Widely-used pesticide may double Parkinson’s risk, study suggests

Long-term residential exposure to chlorpyrifos is linked to more than a 2.5-fold higher risk of Parkinson’s, a study suggests.

The research combines human population data with lab experiments showing how the pesticide damages dopamine-producing brain cells (neurons that make the signalling chemical dopamine), providing biological evidence for the link.

Around 166,000 people in the UK live with Parkinson’s disease, a progressive neurological disorder that causes tremors, stiffness and difficulty with movement.

While genetics plays a role, environmental factors like pesticide exposure are increasingly recognised as important contributors.

The study, conducted by UCLA Health, analysed data from 829 people with Parkinson’s disease and 824 without the condition.

The team used California’s pesticide use reports along with participants’ residential and work addresses to estimate individual exposure to chlorpyrifos over time.

To understand how the pesticide might cause brain damage, researchers exposed mice to aerosolised chlorpyrifos for 11 weeks using inhalation methods that mimic how humans typically encounter the chemical.

They also conducted experiments in zebrafish to identify the specific biological mechanisms of damage.

Mice exposed to the pesticide developed movement problems and lost dopamine-producing neurons, the same cells that die in Parkinson’s.

The exposed mice also showed brain inflammation and abnormal accumulation of α-synuclein, a protein that clumps in Parkinson’s disease.

Zebrafish experiments revealed that chlorpyrifos damages neurons by disrupting autophagy (the cell’s clean-up process for clearing damaged proteins).

When researchers restored this process or removed synuclein protein, the neurons were protected from damage.

Chlorpyrifos has been widely used in agriculture for decades.

Though its residential use was banned in 2001, and agricultural use was restricted in 2021, chlorpyrifos is still used on many crops in the US and widely used in other countries.

Dr Jeff Bronstein, professor of neurology at UCLA Health and the study’s senior author, said: “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.

“The discovery that autophagy dysfunction drives the neurotoxicity also points us towards potential therapeutic strategies to protect vulnerable brain cells.”