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Article

Contribution of Treated Sewage to Nutrients and PFAS in Rivers Within Australia’s Most Important Drinking Water Catchment

by
Katherine G. Warwick
1,
Michelle M. Ryan
1,
Helen E. Nice
2 and
Ian A. Wright
1,*
1
School of Science, Western Sydney University, Penrith, NSW 2751, Australia
2
Department of Water and Environmental Regulation, Government of Western Australia, Joondalup, WA 6027, Australia
*
Author to whom correspondence should be addressed.
Urban Sci. 2025, 9(6), 182; https://doi.org/10.3390/urbansci9060182
Submission received: 27 March 2025 / Revised: 9 May 2025 / Accepted: 14 May 2025 / Published: 22 May 2025
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Abstract

:
This study investigated the contribution that treated effluent from five sewage treatment plants (STPs) made to water and sediment quality in rivers within Sydney’s Warragamba Dam catchment. Warragamba Dam is the main water supply for Australia’s largest city, supplying 90% of water for >5 million people. The catchment rivers are important habitats for biodiversity. The study was prompted by an earlier investigation that discovered elevated perfluorooctane sulfonate PFOS in the liver of a platypus found in a river in the Warragamba catchment. At the site where the PFOS-contaminated platypus was collected, the river sediment had a maximum PFAS content of 8300 ng kg−1. This study collected water upstream and downstream of five STPs and from STP discharges. River sediment samples were collected downstream of STPs for per- and poly-fluoroalkyl substances (PFAS). Water attributes included major ions, salinity, nitrogen, phosphorus, metals, and PFAS. Our study confirmed that STP effluent discharges contributed to river nutrient concentrations favourable to algae. The mean total nitrogen (TN) below STP outfalls was 2820 µg L−1, exceeding catchment guideline (TN < 250 µg L−1) by an order of magnitude. PFAS were detected in 65% of STP effluent samples and in 76.5% of river sediment samples.

1. Introduction

Access to clean and safe drinking water is a universal human right and is recognised as one of the United Nations Sustainable Development Goals (UNSDG’s), number 6—‘Clean water and sanitation’ [1]. The wording of SDG6 recognises that the provision of ‘clean drinking water’ is associated with ‘safely managed sanitation’. The health of many communities across the world has suffered as a result of inadequate sanitation contributing to the contamination of drinking water [2]. Careful collection, transport, and treatment and the safe disposal of treated sewage effluent to the environment is essential for safely managing and disposing of sewage wastes [3].
Centralised, reticulated sewerage systems have progressively been developed and improved from ancient to modern times to provide efficient and hygienic infrastructure for managing sewage and other wastes [4,5]. Effective and safe sewerage systems have allowed modern society to live in urban settlements with reduced risks of disease transmission from community exposure to faecal contamination [6]. From an ecosystem health perspective, a series of landmark studies established that releasing inadequately treated sewage effluent containing harmful contaminants can contaminate water quality and impair river ecology [7,8]. The release of inadequately treated sewage effluent containing elevated nutrients can contribute to waterway eutrophication [9].
A consequence of eutrophication can be the growth of cyanobacterial blooms in waterways [10,11]. The development of cyanobacterial blooms is influenced by several factors, particularly the abundance of nitrogen and phosphorus [12]. This is often due to human activities, including the overuse of artificial fertilizers and poorly treated sewage [9,13]. Cyanobacterial blooms (also known as blue-green algae) can produce hazardous toxins causing multiple adverse impacts [14]. Australian inland waters are particularly vulnerable to cyanobacterial blooms due to elevated nutrients, warm weather, and frequent periods of low river flows [14,15]. Over several years, the Darling Baarka River in western NSW has experienced a series of large fish kills due to eutrophication, cyanobacteria, and depleted river oxygen [16]. Human exposure to cyanobacteria through the consumption of drinking water containing algal toxins, including hepatotoxins and neurotoxins, can cause a range of illnesses, including liver damage [17,18]. Recreational activities in waterways contaminated by cyanobacteria can also trigger a range of human health issues, including skin irritation, gastroenteritis, pneumonia, and liver damage [17]. Cyanobacterial blooms are also well known to be harmful to livestock, dogs, birds, fish, and other wildlife [19,20].
In addition to being a source of nutrients, treated sewage effluent has also been identified as a potential major source of an emerging group of anthropogenic environmental contaminants called ‘per- and poly-fluoroalkyl substances’ (PFAS) [21,22]. There is growing awareness that the many PFAS compounds have the potential to persist in the environment, bioaccumulate in organisms and have adverse health effects on humans [23,24,25]. Up until recently, it was believed that there were approximately 4000 individual PFAS. However, the Organisation for Economic Cooperation and Development’s (OECD) recently revised definition of PFAS (any chemical fluorinated substances that contain at least one fully fluorinated methyl or methylene carbon atom) has resulted in this number increasing significantly. There are currently in excess of 7 million PFAS compounds listed in PubChem [26].
PFAS are highly stable due to strong carbon-fluorine bonds within their molecular structure, a property which has resulted in their extensive development and use in many products since the 1940s [23]. Due to this stability, PFAS are highly resistant to degradation and have been found to accumulate in the environment over extended time periods. This has contributed to their reputation as ‘forever chemicals’ [24]. An area of particular concern is that people may be exposed to PFAS through drinking water [25,27,28]. Contaminated drinking water can be a major pathway for human PFAS exposure. There is a growing concern that regulatory limits for PFAS in many drinking water supplies have not effectively protected people from PFAS [25].
Perfluorooctane sulfonate or perfluorooctane sulfonic acid (PFOS) within the PFAS homologue has been frequently reported in tissue from several species of wildlife across the globe, including remote regions such as the Arctic [29]. A landmark study by Giesy and Kannan [30] also revealed that predatory apex species contained concentrations of PFOS in their tissue that were substantially greater than the concentration of PFOS in their prey. This was one of many studies that revealed that PFOS can bioaccumulate in the organs of animals at higher trophic levels of food chains [29]. Research has reported that two apex riverine species, mink and river otters, bioaccumulate PFOS in their organs, particularly in their liver [31]. The largest concentrations of PFAS were detected from individual mink and otters that had been collected near industry or urban areas [31]. A large and growing literature has now reported concentrations of PFOS and other PFAS in invertebrates, fish, amphibians, reptiles, birds, and mammals worldwide [31,32,33,34,35,36]. The highest PFOS and PFAS concentrations in wildlife have been generally found near contaminated sites. Recently published research that prompted the current study recorded a highly elevated PFOS concentration (390 µg kg−1) in the liver of a deceased platypus collected in the Wingecarribee River in the Warragamba catchment [37]. The Australian and New Zealand Guidelines for Fresh and Marine Water Quality recently published revised default guideline values for PFOS in freshwater systems, based on an extensive chronic toxicity dataset from 35 species across 11 taxonomic groups [38]. The guideline value that is considered applicable for non-air breathing aquatic species in slightly to moderately disturbed systems is 9.1 ng L−1 (acknowledging that due to PFOS being classified as a persistent and bioaccumulatory toxicant, the 99% species protection level applies) [38].
The vulnerability of the Warragamba catchment to water pollution from inadequately treated wastewater was demonstrated by the ‘Cryptosporidium Crisis’ after floods from heavy rains across the catchment in 1998 washed Cryptosporidium and Giardia protozoan parasites into Sydney’s drinking water system, resulting in several weeks of boil-water alerts across the whole city [39,40,41]. Although the exact source of the Cryptosporidium was never discovered, the independent inquiry, by Justice Peter McLellan QC, found that catchment STPs, that were overloaded in wet weather, were considered to be the most likely source [40,41].
Waterways in the Warragamba catchment frequently suffer cyanobacterial blooms. For several years, public health warnings have advised people to avoid contact with affected water at several catchment locations, such as Lake Lyell on the Coxs River and two locations on the Wingecarribee River [42]. Warragamba Dam has occasionally suffered algal blooms. The most serious recorded bloom occurred over several months, starting in August 2007. That bloom of blue-green algae (cyanobacteria) was triggered by floodwaters containing very high nutrient concentrations entering the storage and the bloom rapidly spread to cover 75% of the reservoir’s surface [43,44,45]. The bloom lasted for several months and included Microcystis counts as high as 870,000 cells mL −1 [44].
The purpose of the current study was to investigate the contribution of treated sewage discharges to water quality in five major waterways within the Warragamba Dam drinking water catchment. We aimed to assess water quality focusing on three groups of pollutants: (1) nitrogen and phosphorus, (2) PFAS, and (3) metals. A further aim was to assess the effectiveness of environmental regulations that apply to the discharge of effluent from the STPs. In order to achieve these aims, we assessed water quality at five separate treated sewage discharges across the Warragamba catchment. We collected samples upstream and downstream of the five sewage outfalls. We also collected water samples of the effluent at four of the five outfalls.

2. Materials and Methods

2.1. Study Area

Warragamba Dam is a concrete gravity dam that was constructed (1948–1960) on Warragamba River to provide water security to Australia’s largest city [46]. This was after Sydney suffered severe water shortages, due to drought, from 1939 to 1945 [46,47]. The dam created a very large water impoundment, Lake Burragorang, covering 75 km2 at full storage [47]. The catchment watershed of Lake Burragorang covers 9050 km2. Several rivers feed water from their catchments into Lake Burragorang [48]. The largest river in the catchment is Wollondilly River which flows through Goulburn and drains a large part of the catchment to the south and south-west (Figure 1). The Wingecarribee River is a major tributary of the Wollondilly River that drains water from the Southern Highlands region. The Coxs River is the second largest river flowing into Lake Burragorang. It drains the catchment to the north, including the Blue Mountains and Lithgow area (Figure 1).
Nearly 30% (260,880 ha) of the Warragamba catchment is managed and protected as a Special Area under the Water NSW Act (2014) [48,49]. This includes the water storage and the lands immediately surrounding Lake Burragorang where human access is restricted to protect water quality. Most of the catchment Special Area is naturally forested, has high biodiversity and conservation values and is also co-managed as a National Park, under the National Parks and Wildlife Act (1974) [48,49]. In addition, much of the Warragamba catchment is also given additional protection, as part of the Greater Blue Mountains World Heritage Area, to protect its environmental values [50].
The remaining 70% of the Warragamba catchment, beyond the tightly controlled Special Area, is often called ‘outer catchment’ [42,43,44,45,46,47,48,49]. Much of the outer catchment land has been cleared of natural vegetation and is occupied by a range of agricultural enterprises, including grazing, forestry, viticulture, horticulture, and dairying. The total human population residing in the Warragamba catchment grew by 19.2% from 2006 to 2021 to almost 130,000 [42]. Three of the largest urban areas in the catchment are the City of Lithgow (population 11,071), the City of Goulburn (23,864), and the combined townships of Southern Highlands with 30,802 [42]. Each of these urban areas collect, transport, treat, and dispose of sewage wastewater to catchment streams or rivers.
This study investigated effluent water quality at five of the largest Warragamba catchment STPs. It also investigated the water quality of the stream or river that was recipient of effluent from each STP. We investigated treated effluent from STPs that served Lithgow, Goulburn, Mittagong, Moss Vale, and Bowral (Table 1). All STPs discharged the final treated effluent to nearby streams or rivers, although the Goulburn STP does also irrigate effluent [42]. Sampling was undertaken on either three or four occasions (October 2023 to February 2024) in dry weather conditions, with typical dry-weather stream or river flow. On each occasion, it was intended to collect samples of treated sewage at the outfall. For four of the STPs this was achieved; the exception was Moss Vale STP, where it was not possible to gain safe access. Samples were also collected from the stream or river upstream of the effluent outfall and another sample was collected downstream of the STP outfalls.
Samples were collected in the effluent-receiving creek or river upstream (US) and downstream (DS) of each STP outfall. The distance from the outfall varied according to accessibility. Sampling sites on Iron Mines Creek were 50 m US and 25 m DS of Mittagong STP outfall. For the Moss Vale STP, the sampling sites were on Whites Creek 750 m US and 2 km DS. Bowral STP sites were 120 m US and 80 m DS on Wingecarribee River. Goulburn STP sites were 250 m US and 500 m DS on Wollondilly River. Lithgow sites were 300 m US and 50 m DS of the STP outfall.
All STPs in this study are regulated by the NSW Environment Protection Authority (NSW EPA) under the licence provisions enabled by the Protection of the Environment Operations Act (NSW) using an individual Environmental Protection Licence (EPL) [51]. These licences (Table 1) detail the required environmental performance of each STP. This includes considerations of noise, odour, and liquid effluent emissions. In relation to the current study, each licence specified the name and permitted concentration of several pollutants in the final treated sewage effluent. The suite of pollutants at most STPs included biochemical oxygen demand (BOD), bacteria (E. coli or faecal coliforms), pH, total suspended solids (TSS), ammonia, total nitrogen (TN), and total phosphorus (TP). Each licence also specified the requirements for monitoring the listed pollutants in the STP effluent, usually a 2-week or monthly basis. It also specified the acceptable pollutant concentration results, which were expressed at one or more of the percentiles. These were 50%, 90%, and 100%.
For the current study, we were particularly interested in the nutrients TN, TP, and ammonia. Whilst we were also interested in metals, none of the EPLs contained any discharge limits for metals. Similarly, we were also interested in PFAS, but none were included in any of the EPLs. We also obtained daily river or stream flow volumes for the nearest flow gauging site, based on published long-term median flow statistics [42].

2.2. Water, Sediment, and STP Effluent Sampling

We collected water samples on the stream or river, upstream and downstream, of each of the five STP outfalls. On the same sampling occasion, we also collected samples of treated sewage effluent during release from the STP outfall. We were only able to collect effluent from four of the STPs. We were unable to sample effluent from the Moss Vale STP as there was no safe access, but we collected samples upstream and downstream of the STP outfall into Whites Creek. On each sampling occasion, at each site (upstream, effluent at outfall, and downstream), we collected duplicate water samples for commercial laboratory analysis.
At each sampling site downstream of the STP outfall, three or four random samples of river or stream sediment were collected on one occasion. This was conducted manually in a wadable depth within a zone of accumulated fine sediment. The sediment collection methods followed Australian and New Zealand Guidelines for Fresh and Marine Water [52]. Samples were collected by hand in 125 mL clean and unused glass sampling jars supplied by the Envirolab laboratory. As for water samples, the sediment samples were placed for storage in a cooled and insulated container. Samples were chilled and delivered to the laboratory for analysis.
We also used in situ water quality meters for the measurement of pH (pH units), electrical conductivity (µS cm−1), dissolved oxygen (mg L−1 and % saturation), water temperature (° Celsius), and turbidity (NTU). The calibration of field meters was tested, and adjusted if required, on each sampling occasion. The instruments included the following: A TPS Aqua-CP/A waterproof conductivity–pH meter was supplied by TPS PTY LTD, Brendale, Queensland. Water turbidity was measured using a HACH 2100 P Turbidimeter, supplied from Thermo-Fisher, Seven Hills, New South Wales. Dissolved oxygen (DO) was measured using a YSI Pro-DO 20 dissolved oxygen and temperature meter supplied by Xylem, Brisbane, Queensland. All field meter tests were conducted using five replicate tests per site, waiting for the meter readings to equilibrate (pH, EC, and DO).
The water and sediment samples were immediately cooled after collection and were promptly sent to Envirolab, Chatswood NSW, a commercial, National Association of Testing Authorities (NATA)-accredited laboratory for the determination of total metal concentrations, major ions, and PFAS (PFOS, PFOA (perfluorooctanoic acid), 6:2FTS, 8:2FTS, and PFHxS (perfluorohexanesulfonic acid). A total of 15 total metal concentrations were determined by inductively coupled plasma–mass spectrometry, ion concentrations by inductively coupled plasma atomic emission spectroscopy and PFAS by solid-phase extraction and liquid chromatography tandem mass spectrometry. Quality assurance measures included laboratory duplicates, laboratory blank matrix tests, and recoveries from a blank in 10% of samples, plus surrogate matrix spikes for each sample analysed in accordance with Australian requirements [52].
The laboratory limit of reporting (LOR) for major cations was 0.5 mg L−1; sulphate and chloride 1.0 mg L−1; and bicarbonate 5 mg L−1. The LORs for metals were as follows: iron and aluminium 10 µg L−1, manganese 5 µg L−1, cadmium 0.1 µg L−1, and mercury 0.05 µg L−1 s. The detection limit for all other metals was 1 µg L−1. The PFAS LORs were 10 ng L−1.

2.3. Water Quality Guideline Values for Drinking Water and Protection of Aquatic Biota

The metal results obtained after the testing of samples from upstream, downstream, and STP effluent were compared with WaterNSW ‘water quality benchmarks for catchment streams’ (Table 2).
Water quality results were also compared to the Australian and New Zealand Water Quality default guideline values for the protection of freshwater systems [48] for a suite of metals not covered by WaterNSW benchmarks [49]. For metals, the guideline values for the protection of 95% of aquatic species were selected, as is recommended for slightly to moderately disturbed systems [52]. Since PFOS is a persistent and bioaccumulatory substance, the 99% species protection level was selected in accordance with the national guidance [38].

2.4. Data Analysis

Before conducting any statistical testing, each water quality variable was examined for the heterogeneity of variance using Levene’s test. It was found that many variables were not normally distributed and consequently, a non-parametric statistical analysis technique was used. The Mann–Whitney U test was used to test for significant differences between water quality results from all samples collected upstream of STP discharges compared to all samples collected downstream. All statistical analysis was performed using IBM SPSS Statistics version 29. Some metals were not detected at concentrations above laboratory limits of reporting. In these cases, for data analysis purposes, the result was assumed to be half of the detection limit. Significance values of less than 0.05 were considered significant.

3. Results

3.1. Water Chemistry

3.1.1. General Water Quality

The mean salinity (electrical conductivity) of waterways increased as a consequence of STP effluent inflows. The mean salinity of the rivers and streams was 313 μS cm−1 upstream of STP outfalls. This increased by 43% to 450 μS cm−1 downstream (Table 3). Effluent from four STPs had a mean salinity of 645 μS cm−1. The pattern of salinity in catchment rivers varied according to location (Figure 2). The pH of streams/rivers was slightly reduced from an upstream mean of 8.3 to 8.0 downstream, with STP effluent recording a mean pH of 8.0 (Table 3).
The ionic composition of catchment streams and rivers was modified downstream of STP discharges (Table 3). The pattern of cation domination remains the same upstream (Na > Ca > Mg > K) to downstream. The largest proportional increase in cation concentration was detected for potassium. The mean potassium concentration increased from 2.7 mg L−1 upstream of STP outfalls to 8.6 mg L−1 downstream. The mean concentration of potassium in STP effluent was 13.7 mg L−1, 3.7 times greater than upstream. A similar trend was also found for anions. The overall pattern for mean anion concentration (HCO3 > Cl > SO4) was found upstream and downstream of STP outfalls. However, the mean concentration of anions in STP effluent was different (HCO3 > SO4 > Cl). This was due to the release of STP effluent containing a mean sulphate concentration of 87.7 mg L−1, which resulted in a 311% increase in the mean concentration of sulphate from upstream (12.2 mg L−1) compared to downstream (50.1 mg L−1; Table 3).

3.1.2. Nutrients

The STP effluent discharges increased the concentration of nitrogen and phosphorus downstream of STP outfalls (Table 3). The mean concentration of TN increased significantly from 486 µg L−1, upstream of all outfalls, to 2820 µg L−1 downstream, an increase of 480%. The mean TN concentration of effluent was 4682 µg L−1, which was 8.6 times greater than the mean TN concentration upstream. Mittagong STP effluent had the highest TN concentration (mean 6810 µg L−1) and Lithgow the lowest (mean 2200 µg L−1) (Figure 3a). The predominant form of nitrogen was nitrate. The mean nitrate concentration upstream of the STP outfalls was 173 µg L−1, with nitrate in STP effluent nearly 20 times greater (mean 3608 µg L−1). This increased the mean nitrate concentration downstream of outfalls by just over 1000% to 2049 µg L−1. The STP effluent also significantly increased the concentration of nitrite and ammonia in downstream waterways (Table 3).
The concentration of phosphorus in catchment rivers and streams was significantly increased downstream of STP outfalls (Table 3). The mean concentration of TP, downstream of STP outfalls, increased significantly from 41.3 µg L−1, upstream, increasing by 150%, to 103 µg L−1 downstream. The STP effluent had an overall mean TP concentration of 234 µg L−1, which was 4.7 times greater than the mean TP concentration upstream. The contribution of STP effluent to TP in catchment waterways varied across the different locations. Goulburn effluent contained the most enriched TP (mean 417 µg L−1) with Mittagong the least (mean 85 µg L−1) (Figure 3b).

3.1.3. Metals

There were 10 metals tested in water and effluent samples in this study (Table 3). Based on pooled data, the mean concentration of four of the metals (aluminium, lithium, nickel, and zinc) increased significantly (>0.05) downstream of the STP outfalls. The mean concentration of three metals (barium, iron, and manganese) was smaller downstream of the STP outfall (Table 3). The largest overall increase was recorded for aluminium, which had a mean concentration of 337 µg L−1 upstream of STP outfalls, increasing by 51%, to 479.7 µg L−1 downstream (Figure 3c). The mean aluminium concentration of STP effluent was 506.5 µg L−1. The second largest increase for metals was measured for zinc. It had a mean upstream concentration of 11.4 µg L−1 and was 33% higher downstream (mean 15.2 µg L−1). This mean concentration of zinc is less than the hardness-corrected 95% species protection guideline of 20 µg L−1 [52]. Overall, STP effluent samples had a mean zinc concentration of 26.6 µg L−1.

3.1.4. PFAS

A total of 22 river samples in this study were tested for PFAS (Table 4). They were collected from streams downstream of STP outfalls. We detected measurable amounts (≥0.01 µg L−1) of PFAS in four of the twenty-two samples collected below STPs. The detected concentration, in all cases, was at the lowest LOR (0.01 µg L−1). The most frequently detected PFAS was PFHxS (three of twenty-two samples) and a single sample had a detectable amount of PFOS (0.01 µg L−1). We also tested 22 STP effluent samples for PFAS and detected concentrations (≥0.01 µg L−1) of PFAS in 17 of 22 samples of STP effluent. The detected concentrations of effluent ranged from 0.01 to 0.07 µg L−1. The most frequently detected was PFOS (13 of 22 samples) with a mean concentration of 0.025 µg L−1 in the 13 effluent samples where it was detected (Figure 4a). PFHxS was found at detectable concentrations in seven of twenty-two effluent samples) with a mean concentration of 0.021 µg L−1, across the effluent samples where it was detected.
PFAS chemicals were detected frequently (76.5%) in river sediment samples collected downstream of STP outfalls (Table 5). PFOS frequently (13 detections in 17 samples) was found at detectable concentrations ranging from 0.1 to 7.6 µg kg−1 (mean 1.22 µg kg−1) (Figure 4b). The PFOS concentrations in river sediment samples were highly variable. For example, the river sediment samples collected downstream of Bowral STP were tested for PFOS with results ranging from <LOR to 7.6 µg kg−1, which resulted in large error bars in Figure 4b. Two sediment samples had detectable PFOA at the LOR (0.1 µg kg−1). One sediment sample detected PFHxS (0.6 µg kg−1).

4. Discussion

Results from this study reveal that the disposal of treated STP effluent into Warragamba catchment rivers is contributing to the impairment of river and stream water quality. STP effluent was enriched with nutrients (total nitrogen, ammoniacal nitrogen, and total phosphorus), two metals (aluminium and nickel), and salinity greater than concentrations measured upstream of STP outfalls. The concentration of these pollutants generally exceeded recommended NSW Government catchment guidelines in rivers downstream of the STP outfalls [42].
PFAS were often detected in Warragamba catchment STP effluent but less often, and in much lower concentrations, in river water samples below STP outfalls. However, PFAS were frequently detected in river sediment samples collected downstream of STPs. The mean PFAS concentration of all river sediment samples was 935 ng kg−1. One sampling site had the largest PFAS content. It was the site on the Wingecarribee River at Berrima, downstream from Bowral STP. One sediment sample collected from this site had the highest PFAS content in this study with 8300 ng kg−1, dominated by a PFOS content of 7600 ng kg−1. This was also the location that a platypus was found in a previous study, linked to this one, with an elevated PFOS (390 µg kg−1) content in its liver [37]. We speculate that the accumulation of PFAS in this platypus was probably due to the enriched PFAS content in river sediment that was consumed by the platypus as they foraged amongst the stream bed for invertebrate food. Platypus are known to ingest substantial amounts of sediment in their diet [53].
The contribution of STP effluent to the degradation of Warragamba catchment river water quality is consistent with ‘water pollution’, as defined in the Protection of the Environment Operations (POEO) Act, 1997 [51]. However, although the disposal of STP effluent contained elevated concentrations of total nitrogen, ammonia, and total phosphorus, these were within permitted pollutant concentrations according to their NSW EPA ‘environmental protection’ STP licences (Table 1) [51]. The NSW EPA’s environmental protection licences permit the release of STP effluent into Warragamba catchment waterways containing TN at maximum concentrations ranging from 7500 µg L−1 to 15,000 µg L−1 (Table 1). The TN concentration of STP effluent samples in our study ranged from 1100 to 10,000 µg L−1, with a mean of 4700 µg L−1. Based on pooled results, the discharge of effluent increased the TN concentration in rivers from an upstream mean of 480 µg L−1 by 480% to 2800 µg L−1 downstream. Both upstream and also the downstream nitrogen results exceed WaterNSW’s catchment river TN guideline of <250 µg L−1 [49]. Such elevated concentrations of nitrogen in the Warragamba catchment rivers are known. It relates to one of the key findings from the most recent three-yearly independent catchment and storage audit which reported that the nutrient load of catchment rivers was worsening [42]. Our nutrient findings at least partly explain how elevated nutrient concentrations in Warragamba catchment STP releases and in waterways below the outfalls contribute to problematic cyanobacterial blooms [42,43,44,45].
Our current study also recorded concentrations of total phosphorus and ammonia in catchment STP effluent and in waterways downstream of STP outfalls at concentrations above the WaterNSW guideline of <250 µg L−1 and <13 µg L−1, respectively, indicating the potential for environmental harm. Overall, our study found that STP effluent discharges increased overall TP concentration from 41.3 µg L−1 (upstream) to 102.6 µg L−1 (downstream). This was an increase of 148%. All TP results, including upstream of STPs, exceeded WaterNSW’s catchment TP guideline of <20 µg L−1 [49].
The concentration of nitrogen and phosphorus recorded in Warragamba catchment waterways, below STP outfalls, was broadly similar to the nutrient concentration reported in a western NSW river that experienced harmful algal blooms and major fish kills in 2019 [54]. The catastrophic fish kills occurred at several locations, including at Weir 32 of the Darling-Baarka River, at Menindee. At this location a toxic cyanobacteria bloom had developed with environmental conditions favourable to algal growth, including nitrogen (>2000 µg L−1) and phosphorus (>200 µg L−1) [54,55]. Several locations within the Warragamba catchment have also recorded hazardous algal blooms. For example, Lake Lyell regularly suffers major blooms that result in health warnings [42,56]. Lake Lyell is an artificial impoundment on the Coxs River. It is downstream of Farmers Creek and the Lithgow STP outfall. It is also of heightened human health concern as it is one of the most popular waterways for camping, boating, fishing, and other forms of aquatic recreation in the Warragamba catchment [48]. Over the period of July 2019 to June 2022, this lake was under blue-green health warnings for 118 weeks, with 19 of those weeks at the most dangerous red alert level [42]. A second river often impaired by cyanobacteria warnings in the Warragamba catchment is the Wingecarribee River, in the Southern Highlands region [42].
Sydney’s main drinking water storage, Lake Burragorang, has also demonstrated vulnerability to cyanobacterial blooms [57]. One of the largest documented blooms started in August 2007. This bloom originated in the waters near the water supply off-take, near the dam wall, and later spread to cover a much larger area covering more than 75% of the lake surface [44,45]. The bloom lasted for several months and included Microcystis counts as high as 870,000 cells mL−1 [44]. It was attributed to a combination of water temperature, the seasonal mixing of lake waters, and elevated nitrogen and phosphorus inflows from catchment due to post-drought flood waters [44]. Total nitrogen concentrations in samples collected at the time in the two largest catchments rivers (Wollondilly River and Coxs River) frequently exceeded 1000 µg L−1 and often were above 2000 µg L−1 [44].
Frequently, the total nitrogen concentrations in Lake Burragorang have exceeded the WaterNSW guideline (<350 µg L−1) according to the recent 2019–2022 audit [42]. The audit reported that all nine water sampling stations within Lake Burragorang had median TN concentrations exceeding the <350 µg L−1 stored water guideline, with median concentrations ranging from 550 to 710 µg L−1 [42]. Recently, the phosphorus content in Lake Burragorang has been less enriched, compared to nitrogen. The median phosphorus concentrations in Lake Burragorang waters exceeded the TP stored water guideline (<10 µg L−1) at two of the nine sampling stations, both recording 20 µg L−1 [42]. We recommend that more detailed information on catchment algae, including both chlorophyll and algae monitoring, is regularly conducted on all major Warragamba catchment rivers above and below all STP discharges. This should also include nutrient testing to more thoroughly understand the contribution of STP effluent to the species composition and abundance of waterway algae, including cyanobacteria.
We suggest upgrades to the treatment processes that target the removal of nutrients (and other pollutants) prior to discharge, such that concentrations both in the downstream receiving environment and in Lake Burragorang meet the relevant thresholds set by WaterNSW. Our current study and the recent independent catchment audit both documented the hazardous concentration of nutrients in catchment rivers. With growing catchment populations and subsequent increases in the volume of wastewater, this issue has considerable urgency. Consideration should be given to the ambitious recent goals set by the European Parliament. They recently proposed that urban wastewater treatment imposes stricter targets for greater nutrient removal [58]. For example, their proposal recommends that TN in wastewater discharges be reducing to less than 6 mg L−1. This is considerably less than the currently permitted maximum concentrations in the Warragamba catchment STP discharges. The European Parliament has also expressed a longer-term aim for even more stringent future criteria that will achieve lower pollutant concentrations from the quaternary treatment of wastewater by 2035, particularly where wastewater is discharged to sensitive locations, such as drinking water catchments [58]. Advancements in wastewater treatment using microfiltration technologies offer major improvements in pollutant removal [59]. High-pressure membrane wastewater treatment offers improved removal of micropollutants, such as PFAS chemicals [59].
This current investigation is the first published study of testing for PFAS within a major Australian drinking water catchment with a focus on multiple point-source treated sewage discharges. The study has established that STPs are discharging effluent that contains PFAS into the Warragamba catchment waterways. However, the concentrations of PFAS found in this study (PFOA, PFHxS, and PFOS) in the rivers downstream of the STPs were very low and were well below the Australian Drinking Water Guidelines [60]. Although, the Australian PFAS guidelines are broadly less stringent than the new USEPA guidelines [61]. The Australian Drinking Water Guidelines for PFAS are currently being revised [62] and the recommended new PFOS concentration is likely to be 4 ng L−1, which was less than the LOR in this study. The concentration of PFOS in catchment rivers in this study was also generally lower than the recently revised Australian water quality default guideline value (9.1 ng L−1) for the protection of slightly to moderately disturbed aquatic ecosystems, as relevant to this catchment) [38]. The concentrations of PFAS chemicals in STP effluent in this study were similar, and for some compounds, less than has been reported from other Australian WWTP effluent samples. For example, Coggan et al. [22] reported that the mean concentration of PFOS from 201 effluent samples from 19 WWTPs was 15 ng L−1. In comparison, in this current study, the mean PFOS concentration in STP effluent was 16 ng L−1. The concentration of PFOA in STP effluent in our study (mean = 4 ng L−1) was less than the mean PFOA concentration of 19 ng L−1 reported by Coggan et al. [22].

5. Conclusions

This study has revealed that environmentally hazardous nutrient concentrations were discharged in effluent discharged from five STPs in the Warragamba catchment. When these data are considered in conjunction with other published results, such as the recent Drinking Water Catchment Audit [40], there is a growing need for a reduction of nutrient inputs at a catchment scale. As such, it is suggested that consideration be given to improved nutrient removal treatment for all Warragamba catchment STPs. This is important as nutrient loads are anticipated to increase due to the steadily increasing catchment urban population. This study also shows the presence of PFOA, PFHxS, and PFOS in the treated sewage effluent, with PFHxS and PFOS also measurable in the downstream receiving environment (in river water), and PFOS (in river sediments). One of the sites in this study had a sediment sample containing 8300 ng kg−1 of PFAS, indicating a PFAS sediment bioaccumulation area. While PFOS concentrations in flowing water were generally below Australian guideline values, we suggest consideration should be given to establishing effluent disposal licence requirements that impose concentration limits and require the regular measurement of PFAS. This is particularly important given the dependence on the Warragamba catchment as a drinking water supply. We also recommended that the source and concentration of PFAS in Warragamba catchment STPs and rivers is thoroughly investigated over an extended period of time. Other potential sources of PFAS contamination in the Warragamba catchment could be from landfills or fire training locations that may have used PFAS chemicals [27].

Author Contributions

Conceptualization (I.A.W., K.G.W. and M.M.R.), methodology (I.A.W. and K.G.W.), formal analysis (I.A.W. and K.G.W.), writing—original draft preparation (I.A.W. and K.G.W.), writing—review and editing (I.A.W., M.M.R., K.G.W. and H.E.N.), visualization (I.A.W. and K.G.W.). All authors have read and agreed to the published version of the manuscript.

Funding

This research received funding from Western Sydney University Sustainability Development Goals Project Allowance Grants awarded to KW.

Data Availability Statement

Data supporting the findings of this study are available from the corresponding author upon email request.

Acknowledgments

We acknowledge that this study was conducted on the lands of Aboriginal Nations, including Dharawal, Gundungurra, Ngunnawal, and Wiradjuri. We would like to thank WSU Senior Technical Support Officers, Sue Cusbert and Sharon Armstrong, for their expertise and ongoing support for this project.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
EPLEnvironmental Protection Licence
PFASperfluoroalkyl substances
PFOAperfluorooctanoic acid
PFOSperfluorooctane sulfonate
PFHxSperfluorohexanesulfonic acid
STPsewage treatment plant
WWTPswastewater treatment plants

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Urbansci 09 00182 g001
Figure 1. Study area map showing location of five wastewater treatment plant outfalls (red triangle symbols) and major rivers within the Warragamba Dam drinking water catchment. Australian and NSW map show location of study area at broader scales. The location of the Warragamba catchment is shaded in light blue on the NSW maps.
Figure 1. Study area map showing location of five wastewater treatment plant outfalls (red triangle symbols) and major rivers within the Warragamba Dam drinking water catchment. Australian and NSW map show location of study area at broader scales. The location of the Warragamba catchment is shaded in light blue on the NSW maps.
Urbansci 09 00182 g001
Urbansci 09 00182 g002
Figure 2. Mean water quality (plus/minus standard error of mean) concentration, by STP location, for Electrical conductivity (us/cm−1). The red dotted line indicates the maximum recommended WaterNSW catchment river ‘benchmark’ guidelines [47].
Figure 2. Mean water quality (plus/minus standard error of mean) concentration, by STP location, for Electrical conductivity (us/cm−1). The red dotted line indicates the maximum recommended WaterNSW catchment river ‘benchmark’ guidelines [47].
Urbansci 09 00182 g002
Urbansci 09 00182 g003aUrbansci 09 00182 g003b
Figure 3. Mean water quality (plus/minus standard error of mean) concentration, by STP location, for (a) Total Nitrogen, (b) Total Phosphorus, and (c), Aluminium. The red dotted line indicates the maximum recommended WaterNSW catchment river ‘benchmark’ guidelines [47].
Figure 3. Mean water quality (plus/minus standard error of mean) concentration, by STP location, for (a) Total Nitrogen, (b) Total Phosphorus, and (c), Aluminium. The red dotted line indicates the maximum recommended WaterNSW catchment river ‘benchmark’ guidelines [47].
Urbansci 09 00182 g003aUrbansci 09 00182 g003b
Urbansci 09 00182 g004
Figure 4. (a) Mean PFAS concentration (∑ PFOA, PFOS, and PFHxS) in STP effluent and rivers downstream of STP outfalls. (b) Mean PFOS concentration (plus/minus standard error of mean) in river sediment downstream of STP outfalls.
Figure 4. (a) Mean PFAS concentration (∑ PFOA, PFOS, and PFHxS) in STP effluent and rivers downstream of STP outfalls. (b) Mean PFOS concentration (plus/minus standard error of mean) in river sediment downstream of STP outfalls.
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Table 1. Location and summary details of five Warragamba catchment sewage treatment plants (STP) and corresponding Environment Protection Licence (EPL) details (51). This includes annual volume (mega litres ML), EPL number, date of 5-year licence review, and the location and waterway that effluent is disposed in. The permitted maximum concentration of total nitrogen (TN) and total phosphorus (TP) for specified time percentiles (50%, 90%, and 100%) discharge limits. * River flow is long-term median daily flow [42].
Table 1. Location and summary details of five Warragamba catchment sewage treatment plants (STP) and corresponding Environment Protection Licence (EPL) details (51). This includes annual volume (mega litres ML), EPL number, date of 5-year licence review, and the location and waterway that effluent is disposed in. The permitted maximum concentration of total nitrogen (TN) and total phosphorus (TP) for specified time percentiles (50%, 90%, and 100%) discharge limits. * River flow is long-term median daily flow [42].
LithgowGoulburnMittagongMoss ValeBowral
Lithgow CouncilGoulburn-Mulwaree CouncilWingecarribee Shire CouncilWingecarribee Shire CouncilWingecarribee Shire Council
Annual volume1000–5000 ML1000–s5000 ML1000–5000 ML219–1000 ML1000–5000 ML
EPL number23617421036217311749
EPL 5-year
review		3 October 202411 May 20259 August 202415 January 202615 January 2026
Coordinates of
STP outfall		33.4749° S 150.1351° W34.7370° S 149.7477° W34.4449° S 150.4382° W34.5420° S 150.3572° W34.4998° S 150.3867° W
Discharging toFarmers CkWollondilly RiverNattai River via Iron Mines CkWhites CkWingecarribee River
Treatment
system		Traditional trickling filtration and activated sludge treatment systemMembrane bioreactor and diffused aeration systemIntermittently decanted extended aeration (IDEA) and activated sludgeIntermittently decanted extended aeration (IDEA) and active sludgeIntermittently decanted extended aeration (IDEA) and activated sludge
TN<10 mg L−1 (90%)
<15 mg L−1 (100%)		<10 mg L−1 (90%)
<15 mg L−1 (100%)		<10 mg L−1 (90%)<10 mg L−1 (90%)<7.5 mg L−1 (50%)
<10 mg L−1 (90%)
TP<0.5 mg L−1 (90%)
<1 mg L−1 (100%)		<2 mg L−1 (90%)
<3 mg L−1 (100%)		<0.3 mg L−1 (90%)<0.5 mg L−1 (50%)
<1 mg L−1 (90%)		<0.3 mg L−1 (50%)
<0.5 mg L−1 (90%)
Ammonia<2 mg L−1 (90%)
<5 mg L−1 (100%)		<2 mg L−1 (90%)<2 mg L−1 (90%)<2 mg L−1 (90%)<2 mg L−1 (90%)
* River flow
(ML/day)		Farmers Creek (15.5 ML day−1)Wollondilly River (11.5 ML day−1)Nattai River (5.6 ML day−1)No data available Whites CreekWingecarribee River (30.8 ML day−1)
Table 2. WaterNSW water quality ‘benchmark’ guidelines for drinking water catchment streams and rivers [49].
Table 2. WaterNSW water quality ‘benchmark’ guidelines for drinking water catchment streams and rivers [49].
Indicator (Units)Benchmark Range
pH (pH units)6.5–8.0
Chlorophyll a (µg L−1)<5
Dissolved oxygen (% saturation)90–110
Total nitrogen (µg L−1)<250
Ammoniacal nitrogen (µg L−1)<13
Oxidised nitrogen (µg L−1)<15
Total phosphorus (µg L−1)<20
Filterable reactive phosphorus (µg L−1)<15
Turbidity (NTU)<25
Total aluminium (µg L−1)<55
Total manganese (µg L−1)<1900
Conductivity (μS cm−1)<350
Table 3. Summary results for water quality parameters, collected from waterways upstream and downstream of STP outfalls. Results also provided for effluent from four STPs. The range (minimum to maximum) and mean values are given. Mann–Whitney U test results (significance values) are for comparison of upstream versus downstream for each attribute. Significant (<0.05) differences are bolded.
Table 3. Summary results for water quality parameters, collected from waterways upstream and downstream of STP outfalls. Results also provided for effluent from four STPs. The range (minimum to maximum) and mean values are given. Mann–Whitney U test results (significance values) are for comparison of upstream versus downstream for each attribute. Significant (<0.05) differences are bolded.
Rivers/Streams Receiving STP EffluentSTP Effluent
US vs. DS
(Mann–Whitney)		Upstream Downstream Outfall Discharge
Water Quality
Attribute		SignificanceRange
(Min.–Max.)		Mean Range
(Min.–Max.)		MeanRange
(Min.–Max.)		Mean
pH (pH units)0.0067.0–9.48.37.1–9.48.0 7.1–9.68.0
EC (μS cm−1)<0.00160.7–803.9312.8109.1–893449.5 91–1109645.2
Water temp. (°C)0.06211.9–25.217.912.1–27.519.3 14.7–24.419.7
Turbidity (NTU)0.9341.93–69.817.90.23–55.914.5 0.26–8.83.4
Dissolved oxygen (% saturation)0.33246.1–11080.824.5–231.389.5 64.6–9984.1
Aluminium (µg L−1)0.00450–1300337.0100–1100479.7 20–1000506.5
Barium (µg L−1)0.01610–8135.43–5624.7 3–2010.3
Copper (µg L−1)0.195<1–41.4<1–31.1 <1–71.6
Iron (µg L−1)0.003260–1900673.320–1800421.6 <1–460122.2
Lead (µg L−1)0.017<1–20.7<1–30.6 <1<1
Lithium (µg L−1)0.013<1–112.4<1–194.4 2–5 3.5
Manganese (µg L−1)0.1078–360118.930–35084.5 31–14068.6
Nickel (µg L−1)<0.001<1–30.9<1–21.3 <1–31.7
Strontium (µg L−1)0.38721–23094.926–230 77.1 34–19073.7
Zinc (µg L−1)0.0032–3011.47–3015.2 13–6826.6
Calcium (mg L−1)0.6532–2913.02–2714.1 5.6–2415.7
Sodium (mg L−1)0.0034–8626.68–8037.3 30–14065.9
Potassium (mg L−1)<0.0011–9.12.72–188.6 8.6–1913.7
Magnesium (mg L−1)0.1820.6–228.30.9–2311.2 2–2110.4
Bicarbonate (mg L−1)0.55910–18075.527–14080.1 27–190 95.0
Chloride (mg L−1)0.1044–14041.86–13054.7 20–15057.9
Sulfate (mg L−1)<0.0013–5812.25–11050.161–13087.7
Total nitrogen (µg L−1)<0.001200–1300486400–11,00028221100–10,000 4682
Nitrate (µg L−1)<0.001<5–670172.6110–74002049 310–77003608
Nitrite (µg L−1)<0.001<5–527.1<5–31046.4 <5–790108.6
Ammonia (µg L−1)0.016<5–16049.5<5–1100150.3 <5–1100404
Total phosphorus
(µg L−1)		<0.001<5–9041.3<5–400102.670–500233.8
Table 4. Results for per- and poly-fluoroalkyl substances (PFAS) detected in pooled STP effluent (ng L −1) and in river/stream water samples (ng L −1) collected from waterways downstream of STP outfalls. The minimum to maximum concentrations are provided, and the proportion (%) of samples that had detectable concentrations of PFAS or perfluorooctanoic acid, perfluorooctane sulfonate, or perfluorohexanesulfonic acid (PFOA, PFOS, or PFHxS).
Table 4. Results for per- and poly-fluoroalkyl substances (PFAS) detected in pooled STP effluent (ng L −1) and in river/stream water samples (ng L −1) collected from waterways downstream of STP outfalls. The minimum to maximum concentrations are provided, and the proportion (%) of samples that had detectable concentrations of PFAS or perfluorooctanoic acid, perfluorooctane sulfonate, or perfluorohexanesulfonic acid (PFOA, PFOS, or PFHxS).
LORWaterway Below STP Min.–Max. (Mean)% Samples Containing SubstanceSTP Effluent
Min.–Max. (Mean)		% Samples Containing Substance
PFHxS ≥10 ng L−1 <LOR −10 (1.5)15<LOR −30 (10.5)50
PFOA≥10 ng L−1<LOR0<LOR −20 (4)35
PFOS≥10 ng L−1<LOR −10 (0.5)5<LOR −40 (16)65
PFAS≥10 ng L−1<LOR −10 (2.0)20<LOR −70 (29)65
Table 5. Results for PFAS (ng kg−1) detected in sediment collected in river/stream downstream of STP outfalls. The minimum to maximum concentrations are provided, and the proportion (%) of samples that had detectable concentrations of PFAS or PFOA, PFOS, or PFHxS.
Table 5. Results for PFAS (ng kg−1) detected in sediment collected in river/stream downstream of STP outfalls. The minimum to maximum concentrations are provided, and the proportion (%) of samples that had detectable concentrations of PFAS or PFOA, PFOS, or PFHxS.
LORSediment DS STP
Min.–Max. (Mean)		% Samples Detected Substance
PFHxS (sediment)≥10 ng kg−1<LOR −600 (35.3)5.9
PFOA (sediment)≥10 ng kg−1<LOR −100 (11.8)11.8
PFOS (sediment)≥10 ng kg−1<LOR −7600 (935.3)76.5
PFAS (sediment)≥10 ng kg−1BD −8300 (988.2)76.5
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MDPI and ACS Style

Warwick, K.G.; Ryan, M.M.; Nice, H.E.; Wright, I.A. Contribution of Treated Sewage to Nutrients and PFAS in Rivers Within Australia’s Most Important Drinking Water Catchment. Urban Sci. 2025, 9, 182. https://doi.org/10.3390/urbansci9060182

AMA Style

Warwick KG, Ryan MM, Nice HE, Wright IA. Contribution of Treated Sewage to Nutrients and PFAS in Rivers Within Australia’s Most Important Drinking Water Catchment. Urban Science. 2025; 9(6):182. https://doi.org/10.3390/urbansci9060182

Chicago/Turabian Style

Warwick, Katherine G., Michelle M. Ryan, Helen E. Nice, and Ian A. Wright. 2025. "Contribution of Treated Sewage to Nutrients and PFAS in Rivers Within Australia’s Most Important Drinking Water Catchment" Urban Science 9, no. 6: 182. https://doi.org/10.3390/urbansci9060182

APA Style

Warwick, K. G., Ryan, M. M., Nice, H. E., & Wright, I. A. (2025). Contribution of Treated Sewage to Nutrients and PFAS in Rivers Within Australia’s Most Important Drinking Water Catchment. Urban Science, 9(6), 182. https://doi.org/10.3390/urbansci9060182

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