Revealed: the undisclosed safety data emerging as weedkiller maker faces Parkinson’s lawsuits in US

Syngenta, the Swiss‑headquartered agrochemical giant that inherited paraquat from its predecessor entities, has been accused of withholding critical safety data from the U.S. Environmental Protection Agency (EPA) as the herbicide remains on the market despite bans in dozens of other nations. Internal corporate records, uncovered through litigation in a Pennsylvania state court, reveal that between 2000 and 2018—when paraquat use in the United States nearly tripled—Syngenta failed to disclose analyses showing how rapidly the chemical can permeate untreated clothing, penetrate skin and enter the bloodstream, and how mixing it with surfactants amplifies absorption. The company also omitted studies indicating severe brain‑related risks, including a potential link to Parkinson’s disease, even though federal law obliges manufacturers to report “unreasonable adverse effects.” While Syngenta promoted a 2016 study that portrayed paraquat as safe, the newly released 3,700‑page dossier demonstrates a systematic effort to keep damaging information from regulators.

The omission of these data comes as global concern over paraquat’s health hazards has intensified. Sweden first called for a ban in 2004, and a cascade of countries followed, including China, which halted domestic use a decade ago after its own safety investigations. In the United States, Vermont and California have recently prohibited paraquat, citing epidemiological research that associates the chemical with Parkinson’s disease, and California regulators announced that manufacturers voluntarily ceased sales after new health‑risk findings. Federal lawmakers have also pressed for a nationwide ban, yet the EPA continues to approve paraquat applications on millions of acres, downplaying the scientific consensus and postponing a promised safety‑review roundtable that never materialized. The internal documents show Syngenta’s strategy of emphasizing favorable research while suppressing evidence of rapid dermal absorption and heightened toxicity when combined with surfactants, tactics that mirror those used to discredit health studies linking the product to chronic illnesses.

The revelations arrive amid a wave of Parkinson’s lawsuits filed by individuals alleging that paraquat exposure caused their disease, with thousands of cases pending nationwide. Although a recent Pennsylvania case was dismissed for insufficient proof of exposure, the litigation has already cost Syngenta at least $187 million in a 2021 settlement, with additional undisclosed payouts for subsequent agreements. Earlier this year the company announced it would cease global production of paraquat, claiming the decision was driven by market considerations rather than health concerns, and it maintains that no link to Parkinson’s exists. Nonetheless, the EPA’s stance that there is no “clear link” between paraquat use and adverse health outcomes remains contentious, especially as other pesticide manufacturers continue to sell the chemical in the United States, raising questions about regulatory oversight and the broader implications for public health policy.

⚡ Effects Interpreter