In-Vitro Physiologically Based Extraction Tests of Lunar Regolith Simulants

The U.S. Geological Survey has developed for NASA two lunar regolith simulants (LRSs) that model lunar highland regolith at the proposed South Pole base. These and other simulants are used for abrasion tests on robotics and space suits, habitat construction, testing of oxygen extraction techniques, testing viability of regolith for plant growth, and human health studies.

We are conducting in vitro physiologically based extraction tests (PBETs) on appropriate size fractions of the USGS bulk LRSs and LRS component materials (norite, orthopyroxenite, anorthosite, peridotite, dunite, noritic mill wastes, synthetic glass, minor minerals) using various simulated body fluids as the leaching agents. Some elements (Al, Si, Cr, Fe, Mn, Ti) are highly leached from the LRSs by pH 1.5 simulated gastric fluids, but partially reprecipitate in pH 5-6 simulated intestinal fluids. Thus, some metals may become partially solubilized and available for absorption by the body if LRSs are incidentally ingested through hand-mouth contact or swallowing of dust-bearing mucus cleared from the respiratory tract. In contrast, pH 4.5 simulated alveolar macrophage lysosomal fluids and pH 7.4 simulated lung fluids and serum-based fluids leach much smaller amounts of most elements from the LRSs. Hence, respired LRS dust particles not removed by mucociliary clearance may persist in the lung alveoli or macrophages for some time without dissolving; Fe, Mn, and other elements in such biodurable particles may therefore participate in longer-term chemical reactions that generate deleterious reactive oxygen species.

PBETs provide insights into potential biosolubility, bioaccessibility, and bioreactivity behavior of LRSs in the body, and can be used to help interpret results of in vitro and in vivo toxicity tests of LRSs and actual regolith samples; such toxicity tests are needed to best understand potential toxicological implications of exposures to the LRSs during use, or to the lunar regolith by lunar base inhabitants.