Deposition of Mn from automotive combustion of methylcyclopentadienyl manganese tricarbonyl beside the major highways in the greater Toronto area, Canada

Methylcyclopentadienyl manganese tricarbonyl (MMT) has been used in Canada since 1976 as an antiknock agent in gasoline, completely replacing Pb in 19 90. An early study of much higher Mn concentrations in gasoline showed that the combustion of MMT leads to the formation of inorganic manganese oxides , especially Mn3O4, Recent emission testing by Lawrence Livermore National Laboratory for Ethyl Corp. has shown that Mn is primarily emitted as a phos phate or sulfate along with minor amounts of oxides. The main objective of this research was to analyze the deposition of Mn from MMT to the terrestri al environment beside the major highways in the greater Toronto area (GTA), Canada. The results were compared with Pb and other trace elements such as Al, Ca, Fe, Mg, Cu, Zn, Na, and the Cl- ion (water extractable) to study t he behavior of Mn in soil. The study area was located near major Toronto hi ghways 401 (urban) and 400 (rural), at 43 degrees 67 'N and 79 degrees 37 ' W (latitude and longitude) (278,560 and 47,835 cars/day), respectively. Sur face soil samples (0-5 cm depth) were collected at distances up to 40 m fro m the roadside. Parameters evaluated included total and available Mn and ot her trace elements, particle size, pH, organic content, and cation exchange capacity. Based on high traffic density along 401, higher Mn deposition wa s expected. No significant differences were found between the 401 and 400 B arrie (E+1) sites, attributable to the natural background levels of Mn or i ts contribution by other sources such as Mn-enriched road dust or naturally occurring crustal Mn. However, the 400 King City (Ell) site had significan tly lower Mn levels than did the other three sites, 401 and 400 Barrie. Thi s may be explained by the types of soil along the 401 and 400 sites. The Ki ng City site along 400 was found to be higher in sand content than were the 401 sites. A higher sand content could result in higher leaching of Mn to the bottom layer of the soil. Although MMT has been used continuously for s imilar to 25 years in Canada, its contribution to the terrestrial environme nt has been very low and has not significantly increased Mn levels along th e highways, as demonstrated by this study.