Characterization of Manganese-Containing Particles Collected from the Exhaust Emissions of Automobiles Running with MMT Additive

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 Mn-sulfate with a size ranging between 0.2 and 10 μm. ATEM characterization shows that the isolated particles consist of manganese−oxygen−phosphorus−sulfur (Mn−O−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 evidence-based risk assessment approaches.