Bivalve sentinels sound the alarm: Rare earth elements patterns along the Mediterranean coast

Rare earth elements (REEs), or lanthanides, are naturally occurring elements, whose demand has surged in recent years, driven by their use in green energy, electronics, and medical technologies. Despite their expanding applications, knowledge on REEs pollution, bioaccumulation patterns, and environmental dynamics in marine ecosystems remains limited, and regulatory thresholds are still lacking. This study investigates the distribution and bioaccumulation of REEs along the Mediterranean coasts, encompassing the Tyrrhenian, Ionian, and Adriatic Seas. Juvenile and adult individuals of the edible bivalve Donax trunculus and associated sediments were analyzed to assess REE pollution along the Italian coastline. The ΣREE concentrations in wedge clam tissues reached a maximum of 1.55 μg g^-1, with the highest value recorded at the Lesina site when both life stages were considered together, while sediment concentrations reached up to 68.2 μg g^-1. Notably, REE concentrations did not differ significantly between juvenile clams and adults, suggesting comparable accumulation patterns and potential vulnerability in both life stages. Shale-normalized REE patterns revealed pronounced gadolinium (Gd) anomalies at all sampling sites, indicating a substantial anthropogenic contribution. D. trunculus proved to be an effective sentinel species for REE monitoring, as tissue concentrations were positively correlated with sediment levels and reflected local environmental pressures, including population density, riverine inputs, wastewater treatment plant discharges, and coastal urbanization. Overall, the accumulation of REEs in both biota and sediments highlights the urgent need to expand research on these emerging contaminants, particularly in the Mediterranean Sea, considering their increasing use and potential environmental and food-security risks.