenerate, overt symptoms appear. So even if MMT use does not cause neurotoxic symptoms in the short term, it could be silently undercutting the reserve capacity of the brain. Even a seemingly trivial increase in the rate of neural degeneration of 1% or so could result in accelerating loss of function, so that 50-year-olds end up with brain functions more typically seen in 60 to 80 year-olds.

Hasn't MMT been in use in Canada for over 15 years? Yes, but contrary to Ethyl's assertions, there have been no studies on whether MMT causes any health effects. Recently, one researcher -- who was initially collecting data on a related topic -- noted a higher rate of poor hand-steadiness (an early sign of potential neurological impairment) among middle-aged men with higher levels of manganese in blood compared to those with lower levels; none were occupationally exposed to manganese.

What are the parallels to leaded gasoline? Ironically, MMT is coming onto the market just after leaded gasoline was finally banned at the end of 1995. Back in the 1920s when Ethyl first started making lead-gas additives, it was well known that high exposures to lead were toxic, but there was little data on lower exposures, particularly in children. That's the same situation we're in today with manganese. The public health community in the 1920s raised serious questions about lead additives, just as it has done with manganese today.

What do auto manufacturers think of MMT? Although EPA concluded that MMT does not impair pollution-control systems, the American Automobile Manufacturers Association has concluded that available evidence "...clearly and unequivocally establishes that use of MMT as a fuel additive will cause or contribute to the failure of the emission control systems of some vehicles."