Measurements and future projections of Gd-based contrast agents for MRI exams in wastewater treatment plants in the Tokyo metropolitan area.

Large amounts of Gd-based contrast agents are used in magnetic resonance imaging (MRI) that are then excreted in urine. These agents are subsequently discharged into the environment because they are difficult to remove by usual sewage treatment techniques. In this study, changes of the Gd anomaly during wastewater treatment processes were determined by analyzing wastewater samples and the possibility for future prediction of the changes was evaluated based on the relationship between the Gd anomaly and the number of MRI devices in use. After the wastewater treatment processes, the values of final effluent were increased 1.8 times compared to those of influent, and the Gd anomaly of effluent had a positive correlation to the number of MRI devices. The finding suggested that the changes of environmental impact were predictable based on the number of MRI devices.