Tracing sewage in the marine environment: Altered signatures in ConceptionBay, Chile

Lipid biomarkers are now widely used to trace organic matter in the marine environment. Selected compounds and ratios can be used to identify sources or processes. However. in a study of a particularly contaminated area, the expected signatures were not found (Mudge and Seguel. Bol. Soc. Chil. Quim. 42 (1997) 5). This site has been re-examined to determine why they were ab sent. The concentrations of sterols, fatty acids and alcohol biomarkers of 10 sediment cores from Concepcion Bay, Chile, were quantified by capillary gas chromatography-mass spectrometry. The data obtained from 34 fatty acids , 28 fatty alcohols (C-12-C-30) and 32 sterols from the target study area, indicated that fatty acids from Concepcion Bay sediments were the most abun dant lipids (range 1.6-307 mug g(-1) 1 dry wt) followed by sterols (range 0 .02-25.3 mug g(-1) dry wt). The sewage markers 5 beta -coprostanol and epi- coprostanol were found in the areas close to the Penco-Lirquen disposal pip e. High bacterial activity was also present as indicated by the cholestanol , 18 : 1 omega7. iso, anteiso and branched fatty acids and enhanced odd/eve n ratios of fatty alcohol biomarkers. The sediments from the centre of Conc epcion Bay had a greater marine/algal input characterized by brassicasterol and the marine fatty acids (20 : 4 omega6, 20 : 5 omega3 22 : 6 omega3). T he terrestrial contribution was mainly characterized by beta -sitosterol. C -22-C-26 fatty acids and confirmed by short/long chain ratio of the fatty a lcohols. The distribution of these two markers indicates that the terrestri al matter passing through the sewage system is deficient in short chain fat ty alcohols. The epi-coprostanol/coprosta not versus coprostanol cholestero l plots also indicated selected removal of the stanols leaving apparently h igh cholesterol concentrations. (C) 2001 Elsevier Science Ltd. All rights r eserved.