Exposure to the weed-killer 2,4-D is very common. This pesticide has been used for many years starting with its use in Agent Orange decades ago, as an ingredient in the commonly used Weed and Feed for lawns, even on genetically engineered crops, and on and on. While the pesticide industry tells you it's safe, many studies have found that exposure to it can cause all sorts of health harms.
A recent study found that exposure to 2,4-D is linked to thyroid cancer in rural counties (where the pesticide is used the most). The researchers think that this may be occurring because 2,4-D is "an endocrine disruptor and may be toxic to the thyroid gland". They also point out that biomonitoring studies find that in rural agricultural areas people (especially women and children) have higher amounts of 2,4-D in their urine.
As mentioned in the following article, other studies also find that 2,4-D exposure has thyroid effects. It also points out that one study found 2,4-D in the bodies of 1 in 3 Americans, and another study found the presence of both 2,4-D and dicamba (both herbicides) in all pregnant midwest women studied in 2020-2022.
While the United States EPA does not view 2,4-D as carcinogenic (cancer-causing), other countries and international organizations do.
Bottom line: To lower your own 2,4-D exposure, eat as many organic foods as possible, and don't use pesticides on your lawn. Organic crops and organic lawn care does not allow the use of 2,4-D.
Excerpts from Beyond Pesticides: Thyroid Cancer Associated With Exposure to the Weed Killer 2,4-D, Study Finds
In a study of the herbicide 2,4-D and thyroid cancer in the U.S., researchers find that 2,4-D exposure is significantly associated with greater thyroid cancer incidence in rural counties. Utilizing incidence rates for thyroid cancer for 2017–2021 through the Centers for Disease Control and Prevention (CDC) database and county-level 2,4-D use data from the U.S. Geological Survey, this research, published in Endocrines, highlights a link between pesticide exposure—in areas where agricultural pesticide use is most concentrated—and disproportionate cancer risks.
“The increasing incidence of thyroid cancer in the United States suggests a possible role for environmental exposures that potentially alter thyroid hormone regulation through cellular toxicity,” the authors note. They continue, “2,4-Dichlorophenoxyacetic acid (2,4-D) is a commonly used herbicide that can act as an endocrine disruptor and may be toxic to the thyroid gland.” This study adds to a growing body of evidence showing that exposure to environmental pollutants, including pesticides, plays a role in the epidemiology of thyroid cancer.
Background
2,4-D, one of the first commercialized synthetic herbicides, is still widely used for both agricultural and nonagricultural/residential uses despite decades of scientific literature connecting this chemical to a range of adverse health and environmental effects. Previous research shows that the use of 2,4-D is linked to contamination of surface and ground water, with toxicity to insects and aquatic organisms. (See here and here.) 2,4-D also leaches into drinking water and drifts into nontarget areas, due to its high solubility and poor binding to soil.
The U.S. Environmental Protection Agency (EPA) classifies 2,4-D as a Group D chemical, meaning it is “not classifiable as to human carcinogenicity.” Meanwhile, public health groups and international organizations continue to challenge this stance. As the current study states: “The International Agency for Research on Cancer (IARC) has classified 2,4-D as ‘possibly carcinogenic to humans’ (Group 2B). It has also been shown to impact thyroid and reproductive hormones in animal and mechanistic studies, resulting in the EPA placing it in its Endocrine Disruptor Screening Program for further evaluation of its endocrine-disrupting potential.”
Study Results
To address the lack of research on the epidemiology of 2,4-D and thyroid dysfunction in humans, the current study “explores whether there is an association between thyroid cancer incidence and 2,4-D exposure by integrating US county-level data on herbicide use with age-adjusted thyroid cancer incidence rates and lagged exposure models that account for agricultural intensity and rurality.” The results show a significant positive association between 2,4-D exposure and thyroid cancer incidence specifically in rural counties, which “suggests that higher county-level 2,4-D use in rural areas may be associated with higher thyroid cancer incidence at the ecological level.”
The study confirms previous research showing disproportionate risks for farmworkers and individuals and families living near agriculture. “In rural areas, cropland density is generally higher and homes are closer to treated fields, both of which are associated with greater potential for non-occupational exposure [18,19,20],” the researchers state. They continue: “Biomonitoring studies have also found significantly higher urinary 2,4-D concentrations in people living near treated fields, particularly during application periods and for women and children. A study of private wells in agriculturally intensive northeast Iowa found pesticides and related transformation products, including 35 herbicide-related compounds, in tap water, often exceeding health-based hazard index screening levels.” (See research here, here, here, and here.)
Additional experimental studies show that 2,4-D can cause adverse thyroid-related outcomes. The Agricultural Health Study shows an increased risk of hypothyroidism with 2,4-D exposure, and the National Report on Human Exposure to Environmental Chemicals (NHANES) biomonitoring studies associate urinary 2,4-D metabolites (breakdown products) with altered thyroid hormone profiles. (See here and here.) One case-control study in California also links residential exposure to multiple agricultural pesticides, including 2,4-D, and a higher risk of thyroid cancer.
Previous Coverage
As documented in Daily News, Weed Killer 2,4-D’s Adverse Effect on the Liver Adds to List of Hazards from Food, Lawn, and Water Residues, in addition to its effects including cancer, and reproductive, immune, and nervous system disruption, a review published in Toxics finds that 2,4-D causes significant changes in liver structure and function. 2,4-D can damage liver cells, tissue, and inflammatory responses through the induction of oxidative stress. The liver, the largest solid organ in the human body, is an essential part of the digestive system responsible for blood detoxification, nutrient metabolization, and immune function regulation. However, rates of chronic liver diseases are increasing, representing the second leading cause of mortality among all digestive diseases in the U.S. In fact, researchers warn of the rise in liver disorders and metabolic syndrome among young people. Therefore, reviews like this highlight the research available to make decisions on safeguarding human health from chemical exposure to mitigate further disease outcomes and complications.
According to research published in Environmental Health by scientists at George Washington University, 2,4-D is found in the bodies of one in three Americans. 2,4-D is an herbicide that is increasingly used when weeds growing near genetically engineered (GE) crops have developed resistance to the repeated use of Roundup and other glyphosate-based weed killers.