Toxicity Decreases with the Decay of Environmentally Persistent Free Radicals in Particulate Matter from Incomplete Solid Fuel Burning

Abstract

Environmentally persistent free radicals (EPFRs) have been linked to the generation of reactive oxygen species (ROS) and adverse health effects. However, there remains a knowledge gap regarding the dynamic changes in reactivity and toxicity during the decay process of EPFRs emitted from incomplete solid fuel burning, which are identified as a primary source of EPFRs. Here, we report the decay behavior of EPFRs in particulate matter (PM) emitted from typical solid fuel burning and the associated ROS generation and cytotoxic effects. The EPFRs in freshly produced PM first undergo rapid exponential decay with lifetimes ranging from 15 to 97 h and are categorized as fast-decay EPFRs. The relative content of fast-decay EPFRs was 40.5 ± 15.3%, while the remaining portion, defined as slow-decay EPFRs, displayed an extremely slow rate of decay. ROS generation and cytotoxicity decreased by 38.8 ± 11.4% and 62.5 ± 12.6%, respectively, following the depletion of fast-decay EPFRs, which were further demonstrated to be responsible for the variations in PM reactivity and toxicity. These new findings underscore the importance of considering the decay process of EPFRs in assessments of PM toxicity.