Gadolinium as an emerging pollutant: a review on its occurrence and impacts in aquatic ecosystems

Abstract

Rare earth elements (REEs), despite their name, are highly extracted and widely used metals. Thanks to their unique properties, such as ideal magnetic behaviour and sharply defined energy states, REEs are a strategic resource for many economic sectors such as energetic, nuclear, industrial, medical and digital technology. Gadolinium (Gd) is one of the most commercially exploited REEs, especially in the biomedical field where it is chelated with organic molecules and used as contrast agent in magnetic resonance imaging (MRI). Its wide employment enhances the risk for this element to be potentially released into the environment, in particular into rivers, lakes and coastal areas through industrial wastewaters or through exhausted devices. This scenario may increase the possible risks of contamination for the aquatic environments worldwide. For this reason, in this project, a literature research is performed with the aim to establish the Gd concentrations both in seawater and freshwater as well as in sediments and in biological matrices. In addition, a study on the speciation of this pollutant in the environment is performed, in order to determine its main chemical forms present in waters and sediments. Seawater and freshwater invertebrates and in particular bivalve species, due to their benthic ecology and filter-feeding behavior, are particularly exposed to environmental contaminants and thus potentially affected by REEs exposure in the aquatic environments. Little is known about the biochemical and physiological responses of these marine and freshwater species to REEs and, particularly, to gadolinium exposure. For this reason, increasing attention and research efforts should be focused on this issue. Finally, in this thesis, the biochemical and physiological response caused by gadolinium (Gd) exposure and its possible bioaccumulation in different invertebrate species is assessed, together with the consequent damages to their cellular metabolism. A comparison among studies already published in literature is performed, collecting information on biomarkers activity, bioaccumulation mechanisms and physiological responses after gadolinium exposition in different invertebrate species.