Occupational studies have shown that excess exposure to manganese (Mn) can cause neurotoxic effects though little is known regarding health effects of ambient Mn exposure in children. A ferromanganese refinery in Marietta, OH reports the greatest amount of Mn fugitive air emissions in the nation. The aim of this study was to compare ambient levels of Mn in Marietta with those in a control city (Cambridge, OH) and to compare personal air monitoring results with the results obtained at stationary outdoor sites in Marietta. This study is part of a larger epidemiological study on the neurotoxic effects of Mn exposure in children, the Communities Actively Researching Exposure Study (CARES).
Stationary outdoor air samples were collected at two locations: Marietta College and Robinson Hill Rd, 5 and 2 miles from the refinery, respectively. The sampling was conducted for 8 months at Marietta College (n=83) and during three weeks at the Robinson Hill station (n=8). In Cambridge, 43 miles north of Marietta, stationary sampling was conducted for one week per season (n=10). Stationary samples were collected on Teflon filters for approximately 48 hours using Harvard-type PM2.5 impactors (MS and T Area Sampler; Air Diagnostics, Inc.). Personal air samples were collected on 20 participants, ages 7-9, living in non-smoking households enrolled in CARES. The personal sampling was conducted for 48 hours using PM2.5 samplers (Personal Modular Impactor; SKC Inc). Time weighted average (TWA) distance was computed to determine how far the personal sample was from the Mn refinery, based on reported activities. All air samples were analyzed for PM2.5 mass gravimetrically and for Mn, Al, Cr and Pb using inductively coupled plasma mass spectrometer. Al was selected as a crustal indicator element. Cr and Pb were selected because these elements are emitted from the refinery and other facilities in Marietta.
The PM2.5 mass measured at the three stationary sites varied from 0.07 to 27.5 u/m3 and was not significantly different between the three sites. In contrast, Mn concentrations increased when the distance to the refinery decreased. The geometric mean concentrations (GM) for Cambridge, Marietta College and Robinson Hill were 2.0, 6.7, and 46.1 ng/m3, respectively (ANOVA: p < 0.001). A similar trend was seen for Al and Cr, but the differences were not statistically significant.
Personal samples had higher GM for PM2.5 and for the four metals than respective stationary samples. The largest differences between personal and outdoor stationary results were found with the crustal indicator Al, which was 4.2 times higher in personal than in stationary samples (p=0.03) and with the PM2.5 mass (2.9 times higher; p=0.01). Log-transformed TWA distance was significantly associated with log-transformed personal Mn (p=0.04) and personal Pb (p=0.01) and explained approximately 21% and 29% of the variability in personal exposure to Mn and Pb, respectively. The results indicate that children’s PM2.5 exposure in Marietta is uniform throughout the city. Mn exposure is associated with the child’s residential and school distance to the refinery.