Determination of volatile fatty acids in the hot springs of Vulcano, Aeolian Islands, Italy

Samples of relatively acid hydrothermal fluids were collected in the spring of 1996 from seeps, springs, and wells on the Island of Vulcano in the southern Tyrrhenian Sea and analyzed for volatile fatty acids1 using liquid chromatography. Concentrations of VFAs in the seeps were in the range 65–140 ppb formic, 133–184 ppb acetic, and <100–192 ppb propanoic acids. Spring samples could not be analyzed quantitatively because high salt content effectively “masked” all potential VFA peaks in the corresponding chromatograms, and the concentrations of formic, acetic, and propanoic acids in the wells were <200 ppb. The temperatures of the sampled fluids were between 19.4 and 98.4°C, and the pH measured at in situ temperatures ranged from 1.85 to 6.17. The concentrations of acetic acid in the seeps were generally higher than both those of formic and propanoic acids. This is consistent with concentrations of VFAs in a saline spring near the Dead Sea reported by Kawamura and Nissenbaum as well as with thermodynamic calculations by Helgeson et al. for equilibrium activities of n-carboxylic acids in oil-field waters. Although the measured concentrations of VFAs in the hot springs of Vulcano are modest, thermodynamic calculations indicate that they represent potential energy sources for anaerobic chemotrophic microorganisms.