Investigation of Gadolinium-Based Contrast Agents in Wastewaters and Natural Waters

Gadolinium (Gd) is an element belonging to the lanthanide group, classified among the rare earth elements (REEs), and has been widely used in medicine since the 1980s, particularly in contrast agents for magnetic resonance imaging (MRI), to enhance image quality. Today, anthropogenic gadolinium is considered an emerging microcontaminant, with potential negative effects on both the environment and human health. Gadolinium-based contrast agents (GBCAs) are administered intravenously during diagnostic procedures but are not metabolized by the human body and are instead excreted via urine. These compounds enter the sewage system and, due to their chemical stability, pass through wastewater treatment plants unaltered, eventually being released into rivers, lakes, and coastal seawaters. This leads to a phenomenon known as the “positive gadolinium anomaly,” which refers to a significant increase in Gd concentrations compared to natural background levels. Such anomalies have been observed globally in both freshwater and marine environments. [1] Speciation analyses allow to identify and quantify the different forms in which metals, such as Gd, are present in environmental matrices. This investigation can be carried out by analyzing samples with the hyphenated technique high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS). [2] In this work, a study was conducted to assess the presence of gadolinium in water samples collected from the influent and effluent of a wastewater treatment plant, as well as in seawater samples from the Gulf of Trieste, in the northern Adriatic Sea. Samples were analyzed using ICP-MS to determine total gadolinium, to evaluate the presence of a gadolinium anomaly in the samples. Once the anomaly was confirmed in both marine and wastewater samples, a speciation analysis was performed to detect the presence of specific GBCAs. This analysis involved a different pre-treatment depending on the sample type: wastewater samples were concentrated by evaporation, while seawater samples underwent solid-phase extraction (SPE), then the samples were analyzed by HPLC-ICP-MS. In both wastewater and seawater samples, two macrocyclic contrast agents were identified and quantified, highlighting both the increased use of these GBCAs, generally more stable and safer for humans compared to linear ones, and their widespread occurrence and persistence in aquatic environments, emphasizing the need for targeted environmental monitoring of these contaminants. References: [1] R. Brunjes, T. Hofmann, 2020, Water Research, DOI https:/doi.org/10.1016/j.watres.2020.115966 [2] M. Horstmann, R. Gonzalez de Vega, et. al., 2021, Journal of Analytical Atomic Spectrometry, DOI https://doi.org/10.1039/D0JA00493F