Spatial anomalies of uranium background levels in groundwater of Lower Saxony

Uranium is a trace metal yielding an average concentration in the Earth’s crust of about 2 to 4 mg/kg, and it occurs naturally in low levels in rock, soil, and water. Although widely known for its radioactive properties, at low levels dissolved uranium is more harmful by its chemical toxicity. The World Health Organisation (WHO) recommends a maximum concentration of 30 µg/l uranium in tap water, as well as a tolerable daily intake limit of 0.6 µg/kg body weight. Since 2011, tap water in Germany must not exceed uranium concentrations of 10 µg/l.

The uranium budget of the groundwater in Lower Saxony comprises mainly of geogenic input through water-rock interaction along the hydrological cycle and within the respective hydrogeological units, and possibly through century-old mining activities, and more recently the use of uranium bearing mineral fertilisers in farming. While the vast majority of uranium concentrations are significantly below 10 µg/l with many values below detection limit, some detached areas display elevated uranium with one confined maximum concentration of 124 µg/l. In order to determine uranium background values, statistical analyses accounted for hydrogeological units of the aquifer, land use, and well depths. Anomalous peak concentrations are unlikely to be a result of variations in geogenic background values alone and require further investigations. A possible rise of uranium concentrations caused by a downward shifting redox front, as proposed in other regions in Northern Germany, is yet to be identified in Lower Saxony.