Production of hydroxyl radicals from Fe-containing fine particles in Guangzhou, China

Abstract Reactive oxygen species (ROS) production from ambient fine particles has been correlated with the soluble transition metal content of PM 2.5 , which also has clear association with particle-mediated cardiopulmonary toxicity. Hydroxyl radical ( OH) is the most harmful ROS species through chemical reactions of redox-active particle components. Atmospheric Fe, as the dominant species of the transition metals in the atmosphere, is associated with OH generation in ambient particle extracts. Our results revealed that Fe-containing particles (18,730 in total number) contributed approximately 3.7% on average to all detected particles throughout the summer and winter sampling period in Guangzhou, which was clustered into four distinct particle classes, including Fe-rich, Metal-rich, NaK-rich and Dust-rich. Fe-rich class was the dominant one with a fraction of 61%, followed by Dust-rich (14%), Metal-rich (13%). and NaK-rich (12%). The iron oxide was enriched in the Fe-rich class. OH generation induced by Fe-containing fine particles collected in Guangzhou (GZ) was quantified in a surrogate lung fluid (SLF), and it was found that Fe-containing fine particles were generally much reactive in generating OH in the presence of four antioxidants (200 μM ascorbate, 300 μM citrate, 100 μM reduced l -glutathione, and 100 μM uric acid). The annual average OH amount produced in our samples was 132.98 ± 27.43 nmol OH mg −1 PM 2.5 . OH production had a clear seasonal pattern with higher amount in summer and lower in winter. By measuring the amount of total and SLF-soluble metal in our PM 2.5 samples using ICP-MS, we found that ROS activities were associated with the ionizable Fe through Fenton type reactions in the Guangzhou PM 2.5 . Expected burdens of PM 2.5 derived OH in human lung lining fluid suggests that typical daily particulate matter exposure in Guangzhou is already a concern, and it could produce much higher levels of OH, leading to higher cytotoxicity.