https://ntp.niehs.nih.gov/go/glyphosate

Glyphosate & Glyphosate Formulations

Findings: Evaluation of the herbicide glyphosate, (aminomethyl)phosphonic acid, and glyphosate-based formulations for genotoxic activity using in vitro assays. Environmental Molecular Mutagenesis. March 7, 2023 and Data Tables are now available.
Tractor going across crops

Research Overview

Status: Ongoing
Substances: Glyphosate
Nominated: June 2016

Background Information

Glyphosate, a chemical that controls weeds and grasses, is the most widely used herbicide worldwide. The major reason glyphosate is used so broadly is because many crops have been genetically engineered to be resistant to glyphosate, allowing it to target weeds while leaving resistant crops unaffected. When applied as a mixture with other substances, plants can more readily absorb glyphosate, making it more effective. People can be exposed to glyphosate when they use glyphosate-based formulations (GBFs) on their lawns, gardens, or for landscaping around their homes. It can get on a person’s skin, get in the eyes, or be brought into the body by breathing it in when using it. Residual amounts of glyphosate can also get into a person’s body by ingestion of food or water. Individuals who regularly handle glyphosate products as part of their occupation have higher exposures.

Glyphosate was first nominated to the NTP for testing in 1981, before the development of glyphosate-resistant crops. NTP conducted a series of short-term studies including 13-week toxicity studies of glyphosate in feed, which were published in 1992. At that time, few toxicological effects were observed and there was no evidence of genetic toxicity for endpoints of chromosomal damage (in vivo) or gene mutations (bacterial reverse mutation assay, a.k.a. Ames assay).

In March 2015, the International Agency for Research on Cancer (IARC ) classified glyphosate as "probably carcinogenic to humans" (Group 2A). This was based on "limited" evidence of cancer in humans from epidemiological studies of exposures to GBFs, and "sufficient" evidence of cancer in experimental animals from studies of "pure" glyphosate. IARC also concluded that there was "strong" evidence for genotoxicity, a determination that was based on studies of both glyphosate and GBFs. Additionally, IARC concluded that there was "moderate" evidence for the genotoxicity of (aminomethyl)phosphonic acid (AMPA), a microbial metabolite of glyphosate. Some studies, which are publicly available, suggest that the human intestinal microbiome metabolizes glyphosate to AMPA. The IARC listing was one of the reasons NTP considered conducting further testing in 2016.
Back to Top

NTP Studies & Findings

Human exposure to glyphosate usually occurs in the form of glyphosate-based formulations (GBFs). Few studies have made side-by-side comparisons of the toxicity of glyphosate and GBFs using the same experimental methods. NTP compared the toxicity of both glyphosate and glyphosate formulations, using the same methods. Specifically, NTP study goals were to:

  • Evaluate whether glyphosate causes genotoxicity, or damage to DNA, using the bacterial reverse gene mutation assay (a.k.a. Ames assay), an in vitro micronucleus assay to detect chromosomal damage, and a multiplexed DNA damage assay that distinguishes whether chromosomal damage is due to chromosome breaks or changes in chromosome number. These studies were conducted using human TK6 cells, a cell line that is recommended by the Organization for Economic Cooperation and Development (OECD) for in vitro genetic toxicity assays.
  • Evaluate whether glyphosate induces oxidative damage, the harm that cells and tissues experience when overwhelmed with production of free radicals that can damage protein and DNA. These studies were conducted using several high-throughput screening assays with human liver cells and human skin cells.

The genetic toxicity studies and the high-throughput screening studies compare the effects of glyphosate versus glyphosate-based formulations (GBFs) on measures of genotoxicity, oxidative stress, and cell viability.

What did the studies find?

Glyphosate and (aminomethyl)phosphonic acid (AMPA), a microbial metabolite of glyphosate, did not cause permanent changes to DNA, such as gene mutations or chromosomal damage. These kinds of changes to DNA are often associated with increased risk for cancer.

The highest concentration of glyphosate used in NTP’s human cell culture studies was comparable to an adult man drinking about 16 ounces of a representative glyphosate-based formulation that contains 41% glyphosate.

In NTP’s studies, some glyphosate-based formulations caused DNA damage. Because glyphosate itself did not cause DNA damage in the tests that were used, the DNA damage likely was caused by other components of the formulations. Herbicide product labels list active ingredients, like glyphosate, but other components of formulations are considered "inert" for regulatory purposes and are not reported due to confidential business information (CBI) protection for companies that manufacture herbicides.

Overall, the findings from our genetic toxicity experiments indicate that it is unlikely that glyphosate could cause cancer through a genotoxic mechanism that permanently damages DNA. Our findings do not rule out that exposure to glyphosate might cause cancer through other mechanisms. The results of the high-throughput screening study, which focused on whether glyphosate and GBFs cause oxidative stress, will be submitted for publication consideration later in 2023.

The new findings are similar to results reported in previous NTP studies. Studies conducted by the NTP in 1992 reported that rodents exposed to high levels of glyphosate in feed showed little evidence of toxicity, and there was no evidence of glyphosate causing chromosomal damage to DNA. For these reasons, NTP did not consider conducting a 2-year rodent cancer bioassay of glyphosate.

See the table below for the most up-to-date information on the variety of projects taking place at NTP.

Study Description Status Findings  & Supporting Files

In Vitro Screening Tests

 Human cell-based tests to study DNA damage, oxidative stress, and cell viability Ongoing Supporting files
Genetic Toxicity Testing Human cell-based studies to determine the potential of glyphosate to cause DNA damage (genotoxicity) Completed Supporting files
Back to Top

Research at Other Agencies

United States
International
Back to Top

Informational Resources

The informational resources below provide additional details on NTP's research on glyphosate and glyphosate formulations.

FAQs

Q: Why does NTP care about studying glyphosate?
A: In 1992, NTP reported that rodents exposed to glyphosate in feed showed little evidence of toxicity, and there was no evidence of glyphosate causing damage to DNA. Since then, several public health agencies have reviewed the scientific literature to learn whether exposure to glyphosate is a cancer hazard for humans.

Due to different interpretations of the potential health risks of glyphosate exposure, major public concern about exposure risks, and reported differences in the toxicity of different glyphosate products, NTP has completed additional research on glyphosate and glyphosate-based formulations (GBFs), including testing the potential genetic and mechanistic toxicity.

Q: When will the data become available?
A: NTP has made the data from its genetic toxicity tests available in the Chemical Effects and Biological Systems database. NTP anticipates releasing the high-throughput screening studies, which include the oxidative stress data, later in 2023.

Q: What types of things is NTP testing that are related to glyphosate?
A: NTP is testing glyphosate and several GBFs used for either agricultural or residential purposes. GBFs were selected to span a range of glyphosate concentrations. NTP is also testing (aminomethyl)phosphonic acid (AMPA), a metabolite of glyphosate that is produced by microbes, including the mammalian microbiome.

Substances were tested in the following cell-based genotoxicity assays, in the presence or absence of an exogenous rat liver metabolic activation system:

  • Bacterial mutagenicity assays with S. typhimurium tester strains TA100, TA98, TA97a, TA1535, and E. coli tester strain WP2 to assess gene mutations
  • Micronucleus assay (human TK6 cells) to assess chromosomal damage
  • MultiFlow DNA Damage Assay (human TK6 cells) to identify the mechanism of action for induction of chromosomal damage (chromosome breaks versus chromosome loss)
Presentations
Supporting Documents
Back to Top

Stay Informed & Contact Us

Laptop on wooden desk with email screen

Stay Informed

Subscribe to receive email to stay informed about glyphosate research and other NTP information.

Contact Us

For questions or additional information, email us or use our contact form.

Back to Top