AN INTERNATIONAL study has found widespread uranium contamination in groundwater from aquifers in 16 Indian states. The main source is natural, but human factors such as groundwater-table decline and nitrate pollution may be exacerbating the problem, say researchers from Duke University in the study published in Environmental Science & Technology Letters.
Several studies have linked exposure to uranium in drinking water to kidney diseases. The World Health Organisation has set a provisional safety standard of 30 microgrammes of uranium per litre. Uranium is not, however, included in the list of contaminants monitored under the Bureau of Indian Standards’ Drinking Water Specifications, the study stated.
The researchers sampled water from 324 wells in Rajasthan and Gujarat, and analysed the water chemistry. In a subset of samples, they measured uranium isotope ratios. They also analysed similar data from 68 previous studies of groundwater geochemistry in Rajasthan, Gujarat and 14 other states.
“Nearly a third of all water wells we tested in Rajasthan contained uranium levels that exceed the WHO… safe drinking water standards,” Duke University quoted Avner Vengosh, a professor of geochemistry and water quality at Duke’s Nicholas School of the Environment. “By analysing previous water quality studies, we also identified aquifers contaminated with similarly high levels in 26 other districts in northwestern India and nine districts in southern or southeastern India.”
Factors contributing to the contamination include the amount of uranium in an aquifer’s rocks and various chemical interactions between rock and water. “In many parts of India, these factors co-occur and result in high uranium concentrations in groundwater,” the university quoted PhD student Rachel M Coyte, the lead author of the study.
Human activities, especially over-exploitation of groundwater for irrigation, may have exacerbated the problem. Many of India’s aquifers are composed of clay, silt and gravel carried down from the Himalayas by streams or uranium-rich granitic rocks. When overpumping of these aquifers’ groundwater occurs and their water levels decline, it induces conditions that enhance uranium enrichment in the shallow groundwater that remains.
“One of the takeaways of this study is that human activities can make a bad situation worse, but we could also make it better,” Vengosh said. “The results strongly suggest there is a need to revise current water-quality monitoring programmes in India and re-evaluate human health risks in areas of high uranium prevalence,” he said.
“Including a uranium standard in the Bureau of Indian Standards’ Drinking Water Specification based on uranium’s kidney-harming effects, establishing monitoring systems to identify at-risk areas, and exploring new ways to prevent or treat uranium contamination will help ensure access to safe drinking water for tens of millions in India,” Vengosh said.