Effect of Iron on the Oxidative Capacity of Carbonaceous Nanoparticles

Inhalation of ambient particulate matter (PM2.5) emitted during combustion of fuels has negative impacts on human health. Triggered in part by the generation of reactive oxygen species (ROS) that lead to oxidative stress, significant gaps exist in the understanding of the detailed chemistry of these detrimental effects. Trace metals and carbonaceous material of the nanometer-sized particles contained in PM2.5 have been implicated as key players in causing these effects. Here, the role of Fe is investigated with carbonaceous nanoparticles (CNP) while mimicking simple cellular conditions. By adding environmentally representative and controlled concentrations of Fe(II) or Fe(III) to slurries of different types of CNP, their roles in inducing oxidative stress is monitored with the cellular antioxidant glutathione (GSH). Unique to this study is the use of (i) ligands to solubilize otherwise insoluble Fe(III) and (ii) a recently modified simple fluorometric assay for GSH analysis. Generally, results show that CNP and Fe have a synergistic effect on oxidative potential (OP), which is strongly dependent on the type of CNP and weakly dependent on the strength of the Fe-ligand complex. Highest reactivities were observed with graphene and Fe(III)/Fe(II) complexed with the strongest ligand, namely ethylenediaminetetraacetic acid (EDTA). These results suggest that Fe complexed to strong ligands in the presence of graphene-rich CNP can be redox active and lead to the production of detrimental ROS, providing new information regarding the toxicity of PM in a biologically relevant system and thus help policy makers formulate science-based control measures that benefit public health