Roundup Weedkillers Caused Multiple Cancers in Rats, Large International Study Finds

There’s now more evidence that glyphosate exposure at levels deemed safe by regulatory authorities can cause multiple kinds of cancer, thanks to a new peer-reviewed study published Tuesday in Environmental Health.

The study authors, including researchers from the Ramazzini Institute in Italy and Boston College, examined the impact of glyphosate and two common glyphosate-based weedkiller formulations — Roundup Bioflow, which is used in Europe, and Ranger Pro, a generic version of Roundup used in the U.S.

Both formulations are sold by Bayer, which acquired the Roundup brand and related weedkillers in 2018 when it bought Monsanto.

Researchers gave the weedkillers to groups of rats over two years and compared the results to unexposed groups of rats.

“Our study showed carcinogenic effects in rats at doses that are currently considered safe,” the study’s corresponding author Daniele Mandrioli, M.D., Ph.D., told The Defender.

Mandrioli directs the Cesare Maltoni Cancer Research Center at the Ramazzini Institute.

According to the report, Mandrioli and his colleagues found that rats exposed to glyphosate and both glyphosate-based products developed tumors in multiple places, including the blood (as in, leukemia), skin, liver, thyroid, nervous system, ovary, mammary gland, adrenal glands, kidney, urinary bladder, bone, endocrine pancreas, uterus and spleen.

Prenatal exposure to the weedkiller was “particularly detrimental,” Mandrioli said, noting that 40% of the deaths from leukemia occurred in exposed rats who were less than a year old.

The authors also saw an increase in early deaths for other types of tumors, he added.

Study comes as Bayer seeks immunity from costly lawsuits

It’s been a decade since the World Health Organization’s International Agency for Research on Cancer classified glyphosate as a probable human carcinogen.

Nonetheless, glyphosate-based herbicides are now used more widely than any other herbicide in the world, the authors wrote in their report.

Carey Gillam, who first reported on the study in The New Lede, noted that the study’s findings come amid an “ongoing global debate” on the safety of the ubiquitous weedkiller.

Gillam — author or “The Monsanto Papers: Deadly Secrets, Corporate Corruption, and One Man’s Search for Justice” and “Whitewash: The Story of a Weed Killer, Cancer, and the Corruption of Science” — pointed out that Bayer is facing rising litigation costs as thousands of U.S. users of Roundup and other glyphosate-based herbicides allege the products caused them to develop cancer.

The company has lobbied state legislatures to pass laws that would prevent such lawsuits in the future by granting the pesticide-maker legal immunity. It has also threatened to stop selling Roundup in the U.S. if it doesn’t get greater liability protection.

Last month, Georgia became the second state to shield Bayer from some lawsuits alleging the company failed to warn customers of health dangers. North Dakota passed a similar measure in April.

On April 4, Bayer asked the U.S. Supreme Court for a ruling to nullify existing lawsuits and prevent similar lawsuits in the future.

Many environmental and health activists had hoped the Make America Healthy Again (MAHA) Commission’s recent report would call out glyphosate as a key driver of the chronic disease epidemic in children.

The report named three agrochemicals — atrazine, chlorpyrifos and glyphosate — that children are exposed to through food, water, dust, lawn treatments and household sprays.

However, in its overall assessment of what “The MAHA Report” called “crop protection tools,” the commission said only that “some studies have raised concerns about possible links” between some of the products and children’s health and that human studies on the issue are “limited.”

Glyphosate-based herbicides may be more carcinogenic than straight-up glyphosate

For the new study, the authors gave rats glyphosate alone, or one of the two common glyphosate-based herbicides, via the rats’ drinking water starting at prenatal life for two years. Dosages were 0.5, 5, and 50 milligrams per kilogram (mg/kg) of body weight per day.

The European Union’s (EU) acceptable daily intake for glyphosate is 0.5 mg/kg of body weight. The EU’s “no-observed adverse effect level” (NOAEL) is set at 50 mg/kg body weight/day.

Although the U.S. Environmental Protection Agency in 2017 drafted a daily exposure limit of 1.0 mg/kg per day via food and water, the agency maintains that glyphosate poses no risk to human health as long as it’s used as directed by the product label.

Unexposed groups of rats were used as the control. In total, the study involved 1,020 rats, with equal numbers of males and females.

The authors observed dose-related increases in several rare malignant tumors, including leukemia, liver, ovary and nervous system tumors among rats exposed to glyphosate and glyphosate-based herbicides, compared to unexposed rats.

These increases were also statistically significant when compared with historical rates of tumors among rats used in other studies, they said.

Some of the carcinogenic effects were worse among rats exposed to a glyphosate-based herbicide rather than to glyphosate by itself.

The authors speculated that some other ingredients used in the glyphosate-based herbicide formulas “may enhance the carcinogenicity of glyphosate, particularly in the case of leukemia.”

The study was funded by several Italian and U.S. institutions other than the Ramazzini Institute and Boston College, including the Heartland Health Research Alliance, the Institute for Preventive Health and the Carisbo Foundation.