Water Journal : Water Journal July 2012
refereed paper public health water JULY 2012 81 total of 19 sites on five occasions. This suggested that noteworthy associations between loadings of coprostanol and faecal bacteria may not always occur. The stability of both these parameters in environmental sources may autonomously vary seasonally and by other physical factors affecting their survival and chemical stability. Total sterol content of the water samples based on analysis of eight sterols varied between 370ng/L and 28,000ng/L. The lowest single event for total sterol loading was on the 7 May 2001 water sample collected from Site 3. The highest single event of total sterol loading was on the 19 April 2000 water sample collected from Site 19, whereas the total sterol content at other sites in the rest of the sampling event, as well as the other sampling events, were not as large in number. The levels of coprostanol and 24-ethylcoprostanol seemed to be correlated (r2 = 0.977). The highest single event for coprostanol loading (6864ng/L) was recorded on the 19 April 2000 water sample collected from the Site 2, whereas the coprostanol numbers at other sites in the rest of the sampling event, as well as the other sampling events, were not as large in number. The lowest events for coprostanol loading (less than detection limit) were recorded twice on the 21 March 2000 water samples collected from Site 6 and Site 15, and once on the 28 February 2002 water sample collected from Site 19. Cholesterol levels were generally much higher than combined levels of both coprostanol and 24-ethylcoprostanol. Cholesterol levels did not show close correlation with either coprostanol (r2 = 0.412) or 24-ethylcoprostanol (r2 = 0.443) levels. Cholesterol and 24-ethylcholesterol levels showed good correlation (r2 = 0.876). Combined levels of cholesterol and 24-ethylcholesterol accounted for 79% of total sterol content on average. Identification of faecal pollution sources The average sterol data for these investigations were assessed as per Table 3 criteria (Leeming et al., 1998), as well as using average absolute concentrations of sterols to provide an overall analysis in terms of the percentage of contamination identified as human, herbivore or diffuse (birds etc. or not identifiable). Figure 4 shows graphical presentations for all the sites sampled with a breakdown of average % human, % herbivore and % diffuse sources, ranked in terms of human contribution, in bar chart format. Faecal sterol ratios generally estimated diffuse sources such as birds as the most significant contributing source (ranging from 15% to 100%) of the detected faecal pollution at the majority of these sites (Figure 4). Presence of average herbivore contamination was estimated as minimal for all the sites except for Site 14 (74%) and Site 7 (40%), which were estimated to have significant herbivore contamination. This was considered consistent with land use characteristics of these sites. The contribution from likely human faecal sources was generally estimated as minimal by faecal sterol ratios with the maximum average human contamination at any of these sites being 45% of the total detected faecal pollution. Out of 19 sites, a total of 15 sites was estimated to be impacted by human faecal contamination. Out of these 15 sites, only one site was estimated with > 40%, three sites between 20--40% and 10--20% each and eight sites with < 10% Table 3. Criteria against which samples were identified as having human and/or herbivore faecal contamination. Criteria Group → A B C Criteria to Determine Human Faecal Contamination Ratios → Criteria 1, 2 & 3 all fulfilled Either of 1, 2 or 3 fulfilled If group B criteria not fulfilled, but not all group A criteria fulfilled, then sample is designated intermediate and may require further investigation 1 coprostanol/5α-cholestanol ≥ 0.5 ≤ 0.3 2 epicoprostanol/coprostanol ≤ 0.4 ≥ 0.4 3 coprostanol/cholesterol ≥ 0.1 ≤ 0.05 Criteria to Determine Herbivore Faecal Contamination Ratios → Criteria 4 & 5 both fulfilled Either of 4 or 5 fulfilled If group B criteria not fulfilled, but not all group A criteria fulfilled, then sample is designated intermediate and may require further investigation 4 24-ethylcoprostanol/ 24-ethyl-5α-cholestanol ≥ 0.5 ≤ 0.3 5 24-ethylcoprostanol/ 24-ethylcholesterol ≥ 0.1 ≤ 0.05 A = contaminated sample, B = uncontaminated sample, C = intermediate Source: Leeming et al. (1998) Figure 4. Sources of faecal pollution (% average) as interpreted by faecal sterol ratios at 19 sites during March 2000--February 2002.
Water Journal August 2012
Water Journal May 2012