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Expert warns EPA models underestimated paraquat volatility, flags Parkinson’s risk and alternatives
Summary
An invited expert told the Agriculture, Food Resiliency & Forestry committee that recent data and an October 2025 EPA update show paraquat volatility was vastly underestimated, that epidemiological studies show elevated Parkinson’s risk for exposed populations, and that countries that banned paraquat use practical alternatives.
An invited expert, identified at the hearing as Dr. Mertensen, told the Agriculture, Food Resiliency & Forestry committee on Feb. 18 that recent data reviewed by the U.S. Environmental Protection Agency show prior volatility estimates for the herbicide paraquat were ‘‘4,000 times’’ too low and that the revised modeling raises exposure concerns beyond adjacent fields.
The expert summarized decades of field work and toxicology data, saying ‘‘The LD50 for paraquat is 150 milligrams per kilogram’’ and that paraquat’s acute toxicity is many orders of magnitude greater than most herbicides in current use. He told the committee that applicators often cannot comply with label protective-equipment requirements in hot field conditions, which increases the risk of acute exposure.
Why it matters: Dr. Mertensen said the EPA update (October 2025) and manufacturer-supplied data prompted model revisions and that volatilized paraquat could travel substantial distances. He said EPA model runs indicate concentrations ‘‘of concern’’ could extend roughly 2.7 miles from application sites, potentially affecting migrant worker housing and nearby schools. The expert also cited epidemiological work, including a 13-study meta-analysis, and said pooled results show about a 64% higher likelihood of Parkinson’s disease in populations exposed or living near paraquat-treated fields.
Committee members asked technical and policy questions. Representative Bosley asked directly whether paraquat ‘‘stays where it’s sprayed;’’ Dr. Mertensen replied that recent studies contradict that older assumption and show substantial movement of the compound, especially from foliage. Representative Falmi and others sought information on soil binding and breakdown; Dr. Mertensen said paraquat strongly binds to negatively charged soil particles, persists longer when bound, and is much more volatile from plant surfaces than from bare soil.
Alternatives and international practice: The expert listed alternatives used in locations that have banned paraquat—Spain, China, Turkey and Poland—and identified several chemical alternatives (glyphosate, glufosinate, carfentrazone, paraflufen) plus cultural practices such as cover crops. He said those countries substituted other tools and that high-adoption of cover crops in Vermont could reduce reliance on paraquat.
Regulatory context and next steps: Dr. Mertensen said Syngenta provided data to EPA that influenced the agency’s October 2025 update, that EPA is reassessing paraquat’s reregistration and labeling, and that those processes may be influenced by the new volatility and exposure data. He offered to provide a short written summary and cited papers (including a 2024 California study and a 13-paper meta-analysis) for the committee record.
The hearing concluded with the committee asking staff to add the expert’s materials to the record and with no formal vote taken during this session.
