High F in Palghat Groundwater

Shaji E, the versatile groundwater guy, with a PhD in the Metamorphic Petrology of cordierite gneisses of the Kerala Khondalite Belt, and who is also a one time Young Scientist Awardee of the Kerala Science Congress, of CGWB, Trivandrum has just now published a paper on the high-F content in the groundwater of Palghat in Current Science. He says that

" The country rock, hornblende biotite gneiss, has been identified as the source for this high fluoride for both phreatic as well as deep aquifers. Now how does this fluorine get released from these hard crystalline rocks? Here man and nature conspire: the water is alkaline and depleted in calcium, it resides for a fairly long time in the aquifer zone, and the intensive irrigation in the area creates the additional stress that leads to the dissolution of fluorine-bearing minerals and release of F into the groundwater."