Hydroxyl Radical Generation by Respirable Lunar Analogue Particulate Matter and their Long Term-Persistence in Simulated Lung Fluid

Crewed missions to the Moon and other airless bodies are an important focus of NASA's future mission planning and numerous daunting challenges will have to be resolved before humans are able to explore these worlds safely. Lunar dust represents one of the many hazards that humans will have to contend with when conducting missions on its surface. Previous work has involved the assessment of reactive oxygen species (ROS) generation by various lunar simulants including JSC-1A, NU-LHT-2M, and OB-1. We conducted experiments using electron paramagnetic resonance (EPR) spectroscopy and the spin-trap compound 5,5-Dimethyl-1-Pyrroline-N-Oxide (DMPO), which can trap hydroxyl radicals (OH*) generated in solution. Our results indicate that mineral phases analogous to those found in lunar dust can generate micromolar concentrations of highly reactive OH*, and that iron-silicate minerals are particularly reactive in this regard (Fig. 1). OH* is suspected to be toxic to human lung tissues, has been linked to pulmonary diseases such as bronchogenic carcinoma, and would therefore be of high concern to future astronauts. We will report on the development of EPR-based techniques for assessment of OH-radical production, and the results of our measurements on lunar analogue minerals. We are also conducting lunar analogue mineral (olivine) dissolution experiments in simulated lung fluid (SLF) in order to understand the long-term bio-persistence of lunar minerals in the human lung. Olivine was chosen due to its high reactivity relative to other mineral phases (Fig. 1). Preliminary results indicate that olivine dissolution in SLF is about two orders of magnitude slower than in 0.1 M HCl solution. Inhaled dust particles containing olivine, among other mineral phases, would stay in the human lung for extended periods of time and therefore may have long-term health implications. It is important to understand what effects lunar dust may have on astronauts if dust mitigation methods prove to be inadequate on future missions. Our work furthers understanding of the chemical properties of lunar dust reactivity, which could lead to medical advancements in treating those exposed to lunar dust.

Figure 1. OH* generated per m² for various mineral phases in our experiments.