Faecal Source Tracking
When waterways become contaminated with faeces, an important step in contamination management is identifying the source of the pollution. We have a range of molecular and chemical techniques to help identify the source of faecal contamination of water whether it is from farm, domestic or feral animals, humans or birds. If an initial Colilert® test indicates the presence of high counts of Escherichia coli, one or more assays from a ‘tool box’ of methods are implemented. Each one of these tools is relevant for a particular purpose and when used in conjunction with other tools, can increase the certainty that pollution is derived from a specific source. A faecal source identification strategy is used to determine the most efficient route to identify the likely sources of faecal contamination and includes a decision tree outlining the steps for obtaining the most relevant information for the least financial outlay.
This work is relevant to all personnel with water management responsibilities within local government authorities. ESR has assisted in the prioritisation of water pollution problems and reduced the level of water pollution. Some case histories are described below.
Case 1: High levels of faecal indicators in an open, concrete bottom stormwater drain were identified as human faecal pollution and sourced to a cracked sewer pipe.
Case 2: High levels of faecal indicators were identified in a stream running through a beachside settlement and flowing onto a swimming beach. Human faecal contamination was identified as the source of the pollution. Septic tanks are now being replaced by a community wastewater system
Methods tool box
A poster presentation about the toolbox for faecal source tracking can be found here [PDF, 1.5 MB].
A range of microorganisms is present in faeces, which are specific to their animal hosts. Total DNA is extracted from a water sample and the sample is examined using the polymerase chain reaction (PCR) for DNA from source-specific organisms. The presence of certain microorganisms indicates the source of the faecal contamination. Assays specific for humans, herbivores, dogs and wildfowl are in development.
Analysis of the sterol composition of animal faeces can generate a sterol fingerprint, which can be distinctive, particularly, when discriminating human faeces from other sources.
Fluorescent whitening agents (FWAs) are common constituents of washing powders used to brighten clothing. Most household plumbing systems mix effluent from toilets with ‘grey water’ from washing machines. Consequently, FWAs are usually associated with human faecal contamination in both septic tanks and community wastewater systems. The presence of FWAs indicates human effluent.
In this approach, individual colonies, usually of E. coli or enterococci, are isolated from water samples. These isolates are then fingerprinted using either DNA-based or phenotypic/biochemical based methods to generate an indivdiual profile of each isolate, which is compared with the profiles of isolates in a library of known faecal sources. The library is usually comprised of E. coli or enterococci isolates collected from potential sources of contamination such as human sewage or animal faeces, located in the same environment as the water sample.