Use of MMT in Canadian gasoline: health and environment issues.

Abstract

Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organic derivative of manganese (Mn) used in Canadian gasoline since 1976 as an antiknock agent and to improve octane rating. Combustion products of MMT are mainly a mixture of Mn phosphate and Mn sulfate. In 1997, the Canadian federal government adopted a law (C-29) which banned both the interprovincial trade and the importation for commercial purposes of manganese-based substances, including MMT. However, the government reworded this law in July 1998 so that manganese-based fuel additives were not included in the restrictions. MMT is now approved for use in Argentina, Australia, Bulgaria, the United States, France, Russia, and conditionally in New Zealand. Nevertheless, these countries are not using MMT intensively and they are waiting for strong evidence of the absence of effects on human health. Even after several years of use of MMT in Canada, many uncertainties remain. Different methods were used in order to assess (1) environmental contamination and human exposure to the parental form of MMT, (2) nitrogen oxides (NO(x)) and carbon monoxide (CO) emissions associated with the use of MMT, and (3) qualitative and quantitative assessments of Mn emissions to the environment. The results provide timely information with regard to the impact of MMT on environmental/ecosystem Mn contamination in abiotic and biotic systems as well as on human exposure. Moreover, results raise major concerns with regard to public health effects related to exposure to Mn. Obviously, there is still an important lack of adequate toxicological information and further studies are needed to provide successful implementation of evidence-based risk assessment approaches.