Oxidative stress on plasmid DNA induced by inhalable particles in the urban atmosphere

Plasmid DNA assay is a newly-developed in vitro method to investigate bioreactivity of particles. In this paper, this method was used to study the bioreactivity of PM₁₀ (particulate matter with aerodynamic diameter of less than 10 μm) and PM_2.5 (particulate matter with aerodynamic diameter of less than 2.5 μm). Samples and dust storm particles were collected in 2001 in an urban area, a satellite city and a clean air area in Beijing. A big difference was found for oxidative DNA stress induced by different particulate matter (PM) samples, with the TM50 (particle mass causing 50% damage to DNA) values varying by a factor over 10. This was closely dependent on the sizes of particles as well as the variation in relative proportion of mineral matter. PM_2.5 samples generally impose larger oxidative stress on plasmid DNA than PM₁₀ samples. Airborne particles collected during dust storm episodes, usually with a higher proportion of mineral matter, have a much lower oxidative capacity than those collected during non-dust storm episodes. PM samples and their water-soluble fractions usually have similar biorcactivitics, demonstrating that oxidative capacity of Beijing airborne particles is mainly sourced from their water-soluble fractions.