Electrochemical Filtration of Gadolinium from Patient Urine after Magnetic Resonance Imaging

The widespread use of gadolinium-based contrast agents for magnetic resonance imaging (MRI) in recent decades has led to a growing demand for Gd and raised environmental concerns due to their direct discharge into wastewater systems. In response, we developed an electrochemical filtration method to recover Gd from patient urine following contrast-enhanced MRI. This method involves modifying a conventional vacuum filtration apparatus by introducing electrodes into the filter membrane, creating a strong electric field of ∼5 kV/m and a steep three-zone pH gradient within the filter membrane. These electric and pH fields facilitate the dissociation of Gd-based contrast agents, releasing Gd^III ions, electrophoretic separation of Gd^III and its ligand, and eventually precipitation and trapping of Gd^III as GdPO₄ and Gd(OH)₃ on the filter membrane. Using gadopentetate dimeglumine (GdDTPA) as a model Gd-based contrast agent, we achieved a Gd trapping efficiency of ∼70% for artificial and real urine samples. For macrocyclic Gd-based contrast agents such as gadoterate meglumine (GdDOTA), the Gd trapping efficiency decreased to 25.4% due to the slow dissociation kinetics of macrocyclic contrast agents. However, the trapping efficiency can be improved to ∼40% by allowing the macrocyclic contrast agent to predissociate in an acidic environment before electrochemical filtration. The Gd trapped on the filter membrane can be recovered by thermal treatment in a muffle furnace. After thermal treatment, the reclaimed Gd from the real urine sample was primarily identified as GdPO₄. This electrochemical filtration design offers a straightforward and practical approach to recovering Gd from contrast-enhanced MRI scans, addressing the increasing demand for Gd and helping alleviate concerns about Gd contamination in surface water.