When the United States Environmental Protection Agency (EPA) ordered the phase out of TEL in gasoline in 1973, new fuel additives were sought.

[8] In 1977, the US Congress amended the CAA to require advance approval by the EPA for the continued use of fuel additives such as MMT, ethanol, ethyl tert-butyl ether (ETBE), etc.

[9] The new CAA amendment required a "waiver" to allow use of fuel additives made of any elements other than carbon, hydrogen, oxygen (within certain limits) and nitrogen.

[10] To obtain a waiver, the applicant was required to demonstrate that the fuel additive would not lead to a failure of vehicle emission control systems.

[11] Despite that finding, the EPA ultimately denied the waiver request in 1994 due to uncertainty related to health concerns regarding manganese emissions from the use of MMT.

[12] As a result of this ruling, Ethyl initiated a legal action claiming that the EPA had exceeded its authority by denying the waiver on these grounds.

Opposition from automobile manufacturers and some areas of the scientific community has reportedly prompted oil companies to stop voluntarily the usage of MMT in some of their countries of operation.

"[19] Similarly, NICNAS stated that "[m]inimal public exposure to MMT is likely as a result of spills and splashes of LRP [lead replacement petrol] and aftermarket additives".

The MMT dossier registered in the European Chemical Agency's webpage indicates that before combustion in gasoline, MMT is classified as an acute toxicant by the oral, dermal, and inhalation routes of exposure under the European Union's Classification, Labeling and Packaging Regulation (EC/1272/2008), implementing the Global Harmonized System (GHS) of Classification and Labeling.

However, OSHA has set a permissible exposure limit at a ceiling of 5 mg/m3 for manganese and its compounds, while the National Institute for Occupational Safety and Health recommends workers not be exposed to more than 0.2 mg/m3, over an eight-hour time-weighted average.

Similarly, the 2003 NICNAS report states that the airborne concentrations of manganese as a result of car emissions from vehicles using fuel containing MMT poses no health hazard.

[citation needed] The assessment conducted by NICNAS notes that "[m]anganese, the principle degradation by-product from combustion of MMT, is naturally occurring and ubiquitous in the environment.