Weed killer in our waterways

A controversial chemical herbicide continues to be used within Australia despite both domestic and international studies showing the impact it can have on some animals, including the penis size of our native marsupials.

Wallabies were used in recent studies exploring the potential effects of atrazine. Photo: Troy Guo, via pexels

Banned in the European Union since 2004 because of the risk to human health, recent studies have shown the damaging effect atrazine has on the reproductive organs of some mammals and marsupials. Despite this, 2.7 million kilograms of the chemical continues to be used in Australia each year.

Atrazine is made and manufactured by the Syngenta group, a joint venture between the pharmaceutical giants Novartis and AstraZeneca. The herbicide is used for the control of broadleaved weeds in grass, and 88 products containing the active constituent atrazine have been registered by the Australian Pesticides and Veterinary Medicines Authority (APVMA) as safe for use in agriculture.

The herbicide is valued by farmers and agriculture companies because it is cheap and easily obtained, with very few limitations surrounding its use. It is the third most used herbicide within Australia and is widepsread in Victorian farming.

As recently as 2020, 10 micrograms of the chemical were detected per litre of water at Dookie recreational reserve, behind the Dookie Primary School.

Multiple studies worldwide have now shown the effects atrazine has on a plethora of different animals and organisms. The most famous was performed by Professor Tyrone Hayes at the University of California, Berkeley. His studies, originally commissioned by Syngenta group, found that the herbicide had severe effects on the reproductive organs of frogs – it created a hermaphroditic effect where the frogs would change gender after being exposed to atrazine.

After Prof Hayes ended his relationship with Syngenta to continue studying the effects of the chemical on his own, his studies formed the scientific basis for two class-action lawsuits brought – and settled – by 23 cities and towns across America that accused Syngenta of concealing the dangerous side effects of water contaminated with atrazine.

The European Union announced a ban on the chemical in 2004 because of these risks, in the same month the Environmental Protection Agency in America announced its approval of the use of the chemical.

Professor Andrew Pask, a biology researcher from Melbourne University, has been studying the effect of atrazine in marsupials and has found similar impacts. He cites Prof Hayes’ studies as an inspiration for his own, which show that the chemical directly impacts the reproductive organs of wallabies and mice, reducing the penis size, fertility and reproductive systems of exposed animals. According to Prof Pask, Australia’s marsupial population is facing an extinction rate found nowhere else in the world, which could be further increased because of atrazine exposure.

“A lot of our marsupial species, like kangaroos and big macropodid-type animals, their distribution overlap almost entirely with farmland areas, and they go and graze on the crops. It got me thinking, are our marsupials going to be susceptible to these chemicals,” he said. “We know from a scientific point of view because there are impacts in humans, we know there are impacts in frogs, we know there will be impacts in marsupials because they sit in the middle, but you still have to go through the process of proving this thing is actually going to have an impact.”

By modelling how wallabies would come into contact with atrazine in the wild, Prof Pask says his findings show the chemical has an impact on their reproductive organs.

“We exposed a big group of pregnant wallabies to the contaminated water source, so the only water they had available to them in their little paddock was water that was contaminated with atrazine, mimicking if there was runoff into a dam,” he said. “We know that if anything goes awry with our hormonal development pathways, you end up with penis defects and a smaller penis, particularly things that suppress androgen hormone levels. That’s exactly what we saw with atrazine treatment, the males had incredibly suppressed penis growth.”

The use of the chemical is regulated by the APVMA, and it is considered safe as long as the label instructions are followed. However, atrazine use was last last reviewed in 2010.

“While we need to ensure that exposure to pesticides does not harm native animals, the results of the 2020 study do not provide a basis for the APVMA to reassess the safety of Australian native animals exposed to atrazine,” an APVMA spokesperson said.

“The wallabies in this study were exposed to atrazine at much higher doses and for longer periods than would be expected in the Australian environment.”

Another of Prof Pask’s studies was designed around current regulations for atrazine pollution, and showed that there was reproductive impacts on mice when treated with what is considered a safe level of atrazine. “That paper was really about addressing, if we are going to use atrazine, at least let us set some sensible limits for exposure in our drinking water,” he said.

Other studies performed in Australia have supported Prof Pask’s more recent studies, showing that atrazine significantly reduces the number of macro-invertebrates found in waterways when there was just 20 micrograms of the chemical per a litre of water.

“It’s insanely low how little you put in, we’d dilute the atrazine down in the water and then dilute it down to one in a thousand again, then put a millilitre of that into a bottle and it’s still having those reproductive impacts. It is terrifying when you see what is happening to these animals as a result of such an incredibly small exposure,” Prof Pask said.

The Victorian Farmers Federation would not be interviewed on the use of atrazine in the state, instead releasing the following statement: “VFF supports the use of the Australian Pesticides and Veterinary Medicines Authority (APVMA) approved chemicals (in which atrazine is) in accordance with approval and label use instructions. APVMA is a world recognised body that assess permit applications for each chemical seeking to be used in Australia.”

Prof Pask said ultimately his studies were about ensuring that humans and animals weren’t in contact with dangerous chemicals. “We want to keep on pushing to understand what the impacts of low levels of atrazine are, to provide greater evidence to the regulatory bodies in Australia that we should really stop using this chemical,” he said.


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