Superoxide Release from Macrophages upon Exposure to Secondary Organic Aerosols, Biomass, and Plastic Burning Particulate Matter

We then define the activation threshold as the dose at which cells exhibit a clear increase in superoxide production. Limonene SOA is found to induce the largest amount of superoxide release (∼32 μM) but has the largest activation threshold of 300 μg mL^–1. Naphthalene and toluene SOA show smaller enhancement of superoxide production (∼2.5–7 μM) but have lower activation thresholds from 0.02 to 0.1 μg mL^–1.

Biomass burning PM does not show a clear activation threshold. Plastic burning PM shows a varied response depending on the type of plastic, with PM derived from poly(ethylene terephthalate) (PET) having the highest superoxide production (∼12 μM). The activation thresholds for polystyrene (PS), low-density polyethylene (LDPE), and high-density polyethylene (HDPE) burning PM are very low (∼0.01 μg mL^–1), while those for poly(vinyl chloride) (PVC) and PET burning PM are substantially higher (50–100 μg mL^–1).

Our findings highlight the importance of employing dose–response relationships and superoxide activation thresholds, rather than single-dose comparisons, to evaluate and compare the oxidative stress potential of different PMs more accurately.