Laboratory study on degradation of fatty acids and sterols from urban wastes in seawater

Changes of particulate and dissolved fatty acids and sterols were studied during an in vitro experiment on the degradation, in seawater, of organic matter of urban effluent origin. Incubation of seawater-effluent mixture was done in dark at 15°C and the fatty acids and sterols were analysed by HPLC and GC. Decomposition of total fatty acids and sterols was rapid, with a loss of 90% in the former and 70% in the latter during the first week. Over two months, 95% of both groups were decomposed. Fractionation showed that the dissolved and particulate neutral lipids which are representative of anthropogenic inputs were rapidly degraded, whereas polar lipids, containing bacterial fatty acids initially and polyunsaturated fatty acids later, were synthesized. A synthesis of sterols (cholesterol and βsitosterol) was also observed, especially in the dissolved fraction. These variations are related to successive development of bacterial and bacteriophagal populations. The sterols, and particularly the 5β-stanols, appear to be good tracers for organic matter of urban effluents decomposing in the coastal environment.