Using faecal sterols from humans and animals to distinguish faecal pollution in receiving waters

The sterol content of faeces from humans and 14 species of animals common to rural or urban environments were examined. The major human faecal sterol was the 5β-stanol, coprostanol which constituted ≈ 60% of the total sterols found in human faeces. The sterol profiles of herbivores were dominated by C₂₉ sterols and 5β-stanols were generally in equal or greater abundance than 5-stanols. The principal faecal biomarker of herbivores was 24-ethylcoprostanol. The sterol content of bird faeces was extremely variable and largely dependent on the animals diet. Both 5β and 5 stanols were in very low abundance in birds and dogs faeces from this study presumably due to the absence or low activity of the necessary anaerobic biota required to reduce Δ⁵- or Δ^5,22-sterols to stanols. Cats and pigs were the only animals that had similar faecal sterol profiles to humans. However, the concentration of the principal human biomarker coprostanol was some 10 times more abundant on a dry weight basis in the faeces of humans than in those of cats and pigs. The source specificity of faecal sterol biomarkers is a combination of sterol intake, metabolic production of sterols and the biota resident within the animal's digestive tract. The “sterol fingerprints” of the faeces of humans and animals are sufficiently distinctive to be of diagnostic value in determining whether faecal pollution in water samples are of human or animal origin.