Overview of Use of herbicide linked to Parkinson's is on the rise in the US
This Science Friday segment investigates paraquat, a highly toxic herbicide that is banned in more than 70 countries but still widely used in the U.S. The episode centers on reporting from Mississippi showing unusually high airborne paraquat emissions from a facility that formulates and repackages the chemical, and then turns to a UCLA epidemiologist to explain the strong scientific link between paraquat exposure and Parkinson’s disease.
Key Findings From the Reporting
A Mississippi plant is releasing large amounts of paraquat
- Environmental reporter Delaney Nolan found that a plant in Waynesboro, Mississippi processes paraquat for distribution.
- The facility is reported to have released 47,000 pounds of paraquat into the air in 2024 as a fugitive emission — meaning it is leaking rather than emitting through a smokestack.
- That amount is dramatically higher than other paraquat-handling facilities, which reportedly released only 1 to 5 pounds in the last five years.
The emissions are legal, but poorly regulated
- Paraquat is not regulated as an air pollutant in the same way as ozone or other criteria pollutants.
- Instead, it is tracked through the Toxics Release Inventory, which records toxic chemical releases for public transparency.
- The emissions are legal, though states could theoretically impose stricter limits.
Local Parkinson’s rates are elevated
- Wayne County, Mississippi, has top 7% Parkinson’s mortality rates among reporting counties in the U.S.
- Nolan cautions that this does not prove the current plant’s emissions are the direct cause, since Parkinson’s can develop years after exposure and the area may have had earlier exposures from agriculture or forestry.
What the Science Says About Paraquat and Parkinson’s
The biological link is well understood
Dr. Bieta Ritz, professor of epidemiology at UCLA, explains that the connection between paraquat and Parkinson’s is not just correlational:
- Paraquat causes redox cycling, which produces oxidative stress.
- It can damage mitochondria, especially complex I in the respiratory chain.
- These processes can harm dopamine neurons, the brain cells most affected in Parkinson’s disease.
Human studies support a causal relationship
- Ritz says observational human studies, especially a large California study, show a strong relationship between paraquat exposure and Parkinson’s.
- She estimates the risk may be roughly doubled on average, depending on exposure intensity, duration, and individual susceptibility.
Breathing paraquat may be especially dangerous
- Ritz emphasized that inhaling paraquat may be particularly hazardous because the nose has a direct pathway to the brain through the olfactory bulb.
- Parkinson’s is often associated with early loss of smell and protein changes such as alpha-synuclein aggregation.
Policy and Public Health Implications
U.S. regulation lags behind other countries
- Paraquat is banned in:
- the EU
- the UK
- China
- Brazil
- and more than 70 countries total
Experts argue a ban is overdue
- Ritz said the U.S. should have banned paraquat 25 to 30 years ago, once its toxicity and Parkinson’s-related effects became clear.
- She expressed support for Vermont’s effort to become the first U.S. state to ban paraquat.
Bottom Line
The segment argues that paraquat remains a major public health concern in the U.S.: it is still legal, widely used, and in at least one Mississippi community, being released into the air at unusually high levels. Scientists on the program say the evidence tying paraquat exposure to Parkinson’s is strong enough that a U.S. ban is long overdue.