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Abstract
Humans will again set foot on the moon. The moon is covered by a layer of fine dust, which can pose a respiratory hazard. We investigated the pulmonary toxicity of lunar dust in rats exposed to 0, 2.1, 6.8, 20.8 and 60.6 mg/m3 of respirable-size lunar dust for 4 weeks (6 h/day, 5 days/week); the aerosols in the nose-only exposure chambers were generated from a jet-mill ground preparation of a lunar soil collected during the Apollo 14 mission. After 4 weeks of exposure to air or lunar dust, groups of five rats were euthanized 1 day, 1 week, 4 weeks or 13 weeks after the last exposure for assessment of pulmonary toxicity. Biomarkers of toxicity assessed in bronchoalveolar fluids showed concentration-dependent changes; biomarkers that showed treatment effects were total cell and neutrophil counts, total protein concentrations and cellular enzymes (lactate dehydrogenase, glutamyl transferase and aspartate transaminase). No statistically significant differences in these biomarkers were detected between rats exposed to air and those exposed to the two low concentrations of lunar dust. Dose-dependent histopathology, including inflammation, septal thickening, fibrosis and granulomas, in the lung was observed at the two higher exposure concentrations. No lesions were detected in rats exposed to ≤6.8 mg/m3. This 4-week exposure study in rats showed that 6.8 mg/m3 was the highest no-observable-adverse-effect level (NOAEL). These results will be useful for assessing the health risk to humans of exposure to lunar dust, establishing human exposure limits and guiding the design of dust mitigation systems in lunar landers or habitats.
Acknowledgements
This project was funded by the NASA Human Research Program. We gratefully acknowledge the Apollo Sample Curator for providing an Apollo 14 lunar regolith sample for this study. We thank the members of NASA-assembled Lunar Airborne Toxicity Assessment Group (LADTAG) and Non-Advocate Review Committee, for their advice on the lunar dust toxicity project, and L. Taylor and D. McKay for technical advice on mineralogy of lunar dust. Technical assistance from S. Bassett, S. Zalesak, S. Beck, C. Gonzalez, C. Garza, D. Martin, R. Miller, staffs of NASA JSC Clinical Laboratory and Histology Laboratory of the University Texas Medical Center (Houston) is also gratefully acknowledged. We also thank J. Krauhs and H. Garcia for editorial assistance.