Study of the occurrence of 222Rn and 226Ra in drinking water in Spain.

With the aim of determining the contribution of water to the background of natural radiation in Spain, the 222 Rn concentration levels were measured in domestic drinking water from a large part of the country. The water analyzed, both surface and groundwater, was collected in two areas of very distinct geological characteristics, pre-selected for the likelihood of their containing high levels of 222 Rn. This water was measured using a coaxial detector of high purity Ge. The overall results demonstrate a log-normal distribution of 222 Rn levels, with a geometric and arithmetic means of 10 and 381 Bq L -1 , respectively, and a range between detection limit of 2 Bq L -1 and a maximum of 31,000 Bq L -1 . The 222 Rn concentrations measured in surface water are generally below the detection limit. Significant differences have been found depending on the geological characteristics of the area of reference, although the very distinct concentration levels of 222 Rn found in samples of similar lithology imply the influence of more complex factors in the solution of 222 Rn in water. Due to the relationship between radon and 226 Ra, the concentration of the latter was measured in the same water using radiochemical separation and a scintillation ZnS(Ag) detector. No significant correlation between 226 Ra and 222 Rn concentrations has been observed unless measurements carried out in a high background radiation region are considered separately.