MANGANESE AND LEAD CONCENTRATIONS IN AMBIENT AIR AND EMISSION RATES FROM UNLEADED AND LEADED GASOLINE BETWEEN 1981 AND 1992 IN CANADA - A COMPARATIVE-STUDY

Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organic derivative of manganese (Mn) used as an additive in unleaded gasoline. Its use in Canada has increased since 1976 until it completely replaced lead (Pb) in gasoline in 1990. Canada is the only country in the world to have authorized the replacement of Pb in gasoline by MMT. The aim of this study is to compare the concentrations of Mn, Pb and suspended particulates (TSP) in Montreal air from 1981 to 1992, as well as the emission rates of Mn and Pb from mobile sources from the same period. The atmospheric concentrations of Mn, Pb and TSP were measured by the Montreal Urban Community at three sampling stations located in areas of low and high traffic density. The data on emission rates were obtained from Environment Canada and from the Canadian Petroleum Products Institute. Multiple regression and non-parametric correlation analysis were used to predict and to compare the evolution of the chosen variables. Discriminant analysis was used to determine the variables which best distinguish low and high traffic density areas. The results indicate stable Mn concentrations between 1981 and 1990 followed by a substantial decrease, in spite of annual increases of about 10% in Mn emissions from the combustion of MMT since 1981. The decrease observed since 1991 is attributed to the closing of a ferromanganese plant near Montreal. The decrease in atmospheric Pb concentrations observed since 1981 corresponds to the decrease of about 30% per year of emissions from mobile sources over the same period. A definitive evaluation of the environmental contamination and exposure due to Mn from MMT will require an improved estimation of the dispersion of particulates near motorways using dispersion models, as well as receptor modeling based on the physicochemical analysis of particulates using electron microscopy.