Tracing sewage in the marine environment: altered signatures in Concepción Bay, 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. Quím. 42 (1997) 5). This site has been re-examined to determine why they were absent. The concentrations of sterols, fatty acids and alcohol biomarkers of 10 sediment cores from Concepción Bay, Chile, were quantified by capillary gas chromatography-mass spectrometry. The data obtained from 34 fatty acids, 28 fatty alcohols (C12-C30) and 32 sterols from the target study area, indicated that fatty acids from Concepción Bay sediments were the most abundant lipids (range 1.6-307 microg g(-1) dry wt) followed by sterols (range 0.02-25.3 microg g(-1) drywt). The sewage markers 5beta-coprostanol and epi-coprostanol were found in the areas close to the Penco-Lirquen disposal pipe. High bacterial activity was also present as indicated by the cholestanol, 18:1omega7, iso, anteiso and branched fatty acids and enhanced odd/even ratios of fatty alcohol biomarkers. The sediments from the centre of Concepción Bay had a greater marine/algal input characterized by brassicasterol and the marine fatty acids (20:4omega6, 20: 5omega3 22: 6omega3). The terrestrial contribution was mainly characterized by beta-sitosterol, C22-C26 fatty acids and confirmed by short/long chain ratio of the fatty alcohols. The distribution of these two markers indicates that the terrestrial matter passing through the sewage system is deficient in short chain fatty alcohols. The epi-coprostanol/coprostanol versus coprostanol/cholesterol plots also indicated selected removal of the stanols leaving apparently high cholesterol concentrations.