Gadolinium: a review on concentrations and impacts in marine and coastal systems.

This review synthesizes current knowledge on gadolinium (Gd) contamination in marine and coastal environments from 209 scientific publications. Of these, 83 studies were selected for detailed analysis, focusing specifically on marine invertebrate taxa to ensure a targeted examination of Gd's effects on key sentinel species within this group, with 69 papers (83.1 %) focusing on Gd concentrations in marine and coastal ecosystems, reporting concentrations ranging from 0.00002516 to 1176.77 μg/L. Out of the 83 papers, 14 (16.9 %) were related to Gd ecotoxicological effects through laboratory exposure experiments, with test concentrations ranging from 10 to 5600 μg/L. The studies mainly investigated Gd bioaccumulation and toxicity in marine bivalves (e.g. Mytilus galloprovincialis, Crassostrea gigas, Ruditapes philippinarum), crustaceans (Callinectes sapidus, Crangon crangon) and echinoderms (Paracentrotus lividus, Arbacia lixula). Bivalves were the most studied taxonomic group due to their filter-feeding behavior and role as bioindicators of metal contamination. Laboratory results showed that Gd exposure led to oxidative stress, metabolic disorders and reproductive toxicity, especially in molluscs and echinoderms. M. galloprovincialis showed the highest bioaccumulation, with concentrations exceeding 2.5 μg/g under controlled exposure. Echinoderms, especially sea urchin larvae (P. lividus, Heliocidaris tuberculata), were among the most affected taxa, showing developmental abnormalities such as skeletal malformations and growth retardation. Crustaceans, although less studied, also showed bioaccumulation and enzymatic disorders. Given the persistence of anthropogenic Gd in marine and coastal environments and its increasing medical use, this review highlights the need for improved wastewater treatment technologies, stricter environmental regulations, and further research into the long-term effects on marine biodiversity.