Source-dependent variation in hydroxyl radical production by airborne particulate matter.

Epidemiological studies suggest exposure to airborne particles is responsible for a wide range of adverse health effects, potentially arising from particle-induced oxidative stress. A highly sensitive fluorescence method was employed to measure the production of hydroxyl radical by a broad range of particle types including urban dust, diesel particulate matter, coal fly ash, kaolinite, and silica. Little or no production of *OH was observed in the absence of an added electron donor or H202. In the presence of a biological electron donor (NADPH, 3 mM), the rate of *OH production (ROH) for 3 mg/mL of these particles varied from 23 nM s(-1) for diesel particulate matter (SRM 2975) to 0.20 nM s(-1) for coal fly ash (SRM 2689). No detectable *OH was produced by kaolinite or silica. Hydroxyl radical formation was eliminated under anaerobic conditions and in the presence of catalase, indicating that 02 and H202 are required for its generation. Partial inhibition of *OH formation by superoxide dismutase (SOD) was also observed in some cases, suggesting that superoxide (O2*-) is also involved. The metal chelator deferoxamine mesylate (DFX) in most cases suppressed *OH formation, but diethylenetriaminepentaacetic acid (DTPA) generally enhanced it, implicating metal ion reactions in OH generation as well. The dependence of ROH on NADPH concentration further implicates particle surface reactions in *OH formation. To our knowledge, these measurements provide the first quantitative estimate of ROH for a broad range of particle types.