Natural Radioactivity in Drinking Water Sourced from Groundwater in Central and Northern Queensland

Determination of 210 Pb, 210 Po, 234 U, and 238 U activity concentrations in groundwater sources used for drinking water can improve confidence in ingestion dose assessments used for comparison with radiological governance guidelines, such as the Australian Drinking Water Guidelines. Such results can provide additional guidance information for detailed assessments where water supplies exhibit high relative concentrations of natural radioactivity. Measurements of these radionuclides, as well as the more commonly measured gross alpha and beta, 226 Ra, and 228 Ra activity concentrations, were undertaken for 21 water supplies in regional Queensland, Australia. Groundwater was the primary or only source for these water supplies. Dose assessment using the measured values based on the Australian Drinking Water Guidelines assumed water consumption, and estimates of actual consumption rates in the Australian population were undertaken for different age groups. The validity of assumptions underpinning screening assessments based on gross alpha and gross beta activity results and measurement of 226 Ra and 228 Ra were shown to be valid. The adolescent age group (14-18 y) was identified as a potential critical group for dose assessment where activity concentrations of 226 Ra and 228 Ra were elevated. Other radionuclides, 210 Pb, 210 Po, 234 U, and 238 U were shown to be significant contributors to overall committed effective dose in several water supplies; however, total doses in those supplies were well below the operational dose value of 0.3 mSv from the Australian Drinking Water Guidelines. Improved detection limits for 228 Ra could improve accuracy of dose assessments from drinking water.