Over the past few years, there has been a series of high-profile lawsuits filed against pesticide manufacturers by plaintiffs who claim they developed a serious illness as a result of pesticide exposure. The first of these major lawsuits involved the pesticide glyphosate which is the active ingredient in Roundup, one of the most commonly used pesticides in the United States. Ultimately, thousands of plaintiffs filed suit, claiming that exposure to glyphosate caused them to develop non-Hodgkin’s lymphoma. Other pesticides have been the topic of similar lawsuits. Plaintiffs filed suit against the manufacturers of chlorpyrifos, alleging that exposure to the pesticide had resulted in neurological injuries. Most recently, plaintiffs have been filing claims against the manufacturers of paraquat, linking it to Parkinson’s disease.

As these lawsuits have grown in number, familiar patterns have emerged concerning the types of claims the plaintiffs bring. The cases are largely based on state common law violations, and the same claims appear repeatedly. This is the first post in a series that will explore the various legal claims that are commonly brought in pesticide injury cases. The series will discuss what those claims mean, how they have been treated by judges and juries so far, and why one of them has been appealed to the United States Supreme Court. This first post will provide an overview of the landscape of pesticide litigation that will be discussed in more detail in following posts. Understanding the background of these lawsuits gives context to the legal claims argued by the plaintiffs.

The Importance of State Law Claims in Pesticide Litigation

All of the legal claims that will be discussed in this series are state common law claims. It is therefore important to understand what that means in the context of pesticide litigation.

Very simply, the state law claims raised by plaintiffs in pesticide injury lawsuits are legal arguments based in state common law. The system of common law in the United States was originally copied from English common law. When the American court system was first established, it adopted the then-existing common law of England as a starting point. As the court system in the United States matured, its common law evolved. Many states have since codified aspects of their common law systems.

By raising state law claims, plaintiffs in pesticide injury lawsuits argue that the defendant pesticide manufacturers have violated state law. While pesticides are partially regulated at the state level, they are primarily regulated through the Federal Insecticide, Fungicide, and Rodenticide Act (“FIFRA”), which is a federal statute. Because pesticides are subject to federal regulation, the defendants in pesticide injury lawsuits often argue that the state law claims raised by plaintiffs are preempted by FIFRA and should not have been allowed in court. Preemption is a legal doctrine that refers to the idea that a higher authority of government can displace or “preempt” the authority of a lower level of government when the two come into conflict. In the United States, a state law may be preempted if it conflicts with federal law. Defendants in pesticide injury lawsuits have claimed that some of the state law claims raised by the plaintiffs are preempted by provisions in FIFRA. That issue will be examined further in a later post.


The pesticide glyphosate was first discovered and marketed by Monsanto Company, Inc. (“Monsanto”) in the 1970s under the brand name Roundup. Roundup has been used to target a variety of common weeds, and ultimately became one of the most widely used herbicides in the United States with millions of pounds applied annually.

In order for a pesticide to be legally used in the United States, it must be registered by the Environmental Protection Agency (“EPA”) under the Federal Insecticide, Fungicide, and Rodenticide Act (“FIFRA”). To register a pesticide under FIFRA, EPA must make a finding that use of the pesticide does not cause “unreasonable adverse effects on the environment.” 7 U.S.C. § 136a(c)(5)(C). FIFRA defines “unreasonable adverse effects on the environment” to include “any unreasonable risk to man or the environment[.]” 7 U.S.C. § 136(bb). In other words, for a pesticide to be legally used in the United States, EPA must make a finding that using the pesticide will not be unreasonably dangerous to human health or safety. For decades, glyphosate has been found by EPA to meet the FIFRA standard for registration.

In 2015, the International Agency for Research on Cancer (“IARC”), a part of the World Health Organization, issued an assessment on the potential carcinogenicity of glyphosate. The overall mission of the IARC is to conduct research on cancer prevention. A core element of achieving this mission is the IARC Monographs Programme which evaluates chemical agents to determine whether they are carcinogenic. The IARC conducted such an evaluation of glyphosate in 2015, ultimately issuing a report which found that glyphosate is a “probable human carcinogen.”

In early 2016, plaintiffs began filing lawsuits against Monsanto, alleging that exposure to Roundup had caused them to develop a type of cancer known as non-Hodgkin’s lymphoma. The plaintiffs brought various state law claims, arguing that Monsanto was responsible for their injuries. Eventually, thousands of plaintiffs filed complaints against Monsanto, each bringing the same legal claims. Those claims include: negligence, design defect, failure to warn, and breach of both express and implied warranties.

The first of these lawsuits to go to trial resulted in large wins for the plaintiffs, with juries routinely finding in favor of the plaintiffs on all counts. While many of the lawsuits were ultimately settled, several are still scheduled for trial, and the defendant (Bayer purchased Monsanto in 2018, taking over litigation of the glyphosate lawsuits and becoming the current defendant) has appealed the decisions that found in favor of the plaintiffs. One of those cases is currently on appeal to the United States Supreme Court, though the Court has yet to decide whether it will hear the case.


Chlorpyrifos is an organophosphate insecticide that has been used in the United States since the 1960s. It was originally patented and registered by Dow Chemical Company (“Dow Chemical”), but in recent years has been manufactured by Corteva Inc. (“Corteva”). The pesticide works by converting from chlorpyrifos into chlorpyrifos oxon, a potent neurotoxin, once ingested by a targeted insect or other organism. Chlorpyrifos has been approved for a variety of uses on field crops, horticultural crops, and ornamental plants.

Concerns about chlorpyrifos were first raised in the early 2000s following an EPA review of data submitted by Dow Chemical where EPA determined that chlorpyrifos is toxic to the developing neurological systems of children. In 2007, several environmental groups came together to file a petition with EPA, asking the agency to revoke or modify the pesticide residue tolerances currently set for chlorpyrifos. Before a pesticide can be used on food crops, EPA must set a residue tolerance that represents how much of the pesticide may safely remain on food items introduced into the market place. The 2007 petition relied on studies linking neurodevelopmental issues in children with exposure to chlorpyrifos. It argued that exposure to chlorpyrifos at the current residue tolerance was unsafe, and that the tolerance should be revoked. Without a registered residue tolerance, a pesticide may not be legally used on food crops. After over a decade of litigation, EPA ultimately granted the 2007 petition, citing concerns over health risks to children. EPA’s decision to revoke the tolerance for chlorpyrifos means that the pesticide may no longer be legally applied to food crops.

The first lawsuits from plaintiffs who claimed that they had suffered an injury as the result of chlorpyrifos exposure were filed in 2020. The plaintiffs in the first chlorpyrifos cases were adults suing on behalf of their minor children, alleging that exposure to chlorpyrifos that had been sprayed in fields near where the children lived caused them to develop neurological injuries. Like the glyphosate plaintiffs, the chlorpyrifos plaintiffs raised a series of state law claims in their complaints, including: negligence, failure to warn, and design defect. Since the initial two lawsuits were filed in 2020, other plaintiffs have filed suit, raising identical claims. At the moment, these lawsuits are still progressing through the court system and have yet to reach trial.


EPA approved paraquat for use in 1964. It was originally manufactured and marketed by a company that would eventually become Syngenta, which continues to manufacture and market paraquat today. Paraquat is a broad-spectrum, contact herbicide that controls broadleaf and grass weeds by inhibiting photosynthesis which destroys plant cell membranes. It can be applied as a burn-down treatment prior to planting, but can also be applied directly onto the crops, or as a post-harvest desiccant. Paraquat is registered for use on a variety of crops, but EPA has found that usage data taken from 2014-2018 indicates that paraquat use was highest on soybeans, cotton, corn, grapes, pistachios, and peanuts.

In 1978, EPA classified paraquat as a restricted use pesticide (“RUP”). Under FIFRA, RUPs may only be purchased or applied by certified applicators or someone under the direct supervision of a certified applicator. In general, a pesticide will be categorized as a RUP if its toxicity exceeds certain hazard criteria, the labeling is not adequate to mitigate the hazards, restriction would decrease the risk of adverse effects, and the decrease in risks of the pesticide as a result of restriction would exceed the decrease in benefits. 40 C.F.R. §152.170(a). EPA has recognized paraquat as being highly toxic when inhaled or ingested, which is why it has been classified as a RUP.

The earliest lawsuits concerning paraquat were filed against Syngenta in 2017. In those lawsuits, the plaintiffs claimed that exposure to paraquat caused them to develop Parkinson’s disease. One of the very first of these lawsuits was filed in Illinois state court, but dozens of similar lawsuits have been filed in federal court. In 2021, the federal lawsuits were consolidated into a multi-district litigation, while the state lawsuit is currently awaiting trial. Like the glyphosate and chlorpyrifos plaintiffs, the paraquat plaintiffs raised claims of negligence, design defect, failure to warn, and breach of implied warranties.

Going Forward

These cases are not the first time that plaintiffs have sued pesticide manufacturers for injuries allegedly related to pesticide use. Additionally, glyphosate, chlorpyrifos, and paraquat are not the only pesticides to have been the topic of such lawsuits. However, the three together help to establish the pattern of legal claims that have arisen from the recent wave of pesticide injury litigation. Going forward, this series will explore in-depth the claims most commonly raised in recent pesticide injury lawsuits, and how courts have so far treated those claims.


For more information on the regulation of pesticides from the National Agricultural Law Center, click here.

For more articles about pesticide lawsuits from the National Agricultural Law Center, click here.