Use of Near-Edge- X-ray Absorption Spectroscopy to Speciate Manganese in Airborne Particulate Matter from Six Cities in Continental USA

SAUGATA DATTA (1), Ana M Rule (2), Steven N Chillrud (3), Jana N Mihalic (2), Juan P Ramos-Bonilla (2), Inkyu Han (2), Lisa M Polyak (2), Patrick N Breysse (2), Alison S Geyh (2)

(1) Kansas State University, Kansas, (2) Johns Hopkins Bloomberg School of Public Health, Maryland, (3) Lamont-Doherty Earth Observatory, Columbia University, New York

     Abstract Number: 260
     Last modified: November 9, 2009

Abstract
The Johns Hopkins Particulate Matter Research Center (JHPMRC) is a 5 year study exploring the relationship between health effects and exposure to ambient particulate matter (PM) of differing composition. An important research goal of the JHPMRC is the characterization of ambient particle composition using samples of ambient PM collected from different counties across the country identified by Center epidemiologists as representing greater or lesser risk to health from exposure to ambient PM. It is hypothesized that these differences in health outcome to PM relationships are driven by variations in particle composition, but to date the evidence for this is incomplete. Over the last 2 years, we have collected and characterized ambient PM from 7 counties: Sacramento (CA), Maricopa (AZ), Baltimore (MD), Pinellas (FL), Jefferson (KY), Hennepin (MN), and Harris (TX). Samples of these particles will ultimately be used in toxicological studies to assess potential differential impacts on selected outcomes such as markers of inflammation or cardiac deregulation. It is thus important to characterize these particles, particularly for the most toxic elements.

Manganese is one such element, designated as one of the Hazardous Air Pollutants in the 1990 Clean Air Act. Laboratory and animal studies have shown that the form of Mn contributes to unique effects on enzyme activity in vivo, such that Mn(2+)acetate dihydrate and Mn(3+)pyrophosphate are more cytotoxic than Mn(2+)chloride. Disorders in Mn metabolism, either systemically or locally in the brain, have been linked to a number of neurodegenerative diseases such as Parkinsons or Alzheimers.

Ambient PM samples were collected using a high volume sequential cyclone system, designed by center researchers, that segregates ambient PM into "coarse" (PM > 3.5 µm and < 10 µm) and "fine" bulk PM (PM > ~0.3 µm and <3.5µm). Samples were collected in dry bulk form, stored under argon until analysis, and analyzed without any pretreatment or dissolution to avoid altering oxidation states.

Near Edge Fine structure absorption spectroscopy (XANES) was utilized to evaluate and identify major oxidation states and coordination chemistry of Mn contained in the “fine” PM samples using Linear combination Fitting (LCF) with ATHENA software. Spectra of eight inorganic standard compounds covering all possible oxidation states and the most important coordination chemistry of Mn were also obtained. For each PM sample, the combination with the lowest reduced chi-square was chosen as the most likely fit.

Good fits were obtained for analyzed “fine” PM samples, suggesting the following Mn species:
Maricopa/Phoenix: Mn(2+)Acetate (50% +/-1%), Mn(2+)Oxide (28% +/-2%), & Mn(4+)Oxide (22%+/-1%). Hennepin/Minneapolis: Mn(2+)Acetate (62%+/-3%) and Mn(2+)Oxide (38%+/-3%). Baltimore: Mn(2+)Acetate (52%+/-2%), Mn(2+)Oxide (46%+/-4%), Mn(3+)Oxide (<2%). Sacramento: Mn(2+)Acetate (62%+/-6%), Mn(2+)Chloride (27%+/-5%), Mn(3+)Oxide (11%+/-3%). Harris/Houston: Mn(2+)Oxide (58% +/- 5%), Mn(2+)Acetate (37 % +/-3%), Mn(3+)Oxide (4% +/- 4%). Pinellas/Tampa: Mn(2+)Acetate (45%+/-4%), Mn(2+)Oxide (33%+/-16%), Mn(4+)Oxide (13% +/- 9%), Mn(3+)Oxide (8% +/- 12%). Interpretation of “coarse” analyses is ongoing.

These differences in oxidation state composition of the tested samples indicate regional and seasonal variations in sources and atmospheric chemistry that may eventually help explain differences in health effects found by the epidemiological and toxicological studies.