Environ. Sci. Technol. 1999, 33, 3341-3346
Characterization of Manganese-Containing Particles Collected from the Exhaust Emissions of Automobiles Running with MMT Additive J O S E P H Z A Y E D , * ,† B A N D E H O N G , ‡ A N D G I L L E S L ’ E S P EÄ R A N C E ‡ TOXHUM (Human Toxicology Research Group) and De´partement de me´decine du travail et d’hygie`ne du milieu, Universite´ de Montre´al, Faculte´ de me´decine, C.P. 6128, Succ. Centre-ville, Montre´al, Que´bec, Canada H3C 3J7, and Centre for Characterization and Microscopy of Materials, EÄ cole Polytechnique de Montre´al, C.P. 6079, Succ. Centre-ville, Montre´al, Que´bec, Canada, H3C 3A7
Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organometallic compound used as an octane improver in unleaded gasoline. The objective of this study was to determine the physical and the chemical characteristics of the manganese (Mn) compounds emitted from vehicles using MMT. Particles emitted from the tailpipe were trapped and characterized by scanning electron microscopy (SEM) and X-ray energy dispersive spectrometry (EDS) and by analytical transmission electron microscopy (ATEM). Results support the conclusion that Mn is emitted from the tailpipe primarily as a mixture of Mn-phosphate and Mnsulfate with a size ranging between 0.2 and 10 µm. ATEM characterization shows that the isolated particles consist of manganese-oxygen-phosphorus-sulfur (MnO-P-S) (in order of a descending peak intensity), indicating that Mn-phosphate is the main constituent of the residual particles. Moreover, all the Mn-containing particles investigated were amorphous. Further toxicological studies with a mixture of Mn-phosphate and Mn-sulfate are needed to provide successful implementation of evidencebased risk assessment approaches.
Introduction Methylcyclopentadienyl manganese tricarbonyl (MMT: C9H7MnO3) is an organic derivative of manganese (1, 2). MMT has been used in Canada since 1976 (3), and there was a substantial increase in its utilization over the past few years, in particular since it replaced lead in gasoline in 1990 (4). In 1997, the federal government of Canada adopted a law (C29) which banned both the interprovincial trade and the importation for commercial purposes of manganese-based substances, including MMT. In 1998, the government has abolished this law, and there is still an important lack of adequate toxicological information related to Mn effects after chronic exposure. The use of MMT has given rise to numerous debates on the potential public health risk associated with manganese Corresponding author phone: (514)343-5912; fax: (514)343-2200; e-mail:
[email protected]. † Universite ´ de Montre´al. ‡ E Ä cole Polytechnique de Montre´al. 10.1021/es990709+ CCC: $18.00 Published on Web 08/28/1999
1999 American Chemical Society
TABLE 1. General Characteristics of the Vehicles Tested car model
test no. year
motor
mileage (km)
fuel
Volkswagen Jetta T5 1991 4-L/1.8L 7810 with MMT Plymouth Voyager T11 1987 V-6/3.0L 61 362 with MMT Ford Thunderbird T17 1991 V-6/3.9L 7104 without MMT
emissions, which is the main substance emanating from the combustion of MMT. Many studies in occupational environments have shown that high atmospheric Mn concentrations may have significant effects on human health (5). Most of the results focused on the relationship between Mn exposure by inhalation and neurological signs and symptoms among working populations (6-8). Moreover, many neurodegenerative disorders similar to Parkinson’s disease have been associated with occupational exposure to Mn (9, 10). A preliminary car exhaust study (11) provided qualitative data on the elementary composition of particles collected from a tailpipe. According to the electron microscopy analysis, the Mn-oxide from car exhaust may be agglomerated with other particles, especially with phosphates or sulfates and may thus rarely be found as pure Mn-oxide in the environment. Particle sizes ranged from 0.2 to 50 µm. However, on average, more than 99% of the particles were in the respirable fraction (
