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Dicamba: Concerns about cancer and crop damage · U.S. Right to Know articles

Dicamba is a broad-spectrum herbicide that some scientific studies link to cancer and hypothyroidism. In the European Union, dicamba is classified as a category II <a href="https://health.ec.europa.eu/document/download/4c763cb7-5b29-4477-acf2-2776ddc5f147_en">suspected endocrine disruptor</a>, which means it has the potential to interfere with the body’s hormones and normal functioning. Dicamba caused widespread crop damage to millions of acres of farmland in the United States after the U.S. Environmental Protection Agency (EPA) approved new dicamba applications on cotton and soybean plants that were genetically engineered to tolerate the herbicide.In July 2025, after courts twice blocked its use, the EPA proposed to re-register dicamba for use on dicamba-tolerant GMO cotton and soybeans.<h2 class="wp-block-heading" id="h-thousands-of-crop-harm-complaints">Thousands of crop harm complaints</h2>Before the new dicamba-tolerant GMOs were introduced, Monsanto and BASF <a href="https://www.theguardian.com/us-news/2020/mar/30/monsanto-crop-system-damage-us-farms-documents">knew</a> that dicamba use would likely lead to crop damage on U.S. farms.Soon after the EPA allowed the new uses of dicamba, complaints about crop damage surged across the farming states of Illinois, Indiana, Iowa, Missouri and Arkansas. Dozens of farmers sued pesticide companies Bayer and BASF in an effort to hold them accountable for crop losses. Details on the litigation can be found here: <a href="https://usrtk.org/pesticides/dicamba-papers/">The Dicamba Papers: key documents and analysis</a>.By 2017, the EPA said it had tallied 2,708 official dicamba-related crop injury investigations (as reported by state departments of agriculture) – with more than 3.6 million acres of soybeans impacted, as well as tomatoes, watermelon, cantaloupe, vineyards, pumpkins, vegetables, tobacco, residential gardens, trees and shrubs. <h2 class="wp-block-heading" id="h-federal-courts-twice-blocked-dicamba-registration">Federal courts twice blocked dicamba registration</h2>In 2020, environmental groups <a href="https://www.farmprogress.com/crops/environmental-groups-sue-epa-on-dicamba-registration">sued the EPA</a> over the dicamba drift problem. The U.S. Court of Appeals for the 9th Circuit <a href="https://www.centerforfoodsafety.org/files/125--dicamba-opinion_35970.pdf">ruled against the EPA</a>. The court said the agency had “substantially underestimated” the risks of dicamba, and that the herbicide had caused “undisputed damage.” The EPA re-registered dicamba and environmental groups again challenged them in court. In 2024, a federal court in Arizona <a href="https://nationalaglawcenter.org/wp-content/uploads/2024/02/FILE_3676.pdf">ordered EPA</a> for the second time to vacate the dicamba registration. In July 2025, the EPA <a href="https://www.washingtonpost.com/climate-environment/2025/07/23/banned-herbicide-return-epa-dicambra/">announced plans</a> to <a href="https://www.epa.gov/pesticides/epa-announces-proposed-decision-approve-registration-new-uses-dicamba-outlines-new">re-register dicamba</a>.  <h2 class="wp-block-heading" id="h-what-is-dicamba-nbsp">What is dicamba? </h2>Dicamba (3,6-dichloro-2-methoxybenzoic acid) is a broad spectrum herbicide first registered in 1967. The herbicide is used on agricultural crops, fallow land, pastures, turfgrass and rangeland. Dicamba is also registered for non-agricultural uses in residential areas, including on golf courses.More than 1,000 products sold in the U.S. include dicamba, according to the National Pesticide Information Center. Dicamba's mode of action is as an auxin agonist: it produces uncontrollable growth that leads to plant death.<h2 class="wp-block-heading" id="h-what-are-the-health-concerns-of-dicamba-exposure">What are the health concerns of dicamba exposure?</h2>The EPA states that dicamba is not likely to be carcinogenic, but some studies have found an increased risk of cancer for users of dicamba. Studies have also linked dicamba exposure to increased risk of hypothyroidism. Here are the key studies:<h3 class="wp-block-heading" id="h-cancer">Cancer</h3><a href="https://academic.oup.com/ije/advance-article/doi/10.1093/ije/dyaa066/5827818">Dicamba use and cancer incidence in the agricultural health study: an updated analysis, </a>International Journal of Epidemiology (5.1.20). "Among 49,922 applicators, 26,412 (52.9%) used dicamba. Compared with applicators reporting no dicamba use, those in the highest quartile of exposure had elevated risk of liver and intrahepatic bile duct cancer and chronic lymphocytic leukaemia and decreased risk of myeloid leukaemia."<a href="https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.0901731?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed">A review of pesticide exposure and cancer incidence in the Agricultural Health Study cohort,</a> Environmental Health Perspectives (8.1.10)."We reviewed 28 studies; most of the 32 pesticides examined were not strongly associated with cancer incidence in pesticide applicators. Increased rate ratios (or odds ratios) and positive exposure–response patterns were reported for 12 pesticides currently registered in Canada and/or the United States (alachlor, aldicarb, carbaryl, chlorpyrifos, diazinon, dicamba, S-ethyl-N, N-dipropylthiocarbamate, imazethapyr, metolachlor, pendimethalin, permethrin, trifluralin)."<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1626435/">Cancer Incidence among Pesticide Applicators Exposed to Dicamba in the Agricultural Health Study.</a> Environmental Health Perspectives (7.13.06). "Exposure was not associated with overall cancer incidence nor were there strong associations with any specific type of cancer. When the reference group comprised low-exposed applicators, we observed a positive trend in risk between lifetime exposure days and lung cancer (p = 0.02), but none of the individual point estimates was significantly elevated. We also observed significant trends of increasing risk for colon cancer for both lifetime exposure days and intensity-weighted lifetime days, although these results are largely due to elevated risk at the highest exposure level."<a href="https://cebp.aacrjournals.org/content/10/11/1155.long">Non-Hodgkin’s Lymphoma and Specific Pesticide Exposures in Men</a>: Cross-Canada Study of Pesticides and Health, Cancer Epidemiology, Biomarkers and Prevention (11.01). "Among individual compounds, in multivariate analyses, the risk of NHL was statistically significantly increased by exposure to the herbicides [including dicamba] ... In additional multivariate models, which included exposure to other major chemical classes or individual pesticides, personal antecedent cancer, a history of cancer among first-degree relatives, and exposure to mixtures containing dicamba ...were significant independent predictors of an increased risk for NHL"<h3 class="wp-block-heading" id="h-hypothyroidism">Hypothyroidism</h3><a href="https://ehp.niehs.nih.gov/doi/full/10.1289/EHP3194?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed">Pesticide Use and Incident Hypothyroidism in Pesticide Applicators in the Agricultural Health Study,</a> Environmental Health Perspectives (9.26.18)."In this large prospective cohort of farmers that were occupationally exposed to pesticides, we found that ever-use of four organochlorine insecticides (aldrin, chlordane, heptachlor, and lindane), four organophosphate insecticides (coumaphos, diazinon, dichlorvos, and malathion), and three herbicides (dicamba, glyphosate, and 2, 4-D) was associated with increased risk of hypothyroidism."<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3795845/">Hypothyroidism and pesticide use among male private pesticide applicators in the agricultural health study,</a> Journal of Occupational and Environmental Medicine (10.1.14)."The herbicides 2, 4-D, 2, 4, 5-T, 2, 4, 5-TP, alachlor, dicamba, and petroleum oil were all associated with an increased odds of hypothyroidism"<h3 class="wp-block-heading" id="h-rising-levels-of-dicamba-in-pregnant-women">Rising levels of dicamba in pregnant women</h3><a href="https://www.mdpi.com/2813-3145/3/1/5">Dicamba and 2,4-D in the Urine of Pregnant Women in the Midwest: Comparison of Two Cohorts (2010–2012 vs. 2020–2022)</a>, Agrochemicals (2.16.24). “The percent of pregnant women with detectable levels of dicamba in their urine in the 2020–2022 cohort is 2.5 times higher than in the earlier cohort (2010–2012), and a four-fold increase in mean concentration levels of dicamba was also observed over the same time period.”<h2 class="wp-block-heading" id="h-is-dicamba-in-our-food">Is dicamba in our food?</h2>Just as glyphosate applications in farm fields have been found to leave residues of glyphosate on and in finished foods, such as oatmeal, breads, cereals, etc., dicamba leaves residues in food. Farmers whose produce has been contaminated with dicamba residues via drift have expressed concerns that their products might be rejected or otherwise harmed commercially because of the residue issue.The EPA has set tolerance levels for dicamba in several grains and for the meat of livestock that consume grains, but not for a variety of fruits and vegetables. A tolerance for dicamba in soybeans is set at 10 parts per million, for instance, in the United States, and at 2 parts per million for wheat grain. Tolerances can <a href="https://www.law.cornell.edu/cfr/text/40/180.227">be seen here.</a>The EPA has issued <a href="https://www.epa.gov/ingredients-used-pesticide-products/registration-dicamba-use-dicamba-tolerant-crops#q1">this statement</a> regarding dicamba residues in food: "EPA performed the analysis required by the Federal Food, Drug and Cosmetic Act (FFDCA) and determined that residues on food are 'safe' – meaning that there is a reasonable certainty of no harm to people, including all reasonably identifiable subpopulations, including infants and children, from dietary and all other non-occupational exposure to dicamba."For more reporting and perspectives on the topic of EPA tolerance levels, see our reporting in Environmental Health News:<li><a href="https://www.ehn.org/when-safe-may-not-really-be-safe-2621578745.html">Chemicals on our food: When “safe” may not really be safe:</a> Scientific scrutiny of pesticide residue in food grows; regulatory protections questioned (11.27.18)</li><h2 class="wp-block-heading" id="h-loss-of-effectiveness">Loss of effectiveness</h2>Crop-killing weeds "are advancing across the U.S. northern plains and Midwest, in the latest sign that weeds are developing resistance to chemicals faster than companies including Bayer and Corteva can develop new ones to fight them," reported Rod Nickel and Tom Polansek in a <a href="https://www.reuters.com/markets/commodities/crop-killing-weeds-advance-across-us-farmland-chemicals-lose-effectiveness-2024-01-16/">2024 Reuters investigation</a> based on two dozen interviews and a review of academic papers published since 2021. The <a href="https://www.weedscience.org/Home.aspx">International Survey of Herbicide Resistant Weeds</a>, a global database maintained by a group of scientists in over 80 countries, records "reduced effectiveness for glyphosate, one of the most common herbicides, against 361 weed species, including 180 in the U.S., affecting corn, soy, sugar beets and other crops," Nickel and Polanski wrote. "Some 21 weed species globally showed resistance to dicamba." See our <a href="https://usrtk.org/pesticides/glyphosate-health-concerns/">glyphosate fact sheet</a>.<h2 class="wp-block-heading" id="h-news-coverage">News coverage</h2><a href="https://www.washingtonpost.com/climate-environment/2025/07/23/banned-herbicide-return-epa-dicambra/">Courts banned this herbicide twice. The EPA wants to bring it back</a>. Amudalat Ajasa, Washington Post (7.23.25)<a href="https://theconversation.com/the-herbicide-dicamba-was-supposed-to-solve-farmers-weed-problems-instead-its-making-farming-harder-for-many-of-them-174181">The herbicide dicamba was supposed to solve farmers’ weed problems – instead, it’s making farming harder for many of them</a>. Bartow Elmore, The Conversation (1.26.22)<a href="https://www.agweek.com/business/off-target-dicamba-damage-in-2021-may-be-the-worst-year-yet-in-the-upper-midwest">Off-target dicamba damage in 2021 may be the worst year yet in the Upper Midwest</a>. Michelle Rook, Mikkel Pates, AgWeek (8.2.21)<a href="https://www.arkansasonline.com/news/2021/jul/19/dicamba-loss-looking-likely-for-soybeans/">650,000 acres of soybeans damaged by dicamba this summer, state estimates.</a> Stephen Steed, Arkansas Democrat Gazette (7.19.21)<a href="https://www.stltoday.com/news/local/state-and-regional/buy-it-or-else-inside-monsanto-and-basf-s-moves-to-force-dicamba-on-farmers/article_002f5e83-004d-52de-a686-eef5cb108192.html">‘Buy it or else’: Inside Monsanto and BASF’s moves to force dicamba on farmers</a>. Jonathan Hettinger, St. Louis Post Dispatch (12.6.20)<a href="https://investigatemidwest.org/2020/10/29/epa-documents-show-dicamba-damage-worse-than-previously-thought/">EPA documents show dicamba damage worse than previously thought</a>. Johnathan Hettinger, Midwest Center for Investigative Reporting (10.29.20) <a href="https://www.theguardian.com/us-news/2020/mar/30/monsanto-crop-system-damage-us-farms-documents">Revealed: Monsanto predicted crop system would damage US farms</a>. Carey Gillam, Guardian (3.30.20)<a href="https://revealnews.org/article/scientists-warned-this-weed-killer-would-destroy-crops-epa-approved-it-anyway/">Scientists warned this weed killer would destroy crops. EPA approved it anyway</a>. Liza Gross, Reveal (11.13.18)<a href="https://www.nytimes.com/2017/11/01/business/soybeans-pesticide.html">Crops in 25 States Damaged by Unintended Drift of Weed Killer</a>. Eric Lipton, New York Times (11.1.17) <a href="https://www.washingtonpost.com/business/economy/this-miracle-weed-killer-was-supposed-to-save-farms-instead-its-devastating-them/2017/08/29/33a21a56-88e3-11e7-961d-2f373b3977ee_story.html">This miracle weed killer was supposed to save farms. Instead, it’s devastating them</a>. Caitlin Dewey, Washington Post (8.29.17)