by Carey Gillam
Tests by a US government agency on common weedkilling products made with the chemical glyphosate have found some formulations sold to the public to be genotoxic, meaning they are damaging to human DNA.
But the government scientists at the National Toxicology Program (NTP) say the danger probably lies with added ingredients in the products – not glyphosate.
One of the world’s best-known glyphosate-based products is Monsanto’s Roundup weedkiller.
Monsanto’s German owner Bayer AG is currently mired in litigation brought by tens of thousands of cancer patients who claim exposure to Monsanto’s Roundup and other similar glyphosate-based formulated products made by Monsanto caused their cancers.
Three trial juries have agreed with the plaintiffs’ claims that the products cause cancer. Jury selection is under way this week in two new trials, one in California and one in Missouri.
Monsanto, which brought glyphosate-based herbicides to the market in the 1970s and was acquired by German chemicals giant Bayer in 2018, has long asserted its products do not cause cancer.
The NTP, which is a division of the National Institute of Environmental Health Sciences (NIEHS), has been running cell-based tests to evaluate the genotoxic and cell death potential of nine “high-use” agricultural glyphosate-based formulations, four residential-use glyphosate-based formulations and weedkilling chemicals sometimes included in glyphosate-based products. The scientists also have conducted tests on glyphosate by itself, said an NIEHS spokeswoman, Sheena Scruggs.
The results, which are preliminary, showed genotoxic effects with some formulations but not with the pure glyphosate. Glyphosate did not cause cell death, nor DNA changes in the tests run by NTP, she said.
People are rarely exposed to glyphosate by itself. Human exposure to glyphosate usually occurs in the form of glyphosate-based formulations, according to the NTP.
The group of scientists doing the NTP tests found genotoxic effects with glyphosate-based formulations (GBFs) that include chemicals called surfactants, which help absorption of glyphosate into plants, plus the weedkilling chemicals diquat dibromide, mesotrione and metolachlor, which are found in some of the products. The program did not disclose brand names of the products examined.
Scruggs said the scientists have not been able to specifically study the surfactants used in the products because manufacturers do not have to disclose what is considered to be confidential business information. Product labels typically refer to surfactants only as “other ingredients”.
NTP scientists cannot say if the genotoxic effects are due to the other herbicides mixed in with glyphosate or the surfactants.
“These results suggest that while glyphosate alone lacks genotoxic activity, the genotoxicity of GBFs may require further evaluation,” the NTP said in a summary of its work. The NTP plans to publish a paper on the results by mid-year, said Scruggs.
A Bayer spokesman, Chris Loder, said the tests showed the “vast majority” of the results were negative for genotoxicity. Regulatory reviews support such findings, he said.
The NTP tests were launched after the International Agency for Research on Cancer classified glyphosate as a probable human carcinogen.
The US Environmental Protection Agency (EPA) backs the safety of glyphosate but has not required in-depth carcinogenicity testing of the full glyphosate-based formulated product, focusing research requirements on glyphosate alone.
Internal EPA documents from early 2016 show agency officials seeking to understand the makeup of formulations and asking Monsanto to provide copies of studies analyzing the safety of its fully formulated products.
Other internal communications between EPA and Monsanto show that a key ingredient traditionally used in Roundup products for many years was polyethoxylated tallow amine (POEA). In 2016 European regulators banned the use of POEA in glyphosate-based herbicides due to concerns about toxicity.
It is not clear how much Monsanto itself knew about the toxicity of the full formulations it sold from the 1970s until it became a unit of Bayer in 2018. But internal company emails, which emerged through the Roundup litigation, offer a glimpse into the company’s view.
In one 2003 internal company email, a Monsanto scientist stated: “You cannot say that Roundup is not a carcinogen … we have not done the necessary testing on the formulation to make that statement. The testing on the formulations are not anywhere near the level of the active ingredient.”
Another internal email, written in 2010, said: “With regards to the carcinogenicity of our formulations we don’t have such testing on them directly.” And an internal Monsanto email from 2002 stated: “Glyphosate is OK but the formulated product … does the damage.”