Summary of environmental impacts

BACTERIA and VIRUSES

Bacteria and viruses are important because they can initiate a disease response in humans through either primary contact (e.g. when swimming) or through consumption of contaminated seafood. There are a number of Australian guidelines that assess the acceptability of bathing waters for recreational use, the most recent of which are the ANZECC (1992) guidelines. The guidelines for primary contact state (in part) that: "The median bacterial content in samples of fresh or marine waters taken over the bathing season should not exceed:

*   150 faecal coliform  organisms per 100mL (minimum of five samples taken at regular intervals not exceeding 1 month, with four out of five samples containing less than 600 organisms per 100mL)

*    35 enterococci organisms per 100mL (maximum number in any one sample: 60-100 organisms per 100mL).

Epidemiological studies of waterborne illness indicate that the common causative agents are more likely to be viruses and parasitic protozoans rather than bacteria (Cabelli et al 1982; Seyfried et al 1985; Moore et al 1994).  However, water quality measures are usually framed in terms of faecal coliform concentrations because they are relatively easy to measure and are present in virtually all warm-blooded animals (National Health & Medical Research Council 1990). Most of NSW outfalls have monitoring programs in place that test for faecal coliform bacteria in the surrounding water, particularly at beaches close to the outfall discharge points.

Monitoring of faecal bacteria at the majority of NSW ocean outfalls suggest that the ANZECC guidelines are generally satisfied after allowance for an initial area of treated effluent and seawater mixing (referred to as the “mixing zone”). In Sydney a significant decrease in the number of bacteria and viruses in coastal waters occurred once the outfalls were diverted to deep ocean discharge.

(Impac_7) Last updated May 2000