Oxidative potential induced by metal-organic interaction from PM_2.5 in simulated biological fluids

The oxidative potential (OP) of fine particulate matter (PM_2.5) has recently been proposed as a metric that may prove more indicative of human health effects than the routinely measured PM_2.5 concentration. Observations of exposure to PM_2.5 show most OP are originated from the contribution of transition metals and organics, but the pertinent coupling mechanisms are unclear. Here, we report laboratory observations in four simulated biological fluids (i.e., simulated saliva, surrogate lung fluid, artificial lysosomal fluid, and synthetic serum) that reveal OP of PM_2.5 are significantly induced by prevalent metal complexes formed with nitrogen- and oxygen-containing compounds in low acid environments. Analyses of mass spectra and interaction factors indicate that organic-metal mixture effect in PM_2.5, leading to synergistic, additive to antagonistic effects, which may serve as the dominant mechanism for this OP formation. A metal-organic mixtures origin for OP could explain why PM_2.5 emission controls should emphasize the reduction of key toxic components, rather than just PM_2.5 mass concentration control. SYNOPSIS: This study has investigated the oxidative potential of inhaled atmospheric particulate matter (PM) in four simulated biological fluids, which highlight the importance of metal-organic complexes to the formation of oxidative potential (OP).