Determination of metal-based hydroxyl radical generating capacity of ambient and diesel exhaust particles

Abstract

Numerous studies have suggested the association of reactive oxygen species (ROS) with adverse health effects derived from exposure to airborne particulate matter (PM) and diesel exhaust particles (DEP). This redox activity has been attributed to both inorganic and organic species present in these particles, but a clear distinction has not been established between the contribution of each. This article describes an application of an analytical procedure, based on the reaction of salicylic acid with hydroxyl radical to form dihydroxybenzoate (DHBA) isomers, to measure transition metal-based redox activity associated with ambient and diesel exhaust particles. In the procedure, ascorbic acid (AA) is used as electron source for reduction of metal ions and oxygen to generate superoxide, which is further reduced to hydroxyl radical in the presence of transition metal ions. Hydroxyl radical reacts with salicylate to generate DHBA isomers, which are measured by high-performance liquid chromatography (HPLC) with electrochemical detector. Both copper (Cu) and iron (Fe) ions generated DHBA isomers in a concentration-dependent manner but at different rates. The procedure was applied to DEP and ambient particles and the results showed Cu ion to be the major contributor to DHBA formation. The procedure provides a quantitative measure of transition metal-based redox activity associated with ambient samples with different physicochemical properties.

Acknowledgment

We gratefully acknowledge the ICP-MS analyses conducted by Dr. Amir Liba of the Department of Chemistry and Biochemistry at UCLA.

Declaration of interest: The research described in this article has been funded in part by the U.S. Environmental Protection Agency through grant CR-82805901 to UCLA. However, it has not been subjected to the agency’s required peer and policy review and therefore does not necessarily reflect the views of the agency and no official endorsement should be inferred. The work has also been supported by the Asthma and Outdoor Air Quality Consortium of the South Coast Air Quality Management District (sponsor award 040621), and by the Southern California Environmental Health Science Consortium (SCEHSC), 5P30 ES07048 (funded by NIEHS).