The Lunar Airborne Dust Toxicity Assessment Group (LADTAG) consists of toxicologists, chemists, physicians, astronauts, and geologists from two NASA field centers and from outside the agency. The project research team is embedded in this group. Our research goal is to develop a toxicity database sufficient to support a defensible exposure standard for lunar dust. The primary focus is a dust inhalation standard; however, secondary goals include insight into the hazards posed by entry of the dust into the eye or abrasiveness to the skin. The group was chartered in September 2005, and in November, 2005 the NASA Chief Health and Medical Officer asked the LADTAG to assess the risk from lunar dust exposure and to develop a permissible exposure standard. The group has met five times since the charter meeting: February 2006, December 2006, November 2007, April 2009, and November 2009.
The work of the researchers has not only been reviewed by LADTAG experts outside the agency, it has also been reviewed by the Institute of Medicine, an expert Non-Advocate Review (NAR) Panel, and by and expert Standing Review Panel (SRP). These reviews, and the opinions that developed from them, have originated outside the agency. The NASA research team has responded to the expert opinions, and has adjusted its research plan accordingly.
One of the most difficult problems associated with this project is to determine the best way to activate the surfaces of lunar dust and characterize the persistence of that activation. Chemically reactive dusts are known to be more toxic, and the dust originally returned on Apollo missions has presumably lost its surface reactivity due to traces of oxygen in the preservation gas . Using primarily mineral coupons , stimulant dust [3,4], but also tiny amounts of authentic lunar dust [1,3], we have examined activation by proton bombardment (simulates solar wind), UV irradiation (solar flux), and by mechanical grinding (simulates effect of meteorite impacts). Our research to date points to mechanical damage during meteorite impact as the dominate means of surface activation; however, our conclusions are not final. The chemical index of activation has been either changes in the Raman spectrum  or detection of the hydroxyl radical by a terephthalate assay [1,5]. The persistence of induced chemical reactivity seems to be of the order of a few hours in an environment that would sustain life [1,2].
A key aspect of dust toxicity is the particle size distribution. We have investigated the chemical composition and size distribution of dust that was returned in Apollo sample containers [6,7], performed size-distribution studies of dust trapped in the fabric of Apollo-era spacesuits , and investigated the size distribution of dust from Apollo samples taken from the top surface layer of dust on the moon . Together these results suggest that a considerable portion of the dust that enters the lunar habitat will be in the respirable range, and will contain dust in the ultrafine to nano-size range (0.1 to 0.01 microns). Dust in this size range can be much more toxic than an equivalent mass of larger dust particles of the same chemical composition. Additionally, the presence of reduced iron particles (“nano-iron”) has been characterized because it is a major feature of lunar dust  and the presence of iron can increase the toxicity of dust.
Toxicity investigations in mice using intratracheal instillation of two lunar dust specimens have been completed in cooperation with scientists at the National Institute of Occupational Safety and Health. Preliminary data suggest that the lunar dust samples were only slightly more capable of eliciting toxic effects than TiO2, which is regarded as a non-toxic dust. These were not dusts that had been activated by any of the above procedures. One discovery during this research was that authentic lunar dust is extremely difficult to suspend in an aqueous medium. Solutions designed to mimic lung surfactant (the fluid lining the lungs) were much better at suspending the dust particles. Some of these data and a plan for integrating these findings with those from inhalation studies have been published . The inhalation studies will depend on dry extraction of dust particles in the respirable size range from larger Apollo samples. We have obtained 260 g of lunar dust returned by Apollo, and are perfecting a procedure to dry-fractionate it to a size that is respirable . Part of the remaining dust of larger size will be ground in an inert atmosphere to a respirable size (activated) and used in the inhalation studies.
Studies of the dermal abrasiveness of non-respirable-sized lunar dust to excised pig skin are in progress . Ocular studies are in the planning stage with in vitro or ex vivo testing to precede any in vivo testing, probably according to long-accepted guidelines from the OECD (Organization for Economic Development and Cooperation).
1) Wallace, WT, et al. Lunar dust and lunar simulant activation and monitoring. Meteoritics & Planetary Science 44:961-970, 2009.
2) Kuhlman, KR, et al. Decay of reactivity induced by simulated solar wind implantation of a forsteritic olivine. Lunar and Planetary Conference, 2009.
3) Wallace, WT, et al. Understanding the activation and solution properties of lunar dust for future lunar habitation. Lunar and Planetary Conference, 2009.
4) Tranfield, E, et al. Enhanced chemical reactivity of crystalline quartz by mechanical grinding. Lunar and Planetary Conference, 2009.
5) Tranfield, E, et al. Chemical activation of lunar dust specimens and stimulants. Lunar Science Conference, 2009.
6) Taylor, LA, et al. Mineralogical and chemical characterization of lunar highland soils: Insights into he space weathering of soils on airless bodies. J Geophys Res.
7) Taylor, LA, et al. Shape and size relationship of several lunar dusts: preliminary results. Lunar and Planetary Science Conference, 2009.
8) Lindsay, J, et al. Dust pathways – Forensic engineering. LADTAG, November 6-7, 2007.
9) Noble, S. The clam shell sampling devices. LADTAG, December 8-9, 2009.
10) James, JT, et al. Pulmonary toxicity of lunar highland dust. Paper 09ICES-0354, http://www.sae.org , 2009.
11) Cooper, BL, et al. Extracting respirable particles from lunar regolith for toxicological studies. Earth and Space Conference, 2010.
12) Jones, LR, et al. Abrasive effects of lunar dust, JSC stimulants, and sandpapers on skin and acrylic samples, measured by electrical resistance and confocal microscopy. Lunar Science Conference, 2009