Chemical speciation and toxicity assessment of size-fractionated particulate matter from household solid fuel combustion

Particulate matter (PM) produced from cooking and heating with solid fuels is one of the most important indoor air pollutants and is involved in a number of adverse health effects such as premature deaths and increased mortality of infants and other sensitive population. However, the mechanisms of PM related health effects are still incompletely understood, but a hypothesis under investigation is that many of the adverse health effects may derive from oxidative stress, initiated by the formation of reactive oxygen species (ROS) at the surface of and within target cells. Size-fractionated (i.e. >2.5 μm; 1.0-2.5; 0.5-1.0; 0.25-0.5 and <0.25 μm in diameter) PM samples were collected from representative households used different solid fuels (coal, dung cake, wood, dry leaves and agricultural residues) and were chemically analyzed for elemental carbon (EC), organic carbon (OC), water soluble organic carbon (WSOC) and polycyclic aromatic hydrocarbons (PAHs). The toxicity of the samples was evaluated by means of the dithiothreitol (DTT) activity assay and was related to their chemical speciation by means of correlation analysis. The results indicated a higher redox activity on a per PM mass basis for ultrafine (< 0.25 μm) particles compared to those of larger sizes. The PM redox activity was highly correlated with the organic carbon (OC) content of PM.