Natural radionuclides in drinking water supplies of São Paulo State, Brazil and consequent population doses.

The activity concentrations of 228Ra, 226Ra and 222Rn have been analysed in 452 drinking water supplies of São Paulo State. This study started in 1994 and covered 54% of the 574 existing counties. Concentrations up to 235 and 131 mBq l-1 were observed for 226Ra and 228Ra, respectively, whereas 222Rn concentrations reached 315 Bq l-1. Radiation doses up to 0.3, 0.6 and 3.2 mSv yr-1 were estimated for the critical organs, for the ingestion of 226Ra, 226Ra and 222Rn, respectively. The corresponding committed effective doses reached values of 6 x 10(-3), 2 x 10(-2) and 3 x 10(-1) mSv yr-1, for the same radionuclides. These results indicate that 222Rn makes the highest contribution to the total effective dose.