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

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.