The naturally occurring radioisotopes are Uranium-238, Thorium-232, and Potassium-40 which are present in abundance in different areas across the globe. It is estimated that about 3,51,000 tons of natural uranium (uranite) and 13 million tons of naturally occurring thorium (monazite) are present in India. In Karnataka, about 7300 tons of natural uranium are present in the Gogi, Kanchankayi- Hulkal, and Walkunji- Yallakki belt of the state.
Recently a research paper was published in Current Science on the groundwater situation in 73 villages of the eastern districts of Karnataka found that about 78% of the villages have uranium concentration in groundwater more than the permissible concentration limit of 30 micrograms per liter (World Health Organization standards). This is due to the presence of granite sedimentary rocks. Hence, Atomic Energy Regulatory Board (AERB) has set the permissible limits to 60 micrograms per liter. The study also shows that 48 villages have concentrations of more than 60 micrograms per liter and 12 villages have concentrations of more than 1000 micrograms per liter. The researchers cleared that the concentration of the uranium increased because of the natural reasons not from the anthropogenic activities rather it is due to the joint effect of lowering groundwater table and geological morphology of Karnataka. Gamma-ray spectrometric studies showed that the abundance of naturally occurring radioactive elements (potassium, uranium, and thorium) is high in the eastern part of the state. Geologists suggested that the Karnataka geo-morphology consists of hard rock terrain like ancient granite, schistose, and gneisses rocks. The water circulates into the rocks from the interstitial fractures inside aquifer depths. Hence, the soil-water and rock-water interactions decide the mineral and chemical composition of the groundwater. In Karnataka, the oxidized nature of the soil aggravates from weathering process. During this process, the Uranous ion (U+4) gets converted into Uranyl ion (UO2)+2 which gets dissolved in circulating groundwater. When the groundwater level gets lower, the oxidized weathering becomes more prominent which results in more soil, rock, and water interactions which leads to the release of more uranium in groundwater.
There are many contradictory studies done on the health effects due to uranium content in drinking water which is itself a challenging fact. Uranium can cause nephrological disorders and other health hazards if taken in severely high concentrations. But many studies also cleared that the health effects are not linked to its content in drinking water. The same issue came to light when higher uranium content (5.6–3,410 micrograms per liter) sound in drinking water of drilled wells in Finland and no symptoms were reported among the exposed population.