For the past couple of decades, tens of thousands of people living in rural Sri Lanka have been devastated by kidney failure due to unclear causes, also known as CKDu. Similar incidences of mysterious kidney diseases have emerged in tropical farming communities around the world.

A massive field study of the wells supplying drinking water to the Sri Lankan communities, conducted by researchers at Duke University, has identified a possible culprit—glyphosate, the active compound in Roundup, the most widely used herbicide in the world.

The results of the study were published in Environmental Science and Technology Letters on September 13, 2023.

Roundup is a glyphosate-based herbicide used to control weeds and other pests. Because it is supposed to break down in the environment within a few days to weeks, its use is relatively under-regulated by most public health agencies. But when glyphosate encounters certain trace metal ions that make water hard—like magnesium and calcium—glyphosate-metal ion complexes can form. Those complexes can persist up to seven years in water and 22 years in soil.

“It was always thought that this chemical would break down very quickly in the environment, but it seems to stick around a lot longer than we expected when it complexes in hard water,” said Nishad Jayasundara, the Juli Plant Grainger Assistant Professor of Global Environmental Health at Duke. “We have to consider how glyphosate is interacting with these other elements,