Organic Contamination of San Vicente Bay, Chile

Surface sediment samples from 16 sites in San Vicente Bay were analysed for a range of lipid biomarkers and hydrocarbons. Coprostanol and cholesterol were used to indicate regions of sewage contamination: ratios reached 1.1 adjacent to known discharge points. The fatty alcohol data were used to highlight regions of bacterial and terrestrial biomass. The bacterial fatty acid 18:1ω7 co-varied with the odd/even fatty alcohol ratio and the coprostanol/cholesterol ratio confirming the regions of aerobic bacterial activity near the sewage outlets. The fluoranthene/pyrene ratio together with the ratio between the (three or less/four or more) ring aromatics and total concentration of aromatics demonstrate the extent of crude oil and pyrogenic contamination in the sediments. San Vicente Bay was divided into three principal regions on the basis of this analysis: (a) the highly contaminated northern end with strongly reducing sediments and high concentrations of organic matter, (b) the region adjacent to the sewage outlets with associated bacterial biomass, and (c) the remaining central and southern areas relatively unaffected by the northern discharges. Partial Least Squares path modelling suggests the latter region received less than 50% of the material discharged at the northern end of the Bay.