Reactive oxygen species (ROS) such as peroxide, superoxide, and hydroxyl radicals are

generated intracellularly in cells or when exposed to exogenous toxicants. Results from

previous studies have demonstrated that prolonged exposure to excess ROS lead to

oxidative stress and induce DNA damages, some of which eventually leading to various

human diseases including cancers1. One of the major G oxidation products, 8-oxo-7,8-

dihydro-2'-deoxyguanosine (8-oxodG) was quantitated in the genomic DNA and in the

extracellular fluid of toxicants exposed cells, using LC-MS/MS method of high

sensitivity and selectivity. It may serve as biological dosimeters of exposure to toxicants

and for risk assessment, as well as help study the poorly understood chemical toxicology

of human exposure to airborne particulate matters, e.g. PM2.5.