Uranium and radon in groundwater - An overview of the problem

Radioactive elements occur naturally in the environment. A long-term exposure to the radioactive gas radon (Rn) can lead to lung cancer. In Sweden, 450 cases of lung cancer, mostly among smokers, are registered every year, due to inhalation of radon gas. The ultimate parent element of Rn is uranium (U), which is found in soil and bedrock in varying concentrations. U is also radioactive but causes more harm due to its toxicity; kidney problems arise when uranium is ingested. In some areas of Sweden where municipal water is not available, wells are drilled in bedrock to extract water for drinking purposes and other uses. Groundwater from wells drilled in rock types rich in uranium (e.g. granite) has shown tendency to have both high radon and uranium concentrations. However, high concentrations of radon exceeding the Swedish regulatory limit of 1000 Bq/l have also been observed in bedrock containing low concentrations of uranium (<2 ppm). This observation might indicate that the water came from another bedrock (e.g. pegmatite) at several meters depth, which often goes undetected on geological maps. The uranium concentration in water is usually not routinely measured as an indicator of water quality despite its toxicity. A uranium concentration as high as 445 μg/l (WHO limit is 15 μg/l) was observed in one private well in Stockholm County. The heterogeneous conditions in the subsurface, with respect to geochemistry, groundwater flow, geology and fracture pattern, make the development of a risk prediction model that can be applied at a general scale complex. This paper presents an overview of the problem of natural radioactivity in drinking water from drilled wells in Sweden.