Generation of Hydroxyl Radicals from Ambient Fine Particles in a Surrogate Lung Fluid Solution

While it has been hypothesized that the adverse health effects associated with ambient particulate matter (PM) are due to production of hydroxyl radical (center dot OH), few studies have quantified center dot OH production from PM. Here we report the amounts of center dot OH produced from ambient fine particles (PM25) collected in northern California and extracted in a cell-free surrogate lung fluid (SLF). On average, the extracted particles produced 470 nmol center dot OH mg(-1)-PM2.5 during our 15-month collection period. There was a clear seasonal pattern in the efficiency with which particles generated center dot OH, with highest production during spring and summer and lowest during winter. In addition, nighttime PM was typically more efficient than daytime PM at generating center dot OH. Transition metals played the dominant role in center dot OH production: on average (+/-sigma), the addition of desferoxamine (a chelator that prevents metals from forming center dot OH) to the SLF removed (90 +/- 5)% of center dot OH generation. Furthermore, based on the concentrations of Fe in the PM25 SLF extracts, and the measured yield of center dot OH as a function of Fe concentration, dissolved iron can account for the majority of center dot OH produced in most of our PM2.5 extracts.