title: Estimate of safe human exposure levels for lunar dust based on comparative benchmark dose modeling.
abstract: Brief exposures of Apollo astronauts to lunar dust occasionally elicited upper respiratory irritation; however, no limits were ever set for prolonged exposure to lunar dust. The United States and other space faring nations intend to return to the moon for extensive exploration within a few decades. In the meantime, habitats for that exploration, whether mobile or fixed, must be designed to limit human exposure to lunar dust to safe levels. Herein we estimate safe exposure limits for lunar dust collected during the Apollo 14 mission. We instilled three respirable-sized (∼2 μ mass median diameter) lunar dusts (two ground and one unground) and two standard dusts of widely different toxicities (quartz and TiO₂) into the respiratory system of rats. Rats in groups of six were given 0, 1, 2.5 or 7.5 mg of the test dust in a saline-Survanta® vehicle, and biochemical and cellular biomarkers of toxicity in lung lavage fluid were assayed 1 week and one month after instillation. By comparing the dose--response curves of sensitive biomarkers, we estimated safe exposure levels for astronauts and concluded that unground lunar dust and dust ground by two different methods were not toxicologically distinguishable. The safe exposure estimates were 1.3 ± 0.4 mg/m³ (jet-milled dust), 1.0 ± 0.5 mg/m³ (ball-milled dust) and 0.9 ± 0.3 mg/m³ (unground, natural dust). We estimate that 0.5-1 mg/m³ of lunar dust is safe for periodic human exposures during long stays in habitats on the lunar surface.
authors.affiliation: Space Toxicology Office, National Aeronautics and Space Administration Johnson Space Center, Houston, TX 77058, USA. john.t.james@nasa.gov
authors.forename: John T
authors.initials: JT
authors.lastname: James
authors.forename: Chiu-Wing
authors.initials: CW
authors.lastname: Lam
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Santana
authors.forename: Robert R
authors.initials: RR
authors.lastname: Scully
mesh_terms: D000818:Animals; D015415:Biomarkers; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry / Q000166:cytology; D002452:Cell Count; D004391:Dust; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000378:metabolism; D008954:Models, Biological; D016081:Moon; D016273:Occupational Exposure / Q000009:adverse effects*; D011791:Quartz / Q000633:toxicity; D051381:Rats; D011916:Rats, Inbred F344; D026361:Reactive Nitrogen Species / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D018570:Risk Assessment; D014025:Titanium / Q000633:toxicity
chemical_list: D015415:Biomarkers; D004391:Dust; D026361:Reactive Nitrogen Species; D017382:Reactive Oxygen Species; D011791:Quartz; C009495:titanium dioxide; D014025:Titanium; D007770:L-Lactate Dehydrogenase