Generation of Reactive Oxygen Species Mediated by Humic-like Substances in Atmospheric Aerosols

摘要

Paniculate matter (PM)-mediated reactive oxygen species (BOS) generation has been implicated in health effects posed by PM. Humic-like substances (HULIS) are an unresolved mixture of water-extracted organic compounds from atmospheric aerosol particles or isolated from fog/doudwater samples. In this study, we use a cell-free dithiothreitol (DTT) assay to measure ROS production mediated by HUUS. The HUUS samples are isolated from aerosols collected at a rural location audasuburban location in the Pearl River Delta, China. In our experiments, ROS activities by residue metal ions in the HUUS fraction are suppressed by including a strong chehting agent in the DTT assay. Under conditions of DTT consumption not erceding 90%,the HULIS-catalyied oxidation of DTT follows the zero-order kinetics with respect to DTT conoentration,and the rate tfDTToxidalionis proportional to the dose of HULIS.The ROS activity of the aerosol HULIS,on a per unit mass basis is 2% of the ROS activity by a reference quinone compound, l,4-naphthoquinone and exceeds that of twoaquatic fulvic acids.The HUL1S fraction in the ambient samples tested extubits comparable ROS activities to the organk sohent exrnctable fraction wtoeh would contam compounds such as quinones, a known organic compound class capable of catalyzing generation of ROS in cells. HULIS was found to be the major redo* active constituent of the water-ertractable organic fraction in PM.It is plausible that HULIS contains reversible redox sites, thereby senring as electron carriers to catalyze the formation of ROS. Our work suggests mat HUUS could be an active PM component in generating ROS and former work is wanwted to characterize its redox properties.