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A new study in the journal Environmental Science & Technology and led by researchers at Columbia University Mailman School of Public Health identifies the hidden geological mechanisms behind widespread uranium contamination in Eastern Karnataka, India, where 78% of tested groundwater exceeds safe drinking limits for uranium, and some groundwater uranium contamination reaches levels 75 times the U.S. EPA limit. Uranium exposure can affect the kidneys, bones, and the liver, yet contamination often goes undetected.

The researchers discovered that uranium becomes dangerously mobile in specific underground environments—a finding that could help local communities monitor and manage this health threat. With over 25 million people in the region relying on groundwater for more than 70% of their drinking water, these insights could lead to targeted solutions, such as where to site wells and localized treatment at affected well-heads.

With collaborators from the Divecha Center for Climate Change, Indian Institute of Science, Bangalore, and the Indian Institute of Technology, Jodhpur, the team undertook forensic work to shed light on the conditions responsible for releasing uranium into groundwater. They employed advanced isotopic analysis, which measures tiny variations in atoms called isotopes, to trace the origin of a substance like uranium and its movement through the environment in aquifers found in hard rock. They mapped distinct subsurface conditions governing uranium behavior.

The highest contamination occurs in "oxidizing environments," where underground conditions dissolve uranium into water, while "reducing zones" naturally trap it, preventing it from contaminating drinking water supplies.

"We're moving beyond simply detecting uranium to understanding its origin, movement, and long-term behavior. These insights can guide interventions to protect millions of people," says lead author Arijeet Mitra, Ph.D., a postdoctoral scientist in the Department of Environmental Health Sciences at Columbia Mailman School.

The study's framework, adapted from Columbia's Northern Plains Superfund Research Program, is applicable to other regions dealing with naturally occurring uranium contamination, including several states in the western and midwestern U.S. The research underscores the urgent need for a more robust and long-term monitoring network to track uranium levels and environmental changes.

"How uranium moves in groundwater depends on how oxidizing the water is," says the study's senior author, Anirban Basu, Ph.D., research scientist in the Department of Environmental Health Sciences.

"When there is plenty of oxygen, uranium stays dissolved and flows with the water. But when there is no oxygen—like in deeper layers where certain bacteria break down iron oxides—uranium changes into a form that does not dissolve and settles out as a solid. The proportion of uranium isotopes in the water works like a fingerprint. It helps us track where uranium enters and leaves the water and whether it comes from a nearby or far-away source."

The study is titled "Isotopic Insights into Redox Processes Driving Uranium Distribution in Eastern Karnataka Groundwater."