21
May
Study Finds an Association between Dicamba Use and Increased Risk of Developing Various Cancers
(Beyond Pesticides, May 21, 2020) Use of the herbicide dicamba increases humans’ risk of various acute and chronic cancers, according to research published in the International Journal of Epidemiology by the National Institutes of Health (NIH). Many pesticides are “known or probable” carcinogens (cancer-causing agents), and their widespread use only amplifies chemical hazards, adversely affecting human health. However, past research lacks comprehensive information regarding human health effects associated with long-term pesticide use. This study highlights the significant role that long-term research plays in identifying potential health concerns surrounding registered pesticides, especially as the Environmental Protection Agency (EPA) plans to reaffirm its decision to allow dicamba use on genetically engineered (GE) crops. Nathan Donley, Ph.D., a scientist with the environmental health program at the Center for Biological Diversity, comments: “This sweeping study exposes the terrible human cost of the EPA’s reckless decision to expand the use of dicamba. […]For the EPA to approve widespread use of this poison across much of the country without assuring its safety to people and the environment is an absolute indictment of the agency’s persistent practice of rubber-stamping dangerous pesticides.”
Dicamba—a benzoic acid chemical that controls broadleaf weeds—is one of the most widely applied herbicides in corn production. As a result of weed resistant to weed killers, farmers rely on increased, more frequent applications of dicamba as a control measure. However, with this increase in the chemical’s use, there is growing concern surrounding the dicamba’s potential human health effects.
In this research, NIH researchers analyzed data from an Agricultural Health Study (AHS) involving 49,922 Iowan and North Carolinian pesticide applicators. Applicators reported dicamba use during two enrollment periods: (1993-1997) and (1999-2005). Researchers calculated dicamba exposure using intensity-weighted lifetime-days, cumulative measurements of specific pesticide use, and various incident cancer diagnoses and adjusted for exposure lags of up to 20 years. To assess relative risks (RR) with a 95% confidence interval associated with cancer diagnoses from the initial enrollment periods to 2014/2015, NIH researchers used a multivariable Poisson regression model.
Over half (52.9%) of all pesticide applicators in the study use dicamba. Participants reporting dicamba use are at elevated risk of developing liver and intrahepatic bile duct cancer, and chronic lymphocytic leukemia at the highest exposure level. Additionally, dicamba exposure risks are associated with liver cancer and acute myeloid leukemia linger, as much as 20-years after chemical exposure.
Commercial dicamba use is widespread throughout the U.S., with research findings linking the chemical to neurotoxicity, kidney/liver damage, sensitization/irritation, birth/developmental defects, reproductive damage, and respiratory illnesses. The AHS analysis also associates dicamba use with colon and lung cancer. In addition to human health effects, studies find that dicamba adversely impacts ecological health, causing harm to birds; insects; fish; aquatic organisms; non-target plants; and pollinators, like beetles. Not only do laboratory studies indicate that dicamba alters animal liver function to promote tumor growth and cancer, but they also find that it induces oxidative stress and DNA mutations—all of which are conduits acknowledged to cause cancer. Lastly, extensive dicamba use can induce antibiotic resistance in human pathogens like Escherichia coli and Salmonella eterica. Despite dicamba’s various adverse health associations, it remains available for commercial use in agricultural and non-agricultural settings alike.
Traditionally, dicamba applications are preemergent (applied to the soil before seed planting), but with Monsanto’s 2016 release of dicamba-resistant GE seeds, farmers are spraying dicamba directly on to crops. However, direct spray application increases the risk of dicamba exposure as the chemical is highly volatile, consequently becoming airborne and drifting. Dicamba drift causes significant crop damage and many states, including Arkansas and Missouri, have adopted bans and restrictions of its use. Missouri peach farmer, Bill Bader, suffered huge financial losses after 30,000 peach trees perished due to dicamba drift onto his orchid from adjacent agricultural properties. In 2017, dicamba drift from Arkansas soybean crops led to a fatal shooting after the chemical caused damage to non-target crops nearby. Although hot weather increases dicamba volatility and thus pesticide drift, the strongest drift occurs when growers combine dicamba with pesticides like glyphosate or 2,4-dichlorophenoxyacetic acid (2, 4-D). Dr. Donley concludes, “Just as with glyphosate, we were falsely told that dicamba was completely safe for humans, and there was nothing to worry about.[…] With dicamba’s ability to drift for miles, people in many areas of the country are now routinely forced to breathe in this dangerous pesticide.”
Combining pesticides can have a synergetic impact on human health as the aggregate risks associated with joint pesticide use causes greater damage than individual pesticide use. Dicamba and 2,4-D are the most commonly global agricultural herbicides, both individually and as a mixture. A 2002 study found that women exposed to a mixture of 2,4-D, mecoprop, and dicamba had higher instances of abortion and fetal resorption, at low doses. Argentinian researchers find that both dicamba and 2,4-D induce aquatic organism (fish) toxicity, regardless of concentration, through synergy via the presence of each chemical counterpart in the mixture.
To date, this NIH research is the most comprehensive epidemiological study on dicamba’s association with cancer. However, EPA is set to re-approve dicamba use on genetically engineered cotton and soybeans by the end of the year, since the agency designates the herbicide as “not likely to be carcinogenic to humans.” Due to this designation, EPA allows the expanded use of dicamba without evaluating the cancer risk that dicamba poses. Additionally, EPA approved an expansion of dicamba use in 2018, despite the 5 million acres of crop damage it caused between 2016-2017.
As has been previously stated: “[Beyond Pesticides] has long been critical of EPA’s risk assessment process, which fails to look at chemical mixtures and synergistic effects (or inert ingredients) in common pesticide products, as well as certain health endpoints (such as endocrine disruption), disproportionate effects to vulnerable population groups, and regular noncompliance with product label directions. These deficiencies contribute to its severe limitations in defining real-world poisoning, as captured by epidemiologic studies in Beyond Pesticides’ Pesticide-Induced Diseases Database.”
The adverse health effects of dicamba, drift and resulting exposure, and the aggregate risk of the pesticide being mixed with glyphosate showcases the need for more rigorous pesticide regulation. Revaluation of current policies that ignore the need to evaluate pesticide mixtures can ensure a reduction in pesticide harms, cleaner air, and crop loss. Beyond Pesticides encourages farmers to adopt regenerative organic practices. These practices aim to end the cycle of pesticide resistance, eliminating the need for pesticides—and pesticide mixtures—and the hazards caused by drift. Those impacted by pesticide drift can refer to Beyond Pesticides’ webpage on What to Do in a Pesticide Emergency and contact the organization for additional information.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source: Center for Biological Diversity, International Journal of Epidemiology
