Who done it?: sourcing faecal contamination with sterol biomarkers in the Bay of Plenty

Abstract

The detection of faecal contamination in water is very important for health, aesthetic, ecological and cultural reasons. Management methods to deal with faecal contamination are often difficult to develop until the source of the contamination can be traced. Unfortunately, traditional microbiological indicators of faecal pollution do not differentiate between different sources of contamination. Recently, a group of chemicals called sterols that can be used to indicate the source of faecal contamination has been attracting attention. Sterols are derived from dietary components and from intestinal reactions which produce specific 'fingerprints' of sterols that can be traced to different animals. Although there has been some international research on the application of sterols as molecular markers of faecal contamination, there has been limited work on their use in New Zealand. The aim of this thesis was to refine the methodology for sterol analysis of New Zealand waters and faeces and to test the method in a selected aquatic environment. The area that was selected for sampling and analysis was the Rangitaiki Plains in the Bay of Plenty. During the course of the study, water samples were taken from the Plains' waterways in both winter and summer. Faecal samples from cows, ducks, horses and sewage sludge were also collected. All samples were analysed for coprostanol, cholesterol, campersterol, stigmasterol, stigmastanol and β-sitosterol and the sterol patterns found in water were compared with the patterns found in faecal samples from different sources on the Plains. Close analysis of the composition of sterols in the different faeces revealed that, for ducks, there is no coprostanol or stigmastanol, while for humans, the coprostanol to stigmastanol ratio dominates. For cows and horses, the stigmastanol to coprostanol ratio dominates. Comparison of these ratios with the results from the water samples showed that in both winter and summer, humans are the predominant source of contamination around the sewage treatment facilities. In other areas of the drains and canals of the Plains, there is a mixture of cattle and duck contamination (with a higher contribution from ducks) in the summer, while in the winter ducks appear to be the predominant source of contamination in the drains. Results from the Tarawera River and Matata indicated that in the summer, faecal contamination appeared to be originating from cattle, while in the winter, there was a mixture of cattle and ducks. Results from the Tarawera river may have been influenced by interference from the Tasman Pulp and Paper Mill and the Kawerau digestor which discharges into the River. A comparison with faecal coliform results indicated that total sterol levels correlate well with faecal coliform levels. The results of the monitoring programme are useful for water managers, including the Regional Council, Environment BOP, and will assist management strategies to be tested and developed for farm management, sewage treatment and dairy shed effluent. The study also indicates that if faecal contamination is to be effectively controlled on the Rangitaiki Plains, management strategies will need to be put in place to manage contamination originating from ducks.