Toxic Potential of Lunar Dust: The Determinant Role of Atmospheric Exposure

The potential toxicity of lunar dust (LD), as reported by Apollo astronauts, presents significant concerns for future missions involving extended human presence on the Moon. LD toxicity is hypothesized to be driven by oxidative stress linked to its redox-active properties, with nanophase metallic iron (np-Fe⁰) embedded in its glassy matrix potentially playing a critical role. However, the specific mechanisms underlying its toxicity remain unclear. Environmental changes in atmospheric settings may modify LD's reactivity before exposure, complicating the evaluation of its potential toxicity.

Given the limited availability of real LD samples, the research relys on lunar dust simulants (LDS) for toxicity studies. Yet, the absence of a fully representative LDS limits the accuracy of risk evaluations. This study introduces a novel Simulant Moon Agglutinate (SMA) designed to mimic LD. The SMA consists of a glassy matrix containing np-Fe⁰ and was crushed in an inert atmosphere to replicate the lunar environment. Respirable SMA particles were analyzed for their physicochemical characteristics, oxidative activity, and iron release in simulated body fluids.

Under non-oxidizing conditions, SMA generated a higher level of free radicals, driven by reduced-state iron, and sustained by an electron “reservoir” from zerovalent iron clusters. A molecular mechanism is proposed. After oxidative passivation, SMA exhibited a lower reactivity, which was nonetheless still greater than the reactivity of other simulants, such as JSC-1A-vf. Our findings emphasize the critical role of np-Fe⁰ in oxidative reactions of lunar dust. Notably, SMA did not induce cell membrane damage, suggesting that the mechanisms of LD toxicity may differ significantly from those of terrestrial toxic dusts, such as quartz.