Publicação: Groundwater toxicity due to natural dissolved radionuclides belonging to the U and TH decay series
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2009-01-01
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Primeval radionuclides have survived in detectable amounts since the time of nucleosynthesis and contribute to the terrestrial gamma radiation, whose major contribution comes from 40K and three radioactive series having unstable members with half-lives much shorter than that of each precursor, i.e. Th, U, and U. Thorium and uranium are lithophile elements, being concentrated preferentially in acid igneous rocks compared with intermediate, basic, and ultrabasic varities. 232Th decays to the stable Pb, after 12 disintegrations (7 alpha-type and 5 beta-type). U is the principal isotope of natural U (99.72% abundance) and decays to the stable 206Pb, after 14 disintegrations (8 alpha-type and 6 beta-type). Potential health hazards from some natural radionuclides belonging to these decay series in consuming water have been considered worldwide, with many countries adopting the WHO guideline activity concentration for drinking water quality. In general, the recommendations apply to routine operational conditions of water supply systems. Several national standards for limiting radiation exposure establish maximum permissible radionuclides concentration in drinking water, where, in general, for practical purposes, 0.5 Bq/L for gross alpha and 1 Bq/L for gross beta activity have been used to routine operational conditions of existing or new water supplies. However, additional information concerning to specific radionuclides may be required in some circumstances in order to decide about the drinking water quality in terms of radiological aspects. Special attention must be given when groundwaters are utilized for public water supplies, because water-rock/soil interactions may enhance the presence of natural radionuclides in solution. This chapter reports the radiological implications of the interactions between waters and different rock types occurring in aquifer systems exploited in Brazil. The data here shown demonstrate how some natural radionuclides contribute to the groundwater toxicity evaluated in terms of the WHO guideline activity concentration for drinking water quality.
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Progress on Drinking Water Research, p. 199-240.
