Batch experimental results about the occurrence and fate of Gadolinium in aquifers  

The use of groundwater as a freshwater source must be increased to mitigate the increasing pressure over water resources, resulting from growing population and climate change. However, many aquifers are commonly polluted by a wide range of anthropogenic substances, especially those aquifer located in urban areas. Therefore, to use groundwater resources safely, it is needed to establish the presence and fate of pollutants that can endanger human health. This is the case of Gadolinium. Integrated in Gadolinium-based contrast agents it is harmless and used for medical purposes, but it can cause serious health issues when released in the environment. This research arose during a water sampling campaign undertaken in Barcelona where Gadolinium anomalies (i.e., resulting from anthropogenic activities) were detected in surface and underground water bodies which were hydraulically connected. What was striking was that Gadolinium pollution in groundwater bodies was less frequent and at lower concentrations than in surface water bodies. These observations suggested that Gadolinium was attenuated during its transport through the subsurface. To establish the mechanisms controlling the attenuation of Gadolinium, laboratory based batch experiments were carried out and then modelled using PHREEQC. Experimental results suggested that main process affecting the concentration of Gadolinium was sorption which could reduce considerably its presence in groundwater. Our results contribute to understanding the fate of anthropic Gadolinium in aquifers which is of paramount importance to use groundwater safely.