Dose estimate and risk assessment due to the ingestion of 226Ra, 228Ra and 222Rn in drinking water supplies of Sao Paulo State Brazil

This study aims to determine the activity concentrations of (226)Ra, (228)Ra and (222)Rn in drinking water supplies of Sao Paulo State. Concentrations up to 235 mBq L(-1) and 131 mBq L(-1) were observed for (226)Ra and (228)Ra, respectively, whereas (222)Rn concentrations reached 315 Bq L(-1). Radiation doses up to 0.3 mSv y(-1), 0.6 mSv y(-1) and 3.2 mSv y(-1) were estimated for the critical organs, for the ingestion of (226)Ra, (228)Ra and (222)Rn, respectively. The corresponding committed effective doses reached values of 6x10(-3) mSv y(-1), 2x10(-2) mSv y(-1) and 3x10(-1) mSv y(-1), for the same radionuclides. The lifetime risk of radiation-induced cancer due to the ingestion of these radionuclides is also discussed. In the worst case, a total of 1 radium-induced cancer (1 bone sarcoma) was predicted per million exposed persons, for the ingestion of (226)Ra and (228)Ra. For radon, a higher incidence of fatal stomach cancers found is 373 cases per million exposed persons. These estimates suggest that chronic ingestion of radium and radon at the levels observed in these supply waters would result in an increase in the fatal cancer rate up to 0.2% and 8%, respectively, above the background incidence rate observed in the Southeast region of Brazil.