Uranium anomalies identified using G-BASE data - natural or anthropogenic? A uranium isotope pilot study

The rapid quantitative analysis by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) for uranium isotope ratios has been successfully established and tested. The method is fully documented in this report. The rapid and cost effective nature of the methodology has allowed the analysis of a selection of G-BASE soil and stream sediment archive material to be undertaken, which was not possible previously. These samples were chosen by careful consideration of the findings of previously published G-BASE atlases. During the course of mapping Britain, the G-BASE project has encountered anomalously high concentrations of uranium in several areas, in comparison to the regional background values. Samples from regions believed to be enhanced in uranium due to natural processes alone were chosen to allow the variability of uranium isotope ratios to be quantified, and hence provide an isotopic baseline. Samples which had been recognised during geochemical baseline mapping as having anomalously high uranium concentrations in the locale of nuclear fuel installations were also selected for comparison with this isotopic baseline. As would be expected from literature values, the 238/235U ratio was constant in all the natural enhanced samples, whilst some variation in 238/234U was observed. This was also the case for samples from the urban industrial fringes of Greater Merseyside, which had high concentrations of heavy metal contaminants. In contrast, all samples associated, by proximity, with nuclear fuel facilities were found to have isotope ratios reflecting a contribution from enriched uranium. These results are consistent with the limited suite of RIFE (Radioactivity in Food and the Environment) data available, but are of better precision. Difficulties exist in quantifying the contribution of processing facility uranium to stream sediments and soils, due to the limited information available on the likely composition of the original materials entering the stream course, or soil profile. These factors are highlighted, along with possible further investigations to elucidate dissemination of anthropogenic uranium in the environment.