Reactive Oxygen Species Generation by Lunar Simulants in Simulated Lung Fluid

Abstract:

The current interest in human exploration of the Moon and other airless planetary bodies has rekindled research into the harmful effects of Lunar dust on human health. Our team has evaluated the spontaneous formation of Reactive Oxygen Species (ROS; hydroxyl radicals, superoxide, and hydrogen peroxide) of a suite of lunar simulants when dispersed in deionized water. Of these species, hydroxyl radical reacts almost immediately with any biomolecule leading to oxidative damage. Sustained production of OH radical as a result of mineral exposure can initiate or enhance disease. The results in deionized water indicate that mechanical stress and the absence of molecular oxygen and water, important environmental characteristics of the lunar environment, can lead to enhanced production of ROS in general. On the basis of the results with deionized water, a few of the simulants were selected for additional studies to evaluate the formation of hydrogen peroxide, a precursor of hydroxyl radical in Simulated Lung Fluid. These simulants dispersed in deionized water typically produce a maximum in H₂O₂ within 10 to 40 minutes. However, experiments in SLF show a slow steady increase in H₂O₂ concentration that has been documented to continue for as long as 7 hours. Control experiments with one simulant demonstrate that the rise in H₂O₂ depends on the availability of dissolved O₂. We speculate that this continuous rise in oxygenated SLF might be a result of metal ion-mediated oxidation of organic components, such as glycine in SLF. Ion-mediated oxidation essentially allows dissolved molecular oxygen to react with dissolved organic compounds by forming a metal-organic complex. Results of separate experiments with dissolved Fe, Ni, and Cu and speciation calculations support this notion.