(EP3129455) 1. A method for obtaining an enriched composition of C20-C22 long chain monounsaturated fatty acids, the composition comprising at least 70% by weight of long chain monounsaturated fatty acids, comprising the steps of: a) Mixing an oil composition comprising C20-C22 long chain polyunsaturated fatty acids and at least 15% by weight C20-C22 long chain monounsaturated fatty acids with (i) an organic solvent selected from the group consisting of C1-C5 alcohols and ketones of the formula R1(C=O)R2 wherein R1 and R2 are each independently C1-C5 alkyl; and (ii) a lithium salt to form a mixed composition comprising the lithium salts of long chain monounsaturated fatty acids and the lithium salts of the long chain polyunsaturated fatty acids at 15 °C to 80° C; b) Reducing the temperature of the mixed composition formed in step a such that the lithium salts of the long chain monounsaturated fatty acids form a precipitate; and c) Removing the precipitate to obtain an enriched composition of long chain monounsaturated fatty acids. 2. The method of claim 1 wherein the oil composition is derived from fish, crustaceans, algae, plankton or higher plants. 3. The method of any of the above claims wherein the oil composition comprises a member selected from the group consisting of free fatty acids and fatty acid monoesters. 4. The method of claim 3 wherein the fatty acid monoesters comprise ethyl esters. 5. The method of any of the above claims wherein the oil composition has been subjected to a prior fractionation step to reduce the concentration of saturated fatty acids and/or shorter chain fatty acids. 6. The method of any of the above claims wherein an additional base is added in step a. 7. The method of claim 6 wherein said additional base is potassium hydroxide. 8. The method of any of the above claims wherein the organic solvent is selected from the group consisting of comprises ethanol and acetone. 9. The method of any of the above claims wherein the solvent is added in an amount of between 0.5 and 8 liters per kilogram of oil composition. 10. The method of any of the above claims wherein the lithium salt is selected from the group consisting of lithium carbonate, lithium bicarbonate and lithium hydroxide. 11. The method of claim 10 wherein the lithium salt comprises lithium hydroxide. 12. The method of any of the above claims wherein the lithium salt is added in an amount of between 5 and 70 grams, calculated as lithium, per kilogram of oil composition. 13. The method of any of the above claims wherein the mixed composition is cooled to 10° C or less in step b. 14. The method of claim 1 wherein the oil composition is a fish oil composition. 15. The method of any of the above claims wherein the content of persistent organic environmental pollutants, as measured by the content of PCBs, is reduced by more than 90 % compared to the starting oil composition.
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