The Occurrence of Fatty Acids in Fulvic Acid, A Soil Humic Fraction

Normal fatty acids ranging from C14 to C36 were found to account for a maximal 0.10% of the dry ash‐free weight of a water soluble soil fulvic acid. Only 10.0% of the total fatty acids could be extracted by organic solvents from untreated fulvic acid. The remaining 90.0% was extractable only after methylation of the fulvic acid and adsorption on neutral aluminum oxide. While the nature of the molecular forces that hold the fatty acids to the fulvic acid is still a matter of conjecture, evidence was obtained that reduction of hydrogen bonding by methylation was related to the release of fatty acids by the fulvic acid. Ninety‐five percent of the acids that were isolated were saturated, the remaining 5.0% were unsaturated and branched‐cyclic. The C24 acid was the major component. The overall C‐even to C‐odd carbon atom ratio for all acids was 2.3. The results suggested two different origins for the fatty acids: the C14 to C26 acids may be of microbiological origin, whereas the C27 to C36 acids may have arisen from plants. Weight distribution plots of fatty acids and n‐alkanes extracted from the fulvic acid showed an inverse concentration relationship between the two components with identical carbon numbers. The data reported herein suggest that fulvic acid may act as a vehicle for the mobilization, transport and immobilization of water‐insoluble organic compounds—some of which may be serious pollutants—in an aquatic environment.