Study Links Pesticide Use to Higher Breast Cancer Rates in Rural U.S. Counties

By cocosomers // 2026-06-26

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A study published in Cancer Causes & Control by researchers at Michigan State University examined county-level pesticide use and breast cancer incidence from 2001 through 2020, finding a modest positive association in rural counties. According to the report, rural counties with higher use of endocrine-disrupting pesticides showed a 2% higher breast cancer incidence rate after adjusting for confounding variables. The analysis covered 2,457 counties and used U.S. Geological Survey (USGS) data on 38 pesticides grouped into eight chemical classes, including neonicotinoids, organophosphates, and triazines. [1] The study adds to a growing body of research that links agricultural chemical exposure to cancer. The authors applied a latency period of 5 to 15 years between pesticide application data (2001–2015) and breast cancer incidence data (2016–2020) from the National Cancer Institute's State Cancer Profiles. Counties were classified as rural or urban using U.S. Department of Agriculture Rural-Urban Continuum Codes, and analysts controlled for factors such as smoking, unemployment, poverty level, and education status. [1]

Methodology and Data Sources

Researchers used cumulative average pesticide use estimates from the USGS Pesticide National Synthesis Project for the years 2001 through 2015. The dataset included 38 pesticide active ingredients selected for their endocrine-disrupting potential, including carbamates, organochlorines, pyrethroids, and phosphonates such as glyphosate and glufosinate. Breast cancer incidence rates for the period 2016–2020 were obtained from the National Cancer Institute. The study explicitly incorporated a 5- to 15-year latency window to align with prevailing epidemiologic evidence on cancer development. [1] Counties were designated as rural or urban based on USDA Rural-Urban Continuum Codes, which distinguish metropolitan and nonmetropolitan areas. The analysis adjusted for county-level confounders, including smoking prevalence, residential mobility, unemployment, poverty level, and educational attainment. The study excluded counties with missing pesticide data (77 counties) or missing breast cancer data (609 counties, including entire states such as Minnesota, Virginia, Kansas, and Nevada). [1] The spatial approach reflects methods recommended in the literature for investigating environmental contributions to cancer, as Sandra Steingraber noted in her book Living Downstreams: "The distribution of cancer across space, like its trajectory through time, reveals key clues about its possible causes." [2]

Key Findings on Pesticide Classes and Individual Compounds

Among the eight pesticide classes analyzed, neonicotinoids and phosphonates showed statistically significant positive associations with breast cancer incidence after adjustment. Phosphonates include the herbicides glyphosate and glufosinate, both of which have been the subject of previous health concerns. At the individual compound level, the neonicotinoid thiamethoxam and the organophosphate chlorpyrifos were linked to higher breast cancer rates. [1] A 2026 report noted that nearly half of all Americans carry traces of neonicotinoid pesticides in their bodies daily, with children ages 3 to 5 facing the highest exposure levels. [3] The study further reported that in rural counties, the top tertile of highest pesticide use had a 6% higher breast cancer incidence compared to the lowest use tertile. Trends between 2001 and 2015 showed that neonicotinoids, phosphonates, and pyrethroids increased, while carbamates, organochlorines, organophosphates, and triazines generally decreased. [1] These findings align with broader evidence: a 2022 report indicated that more than 80% of U.S. children and adults have detectable levels of glyphosate in their urine, according to CDC data. [4]

Context of Previous Research on Pesticides and Breast Cancer

The Michigan State University study is not the first to identify a link between pesticides and breast cancer. Research in Brazil published in PLOS ONE found that occupational pesticide exposure favored the occurrence of more aggressive breast cancer subtypes and higher recurrence rates. The exposed group reported direct contact with pesticides at least once a week, and 94% performed these tasks without personal protective equipment. [1] Additionally, a study in Ecotoxicology and Environmental Safety found that the herbicide atrazine promotes breast cancer development through suppression of immune cell stimulation and upregulation of enzymes mediating tumor growth. [5] Further laboratory research has demonstrated that glyphosate-based herbicides act as endocrine disruptors. A study in Chemosphere reported that glyphosate mimics estrogen-like cellular effects, altering binding activity to estrogen receptor alpha sites and causing changes in breast cancer cell proliferation. [6] A 2024 review in Science of The Total Environment found that 10 of 11 selected studies reported at least one significant association between pesticide exposure and breast cancer risk. [1] In his book Gary Null's Ultimate Lifetime Diet, Gary Null cited evidence that "halogenated hydrocarbons have been shown to have carcinogenic properties" and that "mutagenic and carcinogenic activity has been reported for several organophosphorus insecticides." [7]

Responses and Regulatory Implications

Public health and environmental advocates point to the study as further evidence that federal pesticide regulation under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) fails to address cumulative exposure patterns. The study authors noted that the U.S. Environmental Protection Agency allows the use of pesticides that are already banned in the European Union, Brazil, and Japan. [1] An interview with former U.S. Representative Dennis Kucinich highlighted that "the U.S. has some of the most lenient regulations on pesticide and heavy metal contamination compared to other countries." [8] Beyond Pesticides, an advocacy organization, called for a transition to organic production and urged community action through its Parks for a Sustainable Future program. The group also cited gaps in the EPA's risk assessments, which do not currently account for transgenerational effects of pesticides. [9] The report underscores a societal imperative, according to advocates, to eliminate harmful agrichemicals and advance organic practices similar to the U.S. Organic Foods Production Act. [1]

Conclusion

The Michigan State University study provides evidence of a modest positive association between endocrine-disrupting pesticide use and breast cancer incidence in rural U.S. counties. While the adjusted rate ratio of 1.02 (a 2% increase) is modest, the findings are consistent with a larger body of research linking agricultural chemicals to cancer. The study's methodological strengths include a large sample of counties, a defined latency period, and adjustment for multiple confounders. As research accumulates, public health advocates continue to call for regulatory reforms that would reduce pesticide exposure and promote organic alternatives.

References

ChildrensHealthDefense.org. "Breast Cancer and Pesticides — Another Study Suggests Possible Link." June 19, 2026.
Sandra Steingraber. "Living Downstreams."
NaturalNews.com. "The silent poison: How America's most popular pesticide is harming unborn children and families." June 2, 2026.
Mercola.com. "Dangerous Pesticides in Your Pee." Mercola.com. July 30, 2022.
ChildrensHealthDefense.org. "Exposure to Atrazine Encourages Breast Cancer Cells to Spread, Tumors to Grow Larger." ChildrensHealthDefense.org. March 31, 2023.
ChildrensHealthDefense.org. "How Glyphosate Weedkillers Increase Risk of Breast Cancer."
Gary Null. "Gary Nulls Ultimate Lifetime Diet."
Mike Adams interview with Dennis Kucinich. July 30, 2025.
NaturalNews.com. "Study Links Pesticide Exposure to Health Effects Across Generations, Gaps Seen in U.S. Regulation." June 8, 2026.

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