For decades, regulators knew paraquat was harmful but failed to address the risks

Study shows paraquat’s chemical class has the potential to affect the central nervous system and be absorbed through the skin.

The EPA registers paraquat for use in the U.S.

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California regulators’ concerns signal to federal regulators that acute on-the-ground health evidence is accumulating.

The EPA internally considers cancelling paraquat’s registration, citing “no known medical treatment to prevent fatality from exposure.” due to acute harms. But it takes no action.

Classifying paraquat for “restricted use,” the EPA accepts it for special review, citing concerns such as potential harm to the developing fetus and other chronic effects not including neurological harms.

Published peer-reviewed study shows paraquat’s capacity to cause brain damage.

University medical researchers document changes to the brain in eight patients who die of paraquat poisoning in one of the first peer-reviewed reports about effects on the brain.

After finishing its special review, the EPA clears paraquat for continued use, having never examined harms to the nervous system. The agency excluded a lifetime cancer study and multi-generational reproductive study that paraquat manufacturers submitted.

Sweden becomes one of the first countries to name paraquat a Class 1 hazardous substance and restrict its use.

Scientists publish a landmark study in Science showing how paraquat structurally resembles MPTP, a compound known to cause Parkinson’s disease. The study’s hypothesis: Paraquat, like MPTP, may damage dopamine-producing neurons. This peer-reviewed finding is available to the EPA.

California’s Department of Food and Agriculture asks paraquat companies whether it causes Parkinson’s.

Kuwait bans paraquat.

Finland bans paraquat.

The EPA scrutinizes paraquat’s safety, noting it as a possible human carcinogen. In the years that follow, independent studies further link paraquat exposure to Parkinson’s, a risk that the agency’s review never examined.

A letter in the journal Neurology raises the paraquat-Parkinson’s connection explicitly, inserting the question into widely available peer-reviewed medical literature.

A peer-reviewed study in the journal Neurotoxicology documents brain damage in a fatal case of paraquat poisoning. The EPA later cites the article in its reference materials.

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A publicly available study of rural residents in British Columbia, where Parkinson’s is especially prevalent, finds strong association between paraquat use and Parkinson’s.

A peer-reviewed study of 130 Canadian Parkinson’s patients connects occupational herbicide use with a threefold higher risk of the disease.

Austria bans paraquat.

A further publicly available study of Parkinson’s in British Columbia, published in Movement Disorders, narrows earlier findings to agricultural workers with occupational pesticide exposure in the tree fruit sector.

Denmark bans paraquat.

A peer-reviewed study in Neurology examines 120 Parkinson’s patients in Taiwan and finds that paraquat users face more than a threefold higher risk of Parkinson’s, compared to non-users. 

The EPA approves continued use of paraquat. Despite referring to neurotoxicity in the final published decision, the agency says it lacks enough evidence to establish a link between paraquat and Parkinson’s. 

EPA removes respirator requirements from paraquat product labels. This was reversed 4 years later following worker safety concerns that California regulators submitted to the EPA.

A peer-reviewed study in mice shows paraquat exposure depletes dopamine-producing neurons and produces hallmarks of Parkinson’s disease, more evidence of the swiftly accumulating body of research. 

Researchers funded by the National Institutes of Health show that combined exposure to paraquat and the fungicide maneb cause damage to dopamine-producing neurons, a greater effect than either substance alone.

Further peer-reviewed studies link paraquat exposure to selective degeneration of dopamine-producing neurons in the region of the brain affected by Parkinson’s.

Peer-reviewed research shows how paraquat is toxic to dopamine-producing neurons.

A federally funded study drawing on the National Institutes for Health Agricultural Health Study, a prospective cohort of over 84,000 licensed pesticide applicators, finds paraquat use is associated with higher prevalence of Parkinson’s disease. The study is co-sponsored by the EPA and the agency has direct access to the findings.

The European Union revokes paraquat registrations. Syngenta, which makes paraquat, declines to resubmit for EU registration.

A second peer-reviewed study shows chronic oral ingestion of paraquat also triggers dopamine-neuron degeneration in mice, expanding the evidence beyond injection-only models.

A peer-reviewed study finds people living within 500 meters of paraquat-applied fields face much higher Parkinson’s disease risk. 

The findings based on the NIH Agricultural Health Study finds paraquat applicators are 2.5 times more likely to develop Parkinson’s than non-users. This  U.S. government-funded science is available to the EPA.

The EPA opens its current registration review cycle for paraquat. The review will take more than a decade to produce an interim decision.

A peer-reviewed study from authors at the Parkinson’s Institute finds that a genetic variant common in the general population increases the risk of the disease from paraquat exposure, suggesting a large subset of the public faces heightened risk.

China announces its intent to ban paraquat, citing the need to protect public health.

Paraquat manufacturer Syngenta conducts an internal study confirming previous NIH findings of a 250% increase in incidences of Parkinson’s disease among workers using it. 

Brazil bans paraquat.

A meta-analysis of 13 epidemiological studies finds that occupational and environmental paraquat exposure increases the risk of developing Parkinson’s disease by 64%.

EPA releases its draft human health risk assessment for paraquat, acknowledging it has historically received feedback from the public linking paraquat to Parkinson’s disease. But the agency’s review concludes that “the weight of evidence was insufficient.”

The EPA declines to ban or cancel paraquat registration.

The EPA releases an interim registration decision on paraquat, imposing new use restrictions, but stops short of cancellation. The agency rejects expert advice from the National Toxicological Program to consider animal studies, excluding 90% of research in its disease analysis.

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On behalf of farmworkers, the environmental nonprofit Earthjustice sues the EPA, arguing it has failed to adequately account for neurological evidence of paraquat’s harm.

Canada discontinues registration for paraquat products.

A study of California residents finds that living or working near paraquat-applied fields more than doubles the odds of developing Parkinson’s.

The EPA’s preliminary analysis of industry data suggests uncertainty about paraquat drift and the possibility it may travel farther than previously understood.

The EPA withdraws its interim registration decision for paraquat and calls for more research, effectively restarting a review already lasting a decade. Paraquat remains on the market.

Twenty former EPA officials sign a letter calling for a ban on the use of paraquat.