An unseen geological threat
In the central dry zone of Myanmar, particularly in the Magway Region, the primary source of drinking water holds an invisible danger. The groundwater, drawn from tube wells, is naturally contaminated with high levels of fluoride. Concentrations often exceed the World Health Organization's guideline of 1.5 milligrams per liter (mg/L), leading to significant public health issues for the local communities. This contamination is is not from industrial pollution but stems from the region's deep geological history.
The health consequences of long-term exposure to excess fluoride are severe. The most visible effect is dental fluorosis, which causes mottling and pitting of tooth enamel. More debilitating is skeletal fluorosis, a condition that leads to joint pain and stiffness, crippling bone deformities. Because fluoride is colorless and odorless, residents are often unaware of the risk until the chronic symptoms of fluorosis appear. Tens of millions of people worldwide are estimated to have developed dental or skeletal fluorosis from drinking water with high fluoride concentrations.
Geochemistry of the problem
The source of the fluoride lies locked within the Cenozoic-era sedimentary rocks that form the geology of the Central Myanmar Basin. Specifically, the Pegu Group, a thick sequence of shallow-marine sediments deposited during the Miocene epoch, is a primary contributor. These layers of sandstone, shale, and clay contain fluoride-bearing minerals such as fluorapatite, biotite, and various amphiboles.
Several hydrogeochemical processes work together to release this fluoride into the water. The groundwater in this region is naturally alkaline, and a higher pH increases the dissolution of these minerals. An important mechanism involves a process of ion exchange within the aquifer's clay sediments. Calcium ions in the water are swapped for sodium ions present in the clay. This lowers the concentration of calcium in the groundwater. Low calcium levels, in turn, accelerate the dissolution of fluoride-containing minerals like fluorite (calcium fluoride), liberating more fluoride ions into the water supply. This interaction between the water and the ancient rock formations creates the conditions for a widespread public health crisis.