Atrazine: The Endocrine Disrupting Pesticide Causes Breast Cancer  by Jeffrey Dach MD

The Trump administration has just re-authorized the pesticide atrazine for widespread agricultural use. Atrazine is one of the most heavily used herbicides in the United States, and the medical literature leaves no doubt: it is a potent endocrine-disrupting chemical (EDC) linked to breast cancer, other cancers, and infertility.

In my office, I routinely advise women concerned about breast cancer risk to avoid EDC chemical exposures. Pesticides like atrazine act as hormone disruptors, interfering with estrogen, testosterone, and the hypothalamic-pituitary-gonadal axis. The result? Altered cell growth, suppressed immunity, and increased cancer risk. This is not speculation. It is documented in peer-reviewed studies.

Header Image Attribution: Link to Photo on wikimedia commons.  African clawed frog (Xenopus laevis), from Chimanimani in Manicaland, Zimbabwe. December 2012. Source Flickr: Xenopus laevis Author Brian Gratwicke. Creative Commons CC0 1.0 Universal Public Domain Dedication.

Our Stolen Future by Theo Colborn

One of the earliest and most influential warnings came in the groundbreaking 1996 bestseller Our Stolen Future: Are We Threatening Our Fertility, Intelligence, and Survival ? by Theo Colborn. This landmark book exposed how EDC synthetic chemicals in our environment threaten future generations. It laid the foundation for understanding endocrine disruption and specifically highlighted herbicides like atrazine as part of the problem. Decades later, the science has only grown stronger.

Feminization of Male African Frogs

Dr. Tyrone B. Hayes and his team at the University of California, Berkeley, published a landmark study showing that atrazine causes complete feminization and chemical castration in male African clawed frogs Xenopus laevis at extremely low, environmentally relevant doses (as low as 0.1 parts per billion). This work remains one of the most widely cited demonstrations of atrazine’s endocrine-disrupting power in vertebrates.

Hayes, Tyrone B., et al. “Atrazine Induces Complete Feminization and Chemical Castration in Male African Clawed Frogs (Xenopus laevis) Proceedings of the National Academy of Sciences of the United States of America, vol. 107, no. 10, 9 Mar. 2010, pp. 4612–17

Increased Breast Cancer Rates

On the human side, ecological studies have linked atrazine (and triazine herbicides) exposure in drinking water and agricultural areas to higher breast cancer rates. A widely cited 1997 study in Kentucky counties found a statistically significant increase in breast cancer incidence in areas with medium to high atrazine exposure.

Kettles, M. A., et al. “Triazine Herbicide Exposure and Breast Cancer Incidence: An Ecologic Study of Kentucky Counties.” Environmental Health Perspectives, vol. 105, no. 11, Nov. 1997, pp. 1222–27,

A similar ecological analysis in Missouri counties reached comparable conclusions.

Hunter, L. D., et al. “Atrazine Exposure and Breast Cancer Incidence: An Ecologic Study of Missouri Counties.” Toxicological & Environmental Chemistry vol. 90, no. 2, 2008, pp. 293–307,

Mechanism of Action

More recent laboratory and animal work confirms the mechanism. A 2023 study in Ecotoxicology and Environmental Safety showed that atrazine promotes breast cancer development by suppressing immune function and upregulating matrix metalloproteinases (MMPs), accelerating tumor growth, invasion, and spread in mouse models.

Wang, M., et al. “Atrazine Promotes Breast Cancer Development by Suppressing Immune Function and Upregulating MMPs.” Ecotoxicology and Environmental Safety vol. 253, 15 Mar. 2023, article 114691,

Breast Cancer in Mouse Models

Chronic exposure studies in female Sprague-Dawley rats, the gold-standard model for mammary tumor research, showed increased incidence and earlier onset of mammary tumors linked to prolonged estrus and elevated estrogen/prolactin signaling.

Wetzel, Lawrence T., et al. “Chronic Effects of Atrazine on Estrus and Mammary Tumor Formation in Female Sprague-Dawley and Fischer 344 Rats.”Journal of Toxicology and Environmental Health, vol. 43, no. 2, 1994, pp. 169–82, doi:10.1080/15287399409531914.

In November 2025, the International Agency for Research on Cancer (IARC) classified atrazine as “probably carcinogenic to humans” (Group 2A), citing sufficient evidence in animals (including mammary tumors), limited human evidence for non-Hodgkin lymphoma, and strong mechanistic data on hormone disruption, oxidative stress, and immune suppression.

Cattley, Russell C., et al. “Carcinogenicity of Atrazine, Alachlor, and Vinclozolin.” The Lancet Oncology, vol. 27, no. 1, Jan. 2026 [online Nov. 2025], pp. 11–12,

Conclusion:

Atrazine is an endocrine disrupting chemical with documented links to breast cancer and other serious health effects. Re-authorizing its use puts millions at unnecessary risk, especially in agricultural communities where it contaminates drinking water.

In my practice, I emphasize prevention. For women on bioidentical hormone programs, I routinely recommend iodine supplementation (such as Lugol’s Solution or Iodoral) as part of a breast cancer prevention strategy, precisely because environmental EDCs like atrazine increase risk.

If you are concerned about atrazine or other pesticides, talk to your doctor, filter your water, and support policies that protect public health over corporate profits. The science has been warning us for decades, Our Stolen Future told us this was coming. It is time to listen.

Link to related articles: Pesticides and Breast Cancer Connection

Jeffrey Dach MD
7450 Griffin Road, Suite 190
Davie, FL 33314
954-792-4663
my blog:

References

1. Hayes, Tyrone B., et al. “Atrazine Induces Complete Feminization and Chemical Castration in Male African Clawed Frogs (Xenopus laevis).” Proceedings of the National Academy of Sciences of the United States of America, vol. 107, no. 10, 9 Mar. 2010, pp. 4612–17, doi:10.1073/pnas.0909519107. https://www.pnas.org/doi/10.1073/pnas.0909519107.
2. Kettles, M. A., et al. “Triazine Herbicide Exposure and Breast Cancer Incidence: An Ecologic Study of Kentucky Counties.” Environmental Health Perspectives, vol. 105, no. 11, Nov. 1997, pp. 1222–27, doi:10.1289/ehp.971051222. https://pmc.ncbi.nlm.nih.gov/articles/PMC1470339/.
3. Hunter, L. D., et al. “Atrazine Exposure and Breast Cancer Incidence: An Ecologic Study of Missouri Counties.” Toxicological & Environmental Chemistry, vol. 90, no. 2, 2008, pp. 293–307, doi:10.1080/02772240701529012. https://www.tandfonline.com/doi/abs/10.1080/02772240701529012.
4. Wang, M., et al. “Atrazine Promotes Breast Cancer Development by Suppressing Immune Function and Upregulating MMPs.” Ecotoxicology and Environmental Safety, vol. 253, 15 Mar. 2023, article 114691, doi:10.1016/j.ecoenv.2023.114691. https://www.sciencedirect.com/science/article/pii/S0147651323001951.
5. Wetzel, Lawrence T., et al. “Chronic Effects of Atrazine on Estrus and Mammary Tumor Formation in Female Sprague-Dawley and Fischer 344 Rats.” Journal of Toxicology and Environmental Health, vol. 43, no. 2, 1994, pp. 169–82, doi:10.1080/15287399409531914.
6. Cattley, Russell C., et al. “Carcinogenicity of Atrazine, Alachlor, and Vinclozolin.” The Lancet Oncology, vol. 27, no. 1, Jan. 2026 [online Nov. 2025], pp. 11–12, doi:10.1016/S1470-2045(25)00702-8. https://www.thelancet.com/journals/lanonc/article/PIIS1470-2045(25)00702-8/fulltext.
7. Colborn, Theo, et al. Our Stolen Future: Are We Threatening Our Fertility, Intelligence, and Survival? A Scientific Detective Story. Dutton, 1996.
8. EPA Weakens Safeguards for Weed Killer Atrazine, Linked to Birth Defects The reversal is the Trump administration’s third about-face on a toxic pesticide. By Gosia Wozniacka November 20, 2019 CivilEats

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Published on May 19th, 2026 by Jeffrey Dach MD