The inhalation of powdered minerals poses a threat to humans on manned missions to other bodies in our solar system. With rising interest in pursuing manned missions to the Moon, it is imperative that research be done in order to assess the hazards associated with lunar regolith. EPR (Electron Paramagnetic Resonance) spectroscopy is a technique used to detect the presence of unpaired electrons in oxidative radical species produced from mineral slurries and transition metals. Mixing powdered minerals with solutions is known to produce hydroxyl radicals via Fenton reaction (1,2). The Fenton reaction is a cyclic reaction in which hydrogen peroxide oxidizes ferrous iron to ferric iron and produces hydroxyl ions and radicals. These radicals are then able to move throughout the body and eventually induce cell apoptosis (3). Currently, we are using albite, forsterite, and quartz for our experiments. While these minerals may not be ideal lunar analogues, they are known to produce hydroxyl radicals in solution, and are readily obtained from commercial suppliers. For EPR measurement of mineral powders, the three minerals were pulverized in a Retsch agate ball mill grinder for 5 min at 350 rpm. The samples were then analyzed using a Magnettech MS400 X-band EPR spectrometer. EPR spectra from albite display features consistent with an aluminum oxygen radical bridge (4), as well as ferric iron, likely present as a contaminant. Quartz spectra displayed a peak similar to albite in the same region as the ferric iron contaminant. Further studies will be conducted in an attempt to resolve the species identification. Forsterite displayed the largest spectral absorption from ferric iron of all of the studied minerals. For measurement of OH-radical production, albite, forsterite, quartz, and CSM-CL (Colorado School of Mines-Colorado Lava) lunar simulant were pulverized for 0, 5, 15, and 30 minutes. Approximately 200 mg of each pulverized sample was incubated in a 50 μM DMPO (5,5-dimethyl-1-pryrroline-N-oxide) solution for 5, 15, and 30 minutes. The resulting mineral slurries were then filtered with a 0.45 μM syringe. The filtrate was then analyzed for OH-radical concentration using the EPR spectrometer. Hydroxyl radical concentrations were the highest for forsterite, followed by CSM-CL, and quartz. Albite did not produce OH-radical; we will verify this result in the near future. Our expectation was that hydroxyl radical concentration would rise as a function of incubation time and grind time (2). However, it was observed that this was not the case, possibly due to surface radical annealing reactions that take place during the grinding process. Near term plans include hydroxyl radical concentration measurements in SLF (simulated lung fluid), which will provide a better assessment of radical production in a biological fluid simulant.
(1)Turci, F. et al. (2015), Astrobiology (2) Hurowitz, J. et al. (2007), Earth Planet. Sci. Lett.
(3) Harrington et al., (2012), Geochem. Trans. (4) Petrov, I. et al. (1989), Am. Mineral.