EFFECTS OF HUMAN ACTIVITIES ON URANIUM CYCLING IN GROUNDWATER GEOCHEMISTRY IN A RURAL AREA IN BULGARIA

The geochemistry of three drinking water types (wells, springs, and tap) in a rural area of Northern Bulgaria was investigated. 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. Endemic villages mainly occur over Cretaceous limestone, sandstones, calcareous sandstones, glauconitie sandstones, and in localized areas Quaternary alluvial deposits. Non-endemic villages occur mainly on the area characterized by 10 to 60 meter thick Quaternary loess deposits that overlie 50 to 1000 meters of Neogene clays/marls, clayey limestones, and limestones Water quality significantly varied as a function of water type, but it appears that human activities have influenced all three 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. 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. 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; agricultural activities have influenced geochemical processes; and this influence could result in an increased risk of human exposure to U.