With novel methods to provide a big-picture view of the overlap between high pesticide use and cancer incidence across the U.S., a new study has again linked pesticide exposure to a range of cancers.
The study by Jacob Gerken, D.O., and colleagues titled “Comprehensive assessment of pesticide use patterns and increased cancer risk,” published in Frontiers in Cancer Control and Society, examines the association between high-pesticide use and cancer diagnoses along with smoking incidence data and the Social Vulnerability Index, a measure used by the Centers for Disease Control and Prevention (CDC) that includes variables such as poverty, poor housing and exposures to natural disasters and chemical spills.
The researchers consider 69 pesticides used in agriculture that are monitored by the U.S. Department of Agriculture. They use U.S. Geological Survey data to map areas of similar crops and pesticide use patterns and incorporate public health data from the CDC to develop their final picture.
In terms of threats to health, cancer remains top of mind for most people. Globally, about 10 million people die of cancer each year.
And while treatments for cancer and survival times have burgeoned over the years, many cancers — particularly colorectal and breast cancer — are on the increase, and the increase is most dramatic among people between 55 and 64. At the same time, the evidence of pesticides’ role in cancer incidence is also increasing.
Pesticides have been linked to numerous diseases, including Parkinson’s, dementia, allergies and diabetes, as well as many cancers. But the science behind pesticide-cancer associations is contested turf, with much resistance being mounted by the pesticide industry and skepticism being expressed by regulatory scientists.
For example, in 2022 Beyond Pesticides discussed evidence that the U.S. Environmental Protection Agency (EPA) colluded with Monsanto in 2017 to downplay the carcinogenic effects of glyphosate, even after the International Agency for Research on Cancer had made the connection in 2015.
An important assumption of the study, the authors write, is that “more pesticide use leads to higher cancer incidence” because “no evidence has ever been reported of pesticides reducing cancer rates.”
However, as is standard in epidemiological research, they stop short of drawing direct causal connections between pesticides and cancer because the study is population-based and does not reach the level of individuals.
Yet they do find associations between “pesticide use and increased incidence of leukemia; non-Hodgkin lymphoma; bladder, colon, lung, and pancreatic cancer; and all cancers combined that are comparable to smoking for some cancer types.”
Different pesticides correlate with added risks for different cancers, but overall there is strong evidence that most pesticides add risks for multiple cancer types as well as particular cancers. That is, it is not a one-pesticide, one-cancer association.
For example, atrazine adds risk for all cancers and colon cancers; dicamba is consistently at the top of the list in regions where there is a high risk of colon cancer and pancreatic cancer; and glyphosate is at the top in areas with a high risk of all cancers, colon cancer and pancreatic cancer.
Because the study also accounts for social vulnerability factors and smoking, it measures these against cancer types, overall cancer incidence and pesticide use patterns.
The researchers find that for some cancers, smoking is clearly the biggest risk factor, but pesticides are far more influential than social vulnerabilities or population size for individual cancer types.
For non-Hodgkin lymphoma, bladder cancer and leukemia, pesticides actually outpace smoking. For pancreatic cancer, smoking is the highest risk factor by orders of magnitude compared to other variables.
The current study contrasts with a 2018 analysis of glyphosate and cancer based on the Agricultural Health Study of 89,000 farmers and their spouses, which found no increased risk between glyphosate and lymph system cancers.
However, Gerken and colleagues point out that the Agricultural Health Study study population focused only on a subset of the whole communities that are embedded in agricultural areas, and observed that the whole population — not just farmers — is repeatedly exposed to multiple pesticides and frequent spray drift events.
The Agricultural Health Study is an ongoing program of the National Institutes of Health and the National Institute of Environmental Health Sciences.
Gerkin and colleagues assert that “organic farms that do not use pesticides often have 15%-50% lower yields compared to conventional farms.” This is somewhat misleading, as Beyond Pesticides has been established numerous times, and depends heavily on how the effects of pesticides are measured.
For example, Beyond Pesticides has covered how plant diversity in fields fosters productivity, and how pesticides’ harms to pollinators reduce productivity.
However, the study authors conclude that the highest cancer risk is associated with regions of the country with the highest pesticide use, making it clear that any increased productivity based on pesticides comes at an unacceptable price.
According to the 2023 review by New York University professor Leo Trasande, M.D., and colleagues titled “Exposures to pesticides and risk of cancer: Evaluation of recent epidemiological evidence in humans and paths forward”:
“Most evidence suggesting pesticide carcinogenicity — in the [2017] International Agency for Research on Cancer (IARC) report [reviewing tetrachlorvinphos, parathion, malathion, diazinon and glyphosate] and elsewhere — has come from animal and mechanistic studies, as the epidemiology literature was insufficient to draw conclusions.
“Epidemiologic evidence has since increased in both quantity and quality, and now covers many other pesticides that were not included in IARC’s review, or in those of other national and international agencies.”
Trasande and colleagues conclude that “there is sufficient evidence for action to regulate pesticides based on their carcinogenicity.”
Regarding glyphosate, they also point out that regulators have mostly focused on the technical compound and ignored the more complex glyphosate-based formulations, for which the evidence of carcinogenicity is stronger than for technical glyphosate.
And while the 2015 IARC report considered only peer-reviewed literature, the EPA and the European Food Safety Assessment included “industry studies conducted by private companies that register the chemicals in question.”
This question of regulatory capture by industry affects every aspect of pesticide policy. Trasande and colleagues noted that “calls have been made within the scientific community for more independently conducted epidemiological research.”
There has been little success so far. A typical example of the pesticide industry’s influence on the scientific literature is a 2021 paper, “Cancer and occupational exposure to pesticides: an umbrella review,” by Carol J. Burns, Ph.D., and Daland R. Juberg, Ph.D.
The authors found that “there was neither strong nor consistent epidemiologic data supportive of a positive association between pesticide exposure in occupational settings and cancer.” Burns’ affiliation is listed as “Sanford, USA,” while Juberg’s is “Indianapolis, USA.”
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These are completely inadequate identifications and are clearly an attempt to hide their industry connections. Further investigation reveals that Burns worked for the Dow Chemical Company for 21 years, while Juberg worked for the Dow Chemical Company for 15 years and is now retired from Corteva Agriscience.
Both are ostensibly independent consultants. Corteva is a spinoff from DowDupont. The study was funded by CropLife International. Studies have shown that there is a strong association between the conclusions of studies and review papers and their funding sources.
The current study by Gerken and colleagues is a significant addition to the epidemiologic literature on cancer and pesticides.
It is, the authors assert, “the first comprehensive evaluation of cancer risk from a population-based perspective at the national level.”
By accounting for possible confounders such as smoking, poverty and exposure to disasters, the authors have clarified that there is an undeniable link between pesticide exposure and cancer incidence.
The mechanism of carcinogenesis is not yet exactly clear for individual cancers, although it is obvious that smoking and pesticide exposure provide a lethal double dose of risk. This likely affects most of the very groups that do the bulk of agricultural work, have little job security, no health insurance and few other resources.
The authors point out one step that could help get the point across to farmers, government officials, healthcare professionals and the pesticide industry:
“If, when buying a new property, purchasers were notified that the land is in proximity to particularly elevated levels of pesticides or the use of certain pesticides that may be especially harmful, then public awareness of this issue would rise, garnering the attention that this issue calls for.
“The safety of these chemicals needs to be approached with more skepticism. Healthcare officials in these regions should exercise a level of skepticism of the safety of the chemicals used.”
Originally published by Beyond Pesticides.
