Dacthal herbicide lawsuit: thyroid damage and fetal harm claims

Why the Dacthal litigation is an emerging mass tort opportunity

On August 6, 2024, the U.S. Environmental Protection Agency (EPA) took the extraordinary step of issuing an emergency suspension order for Dacthal (also known as DCPA, or dimethyl tetrachloroterephthalate), a widely used herbicide manufactured by AMVAC Chemical Corporation. This was only the second time in nearly 40 years that the EPA had invoked its emergency suspension authority under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) — a measure reserved for situations where continued use poses an imminent hazard to human health.

The EPA's action was driven by compelling scientific evidence that exposure to Dacthal and its breakdown products causes disruption of thyroid hormone levels, particularly in pregnant women and developing fetuses. Thyroid hormones are essential for fetal brain development, and even temporary disruption during critical windows of pregnancy can result in irreversible developmental harm, including reduced IQ, impaired motor skills, and long-term neurodevelopmental disabilities.

For personal injury attorneys and mass tort law firms, the Dacthal litigation represents a significant and growing opportunity. The combination of a dramatic regulatory action, clear scientific evidence of harm, an identifiable manufacturer (AMVAC Chemical Corporation), and large populations of exposed individuals creates a fertile landscape for plaintiff acquisition and case building. This guide provides everything PI attorneys need to know about the Dacthal herbicide litigation.

What is Dacthal and how was it used?

The chemistry and application of DCPA

Dacthal (dimethyl tetrachloroterephthalate, or DCPA) is a pre-emergent herbicide used to control annual grasses and certain broadleaf weeds. It has been registered for use in the United States since 1958 and has been applied primarily to vegetable crops, including broccoli, Brussels sprouts, cabbage, onions, peppers, tomatoes, and other produce. It has also been used on turf grass, ornamental plants, and cotton in some regions.

DCPA works by inhibiting cell division in germinating seedlings, preventing weed growth before the crop emerges. It is typically applied directly to soil before planting or at the time of transplanting. The chemical is persistent in the environment and can remain in soil for months after application.

How widely was Dacthal used?

Dacthal has been used on millions of acres of U.S. farmland over its decades on the market. The herbicide was particularly prevalent in regions with large-scale vegetable farming operations, including California's Central Valley, the Pacific Northwest, the Midwest, and parts of the Southeast. While DCPA was not as widely recognized by consumers as herbicides like Roundup, it was a staple of commercial agriculture and was applied in significant quantities near communities, schools, and residential areas adjacent to farmland.

AMVAC Chemical Corporation: the manufacturer

AMVAC Chemical Corporation, a subsidiary of American Vanguard Corporation, is the sole U.S. registrant and manufacturer of Dacthal. AMVAC acquired the Dacthal product line and has been responsible for its production, marketing, and regulatory compliance. As the sole manufacturer, AMVAC is the primary defendant in emerging Dacthal litigation.

The EPA emergency suspension: a historic regulatory action

Under FIFRA, the EPA has the authority to issue an emergency suspension of a pesticide registration when the agency determines that continued use poses an imminent hazard to human health or the environment. This is the most severe regulatory action available under FIFRA and is used only in extraordinary circumstances. Prior to the Dacthal suspension, the EPA had not exercised this authority since the 1980s.

On August 6, 2024, the EPA issued an emergency suspension order for all Dacthal products, effective immediately. The order prohibited the sale, distribution, and use of Dacthal throughout the United States.

"EPA determined that DCPA is so dangerous that it needs to be removed from the market immediately. Unborn babies whose mothers are exposed during pregnancy could experience changes to fetal thyroid hormone levels, and these changes are generally linked to low birth weight, impaired brain development, decreased IQ, and impaired motor development later in life." — EPA Deputy Administrator Janet McCabe, August 2024

AMVAC's failure to provide required health data

A critical element of the EPA's enforcement action is the allegation that AMVAC Chemical Corporation repeatedly failed to submit required health and safety data about Dacthal to the EPA. The agency issued multiple data call-in notices over a period of years, requiring AMVAC to conduct and submit studies on the health effects of DCPA exposure. According to the EPA, AMVAC failed to comply with these requirements, effectively obstructing the agency's ability to assess the risks of the product and take timely action to protect public health.

This failure to provide required data is significant for litigation because it suggests that AMVAC was either aware of or deliberately avoided learning about the health risks of its product. Plaintiffs' attorneys can argue that AMVAC's obstruction delayed regulatory action and prolonged the period during which workers and communities were exposed to a dangerous chemical.

The science: how Dacthal disrupts thyroid hormones

The role of thyroid hormones in human health

Thyroid hormones (primarily thyroxine, or T4, and triiodothyronine, or T3) are essential regulators of metabolism, growth, and development. In adults, thyroid hormone disruption can cause hypothyroidism (underactive thyroid), leading to fatigue, weight gain, cognitive impairment, and other symptoms. However, the consequences of thyroid disruption are most severe during pregnancy and fetal development.

Fetal thyroid hormone disruption: the critical window

During the first trimester of pregnancy, the fetus depends entirely on maternal thyroid hormones for brain development, as the fetal thyroid gland does not begin functioning until approximately the 12th week of gestation. Even after the fetal thyroid begins functioning, it continues to rely heavily on maternal hormones throughout pregnancy. Any disruption of maternal thyroid hormone levels during pregnancy — even temporary or subclinical disruption — can have permanent consequences for the developing fetus.

How DCPA and its metabolites disrupt thyroid function

DCPA and its breakdown products (metabolites) interfere with thyroid hormone synthesis and regulation through several mechanisms. The primary metabolites of DCPA, particularly tetrachloroterephthalic acid (TPA), have been shown to inhibit thyroid peroxidase (TPO), a key enzyme in the synthesis of thyroid hormones. Inhibition of TPO reduces the production of T4 and T3, leading to hypothyroidism. Additionally, DCPA metabolites may interfere with the transport and metabolism of thyroid hormones, further disrupting the hormonal balance necessary for normal fetal development.

Who is exposed to Dacthal? Identifying at-risk populations

This exposure population is particularly significant because many farmworkers are women of childbearing age, and exposure during pregnancy creates the most severe health risks. Additionally, farmworkers often have limited access to healthcare, may not be aware of their exposure to harmful chemicals, and face language and cultural barriers that make it difficult to identify their potential legal claims.

Qualifying criteria for Dacthal herbicide claims

1. Agricultural workers who applied Dacthal or worked in fields treated with the herbicide and subsequently developed thyroid disorders, thyroid cancer, or other thyroid-related health conditions.
2. Pregnant women who were exposed to Dacthal during pregnancy (through occupational exposure, community exposure, or household contact) and whose children were born with low birth weight, developmental delays, neurodevelopmental disorders, or other conditions linked to fetal thyroid hormone disruption.
3. Children who were exposed to Dacthal in utero or during early childhood and who have been diagnosed with developmental disabilities, reduced cognitive function, motor impairments, or other conditions consistent with thyroid hormone disruption.
4. Community residents who lived near farmland treated with Dacthal and who developed thyroid disorders or whose children experienced developmental harm.

Types of injuries and damages

• Thyroid disorders: Hypothyroidism, thyroid cancer, goiter, thyroiditis, and other conditions affecting thyroid function.
• Fetal and child developmental harm: Low birth weight, reduced IQ, developmental delays, impaired motor function, ADHD, autism spectrum disorder, and hearing impairment.
• Reproductive harm: Infertility, pregnancy complications, and adverse birth outcomes potentially linked to thyroid hormone disruption.
• Economic damages: Medical expenses, lost wages, costs of special education and developmental services, and diminished earning capacity.

The legal landscape: emerging Dacthal litigation

Current state of litigation

The Dacthal litigation is in its early stages. Lawsuits have been filed against AMVAC Chemical Corporation in multiple jurisdictions, alleging that the company knew or should have known about the thyroid-disrupting effects of its product, failed to adequately warn users and exposed communities, and deliberately withheld required health data from the EPA. As more lawsuits are filed, it is possible that the Judicial Panel on Multidistrict Litigation (JPML) may consolidate federal cases into an MDL.

Potential legal theories

• Strict product liability: Arguing that Dacthal is a defective and unreasonably dangerous product due to its thyroid-disrupting properties.
• Failure to warn: Arguing that AMVAC failed to provide adequate warnings about the health risks of Dacthal, particularly the risks to pregnant women and developing fetuses.
• Negligence: Arguing that AMVAC breached its duty of care by failing to conduct adequate safety testing, failing to comply with EPA data requests, and continuing to market a product it knew or should have known was harmful.
• Fraud and concealment: Arguing that AMVAC deliberately withheld health data from the EPA to avoid regulatory action, thereby prolonging the period of harmful exposure.

Potential damages in Dacthal cases

Comparison to other pesticide and herbicide litigation

Roundup (glyphosate) litigation

The Roundup glyphosate litigationis the most prominent precedent for herbicide mass tort cases. While the specific health effects differ (Roundup is alleged to cause Non-Hodgkin's lymphoma, whereas Dacthal is alleged to cause thyroid disruption and fetal harm), the legal theories and litigation strategies are analogous. The Roundup litigation demonstrated that juries are willing to hold manufacturers liable for herbicide-related health effects and to award substantial damages, including billions of dollars in punitive damages.

PFAS and environmental contamination parallels

The Dacthal litigation also shares characteristics with the PFAS forever chemicals litigation, particularly the concept of community-wide exposure through contaminated water and soil, the persistence of the chemical in the environment, and the potential for multigenerational harm. The Camp Lejeune water contamination litigation provides another parallel, particularly in its focus on exposure through contaminated water supplies and the long latency periods between exposure and the manifestation of health effects.

Statute of limitations for Dacthal claims

When does the clock start?

For Dacthal cases, the statute of limitations likely begins running when the plaintiff discovers or should have discovered the connection between their injury and Dacthal exposure. Given that the EPA's emergency suspension was issued in August 2024, many potential plaintiffs may have become aware of the risk only recently, which could preserve their claims even if their exposure occurred years ago.

Special considerations for children's claims

Claims on behalf of children who were harmed by prenatal Dacthal exposure are subject to different limitations rules in most states. Many states toll (suspend) the statute of limitations for minors, meaning the limitations period does not begin running until the child reaches the age of majority. This means that claims for children injured by in-utero exposure may remain viable for many years.

Environmental justice dimensions

The Dacthal litigation has significant environmental justice dimensions. Agricultural workers — many of whom are immigrants, people of color, and members of economically disadvantaged communities — bear a disproportionate burden of pesticide exposure. These communities often lack political power, access to healthcare, and information about their legal rights. The Dacthal case highlights the broader issue of pesticide safety and the need for stronger protections for agricultural workers.

Parallel mass tort opportunities for Dacthal attorneys

Attorneys building a Dacthal practice should consider complementary mass tort opportunities. The Roundup glyphosate litigation and the AFFF firefighting foam litigation involve related legal theories and may draw from overlapping plaintiff populations. The PFAS water contamination claims share many characteristics with Dacthal cases. The broader mass tort landscape also includes pharmaceutical claims such as the Ozempic gastroparesis litigation and the Depo-Provera meningioma litigation.