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 ad jacent to a multilane highway in the Greater Toronto Area (GTA), Ontario. T he annual average daily traffic (AADT) volume was approximately 333 700 veh icles in 1993. Soil sampling was conducted at two different sites along the highway to determine the concentration and extent of Mn deposition from me thylcyclopentadienyl manganese tricarbonyl, MMT (a gasoline additive). Samp les 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 excha nge capacity. Mn concentrations decreased with increasing distance from roa dside. Pb concentrations changed little from values reported in 1990, but h ave moved deeper into the soil, indicating a cessation of atmospheric depos ition. In contrast, exchangeable Mn concentrations decreased with soil dept h indicating recent atmospheric deposition. Although Mn concentration in so il decreased with the increase in the distance and the depth adjacent to th e multilane highway, the difference was not statistically significant withi n the sites. More research is needed to provide better understanding of the extent of MMT and the complex behaviour of Mn contamination in the terrest rial urban environment.