Geerd Ahlrich Smidt

• Phosphorus (P) mineral fertilisers are found to contain high concentrations of uranium (U) (up to 206 mg U kg-1) and other trace elements (TE), such as Cd, Pb, Ni, Cu, Zn, Th, Nb, Sr, V, and rare earth elements. The content of U and other trace elements is depended on the sedimentary of igneous origin of the rock phosphate. In this study, the production of P fertilisers has been shown to contaminate top soil horizons with U and other trace elements in the close vicinity of a factory located in Southern Brazil. In contrast to this point source, agricultural P fertilisation leads to a diffuse contamination of the agro-ecosystem with U and other fertiliser-derived trace elements on a large scale. Top soil horizons of arable land accumulate fertiliser-derived U. According to the geochemical behaviour of U(VI) species under oxidising conditions, the mobilisation capacity for U in top soil horizons is considered to be high, contrary to other fertiliser-derived heavy metals (e.g. Cd). Hence, it is assumed that U can be leached to shallow groundwater and can reach fresh water resources potentially used for drinking water supply. The aims of this study were to investigate the concentration of U and other contaminants in P fertilisers, to identify geochemical processes of fertiliser-derived U mobility and mobilisation from arable top soil horizons to the groundwater, and to evaluate the origin of U in German groundwater and tap water. This study presents the broadest recent data set on regional distribution of U concentrations in German tap water to which 76 % of the German population has access. The mean U concentration was 0.68 æg L-1, the median 0.50 æg L-1. 1.3 % or 1 million of the 80.6 million inhabitants in Germany are exposed to U concentrations in tap water which are higher than the German drinking water threshold limit of 10 æg L-1. The regional distribution of U concentrations largely agrees with the geological setting reported for mineral waters, however, in addition evidence for fertiliser-derived U in tap water was found in certain areas in Northern and Southern Germany. To test the hypothesized fertiliser-derived U leaching to groundwater, samples from different depths were taken in an area intensively used for cropping production in Lower Saxony. The correlation between fertiliser-derived nitrate (NO3-) and U especially in shallow (< 15 m) groundwater samples indicates the anthropogenic origin of U. However, there is not yet a clear picture of quantities and processes of U leaching from fertilised soil into groundwater. The future aim is to investigate these processes of U migration via isotope fingerprinting and geochemical modelling to provide a solid foundation for future risk assessment.