Concerned the chemical may be linked to a kidney disease killing agricultural workers, Sri Lanka this week ordered a ban on glyphosate, the active ingredient in Monsanto’s top-selling herbicide Roundup.

The move comes weeks after publication of a new study in Sri Lanka suggesting glyphosate as the leading culprit for the illness. The paper did not provide new scientific evidence, but laid out a detailed theory that the use of glyphosate in areas with heavy metals in the drinking water is causing the chronic kidney disease. Roundup is the top selling herbicide in the world, and Monsanto said the newest study is built upon untested theory rather than hard data.

“Glyphosate acts as a carrier or a vector of these heavy metals to the kidney,” said Dr. Channa Jayasumana, the study’s principal author.

For more than two years, the International Consortium of Investigative Journalists has examined a mysterious form of kidney disease that has killed tens of thousands of agricultural workers in Central America, Sri Lanka and India. The malady is suspected by scientists to be caused by a combination of factors including chronic dehydration from hard labor in tropical heat and exposure to toxins such as pesticides, but its origins have yet to be fully uncovered.

Wednesday’s announcement by Sri Lanka was the most dramatic measure taken to date to combat the illness. The legislature in El Salvador approved a ban on dozens of agrochemicals including glyphosate last September, but the proposal has so far not been signed into law.

“An investigation carried out by medical specialists and scientists has revealed that kidney disease was mainly caused by glyphosate,” Special Projects Minister S.M Chandrasena told reporters in Sri Lanka. “President Mahinda Rajapaksa has ordered the immediate removal of glyphosate from the local market soon after he was told of the contents of the report.”

Roundup is used all over the world, including in countless areas that do not suffer from this distinct form of kidney disease.

“There are no epidemiologic studies suggesting that exposures to glyphosate-based products are associated with renal disorders either in Sri Lanka or elsewhere,” said Monsanto spokesman Thomas Helscher. “The paper presents a theory, the theory has not been tested, and there are a significant number of publications supported by data that make the Jayasumana hypothesis quite unlikely to be correct.”

Sri Lanka’s ban represents a triumph for Jayasumana, a researcher who has long insisted that pesticides and the heavy metals arsenic and cadmium are responsible for the disease.

While he has transformed in Sri Lanka from a resented outsider — a government official once denounced his theories as “arsenic terrorism” — to a respected voice in official policy, some scientists question the evidence behind the pesticide theories, considering them plausible but largely unproven.

Jayasumana’s study does not include laboratory or field tests, and appeared in a little-known “open access” journal in which publishing fees are paid by the authors.

“Banning of pesticides is to be supported under the precautionary principle, since they may be potentially related to CKD,” said Dr. Catharina Wesseling of the Program on Work, Environment and Health in Central America (SALTRA). “However, although beneficial for worker’s health, we should not expect that this will solve the epidemic in Central America.”

Jayasumana’s article contends that glyphosate, which forms powerful chemical bonds with heavy metals, enters into compounds that persist in drinking water until they break down in people’s kidneys. It is the combination of heavy water and Roundup or other glyphosate products, he argued, that places the population at risk.

“I think we can explain the geographical distribution as well as the time problem with our hypothesis,” Jayasumana said, in reference to the epidemic’s unusual geography and its surge in all of the affected regions during the 1990s.

Jayasumana contends Monsanto failed in its obligations to warn the public of the health risks posed by glyphosate when used in areas with heavy water. Glyphosate was originally patented as a chelating agent — a substance useful for its ability to form strong chemical bonds with metals — so Monsanto was aware of these properties, Jayasumana said.

“I don’t see any warnings on the bottle or on the label,” he said. “I feel it’s a fault by Monsanto.”

Official studies in Sri Lanka have found heavy metals and pesticides including glyphosate in the environment of affected areas and in urine samples of kidney patients. One study published last August by Sri Lankan health officials in partnership with the World Health Organization found that urine samples of sick patients had elevated levels of cadmium, and that 65 percent of patients’ urine samples also had traces of glyphosate.

El Salvador has also identified traces of heavy metals in a small number of affected communities, and glyphosate is used widely in the country. Dr. Carlos Orantes, the director of El Salvador’s national research program into the epidemic, said his team is working on developing a map of areas with hard water within El Salvador’s borders.

“Our primary principal is to protect human lives,” said Orantes, a proponent of banning pesticides including glyphosate in El Salvador.

This story was published by The Center for Public Integrity, a nonprofit, independent investigative news outlet. For more of its stories on this topic go to publicintegrity.org.