Ethyl argues that MMT helps the environment because, without it, oil companies have to employ a more intensive refining process that consumes slightly more crude oil to produce a given quantity of gasoline. There is also some evidence that MMT reduces auto emissions of nitrogen oxides. Ethyl's assertions that MMT is safe do not withstand scientific scrutiny, according to Herbert Needleman.
Laboratory studies show that manganese crosses the placenta and retards growth in fetal rodents.
When inserted into the brain cells of rats, it disturbs the normal functioning of the cells. Ethyl claims that MMT has been used safely in Canada for 19 years. But no systematic studies of manganese in humans have been done in Canada or elsewhere. Based on historical experience with leaded gasoline, Needleman says Ethyl should be made to prove MMT is safe rather than being allowed to put its product on the market until is proven unsafe. Since the early 1990's MTBE has been added up to 15 percent to enhance gasoline combustion and reduce tailpipe emissions.