That borewells have depleted groundwater reserves sharply since the 1980s when they were brought on a largescale is something we all know. What is not known is that borewells also increase the groundwater contamination levels and increase the threat of fluorides and arsenic.
When rice fields are covered with floodwater, oxygen doesn’t enter the soils quickly. Aerobically respiring microbes then use other substrates to sustain their metabolism such as iron minerals found in the soil.
This leads to dissolution of minerals and the release of arsenic into the water. Arsenic then enters floodwaters and is carried to the rivers when floods recede. Ten centimeters of stagnant water in a field of paddy can lead to arsenic release from the soil but is not enough for its removal to a river.
(Pic: Savita Hiremath)