Exposure of taxi drivers and office workers to total and respirable manganese in an urban environment.

This research measured the exposure of two groups of workers to respirable and total manganese (Mn) and characterized the Mn particles emitted from an automobile tailpipe. The exposure of 20 office workers and 9 taxi drivers in Toronto to total airborne Mn and respirable Mn was measured over a 7-day period, 24 hours per day. Subjects were asked to wear two pumps (one included a size-selective cyclone that collected the respirable particles), and two battery chargers were supplied to each person so that the pump batteries could be recharged overnight while sampling continued. All filters were analyzed by neutron activation. In addition, Mn particles emitted from a car were collected directly at the exhaust. Particles were observed using secondary electron images in a scanning electron microscope (SEM), and their elemental composition was determined by energy dispersive x-ray spectrometry. The Mn concentrations obtained for the group of office workers ranged from 0.001 to 0.034 microgram/m3 for respirable Mn and from 0.002 to 0.044 microgram/m3 for total Mn. For the taxi drivers the Mn concentrations ranged from 0.007 to 0.032 microgram/m3 for respirable Mn and from 0.008 to 0.073 microgram/m3 for total Mn. There was a significant difference (p < 0.05) between the two groups for both respirable and total Mn. SEM analysis showed that the particles were mostly heterogeneous agglomerates varying from 1 to 100 microns. Even if the specific exposure to Mn from automobiles has not been directly established, these results suggest that the related increase of exposure may be limited.