Speciation Investigation of Gadolinium Based Contrasting Agents in Wastewater and Seawater of the Northern Adriatic Sea

The contaminants of emerging concern is a class in constant evolution since new compounds which may present toxicity towards the biota are continuously detected in the environment, especially in water bodies. Among these substances, gadolinium based contrasting agents (GBCAs) are regarded as possible contaminants of relevance due to their widespread use in medicine1. Substances containing gadolinium are used as contrasting agents in magnetic resonance imaging (MRI) analyses due to the paramagnetic properties of Gd; since gadolinium ion in its free from, Gd3+, is highly toxic, it is administered before MRI examination as a complex with an organic ligand which ensure a high stability of the compound avoiding the release of free Gd ions into the body fluids1. The high stability implicates that GBCAs are persistent also in the environment, and indeed their concentration in the aquatic ecosystems is expected to increase, possibly leading to adverse effects. In this work, we investigated the presence of two GBCAs, namely gadoterate meglumine (Gd-DOTA) and gadoteridol (Gd-HP-DO3A), in two different aqueous matrices, wastewater both at the entrance and at the exit of a wastewater treatment plant in Trieste, and seawater collected in the gulf of Trieste near the WWTP’s pipeline.The wastewater samples were pre-concentrated by evaporation, while the seawater samples, presenting a high salinity, needed a specific treatment consisting in a solid phase extraction to remove the saline components in order to prevent interferences during analysis2. The determination of GBCAs was carried out by HPLC-ICP-MS using an anion exchange column and a mixture of 125 mM ammonium nitrate buffer at pH 9 and MilliQ water in a 25:75 ratio as a mobile phase. The isotopes 157Gd and 158Gd were monitored. The high recoveries obtained for Gd-DOTA and Gd-HP-DO3A proved the validity of the two sample preparation methods. The results showed the presence of both substances in the samples analysed, in the range between 0.1 and 50 ng/L; indeed, higher concentrations were found in the wastewater matrices, while the concentration was lower in the seawater samples, providing information on the environmental pathway of these compounds. References: [1] R. Brünjes, T. Hofmann, Water Research 2020, 182, 115966. [2] M. Horstmann, R. Gonzalez de Vega, D.P. Bishop, U. Karst, P.A. Doble, D. Clases, Journal of Analytical Atomic Spectrometry 2021, 36, 767 – 775.