Natural radioactivity in drinking water in private wells in Finland

Natural radioactivity in drinking water was determined in population-based random study of 472 private wells. The mean concentrations of Rn-222, Ra-226, U-234, U-238, Pb-210 and Po-210 in drilled wells were 460, 0.05, 0.35, 0.26, 0.04 and 0.05 Bq l(-1), and in wells dug in the soil were 50, 0.016, 0.02, 0.015, 0.013 and 0.007 Bq l(-1), respectively. Approximately 10% of the drilled wells exceeded a radon concentration of 1000 Bq l(-1) and 18% a uranium concentration of 15 μ g l(-1). The mean annual effective dose from natural radionuclides for a drilled well user was 0.4 mSv and 0.05 mSv for a user of a well dug in the soil. The effective dose arising from Rn-222 was 75% of the total of all natural radionuclides for drilled well users. As regards long-lived radionuclides, Po-210 and Pb-210 caused the largest portion of the effective dose. The dose arising from U-238, U-234 and Ra-226 was only 8% of the total of all natural radionuclides.