Lead was replaced by methylcyclopentadienyl manganese tricarbonyl (MMT) as an antiknock agent in gas a dozen years ago in Canada, but MMT may cause damage to the nervous system. In fact, exposure to high concentrations of manganese can lead to neurological disorders similar to Parkinson's disease. Cars emit different chemical forms of manganese as MMT combustion products. “The nervous system is the prime target for the harmful effects associated with manganese, and the olfactory bulb can accumulate fairly large quantities of the element,” notes toxicologist Joseph Zayed, referring to a long-term survey report submitted to Health Canada in 2002.

To reach this conclusion, the director of the Interuniversity Toxicology Centre and professor in the Université de Montréal Faculty of Medicine conducted studies on animals and humans whose environment contains MMT produced manganese. “There is no cause for alarm,” notes the researcher, “but our research shows that the problem of contamination by MMT produced manganese is very real; the potential risk for public health must be well documented, in particular as regards more sensitive subgroups, such as the elderly and persons with liver dysfunction. Detailed epidemiological studies should be performed on these populations.”

Of the different animals used by professor Zayed’s group, rats in particular were exposed to different concentrations of manganese. High concentrations of the metal were found in their brains. The olfactory bulb was most severely affected. An article on this topic has just appeared in a major journal, Toxicology and Applied Pharmacology. Other rats in which hepatic dysfunctions have been deliberately induced had more than double the normal concentrations of manganese in some parts of their brains. Similar experiments have not been tried with human subjects, obviously, but it is believed that the results from the animal model could apply to humans, especially individuals with liver problems such as cirrhosis. In fact, autopsies have revealed higher levels of manganese in the brains of people who suffered from hepatic dysfunction.

Canada is the first country in the world to adopt a policy on the use of MMT in gasoline on a wide scale, but France and Australia are following suite. Others, such as the United States, Russia, Bulgaria and New Zealand, may follow their lead. In the United States, there is a vocal opposition movement, while the Environmental Protection Agency has started legal proceedings to bar the additive, favouring methyl tertiary butyl ether (MTBE) instead. But research has demonstrated that this substance also produces toxic effects.

Researcher: Joseph Zayed
Telephone: (514) 343-5912
Email: joseph.zayed@umontreal.ca
Funding: Health Canada (Toxic Substances Research Initiative)