Background

Manganese is a neurotoxin and heavy metal. The combustion of MMT in gasoline releases manganese phosphates, manganese sulfates, and manganese oxides into the air. When inhaled, these compounds may enter the bloodstream through the lungs and deliver dangerous doses of manganese to the brain, where accumulation can lead to Parkinsons-like symptoms including loss of motor control, memory loss, erratic behavior, and brain cell death. A recent study carried out in Mexico City found that exposure to both manganese and lead in early childhood led to exacerbated neurodevelopmental deficiencies and that the impacts of coexposure were more severe than expected based on exposure to each metal alone. There is no known treatment or cure.

The ICCT’s work in this area is summarized here and here.

A rare consensus exists among automakers, refiners, and the public health community in favor of restricting the use of manganese compounds in fuels. But regulation remains uneven, in part because of vigorous efforts by the manufacturer of MMT, Afton Chemical, to promote its use and contest proposed restrictions. This continues a pattern set by Afton’s predecessor the Ethyl Corporation, which for decades avoided restrictions on tetraethyl lead and manganese-based additives.

Public health professionals agree about the threat and the remedy. In 2003 the American Academy of Pediatrics recommended phasing out MMT from gasoline. The 2007 Brescia Declaration on Prevention of Neurotoxicity of Metals called for an immediate halt to the addition of organic manganese compounds to gasoline.

Automakers also want to eliminate MMT in fuels, for the very different reason that it damages emissions control components. To maintain emission and engine performance, BMW, General Motors, Honda, and Toyota and others have jointly defined standards for unleaded gasoline that explicitly exclude metallic additives, including MMT.

In 2009 the European Union adopted amendments to its fuel quality directive that set an interim limit on MMT in fuel of 6 mg of manganese per liter, falling to 2 mg/L in 2014, and also required labeling of fuel containing metallic additives. That put Europe in line with trends elsewhere, especially in the developed countries. The U.S. prohibits manganese entirely from reformulated gasoline, which constitutes more than 60 percent of the U.S. fuel supply, and California bans manganese entirely. Oil refiners voluntarily exclude manganese additives from the remainder of the U.S. supply, as well as from the fuel supply in Canada, the European Union, Japan, India, and Indonesia. The extent to which MMT is used in fuels elsewhere is impossible to determine with confidence, as Afton does not make public the list of countries where it is sold.