5α(H)-cholestan-3α-ol in sediments: Characterization and geochemical significance

The top five centimeters of sediment collected at the deepest point of Lake Léman (Switzerland), 309 meters below water level, contain concentrations of 5α(H)-cholestan-3α-ol (epicholestanol) up to 10% of the total sterol content. Isobutane chemical ionization mass spectrometry and coinjection with an authentic standard on a SP-1000 glass capillary column were used in order to successfully characterize this epimer of cholestanol.The distribution of this stanol throughout the sediment core studied suggests in situ bacterial production. The change in concentration of epicholestanol with depth is different from those found for other C₂₇ stanols, such as cholestanol or coprostanol. It is probably the result of a change in the bacterial fauna in the most recently deposited sediment, related to the increasing eutrophication of the lake rather than the consequence of its lower stability due to the axial conformation of the OH substituent.