Development of a Manganese Speciation Method for Atmospheric Aerosols in Biologically and Environmentally Relevant Fluids

Abstract

Because the health effects of manganese are dependent its oxidation-state, we have improved upon oxidation-state resolved methods to quantify soluble manganese in atmospheric aerosols. Two spectrophotometric methods were adapted for measurements in atmospheric aerosols in order to measure total soluble manganese (Mn _sol ) and soluble oxidized manganese [Mn(III) and Mn(IV), Mn _ox ]. Using the formaldoxime method, we noted a detection limit two orders of magnitude better than past studies using trace-metal clean techniques and a 1 meter path-length spectrophotometric cell. Extractions of co-located aerosol samples were performed in four environmentally or biologically relevant extract solutions and processed for soluble manganese analysis. The quantity of manganese extracted was a strong function of the fluid, and the greatest amount of manganese was extracted in the rain-water surrogate (acetate buffered solution). Mn _sol in East St. Louis, IL, USA (6–20% of the total manganese) was less than the Mn _sol in aerosols collected in Toronto, ON, Canada (40% of the total). Mn _ox was not detected in the PM10 samples collected in East St. Louis, however Mn _ox accounted for around 30% of the PM2.5 soluble manganese in Toronto. Mn _ox was not detected in the coarse fraction in Toronto, which may imply that soils are not a source of Mn _ox at this site. Oxidized manganese was not recoverable from extracts of samples from East St. Louis spiked with 1 μg Mn _ox L⁻¹. This implies that a soluble component of the aerosol is responsible for reduction of oxidized manganese and that the chemical form of manganese in aerosols can quickly change when it comes into contact with a fluid.

Acknowledgments

This study was supported by the Health Effects Institute (HEI) grant #02-11. We thank Jay Turner, Jay Hill, and Eric Ryszkiewicz at the Midwest Supersite in East St. Louis, IL for providing us access to the site and assistance with obtaining samples. We also thank Helen Manolopolous for collecting PM samples in Toronto. We thank Jeff DeMinter, John Strauss, Chris Worley, Dustan Helmer, Joel Overdier, and Noel Stanton at the Wisconsin State Laboratory of Hygiene for their roles in the ICPMS analysis and filter preparation.