Carboxylate anion generation in aqueous solution from carbonate radiolysis, a potential route for abiotic organic acid synthesis on Earth and beyond Article - Juin 2021

Johan Vandenborre, Laurent Truche, Amaury Costagliola, Emeline Craff, Guillaume Blain, Véronique Baty, Ferid Haddad, Massoud Fattahi

Johan Vandenborre, Laurent Truche, Amaury Costagliola, Emeline Craff, Guillaume Blain, Véronique Baty, Ferid Haddad, Massoud Fattahi, « Carboxylate anion generation in aqueous solution from carbonate radiolysis, a potential route for abiotic organic acid synthesis on Earth and beyond  », Earth and Planetary Science Letters, juin 2021, p. 116892. ISSN 0012-821X

Abstract

Low molecular weight carboxylate anions such as formate (HCOO−), acetate (CH3COO−) and oxalate (C2O ) have been shown to play an important role in supporting deep subsurface microbial ecosystems. Their origin whether biological or abiotic is currently highly debated, but surprisingly radiolytic production has rarely been considered, as it is the case for H2. Here, we address this question through dedicated irradiation experiments. Aqueous solutions containing carbonate, formate, acetate or oxalate have been irradiated using both the 60.7 MeV α-beam of the ARRONAX cyclotron (Nantes, France) and 661.7 keV γ-Ray in order to reveal the mechanism and chemical yield of radiation-induced dissolved carbonate degradation. The yields (G-values) of carboxylate anions production/degradation in low-concentration carbonate solution (0.01 to 1 mmol L−1) are measured. Carbonate degradation occurs through three consecutive steps (Carbonate Formate Acetate Oxalate) involving formate radical (CO2−•), dihydrogen (H2), and carbon dioxide (CO2) generation. Dissolved carbonate radiolysis provides a consistent pathway for both enhancing two-fold the radiolytic H2 production compared to pure water and generating carboxylic species, chiefly oxalate, readily available for microbes. Radiation-induced carbonate degradation may produce substantial amount (millimolar concentration) of carboxylate anions in ancient groundwaters from deep crystalline bedrocks. Subsurface lithoautotrophic microbial ecosystems may not only be supported by radiolytic H2 but also by carboxylate species from carbonate radiolysis. Carbonate radiolysis can be also an endogenous source of carboxylate species on Mars and other planetary bodies.

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