A Michigan State University analysis of more than 2,400 U.S. counties found a modest association between endocrine-disrupting pesticide use and higher breast cancer incidence in rural areas.
By yourNEWS Media Newsroom
Rural U.S. counties with heavier use of certain endocrine-disrupting pesticides had higher breast cancer incidence rates than counties with lower use, according to a Michigan State University study published in Cancer Causes & Control.
The study examined county-level pesticide use from 2001 through 2015 and breast cancer incidence from 2016 through 2020, applying a 5- to 15-year latency period between chemical application and cancer diagnosis. Researchers found that rural counties with higher use of endocrine-disrupting pesticides had a 2% higher breast cancer incidence rate after adjustment for other factors.
The analysis covered 2,457 counties and used pesticide data from the U.S. Geological Survey Pesticide National Synthesis Project. Researchers examined 38 pesticide active ingredients grouped into eight chemical classes, including neonicotinoids, organophosphates, triazines, carbamates, organochlorines, pyrethroids and phosphonates such as glyphosate and glufosinate.
Breast cancer incidence rates came 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, which separate metropolitan and nonmetropolitan areas.
The researchers adjusted for county-level factors that could affect cancer rates, including smoking prevalence, residential mobility, unemployment, poverty and education levels. The study excluded 77 counties missing pesticide data and 609 counties missing breast cancer data, including entire states such as Minnesota, Virginia, Kansas and Nevada.
The spatial approach reflects a broader method used in environmental cancer research. In “Living Downstreams,” Sandra Steingraber wrote, “The distribution of cancer across space, like its trajectory through time, reveals key clues about its possible causes.”
The Michigan State researchers found statistically significant positive associations between breast cancer incidence and two pesticide classes after adjustment: neonicotinoids and phosphonates. Phosphonates include glyphosate and glufosinate, herbicides that have previously drawn health scrutiny.
At the individual chemical level, the study linked higher breast cancer rates to thiamethoxam, a neonicotinoid, and chlorpyrifos, an organophosphate.
The researchers also found that rural counties in the highest pesticide-use tertile had a 6% higher breast cancer incidence rate than counties in the lowest tertile. From 2001 to 2015, use of neonicotinoids, phosphonates and pyrethroids increased, while carbamates, organochlorines, organophosphates and triazines generally declined.
The findings add to previous research examining agricultural chemical exposure and breast cancer risk. A 2026 report noted that nearly half of Americans carry traces of neonicotinoid pesticides in their bodies daily, with children ages 3 to 5 facing the highest exposure levels. A 2022 report, citing CDC data, found that more than 80% of U.S. children and adults had detectable glyphosate levels in their urine.
Previous studies have also examined breast cancer outcomes among people with occupational pesticide exposure. Research in Brazil published in PLOS ONE found that pesticide exposure favored more aggressive breast cancer subtypes and higher recurrence rates. In that study, exposed participants reported direct contact with pesticides at least once a week, and 94% performed those tasks without personal protective equipment.
Other research has focused on specific pesticides. A study in Ecotoxicology and Environmental Safety found that atrazine promoted breast cancer development by suppressing immune cell stimulation and increasing enzymes involved in tumor growth. Laboratory research published in Chemosphere reported that glyphosate-based herbicides acted as endocrine disruptors by mimicking estrogen-like cellular effects, altering binding activity at estrogen receptor alpha sites and changing breast cancer cell proliferation.
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.
In “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.”
The Michigan State study’s findings have prompted renewed attention from public health and environmental advocates who argue that federal pesticide regulation does not fully address cumulative exposure. The study authors noted that the U.S. Environmental Protection Agency permits use of some pesticides that have been banned in the European Union, Brazil and Japan.
An interview with former U.S. Rep. Dennis Kucinich also highlighted concerns over regulation, stating that “the U.S. has some of the most lenient regulations on pesticide and heavy metal contamination compared to other countries.”
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 what it described as gaps in EPA risk assessments, including a lack of accounting for transgenerational pesticide effects.
Advocates said the research supports efforts to reduce harmful agrichemical exposure and expand organic practices modeled on the U.S. Organic Foods Production Act.
The Michigan State findings do not prove that pesticides caused breast cancer in the counties studied. The authors described the association as modest, and the adjusted rate ratio of 1.02 represents a 2% increase. Still, the study’s large county sample, latency window and adjustment for multiple confounders add weight to broader research connecting agricultural chemical exposure with cancer risk.
As additional studies examine pesticide exposure, endocrine disruption and cancer outcomes, public health advocates are expected to continue pressing for tighter regulation and greater use of organic alternatives. The Michigan State study adds county-level evidence that pesticide use patterns may be an important factor in understanding breast cancer incidence in rural communities.
Source: Natural News
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