Glyphosate is a chemical compound used as the active ingredient in the world’s most widely applied herbicide. You’ve likely encountered it under the brand name Roundup, though it’s sold under dozens of other names as well. It works by blocking a specific biological pathway that plants need to survive, making it effective at killing weeds in agricultural fields, residential lawns, and public spaces. Glyphosate has also become one of the most debated chemicals in modern agriculture, with major regulatory agencies disagreeing about whether it poses a cancer risk to humans.
How Glyphosate Kills Plants
Glyphosate targets an enzyme that plants, fungi, and bacteria rely on to produce three essential amino acids: tyrosine, phenylalanine, and tryptophan. These amino acids are building blocks for proteins, and without them, the organism can’t grow or survive. The enzyme sits within a metabolic process called the shikimate pathway, which exists in plants and microorganisms but not in mammals, birds, or fish. This is the core reason glyphosate was long considered safe for humans: it disrupts a biological system that human cells simply don’t have.
When sprayed on a plant, glyphosate is absorbed through the leaves and transported throughout the entire organism, including the roots. Because it moves systemically, it doesn’t just damage the surface tissue. It shuts down the plant’s ability to make critical proteins from the inside out, typically killing it within one to three weeks.
Where Glyphosate Is Used
The EPA has established tolerances for glyphosate on a wide range of food crops, including corn, soybeans, oil seeds, grains, and some fruits and vegetables. Its use expanded dramatically after the introduction of genetically modified crops engineered to tolerate it, allowing farmers to spray entire fields to kill weeds without harming the crop itself. This made glyphosate central to large-scale commodity farming.
Beyond agriculture, glyphosate is used to manage vegetation along roadsides, railways, and utility corridors, and it remains a popular option for homeowners dealing with weeds in driveways, gardens, and lawns. Its broad-spectrum action, meaning it kills nearly all plants it contacts, makes it versatile but also requires careful application to avoid damaging desired vegetation.
What Happens to Glyphosate in the Environment
Once glyphosate reaches soil, microorganisms begin breaking it down into a compound called AMPA (aminomethylphosphonic acid). Glyphosate itself can persist in soil for up to 280 days, but AMPA sticks around even longer, with a half-life reaching up to 958 days. That means AMPA can linger in soil for roughly three times as long as the original herbicide. AMPA is also produced as a breakdown product of certain household detergents, so it enters the environment from multiple sources.
This persistence matters because both glyphosate and AMPA can be detected in waterways, where runoff carries them from treated fields. The long environmental lifespan of AMPA in particular has drawn increasing scientific attention, though research into its specific ecological effects is still limited compared to glyphosate itself.
Glyphosate Residues in Food
Trace amounts of glyphosate regularly show up in food. The FDA tested 879 samples of corn, soybean, milk, and egg products and found that roughly 59% of the corn and soy samples contained detectable residues of glyphosate. However, all samples fell below the tolerance levels set by the EPA, which range from 0.1 to 400 parts per million depending on the crop. Grains like oats and wheat, which are sometimes treated with glyphosate shortly before harvest to speed drying, tend to carry higher residue levels than other foods.
The Cancer Debate
The biggest controversy around glyphosate centers on whether it causes cancer, and the answer depends on which authority you ask. In 2015, the International Agency for Research on Cancer (IARC), a branch of the World Health Organization, classified glyphosate as “probably carcinogenic to humans.” IARC based this on limited evidence from human studies, sufficient evidence from animal experiments, and strong evidence that glyphosate can damage DNA. Several of the human studies IARC reviewed showed increased rates of non-Hodgkin lymphoma among people occupationally exposed to glyphosate, and the combined data across studies reached statistical significance.
The EPA reached the opposite conclusion. Its scientists independently evaluated the available data and found no risks of concern to human health from current uses, stating that glyphosate is “not likely to be carcinogenic to humans.” This position is shared by regulatory agencies in Canada, Australia, the European Union, Germany, New Zealand, and Japan, as well as the joint FAO/WHO pesticide residue panel.
In 2022, a U.S. appeals court vacated the human health portion of the EPA’s interim decision on glyphosate, directing the agency to better explain its cancer findings and incorporate current scientific evidence. The EPA is currently updating that evaluation. Meanwhile, the agency has maintained that its underlying scientific conclusion about glyphosate’s safety has not changed.
The disagreement largely comes down to methodology. IARC evaluates whether a substance is capable of causing cancer under any circumstances, including high-dose occupational exposure. Regulatory agencies like the EPA assess whether the substance causes harm at the doses people actually encounter in real life. Both approaches are scientifically valid, but they answer fundamentally different questions, which is why they can look at overlapping evidence and reach different conclusions.
Effects on Honeybees and Gut Bacteria
Because glyphosate targets an enzyme found in bacteria, it can affect microorganisms beyond the ones that live in soil. Research published in mSystems found that sublethal doses of glyphosate reduced populations of beneficial bacteria in honeybee guts, regardless of the bees’ age or when exposure occurred. The most affected species was Snodgrassella alvi, a key gut bacterium whose numbers dropped in a dose-dependent pattern, meaning higher glyphosate concentrations caused steeper declines.
These gut changes weren’t immediately fatal, but bees exposed to higher concentrations (0.1 to 1.0 millimolar) showed increased mortality over time in laboratory conditions compared to unexposed bees. The practical concern is that weakened gut bacteria could leave bees more vulnerable to pathogens and environmental stress, compounding other threats to pollinator health. Interestingly, bees exposed to the lowest dose in one experiment actually survived longer than control bees, a finding researchers did not fully explain.
What Glyphosate Is, Chemically
Glyphosate’s chemical name is N-phosphonomethylglycine, and its molecular formula is C₃H₈NO₅P. It’s an organophosphorus compound, but it belongs to a different chemical family than organophosphate insecticides like malathion or chlorpyrifos, which work by attacking the nervous system. Glyphosate is a relatively simple molecule: essentially the amino acid glycine with a phosphonate group attached. It dissolves readily in water, which is why commercial formulations are typically sold as liquid concentrates. The surfactants and other ingredients mixed into those formulations have their own toxicity profiles and are sometimes more irritating to skin and eyes than the glyphosate itself.