An herbicide commonly used by Americans on their lawns and in their city parks has been labeled a carcinogen by the World Health Organization.
Glyphosate, the compound most commonly sold under the brand name Roundup, is the most widely used herbicide on Earth. It is an ingredient in more than 750 products.
A group of 17 scientists affiliated with the WHO’s International Agency for Research on Cancer concluded that glyphosate is “probably carcinogenic to humans.”
The scientists explained that
Glyphosate and glyphosate formulations induced DNA and chromosomal damage in mammals, and in human and animal cells in vitro. One study reported increases in blood markers of chromosomal damage (micronuclei) in residents of several communities after spraying of glyphosate formulations.
Studies in several countries, including Canada, Sweden, and the United States, indicate that exposure to glyphosate is linked to non-Hodgkins lymphoma. The herbicide persists in the air, water, and food and other research shows that farm workers absorb the compound into their blood and urine.
The studies that IARC relied upon in reaching its conclusion are not new to the debate over glyphosate’s toxicity. They were considered by the European Union in an evaluation of the substance’s epidemiological safety in 2010. The EU decided then that glyphosate poses no risk to human health.
In the United States, the Environmental Protection Agency most recently authorized production and use of glyphosate in 1993.
Monsanto Corp., the manufacturer of Roundup, disputed the WHO study in a statement.
“We don’t know how IARC could reach a conclusion that is such a dramatic departure from the conclusion reached by all regulatory agencies around the globe,” Dr. Philip Miller, the company’s vice president for global regulatory affairs, said.
On the other hand, a toxicologist at the United Kingdom’s Brunel University advised caution.
“Home gardeners especially should exercise the utmost care when they use weedkillers that contain glyphosate,” Prof. Andreas Kortenkamp said in a statement.
One unclear aspect of the IARC conclusion is the degree of exposure to glyphosate that would be necessary to raise the risk of cancer in humans.
“The IARC process is not designed to take into account how a pesticide is used in the real world – generally there is no requirement to establish a specific mode of action, nor does mode of action influence the conclusion or classification category for carcinogenicity,” Dr. Alan Boobis, a biochemical pharmacologist at Imperial College London, said.
IARC also examined several popular insecticides, including malathion, parathion, and tetrachlorvinphos, and the herbicide diazinon.
Malathion is the world’s most commonly used organophosphate insecticide, with about 15 million pounds sprayed each year. Used on a wide variety of agricultural products, in the past it has also been widely sprayed to combat Mediterranean fruit flies, boll weevils, and mosquitoes that carry the West Nile virus.
Parathion is also an organophosphate insecticide. Most commonly applied to cotton, rice, and fruit trees, the compound is considered “highly acutely toxic” to humans and a possible human carcinogen by EPA.
According to data gathered by the Pesticide Action Network, parathion is also highly toxic to many other organisms.
Tetrachlorvinphos, another organophosphate insecticide, is used to kills ticks and fleas. The substance is commonly found in pet flea collars.
TCVP, as the insecticide is known, is a likely neurotoxin and carcinogen, according to a study conducted by the environmental advocacy organization Natural Resources Defense Council. NRDC concluded that TCVP use in pet flea collars raises the risk of cancer and neurological damage in children by about 1,000 times over the risk acceptable under applicable federal law.
Litigation challenging EPA’s decision to allow use of TCVP is pending in a U.S. court of appeals.
IARC classified malathion and diazinon, like glyphosate, as “probably carcinogenic to humans,” and determined parathion and tetrachlorvinphos to be “possibly carcinogenic.”
A paper documenting the IARC conclusions was published Friday in The Lancet.