Water Journal : Water Journal July 2012
public health refereed paper technical features 80 JULY 2012 water behaved in wet weather, water samples were collected from a total of 19 sites identified within 48 hours of targeted significant rainfall events (> 25 mm) on five occasions between March 2000 and February 2002. Sampling details including sampling dates, number of sites, sampling parameters and rainfall data are presented in Table 2. Bacterial analysis Water samples for microbiological assessment were collected in 500mL polystyrene sterile bottles. All samples were analysed by Hunter Water Laboratories within 24 hours for faecal indicator bacteria as outlined in Table 2 using APHA (1998) methods. Faecal sterol analysis Water samples for sterol analysis were collected in 5L clean plastic containers. The water samples were filtered through Advantec grade GF75 glass fibre filters (150mm diameter, 0.7μm pore size) to collect fractions of particulate matters. The filters were frozen and were then sent overnight on ice to CSIRO's Marine and Freshwater Research division in Hobart, Tasmania, for analysis of faecal sterols as outlined in Table 2. The particulate fractions for faecal sterol analysis were extracted quantitatively by a modified one-phase CH2Cl2-MeOH Bligh and Dyer method. Gas chromatography and flame ionisation detector were used for analysis of sterol fractions using 5α-cholestane as an internal standard (Leeming et al., 1998). Results and Discussion The samples collected from all 19 sites during five sampling events over the two-year sampling period were initially assessed by comparing the average values of faecal bacterial indicators and faecal sterols for each of the site, as shown in Figure 2 and Figure 3. Microbiological water quality An assessment of the faecal indicator bacteria generally showed events of high loading except for Site 4 and Site 14 on all five separate occasions following significant rain events (Figure 2). These high bacterial load events rendered the water quality unsuitable at several of these 19 sites for primary contact such as swimming or bathing according to ANZECC (2000) guideline values of 150 thermotolerant coliform organisms/100mL or 35 enterococci organisms/100mL. Among all five sampling events, generally the lowest bacterial numbers were recorded for the sampling event undertaken on 19 April 2000. The lowest single event was on the 7 May 2001 water sample collected from Site 4, whereas the bacterial numbers at other sites in the rest of the sampling event were elevated. The highest single event was on the 28 February 2002 water sample collected from Site 8, whereas the elevated numbers at other sites in the rest of the sampling event, as well as the other sampling events, were not as large in number. There were good correlations between the measures of thermotolerant coliforms, Escherichia coli, faecal streptococci and enterococci (r2 ranged between 0.589 and 0.959) in the water samples collected from a total of 19 sites on five occasions over the two-year period. However, correlations of these bacterial indicators with Clostridium perfringens were weak to moderate (r2 ranged between 0.354 and 0.608). Faecal sterol loading An assessment of the faecal sterols showed only sporadic events of high loadings for various sites throughout the five sampling events during the two-year sampling period (Figure 3), which were generally inconsistent with the periods of high bacterial loading. Unlike bacterial numbers, generally the lowest and highest sterol concentrations were recorded for the sampling events undertaken on 7 May 2001 and 19 April 2000, respectively. The levels of coprostanol did not show good correlations with the populations of thermotolerant coliforms (r2 = 0.239), Escherichia coli (r2 = 0.17), enterococci (r2 = 0.076), faecal streptococci (r2 = 0.159) and Clostridium perfringens (r2 = 0.03) from the water samples collected from a Table 2. Sampling details. Sampling Date No. of Sites Sampled Sampling Parameters Rainfall (mm)* Bacterial Indicators Faecal Sterols 21/03/2000 7 Thermotolerant coliforms, Escherichia coli, faecal streptococci, enterococci and Clostridium perfringens Coprostanol, epicoprostanol, cholesterol, 5α-cholestanol, 24-ethylcoprostanol, 24-ethyl-epi-coprostanol, 24-ethylcholesterol and 24-ethyl-5α-cholestanol 52.0 19/04/2000 18 25.9 09/03/2001 11 41.6 07/05/2001 11 77.2 28/02/2002 11 45.0 * Collective rainfall of prior 48 hours leading to sampling date. Source: Bureau of Meteorology (BoM) website. Figure 2. Average faecal bacterial indicators (cfu/100mL) at 19 sites during March 2000--February 2002. Figure 3. Average coprostanol and 24-ethylcoprostanol concentrations (ng/L) at 19 sites during March 2000--February 2002.
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