A Novel Approach to Characterize the Speciation and Toxicity of Metals in Atmospheric Particulate Matter

University Of Maryland Baltimore County, Baltimore MD

Investigators

Abstract

Airborne particles, or particulate matter (PM), impart numerous detrimental effects on human health. Metals are present at trace levels in PM, but these metals are hypothesized to have enhanced toxicity to humans compared to other constituents that are present in particles at much greater levels. Metals in PM take different chemical forms, and metal toxicity through other routes of exposure is affected by these different chemical forms. The aims of this work are (i) to develop a new method to determine the chemical forms of important metals in PM, and (ii) to link the different metal species to PM toxicity. This work will contribute to the training and education of undergraduate and graduate students in chemical and environmental engineering. If successful, this project will provide new insights on how to identify and quantify toxic metal exposure from PM matter in different environments. PM is a ubiquitous component of the atmosphere and influences climate and human health. PM is comprised of a diverse array of chemical species that reflect the numerous sources and processes that contribute to PM levels. Although metals typically constitute a small fraction of PM mass, epidemiological and toxicological studies have associated metals with a number of human health effects. This suggests that some metals have an enhanced toxicity compared to other chemical species found in PM. Previous studies linked metals with the generation of reactive oxygen species (ROS), providing a likely explanation for their role in adversely affecting health. Despite the evidence from epidemiological and toxicological studies, a clear understanding of the toxicity of specific PM metals is currently lacking. This limitation is due in part to a lack current measurement methods that can simultaneously characterize the oxidation state and speciation of the full suite of metals present in PM. These metals can exist in multiple oxidation states and chemical forms, and the toxicity of metals in PM is likely related to these characteristics. The aim of this proposal is to develop a new approach to simultaneously determine the oxidation state and chemical speciation for a suite of PM metals that are linked with enhanced toxicity: V, Ni, Zn, Cu, Fe, Cr, and Mn. This approach will use a combination of direct measurements and thermodynamic equilibrium modeling to determine the speciation of metals in PM. The metal speciation will be combined with ROS activity measurements to provide unprecedented insight into the chemical species in PM most likely to induce oxidative stress. Once this approach is validated in the laboratory, it will be applied to characterize the toxicity of PM metals in an urban environment. Metal speciation is strongly affected by both the pH and oxidation-reduction potential (ORP). This study will significantly advance understanding of metal speciation in PM because it will directly account for the pH and ORP in atmospheric particles. This represents the first study to link metal speciation in PM with these two controlling variables. The new approach will ultimately be developed for widespread application to future studies, including potential applications to archived PM data sets. This also represents the first study to link ROS activity with simultaneous determinations of metal oxidation state and speciation in PM. This research will provide significant insight into the sources and processes that influence PM toxicity. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.