Environmental contamination and human exposure to airborne total and respirable manganese in montreal

Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organometallic compound used as an octane improver in unleaded gasoline. The combustion of MMT leads to the formation of manganese (Mn) oxides, mainly Mn3O4. The objective of this study is to assess the variations over time and space of respirable (Mn-R) and total (Mn-T) Mn in the urban atmosphere and to evaluate human exposure by inhalation. Two sampling sites were selected on the island of Montreal based on their local traffic density (municipal botanical garden, C- = 10,000-15,000 vehicles d(-1); Montreal Waterworks, C+ = 100,000-130,000 vehicles d(-1)). Air samplings were made during the day at stations located 10 m from the road using portable pumps, some of which were equipped with a cyclone. Mn-R and Mn-T and other metals were measured on Teflon filters by neutron activation. Mn exposure doses by inhalation were calculated using Monte-Carlo simulations. Mn-R and Mn-T average concentrations were significantly higher at site C+ (Mn-R = 0.024 mu g m(-3); Mn-T = 0.050 mu g m(-3)) than at site C- (Mn-R = 0.015 mu g m(-3); Mn-T = 0.027 mu g m(-3)). Temporal profiles at sites C+ and site C- were similar, with a coefficient of correlation of 0.24 for Mn-R and 0.26 for Mn-T. Trend analyses (ARIMA) also showed that the period of the week (work days vs. off days) was significantly related to Mn-R and Mn-T variations at both sites. The average exposure dose by inhalation to Mn-R and Mn-T ranged from 0.001 to 0.030 mu g kg(-1) day(-1) and 0.001 to 0.05 mu g kg(-1) day(-1). Mn-R and Mn-T concentrations reflected a positive relationship with traffic density. However, it remains difficult to attribute these results directly to the combustion of MMT in unleaded gasoline. On average, the Mn-R and Mn-T inhalation doses were 2 to 15 times lower than the reference dose (RfC) proposed by the U.S. Environmental Protection Agency (EPA) for the general population.