ENHANCED CONCENTRATIONS OF NATURALLY OCCURRING URANIUM IN KARST GROUNDWATER DUE TO AGRICULTURAL ACTIVITIES

The geochemistry of three drinking water types (wells, springs, and tap) in a rural area of Northern Bulgaria was investigated to gain an understanding of how human activities might influence natural geochemical processes in a carbonate aquifers system. The area is highly agricultural with the portion of the population affected by Balkan endemic nephropathy (BEN). Previous work suggested that there may be a relationship between the occurrence of BEN and differences in regional geology which may affect water quality. Water quality significantly varied as a function of type, but it appears that human activities have influenced all types, with wells being the most impacted. Except for possibly U, elemental concentrations do not seem to be a concern. Nitrate levels are high, most likely from agriculture practices and might be considered a health risk. Multivariate analysis indicates the pattern of water geochemistry for the cluster of endemic villages differs from surrounding non-endemic villages and may be explained by differences in underlying geology, supporting the hypothesis. Ca and Mg concentrations are not correlated while Mg and U concentrations are, whether samples are from endemic or non-endemic villages. These observations are interpreted to indicate that Mg and U concentrations result from the enhanced dissolution of limestone, equilibrium of the water with calcite, and the conservative behavior of Mg, and U. These processes work to decouple Ca and Mg concentrations in the system. Enhanced dissolution is related to the addition of anthropogenic chemicals including NO₃ and PO₄. These two chemicals aid in the conservative behavior of U by poising the redox state of the water to prevent the reduction of U and forming ion pairs that increases mobility; respectively. This study has revealed that the general water quality in this rural area, whether in endemic or non-endemic villages, is poor and that agricultural activities have disrupted geochemical processes. This could result in an increased risk of exposure to U. More work needs to be done on understanding the geochemical processes influencing rural water supplies to address not only historical heath issues (e.g., BEN, exposure to NO₃) but also newly discovered or immerging environmental health issues (e.g., exposure to U, pesticides).