Numerous studies have shown an association between increased levels of particulate matter (PM) and the exacerbation of lung diseases. The exact means by which PM produces these effects remain unclear. Generation of reactive oxygen species such as the hydroxyl radical (OH), is one of the hypothesized mechanisms. However, the importance OH of production by PM remains uncertain due to a lack of sensitive and selective methods for its determination.

In this work, a highly-sensitive fluorescence-based technique was employed to quantify the magnitude of .OH generated by a wide range of airborne particulate matter. The generated .OH was measured in the presence and absence of biological electron donor. Little or no production of .OH was observed in the absence of the added electron donor. For some but not all particles, .OH production was increased substantially when a biological electron donor was present. No detectable .OH was produced by kaolinite or silica.

The mechanism(s) of .OH generation by airborne particulate matter were investigated. The presence of dioxygen, hydrogen peroxide, superoxide and metal chelators significantly affected .OH production by the particles. The results indicate that metals and organic constituents are involved in .OH production by particles and occur through both homogeneous and heterogeneous reactions.

The effect of different airborne particles on .OH generation in the presence of two different cell lines, lung epithelial cells (BEAS-2b) and mouse epidermal cells (JB6) were investigated. In addition, two different toxicological methods were employed to investigate cell viability in the presence of different airborne particles. Based on our results, some .OH production was observed in the presence of these cell lines when exposed to diesel particulate matter and urban dust, but rates of cell death did not correlate with the .OH production rate. Further, silica particles, which exhibited no evidence of .OH production, produced the most rapid cell death.

On the other hand, both cell death and hydroxyl radical formation were dramatically enhanced when an external biological reductant, NADPH, was added to a suspension of cells and urban dust. In this situation, the high flux of .OH is the likely factor causing cell death.