Assessment of marine macroalgae potential for gadolinium removal from contaminated aquatic systems

Gadolinium (Gd) is a rare earth associated with hospital and urban wastewaters due to its application as a contrast agent for magnetic resonance imaging. In this work, the uptake of Gd from contaminated seawater by three living marine macroalgae, Ulva lactuca (Chlorophyta), Fucus spiralis (Phaeophyta) and Gracilaria sp. (Rhodophyta) was studied along 72 h. Surface analysis (FTIR), water content, kinetic modelling, and Gd quantification in seawater and biomass were performed. All species were able to accumulate Gd from seawater with 10, 157, and 500 μg Gd L^-1, although green and red macroalgae performed better, following the order: green > red > brown. Removal efficiencies reached 85%, corresponding to a bioconcentration factor of 1700. In more complex solutions that intended to mimic real contaminated environments, namely mixtures with other rare earth elements (Y, La, Ce, Pr, Nd, Eu, Tb, Dy), and with potentially toxic elements commonly found in wastewaters (Cr, Ni, Cu, Cd, Hg, Pb), at two salinities (10 and 30), the macroalgae kept its efficiency: 84% and 88% of removal by green and red macroalgae, respectively. Overall, findings evidence that living macroalgae could be a countermeasure to the increasing anthropogenic enrichment of Gd observed in the aquatic environment.