Degradation of fatty acid methyl esters in biodiesels exposed to sunlight and seawater

The degradation of fatty acid methyl esters (FAMEs) has been characterized in selected biodiesels exposed to sunlight and seawater, and markers are identified that can be used to match a weathered biodiesel spill to its source. Samples of one synthetic and three commercial biodiesels were subjected to a regime of controlled weathering for 71 days. Experiments were designed to promote photo-oxidation, biodegradation or a combination of both processes. The FAME compositions of the biodiesels were measured by GC-MS at various times. Unsaturated FAMEs were preferentially degraded by photo-oxidation. Saturated C16 and C18 FAMEs were the most persistent compounds. The diagnostic ratio C16:0/(C16:0 + C18:0), calculated from the peak area of the total ion chromatograms (TICs), varied by less than 2% (RSD) during 71 days of weathering and could be used to distinguish among the biodiesels studied.