The term "technogenic particles" is used to describe airborne particulate matter (PM) produced during industrial processes. The most common of these is "fly ash" produced during combustion of solid and liquid fossil fuels. Coal fly ash is derived from the mineral and metal contaminants within coal in which particles (1) are distinctly spherical in shape, (2) are composed of 60-90% glass, and (3) often contain a range of contaminant metals. In addition, particles may contain recrystallized minerals, mainly quartz, mullite, and hematite; both quartz and mullite are recognized respiratory hazards. Fly ash particles from both UK and Chinese coal-burning power stations were characterized by field emission-scanning electron microscopy (morphology and size), x-ray diffraction (crystallinity and minerals), and inductively coupled plasma-mass spectroscopy (elemental composition). PM(10) samples were separated from bulk fly ash by a dry dust separator system. The plasmid scission assay (PSA) was used to measure damage produced by fly ash to plasmid bacteriophage PhiX174 RF DNA. The supercoiled DNA was either damaged or severely damaged by reactive oxygen species (ROS) generated by the fly ash at different concentrations. Geochemical analyses confirmed that the fly ash particles are predominantly glass, with a minor component of the minerals quartz, hematite, and mullite. Fly ash particles also contained a range of metals contaminants; however, these were mostly bound into the glass with only a small proportion potentially bioaccessible. PSA data showed that fly ash exhibited significant oxidative capacity when compared to negative control (MB H(2)O), indicating that ROS are likely to be the driving force underlying fly ash bioreactivity.