Characterization of low-molecular-weight organic acids isolated from the Toarcian argillite pore water (Tournemire site, France)

Bacterial activity in the near-field environment of radioactive waste disposal facilities in deep argillaceous rocks is currently under investigation. Bacterial development could be enhanced by the availability of low-molecular-weight organic acids (LMWOA) dissolved in the pore water of clayey rocks. This study firstly aimed at isolating and characterizing the LMWOA of the Toarcian argillite from the Tournemire Underground Research Laboratory (France, Aveyron). It also aimed at assessing the disturbing effects that could be induced by a disposal facility on the type and release of LMWOA (exposure to oxygen, alkaline pH, temperature increase). Under the experimental conditions investigated at 60 °C, the mean dissolved organic carbon (DOC) is about 15 mg L−1 with a LMWOA proportion of 35 %. The main LMWOA are composed of formate, fumarate, propionate, acetate, and lactate. DOC is mainly influenced by both temperature and pH increases, whereas the LMWOA type nature and release are more specifically affected by the exposure to oxygen.