The Study of Molecular Markers of Human Activity: The Use of Coprostanol in the Soil as an Indicator of Human Faecal Material

Coprostanol (5β-cholestan-3β-ol) is a metabolic product of cholesterol, formed by microbial action in the mammalian gut (the usual product of cholesterol reduction outside the gut, in mammalian tissues and sediments, is 5α-cholestan-3β-ol). Coprostanol is the major sterol in human faeces, and has been routinely studied as a marker of (modern) sewage pollution in marine and lacustrine sediments. This has led to the search for coprostanol in archaeological soils, in order to detect the presence of faecal material. Solvent extraction of the soil total lipids was followed by fractionation using thin layer chromatography, to isolate the steroids present in the soil. These were then analysed by combined gas chromatography/mass spectrometry (GC/MS), using selected ion monitoring (SIM) to detect and quantify specific compounds. Samples from a range of sources were analysed, including modern latrine deposits, a 17th-century garderobe, a mediaeval garderobe and two suspected Roman cess-pits. Coprostanol and its homologues were detected not only in the modern and aged cess samples, but also in the control samples, suggesting its ubiquitous occurrence in the environment, albeit at a low concentration. However, by measuring the relative abundances and ratios of the 5β-stanols, a chemical signature distinctive of faecal material could be established, independent of the simple occurrence of coprostanol in the soil. It was shown that coprostanol, and its homologues produced by the same microbial mechanism in the gut, were reliable markers of the presence of faeces in soils when found in the appropriate relative abundances. A method of analysing very small quantities of specific molecular marker compounds preserved in soils has thus been applied to archaeological materials, enabling a particular organic residue to be identified where conventional physical methods of analysis might not be successful.