Evaluate the impact of PM in different macrophage types under the influence of seasonal changes and anthropogenic activities.

Particulate matter (PM) in air pollution has become a major environmental concern due to its potential health impacts, which vary seasonally and with human activities. While PM is often monitored for concentration, its chemical composition is equally important, especially regarding its effects on the immune system, which remain poorly understood. This study investigates the biological effects of PM2.5 on macrophages collected in different seasons and during COVID-19 restrictions in Taiwan. The experiments revealed significant seasonal variations in metal and polycyclic aromatic hydrocarbons (PAHs) content in PM2.5, with summer having the highest metal levels and winter the highest PAHs. Exposure to PM2.5 increased cell biotoxicity, correlating with higher PM2.5 concentrations. Further analysis showed that PM2.5 exposure polarized macrophages into the M1 type, triggering inflammatory cytokines, increased ROS levels, cell growth arrest, and apoptosis. Notably, PM2.5 from summer exhibited the highest biotoxicity. The study also identified four metals (Fe, Ti, Co, Sb) as key contributors to biotoxicity. PM2.5 collected during COVID-19 Level 2 Alert showed higher concentrations of these metals, resulting in greater toxicity to macrophages. This research underscores how seasonal changes and human activities influence PM2.5's impact on the immune system, contributing to air pollution control efforts.