Exposure of urban ecosystems to Mn and Pb contaminants from gasoline additives beside a major highway in the Greater Toronto Area, Canada

A study of manganese (Mn) and lead (Pb) deposition in soil was conducted adjacent to a multilane highway in the Greater Toronto Area (GTA), Ontario. The annual average daily traffic (AADT) volume was approximately 333 700 vehicles in 1993. Soil sampling was conducted at two different sites along the highway to determine the concentration and extent of Mn deposition from methylcyclopentadienyl manganese tricarbonyl, MMT (a gasoline additive). Samples were collected at distances up to 160 metres from the roadside, at each site. Parameters evaluated included total and exchangeable Mn and Pb (from historic use of leaded gasoline), soil particle size, pH, and cation exchange capacity. Mn concentrations decreased with increasing distance from roadside. Pb concentrations changed little from values reported in 1990, but have moved deeper into the soil, indicating a cessation of atmospheric deposition. In contrast, exchangeable Mn concentrations decreased with soil depth indicating recent atmospheric deposition. Although Mn concentration in soil decreased with the increase in the distance and the depth adjacent to the multilane highway, the difference was not statistically significant within the sites. More research is needed to provide better understanding of the extent of MMT and the complex behaviour of Mn contamination in the terrestrial urban environment. Key words: manganese, lead, soil, methylcyclopentadienyl manganese tricarbonyl (MMT); gasoline additive; urban environment; greater Toronto area (GTA), Canada