For regular golfers, a beloved pastime could be posing a significant threat to long-term neurological health. A landmark study from the University of California Los Angeles (UCLA) has identified a specific pesticide commonly applied to golf courses as a major environmental risk factor, potentially doubling the likelihood of developing Parkinson's disease.
The Pesticide in Question: Chlorpyrifos
The research, published in the journal Molecular Neurodegeneration, focused on the chemical chlorpyrifos. This pesticide has been widely used since 1965 on agricultural crops, forestry, and maintained grassy areas, including golf courses. The study analysed data from 829 people living with Parkinson's and 824 without the condition in California, tracking their pesticide exposure over a period of at least 30 years.
By comparing state pesticide use reports with participants' home and work addresses, the team established a clear link. Individuals with the highest exposure to chlorpyrifos faced a 2.5-fold increased risk of Parkinson's disease compared to those with the least exposure. Notably, exposures occurring 10 to 20 years before disease onset showed a stronger association than those in the decade immediately prior.
Biological Mechanism Revealed in Animal Models
To understand causality, the scientists conducted parallel experiments on mice and zebrafish. Mice exposed to aerosolised chlorpyrifos for 11 weeks developed movement issues and, critically, lost an average of 26% of their dopamine-producing neurons, a hallmark of Parkinson's. Their brains also showed inflammation and a build-up of the protein alpha-synuclein.
In zebrafish, which share roughly 70% of their genes with humans, the team discovered the likely toxic mechanism. Chlorpyrifos appears to damage neurons by disrupting autophagy—the body's essential process for recycling old cells to create new, healthy ones.
Senior author Dr Jeff Bronstein, a professor of neurology at UCLA Health, stated: 'This study establishes chlorpyrifos as a specific environmental risk factor for Parkinson's disease, not just pesticides as a general class. By showing the biological mechanism in animal models, we've demonstrated that this association is likely causal.'
Regulatory Landscape and UK Context
The findings add to ongoing concerns about chlorpyrifos. In April 2021, the US Environmental Protection Agency moved to ban its use on food, but a 2023 court ruling overturned the federal ban, leaving states to set their own rules. In the UK, the use of chlorpyrifos was banned in 2016, following a similar prohibition by the European Union in 2020.
However, the progressive nature of Parkinson's disease, which affects around 1 million Americans and is diagnosed in 90,000 annually in the US, means many current patients were likely exposed decades before such bans. The Parkinson's Foundation estimates 1.2 million Americans will be living with the condition by 2030. Chlorpyrifos remains permitted for use on golf courses in the United States.
The UCLA researchers suggest that people with known historical exposure should be monitored for neurological symptoms. Furthermore, their discovery that autophagy dysfunction drives the neurotoxicity points toward potential future therapies to protect vulnerable brain cells.
This study contributes to a growing body of evidence implicating environmental factors in the rise of Parkinson's. Previous research has linked the disease to air pollution (PM2.5) and prolonged exposure to loud noise. With no cure currently available, identifying and mitigating such risks becomes increasingly vital for public health.
