In early September 2024, Friends of the Earth applied to Melbourne Water in a Freedom of Information request concerning detections of PFAS chemicals since 2022 and pesticides in Melbourne's drinking water supplies since 2017. After a lengthy process information was provided on the 30th of December. In terms of PFAS there were no detections. This is partly due to Melbourne Water's third round of PFAS testing which commenced in August 2024. Prior to this date, Melbourne Water conducted PFAS testing at seven locations between 2010-11 and 2014-17. PFAS chemicals were detected at Lilydale Water Treatment Plant in 2010 and also twice at the Yarra River offtake to Sugarloaf Reservoir in 2011 and 2015.  It appears that PFAS chemicals have recently been detected by Melbourne Water, but they were detected after the FoI application was sent in.

In terms of pesticides, impacts on the Yarra River and Sugarloaf Reservoir have long been a concern to Friends of the Earth. Water from the Yarra River is pumped into Sugarloaf Reservoir where it is stored prior to treatment. The water is then treated at Winneke Treatment Plant before being distributed to Melbourne's northern and western suburbs. The Winneke Treatment Plant was never designed to properly filter out micropollutants such as pesticides, microplastics and PFAS. 

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The offtake to Sugarloaf Reservoir is located on the Yarra River in Yering Gorge, north west of Lilydale.

There were 173 pesticide detections by Melbourne Water since November 2019. 155 detections (89.6%) were from the Yarra River near Sugarloaf, with a dozen detections after treatment at Winneke Treatment Plant. This represents the first time that pesticides have been detected after treatment at Winneke. It is well known that standard forms of water treatment will not remove all micro-pollutants from water. It is also clear that retaining water with pesticide residues in a reservoir the size of Sugarloaf may not dilute the contaminant to undetectable levels. One wonders what the PFAS levels actually are in Sugarloaf Reservoir.

Map of Sugarloaf Reservoir. The Yarra pumps can be seen at the bottom left/centre of image. Water is pumped from the Yarra into Sugarloaf Reservoir. Sugarloaf also receives water from the Maroondah Reservoir and in times of low water availability from the North-South Pipeline (sourced from the Goulburn River near where PFAS has recently been detected).  After storage, the water is treated at Winneke Treatment Plant, which can be seen at the left of the reservoir in the image. The Winneke Treatment plant utilises sand and membrane filters. Water from Winneke is then piped to mainly northern and western suburbs of Melbourne.

Average Simazine detections after treatment at Winneke totaled 0.036µg/L* or 0.18% of the Australian Drinking Water Guidelines. Post treatment, Simazine was detected seven times, Metolachlor four times and MCPA once over the five year period. (*µg/L refers to parts per billion, or micrograms per litre)

The detections after treatment from Winneke were all very low, with the highest being for Simazine at 0.06µg/L in November 2019. On the same day that Simazine was detected, the herbicides MCPA and Metolachlor were also detected at 0.02µg/L. In terms of drinking water guidelines, the Australian Drinking Water Guidelines have a guideline for Simazine set at 20µg/L, MCPA at 40µg/L and Metolachlor at 300µg/L. There were eight separate dates between 2019 and 2024 when pesticides were detected after treatment at Winneke.

The old Engineer's 'chestnut'. The solution to pollution is dilution?

The Yarra River catchment upstream of Sugarloaf Reservoir. If a pesticide is detected in the Yarra how do you identify the source? Testing by Melbourne Water is the only long term pesticide monitoring carried out in the catchment. If pesticides are detected in Yering Gorge, how many more kilometers of the river could be impacted by these chemicals?

Detections were dominated by herbicides (~90%). It was also odd that there were no detections of fungicides.

In terms of 155 pesticide detections in the Yarra River at the offtake to Sugarloaf, the most detections were for Simazine, MCPA, Metolachlor, Triclopyr and Imidacloprid. There were also two detections of Atrazine, two for DEET and one for Diuron. 

Detections of pesticides at Sugarloaf Offtake were dominated by detections in October, September, June and May. This perhaps reflects the time of year when pesticides are more frequently applied and when water flows in the Yarra increase.

Total detections per volume of pesticide, were dominated by Simazine and DEET. The highest detection of any pesticide was a detection of DEET of 3.4µg/L in February 2023 which accounted for 87% of the total amount of DEET detected from 2 positive samples. Average detections of simazine were 0.1µg/L which is the same level as the European Precautionary guideline.

Sugarloaf Reservoir. Water is stored here before being treated at Winneke Treatment Plant

Ecological Guidelines

In 2017 the Victorian State Government estabished the Wilip-Gin Birrarung murron Act in order to protect the Yarra River/Birrarung for future generations alongside traditional owners and the community. The legislation identifies the river and its corridor as a single living and integrated natural entity for protection. It is unclear how (or if) this act protects Birrarung from toxic pollution. Agricultural chemicals would be one of multiple toxic pollution sources entering Birrarung.

Guideline levels for some pesticides and other contaminants are listed in the ANZECC Guidelines. The Draft Guideline Values (DGV's) are an attempt to set levels for contaminants in a way that supposedly protects the majority of species in freshwater and marine waters. In very simplistic terms if a waterway is already degraded (eg an urban waterway) it is assumed that some species loss has already occurred.  The guidelines therefore allow for higher levels of contaminants in more degraded waterways than those that are pristine and where species loss has not been as impacted. The highest DGV/trigger level afforded by the ANZECC guidelines are 99%, followed by 95%, 90% and 80% for the most impacted waterways. The guidelines also reflect the fact that some contaminants are more toxic than others to a range of aquatic organisms. The more toxic the substance to aquatic life, the lower the guideline level. Generally, these guidelines are not legally enforceable and they are regarded as being a generic starting point for assessing water quality. A cynic could also suggest that such guidelines allow for continuing toxic pollution of waterways.

Of the pesticides detected by Melbourne Water, five of the detected pesticides have ANZECC Guidelines. In terms of the two most frequently detected pesticides in the Yarra River, Metolachlor has a 99% DVG/trigger level 726 times lower than Simazine. According to the ANZECC Guidelines, clearly Metolachlor is the worst 'offender' in terms of possible ecological impacts. Metolachlor even has a lower ANZECC 99% DVG/trigger level than PFOS. Metolachlor also has a 99% DGV over 21,000 times less than Glyphosate!!!

The table below highlights detections above the ANZECC trigger levels. All of the Metolachlor detections would have exceeded the 99% trigger level, with one exceeding the 95% trigger level. The
95% species protection level for Metolachlor in freshwater (0.46µg/L) is recommended for adoption in the assessment of slightly to moderately disturbed ecosystems. The Yarra River upstream of Yering Gorge could be described as a slightly to moderately disturbed ecosystem, however how does this definition apply if one accepts the river as a single living integrated natural entity? Also, why does this section of the Yarra that provides drinking water to millions of people not warrant the highest environmental protection standards?

This graph highlights the Melbourne Water detections in comparison to the ANZECC DGV's of 99% and 95%. The graph does not include samples when Metolachlor was not detected. Metolachlor was detected in almost 13% of all samples.

The average levels of Metolachlor detected in the Yarra River at the offtake to Sugarloaf Reservoir between 2020-2024, were over 8 times higher than the 99% DGV/trigger level.

What is Metolachlor?

Metolachlor is a herbicide used to control certain annual grasses and broadleaved weeds. In the upper Yarra Catchment its main use would be on pastures and on barley and oat crops but also would be allowed to be used in vegetable crops such as beans, maize, sweet corn, broccoli, cabbages, brussels sprouts and cauliflowers. 32 products containing Metolachlor and 57 products containing S-Metolachlor are listed on the APVMA's Pubcris website. S-Metoachlor is a more active isomer version of Metolachlor giving it more weed control activity. It is unclear if Melbourne Water detected Metolachlor or S-Metolachlor. S-Metolachlor was banned in Europe in 2023 due largely to water pollution issues and after concerns were raised particularly in France. 

Metolachlor is moderately toxic to fish and can have a half life in water for 200 days and has a high capacity to pollute groundwater. Metaloachlor is toxic to aquatic plants and algae. Essentially then, Metolachlor leaching into waterways could impact the base of the aquatic food chain further creating problems for primary consumers such as zooplankton, small fish and crustaceans. On the Australian Pesticide Map, Metolachlor is the fifth most frequently detected pesticide in Australian waterways after Atrazine, Simazine, Diuron and MCPA. The highest levels of Metolachlor detected in Australia appear to be in the Willbriggie Irrigation Area in southern NSW in the early 1990's. It is frequently detected in water supplies in Queensland.

Prior pesticide testing

Prior to 2017 Anthony Amis had also sent off Freedom of Information requests to Melbourne Water for pesticide data. Information had been received from July 2010 when more regular sampling by Melbourne Water begun. Previous to 2010 almost no pesticide testing in the Yarra River occurred by Melbourne Water.  51 positive pesticide samples had been detected between 2010 to 2017. That represents a quarter of the total amount of detections between 2010-2024, meaning that 75% of positive pesticide samples at the Yarra River offtake have occurred since 2020, with the bulk occurring in 2021. It is unclear if the frequency of testing for pesticides has increased after 2020, which could account for this sharp increase. Has there been an increase in pesticide use in the catchment since 2020? Almost 94% of all detections were accounted for by Simazine, MCPA, Metolachlor, Triclopyr, DEET and Imidacloprid. Average total pesticide detections was 0.732µg/L between 2010-17 compared to 0.0979µg/L 2020-2024.

What caused the 2020-2021 spike? 71.6% of all detections 2020-2024 were in 2021/22 with 83% occurring over 4 months (May-June, Sep-Oct). However, 81% of the total quantity of herbicides were detected in September, October, January and November. Replicate samples appear to have occurred over three days in 2021 which probably helps explain a very small percentage of the 2021 spike. The spike could also be explained by an increase in test regimes. Metolachlor was detected in 12.7% of all samples between 2020-2024, Simazine in 17.1% of all samples, MCPA in 12.8% of all samples, Triclopyr in 5.8% of all samples and Imidacloprid in 5.7% of all samples.

Yarra River Stream flow will also be a key factor, with high pesticide loads corresponding to high Yarra flows. This graph of stream flows at Yering Pump Station, Yering Gorge shows a increase in stream flow during October 2021, which corresponds closely to a number of pesticide detections between October 17 to October 20 of that year. Although high stream flows could dilute pesticide residues it could also correspond to more pesticides and pollutants washing into the river from upstream.

It is clear that pesticides put the Yarra River at risk. The best option would appear to ban the use of Metolachlor in the Yarra River catchment and severely restricting the use of pesticides in the Yarra River catchment, particularly Simazine whose average detection level exceeded 0.1µg/L.

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