Resolution of the mediators of in vitro oxidative reactivity in size-segregated fractions that may be masked in the urban PM10 cocktail

Abstract

PM10 (particulate matter 10μm or less in aerodynamic diameter) has consistently been linked with adverse human health effects, but the physicochemical properties responsible for this effect have not been fully elucidated. The aim of this work was to investigate the potential for carbon black (CB) particles and PM to generate ROS (Reactive Oxygen Species) and to identify the physicochemical properties of the particles responsible for in vitro oxidative reactivity (OR). PM10 was collected in 11 size fractions at a traffic site in Swansea, UK, using an Electrical Low Pressure Impactor (ELPI). The PM physicochemical properties (including size, morphology, type, and transition metals) were tested. The plasmid scission assay (PSA) was used for OR testing of all particles. The ultrafine and fine PM fractions (N28–2399; 28–2399nm) caused more DNA damage than coarse PM (N2400–10,000), and the increased capacity of the smaller particles to exhibit enhanced (OR) was statistically significant (p<0.05). The most bioreactive fraction of PM was N94–155 with a toxic dose (TD50; mass dose capable of generating 50% plasmid DNA damage) of 69μg/ml. The mean TD35 was lower for PM than CB particles, indicating enhanced OR for PM. A difference between CB and PM in this study was the higher transition metal content of PM. Zn was the most abundant transition metal (by weight) in the ultrafine–fine PM fractions, and Fe in the fine–coarse PM. Through this comparison, part of the observed increased PM OR was attributed to Zn (and Fe). In this study PM-derived DNA damage was dependent upon; 1) particle size, 2) surface area, and 2) transition metals. This study supports the view that ROS formation by PM10 is related to physicochemistry using evidence with an increased particle size resolution.