Evaluating potential applications of faecal sterols in distinguishing sources of faecal contamination from mixed faecal samples

Faecal samples from humans, herbivores, carnivores and birds as well as samples from septic tanks and effluents from a sewage treatment plant (STP) were extracted and analyzed by gas chromatography–mass spectrometry for faecal sterols including coprostanol, epicoprostanol, cholestanol, cholesterol, stigmasterol, campesterol, 24-ethylcoprostanol and β–sitosterol. Coprostanol was observed in the highest concentrations from the human derived samples, but it was also present in substantial quantities in a range of herbivores. There was no unique marker of human faecal contamination. Multivariate analyses revealed that the faecal sterol profiles were significantly different between the four groups of animals (Wilks’ lambda=0.007, P<0.002), and coprostanol and 24-ethylcoprostanol were the major discriminant factors. However, when faecal samples were mixed, the confounding of faecal sterol levels prevented accurate identification of contributing species. Conversely, faecal sterol ratios were highly efficient at identifying which mixtures contained human contribution, but could not appropriately determine percentage contributions of sources.