Oxidative stress mediated by production of reactive oxygen species (ROS) is a hypothesized mechanism for particulate matter related health effects. Fe(II) is a key player in ROS formation in aqueous solutions, including surrogate lung fluid (SLF) solutions containing lung antioxidants, chelators and the ionic strength of lung-lining fluid. Humic-like substances (HULIS) from biomass burning aerosols interacts with transition metals, but its effect on ROS formation is not well known. We use Fulvic Acid (FA) as a surrogate for HULIS and investigate its effect on OH formation from Fe(II) in SLF. In the absence of FA, ascorbate and citrate enhance OH production from Fe(II). FA introduces competing ligands that strongly chelate Fe. A series of experiments were performed to probe the effect of FA on Fe-mediated ROS formation. For the first time, a chemical kinetics model was developed to explain the behavior of the Fe(II), SLF and FA system. The model combined with experimental results are used to find best-fit rate coefficients for key reactions: Fe-mediated reduction of O2 to O2-, and the Fenton reaction, (destruction of H2O2 to produce OH). The results indicate FA enhances Fe-mediated reduction of O2 to O2- and the destruction of H2O2 to OH by factors of 30 -80; chelation by citrate produces similar enhancements. The resulting kinetics model agrees well with both the experimental results and thermodynamic calculations of chemical speciation for 0 and 5 µg/mL FA. Both the kinetics and thermodynamic models are less successful at predicting further enhancements to OH formation at higher FA. Addition of Fe to ambient biomass burning aerosol (BBA) is also shown to enhance OH formation relative to the sum of BBA and Fe separately.

Kinetics, thermodynamics, HULIS, metal solubility and the interplay of superoxide, hydroxyl radical and hydrogen peroxide

254th National Meeting (2017)

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