Nestled high in the Eastern Himalayas, the Tawang district of Arunachal Pradesh is often celebrated for its crystal-clear rivers, glacial lakes, and sacred monasteries. But beneath the serenity of its turquoise waters lies a less visible and deeply troubling reality: dangerously high levels of fluoride contamination.
Fluoride (F⁻), a mineral naturally found in soil and rocks, is well-known for its protective role in dental health. It strengthens enamel and helps prevent tooth decay, which is why it’s commonly added to toothpaste and even piped into public water systems in several countries. But when fluoride goes unchecked particularly in drinking water it becomes a toxin with serious health consequences.
In many parts of India, fluoride contamination is blamed on industrial waste or agricultural runoff. But Tawang, tucked away in the far western reach of Arunachal Pradesh, tells a different story. In this remote district, there are no aluminium smelters, no fertiliser factories, no coal plants. Yet, recent research shows that fluoride levels here far exceed safe limits not because of human activity, but because of the land itself.
In 2022, scientists from DRDO Tezpur reported fluoride concentrations as high as 21.86 mg/L in surface water samples taken from rivers and high-altitude lakes in the region. To put that in context, the World Health Organization’s safe limit is 1.5 mg/L. In another study conducted in 2024, researchers from NERIST, Itanagar found that Sangetsar Tso (Madhuri Lake), a popular tourist destination had fluoride levels of 7.11 mg/L, more than four times the WHO threshold. A study by Dutta and Gupta (2022) showed fluoride concentrations ranging from below 0.2 to 12.5 mg/L in samples collected from the thermal springs of Tawang and adjoining West Kameng district.
We believe the answer lies in the rocks. Tawang’s bedrock is rich in garnet-biotite schist, a metamorphic rock known to contain fluoride-bearing minerals such as biotite and hornblende. Similar geological formations in Xinjiang, China, have been linked to fluoride contamination in Ulungur Lake, where weathering of these minerals has led to high fluoride buildup in lake water.
What’s happening in Tawang appears to follow the same pattern. Natural weathering, driven by rainfall, erosion, and temperature variation, slowly leaches fluoride from these rocks into the lakes, rivers, and possibly even groundwater. It’s a classic case of geogenic contamination — one that’s dangerously easy to overlook because it isn’t tied to visible pollution.
While current evidence strongly supports a natural geological origin for fluoride in the region, the potential contribution of other sources whether anthropogenic or less evident natural pathways cannot be entirely ruled out. To date, no such alternative sources have been systematically identified or documented in peer-reviewed studies of the area. This gap highlights the need for further research to comprehensively characterise all potential fluoride sources, particularly given the hydrogeological complexity of the region. All the cited studies above consistently point to geogenic sources, such as the natural weathering of fluoride-bearing rocks, as the most probable cause of fluoride contamination in the region.
Possible health implications
The health implications are far-reaching. Excess fluoride consumption over time can lead to dental and skeletal fluorosis, both irreversible. It affects bones, joints, teeth, and in severe cases, leads to physical deformities. Neurological damage, thyroid problems, and even reproductive issues have been linked to long-term fluoride exposure. Children and the elderly are particularly vulnerable.
Despite these dangers, awareness on the ground remains limited. Many villagers may already be showing signs of early-stage fluorosis — stiff joints, tooth discoloration, chronic fatigue — without understanding the root cause.
The way forward begins with comprehensive testing and a clear mapping of vulnerable areas. Identifying hotspots is crucial to prioritising interventions. Once mapped, authorities may install defluorination systems — such as activated alumina filters or reverse osmosis units — particularly in public buildings like schools, Anganwadi centres, and PHCs. For many households, rainwater harvesting could offer a fluoride-free alternative. But water solutions alone aren’t enough. A reassessment of local medical records and community health surveys is urgently needed to detect undiagnosed cases of fluorosis. Simultaneously, awareness campaigns must be rolled out to educate communities about the risks of fluoride in water and how to recognise symptoms early.
Tawang’s case is a wake-up call: even the most remote and picturesque places are not immune to invisible threats. With the right blend of science, policy, and community participation, it is still possible to protect future generations from the long-term effects of fluoride exposure — before it’s too late.
Aribam Rocky Sharma is Project Scientist-I, NMSHE, State Climate Change Cell, Government of Arunachal Pradesh
Dani Yaming is Project Associate-II, NMSHE, State Climate Change Cell, Government of Arunachal Pradesh
Views expressed are the authors’ own and don’t necessarily reflect those of Down To Earth