A study of the relationships between Parkinson's disease and markers of traffic-derived and environmental manganese air pollution in two Canadian cities

There is concern that industrial emissions of manganese (Mn) and the use of Mn-containing compounds as fuel additives might increase the population risk of Parkinson's disease (PD)-like disorders. We investigated associations between the diagnosis and treatment of PD and markers of exposure to vehicle exhaust and industrial emissions of Mn within a cohort of 110,000 subjects in the cities of Toronto and Hamilton, Canada. Methylcyclopentadienyl manganese tricarbonyl (MMT) has been added to Canadian gasoline since 1976 and steelmaking in Hamilton emits Mn to the air. Using residential postal codes, subjects were mapped to: (1) residence locations close to traffic and to neighbourhood levels of NO2, as markers of traffic-generated air pollution (TGAP); and, (2) neighbourhood levels of ambient Mn in Hamilton, as measured by the Mn fraction of total suspended particulate. Subjects were linked to Ministry of Health administrative databases, 1992-1999, to identify physicians' diagnoses of PD and prescriptions for l-Dopa containing medications. In Toronto, we found no association between PD and the markers of TGAP. In Hamilton, the odds ratio for a physician's diagnosis of PD was 1.034 (1.00-1.07) per 10 ng/m3 increase in Mn in TSP. The estimate of the "doubling exposure" for physician-diagnosed PD was about 150 ng/m3 Mn in TSP. Examination of prevalence curves suggested that exposure to ambient Mn advances the age of diagnosis of PD, consistent with the theory that exposure to Mn adds to the natural loss of neurons attributable to the aging process.