The connection between cancer and glyphosate, the active ingredient in Bayer/Monsanto’s Roundup herbicide, has been headline news over the past months.
Juries have awarded multi-million-dollar awards to plaintiffs who claim that their use of the herbicide was at least partially responsible for their development of non-Hodgkin’s lymphoma. A recently published study from University of Washington backs this claim; the researchers found that glyphosate increases the risk of non-Hodgkin’s lymphoma by 41%.1 Increased cancer risk is not the only—or possibly even the most significant—negative effect from glyphosate and other herbicides used in agriculture.
A 2015 study by Brigitta Kurenbach and colleagues found that glyphosate and other herbicides (dicamba and 2,4-D) are contributing to antibiotic resistance in pathogens. In a laboratory, they exposed colonies of Escherichia coli and Salmonella enterica serova Typhimurium to one of these three common herbicides or to combinations of the herbicides. They then measured the bacterial response to five different types of antibiotics: ampicillin, ciprofloxacin, chloramphenicol, kanamycin, and tetracycline. Roundup increased E. coli‘s and salmonella’s tolerance to kanamycin and ciprofloxacin and had no effect or increased susceptibility to ampicillin, chloramphenicol, and tetracycline. The salmonella bacterium become more resistant to ampicillin, ciprofloxacin, chloramphenicol, and tetracycline but more susceptible to kanamycin after being exposed to non-lethal doses of 2,4-D or dicamba. E. coli had a similar response to dicamba and 2,4-D except it did not show more tolerance to ampicillin. The amount needed to cause a detectable change was lower than the label-specified herbicide application rate.
Increased resistance means higher doses of antibiotics are needed.
Kurenback et al cite a 2013 study in which a majority of hospitalized patients did not get high enough doses to affect cipro-susceptible strains of E. coli, Klebsiella spp., Enterobacteriaceae, Proteus spp., and Pseudomonas aeruginosa. Kurenbach and colleagues state: “This increasingly chemically potent world necessitates a rethinking of how we measure and regulate exposures to common products. Testing each compound in isolation and only for severe effects on microbes, as is done during risk evaluation of herbicides, may underestimate its role in the emergence of antibiotic resistance phenotypes.”
The widespread use of antibiotics in livestock animals has been pointed to as one reason that bacteria are becoming increasingly antibiotic resistant. But herbicides may be another, possibly even more important, factor. Soybeans that are genetically engineered to withstand dicamba and 2,4-D are now being grown in the US.2 What effects might these herbicides be having on the microbiota (pathogenic and beneficial) in our gastrointestinal tract?
- Holtz J. UW Study: Exposure to chemical in Roundup Increases Risk for Cancer. February 13, 2019. https://www.washington.edu/news/2019/02/13/uw-study-exposure-to-chemical-in-roundup-increases-risk-for-cancer/
- Hettinger J. Volatile pesticide to be sprayed on soybeans and cotton. March 26, 2019. https://investigatemidwest.org/2019/03/26/last-year-it-was-dicamba-this-year-its-24-d/
For more, see J. Klotter, Shorts: Herbicides and Antibiotic Resistance. Townsend Letter. July 2018:21-22.
