Inter-continental variability in the relationship of oxidative potential and cytotoxicity with PM mass.

Most fine ambient particulate matter (PM)-based epidemiological models use globalized concentration-response (CR) functions assuming that the toxicity of PM is solely mass-dependent without considering its chemical composition. Although oxidative potential (OP) has emerged as an alternate metric of PM toxicity, the association between PM mass and OP on a large spatial extent has not been investigated. In this study, we evaluate this relationship using 385 PM samples collected from 14 different sites across 4 different continents and using 5 different OP (and cytotoxicity) endpoints. Our results show that the relationship between PM mass vs. OP (and cytotoxicity) is largely non-linear due to significant differences in the intrinsic toxicity, resulting from a spatially heterogeneous chemical composition of PM. These results emphasize the need to develop localized CR functions incorporating other measures of PM properties (e.g., OP) to better predict the PM-attributed health burdens.