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

Abstract

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

Deposition of Mn from Automotive Combustion of Methylcyclopentadienyl Manganese Tricarbonyl beside the Major Highways in the Greater Toronto Area, Canada

“…But in all cases, the Mn levels were found to be below the safe levels of Mn in surface soil as recommended by OMOE. 34,44 No significant difference was observed in any of the total trace metal concentrations at the east and west sides of site E +2 . As described previously, E +2 is at the same elevation as the pavement, while E +1 is slightly elevated, which may alter the deposition of Mn from automobile emissions.…”

“…Four sites (two wooded and two unwooded) extending east/west of highway 400 and north/south along highway 401, located 43º 67' N and 79º 37' W (latitude and longitude) of the GTA, respectively, were chosen for the study (Figure 1 34 to reduce vehicle noise affecting the community near the highways. These sites were chosen to examine the wind eddying effect, as wind eddying may concentrate Mn deposits on the leeward side of some of the sound barriers.…”

“…These levels were found to be below the safe levels recommended by the OMOE for ordinary soil. 34,44 Total Pb concentration in the surface soil at site E +3 was found to be significantly different (as Pb was introduced to gasoline 50 years ago) with distance from the highway. This may be because Pb is very immobile in soil.…”

“…The levels were found to be within the safe soil levels of Mn as recommended by OMOE. 34,44 Increasing urbanization has led to a large increase in the range of trace metal levels in urban environments. 43 This is probably the main reason why sites E +3 and E +4 showed a higher level of total trace metal concentrations in the surface soil as compared with the rural sites.…”

“…Because MMT has been used in gasoline in Canada for ~25 years, higher soil Mn levels were expected beside the highways; however, they were found not to be elevated. 34,44 Urban Sites. Significant differences were found between the mean values (p < 0.05) of total Mn in surface soil at the north and south sides of E +4 (see Table 4a).…”