Parkinson’s pesticide push

Many of WA’s top neurologists are backing a locally led push to ban a farm chemical that some believe could be linked to Parkinson’s disease.

By Cathy O’Leary


Perth neurologist David Blacker does not know whether his diagnosis of Parkinson’s disease is linked to a common herbicide, but he believes it is not worth taking the risk.

Dr Blacker – along with many of his colleagues – is calling on the country’s chemical regulator to ban the controversial weedkiller paraquat, which grain growers say is vital to crop production and food supply.

Parkinson’s is a progressive brain disorder that affects the nervous system, but symptoms generally develop over years and can affect movement, sleep, mental health and cognitive function. It is believed that more than 150,000 Australians have Parkinson’s, and it is thought to be the fastest growing neurological disorder in the world.

According to the World Health Organization, there is no known cause of the disease but exposure to pesticides may increase the risk.

Dr Blacker suspects his diagnosis of early onset Parkinson’s disease in 2018 could be partly linked to his exposure to agricultural chemicals while growing up in the Wheatbelt, where he played and worked in areas that had been sprayed with herbicides.

A neurologist specialising in stroke for more than 20 years, his diagnosis forced him to retire from clinical work last year, although he still works in medical research at Perth’s Perron Institute and in Parkinson’s disease advocacy.

Perth neurologist David Blacker
First concerns

Dr Blacker says that while people joke about doctors’ poor handwriting, it was seeing how his own writing had deteriorated over years – as well as watching the movements of Parkinson’s patients in the clinic – that led to his concerns that something was amiss and his subsequent diagnosis. 

His submission is one of 168 made to the Australian Pesticides and Veterinary Medicines Authority (APVMA), which is reviewing the use of paraquat and the related chemical diquat.

While the authority has proposed some limits on the use of the chemicals, it rejects the view that they are unsafe and says, “the overwhelming weight of evidence is that paraquat does not induce neurotoxicity.”

The APVMA says it is working its way through the submissions, as well as reviewing the science and data, but a final decision is not expected until midway next year.

While grain industry and farming bodies have weighed heavily into the debate, arguing restrictions on the use of paraquat in cropping systems will hurt agriculture, 29 of the submissions have been from doctors and health organisations, with many calling for a ban.

Dr Blacker wrote a private submission but ended up with a strong quorum of doctors who co-signed it, with 41 West Australian colleagues, including 32 neurologists, eight movement disorders specialists and 11 professors.

The submission reads like the who’s who of WA neurology, with Professors Graeme Hankey, Bill Carroll, Frank Mastaglia and Peter Silbert among the signatories.

The Australian and New Zealand Association of Neurologists and the Movement Disorders Society of Australia and New Zealand have also made submissions supporting a ban, with the ANZAN describing Australia as an “outlier.”

MDSANZ president Carolyn Sue is a world-renowned expert in movement disorders. In a submission to the regulator, she described the paraquat situation as a critical public health issue.

“The evidence supporting this connection is compelling and warrants immediate action to protect public health,” she wrote. “The health risks associated with this herbicide far outweigh any potential benefits, and alternatives are available that do not pose such severe threats to human health.”

Parkinson’s Australia, which has an online petition calling for paraquat to be banned, argues that 70 countries have banned its use due to its severe health risks, including strong links to Parkinson’s disease. The group maintains paraquat poses a serious health risk to farmers, agricultural workers and the public.

Dr Blacker says the doctors who have called for the ban are not activists, but rather medical experts, including global leaders in Parkinson’s disease.

“It started out with me doing my submission as an individual and grabbing support from other neurologists and then organisations, and by the end I had over 40 signatures – and there’s not that many neurologists and neuroscientists, so I’ve ended up with about 90% of the practising adult neurologists,” Dr Blacker told Medical Forum.

“I said what I thought was wrong with the assessment by the APVMA, which had conclusions including that the overwhelming weight of evidence was that there wasn’t any neurotoxicity and the link to Parkinson’s was not proven.

“I took objection to that because over the last few years there has been accumulating evidence that that’s not the case. The incidence of Parkinson’s disease worldwide is escalating quite rapidly over the past decade, and the leading experts in the world believe it’s probably linked to a number of factors including air pollution, exposure to toxins and exposure to herbicides specifically.

“The thing that stands out about paraquat is that biologically it causes damage to the brain, like Parkinson’s disease.”

Dr Blacker said in his submission that it was not just an agricultural problem – it was also a health problem, as well as an environmental problem. And there were emerging epidemiological studies that had shown that exposure to paraquat did increase the risk of Parkinson’s.

“This is always a tricky business because previous research has relied on looking backwards at people’s previous history, say 20 or 30 years when it’s a bit hard to know what you were exposed to, so that’s been one of the criticisms,” he said.

“But more recently, in February this year, a group from California published a much more objectively based paper where they’ve had excellent records on which counties have used paraquat. 

“They have a really good idea of the dose of it, and they lined it up with maps of where people lived and worked, and where paraquat was used, to see if there were any linkages, and if you lived less than 500 metres from a paraquat field, your risk was increased. But that wasn’t mentioned in the APVMA report.”

Farmers’ groups have accused campaigners against paraquat of scaremongering and argue there is no established causal link.

But Dr Blacker and some leading figures in this field have come down very hard on this, arguing there is a strong link.

“An association doesn’t always mean causation, but this is being played on,” he said. “My core argument is that the data is accumulating, and the scenario of requiring us to prove that something is doing harm before we do anything about it is completely different to what I do as a medical researcher.

“If we’re developing a drug, we have to prove it’s safe before we can expose people to it, so the approach with paraquat is completely illogical.

“And the fact of the matter is that more than 67 other countries have been able to make the change, and the fact that there are alternatives there, it’s just asbestos all over again.”

Dr Blacker said he was surprised by the reactions from leaders of the farming community to any change affecting their crop yield rather than being concerned about the safety of their members.

“There is also a perception being portrayed that the farmers are all against it but that is absolutely not the case, and one very senior farmer in the Wheatbelt has been speaking out saying this pesticide must be banned.”

The leading farm peak body, the National Farmers’ Federation, said in its submission that paraquat and diquat are widely used in Australian agriculture, supporting the production of grains, cotton, horticulture, sugarcane, rice, wine and various pastures.

The herbicides were critical to minimum and no-tillage farming practices, allowing farmers to better manage glyphosate resistance in a variety of weeds. They were also commonly used to get crops ready for harvest. 

“Farmers rely on essential chemical products, including paraquat and diquat, to maintain yields and farm sustainably in an increasingly changing, challenging and volatile climate. The chemicals provide cost-effective protection against crop yield losses across Australia,” the NFF wrote.

“The APVMA proposes to remove a number of current uses at rates of application that pose an unacceptable risk to the environment, as determined on the data available at this time. The proposed regulatory decisions will have a significant and adverse impact on the agricultural sector, rendering the use of the chemicals impractical or ineffective in many circumstances.”

The NFF said Australian farmers were extremely concerned about the impact of the proposed decisions on their ability to farm sustainably and productively.

“Misinformation, particularly when linked to technical assessments undertaken as a component of APVMA reviews, is not in the interests of the Authority, the agricultural sector or the general public,” it said.

Syngenta, the company that first manufactured paraquat, also maintains that the chemical does not cause Parkinson’s disease and is safe to use if the label is followed.

And grain-growing organisations have called for the APVMA not to rush its review of diquat and paraquat. Grain Producers Australia said no deadlines should be put on the review by the Federal Government.

APVMA chief executive Scott Hansen said the regulator had received submissions from across industry, community, medical and public health sectors.

“We recognise that there is heightened interest in paraquat, both from those who rely on it as a key tool in farm management, as well as those who have concerns of a possible link between paraquat and Parkinson’s disease,” Mr Hansen said.

“The APVMA is committed to completing a rigorous scientific assessment and will take the necessary time to consider all the evidence provided to us during the public consultation. We expect to publish a final regulatory decision on paraquat in mid-2025.

“However, we take human health risks seriously and should new evidence emerge out of this consultation process that shows an imminent risk to human health, then we have the power to take quick action.”

In his submission, Dr Blacker and his colleagues called on the APVMA to take that swift action.

“Even if there are doubts about the weight of current evidence regarding causation, to continue to allow use of paraquat while safer options exist, continues to risk exposing more and more people to an increased risk of developing Parkinson’s disease,” Dr Blacker wrote.

“I find this to be illogical and unethical. I encourage further research to obtain as much knowledge as possible but believe this should not delay acting now.”

Dr Blacker told Medical Forum there would be costs associated with a ban on paraquat, but it had to be borne against the health costs.

“I would hope they will listen to the medical experts, and it gets some traction,” he said. 

What is paraquat:

  • Paraquat and the related diquat, are fast-acting, non-selective herbicides that kill most plants on contact
  • Farmers’ groups say it is an important tool for managing weeds and farming sustainability
  • It is banned in 70 countries – and the number is growing – due to its toxicity but is still widely used in Australia
  • Critics argue there is growing scientific evidence linking paraquat to the development of Parkinson’s disease.