Australia’s top neurologists say they are being ignored by chemical regulators considering the future of a controversial herbicide linked to Parkinson’s disease.
Dozens of the country’s top movement disorders experts say the Australian Pesticides and Veterinary Medicines Agency (APVMA) was not involved during the review.
There are growing concerns that “real world data” about the link between paraquat and Parkinson’s disease is being ignored.
The regulator’s final decision on the herbicide is expected to be made in the middle of this year.
Movement disorders expert Associate Professor Wesley Thevasasan said he and other experts had submitted their comments to the regulator during the public consultation process, but had not heard any further communication.
“We haven’t heard anything from APVMA.” Dr. Thevasathan said.
Melbourne-based neurologist Dr Wesley Thevasasan, who treats thousands of Parkinson’s patients, says there are too many farmers. (ABC News: Charlotte King)
Dr Thevathasan is a Parkinson’s disease expert who works at several hospitals, the University of Melbourne and the Florey Institute.
“Myself, other scientific bodies, a group of neurologists and some of Australia’s leading scientific minds and organizations with an interest in Parkinson’s disease have submitted submissions, but to my knowledge none of us have been contacted by the APVMA.”
Paraquat and the related herbicide diquat are fast-acting herbicides that agricultural groups say are essential for controlling resistant weeds.
What is paraquat?
- Diquat, related to paraquat, is a fast-acting, non-selective herbicide that will kill most plants on contact.
- Farmers’ groups say paraquat is an important tool to control weeds and practice sustainable agriculture
- Although it is banned in more than 67 countries due to its toxicity, it is still widely used in Australia.
- Growing scientific evidence links paraquat to the development of Parkinson’s disease
These chemicals have been under review by the APVMA since 1997 and are banned in the EU, UK and China due to their toxicity.
In its 2024 proposed regulatory decision, the APVMA stated that “available epidemiological data are insufficient to conclude an association between paraquat exposure and neurotoxicity (including Parkinson’s disease) in occupational settings.”
Dr Thevasasan said the position contradicted the “global consensus” in the field that exposure to paraquat is closely linked to the subsequent development of Parkinson’s disease.
He said the evidence base used by APVMA to date has given “little weight” to recent human studies.
“There are now multiple epidemiological and real-world exposure studies suggesting that paraquat increases the risk of Parkinson’s disease by approximately three times.” Dr. Thevasathan said.
Parkinson’s disease is a progressive, incurable neurological disease that affects movement and can cause stiffness and uncontrollable tremors.
Is there a link between increasing rates of Parkinson’s disease and common agricultural chemicals?
Dr. Thevasathan is not the only expert to express concern. More than 70 medical professionals and clinicians from major hospitals, research institutes and movement disorder clinics across Australia have also been named in the submission highlighting the evidence linking paraquat to Parkinson’s disease.
Dr Kerry Bertram, a neurologist and president of the Movement Disorders Association of Australia and New Zealand, said: “Unless we can prove a link, it is always concerning to suggest that something is considered safe, rather than showing some level of safety, as is the case with other serious exposures such as drugs.”
“Other jurisdictions around the world have looked at the same level of data and made very different decisions, which are not only to restrict use, but to actually ban the sale of paraquat within their countries,” Dr. Bertram said.
The APVMA did not respond to specific questions from the ABC, but in a statement acknowledged “concerns about the link between paraquat exposure and Parkinson’s disease” and said health and safety “are central considerations.”
The regulator confirmed to the ABC that it had signed a nine-month, $109,000 contract with public relations firm GRACosway, which specializes in crisis communications.
“As an independent regulator, APVMA must follow a rigorous legal process and cannot pre-empt or publicize the outcome of a final decision before it is formally announced,” the APVMA said in a statement.
“The APVMA is using its full regulatory authority to quickly complete its long-standing chemical reviews,” said Anthony Chisholm, a spokesperson for the Assistant Secretary of Agriculture.
“Australians can have confidence that APVMA’s decisions are based on the best available science to improve health and safety outcomes for people, animals and the environment,” they said.
precautionary principle
According to the World Health Organization’s (WHO) Global Burden of Disease Study, Parkinson’s disease is “the world’s fastest growing neurological disease in terms of disability and death.”
“We know that perhaps 10 to 15 per cent of cases[of Parkinson’s disease]have a genetic cause, but what about the other 80, 85 per cent?” Professor David Blacker said.
Dr. Blacker was diagnosed with early-onset Parkinson’s disease in 2018, prompting him to investigate the origins of the disease. (Supplied)
Professor Blacker is not only a neurologist and movement disorder specialist, but he also suffers from Parkinson’s disease.
He said the “precautionary principle” needed to be considered.
“If you are participating in activities that increase the risk of harm to humans or the environment, it is possible to take precautions even if a causal relationship is not well established.”
Professor Blacker also submitted a submission to the APVMA, but has not received any follow-up investigation.
Farm groups say paraquat is ‘essential’
Despite longstanding health concerns, the agricultural industry has come to rely on paraquat for weed control.
Some weeds are resistant to glyphosate, also known as Roundup, and tilling fields can disrupt soil structure and moisture.
“Without viable and effective access to paraquat and diquat products, farmers may be forced to return to traditional tillage to manage weeds and resistance,” the National Farmers Federation (NFF) said in its submission to the APVMA review.
As Australian farmers adopt no-till farming, they are increasingly relying on chemicals to control weeds. (clint jasper)
NFF chairman Hamish McIntyre, himself a large acre farmer, said paraquat was a “necessity”.
“Thanks to products like glyphosate and paraquat, we’ve been able to transform Australia’s farming system. We farm on a drier continent than many of our competitors, so every bit of moisture is so important to us.”
Mr McIntyre said there were no comparable alternatives to paraquat, and other options required long waits before returning to the paddock after spraying.
“We also have phenoxy-type herbicides, but those have plant growth issues,” he said.
“We will take guidance from independent regulators and if they say it is appropriate to withdraw a particular chemical reaction, we will follow that guidance.”
“Volatilization” of paraquat
The international situation has also changed. In November 2025, the U.S. Environmental Protection Agency (EPA) announced that new vapor pressure studies have increased uncertainty about the potential for paraquat to volatilize or migrate into the air as vapor, posing an increased risk to workers and bystanders.
The U.S. Environmental Protection Agency said, “New vapor pressure studies have shown that paraquat vapor pressure values are higher than those previously used in EPA’s risk assessment.”
“Vapor pressure is an important parameter that influences how much pesticide surface residues transform into gaseous vapors that can travel through the air, potentially impacting workers and bystanders who live or work near or adjacent to treated fields.”
Paraquat is listed as a Schedule 7 poison in Australia and requires a permit to purchase. (Supplied)
The agency has not reached a conclusion and its review is ongoing.
APVMA later said it was “reconsidering the assessment of paraquat’s variability” before finalizing its regulatory decision.
“This additional time will allow us to consider the latest review and refine APVMA’s risk assessment if necessary,” the agency said late last year.
As of 2024, the APVMA’s latest technical report states that paraquat is “unlikely to have harmful effects on humans” “if registration conditions and label instructions are followed.”
The regulator did not respond to ABC’s questions about whether this remains the agency’s position after review of new vapor pressure data by the U.S. Environmental Protection Agency.
First US state bans paraquat
Last week, Vermont became the first U.S. state to ban paraquat, marking a significant departure from federal policy.
Like Australia, the US Environmental Protection Agency (EPA) continues to allow limited use of pesticides despite continuing health concerns.
The herbicide paraquat is highly toxic and users must follow strict regulations and precautions. (Provided by: Jake Hamilton)
Professor Blacker recently attended the World Parkinson’s Disease Congress in the United States and is keeping a close eye on Vermont’s ban.
“In anticipation of that, at least a dozen states are specifically preparing to introduce legislation to ban paraquat,” Professor Blacker said.
“We know that California has been considering a phase-out system for several years…About a dozen states in total have considered implementing a phase-out system, but Vermont was the first to come up with that plan.”
What is epidemiology?
At the heart of the tension between clinicians and regulators is their emphasis on epidemiology, the study of disease patterns in human populations, over laboratory experiments.
Although it is impossible to test paraquat on humans, real-world exposure data could be just as convincing, Dr. Thevasasan said.
“Multiple epidemiological studies by various groups of scientists have shown that people exposed to paraquat have an approximately three times higher risk (of developing Parkinson’s disease).”
Farm lobby seeks to silence paraquat debate
Dr Thevasasan said the risk is greater with chronic exposure and is related to dose.
“You’ll probably never get anything better than this,” he said.
“It’s the same method that we used to prove or show that smoking causes lung cancer, and we showed that asbestos causes lung disease and lung cancer. It’s the same methodology.”
The APVMA has previously said that research and analysis of studies may result in “conclusions that differ from those of the study authors.”
“To inform the regulatory decision on the proposed paraquat proposal, APVMA reviewed extensive research on paraquat, including animal studies and epidemiological studies, as well as the conclusions reached by the U.S. Environmental Protection Agency.”
