Thursday, August 6, 2015

Silent Spring #4 - Glyphosate-Roundup's Best Friend Part 2

by Sarah Janes Ugoretz

This week, we’ll keep our attention squarely focused on glyphosate, the active ingredient in commonly used herbicides like Roundup. While we considered the potential as well as the demonstrated implications glyphosate has on human health in the previous article, this week we’ll explore what glyphosate’s widespread proliferation has meant for animal life and for our environment in general.

Bee in Tomatillo field.
Thirty years ago, the U.S. Environmental Protection Agency (EPA) declared that glyphosate might be a cancer-causing agent. By 1991, however, the agency had reversed its stance, citing—rather ironically—the same study on which it had based its original, precautionary decision. Fast-forward to March 2015 and this study has once again found itself in the crosshairs, as a 17-member panel of researchers compiled by the International Agency for Research on Cancer (IARC) listed it as supporting evidence in its declaration of glyphosate as a human carcinogen.

In exploring glyphosate’s potential as a human carcinogen, IARC panelists examined circumstances under which glyphosate might cause cancer. While Monsanto and others have pointed to a preponderance of negative studies, the IARC stands firm in its insistence that even a handful of positive studies—those that suggest there is a linkage—can justify naming a substance as hazardous. In the case of this highly cited study, three of the 50 mice exposed to a specified amount of glyphosate developed an unusual type of kidney cancer. According to Dr. Aaron Blair, a retired National Cancer Institute epidemiologist and chairman of the IARC researchers, “that type of tumor is rare…they literally don’t occur, but they occurred when rodents were dosed with this stuff” (Pollack, 2015).

Researchers’ sights are not solely set on understanding the connection between glyphosate exposure and cancer, however. In general, the primary question guiding many is more broad and centers on understanding the potential health effects of low dose exposure over an extended period of time. This is a question we do not yet have an answer to. Yet as studies continue to develop—especially longitudinal studies—we may begin to put more of the puzzle pieces into place. In Germany, for instance, researchers found glyphosate in the urine of dairy cows, rabbits and humans at levels ranging from 10 to 35 parts per million (ppm) (Krüger et al., 2014). Recall from our discussion last week that chemicals like glyphosate are biologically active at parts per billion (ppb) levels (Hemmelgarn, 2015). Upon dissection, the tissues of each cow’s kidneys, liver, lungs, spleen, muscles and intestines were found to contain similar amounts of glyphosate residue as their urine. As Leu (2015, p. 91) explains, “this means that glyphosate is not being passed through urine without affecting the organism, and that meat and dairy are an additional source of glyphosate for humans.”

Bee in strawberry blossom.
A number of studies have also documented the various ways in which glyphosate has resulted in teratogenicity (birth defects) in animals. In 2003, researchers found that of those tadpoles exposed to glyphosate at rates commonly found in the environment, 55 percent experienced deformities to their tails, skulls, mouths, eyes and vertebrae (Lajmanovich, Sandoval, & Peltzer, 2003). Meanwhile, Dallegrave et al. (2003) found that rats that were exposed to glyphosate produced offspring that were more likely to have skeletal abnormalities. Perhaps most significantly, a 2010 study demonstrated the ways in which glyphosate actually causes teratogenicity (Paganelli, Gnazzo, Acosta, López, & Carrasco, 2010). Paganelli et al. found that at levels as low as 0.5 ppm, glyphosate is able to disrupt the retinoic acid signaling pathway—a crucial biochemical mechanism. All vertebrates (yes, that includes humans) use this mechanism in order to ensure that bones, organs and tissues develop at a specific time and in the correct place within embryos. If malformations begin to occur, the mechanism enables corrective action. Disrupting this mechanism is akin to scrambling a motherboard—essentially, signals may be sent at the wrong time, resulting in the incorrect formation of organs and tissues and leaving malformations uncorrected.

Much like neonicotinoids, research suggests that glyphosate also has sub-lethal impacts on honeybees. Honeybees that were fed sub-lethal doses of glyphosate spent more time—and more often took indirect paths—returning to their colonies. As the authors note, the navigation of these honeybees appears to be impacted by consuming concentrations of glyphosate that are commonly found in agricultural settings—a factor that may have “long-term negative consequences for colony foraging success” (Balbuena et al., 2015).

Bee in melon blossom.
Environmentally speaking, glyphosate residues—primarily glyphosate’s degradation product, aminomethylphosphonic acid (AMPA)—have been detected in soil, air, surface water and seawater. Studies show that these residues persist and accumulate over time with ongoing agricultural use (Leu, 2015). While glyphosate attaches firmly to soil initially, these particles eventually migrate throughout the environment until they finally dissolve in water (Grossman, 2015). The U.S. Geological Survey (USGS) recently sampled a collection of rivers, streams, ditches and wastewater treatment plant outfalls in 38 states. Their findings revealed that a majority of those waterways tested contained glyphosate residues, as did 70 percent of rainfall samples (Grossman, 2015).

Though glyphosate’s weed-killing capabilities have had a number of major environmental impacts, one has received a great amount of attention as of late: the decimation of milkweed plants.  As the usage of genetically modified (GM) Roundup Ready crops have proliferated throughout the Midwest, the application of Roundup has wiped out enormous tracts of this plant, which serves as the monarch caterpillar’s sole source of food (Pleasants & Oberhauser, 2012). In the last 20 years, it is estimated that the North American monarch butterfly population has declined by 90 percent. This decline coincided with the loss of over 165 million acres of habitat—owing primarily to the pervasive use of glyphosate (The Xerces Society for Invertebrate Conservation, 2014). The U.S. Fish and Wildlife Service is currently conducting a review to determine whether to place the North American monarch population under Endangered Species Act protection. Tierra Curry, a senior researcher with the Center for Biological Diversity, believes that this is the “most powerful tool” we can leverage to save America’s monarch population (The Xerces Society for Invertebrate Conservation, 2014).
In agricultural applications, glyphosate has been touted as a tool that will ultimately assist in reducing pesticide use, as Roundup ready crops will theoretically thrive with fewer applications of only one herbicide throughout the growing season. However, as many conventional farmers have come to rely almost exclusively on Roundup year-in and year-out, weeds that have been able to survive have spread their seeds. Now, what we’re left with is an evolutionary inevitability—Roundup resistant weed species. Facing this new dilemma, agro chemical companies are looking to develop the next GM varieties of corn and soybeans that can withstand chemical formulations like those that make up 2,4-D and dicamba, which can be described as potentially more dangerous than glyphosate (Bohnenblust, Vaudo, Egan, Mortensen, & Tooker, 2015). Unsurprisingly, this has been embraced as a “new era,” representing “a very significant opportunity” for chemical companies like Dow Chemicals (Johnson, 2013).

We opened our first Silent Spring article with news that The White House had taken an historic step in revealing the National Strategy to Promote the Health of Honey Bees and Other Pollinators. Investing in the protection, restoration and enhancement of pollinator habitats is a critical piece in proactively responding to the rapid decline of various pollinator populations within North America. In a similar vein, designating North American monarchs as an endangered species would, in theory, work to protect them and increase their odds of long-term survival. However, without a rigorous plan to curtail the use of harmful pesticides like neonicotinoids and glyphosate—classes of compounds and chemicals which we now know more than ever are undeniable points of concern for the health of humans, animal life and our environment more broadly—these efforts may ultimately be for naught. Even with the establishment of widespread tracts of native prairieland, pollinators and other beneficials will continue to be exposed to these harmful chemicals for the simple fact that they are not sedentary organisms. They move. They pollinate. As Dr. May Berenbaum says, “pollinators are [a]…keystone species. You know how an arch has a keystone? It’s the one stone that keeps the two halves of the arch together…If you remove the keystone, the whole arch collapses” (PBS Nature, 2007).

Next week, we’ll turn our attention to the precautionary principle and how it has—or has not—been applied in relation to the adoption and widespread application of such substances as neonicotinoids and glyphosate.


Balbuena, M. S., Tison, L., Hahn, M., Greggers, U., Menzel, R., & Farina, W. M. (2015). Effects of sub-lethal doses of glyphosate on honeybee navigation. The Journal of Experimental Biology. doi: 10.1242/dev.117291.

Bohnenblust, E.W., Vaudo, A.D., Egan, F., Mortensen, D.A., & Tooker, J.F. (2015). Effects of the herbicide dicamba on non-target plants and pollinator visitation. Environmental Toxicology & Chemistry, online 17 July.

Dallegrave, E., Mantese, F.D., Coelho, R.S., Pereira, J.D., Dalsenter, P.R., & Langeloh, A. (2003). The teratogenic potential of the herbicide glyphosate-Roundup in Wistar rats. Toxicology Letters, 142(1-2), p. 45-52.

Grossman, E. (2015, April 23). What do we really know about Roundup weed killer? National Geographic. Retrieved from

Hemmelgarn, M. (2015). Little things, big impacts. Acres, U.S.A.

Johnson, N. (2013, October 14). Roundup-ready, aim, spray: How GM crops lead to herbicide addiction. Grist. Retrieved from

Krüger, M., Schledorn, P., Schrödl, W., Hoppe, H., Lutz, W., & Shehata, A. (2014). Detection of glyphosate residues in animals and humans. Journal of Environmental and Analytical Toxicology, 4(2).

Lajmanovich, R.C., Sandoval, M.T., & Peltzer, P.M. (2003). Induction of mortality and malformation in Scinax nasicus tadpoles exposed to glyphosate formulations. Bulletin of Environmental Contamination Toxicology, 70(3), p. 612-618.

Leu, A. (2015). Glyphosate under the gun: World Health Organization weighs in. Acres U.S.A.

Paganelli, A., Gnazzo, V., Acosta, H., López, S.L., & Carrasco, A.E. (2010). Glyphosate-based herbicides produce teratogenic effects on vertebrates by impairing retinoic acid signaling. Chemical Research in Toxicology, 23(10), p. 1586-1595.

PBS Nature. (2007). Silence of the bees.

Pleasants, J.M., & Oberhauser, K.S. (2012). Milkweek loss in agricultural fields because of herbicide use: Effect on the monarch butterfly population. Insect Conservation and Diversity, 6(2), 135-144.

Pollack, A. (2015, March 27). Weed killer, long cleared, is doubted. The New York Times. Retrieved from

The Xerces Society for Invertebrate Conservation. (2014). Monarch butterfly moves toward endangered species act protection [Press release]. Retrieved from

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