Research studies conducted over the past several decades have established a strong association between prolonged exposure to paraquat and the development of Parkinson’s disease, a progressive neurodegenerative disorder affecting the central nervous system. In people with Parkinson’s disease, nerve cell damage in the brain causes a drop in dopamine levels, which leads to symptoms like stiffness, tremors, slowed movement, and impaired posture and balance.

Recent research has shown that paraquat can destroy these same dopamine-producing neurons in the brain, the loss of which is a key factor in the progression of Parkinson’s disease. In 2017, the journal Nature Chemical Biology published a study suggesting that paraquat causes cell death via a phenomenon called oxidative stress, which is an imbalance between the production of oxygen reactive species (free radicals) and the body’s ability to repair their harmful effects. In humans, oxidative stress is believed to be involved in the development of Parkinson’s disease and other diseases. In another study conducted by the National Institute of Health in July 2011, researchers found that farmers who use paraquat have a 2.5-times (250%) greater risk of developing Parkinson’s disease.

There is also evidence of a possible Parkinson’s risk among people who live near farmland and other areas where paraquat is sprayed and are thus exposed to paraquat present in the environment. In one study published in the journal Toxicological Sciences in December 2020, researchers found that repeated exposure to low levels of paraquat in the air may allow the pesticide to enter the brain and accumulate there, where it can cause olfactory impairment, an early sign of Parkinson’s disease. “Inhalation can provide a direct route of entry to the brain,” says Timothy Anderson, a graduate student and lead author of the paraquat study. “If you inhale something and it goes into your nose, it can actually enter the neurons responsible for sense of smell, and travel into the brain.” The researchers concluded that their findings “support the need for establishing protective regulations for applying neurotoxic pesticides, such as [paraquat], in order to protect public health.”

Lawsuits Alleging Parkinson’s Disease from Paraquat

The use of weed killers in the U.S. is controversial. For decades, paraquat has been sprayed on soybean fields and other crops across the country – even more so recently with the emergence of glyphosate-resistant weeds – with little regard for the possible impact of paraquat use on human health. In 2016, the U.S. Environmental Protection Agency announced that it would investigate the possible human health risks of paraquat exposure, the final results of which are expected to be released in 2022. In the meantime, workers and other individuals who were exposed to paraquat and were subsequently diagnosed with Parkinson’s disease are pursuing paraquat lawsuits against the makers of paraquat-based weed killers like Gramoxone, Blanco, Devour and Parazone. The paraquat lawsuits allege, among other things, that the herbicide manufacturers failed to: adequately research the potential link between paraquat and Parkinson’s disease; warn consumers about the risk of Parkinson’s disease from paraquat exposure; or ensure that paraquat applicators, mixers, and loaders received adequate protective equipment to minimize their risk of harmful paraquat exposure.