Conversion of Oleic Acid to Saturated Fatty Acids in Severn Estuary Sediments

Abstract

THE upper, biologically active, layers of Recent aquatic sediments contain considerable quantities of saturated and unsaturated long chain fatty acids1–3, presumsably from the living and dead organisms found there4,5. Although fatty acids are major constituents of organisms, in the upper layers of sediments, their concentration is of the same order of magnitude as that of sterols6,7, usually minor constituents of organisms. The ratio of fatty acids to total organic carbon in marine sediment is at least ten times lower than in plankton1, again indicating that fatty acids are subject to rapid changes in the sediment. Palmitic acid (C16:0) is the most abundant saturated fatty acid in organisms, and oleic acid (C18:1) the most widely distributed and plentiful of all fatty acids4,5. The lower, biologically less active, layers of sediments, contain little or no unsaturated fatty acid; palmitic acid is the most abundant of the fatty acids1,2,8. This difference between the upper and lower layers is unlikely to be the consequence simply of hydrogenation of the carbon–carbon double bands, for in this case the proportion of stearic acid (C18:0) in the lower layers and the concentrations of saturated fatty acids would be larger. These reactions could occur by chemical and/or biological means, perhaps through the large number of anaerobes present in upper layers of sediments9,10.