Complexation of Iron and Copper in Ambient Particulate Matter and Its Effect on the Oxidative Potential Measured in a Surrogate Lung Fluid

We investigated the complexation state of atmospheric iron and copper and its impact on the oxidative potential (OP) of ambient PM_2.5 (PM, particulate matter). A novel fractionation scheme was developed to segregate three different fractions of Fe and Cu present in ambient PM_2.5: (i) complexed with hydrophobic organic compounds, (ii) complexed with hydrophilic organic compounds, and (iii) free or inorganic metal fraction. A solid phase extraction (C-18) column was used to separate these fractions. The fractionation scheme applied to the ambient PM_2.5 samples collected from an urban site showed that up to 70–90% of water-soluble Fe and Cu were complexed with the organic compounds. The capability of the complexes of Fe­(II) and Cu­(II) with Suwanee river fulvic acid (SRFA), a proxy for the atmospheric organic compounds, to generate reactive oxygen species (ROS) (·OH and H₂O₂) in a surrogate lung fluid (SLF) was measured. The complex of Fe–SRFA showed a strong synergistic effect in the generation of ·OH in SLF, while that of Cu–SRFA showed an additive effect. Overall, our results indicate that organic complexation of the metals in ambient PM could significantly alter their OP and needs to be considered while assessing their health impacts.