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For decades now, scientists have linked exposure to pesticides to an increased risk of Parkinson’s Disease (PD). A study published in 2000, for instance, found that people exposed to pesticides in the home or garden may have a significantly higher risk of PD. Many other studies both before and after this one showed that occupational exposure to these chemicals—particularly among farmers and farm workers—was a risk factor for the disease.

More recently, the focus has turned to one particular pesticide as being particularly concerning: paraquat. There are now efforts underway to eliminate the use of paraquat because of evidence showing its toxic effects on humans.

What is Paraquat?

According to the Environmental Protection Agency (EPA), paraquat dichloride, commonly referred to as “paraquat,” is one of the most widely used herbicides in the U.S. Often called “Gramoxone” (a brand name product), it is an important tool for the control of weeds in many agricultural and non-agricultural settings, and is also used to desiccate crops like cotton before harvest.

Paraquat’s Connection to PD

Initial studies on paraquat were mainly inconclusive when it came to its potential connection to PD. In 2010, researchers reported that the herbicide had been linked to PD in epidemiological studies and animal studies, but “evidence that human exposure to the chemical results in an increased risk for PD is rather limited….”

In a later 2012 study, scientists came to the same conclusion, noting that the current literature did not provide enough evidence proving a relationship between paraquat and PD.

Later studies, however, have found more evidence of a link between the two. In 2018, researchers from the University of Guelph found that low-level exposure to pesticides like paraquat and maneb disrupted cells in a way that mimics the effects of mutations known to cause PD. Adding the effects of these chemicals to a predisposition for PD—in individuals at genetic risk for the disease, for instance—increases the risk of disease onset.

In 2019, researchers conducted a systematic review of the literature and found that PD occurrence was 25 percent higher in participants exposed to paraquat. Results from a subgroup analysis also indicated a higher PD frequency in those who were exposed to the herbicide for longer periods.

EPA Slow to Condemn Paraquat

The EPA states that paraquat is highly toxic and that one small sip can be fatal. Yet in the 2019 draft human health risk assessment, the agency found “no dietary risks of concern associated with paraquat when it is used according to the label instructions.” After reviewing over 70 articles that investigated the potential health risks of paraquat, including PD and cancer, the EPA concluded that “there is insufficient evidence to link registered paraquat products to any of the health outcomes investigated, including Parkinson’s Disease, when used according to the label.”

Nevertheless, the EPA proposed additional protections in October 2020 to reduce exposure to paraquat, including but not limited to:

  • prohibiting aerial application except when desiccating cotton fields
  • prohibiting pressurized handgun and backpack sprayer application methods
  • limiting the maximum application rate for alfalfa
  • requiring enclosed cabs or PF10 respirators if the area treated in a 24-hour period is 80 acres or less
  • adding mandatory spray drift management label language

The EPA has also limited the use of the pesticide only to licensed applicators.

Lawmakers Seek to Ban Paraquat from Use In the U.S.

With the growing evidence supporting a connection between paraquat and PD, some lawmakers are taking action. In July 2019, Representative Nydia Velasquez (D-NY) introduced the Protect Against Paraquat Act of 2019 (HR 3817) seeking to eliminate the use of paraquat in the U.S.

China, the European Union, and more than 30 other countries around the world have already banned paraquat.

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