Abstract
This study investigated the magnitude of wet weather overflow (WWO)-driven sewage pollution in an urban lake (Lake Parramatta) located in Sydney, New South Wales, Australia. Water samples were collected during a dry weather period and after two storm events, and tested for a range of novel and established sewage- [Bacteroides HF183, crAssphage CPQ_056 and pepper mild mottle virus (PMMoV)] and animal feces-associated (Bacteroides BacCan-UCD, cowM2 and Helicobacter spp. associated GFD) microbial source tracking marker genes along with the enumeration of culturable fecal indicator bacteria (FIB), namely Escherichia coli (E. coli) and Enterococcus spp. The magnitude of general and source-specific fecal pollution was low in water samples collected during dry weather compared to storm events. The levels of HF183, crAssphage and PMMoV in water samples collected during storm events were as high as 6.39, 6.33 and 5.27 log10 GC/L of water, respectively. Moderate to strong positive correlations were observed among the quantitative occurrence of sewage-associated marker genes. The concentrations of HF183 and PMMoV in most storm water samples exceeded the risk benchmark threshold values established in the literature for primary contact recreators. None of the samples tested was positive for the cowM2 (cow) marker gene, while BacCan-UCD (dog) and GFD (avian) animal-associated markers were sporadically detected in water samples collected from both dry weather and storm events. Based on the results, the ongoing advice that swimming should be avoided for several days after storm events appears appropriate. Further research to determine the decay rates of sewage-associated marker genes in relation to each other and enteric viruses would help refine current advice. Microbial source tracking approaches employed in this study provided insights into sources of contamination over currently used FIB.
Highlights
The primary risk associated with fecal pollution is human health
The mean concentration of E. coli (EC) in storm events 1 and 2 samples were significantly (p < 0.05) different from those samples collected in dry weather event at 0.5 m below the water surface but not at depth 1 m above the bottom of the lake
The concentrations of the HF183 in all quantifiable samples exceeded the established GI risk benchmarks for 30 or 36 GI illness/1,000 primary contact recreators for a swimming event, suggesting that swimming immediately after the storm event may pose a human health risk. Concentrations of both culturable fecal indicator bacteria (FIB) in lake water samples during the dry weather event suggested the occurrence of low levels of fecal pollution
Summary
The primary risk associated with fecal pollution is human health. Fecally contaminated water may contain numerous pathogens with low infectious doses with the potential to cause diseases in recreational water users[1]. To understand the human health risks associated with fecally contaminated water, it is ideal to screen for pathogens. It is impractical, time-consuming, cost-prohibitive and technologically challenging to screen water samples for all potential pathogens. Sewerage systems in Australia are designed with overflow (emergency relief) structures that release untreated sewage into the environmental waters when the capacity is surpassed[23] This design is employed to minimize human-health risk from discharges within properties. Wet weather overflows (WWOs) are caused by the infiltration of water into the sewage system during heavy rainfall to a point at which the hydraulic capacity of the system is exceeded When such an event occurs, environmental and recreational waters receive sewage-contaminated stormwater, which may have an adverse impact on human and ecosystem health
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