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| Gene Cernan, soon after the completion of the third and last EVA of Apollo 17, also the final EVA of the Apollo program. His moon suit carries a heavy accumulation of lunar dust, as does his skin. Three years earlier mission planners had been worried about astronauts, along with their spacecraft, sinking into the accumulation of dust on the surface. After Apollo, and decades later, mitigating the clinging affect of dust on equipment and human life remains a problem evading easy solution [Schmitt/AS17-145-22224]. |
Dag Linnarsson, et al.
Karolinska Institutet, Stockholm/ESA
Karolinska Institutet, Stockholm/ESA
Abstract - The formation, composition and physical properties of lunar dust are incompletely characterized with regard to human health. While the physical and chemical determinants of dust toxicity for materials such as asbestos, quartz, volcanic ashes and urban particulate matter have been the focus of substantial research efforts, lunar dust properties, and therefore lunar dust toxicity may differ substantially. In this contribution, past and ongoing work on dust toxicity is reviewed, and major knowledge gaps that prevent an accurate assessment of lunar dust toxicity are identified. Finally, a range of studies using ground-based, low-gravity, and in situ measurements is recommended to address the identified knowledge gaps. Because none of the curated lunar samples exist in a pristine state that preserves the surface reactive chemical aspects thought to be present on the lunar surface, studies using this material carry with them considerable uncertainty in terms of fidelity. As a consequence, in situ data on lunar dust properties will be required to provide ground truth for ground-based studies quantifying the toxicity of dust exposure and the associated health risks during future manned lunar missions.
Introduction - The current renewed interest in human exploration of the Moon is driven not only by an urge to expand the human presence to other celestial bodies, but also by genuine scientific interest. Many aspects of the origin and evolution of the Earth and the other bodies in our solar system remain unclear. The Moon is thought to hold important information about the time when our own planet was formed, and humans remain capable of much more intelligent and adaptive exploration of the Moon than even the most sophisticated robotic and remote-controlled devices (e.g., Crawford et al., 2012). Identification and retrieval of representative or exotic mineral specimens, and drilling deep into the lunar subsurface are examples of tasks for which astronauts are superior to machines. The most compelling argument for human exploration is the unique ability of humans to identify and quickly assess the unexpected, enabling real time adjustment of a pre-planned exploration strategy.
Although humans have landed on and returned from the Moon during the Apollo era, it is still a formidable challenge to secure the health and safety of astronauts during Moon missions. Challenges for future missions include long-term low- or microgravity, radiation exposure, and the maintenance of a number of life support systems during a much longer period than was the case during the Apollo flights (e.g., Cain, 2010, 2011).
One of the biggest challenges may be related to the presence of dust on the lunar surface. The ubiquity of fine dust particles on the surface of the Moon plays an important and often dual role in many aspects of human lunar exploration. On the one hand, identifying the mineralogical and chemical composition of the dust fraction of lunar soils can provide in situ geological context for both robotic and human landing sites. In addition, lunar dust may be an ideal starting material for a range of future in situ resource utilization activities on the Moon (e.g., Taylor et al., 2005), and dust is an important component of the lunar exosphere (Horanyi and Stern, 2011).
On the other hand, dust can adversely affect the performance of scientific and life-support instruments on the lunar surface. Fine dust was spread over all parts of the Apollo astronauts space suits, ending up in the habitat (Figure 1a), resulting in astronaut exposure times of several days. The Apollo astronauts reported undesirable effects affecting the skin, eyes and airways that could be related to exposure to the dust that had adhered to their space suits during their extravehicular activities, and was subsequently brought into their spacecraft (Figure 1b).
Dust exposure and inhalation could have a range of toxic effects on human lunar explorers, especially if longer exposure times become the norm during future manned exploration missions. There is therefore a need to assess the risks to health. The physical and chemical determinants of dust toxicity for terrestrial materials such as asbestos, quartz, volcanic ashes and urban particulate matter have been studied in great detail, and lunar dust simulant (synthesized from terrestrial volcanic material) has been found to exhibit toxic effects (Lam et al., 2002; Latch et al., 2008; Loftus et al., 2010). Unique features of actual lunar dust (described in more detail in section 3), resulting from its formation by (micro)meteoroid impacts and its extended radiation exposure in the absence of oxygen and humidity, could lead to toxic effects significantly exceeding those of simulants made from Earth materials. At present, the formation, composition and physical properties of lunar dust remain incompletely characterized with regard to human health.
In a micro-/hypo-gravity environment the risk of inhalation of dust is increased due to reduced gravity-induced sedimentation. Inhaled particles tend to deposit more peripherally and thus may be retained in the lungs for longer periods in reduced gravity as will be the case in a future lunar habitat (Darquenne and Prisk, 2008; Peterson et al., 2008). Inhalation of particles of varying size may affect the respiratory and cardiovascular systems in deleterious ways leading to airway inflammation and increased respiratory and cardiovascular morbidity (Frampton et al., 2006; Sundblad et al., 2002).
In this contribution, we review our knowledge of the physical chemistry determinants of dust toxicity, of the composition and size of lunar dust, and all aspects related to its toxicity. We identify a number of knowledge gaps that need to be filled to constrain the required extent of mitigation activities protecting astronauts from the potentially toxic effects of lunar dust during and after a stay on the Moon. We also recommend a range of future studies using ground-based, low-gravity, and in situ measurements on the lunar surface to better constrain lunar dust toxicity.
Although humans have landed on and returned from the Moon during the Apollo era, it is still a formidable challenge to secure the health and safety of astronauts during Moon missions. Challenges for future missions include long-term low- or microgravity, radiation exposure, and the maintenance of a number of life support systems during a much longer period than was the case during the Apollo flights (e.g., Cain, 2010, 2011).
One of the biggest challenges may be related to the presence of dust on the lunar surface. The ubiquity of fine dust particles on the surface of the Moon plays an important and often dual role in many aspects of human lunar exploration. On the one hand, identifying the mineralogical and chemical composition of the dust fraction of lunar soils can provide in situ geological context for both robotic and human landing sites. In addition, lunar dust may be an ideal starting material for a range of future in situ resource utilization activities on the Moon (e.g., Taylor et al., 2005), and dust is an important component of the lunar exosphere (Horanyi and Stern, 2011).
On the other hand, dust can adversely affect the performance of scientific and life-support instruments on the lunar surface. Fine dust was spread over all parts of the Apollo astronauts space suits, ending up in the habitat (Figure 1a), resulting in astronaut exposure times of several days. The Apollo astronauts reported undesirable effects affecting the skin, eyes and airways that could be related to exposure to the dust that had adhered to their space suits during their extravehicular activities, and was subsequently brought into their spacecraft (Figure 1b).
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| Figure 2. Steps of cell and tissue interaction with nano and micron-sized particles in the lung. When attained the alveolar space the particle may react with endogenous molecules (step 1). The particle may then be cleared out of the lung either through the mucociliary escalator (step 2) or through alveolar macrophage (AM) clearance (step 3). If reactive, AM activation will follow with release of several factors and recruitment of other immune cells (AM and polymorphonucleate cells, PMN), eventual cell death and establishment of permanent cycles of ingestion (step 4). This process produces chronic inflammation (step 5). Combined with the direct action of the particle (step 6) this will cause damage to the target cells (epithelial, endothelial). If the particle is nano-sized, it may easily escape from the lung to the pleura and to systemic circulation (step 7). |
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| Figure 3. The role of particle and cell derived free radicals and reactive oxygen species (ROS) in cell damage, oxidative stress and diseases. |
In a micro-/hypo-gravity environment the risk of inhalation of dust is increased due to reduced gravity-induced sedimentation. Inhaled particles tend to deposit more peripherally and thus may be retained in the lungs for longer periods in reduced gravity as will be the case in a future lunar habitat (Darquenne and Prisk, 2008; Peterson et al., 2008). Inhalation of particles of varying size may affect the respiratory and cardiovascular systems in deleterious ways leading to airway inflammation and increased respiratory and cardiovascular morbidity (Frampton et al., 2006; Sundblad et al., 2002).
In this contribution, we review our knowledge of the physical chemistry determinants of dust toxicity, of the composition and size of lunar dust, and all aspects related to its toxicity. We identify a number of knowledge gaps that need to be filled to constrain the required extent of mitigation activities protecting astronauts from the potentially toxic effects of lunar dust during and after a stay on the Moon. We also recommend a range of future studies using ground-based, low-gravity, and in situ measurements on the lunar surface to better constrain lunar dust toxicity.
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