Distinguishing Possum and Human Faeces Using Faecal Sterol Analysis

New Zealand has over 70 million possums (Trichosurus vulpecula), which collectively produce over 1.5 million kg dry weight of faeces per day. In this study we evaluated whether faecal sterol analysis could be used to identify faecal pollution from possums, and distinguish it from faeces from humans and other animals. Possum faeces contain significant levels of sterols. However there are a number of distinctive features of the sterol profile of possums which could be used to distinguish possum faeces from other sources. Similar to human faeces, possums contain high levels of coprostanol which distinguishes them from herbivores such as sheep and cattle. However in contrast to human faeces, possum faeces contain high levels of 24-ethylcoprostanol. Ratios based on these differences (coprostanol/cholestanol > 6.0 and coprostanol/24-ethylcoprostanol < 1), when both present, appear indicative of possum faeces. Based on a survey of river water samples, possum faeces was not a significant contamination source in New Zealand. Source determinations should be supported by other faecal source tracking tools and consideration of potential sources actually present in a catchment.