It’s been a tough time for the world’s most popular herbicide.
Two weeks ago, the World Health Organization’s cancer research arm designated glyphosate as a "probable" carcinogen. It was immediately labeled a clear danger by opponents of large-scale industrial agriculture, and concurrently brushed off by Monsanto Co. and technology-focused scientific organizations.
Glyphosate is better known by its Monsanto-given name, Roundup. It was registered for use in 1974 and is today used on more than 700 different crops. Today, it is an accessible herbicide worldwide that is widely considered to be less toxic than many alternatives.
Criticisms have dogged glyphosate for a while. Its use goes hand in hand with first-generation genetically engineered Roundup Ready crops — whose DNA has been altered to withstand applications of the herbicide — which are viewed with skepticism from the general public.
Spraying the herbicide kills milkweed, a critical plant for the survival of the imperiled monarch butterfly. Consistent use by farmers has also facilitated the evolution of herbicide-resistant weeds, a headache for growers who have relied on Roundup for decades. And glyphosate is also a key ingredient in Enlist Duo, a recently approved herbicide in 15 states whose registration sparked a lawsuit from the Natural Resources Defense Council.
All these are factors as U.S. EPA gets set to review the chemical this year as part of its periodic review process for pesticides, starting with an update of the human health and ecological risk assessments. Environmental groups hope the cancer link will serve as a catalyst to restrict the pesticide.
"We want them to go back in light of this, to no longer put glyphosate aside," said Mary Ellen Kustin
, a legislative and policy analyst with the Environmental Working Group who co-signed a letter asking EPA to weigh the WHO International Agency for Research on Cancer’s (IARC) finding in its review. The groups have also expressed concern that 2,4-D could be linked to non-Hodgkin’s lymphoma and that the combination with glyphosate could amplify the risk to applicators.
Monsanto has pushed back on the credibility of the report, saying that findings published in the journal Lancet Oncology mischaracterized the scientific literature and linked the herbicide primarily to non-Hodgkin’s lymphoma, a cancer of the lymph nodes, in a "bucket diagnosis that is no longer used in pathology," according to one researcher (E&ENews PM, March 24). This is because many factors can increase one’s chance of developing the disease, from age to taking medications that suppress the immune system.
Still, even those skeptical of the cancer announcement don’t deny its hit to glyphosate.
"It’s nontrivial that it’s IARC," said James Aidala, a senior government consultant with Bergeson & Campbell PC and former assistant administrator for EPA’s chemical safety office under President Clinton. EPA is "going to have to respond to this question of whether the occupational exposure is what they thought it was beforehand. … They really have to scientifically look at the question."
Glyphosate has long been considered less toxic than other widely used herbicides. It blocks a plant’s ability to create the necessary proteins for growth and breaks down easily in the soil, reducing the risk of a presence in nearby water bodies.
Aidala remembers being impressed with the low toxicity profile in his time at EPA.
"Unless you’re green it’s not going to hurt you," Aidala said. "That’s why it was like, ‘Whoa, this is pretty cool.’"
IARC’s designation of a "probable" carcinogen can be a difficult concept to grasp for the general public.
On a scale from 1 to 4, where 1 means there is sufficient evidence in humans to link something as a carcinogenic risk factor, glyphosate was put at 2A. This means there is "limited evidence of carcinogenicity in humans" and "sufficient evidence" in laboratory animals, based on two statistical tests.
Other items in the 2A group include a compound that forms in fried foods, roofing tar and the occupational risks that come with working as a barber or hairstylist. Items in the 1 category include well-documented risks like smoking, but also drinking alcohol, taking hormone pills and breathing particulate matter in outdoor air.
The IARC study relies on three "case control" studies, which compare one group of people with cancer (in this case, non-Hodgkin’s lymphoma) with a similar demographic without cancer and compare risk factors between the two groups, Andrew Kniss, associate professor in weed biology at the University of Wyoming, explained in a blog post. Kniss wrote the blog as someone who works regularly with herbicides. He did not respond to a request for an interview.
The most common confounding variable, Kniss said, was exposure to other pesticides. This is an important point, given that farmers and pesticide applicators who use glyphosate typically also employ other chemicals that a non-farming population can avoid.
"[We] probably also inhale more dust and fertilizers. We are out in the sun a lot. We probably also get exposed to more hydraulic fluid and wake up earlier than the general population. These things are extremely difficult to control for in a case control study," Kniss wrote. "There is nothing here that I think can tarnish glyphosate’s reputation as a very safe pesticide. But that doesn’t mean that we should throw caution to the wind and douse ourselves in it."
In a statement, EPA said it would update the existing human health and ecological risk assessments "based on the best available scientific data."
"We will determine whether any risk mitigation is needed to ensure that glyphosate can continue to be used without unreasonable risks to people or the environment, including species like the monarch butterfly," EPA said. "If at any time EPA discovers that the use of a registered pesticide may result in unreasonable adverse effects on people or the environment, we will take action to remove it from the marketplace or limit its use."
There’s also a possibility that restrictions could be placed if the Fish and Wildlife Service decides to list the monarch butterfly under the Endangered Species Act. However, FWS is not set to make a decision on listing the butterfly for at least another year.
In terms of business, glyphosate use won’t be slowing down.
The rise in popularity of no-till farming is boosting demand for genetically engineered Roundup Ready crops, which when used in concert with glyphosate lower the need to dig out weeds in fields.
Although regulations are expected to shift, primarily in Europe, to avoid glyphosate-resistant weeds, the largest manufacturers are adapting by pushing integrated weed management systems that avoid using any one herbicide exclusively.
Rising demand for Roundup Ready crops in the United States, Brazil, Argentina, South Africa, India and China will bolster demand for glyphosate, according to a February report from Albany, N.Y.-based Transparency Market Research.
The Asia-Pacific region’s demand alone is expected to grow at a compound annual growth rate of 7 percent between now and 2019.