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Are Queenslanders "Microdosing" on Weedkillers in their drinking water?

The answer to this question, is probably yes depending on where you live. 

Pesticides in waterways are a common occurrence. Pesticides can wash off land particularly during rainfall events. If a community’s drinking water supply is located on a waterway downstream of where these chemicals are applied, there is a risk that the water could contain pesticide residues. Pesticides can also pollute groundwater. Some communities rely on bore water for drinking water. Pesticides can also move on air currents through a phenomenon called spray drift and end up in water supplies.

If the water supply offtake is connected to a water treatment plant then it is likely that pesticides in the source water, if present, will be significantly reduced or even eliminated by the treatment process employed. Powder Activated Carbon (PAC) is a relatively common method of reducing (but not entirely eliminating) pesticides in water, but not every water treatment plant will use PAC and standard water treatment facilities are not successful in removing pesticides. Once the treated water leaves the water treatment plant it is transported in the reticulation network to customer taps.

Original photo taken 8 Jan 2006 by Nick J

The number one concern of water authorities however are the dangers of micro-biological contaminants in the raw water which if found in the reticulated system can cause very serious health problems.  

A number of other chemicals and substances can also be present in the raw, treated and reticulated water. Some chemicals are added at water treatment plants, such as chlorine, which in turn can create disinfection by-products. Pipes and plumbing can also have residues of heavy metals such as lead. Pesticides are generally regarded lower down the list of concerns for water authorities.

Another complicating factor is pesticide testing. This is costly with some samples costing hundreds of dollars each. To regularly test for the suite of possibly hundreds of pesticides used within a catchment around the year is an extremely costly exercise. As a result, some water authorities restrict their pesticide testing to once year or in some cases not at all. To add to the problem, in Queensland, local councils (often cash-strapped) are generally responsible for guaranteeing (and testing) safe drinking water to residents. Pesticide testing may be a low priority.

Users of pesticides are also under no obligation to inform the local council exactly what they are spraying. The more agriculture in a catchment, the higher the chances of pesticide runoff. Many of the catchments in coastal northern Queensland have large amounts of land devoted to crops such as sugarcane and bananas. Pesticides such as Atrazine can be used up to 3.3kg/ha in sugarcane, which may not sound like a lot, however pesticides can impact on water supplies less than parts per billion*, so it does not take alot of chemical to tarnish a water supply. (*One part per billion is equivalent to one drop in an Olympic size swimming pool). Many farms have also been established in high risk/runoff locations making relocation or retirement of farms unlikely.

Pesticide Reporting Portal

That being said, some of the most thorough pesticide testing in Australia has been conducted by the Queensland Government over the past decade. The Pesticide Reporting Portal provides a wealth of information on pesticide detections in a number of Queensland waterways, with a particular focus on waterways that flow into the Great Barrier Reef.

By accessing information from the Portal, over 72,000 pesticide detections from 39 current locations have been sighted by FoE. The amount of data in some cases stretches back to 2011. From these 39 locations, FoE determined that only 7[***] of the current testing locations were located in domestic water supplies.

These included: The Haughton River at Giru (just downstream from the towns offtake), the Pioneer River at Dumbleton Weir Mackay (the offtake to Mackay’s drinking water), the Fitzroy River at Rockhampton (near Rockhampton’s offtake) and Comet Weir (near the small town of Comet’s drinking water supply). The portal gives a unique insight into pesticide contamination of Australian waterways.

The timing of testing varied between these locations ranging back to 2011 for the Pioneer River (5647 positive samples) and Comet River (1628 positive samples), 2017 for the Haughton River (871 positive samples) and 2014 for the Fitzroy River (1976 positive samples). The testing also found 874 positive samples in the Burnett River (Bundaberg) from August 2017.

(*The city of Bundaberg sources drinking water from the Burnett River and bores. The location where the Queensland Government testing is conducted takes place 5km downstream of Branyan Water Treatment Plant offtake. The Government also have a testing location on Spliters Creek which flows into the Burnett River about 1km downstream of the Branyan WTP offtake. Nevertheless, testing of 6 water reservoirs at Bundaberg by the local council has revealed the presence of pesticides. Reservoirs fed by bore water have tested positive for the herbicide Bromacil.  A number of other Reservoirs are supplied water from Sun Water (eg The Gooburrum Main Channel sourced from Burnett River feeds into the Vecillios Road Reservior) and pesticides have also been found in these reservoirs. Sunwater also use the herbicide Acrolein to control weeds in their channels).

(*The town of Ingham relies primarily on bore water, however the town can draw from the Herbert River as an alternative. Queensland Government testing has recorded almost 2400 pesticide detections in the Herbert River since August 2011. The testing location appears to be in close proximity to the Water Treatment Plant. 23 pesticides have been detected with the most frequently detected being Diuron, Imidacloprid, Atrazine and 2,4-D. Of the 12 bores at Ingham, local council testing has found traces of Atrazine in 5 bores and Imidacloprid in 9. Imidacloprid is a neonicotinoid insecticide with no Australian Drinking Water Guideline).

(*The town of Innisfail relies on drinking water from the Johnstone River. Queensland Government testing has recorded over 760  pesticide detections in the North Johnstone River since February 2012. The current Queensland testing location at Goondi is a couple of kilometres downstream from the Innisfail offtake. 16 pesticides have been detected with the most frequently detected being Imidacloprid, Diuron and 2,4-D. Local Government testing has found traces of 6 pesticides in the Innisfail raw water supply with the most frequently detected being Imidacloprid. The highest detection being 0.23µg/L).

Bundaberg: Approximate location of the Branyan WTP marked with wavy lines. Queensland Government testing points marked with blue pins. WTP samples therefore would not be 'influenced' by Spliters Creek. Spliters Creek flows into the Burnett River upstream of the Qld Govt Bundaberg/Burnett River testing site. The Burnett River site is also well downstream of the WTP offtake but will be influenced by whatever is washing down Spliters Creek and Bundaberg itself. Spliters creek pesticide samples were dominated by Metolachlor, Atrazine and 2,4-D. Branyan WTP over the past few years has recorded detections of: Atrazine, Hexazinone, Metolachlor, 2,4-D, Dalapon and Tebuthiuron at levels averaging 0.07% of Australian Drinking Water Guideline levels.

Four different water supplies

To standardise the test results the following graph looks at pesticide detections from four water supplies (excluding Bundaberg, Ingham and Innisfail) since October 2017. The graph shows that in terms of total pesticide amounts detected by the Queensland Government tests, Diuron and Atrazine were the biggest problem chemical for the Pioneer River at Dumbleton Weir Mackay, with Tebuthiuron being most problematic for the Fitzroy River Rockhampton and Comet River at Comet Weir. Atrazine and Tebuthiuron were the most frequently detected pesticides at Giru over the 5 ½ year period.

The graph below shows that the largest pesticide detection volumes of the Haughton, Pioneer, Fitzroy and Comet Rivers over 5 ½ years were detected in the Pioneer River at Mackay, followed by the Comet River, Fitzroy River and Haughton River. This shows that in terms of drinking water and risks associated with pesticides, Mackay would appear to be the standout.

The graph does not provide insight into what chemical loads have been coming down the Pioneer River for many years. Out of 16,500 tests carried out by the Queensland Government at Dumbleton Weir on the Pioneer River between 2011 and 2023, 34% were positive for pesticides. Of these tests 92.7% of samples tested positive for Diuron and 87% were positive for Atrazine. What this means is that almost every sample of water taken from Dumbleton Weir will contain Atrazine and Diuron. The average level of detection of both was around 0.5µg/L, well under the Australian Drinking water guideline for both herbicides (20µg/L), but 5 times higher than the European Guideline and for Atrazine 5 times higher than the level required to cause issues with hormones.

Of the 39 waterways tested for pesticides over the past decade average levels in the Pioneer River came in at 11th in the waterways tested for across catchments flowing into the Great Barrier Reef.

Atrazine has been found to cause hormonal changes in amphibians at 0.1µg/L. It is banned in Europe.  There are no Australian drinking water guidelines for Fluroxypur, Imidacloprid and Tebuthiuron. In fact FoE found in 2016 that 41% of pesticides detected in Australian waterways do not have Australian Drinking Water guidelines. 

Atrazine Diversion

Non-legally enforceable guidelines for many agricultural chemicals and other substances in drinking water are set by the National Health and Medical Research Council. Safe is debatable term. To determine safe levels of pesticides, human testing is not allowed, so testing is conducted on animals. For Atrazine the No Observed Effect Level (NOEL) was based on a 2 year study of rats. This amount was then divided by 100 which incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variation. An estimation of body weight of a 70kg male drinking 2L of water a day is also included in the calculation to determine 'safe' dose.

Are impacts on the endocrine system and other issues concerning long term low level exposure to pesticide included in these estimations? The guidelines also do not take into account impacts from mixtures of low levels of chemicals, where synergistic effects may occur. Are these effects included in the 100 'safety factor'? If so how?  It's also interesting to note that the Australian drinking water guideline for Atrazine (set 12 years ago) is 20µg/L. In Europe, pesticides have a drinking water guideline of 0.1µg/L. In the United States the drinking water guideline for Atrazine is set at 3µg/L and long term exposure above this level is linked to cardiovascular system or reproductive problems. The Australian guideline prior to 2011 was 40µg/L.

Australian scientists have recently called for Atrazine to be withdrawn in Australia for its effect on male fertility.

Other studies have stated: "Current regulatory levels for chronic exposure are based on no observed adverse effect levels (NOAELs) of these LH alterations in rodent studies. Atrazine has also been studied for its effects on the central nervous system and neurotransmission. The European Union (EU) recognized the health risks of atrazine exposure as a public health concern with no way to contain contamination of drinking water. As such, the EU banned atrazine use in 2003. The United States recently reapproved atrazine’s use in the fall of 2020. Research has shown that there is a wide array of adverse health effects that are seen across multiple models, exposure times, and exposure periods leading to dysfunction in many different systems in the body with most pointing to a neuroendocrine target of toxicity."

The following graphic reveals some of the complexities grappling researchers studying impacts of Atrazine and its metabolites.

Source of this graphical representation

Local Government to the Rescue?

In terms of impacts to drinking water, the Queensland Government test data can only surmise what is potentially ending up in consumer taps. It is highly unlikely that local Government authorities were testing their water treatment plants at the time that the Queensland Government was doing their monitoring. Some councils monitor for pesticides on an annual basis. Others test every few months using grab samples which really only give a chemical amount for an instant in time. Generally speaking if the grab tests show a level of pesticide at a level above the drinking water guidelines, further testing and management protocols should apply.

To try and ascertain what is being detected by Queensland local government, some of the information is published in various council Drinking Water Quality Management Plans which in some cases are published annually. After wading through a number of these plans it was determined that 12 shires published pesticide test results at some time over the past decade. There are however 77 local government areas in Queensland, so the scale of the issue is probably much larger than acknowledged.

Looking at the regional council data, FoE found over 1000 pesticide detections with a maximum detection average of 0.98µg/L. The 1000 test results however included samples taken in raw water, treatment plant water and reticulated water. Once the reticulated water samples were isolated a total of 204 positive detections in reticulated water supplies were found. The maximum detection average level in reticulated supplies was 3.9µg/L. It should be highlighted that there was a general lack of consistency in what defined treated as opposed to reticulated water. The numbers were also skewed by the Mackay incident of Feb & March 2013 where both Diuron and Atrazine were detected at the Nebo Road treatment plan at almost 20 times higher than the Australian Drinking Water Guideline (or 3900 and 3500 times higher than the European Guideline). It is unclear what amounts of Atrazine and Diuron ended up being consumed in Mackay as a result of this incident, but if this incident is removed from the spreadsheet the maximum pesticide detection average in reticulated water drops to 0.265µg/L.

Average detection levels in comparison to the Australian Drinking Water Guidelines for pesticides with guideline levels was 39.68%, once again including the 2013 spike of Atrazine and Diuron at Mackay. If the 2013 Nebo Road WTP incident is removed, the average pesticide detection level is 1.97% of current Australian Drinking Water Guideline Levels. 1.97% of guideline levels does probably not warrant much attention from water authorities, as there will be other chemicals found at much higher levels in water supplies which will take priority.

Friends of the Earth produced a report in 2017 looking at pesticide detections in Victorian water supplies for the years 2007-16. That report found that the average pesticide detection in mostly raw water was 0.46µg/L, with the average pesticide level in comparison to Australian Drinking Water Guidelines was 0.98%.

Source: Mackay Regional Council Drinking Water Quality Management Plan 2013/14. How was the community notified about this incident. What amounts of Diuron and Atrazine ended up in reticulation? What areas of Mackay had the highest levels and for how long? Were there health impacts eg pregnant women?

The most positive test results according to various Drinking Water Quality Management Plans, from raw, treated and reticulated local council samples came from Western Downs Shire (274), followed by Bundaberg Shire (177), Mackay Shire (164), Banana Shire (149), Central Highlands Shire (127), Burdekin Shire (99), Flinders Shire (36), Hinchinbook Shire (33), Issac Shire (20), Cassowary Shire (14), Maranoa Shire (14) and Tablelands Shire (13). There was little consistency across these shires in terms of reporting data with some conducting testing one year, but then not following up the year after. Some of the test results were published, with others not.

19 separate pesticides were detected by local government testing, with Atrazine and its metabolites making up 49.5% of all detections, followed by Metolachlor 13.2% and Tebuthiuron 11.3%.

Interestingly there was no positive samples for Rockhampton. Whilst the Fitzroy River doesn’t seem to have the same pesticide loads as the Pioneer River at Mackay, the lack of positive detections is possibly explained by a lack of testing for pesticides used within the Fitzroy catchment by Rockhampton Shire. It is unclear whether the council actually test for the main pesticides found in the Fitzroy River by the Queensland Government namely, Tebuthiuron, Metolachlor, Atrazine, Terbuthylazine, 2,4-D, Simazine, Fluroxypur etc.

From FoE’s assessment approximately 300,000 people in Queensland in approximately 12 shires have been exposed to pesticides in the drinking water over the past decade. The main concern areas being Mackay, Marian, Bundaberg, Ayr, Home Hill, Giru/Cungulla, Ingham, Biloela, Capella, Comet, Prairie, Baralaba and Jandowae.

It is likely that similar results would occur in many other regions of Australia.

The Queensland situation appears to be quite serious, particularly if one also factors in ecological impacts of application of pesticides. European guidelines suggest that any pesticide detection >0.1µg/L in a water supply need to be investigated by authorities to understand the source of the pollution and to try and stop the pollution occurring. Queensland Government testing suggest that the 0.1µg/L level was breached over 27,000 times over the past decade. Investigators would be hard pressed to find the source of the pesticides, considering their widespread use throughout Queensland.

Top ten detections of pesticides in Queensland domestic water supplies according to Council water quality management plans.

Location Pesticide Council Supply Amount (max) Australian Drinking Water Guidelines =1
Nebo Road WTP Feb 2013 Diuron Mackay Treatment Plant 390µg/L 19.5x
Nebo Road WTP Feb 2013 Atrazine Mackay Treatment Plant 350µg/L 17.5x
Prairie 2017/18 Heptachlor Flinders Raw 0.371µg/L 1.237x
Tinnaroo Park 2016/17 Thiometon Tablelands Raw 4.3µg/L 1.075x
Biloela Bore 2017/18 Dicofol Banana Raw 3.2µg/L 0.8x
Biloela 2017/18 Dicofol Banana Potable? 3.2µg/L 0.8x
River Park Res. 2019/20 Fipronil Bundaberg Raw 0.55µg/L 0.785x
Baralaba Jan/Mar 2015 Dicofol Banana Treatment Plant 2.9µg/L 0.725x
Jandowae Bore 2 27/9/16 Dieldrin Western Downs Raw 0.2µg/L 0.667x
Jandowae Bore 2 28/1/15 Dieldrin Western Downs Raw 0.2µg/L 0.667x
Jandowae Bore 2 29/7/15 Dieldrin Western Downs Raw 0.2µg/L 0.667x
Jandowae Bore 2 4/11/15 Dieldrin Western Downs Raw 0.2µg/L 0.667x

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