Appendix A Indicators and guidelines
Bacterial indicators
The assessment of water quality under the Beachwatch Partnership Program (BPP) during the 2007–2008 summer season was based primarily on the level of bacterial contamination. Faecal coliforms and enterococci were the bacterial indicators used.
Faecal coliforms, also known as thermotolerant coliforms, are a group comprised of the organisms Escherichia coli, Klebsiella pneumoniae and Enterobacter aerogenes. Faecal coliforms are strongly associated with faecal waste and therefore are excellent indicators of recent faecal contamination. Faecal coliforms are not reliable indicators of aged faecal contamination, owing to their short survival times in marine waters.
Enterococci are a subgroup of faecal streptococci and include four streptococci species: Streptococci faecalis, S. faecium, S. gallinarum and S. avium. In contrast to faecal coliforms, enterococci survive for longer periods in seawater and are thus good indicators of the presence of aged faecal contamination.
Most pathogens are not easily detected in water. Where reliable laboratory methods exist, they generally require the collection of large volumes of water, analysis is costly, and it can take a week or more to obtain a result. In addition, decisions about how many and which specific pathogens to test for need to be made.
Owing to these difficulties, indicator organisms are used as fundamental monitoring tools for assessing the potential presence of pathogenic organisms. An indicator organism should:
1) be easily detectable by using simple laboratory tests
2) generally not be present in unpolluted waters
3) appear in concentrations that can be correlated with the extent of the contamination
4) survive under similar conditions as the pathogens of concern.
The most common indicator organisms are enteric bacteria, such as faecal coliforms and enterococci. These bacteria are excreted in faeces, are usually harmless, and are rarely present in unpolluted waters. Bacteria are much easier to detect than viruses and protozoans, and enumeration methods have been developed for commercial-scale analysis.
Limitations
Bacterial indicators are imperfect measures of the health risks associated with swimming in recreational waters. Limitations associated with the use of bacterial indicators include the following:
1) Bacterial indicators demonstrate the presence of faecal material, not necessarily the presence of viable pathogens.
2) Analysis of bacterial indicators takes 24 to 48 hours, so it is not possible to know the potential risk at the time of swimming.
3) Bacterial indicators vary in their ability to predict potential risks to human health. Some indicators have been shown to have a greater statistical relationship to disease than others.
Australian guidelines
Recreational water quality guidelines provide an indication of the probability of swimmers developing illnesses derived from the water, but the actual risk depends on many factors. These factors include, in particular, the bacterial indicator to pathogen ratio, which varies with time and is usually unknown.
The NHMRC recently released new guidelines for managing recreational risks in water (NHMRC 2008). These new guidelines are largely based on the World Health Organisation guidelines published in 2003 (WHO 2003). They include a preventive approach to the management of recreational waters that focuses on developing an understanding of all potential influences on a recreational water body, through local assessment and management of hazards and of factors that may lead to hazards. Once the new guidelines have been considered by the NSW Government Beachwatch will review its monitoring and reporting protocols on the basis of these new guidelines.
The two guidelines for assessing recreational water quality currently used in NSW are:
These guidelines include criteria for microbiological, physical and chemical parameters.
The NHMRC (1990) microbiological guidelines are presented in Table A1, and the ANZECC (2000) guidelines for primary contact recreation in Table A2. The NHMRC (1990) guidelines were used for compliance assessment in the BPP.
Table A1: NHMRC (1990) guidelines used for compliance assessment in the BPP
Marine or estuarine waters are considered unsuitable for swimming if, for five samples taken at regular intervals over a period not exceeding one month: - the median faecal coliform density exceeds 150 cfu/100 mL; or
- the second-highest faecal coliform density is equal to or greater than 600 cfu/mL; or
- the geometric mean enterococci density exceeds 33 cfu/100 mL.
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Note: The guideline for enterococci appears as Note 1 in the NHMRC (1990) guidelines
Table A2: ANZECC (2000) microbiological guidelines
The median bacterial content in samples of fresh or marine waters taken over the bathing season should not exceed: |
Page last updated: 26 February 2011
