Discriminating faecal pollution: A case study of stormwater entering Port Phillip Bay, Australia

This investigation was designed to provide preliminary information to the Environment Protection Authority concerning the input of faecal matter to stormwater drains in the Rippleside area of Geelong, Victoria. Results derived from the combined use of sterol biomarkers (e.g. coprostanol and 24-ethylcoprostanol) and four sub-groups of bacterial indicators (e.g. thermotolerant coliforms, E. coli, faecal streptococci and enterococci) indicated that during wet weather, all sites sampled were affected by significant human faecal contamination. Ratios of coprostanol to bacterial indicators were similar to those for samples collected from nearby sewer mains. During dry weather, there were still severely elevated levels of faecal contamination based on bacterial indicators, but correspondingly low concentrations of faecal sterols suggesting minimal human or herbivore faecal contamination. The origin of the majority of the faecal pollution in dry weather therefore remains to be fully explained. It is clear from this and related studies that the combined measurement of faecal sterols and bacterial indicators can greatly assist distinguishing sources of faecal pollution. It is also shown for aquatic environments that the measurement of coprostanol or other single indicators alone, is inadequate to fully discern faecal contamination from human sources. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.