Adenine oxidation by pyrite-generated hydroxyl radicals

Pyrite (FeS2), the most common metal sulfide mineral associated with coal and metal mine waste, has been shown to generate hydrogen peroxide (H2O2) [1,2] and hydroxyl radicals (？OH) [3,4] when placed in water. In the presence of dissolved molecular oxygen, ferrous iron associated with pyrite can form superoxide anion (O2？)- (eq. 1), which reacts with ferrous iron to form H2O2 (eq. 2) and eventually ？OH (Fenton reaction, eq. 3).The formation of reactive oxygen species (ROS) such as H2O2 and ？OH is significant because of their reactivity; ？OH will typically react with nearly all molecules in aqueous solution at diffusion-limited rates [5]. Their extreme reactivity has been implicated in causing or contributing to disease and aging in humans [6-10]. Particles other than pyrite such as asbestos [11] and quartz [10] have also been shown to induce the formation of ？OH in lung cells that have been exposed to the particles. The particulate-induced formation of ？OH has been linked with oxidative stress [12,13] and genotoxicity [14,13]. Hence, ？OH formation in vitro and in vivo has been used as an indicator for mineral-induced toxicity potential [14,13,12,16,6].The extremely short half-life of ？OH hinders detection and quantification of ？OH concentrations directly [5]. Instead, detection requires the reaction of ？OH with a target molecule. Upon reaction, characteristics of the target molecule such as light absorption [2], fluorescence [17-19], or electron spin resonance [20-23] may change. The detection of these changes is then used to determine the presence and concentration of ？OH and other ROS. In the presence of cells or in tissue, the products of particle-induced radical oxidation include DNA strand-breaks [24,14], RNA degradation [4], and nucleobase oxidation [25-27]. Nucleic acids react with ？OH by hydrogen abstraction at the sugar or addition to the bases, both resulting in radical moieties and de-polymerization [28,29,24]. Oxidized base reaction products are typicall